Author name code: lindsey
ADS astronomy entries on 2022-09-14
author:"Lindsey, Charles A."
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Title: What is Exceptional about Solar Activity in the Early Phase
of Cycle 25?
Authors: Jain, Kiran; Lindsey, Charles; Tripathy, Sushanta C.
Bibcode: 2021RNAAS...5..253J
Altcode:
Solar Cycle 25 began in 2019 December and has been progressing nominally
since. However, a closely associated pair of strong active regions,
NOAA 12786 and 12785, emerged in 2020 November. The greater, northern
component, 12786, attained a maximum sunspot area of 1000 μHemi. The
sudden, uncharacteristic emergence of such a large concentration
of intense magnetic flux in the early phase of the solar cycle has
not been seen in previous cycles. Although the active region pair
survived for two Carrington rotations, it did not produce any X- or
M-class flares. Here we remark on the evolution of NOAA 12786 and
12785, first in the Sun's invisible and subsequently the visible
hemispheres, and compare the irradiance and other characteristic
profiles it manifested in the early ascending phase of cycle 25 with
those of previous solar cycles.
Title: Evidence for Top Quark Production in Nucleus-Nucleus Collisions
Authors: Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Ambrogi, F.;
Bergauer, T.; Dragicevic, M.; Erö, J.; Escalante Del Valle, A.;
Frühwirth, R.; Jeitler, M.; Krammer, N.; Lechner, L.; Liko, D.;
Madlener, T.; Mikulec, I.; Rad, N.; Schieck, J.; Schöfbeck, R.;
Spanring, M.; Templ, S.; Waltenberger, W.; Wulz, C. -E.; Zarucki,
M.; Chekhovsky, V.; Litomin, A.; Makarenko, V.; Suarez Gonzalez, J.;
Darwish, M. R.; De Wolf, E. A.; Di Croce, D.; Janssen, X.; Kello,
T.; Lelek, A.; Pieters, M.; Rejeb Sfar, H.; Van Haevermaet, H.; Van
Mechelen, P.; Van Putte, S.; Van Remortel, N.; Blekman, F.; Bols,
E. S.; Chhibra, S. S.; D'Hondt, J.; De Clercq, J.; Lontkovskyi, D.;
Lowette, S.; Marchesini, I.; Moortgat, S.; Python, Q.; Tavernier, S.;
Van Doninck, W.; Van Mulders, P.; Beghin, D.; Bilin, B.; Clerbaux, B.;
De Lentdecker, G.; Delannoy, H.; Dorney, B.; Favart, L.; Grebenyuk,
A.; Kalsi, A. K.; Makarenko, I.; Moureaux, L.; Pétré, L.; Popov,
A.; Postiau, N.; Starling, E.; Thomas, L.; Vander Velde, C.; Vanlaer,
P.; Vannerom, D.; Wezenbeek, L.; Cornelis, T.; Dobur, D.; Khvastunov,
I.; Niedziela, M.; Roskas, C.; Skovpen, K.; Tytgat, M.; Verbeke, W.;
Vermassen, B.; Vit, M.; Bruno, G.; Bury, F.; Caputo, C.; David, P.;
Delaere, C.; Delcourt, M.; Donertas, I. S.; Giammanco, A.; Lemaitre,
V.; Prisciandaro, J.; Saggio, A.; Taliercio, A.; Teklishyn, M.;
Vischia, P.; Wuyckens, S.; Zobec, J.; Alves, G. A.; Correia Silva,
G.; Hensel, C.; Moraes, A.; Aldá Júnior, W. L.; Belchior Batista
Das Chagas, E.; Carvalho, W.; Chinellato, J.; Coelho, E.; Da Costa,
E. M.; Da Silveira, G. G.; De Jesus Damiao, D.; Fonseca De Souza, S.;
Malbouisson, H.; Martins, J.; Matos Figueiredo, D.; Medina Jaime, M.;
Melo De Almeida, M.; Mora Herrera, C.; Mundim, L.; Nogima, H.; Rebello
Teles, P.; Sanchez Rosas, L. J.; Santoro, A.; Silva Do Amaral, S. M.;
Sznajder, A.; Thiel, M.; Tonelli Manganote, E. J.; Torres Da Silva
De Araujo, F.; Vilela Pereira, A.; Bernardes, C. A.; Calligaris,
L.; Fernandez Perez Tomei, T. R.; Gregores, E. M.; Lemos, D. S.;
Mercadante, P. G.; Novaes, S. F.; Padula, Sandra S.; Aleksandrov, A.;
Antchev, G.; Atanasov, I.; Hadjiiska, R.; Iaydjiev, P.; Misheva, M.;
Rodozov, M.; Shopova, M.; Sultanov, G.; Bonchev, M.; Dimitrov, A.;
Ivanov, T.; Litov, L.; Pavlov, B.; Petkov, P.; Petrov, A.; Fang, W.;
Guo, Q.; Wang, H.; Yuan, L.; Ahmad, M.; Hu, Z.; Wang, Y.; Chapon, E.;
Chen, G. M.; Chen, H. S.; Chen, M.; Jiang, C. H.; Leggat, D.; Liao,
H.; Liu, Z.; Sharma, R.; Spiezia, A.; Tao, J.; Wang, J.; Zhang, H.;
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A.; Li, J.; Li, L.; Li, Q.; Lyu, X.; Mao, Y.; Qian, S. J.; Wang, D.;
Wang, Q.; Xiao, J.; You, Z.; Gao, X.; Xiao, M.; Avila, C.; Cabrera,
A.; Florez, C.; Fraga, J.; Sarkar, A.; Segura Delgado, M. A.; Mejia
Guisao, J.; Ramirez, F.; Ruiz Alvarez, J. D.; Salazar González,
C. A.; Vanegas Arbelaez, N.; Giljanovic, D.; Godinovic, N.; Lelas,
D.; Puljak, I.; Sculac, T.; Antunovic, Z.; Kovac, M.; Brigljevic, V.;
Ferencek, D.; Majumder, D.; Mesic, B.; Roguljic, M.; Starodumov, A.;
Susa, T.; Ather, M. W.; Attikis, A.; Erodotou, E.; Ioannou, A.; Kole,
G.; Kolosova, M.; Konstantinou, S.; Mavromanolakis, G.; Mousa, J.;
Nicolaou, C.; Ptochos, F.; Razis, P. A.; Rykaczewski, H.; Saka, H.;
Tsiakkouri, D.; Finger, M.; Finger, M.; Kveton, A.; Tomsa, J.; Ayala,
E.; Carrera Jarrin, E.; Salama, E.; Lotfy, A.; Mahmoud, M. A.; Bhowmik,
S.; Carvalho Antunes De Oliveira, A.; Dewanjee, R. K.; Ehataht,
K.; Kadastik, M.; Raidal, M.; Veelken, C.; Eerola, P.; Forthomme,
L.; Kirschenmann, H.; Osterberg, K.; Voutilainen, M.; Brücken, E.;
Garcia, F.; Havukainen, J.; Karimäki, V.; Kim, M. S.; Kinnunen, R.;
Lampén, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Lindén, T.;
Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Luukka, P.; Tuuva, T.;
Besancon, M.; Couderc, F.; Dejardin, M.; Denegri, D.; Faure, J. L.;
Ferri, F.; Ganjour, S.; Givernaud, A.; Gras, P.; Hamel de Monchenault,
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J.; Rosowsky, A.; Sahin, M. Ö.; Savoy-Navarro, A.; Titov, M.; Yu,
G. B.; Ahuja, S.; Amendola, C.; Beaudette, F.; Bonanomi, M.; Busson,
P.; Charlot, C.; Davignon, O.; Diab, B.; Falmagne, G.; Granier de
Cassagnac, R.; Kucher, I.; Lobanov, A.; Martin Perez, C.; Nguyen, M.;
Ochando, C.; Paganini, P.; Rembser, J.; Salerno, R.; Sauvan, J. B.;
Sirois, Y.; Zabi, A.; Zghiche, A.; Agram, J. -L.; Andrea, J.; Bloch,
D.; Bourgatte, G.; Brom, J. -M.; Chabert, E. C.; Collard, C.; Fontaine,
J. -C.; Gelé, D.; Goerlach, U.; Grimault, C.; Le Bihan, A. -C.; Van
Hove, P.; Asilar, E.; Beauceron, S.; Bernet, C.; Boudoul, G.; Camen,
C.; Carle, A.; Chanon, N.; Chierici, R.; Contardo, D.; Depasse, P.;
El Mamouni, H.; Fay, J.; Gascon, S.; Gouzevitch, M.; Ille, B.; Jain,
Sa.; Laktineh, I. B.; Lattaud, H.; Lesauvage, A.; Lethuillier, M.;
Mirabito, L.; Torterotot, L.; Touquet, G.; Vander Donckt, M.; Viret,
S.; Khvedelidze, A.; Tsamalaidze, Z.; Feld, L.; Klein, K.; Lipinski,
M.; Meuser, D.; Pauls, A.; Preuten, M.; Rauch, M. P.; Schulz, J.;
Teroerde, M.; Eliseev, D.; Erdmann, M.; Fackeldey, P.; Fischer, B.;
Ghosh, S.; Hebbeker, T.; Hoepfner, K.; Keller, H.; Mastrolorenzo,
L.; Merschmeyer, M.; Meyer, A.; Millet, P.; Mocellin, G.; Mondal,
S.; Mukherjee, S.; Noll, D.; Novak, A.; Pook, T.; Pozdnyakov, A.;
Quast, T.; Radziej, M.; Rath, Y.; Reithler, H.; Roemer, J.; Schmidt,
A.; Schuler, S. C.; Sharma, A.; Wiedenbeck, S.; Zaleski, S.; Dziwok,
C.; Flügge, G.; Haj Ahmad, W.; Hlushchenko, O.; Kress, T.; Nowack,
A.; Pistone, C.; Pooth, O.; Roy, D.; Sert, H.; Stahl, A.; Ziemons,
T.; Aarup Petersen, H.; Aldaya Martin, M.; Asmuss, P.; Babounikau,
I.; Baxter, S.; Behnke, O.; Bermúdez Martínez, A.; Bin Anuar,
A. A.; Borras, K.; Botta, V.; Brunner, D.; Campbell, A.; Cardini,
A.; Connor, P.; Consuegra Rodríguez, S.; Danilov, V.; De Wit, A.;
Defranchis, M. M.; Didukh, L.; Domínguez Damiani, D.; Eckerlin, G.;
Eckstein, D.; Eichhorn, T.; Elwood, A.; Estevez Banos, L. I.; Gallo,
E.; Geiser, A.; Giraldi, A.; Grohsjean, A.; Guthoff, M.; Haranko, M.;
Harb, A.; Jafari, A.; Jomhari, N. Z.; Jung, H.; Kasem, A.; Kasemann,
M.; Kaveh, H.; Keaveney, J.; Kleinwort, C.; Knolle, J.; Krücker,
D.; Lange, W.; Lenz, T.; Lidrych, J.; Lipka, K.; Lohmann, W.; Mankel,
R.; Melzer-Pellmann, I. -A.; Metwally, J.; Meyer, A. B.; Meyer, M.;
Missiroli, M.; Mnich, J.; Mussgiller, A.; Myronenko, V.; Otarid, Y.;
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A.; Savitskyi, M.; Scheurer, V.; Schütze, P.; Schwanenberger,
C.; Shevchenko, R.; Singh, A.; Sosa Ricardo, R. E.; Tholen, H.;
Tonon, N.; Turkot, O.; Vagnerini, A.; Van De Klundert, M.; Walsh,
R.; Walter, D.; Wen, Y.; Wichmann, K.; Wissing, C.; Wuchterl, S.;
Zenaiev, O.; Zlebcik, R.; Aggleton, R.; Bein, S.; Benato, L.; Benecke,
A.; De Leo, K.; Dreyer, T.; Ebrahimi, A.; Feindt, F.; Fröhlich, A.;
Garbers, C.; Garutti, E.; Gonzalez, D.; Gunnellini, P.; Haller, J.;
Hinzmann, A.; Karavdina, A.; Kasieczka, G.; Klanner, R.; Kogler, R.;
Kurz, S.; Kutzner, V.; Lange, J.; Lange, T.; Malara, A.; Multhaup, J.;
Niemeyer, C. E. N.; Nigamova, A.; Pena Rodriguez, K. J.; Reimers, A.;
Rieger, O.; Schleper, P.; Schumann, S.; Schwandt, J.; Schwarz, D.;
Sonneveld, J.; Stadie, H.; Steinbrück, G.; Vormwald, B.; Zoi, I.;
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E.; Caspart, R.; Chwalek, T.; De Boer, W.; Dierlamm, A.; El Morabit,
K.; Faltermann, N.; Flöh, K.; Giffels, M.; Gottmann, A.; Hartmann,
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Shvetsov, I.; Simonis, H. J.; Ulrich, R.; Wassmer, M.; Weber, M.;
Wöhrmann, C.; Wolf, R.; Wozniewski, S.; Anagnostou, G.; Asenov, P.;
Daskalakis, G.; Geralis, T.; Kyriakis, A.; Loukas, D.; Paspalaki,
G.; Stakia, A.; Diamantopoulou, M.; Karasavvas, D.; Karathanasis, G.;
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A.; Papavergou, I.; Saoulidou, N.; Theofilatos, K.; Vellidis,
K.; Vourliotis, E.; Bakas, G.; Kousouris, K.; Papakrivopoulos,
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Gianneios, P.; Katsoulis, P.; Kokkas, P.; Mallios, S.; Manitara, K.;
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M.; Chudasama, R.; Csanad, M.; Gadallah, M. M. A.; Major, P.; Mandal,
K.; Mehta, A.; Pasztor, G.; Surányi, O.; Veres, G. I.; Bencze, G.;
Hajdu, C.; Horvath, D.; Sikler, F.; Veszpremi, V.; Vesztergombi,
G.; Beni, N.; Czellar, S.; Karancsi, J.; Molnar, J.; Szillasi, Z.;
Teyssier, D.; Raics, P.; Trocsanyi, Z. L.; Ujvari, B.; Csorgo, T.;
Lökös, S.; Nemes, F.; Novak, T.; Choudhury, S.; Komaragiri, J. R.;
Kumar, D.; Panwar, L.; Tiwari, P. C.; Bahinipati, S.; Dash, D.; Kar,
C.; Mal, P.; Mishra, T.; Muraleedharan Nair Bindhu, V. K.; Nayak,
A.; Sahoo, D. K.; Sur, N.; Swain, S. K.; Bansal, S.; Beri, S. B.;
Bhatnagar, V.; Chauhan, S.; Dhingra, N.; Gupta, R.; Kaur, A.; Kaur,
A.; Kaur, S.; Kumari, P.; Lohan, M.; Meena, M.; Sandeep, K.; Sharma,
S.; Singh, J. B.; Virdi, A. K.; Ahmed, A.; Bhardwaj, A.; Choudhary,
B. C.; Garg, R. B.; Gola, M.; Keshri, S.; Kumar, A.; Naimuddin, M.;
Priyanka, P.; Ranjan, K.; Shah, A.; Bharti, M.; Bhattacharya, R.;
Bhattacharya, S.; Bhowmik, D.; Dutta, S.; Ghosh, S.; Gomber, B.;
Maity, M.; Mondal, K.; Nandan, S.; Palit, P.; Purohit, A.; Rout,
P. K.; Saha, G.; Sarkar, S.; Sharan, M.; Singh, B.; Thakur, S.;
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Shukla, P.; Aziz, T.; Bhat, M. A.; Dugad, S.; Kumar Verma, R.; Sarkar,
U.; Banerjee, S.; Bhattacharya, S.; Chatterjee, S.; Das, P.; Guchait,
M.; Karmakar, S.; Kumar, S.; Majumder, G.; Mazumdar, K.; Mukherjee,
S.; Roy, D.; Sahoo, N.; Dube, S.; Kansal, B.; Kapoor, A.; Kothekar,
K.; Pandey, S.; Rane, A.; Rastogi, A.; Sharma, S.; Bakhshiansohi,
H.; Chenarani, S.; Etesami, S. M.; Khakzad, M.; Mohammadi Najafabadi,
M.; Naseri, M.; Felcini, M.; Grunewald, M.; Abbrescia, M.; Aly, R.;
Aruta, C.; Calabria, C.; Colaleo, A.; Creanza, D.; De Filippis, N.;
De Palma, M.; Di Florio, A.; Di Pilato, A.; Elmetenawee, W.; Fiore,
L.; Gelmi, A.; Iaselli, G.; Ince, M.; Lezki, S.; Maggi, G.; Maggi,
M.; Margjeka, I.; Merlin, J. A.; My, S.; Nuzzo, S.; Pompili, A.;
Pugliese, G.; Ranieri, A.; Selvaggi, G.; Silvestris, L.; Simone,
F. M.; Venditti, R.; Verwilligen, P.; Abbiendi, G.; Battilana, C.;
Bonacorsi, D.; Borgonovi, L.; Braibant-Giacomelli, S.; Campanini, R.;
Capiluppi, P.; Castro, A.; Cavallo, F. R.; Ciocca, C.; Cuffiani, M.;
Dallavalle, G. M.; Diotalevi, T.; Fabbri, F.; Fanfani, A.; Fontanesi,
E.; Giacomelli, P.; Grandi, C.; Guiducci, L.; Iemmi, F.; Lo Meo,
S.; Marcellini, S.; Masetti, G.; Navarria, F. L.; Perrotta, A.;
Primavera, F.; Rossi, A. M.; Rovelli, T.; Siroli, G. P.; Tosi, N.;
Albergo, S.; Costa, S.; Di Mattia, A.; Potenza, R.; Tricomi, A.; Tuve,
C.; Barbagli, G.; Cassese, A.; Ceccarelli, R.; Ciulli, V.; Civinini,
C.; D'Alessandro, R.; Fiori, F.; Focardi, E.; Latino, G.; Lenzi, P.;
Lizzo, M.; Meschini, M.; Paoletti, S.; Seidita, R.; Sguazzoni, G.;
Viliani, L.; Benussi, L.; Bianco, S.; Piccolo, D.; Bozzo, M.; Ferro,
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Dini, P.; Gennai, S.; Ghezzi, A.; Govoni, P.; Guzzi, L.; Malberti,
M.; Malvezzi, S.; Menasce, D.; Monti, F.; Moroni, L.; Paganoni, M.;
Pedrini, D.; Ragazzi, S.; Tabarelli de Fatis, T.; Valsecchi, D.; Zuolo,
D.; Buontempo, S.; Cavallo, N.; De Iorio, A.; Fabozzi, F.; Fienga,
F.; Iorio, A. O. M.; Layer, L.; Lista, L.; Meola, S.; Paolucci,
P.; Rossi, B.; Sciacca, C.; Voevodina, E.; Azzi, P.; Bacchetta,
N.; Bisello, D.; Boletti, A.; Bragagnolo, A.; Carlin, R.; Checchia,
P.; De Castro Manzano, P.; Dorigo, T.; Dosselli, U.; Gasparini, F.;
Gasparini, U.; Hoh, S. Y.; Margoni, M.; Meneguzzo, A. T.; Presilla, M.;
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M.; Zanetti, M.; Zotto, P.; Zucchetta, A.; Zumerle, G.; Braghieri,
A.; Calzaferri, S.; Fiorina, D.; Montagna, P.; Ratti, S. P.; Re,
V.; Ressegotti, M.; Riccardi, C.; Salvini, P.; Vai, I.; Vitulo, P.;
Biasini, M.; Bilei, G. M.; Ciangottini, D.; Fanò, L.; Lariccia, P.;
Mantovani, G.; Mariani, V.; Menichelli, M.; Moscatelli, F.; Rossi, A.;
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Bagliesi, G.; Bertacchi, V.; Bianchini, L.; Boccali, T.; Castaldi, R.;
Ciocci, M. A.; Dell'Orso, R.; Di Domenico, M. R.; Donato, S.; Giannini,
L.; Giassi, A.; Grippo, M. T.; Ligabue, F.; Manca, E.; Mandorli, G.;
Messineo, A.; Palla, F.; Rizzi, A.; Rolandi, G.; Roy Chowdhury, S.;
Scribano, A.; Shafiei, N.; Spagnolo, P.; Tenchini, R.; Tonelli, G.;
Turini, N.; Venturi, A.; Verdini, P. G.; Cavallari, F.; Cipriani,
M.; Del Re, D.; Di Marco, E.; Diemoz, M.; Longo, E.; Meridiani, P.;
Organtini, G.; Pandolfi, F.; Paramatti, R.; Quaranta, C.; Rahatlou, S.;
Rovelli, C.; Santanastasio, F.; Soffi, L.; Tramontano, R.; Amapane,
N.; Arcidiacono, R.; Argiro, S.; Arneodo, M.; Bartosik, N.; Bellan,
R.; Bellora, A.; Biino, C.; Cappati, A.; Cartiglia, N.; Cometti, S.;
Costa, M.; Covarelli, R.; Demaria, N.; Kiani, B.; Legger, F.; Mariotti,
C.; Maselli, S.; Migliore, E.; Monaco, V.; Monteil, E.; Monteno, M.;
Obertino, M. M.; Ortona, G.; Pacher, L.; Pastrone, N.; Pelliccioni,
M.; Pinna Angioni, G. L.; Ruspa, M.; Salvatico, R.; Siviero, F.; Sola,
V.; Solano, A.; Soldi, D.; Staiano, A.; Trocino, D.; Belforte, S.;
Candelise, V.; Casarsa, M.; Cossutti, F.; Da Rold, A.; Della Ricca,
G.; Vazzoler, F.; Dogra, S.; Huh, C.; Kim, B.; Kim, D. H.; Kim, G. N.;
Lee, J.; Lee, S. W.; Moon, C. S.; Oh, Y. D.; Pak, S. I.; Sekmen, S.;
Yang, Y. C.; Kim, H.; Moon, D. H.; Francois, B.; Kim, T. J.; Park,
J.; Cho, S.; Choi, S.; Go, Y.; Ha, S.; Hong, B.; Lee, K.; Lee, K. S.;
Lim, J.; Park, J.; Park, S. K.; Roh, Y.; Yoo, J.; Goh, J.; Gurtu,
A.; Kim, H. S.; Kim, Y.; Almond, J.; Bhyun, J. H.; Choi, J.; Jeon,
S.; Kim, J.; Kim, J. S.; Ko, S.; Kwon, H.; Lee, H.; Lee, K.; Lee, S.;
Nam, K.; Oh, B. H.; Oh, M.; Oh, S. B.; Radburn-Smith, B. C.; Seo, H.;
Yang, U. K.; Yoon, I.; Jeon, D.; Kim, J. H.; Ko, B.; Lee, J. S. H.;
Park, I. C.; Watson, I. J.; Yoo, H. D.; Choi, Y.; Hwang, C.; Jeong,
Y.; Lee, H.; Lee, J.; Lee, Y.; Yu, I.; Veckalns, V.; Juodagalvis, A.;
Rinkevicius, A.; Tamulaitis, G.; Wan Abdullah, W. A. T.; Yusli, M. N.;
Zolkapli, Z.; Benitez, J. F.; Castaneda Hernandez, A.; Murillo Quijada,
J. A.; Valencia Palomo, L.; Castilla-Valdez, H.; De La Cruz-Burelo,
E.; Heredia-De La Cruz, I.; Lopez-Fernandez, R.; Sanchez-Hernandez,
A.; Carrillo Moreno, S.; Oropeza Barrera, C.; Ramirez-Garcia, M.;
Vazquez Valencia, F.; Eysermans, J.; Pedraza, I.; Salazar Ibarguen,
H. A.; Uribe Estrada, C.; Morelos Pineda, A.; Mijuskovic, J.; Raicevic,
N.; Krofcheck, D.; Bheesette, S.; Butler, P. H.; Ahmad, A.; Asghar,
M. I.; Awan, M. I. M.; Hassan, Q.; Hoorani, H. R.; Khan, W. A.; Shah,
M. A.; Shoaib, M.; Waqas, M.; Avati, V.; Grzanka, L.; Malawski, M.;
Bialkowska, H.; Bluj, M.; Boimska, B.; Frueboes, T.; Górski, M.;
Kazana, M.; Szleper, M.; Traczyk, P.; Zalewski, P.; Bunkowski, K.;
Byszuk, A.; Doroba, K.; Kalinowski, A.; Konecki, M.; Krolikowski,
J.; Olszewski, M.; Walczak, M.; Araujo, M.; Bargassa, P.; Bastos, D.;
Di Francesco, A.; Faccioli, P.; Galinhas, B.; Gallinaro, M.; Hollar,
J.; Leonardo, N.; Niknejad, T.; Seixas, J.; Shchelina, K.; Toldaiev,
O.; Varela, J.; Afanasiev, S.; Gavrilenko, M.; Golunov, A.; Golutvin,
I.; Gorbounov, N.; Gorbunov, I.; Kamenev, A.; Karjavine, V.; Korenkov,
V.; Lanev, A.; Malakhov, A.; Matveev, V.; Moisenz, P.; Palichik, V.;
Perelygin, V.; Seitova, D.; Shmatov, S.; Smirnov, V.; Teryaev, O.;
Voytishin, N.; Zarubin, A.; Gavrilov, G.; Golovtcov, V.; Ivanov, Y.;
Kim, V.; Kuznetsova, E.; Murzin, V.; Oreshkin, V.; Smirnov, I.; Sosnov,
D.; Sulimov, V.; Uvarov, L.; Volkov, S.; Vorobyev, A.; Andreev, Yu.;
Dermenev, A.; Gninenko, S.; Golubev, N.; Karneyeu, A.; Kirsanov, M.;
Krasnikov, N.; Pashenkov, A.; Pivovarov, G.; Tlisov, D.; Toropin, A.;
Epshteyn, V.; Gavrilov, V.; Lychkovskaya, N.; Nikitenko, A.; Popov,
V.; Pozdnyakov, I.; Safronov, G.; Spiridonov, A.; Stepennov, A.;
Toms, M.; Vlasov, E.; Zhokin, A.; Aushev, T.; Chistov, R.; Danilov,
M.; Parygin, P.; Philippov, D.; Polikarpov, S.; Andreev, V.; Azarkin,
M.; Dremin, I.; Kirakosyan, M.; Terkulov, A.; Baskakov, A.; Belyaev,
A.; Boos, E.; Dudko, L.; Ershov, A.; Gribushin, A.; Kodolova, O.;
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Bibcode: 2020PhRvL.125v2001S
Altcode:
Ultrarelativistic heavy ion collisions recreate in the laboratory
the thermodynamical conditions prevailing in the early universe up to
10-6 sec , thereby allowing the study of the quark-gluon
plasma (QGP), a state of quantum chromodynamics (QCD) matter with
deconfined partons. The top quark, the heaviest elementary particle
known, is accessible in nucleus-nucleus collisions at the CERN
LHC, and constitutes a novel probe of the QGP. Here, we report the
first evidence for the production of top quarks in nucleus-nucleus
collisions, using lead-lead collision data at a nucleon-nucleon
center-of-mass energy of 5.02 TeV recorded by the CMS experiment. Two
methods are used to measure the cross section for top quark pair
production (σt t ¯ ) via the selection of charged
leptons (electrons or muons) and bottom quarks. One method relies
on the leptonic information alone, and the second one exploits,
in addition, the presence of bottom quarks. The measured cross
sections, σt t ¯=2.5 4-0.74+0.84 and
2.03-0.64+0.71 μ b , respectively, are compatible
with expectations from scaled proton-proton data and QCD predictions.
Title: Submerged Sources of Transient Acoustic Emission from Solar
Flares
Authors: Lindsey, Charles; Buitrago-Casas, J. C.; Martínez Oliveros,
Juan Carlos; Braun, Douglas; Martínez, Angel D.; Quintero Ortega,
Valeria; Calvo-Mozo, Benjamín; Donea, Alina-Catalina
Bibcode: 2020ApJ...901L...9L
Altcode:
We report the discovery of ultra-impulsive acoustic emission from
a solar flare, emission with a seismic signature that indicates
submersion of its source approximately a Mm beneath the photosphere
of the active region that hosted the flare. Just over two decades ago
V. V. Zharkova and A. G. Kosovichev discovered the first acoustic
transient released into the Sun's interior by a solar flare. These
acoustic waves, refracted back upward to the solar surface after
their release, make conspicuous Doppler ripples spreading outward
from the flaring region that tell us a lot about their sources. The
mechanism by which these transients are driven has stubbornly eluded
our understanding. Some of the source regions, for example, are devoid
of secondary Doppler, magnetic, or thermal disturbances in the outer
atmosphere of the source regions that would signify the driving agent
of an intense seismic transient in the outer atmosphere. In this
study, we have applied helioseismic holography, a diagnostic based
upon standard wave optics, to reconstruct a 3D image of the sources
of acoustic waves emanating from the M9.3-class flare of 2011 July
30. These images contain a source component that is submerged a full
Mm beneath the active-region photosphere. The signature of acoustic
sources this deep in the solar interior opens new considerations into
the physics that must be involved in transient acoustic emission from
flares—and possibly of flare physics at large. We develop analogies
to seismicity remotely triggered by tremors from distant earthquakes,
and consider prospects of new insight into the architecture of magnetic
flux beneath flaring active regions.
Title: Ultra-impulsive Solar Flare Seismology
Authors: Martínez, Angel D.; Quintero Ortega, Valeria; Buitrago-Casas,
J. C.; Martínez Oliveros, Juan Carlos; Calvo-Mozo, Benjamín;
Lindsey, Charles
Bibcode: 2020ApJ...895L..19M
Altcode:
We examine a strong, coherent, highly impulsive acoustic
transient radiated into the solar interior by the flare
SOL20110730T02:04-M9.3. The acoustic spectrum of this transient
extends out to 10 mHz. The fine diffraction limit of this
high-frequency component of the flare acoustic transient allows us
to discriminate different source components in operation during the
flare. Acoustic-source power density maps of the 10 mHz component show
sources that are compact to within the now 760 km diffraction limit of
local helioseismic diagnostics for this frequency. One of the acoustic
sources found is bifurcated across a sharp penumbral magnetic boundary,
the component in the stronger magnetic field temporally lagging its
partner. The facility to discriminate this level of acoustic-source
detail could open the door to a long sought after understanding
of the mechanics of transient emission from solar flares, still
a mystery two decades after its discovery. It also suggests that
helioseismic observations of higher cadence and spatial resolution
could reveal coherent acoustic emission at even higher frequencies,
with proportionately further potential benefits to solar seismology
and its growing domain of applications.
Title: Using the Butterfly Effect to Probe How the Sun Generates
Acoustic Noise
Authors: Lindsey, Charles; Rempel, Matthias
Bibcode: 2020SoPh..295...26L
Altcode:
A major encumbrance to recognition of individual episodes of noise
emission is the accumulation over hours of other noise emitted long
before. This is true in simulations just as it is in the solar
environment itself. The composite seismic signature of acoustic
radiation accumulated over preceding hours drowns out the signature
of newly emitted "acoustic pings." This problem could be alleviated in
simulations by periodically damping the accumulated acoustic radiation
- if this can be done benignly, i.e. in such a way that the onset
transient of the damping (and its subsequent termination) does not emit
its own acoustic noise. We introduce a way of doing this based upon a
study of the butterfly effect in compressible radiative MHD simulations
of convection that excites p-modes. This gives us an encouraging preview
of what further development of this utility offers for an understanding
of the character of p-mode generation in convective atmospheres.
Title: Comparison of Helioseismic Far-Side Active Region Detections
with STEREO Far-Side EUV Observations of Solar Activity
Authors: Liewer, P. C.; Qiu, J.; Lindsey, C.
Bibcode: 2017SoPh..292..146L
Altcode: 2017arXiv170907801L
Seismic maps of the Sun's far hemisphere, computed from Doppler
data from the Helioseismic and Magnetic Imager (HMI) on board the
Solar Dynamics Observatory (SDO) are now being used routinely
to detect strong magnetic regions on the far side of the Sun
(http://jsoc.stanford.edu/data/farside/). To test the reliability of
this technique, the helioseismically inferred active region detections
are compared with far-side observations of solar activity from the
Solar TErrestrial RElations Observatory (STEREO), using brightness in
extreme-ultraviolet light (EUV) as a proxy for magnetic fields. Two
approaches are used to analyze nine months of STEREO and HMI data. In
the first approach, we determine whether new large east-limb active
regions are detected seismically on the far side before they appear
Earth side and study how the detectability of these regions relates
to their EUV intensity. We find that while there is a range of EUV
intensities for which far-side regions may or may not be detected
seismically, there appears to be an intensity level above which they
are almost always detected and an intensity level below which they
are never detected. In the second approach, we analyze concurrent
extreme-ultraviolet and helioseismic far-side observations. We
find that 100% (22) of the far-side seismic regions correspond to an
extreme-ultraviolet plage; 95% of these either became a NOAA-designated
magnetic region when reaching the east limb or were one before crossing
to the far side. A low but significant correlation is found between the
seismic signature strength and the EUV intensity of a far-side region.
Title: What can He II 304 Å tell us about transient seismic emission
from solar flares?
Authors: Lindsey, C.; Donea, A. C.
Bibcode: 2017IAUS..327..113L
Altcode:
After neary 20 years since their discovery by Kosovichev and Zharkova,
the mechanics of the release of seismic transients into the solar
interior from some flares remain a mystery. Seismically emissive
flares invariably show the signatures of intense chromosphere
heating consistent with pressure variations sufficient to drive
seismic transients commensurate with helioseismic observations-under
certain conditions. Magnetic observations show the signatures of
apparent magnetic changes, suggesting Lorentz-force transients that
could likewise drive seismic transients-similarly subject to certain
conditions. But, the diagnostic signatures of both of these prospective
drivers are apparent over vast regions from which no significant
seismic emission emanates. What distinguishes the source regions of
transient seismic emission from the much vaster regions that show the
signatures of both transient heating and magnetic variations but are
acoustically unproductive? Observations of acoustically active flares
in He II 304 Å by the Atomospheric Imaging Assembly (AIA) aboard the
Solar Dynamics Observatory (SDO) offer a promising new resource with
which to address this question.
Title: Advances in Predicting Magnetic Fields on the Far Side of
the Sun
Authors: Lindsey, C. A.
Bibcode: 2016AGUFMSH42B..01L
Altcode:
Techniques in local solar seismology applied to observations of
seismic oscillations in the Sun's near hemisphere allow us to map
large magnetic regions in the Sun's far hemisphere. Seismic signatures
are not nearly as sensitive to magnetic flux as observations in
electromagnetic radiation. However, they clearly identify and locate
the 400 or so largest active regions in a typical solar cycle, i.e.,
those of most concern for space-weather forecasting. By themselves,
seismic observations are insensitive to magnetic polarity. However,
the Hale polarity law offers tantalizing avenues for guessing polarity
distributions from seismic signatures as they evolve. I will review what
we presently know about the relationship between seismic signatures
of active regions and their magnetic and radiative properties, and
offer a preliminary assessment of the potential of far-side seismic
maps for space-weather forecasting in the coming decade.
Title: Comparison of Far-Side Helioseismic Predictions of Active
Regions from SDO/HMI with Far-side Observations of Solar Activity
from STEREO/EUVI
Authors: Liewer, Paulett C.; Hall, Jeffrey R.; Lindsey, Charles;
Qiu, Jiong
Bibcode: 2016shin.confE..29L
Altcode:
Space weather predictions can be greatly improved with
good predictions of magnetic fields on the far side of the
Sun. Dopplergrams from SDO/HMI are being used routinely to predict
strong magnetic field regions on the far side using helioseismology
(http://jsoc.stanford.edu/data/farside/). The Dopplergrams are processed
to produce seismic Carrington maps where regions of large (negative)
seismic phase shift are interpreted as regions of strong magnetic
field. Previously, we have tested the reliability of helioseismic
far-side active region predictions from both GONG and HMI using a
qualitative comparison with far-side observation of solar activity
from the Solar TERrestrial Relations Observatory (STEREO) (Liewer et
al., Sol. Phys. 2012, 2014) using brightness in EUVI 304Å images as
a proxy for strong magnetic fields. By visual comparison of these
seismic maps with 304Å Carrington maps, we determined whether or
not solar activity, as evidenced by brightness in EUV, is observed
at the predicted locations and whether or not new active regions
are predicted before they appear Earthside. We found that for all
heliseismic far-side strong field regions, there was a corresponding
bright region in EUV. However, the converse was not true: some regions
bright in EUV were not seen in the seismic maps. The comparisons are
now being extended to quantify the relationship between the seismic
signal and the EUV brightness to increase our understanding of why only
some of the regions bright in EUV are seen in the seismic maps. Here
we present preliminary results of this quantitative comparison.
Title: Seismic Mapping of the Sun's Far Hemisphere for Applications
in Space-Weather Forecasting
Authors: Lindsey, Charles; Werne, Joseph; Hill, Frank
Bibcode: 2016shin.confE..36L
Altcode:
Magnetic regions in the Sun's outer atmosphere exert a major impact
on space weather at Earth. Magnetic regions in the far hemisphere
appear to exert relatively little immediate impact, but, because the
Sun rotates, these regions cross into the near hemisphere somewhat
suddenly and without warning--except for our ability to monitor the
Sun's far hemisphere. Monitoring of the Sun's far hemisphere therefore
becomes crucial to space-weather forecasting on time scales ranging from
a few days to a few weeks. For the past several years, this need has
been well served by NASA's twin STEREO spacecraft, which, since 2011,
have been in positions to view the entirety of the Sun's far hemisphere
directly. Beginning in about 2019, STEREO coverage of the far hemisphere
will begin to diminish, as both of the STEREO spacecraft drift back to
Earth's side of the solar system. For most of the succeeding decade,
solar seismology will be the only means of detecting and accurately
locating large, newly emerging active regions that covers the entirety
of the Sun's far hemisphere. We will review the development of
seismology of the Sun's far hemisphere from the 1990s to present. We
will summarize recent developments in seismic sensing of the Sun's
far hemisphere, describing its basic capabilities and limitations as a
tool for detecting and locating new emerging magnetic flux in the Sun's
far hemisphere and forecasting its subsequent transit across the Sun's
eastern limb. We will also offer projections on coming improvements in
far-side solar seismology of likely value to space-weather forecasters.
Title: Solar chromosphere: a portal for sunquakes
Authors: Donea, A. C.; Lindsey, C. A.
Bibcode: 2015AGUFMSH22A..02D
Altcode:
Recent solar images from instruments such as IRIS, FIRS, IBIS and SDO
reveal interesting properties of the chromosphere and other layers
above flaring active regions . These may finally give us some clues on
why some solar flares allow an energy input back into the photosphere,
generating sunquakes. We will discuss recent observations of sunquakes
and analyse the main role of the "right chromosphere" for a sunquake
event.
Title: A Statistical Correlation of Sunquakes Based on Their Seismic
and White-Light Emission
Authors: Buitrago-Casas, J. C.; Martínez Oliveros, J. C.; Lindsey,
C.; Calvo-Mozo, B.; Krucker, S.; Glesener, L.; Zharkov, S.
Bibcode: 2015SoPh..290.3151B
Altcode: 2015arXiv150207798B; 2015SoPh..tmp..169B
Several mechanisms have been proposed to explain the transient seismic
emission, i.e. "sunquakes," from some solar flares. Some theories
associate high-energy electrons and/or white-light emission with
sunquakes. High-energy charged particles and their subsequent heating
of the photosphere and/or chromosphere could induce acoustic waves in
the solar interior. We carried out a correlative study of solar flares
with emission in hard X-rays, enhanced continuum emission at 6173 Å,
and transient seismic emission. We selected those flares observed by
the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
with a considerable flux above 50 keV between 1 January 2010 and
26 June 2014. We then used data from the Helioseismic and Magnetic
Imager onboard the Solar Dynamic Observatory to search for excess
visible-continuum emission and new sunquakes not previously reported. We
found a total of 18 sunquakes out of 75 flares investigated. All of the
sunquakes were associated with an enhancement of the visible continuum
during the flare. Finally, we calculated a coefficient of correlation
for a set of dichotomic variables related to these observations. We
found a strong correlation between two of the standard helioseismic
detection techniques, and between sunquakes and visible-continuum
enhancements. We discuss the phenomenological connectivity between these
physical quantities and the observational difficulties of detecting
seismic signals and excess continuum radiation.
Title: Active Region Morphologies Selected from Near-side Helioseismic
Data
Authors: MacDonald, G. A.; Henney, C. J.; Díaz Alfaro, M.; González
Hernández, I.; Arge, C. N.; Lindsey, C.; McAteer, R. T. J.
Bibcode: 2015ApJ...807...21M
Altcode:
We estimate the morphology of near-side active regions using near-side
helioseismology. Active regions from two data sets, Air Force Data
Assimilative Photospheric flux Transport synchronic maps and Global
Oscillation Network Group near-side helioseismic maps, were matched and
their morphologies compared. Our algorithm recognizes 382 helioseismic
active regions between 2002 April 25 and 2005 December 31 and matches
them to their corresponding magnetic active regions with 100% success. A
magnetic active region occupies 30% of the area of its helioseismic
signature. Recovered helioseismic tilt angles are in good agreement with
magnetic tilt angles. Approximately 20% of helioseismic active regions
can be decomposed into leading and trailing polarity. Leading polarity
components show no discernible scaling relationship, but trailing
magnetic polarity components occupy approximately 25% of the area of the
trailing helioseismic component. A nearside phase-magnetic calibration
is in close agreement with a previous far-side helioseismic calibration
and provides confidence that these morphological relationships can
be used with far-side helioseismic data. Including far-side active
region morphology in synchronic maps will have implications for coronal
magnetic topology predictions and solar wind forecasts.
Title: Active Region Morphologies Selected From Near-side Helioseismic
Data
Authors: MacDonald, Gordon Andrew; Henney, Carl; Diaz Alfaro, Manuel;
Gonzalez Hernandez, Irene; Arge, Nick; Lindsey, Charles; McAteer, James
Bibcode: 2015TESS....111302M
Altcode:
We estimate the morphology of near-side active regions using near-side
helioseismology. Active regions from two data sets, ADAPT synchronic
maps and GONG near-side helioseismic maps, were matched and their
morphologies compared. Our algorithm recognizes 382 helioseismic active
regions between 2002 April 25 and 2005 December 31 and matches them
to their corresponding magnetic active regions with 100% success. A
magnetic active region occupies 30% of the area of its helioseismic
signature. Recovered helioseismic tilt angles are in good agreement with
magnetic tilt angles. Approximately 20% of helioseismic active regions
can be decomposed into leading and trailing polarity. Leading polarity
components show no discernible scaling relationship, but trailing
magnetic polarity components occupy approximately 25% of the area of the
trailing helioseismic component. A nearside phase-magnetic calibration
is in close agreement with a previous far-side helioseismic calibration
and provides confidence that these morphological relationships can
be used with far-side helioseismic data. Including far-side active
region morphology in synchronic maps will have implications for coronal
magnetic topology predictions and solar wind forecasts.
Title: Testing the Reliability of Predictions of Far-Side Active
Regions from Helioseismology Using STEREO Far-Side Observations of
Solar Activity
Authors: Liewer, P. C.; González Hernández, I.; Hall, J. R.; Lindsey,
C.; Lin, X.
Bibcode: 2014SoPh..289.3617L
Altcode: 2014SoPh..tmp...83L
We test the reliability of helioseismic far-side active-region
predictions, made using Dopplergrams from both the Helioseismic and
Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO)
and the Global Oscillation Network Group (GONG), by comparison with
far-side observation of solar activity from the Solar TErrestrial
RElations Observatory (STEREO). Both GONG and HMI produce seismic
Carrington maps that show strong magnetic-field regions, labeling
predictions of far-side active regions that have a probability ≥
70 %. By visual comparison of these prediction maps with STEREO
extreme ultraviolet (EUV) Carrington maps, we determine whether or
not solar activity, as evidenced as brightness in EUV, is observed
at the predicted locations. We analyzed nine months of data from 2011
and 2012. For both GONG and HMI, we find that for approximately 90 %
of the active-region predictions, activity/brightness is observed in
EUV at the predicted location. We also investigated the success of GONG
and HMI at predicting large active regions before they appear at the
east limb as viewed from Earth. Of the 27 identified large east-limb
active regions in the nine months of data analyzed, GONG predicted 15
(55 %) at least once within the week prior to Earth-side appearance and
HMI predicted 13 (48 %). Based on the STEREO far-side EUV observations,
we suggest that 9 of the 27 active regions were probably too weak to be
predicted while on the far side. Overall, we conclude that HMI and GONG
have similar reliability using the current data-processing procedures.
Title: Forecasting Applications of Seismic Monitoring of the Sun's
Far Hemisphere
Authors: Lindsey, Charles; Donea, Alina-Catalina
Bibcode: 2014shin.confE.165L
Altcode:
Most of the solar influence on space weather in the terrestrial
neighborhood appears to emanate from magnetic regions in the Sun's
near hemisphere, i.e., that facing Earth. Because of solar rotation,
long-lived active regions in the far hemisphere generally rotate
into the near hemisphere within a week or two. Because of this,
space-weather forecasting over periods much exceeding a few days
can be greatly facilitated by the monitor of magnetic regions in
the Sun's far hemisphere. Computational seismic holography of the
Sun's far hemisphere provides us with such a monitor. We will review
recent improvements in seismic monitoring of the Sun's far hemisphere,
and outline prospective resources for further improvements. We will
also review developing applications of far-side seismic monitoring to
space-weather forecasting.
Title: The Role of Magnetic Fields in Transient Seismic Emission
Driven by Atmospheric Heating in Flares
Authors: Lindsey, C.; Donea, A. -C.; Martínez Oliveros, J. C.;
Hudson, H. S.
Bibcode: 2014SoPh..289.1457L
Altcode: 2013arXiv1303.3299L; 2014SoPh..tmp....9L
Transient seismic emission in flares remains largely mysterious. Its
discoverers proposed that seismic transients are driven by impulsive
heating of the flaring chromosphere. Simulations of such heating
show strong shocks, but these are damped by heavy radiative losses
as they proceed downward. Because compression of the gas the shock
enters both heats it and increases its density, the radiative losses
increase radically with the strength of the shock, leaving doubt
that sufficient energy can penetrate into the solar interior to
explain helioseismic signatures. We note that simulations to date
have no account for strong, inclined magnetic fields characteristic
of transient-seismic-source environments. A strong horizontal magnetic
field, for example, greatly increases the compressional modulus of the
chromospheric medium, greatly reducing compression of the gas, hence
radiative losses. Inclined magnetic fields, then, must be fundamental
to the role of impulsive heating in transient seismic emission.
Title: Transient Artifacts in a Flare Observed by the Helioseismic
and Magnetic Imager on the Solar Dynamics Observatory
Authors: Martínez Oliveros, J. C.; Lindsey, C.; Hudson, H. S.;
Buitrago Casas, J. C.
Bibcode: 2014SoPh..289..809M
Altcode: 2013arXiv1307.5097M
The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO) provides a new tool for the systematic observation
of white-light flares, including Doppler and magnetic information as
well as continuum. In our initial analysis of the highly impulsive -ray
flare SOL2010-06-12T00:57 (Martínez Oliveros et al., Solar Phys.269,
269, 2011), we reported the signature of a strong blueshift in the
two footpoint sources. Concerned that this might be an artifact due
to aliasing peculiar to the HMI instrument, we undertook a comparative
analysis of Global Oscillation Network Group (GONG++) observations of
the same flare, using the PArametric Smearing Correction ALgorithm
(PASCAL) algorithm to correct for artifacts caused by variations in
atmospheric smearing. This analysis confirms the artifactual nature
of the apparent blueshift in the HMI observations, finding weak
redshifts at the footpoints instead. We describe the use of PASCAL
with GONG++ observations as a complement to the SDO observations
and discuss constraints imposed by the use of HMI far from its design
conditions. With proper precautions, these data provide rich information
on flares and transients.
Title: Chromospheric and Coronal Observations of Solar Flares with
the Helioseismic and Magnetic Imager
Authors: Martínez Oliveros, Juan-Carlos; Krucker, Säm; Hudson, Hugh
S.; Saint-Hilaire, Pascal; Bain, Hazel; Lindsey, Charles; Bogart,
Rick; Couvidat, Sebastien; Scherrer, Phil; Schou, Jesper
Bibcode: 2014ApJ...780L..28M
Altcode: 2013arXiv1311.7412M
We report observations of white-light ejecta in the low corona, for
two X-class flares on 2013 May 13, using data from the Helioseismic
and Magnetic Imager (HMI) of the Solar Dynamics Observatory. At least
two distinct kinds of sources appeared (chromospheric and coronal),
in the early and later phases of flare development, in addition to
the white-light footpoint sources commonly observed in the lower
atmosphere. The gradual emissions have a clear identification
with the classical loop-prominence system, but are brighter than
expected and possibly seen here in the continuum rather than line
emission. We find the HMI flux exceeds the radio/X-ray interpolation
of the bremsstrahlung produced in the flare soft X-ray sources by at
least one order of magnitude. This implies the participation of cooler
sources that can produce free-bound continua and possibly line emission
detectable by HMI. One of the early sources dynamically resembles
"coronal rain", appearing at a maximum apparent height and moving
toward the photosphere at an apparent constant projected speed of 134
± 8 km s-1. Not much literature exists on the detection of
optical continuum sources above the limb of the Sun by non-coronagraphic
instruments and these observations have potential implications for our
basic understanding of flare development, since visible observations
can in principle provide high spatial and temporal resolution.
Title: Computational Seismic Holography of Transient Seismic Emission
from Flares
Authors: Lindsey, C.; Donea, A. -C.; Martínez Oliveros, J. C.
Bibcode: 2013ASPC..478..323L
Altcode:
Conceived as an optimal basis for local helioseismology, computational
seismic holography applies basic principles of optics to helioseismic
signatures of waves that travel through the Sun's interior, including
its far hemisphere. Objects of its diagnostic applications include
the thermal and magnetic structure of active regions, sources of
seismic emission from the quiet Sun, active regions in the Sun's far
hemisphere, and transient seismic emission from flares. The monitor
of active regions in the Sun's far hemisphere is described by another
paper in these proceedings. This paper reviews the application of
computational seismic holography as a diagnostic of transient seismic
emission from flares.
Title: Statistics of Local Seismic Emission from the Solar Granulation
Authors: Lindsey, Charles; Donea, Alina-Catalina
Bibcode: 2013JPhCS.440a2044L
Altcode: 2013arXiv1307.1336L
We apply computational seismic holography to high-frequency helioseismic
observations of the quiet Sun from SDO/HMI to locate predominant
sources of seismic emission with respect to the structure of the solar
granulation. The regions of greatest seismic emission are the edges of
photospheric granules. Seismic emission from regions whose continuum
brightnesses are 95-100% of the mean, as resolved by HMI, are about
2.5 times as emissive as regions whose brightnesses are 100-104% of the
mean. The greater seismic emissivity from regions whose brightnesses are
somewhat less than the mean is roughly in line with expectations from
an understanding that attributes most seismic emission to cool plumes
plummeting from the edges of granules. However, seismic emission from
regions whose continuum brightnesses significantly exceed 104% of the
mean is also remarkably high. This unexpected feature of high-frequency
seismic emission from the solar granulation begs to be understood.
Title: Far-side helioseismic maps: the next generation
Authors: González Hernández, Irene; Lindsey, Charles; Braun,
Douglas C.; Bogart, Richard S.; Scherrer, Philip H.; Hill, Frank
Bibcode: 2013JPhCS.440a2029G
Altcode:
For more than a decade, far-side seismic maps of medium-to-large active
regions have proven their capability as a space weather forecasting
tool. In the last few years, these maps have started to serve another
purpose: complementing the front side observations that are input to
different solar models. Photospheric flux transport as well as solar
spectral irradiance models have been shown to produce improved results
when incorporating the far-side seismic maps as well as providing
better forecasting. The challenge for the future is twofold: Far-side
seismic monitoring needs to be more sensitive, and it needs to offer
more information. We present here initial steps towards fulfilling
these goals using higher resolution input images, adding extra skips
to the analysis and changing the presentation of the maps.
Title: A survey in WL and HXR emission on the energetic solar flares
ocurred during the beginning of the 24 solar cycle and their possible
relation with the generation of seismic signals
Authors: Buitrago-Casas, J. C.; Martinez Oliveros, J.; Lindsey, C.;
Glesener, L.; Calvo-Mozo, B.
Bibcode: 2012AGUFMSH43B2163B
Altcode:
Solar flares are explosive phenomena, thought to be driven by magnetic
free energy accumulated in the solar corona. Some flares release seismic
transients, "sunquakes", into the Sun's interior. Different mechanism
are being considered to explain how sunquakes are generated. We are
conducting a survey of HXR, white-light and seismic emission from X- and
M-class flares in the early ascending phase of solar cycle 24. Seismic
diagnostics are based upon standard time-distance techniques, including
seismic holography, applied to Dopplergrams obtained by HMI/SDO and
GONG. The relation between HXR and white-light emissions may carry
important information on impulsive chromospheric heating during flares,
a prospective contributor to seismic transient emission, at least in
some instances.
Title: Studying "beating" patterns of modes between North and South
hemispheres' solar cycles
Authors: Williamson, E.; Featherstone, N.; Lindsey, C.; Dikpati, M.
Bibcode: 2012AGUFMSH41D2128W
Altcode:
The periodic appearance and equator-ward migration of sunspots on
the solar surface, the telltale sign of the 22-year solar cycle, is a
process that does not operate symmetrically between the northern and
southern hemispheres. We characterize the similarities and differences
between the two hemispheres using a Fourier modal decomposition of the
sunspot area record for each cycle. For this purpose we use long-term
spot area data available since 1878. Our goals are first to see how
well the individual cycle shapes can be described in terms of a few
modes, second to characterize the asymmetries and symmetries between
different hemispheres in terms of the interference of these individual
modes, and third to establish whether or not any long term trends are
evident when the data is viewed in this way. More specifically, we are
interested in trends that might aid in the development of predictive
capability for future cycles. We analyze the resulting amplitudes and
phase shifts between cycles and hemispheres and find that individual
cycles can be well represented by as few as 5 modes. Cycles with a
high maximum total area tend to have a large variation in strength
of harmonics, and correspondingly cycles with a small maximum total
area tend to have little variation in strength of harmonics. A large
difference between the amplitude of the fundamental mode in the north
and south does not necessarily correspond to a large difference between
north and south at higher harmonics.
Title: Magneto-Acoustic Energetics Study of the Seismically Active
Flare of 15 February 2011
Authors: Alvarado-Gómez, J. D.; Buitrago-Casas, J. C.;
Martínez-Oliveros, J. C.; Lindsey, C.; Hudson, H.; Calvo-Mozo, B.
Bibcode: 2012SoPh..280..335A
Altcode: 2012arXiv1203.3907A; 2012SoPh..tmp..131A
Multi-wavelength studies of energetic solar flares with seismic
emissions have revealed interesting common features between
them. We studied the first GOES X-class flare of Solar Cycle 24,
as detected by the Solar Dynamics Observatory (SDO). For context,
seismic activity from this flare (SOL2011-02-15T01:55-X2.2, in NOAA
AR 11158) has been reported by Kosovichev (Astrophys. J. Lett.,
734, L15, 2011) and Zharkov et al. (Astrophys. J. Lett., 741, L35,
2011). Based on Dopplergram data from the Helioseismic and Magnetic
Imager (HMI), we applied standard methods of local helioseismology
in order to identify the seismic sources in this event. RHESSI hard
X-ray data are used to check the correlation between the location of
the seismic sources and the particle-precipitation sites in during
the flare. Using HMI magnetogram data, the temporal profile of
fluctuations in the photospheric line-of-sight magnetic field is used
to estimate the magnetic-field change in the region where the seismic
signal was observed. This leads to an estimate of the work done by the
Lorentz-force transient on the photosphere of the source region. In this
instance, this is found to be a significant fraction of the acoustic
energy in the attendant seismic emission, suggesting that Lorentz forces
can contribute significantly to the generation of sunquakes. However,
there are regions in which the signature of the Lorentz force is much
stronger, but from which no significant acoustic emission emanates.
Title: Web-based Comprehensive Data Archive of Seismically Active
Solar Flares
Authors: Besliu-Ionescu, Diana; Donea, Alina; Cally, Paul; Lindsey,
Charles
Bibcode: 2012asst.book...31B
Altcode:
Some solar flares can release acoustic transients into the solar
subsurface of the active regions that host them. Most of the acoustic
power in these transients propagates something like 10-30 Mm beneath
the photosphere before it is refracted back to the surface, where it
raises a significant disturbance. In the strongest of these "sunquakes",
the manifestation of this transient in helio-seismic movies is an
outwardly expanding surface ripple that becomes conspicuous about
20 minutes after the impulsive phase of the flare. These "sunquakes"
offer a powerful diagnostic of wave propagation in the active region
photosphere and of the structure and dynamics of the subphotosphere. We
will present here a detailed description of our comprehensive survey
of the SOHO-MDI database for acoustic signatures from flares and the
technique used in this process. The results of the survey are presented
in a database of seismic sources generated by X and M class solar flares
during 1996-2007. It is based on a table format showing the general
characteristics of the acoustically active flares, and the times of the
solar quakes (beginning, maximum and end). The database is linked to
a composite of images of the seismic sources in different wavelengths.
Title: Confronting a solar irradiance reconstruction with solar and
stellar data
Authors: Judge, P. G.; Lockwood, G. W.; Radick, R. R.; Henry, G. W.;
Shapiro, A. I.; Schmutz, W.; Lindsey, C.
Bibcode: 2012A&A...544A..88J
Altcode:
Context. A recent paper by Shapiro and colleagues (2011, A&A,
529, A67) reconstructs spectral and total irradiance variations of
the Sun during the holocene. Aims. In this note, we comment on why
their methodology leads to large (0.5%) variations in the solar TSI on
century-long time scales, in stark contrast to other reconstructions
which have ∼ 0.1% variations. Methods. We examine the amplitude
of the irradiance variations from the point of view of both solar
and stellar data. Results. Shapiro et al.'s large amplitudes arise
from differences between the irradiances computed from models A and C
of Fontenla and colleagues, and from their explicit assumption that
the radiances of the quiet Sun vary with the cosmic ray modulation
potential. We suggest that the upper photosphere, as given by model A,
is too cool, and discuss relative contributions of local vs. global
dynamos to the magnetism and irradiance of the quiet Sun. We compare
the slow (>22 yr) components of the irradiance reconstructions with
secular changes in stellar photometric data that span 20 years or less,
and find that the Sun, if varying with such large amplitudes, would
still lie within the distribution of stellar photometric variations
measured over a 10-20 year period. However, the stellar time series
are individually too short to see if the reconstructed variations will
remain consistent with stellar variations when observed for several
decades more. Conclusions. By adopting model A, Shapiro et al. have
over-estimated quiet-Sun irradiance variations by about a factor of
two, based upon a re-analysis of sub-mm data from the James Clerk
Maxwell telescope. But both estimates are within bounds set by current
stellar data. It is therefore vital to continue accurate photometry of
solar-like stars for at least another decade, to reveal secular and
cyclic variations on multi-decadal time scales of direct interest to
the Sun.
Title: Determination of Electromagnetic Source Direction as an
Eigenvalue Problem
Authors: Martínez-Oliveros, Juan C.; Lindsey, Charles; Bale, Stuart
D.; Krucker, Säm
Bibcode: 2012SoPh..279..153M
Altcode: 2012arXiv1205.2393M; 2012SoPh..tmp...98M
Low-frequency solar and interplanetary radio bursts are generated at
frequencies below the ionospheric plasma cutoff and must therefore
be measured in space, with deployable antenna systems. The problem
of measuring both the general direction and polarization of an
electromagnetic source is commonly solved by iterative fitting
methods such as linear regression that deal simultaneously with both
directional and polarization parameters. We have developed a scheme
that separates the problem of deriving the source direction from that of
determining the polarization, avoiding iteration in a multi-dimensional
manifold. The crux of the method is to first determine the source
direction independently of concerns as to its polarization. Once
the source direction is known, its direct characterization in terms
of Stokes vectors, in a single iteration if desired, is relatively
simple. This study applies the source-direction determination to radio
signatures of flares received by STEREO. We studied two previously
analyzed radio type III bursts and found that the results of the
eigenvalue decomposition technique are consistent with those obtained
previously by Reiner et al. (Solar Phys.259, 255, 2009). For the type
III burst observed on 7 December 2007, the difference in travel times
from the derived source location to STEREO A and B is the same as the
difference in the onset times of the burst profiles measured by the
two spacecraft. This is consistent with emission originating from a
single, relatively compact source. For the second event of 29 January
2008, the relative timing does not agree, suggesting emission from
two sources separated by 0.1 AU, or perhaps from an elongated region
encompassing the apparent source locations.
Title: The Height of a White-light Flare and Its Hard X-Ray Sources
Authors: Martínez Oliveros, Juan-Carlos; Hudson, Hugh S.; Hurford,
Gordon J.; Krucker, Säm; Lin, R. P.; Lindsey, Charles; Couvidat,
Sebastien; Schou, Jesper; Thompson, W. T.
Bibcode: 2012ApJ...753L..26M
Altcode: 2012arXiv1206.0497M
We describe observations of a white-light (WL) flare
(SOL2011-02-24T07:35:00, M3.5) close to the limb of the Sun, from which
we obtain estimates of the heights of the optical continuum sources and
those of the associated hard X-ray (HXR) sources. For this purpose, we
use HXR images from the Reuven Ramaty High Energy Spectroscopic Imager
and optical images at 6173 Å from the Solar Dynamics Observatory. We
find that the centroids of the impulsive-phase emissions in WL and HXRs
(30-80 keV) match closely in central distance (angular displacement
from Sun center), within uncertainties of order 0farcs2. This directly
implies a common source height for these radiations, strengthening the
connection between visible flare continuum formation and the accelerated
electrons. We also estimate the absolute heights of these emissions
as vertical distances from Sun center. Such a direct estimation has
not been done previously, to our knowledge. Using a simultaneous 195
Å image from the Solar-Terrestrial RElations Observatory spacecraft
to identify the heliographic coordinates of the flare footpoints,
we determine mean heights above the photosphere (as normally defined;
τ = 1 at 5000 Å) of 305 ± 170 km and 195 ± 70 km, respectively, for
the centroids of the HXR and WL footpoint sources of the flare. These
heights are unexpectedly low in the atmosphere, and are consistent
with the expected locations of τ = 1 for the 6173 Å and the ~40 keV
photons observed, respectively.
Title: On The Energetics Of Seismic Excitation Mechanisms
Authors: Martinez Oliveros, Juan Carlos; Bain, H.; Krucker, S.; Donea,
A.; Hudson, H.; Lin, R. P.; Lindsey, C.
Bibcode: 2012AAS...22020503M
Altcode:
Some solar flares emit strong acoustic transients into the solar
interior during their impulsive phases (Kosovichev and Zharkova,
1998). These transients penetrate thousands of kilometers beneath the
active region photosphere and refract back to the surface, where they
produce a characteristic helioseismic signature tens of thousands
of kilometers from their origin over the succeeding hour. Several
mechanisms of seismic excitation have been proposed, ranging from
hydrodynamic shocks to Lorentz force perturbations. However, regardless
of the mechanism of generation, it is clear that not all flares induce
an acoustic response in the interior of the Sun. A concrete hypothesis
or theory about the nature of this is still a topic of ongoing
investigations. For some particular flares, we present a comparative
study between the energy deposited by the proposed mechanisms of seismic
excitation and the acoustic energy deduced using holographic techniques.
Title: Physics of Transient Seismic Emission from Flares
Authors: Lindsey, Charles A.; Donea, A.; Malanushenko, A.
Bibcode: 2012AAS...22020409L
Altcode:
We consider the physics of seismic activity in solar flares, i.e., the
release of powerful seismic transients into the solar interior during
the impulsive phases of some flares. Recent work by Hudson, Fisher,
Welsch and Bercik has attracted a great deal of positive attention
to the possible role of Lorentz-force transients in driving seismic
transient emission in flares. The implications of direct involvement
by magnetic forces in seismic transient emission, if this could be
confirmed, would be major, since magnetic fields are thought to hold
the energy source of the flares themselves. The energy invested into
acoustic transients is a small fraction of the total released by the
flare, but requires a massive impulse many times that required to
accelerate high-energy electrons into which the energy is initially
thought to be invested. What does this say about a flare mechanism that
sometimes does both? We discuss some of the outstanding diagnostic
questions that confront the recognition of magnetic-field transients
associated with Lorentz force transients based on resources HMI,
Hinode, AIA and other facilities offer us.
Title: Direct Measurement Of The Height Of A White-light Flare
Authors: Hudson, Hugh S.; Martinez-Oliveros, J.; Krucker, S.; Hurford,
G.; Thompson, W.; Schou, J.; Couvidat, S.; Lindsey, C.
Bibcode: 2012AAS...22020441H
Altcode:
We have used RHESSI and HMI observations to observe hard X-ray and
white-light continuum sources of the limb flare SOL2011-02-24, and
find the source centroids to coincide within errors of about 0.2 arc s,
with the conclusion that the emissions form at the same height in the
atmosphere. This greatly strengthens the known association between
non-thermal electrons and white-light continuum formation. We also
use STEREO observations to find the heliographic coordinates of the
flare. This determines the projected height of the photosphere directly
below the flare emissions. With this information, the RHESSI metrology
determines the absolute height of the sources to be remarkably low
in the solar atmosphere: the two footpoints have comparable heights,
which we estimate at about 290 +- 138 km above the photosphere. This
location lies significantly below the visible-light limb height,
estimated at 500 km by Brown & Christensen-Dalsgaard (1998), and
the height of optical depth unity to Thomson scattering, estimated
at a higher altitude. The results are not consistent with any current
models of these processes.
Title: Do We Understand Why Most Solar Flares Do Not Generate Quakes?
Authors: Donea, Alina; Lindsey, C.
Bibcode: 2012AAS...22051603D
Altcode:
While some flares release power seismic transients into the solar
interior, it is clear that only a minority of even X-class flares do
this. Strangely, some major flares of the past cycle 23 were seismically
inactive. For cycle 24, we undertake a comparative multiwavelength
analysis of a seismically powerful flare and a seismically inactive one,
to understand, observationally and physically, the basic properties
that distinguish acoustically active flares and the physics that
determines why some flares release powerful seismic transients while
others do not. Mechanisms of seismic generation will be discussed,
focusing on the roles of thick-target heating by high-energy particles,
radiative heating by white-light emission, and Lorentz-force transients.
Title: Far-side seismic maps with HMI
Authors: Gonzalez Hernandez, I.; Lindsey, C. A.; Bogart, R. S.;
Scherrer, P. H.; Hill, F.
Bibcode: 2011AGUFMSH12A..01G
Altcode:
Seismic maps of the far side of the Sun have proven their capability
to locate and track medium to large active regions on the non-visible
hemisphere. Waves that travel all the way from the far side to the
front side carry information of the magnetic perturbations that they
encounter. The seismic holography technique makes use of the observation
of waves at the front side of the Sun and compares them to a model to
map areas of strong magnetic field on the far side. Recent improvements
to these maps include a more accurate determination of the location of
the active region, automatic highlighting of candidates, and calibration
in terms of the magnetic field strength. Since the launch of SDO,
the Helioseismic Magnetic Imager(HMI) has been providing maps of the
far-side activity. We discuss here strategies to optimize these far-side
maps as well as how to include extra information (such as realistic
error estimates and area determination) in order to use these maps as
input to irradiance and photospheric flux-transport models. Far-side
direct observations from STEREO will help to reach these goals.
Title: Far-side imaging tools, front-side imaging, and EUV solar
irradiance forecasting
Authors: Fontenla, J. M.; Quemerais, E.; Lindsey, C. A.
Bibcode: 2011AGUFMSH12A..03F
Altcode:
Currently we are in an advanced stage of the development of an
application of both far-side and front-side imaging to EUV solar
irradiance forecast. The basic method and its application to one case
were described by Fontenla et al. (2009). This method uses a combination
of several techniques for far-side imaging with front-side images at
various wavelengths, and EUV spectral synthesis. This presentation
shows that all these techniques should be used in concert to produce
a reasonably accurate EUV irradiance forecast at Earth and other
planets. The combination of SOHO/SWAN Ly alpha backscattering, far-side
helioseismic images, and front-side imaging resolves the weaknesses
of each technique by itself. In particular, the presentation will show
how the SOHO/SWAN data plays a very important role in this combination
by supplying unique EUV data (Ly alpha) that is not directly inferred
by helioseismic methods. The SOHO/SWAN data plays a key role in the
combination by allowing us to infer the evolution in EUV brightness of
the active regions on the far-side of the Sun. However, because this
method does not provide a good localization of the emission sources
in the Sun, it needs to me complemented by the good localization
that helioseismology provides. Because the Ly alpha backscattering is
sensitive to active network and plage these images provide essential
information for determining the far-side evolution of components to the
solar flux that are not detected by helioseismology but have important
effects on the EUV irradiance. However, again because of the poor
localization of these features in backscattering images, front side
imaging is also a necessary complement that helps in the localization
on the solar surface of the changes observed in the SOHO/SWAN images.
Title: Method of cleaning images of the GONG++ network applied to
seismically active flares
Authors: Buitrago-Casas, J. C.; Alvarado, J. D.; Martinez Oliveros,
J. C.; Lindsey, C. A.; Donea, A.; Calvo-Mozo, B.
Bibcode: 2011AGUFMSH13B1935B
Altcode:
The GONG++ network has been widely used in helioseismologic
analysis. However, like it is a terrestrial observatories network
the images are highly perturbed by the atmospheric variability, doing
it some impractical to be used in helioseismic techniques on compact
regions over the solar surface. In this work we discussed briefly the
cleaning techniques on the images proposed by Lindsey and Donea (2008)
to reduce the noise caused by the atmospheric smearing but now using in
it a laplacian of nine points instead of five points, like was proposed
originally by the authors, to correct the atmospheric smearing. This
method is applied to Dopplergrams of the seismically active flares
observed by GONG and compared with those taken by SOHO/MDI and SDO/HMI.
Title: Determination of Electromagnetic Source Direction of the 01
August 2011 Type II Burst
Authors: Martinez Oliveros, J. C.; Bale, S.; Lindsey, C. A.
Bibcode: 2011AGUFMSH22A..05M
Altcode:
Low frequency solar and interplanetary radio bursts are generated at
frequencies below the ionospheric plasma cutoff and must therefore
be measured in space, with deployable antenna systems. We present
a new radio direction-finding technique that separates the problem
of deriving the source direction from that of a determination of
polarization. The crux of the method is to first determine the source
direction independently of concerns as to its polarization. Once
the source direction is known, its direct characterization in terms
of Stokes vectors in a single iteration, if desired, is relatively
simple. This study applies the source-direction determination to radio
signatures of flares received by STEREO. We studied a radio type-II
burst, obtaining the direction of arrival of the radio emission and
compared the obtained positions with white-light observations.
Title: Effects of Radiative Transfer on Helioseismic Signatures in
Active Regions
Authors: Lindsey, C. A.; Fontenla, J. M.
Bibcode: 2011AGUFMSH43A1928L
Altcode:
Models of active regions based on helioseismology have been
heavily based on acoustics in which compression is assumed to be
adiabatic. Acoustics in the outer atmospheres of the quiet Sun
and active regions are thought to depart strongly from adiabatic
compression, due to radiative-transfer effects. If these departures were
similar in active regions and the quiet Sun, they could plausibly be
ignored. However, this is unlikely, because the radiative environments
in active regions are different from those in the quiet Sun. We
discuss efforts to simulate acoustics in photospheric/chromospheric
media with an account of radiative-transfer effects in both the quiet
Sun and active regions.
Title: Observational Analysis of Photospheric Magnetic Field
Restructuring During Energetic Solar Flares
Authors: Alvarado, J. D.; Buitrago, J. C.; Martinez Oliveros, J.;
Lindsey, C. A.; Abbett, W. P.; Fisher, G. H.
Bibcode: 2011AGUFMSH13B1944A
Altcode:
The magnetic field has proven to be the main driver in the behavior,
dynamics and evolution of several solar atmospheric phenomena including
sunspots, plages, faculae, CME's and flares. Observational evidence of
photospheric magnetic field restructuring during energetic flares have
shown an enhancement of the transversal field component suggesting
an apparent relation between this process with the generation of
``sunquakes'', expanding ripples on the solar photosphere as a
result of the momentum-energy transfer into the solar photosphere
and subphotosphere. In this work we present a doppler and magnetic
observational study of some recent energetic flaring events (X and
M type of the 24th solar cycle) trying to find possible acoustic
signatures and make a characterization of the photospheric magnetic
field evolution during those flares, being this the observational
basis of a future numerical modeling of the field restructuring during
this phenomenon.
Title: Method of cleaning images of the GONG++ netw
Authors: Buitrago-Casas, J. C.; Alvarado-Gómez, J. D.;
Martínez-Oliveros, J. C.; Lindsey, C.; Donea, A. -C.; Calvo-Mozo, B.
Bibcode: 2011sdmi.confE..30B
Altcode:
The GONG++ network has been widely used in helioseismic
analysis. However, because the GONG observatories are ground
based, its images are subject to smearing by the terrestrial
atmosphere. Temporal variations in atmospheric smearing introduce
noise in helioseismic observations of active regions. In this work,
we summarize techniques Lindsey and Donea (2008) applied to Postel
projections of GONG active-region observations to reduce this noise. We
introduce improvements based de-smearing techniques that take a warpage
in Postel projections of active regions away from disk center. We have
applied the method to GONG++ Doppler observations of seismically active
flares and compared the results with Doppler seismic observations by
SOHO/MDI and SDO/HMI.
Title: Flare Seismology from SDO Observations
Authors: Lindsey, Charles; Martinez Oliveros, Juan Carlos; Hudson, Hugh
Bibcode: 2011sdmi.confE..10L
Altcode:
Some flares release intense seismic transients into the solar
interior. These transients are the sole instance we know of in which
the Sun's corona exerts a conspicuous influence on the solar interior
through flares. The desire to understand this phenomenon has led to
ambitious efforts to model the mechanisms by which energy stored in
coronal magnetic fields drives acoustic waves that penetrate deep
into the Sun's interior. These mechanisms potentially involve the
hydrodynamic response of the chromosphere to thick-target heating
by high-energy particles, radiative exchange in the chromosphere
and photosphere, and Lorentz-force transients to account for
acoustic energies estimated up to at 5X10^27 erg and momenta of
order 6X10^19 dyne sec. An understanding of these components of
flare mechanics promises more than a powerful diagnostic for local
helioseismology. It could give us fundamental new insight into
flare mechanics themselves. The key is appropriate observations
to match the models. Helioseismic observations have identified the
compact sources of transient seismic emission at the foot points of
flares. The Solar Dynamics Observatory is now giving us high quality
continuum-brightness and Doppler observations of acoustically active
flares from HMI concurrent with high-resolution EUV observations from
AIA. Supported by HXR observations from RHESSI and a broad variety
of other observational resources, the SDO promises a leading role in
flare research in solar cycle 24.
Title: Transient Artifacts in SDO/HMI Flare Observations
Authors: Martinez Oliveros, Juan Carlos; Lindsey, C.; Hudson, H.;
Schou, J.; Couvidat, S.
Bibcode: 2011SPD....42.2123M
Altcode: 2011BAAS..43S.2123M
The Helioseismic and Magnetic Imager (HMI) on SDO provides a new
tool for the systematic observation of white-light flares, including
Doppler and magnetic information as well as continuum. In our initial
analysis of the highly impulsive gamma-ray flare SOL2010-06-12T00:57
(Martinez-Oliveros et al. 2011), we detected an apparently artifactual
blue shift in the two footpoint sources. We have now deployed the PASCAL
algorithm for the same flare as viewed in GONG++ data. This algorithm
makes it possible to obtain much better photometry (plus Doppler and
magnetic measurements) from the ground-based data. Using GONG++ we
have demonstrated the artifactual nature of the apparent blueshift,
finding instead weak redshifts at the foopoints. We discuss the flare
physics associated with these observations and describe the use of
PASCAL (with GONG++ or other ground-based data) as a complement to
the systematic SDO data.
Title: First Steps toward Seismic Holography of the Tachocline
Authors: Diaz Alfaro, Manuel; González Hernández, I.; Pérez
Hernández, F.; Lindsey, C.
Bibcode: 2011SPD....42.1617D
Altcode: 2011BAAS..43S.1617D
The solar dynamo is thought to be generated at the tachocline and the
deepest layers of the convection zone. Yet much about these layers or
how this mechanism works remains unknown. In this work we present the
first of a series of steps in order to apply helioseismic holography
to the study of the tachocline. Traditionally a plane-parallel
approximation has been used for the calculation of the pupil for
earthside seismic holography. In this work we have used a spherically
symmetric model for the pupil to map an active region in the frontside
of the Sun to test its potential. We also present the theoretical
background to use a spherical polar expansion to calculate the Green's
functions instead of the usual acoustic ray path approximation. These
new Green's functions will allow to reach the deepest layers of the
convection zone with more accuracy.
Title: On the Magnetic Field Variations and HXR Emission of the
First X-class Flare in the 24th Solar Cycle
Authors: Martinez Oliveros, Juan Carlos; Alvarado Gomez, J.; Buitrago
Casas, J.; Lindsey, C.; Hudson, H.; Calvo-Mozo, B.
Bibcode: 2011SPD....42.2225M
Altcode: 2011BAAS..43S.2225M
Multi-wavelength studies of energetic solar flares with seismic
emissions have revealed interesting common features between them. We
studied the first seismically active flare of the 24th solar cycle (SOL2011-02-15T01:52 X2.2) detected by HMI/SDO (Kosovichev, 2011)
using a pixel-by-pixel light-curve characterization of the fluctuations
of the photospheric longitudinal magnetic field based on HMI data. For
context we used HXR RHESSI data to find a correlation between these
sources and the spatial location of the transient longitudinal magnetic
field changes in the photospheric region where this flare took place.
Title: Magnetic Oscillations Mark Sites of Magnetic Transients in
an Acoustically Active Flare
Authors: Lindsey, Charles A.; Donea, A.; Hudson, H. S.; Martinez
Oliveros, J.; Hanson, C.
Bibcode: 2011SPD....42.2207L
Altcode: 2011BAAS..43S.2207L
The flare of 2011 February 15, in NOAA AR11158, was the first
acoustically active flare of solar cycle 24, and the first observed by
the Solar Dynamics Observatory (SDO). It was exceptional in a number
of respects (Kosovichev 2011a,b). Sharp ribbon-like transient Doppler,
and magnetic signatures swept over parts of the active region during
the impulsive phase of the flare. We apply seismic holography to a 2-hr
time series of HMI observations encompassing the flare. The acoustic
source distribution appears to have been strongly concentrated in a
single highly compact penumbral region in which the continuum-intensity
signature was unusually weak. The line-of-sight magnetic transient
was strong in parts of the active region, but relatively weak in
the seismic-source region. On the other hand, the neighbourhoods of
the regions visited by the strongest magnetic transients maintained
conspicuous 5-minutes-period variations in the line of sight magnetic
signature for the full 2-hr duration of the time series, before
the flare as well as after. We apply standard helioseismic control
diagnostics for clues as to the physics underlying 5-minute magnetic
oscillations in regions conducive to magnetic transients during a
flare and consider the prospective development of this property as
an indicator of flare potentiality on some time scale. We make use of
high-resolution data from AIA, using diffracted images where necessary
to obtain good photometry where the image is otherwise saturated. This
is relevant to seismic emission driven by thick-target heating in the
absence of back-warming. We also use RHESSI imaging spectroscopy to
compare the source distributions of HXR and seismic emission.
Title: Imaging Spectroscopy of a White-Light Solar Flare
Authors: Martínez Oliveros, J. C.; Couvidat, S.; Schou, J.; Krucker,
S.; Lindsey, C.; Hudson, H. S.; Scherrer, P.
Bibcode: 2011SoPh..269..269M
Altcode: 2011SoPh..tmp....7M; 2010arXiv1012.0344M
We report observations of a white-light solar flare
(SOL2010-06-12T00:57, M2.0) observed by the Helioseismic Magnetic
Imager (HMI) on the Solar Dynamics Observatory (SDO) and the Reuven
Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The HMI data
give us the first space-based high-resolution imaging spectroscopy
of a white-light flare, including continuum, Doppler, and magnetic
signatures for the photospheric Fe I line at 6173.34 Å and its
neighboring continuum. In the impulsive phase of the flare, a bright
white-light kernel appears in each of the two magnetic footpoints. When
the flare occurred, the spectral coverage of the HMI filtergrams (six
equidistant samples spanning ±172 mÅ around nominal line center)
encompassed the line core and the blue continuum sufficiently far from
the core to eliminate significant Doppler crosstalk in the latter, which
is otherwise a possibility for the extreme conditions in a white-light
flare. RHESSI obtained complete hard X-ray and γ-ray spectra (this
was the first γ-ray flare of Cycle 24). The Fe I line appears to be
shifted to the blue during the flare but does not go into emission; the
contrast is nearly constant across the line profile. We did not detect
a seismic wave from this event. The HMI data suggest stepwise changes
of the line-of-sight magnetic field in the white-light footpoints.
Title: Forecasting Solar EUV Irradiance, Validation and Automation
Authors: Fontenla, J. M.; Gonzalez Hernandez, I.; Quémerais, E.;
Lindsey, C.; Mason, J. P.
Bibcode: 2010AGUFMSM51A1751F
Altcode:
A new forecasting technique of the EUV solar irradiance was developed
and a test case tried. This method is based on physical semi-empirical
models of the solar atmosphere that are essentially different from
empirical proxies based only on mathematical correlation. The physics
based forecast can readily incorporate the large body of solar physics
and radiative transfer knowledge, and any future developments in the
understanding of the physical processes that operate in the solar
atmosphere. In this paper it is shown how this forecast method is
applied to a wide range of wavelengths and produces indices related to
Earth upper atmospheric processes that can be correlated to observed
patterns, as well as full spectra in the range 0.2 nm to 12 micron that
can be utilized in GCM models. It is also shown how the forecast method
is now in the process of being automated and applied to the onset of the
solar activity cycle 24. In addition to the GONG and SWAN helioseismic
and Ly alpha backscattering data, respectively, and the ground-based
PSPT data, new measurements by SDO instruments (AIA and EVE) are being
used to feed current data into the forecast technique. Furthermore,
SDO/EVE data is starting to being used to validate the forecast in a
substantial part of the UV range, from 6 to 100 nm.
Title: Seismic Discrimination of Thermal and Magnetic Anomalies in
Sunspot Umbrae
Authors: Lindsey, C.; Cally, P. S.; Rempel, M.
Bibcode: 2010ApJ...719.1144L
Altcode:
Efforts to model sunspots based on helioseismic signatures need to
discriminate between the effects of (1) a strong magnetic field that
introduces time-irreversible, vantage-dependent phase shifts, apparently
connected to fast- and slow-mode coupling and wave absorption and (2)
a thermal anomaly that includes cool gas extending an indefinite depth
beneath the photosphere. Helioseismic observations of sunspots show
travel times considerably reduced with respect to equivalent quiet-Sun
signatures. Simulations by Moradi & Cally of waves skipping
across sunspots with photospheric magnetic fields of order 3 kG show
travel times that respond strongly to the magnetic field and relatively
weakly to the thermal anomaly by itself. We note that waves propagating
vertically in a vertical magnetic field are relatively insensitive to
the magnetic field, while remaining highly responsive to the attendant
thermal anomaly. Travel-time measurements for waves with large skip
distances into the centers of axially symmetric sunspots are therefore
a crucial resource for discrimination of the thermal anomaly beneath
sunspot umbrae from the magnetic anomaly. One-dimensional models of
sunspot umbrae based on compressible-radiative-magnetic-convective
simulations such as by Rempel et al. can be fashioned to fit
observed helioseismic travel-time spectra in the centers of sunspot
umbrae. These models are based on cooling of the upper 2-4 Mm of the
umbral subphotosphere with no significant anomaly beneath 4.5 Mm. The
travel-time reductions characteristic of these models are primarily
a consequence of a Wilson depression resulting from a strong downward
buoyancy of the cooled umbral medium.
Title: Magnetic Connectivity of the CME Event on December 31, 2007
Authors: Martinez Oliveros, Juan Carlos; Raftery, C.; Agueda, N.;
Krucker, S.; Bale, S.; Lindsey, C.
Bibcode: 2010AAS...21640624M
Altcode:
Dynamical changes in the solar magnetic field are responsible for
coronal mass ejections (CMEs), one of the most violent phenomena
observed in the Sun. During a CME, mass is lifted away from the Sun and
accelerated into the interplanetary medium, sometimes interacting with
the Earth or other planets. Some of these CMEs produce radio emission,
including type II bursts, which are generated by a strong upstream
interplanetary (IP) shocks. The emission is strongest in regions
where the direction of the IP shock is quasi-perpendicular to the
interplanetary magnetic field. Due to small-scale shock structure, this
occurs at various sites along the shock front. We study the different
emissions associated with the CME observed on 2007 December 31 using
data from the RHESSI, Proba-2/SWAP, and STEREO A/B spacecraft. We track
and probe the CME and associated shock signatures from its origin in
the lower corona through the interplanetary medium.
Title: Amplitudes of High-Degree p Modes in the Quiet and Active Sun
Authors: Burtseva, O.; Tripathy, S. C.; Hill, F.; Kholikov, S.;
Raouafi, N. -E.; Lindsey, C.
Bibcode: 2009ASPC..416..293B
Altcode: 2009arXiv0904.0440B
We investigate mode amplitudes in the active and quiet Sun in both
maximum and minimum phases of the solar activity cycle. We confirm
previous studies showing that p-mode amplitudes at solar minimum are
higher than at solar maximum. We mask active regions of a certain
magnetic field strength and compare the masked and unmasked acoustic
power. After applying the masks, the preliminary analysis indicates
that the amplitude decreases over all degrees during solar minimum,
compared to the unmasked case, while at solar maximum the amplitude
first decreases up to l∼300 and then increases at higher degrees.
Title: Solar-Stellar Dynamos as Revealed by Helio- and
Asteroseismology: GONG 2008/SOHO 21
Authors: Dikpati, M.; Arentoft, T.; González Hernández, I.; Lindsey,
C.; Hill, F.
Bibcode: 2009ASPC..416.....D
Altcode:
No abstract at ADS
Title: Improving the Prediction Capability of Seismic Far-Side Maps
Authors: González Hernández, I.; Scherrer, P.; Hill, F.; Lindsey,
C.; Braun, D.
Bibcode: 2009ASPC..416...87G
Altcode:
Both the Michelson Doppler Imager (MDI) and the Global Oscillation
Network Group (GONG) projects produce daily seismic maps of surface
magnetic activity on the non-visible hemisphere of the Sun. The
technique has proven useful to detect and follow large active regions
before they appear to face the Earth. This work demonstrates an
improvement in the detection capability of the technique by applying
the results of new research. We calibrate the daily far-side maps in
terms of characteristics of the active region, such as total area and
magnetic flux strength, apply a relationship between the strength of
the persistent signal and the success rate to automatically highlight
possible candidates, and remove solar-cycle variations to stabilize
the signal.
Title: Can Sunspot Moats Tell Us β for the Solar Dynamo?
Authors: Lindsey, C.
Bibcode: 2009ASPC..416..155L
Altcode:
The structure and geometry of moats surrounding decaying sunspots are
probably closely related to the structure of the magnetic flux tubes
in the upper 2-3 Mm beneath the sunspot photosphere. An understanding
of this relationship offers important clues about β, the ratio of gas
pressure to magnetic pressure, in rising magnetic flux tubes before
they encounter the overlying photosphere. This could provide deep
insight into the physics of the solar dynamo.
Title: Solar irradiance forecast and far-side imaging
Authors: Fontenla, J. M.; Quémerais, E.; González Hernández, I.;
Lindsey, C.; Haberreiter, M.
Bibcode: 2009AdSpR..44..457F
Altcode:
This paper presents a new approach to forecasting short-term Lyα solar
irradiance variations due to the presence and evolution of magnetically
heated regions in the Sun's outer atmosphere. This scheme is based
on images of the solar disk at key wavelengths, currently Ca II K
filtergrams, maps of backscattered solar Lyα from the interplanetary
medium, and helioseismic images of large far-side active regions. The
combination of these resources allows accurate forecasts of the
UV solar irradiance several days in advance. The technique takes
into consideration the evolution of recently observed activity on
the Sun's near surface as well as active regions on the Sun's far
side. The far-side helioseismic maps and the Lyα backscattering are
very important, because of the long period of time features spend on
the Sun's far side compared with their typical evolution time and their
relatively sudden appearance on the near side. We describe the basics
of the forecasting technique and apply it to a case study that shows
how the technique dramatically improves Lyα irradiance forecasting. An
extension of the technique described here promises realistic forecasts
of the entire FUV/EUV solar spectral irradiance spectrum.
Title: Statistical Analysis of the Success Rate of the Far-Side
Seismic Mapping of Active Regions.
Authors: Gonzalez-Hernandez, Irene; Scherrer, P.; Lindsey, C.; Hill,
F.; Braun, D.
Bibcode: 2009SPD....40.0707G
Altcode:
Seismic maps of the non-visible side of the Sun (far side) have been
used for almost a decade to follow large active regions before they
rotate to face the Earth. Preliminary efforts to quantify the success
rate of the used technique (seismic holography) have been published
with limited data. However, a thorough study is needed to further
understand the limitations of the technique in terms of size and
strength of the active regions detected and to reveal clues as to how
to improve it. We have analyzed three complete years of far-side
seismic maps calculated using both Global Oscillation Newtwork group
(GONG) and Michelson Doppler Imager (MDI) data and matched the far-side
candidates with associated active regions as recorded by the NOAA
database. Here we present the results.
Title: Discriminating Thermal and Magnetic Seismic Anomalies in
Sunspot Umbrae
Authors: Lindsey, Charles A.; Cally, P. S.
Bibcode: 2009SPD....40.0702L
Altcode:
Efforts to model sunspots based on helioseismic signatures are
confronted by the need to discriminate between two significantly
separate anomalies: (1) a strong magnetic field that introduces
time-irreversible, vantage-dependent phase shifts apparently connected
to fast- and slow-mode coupling and wave absorption, and (2) a thermal
anomaly that includes cool gas extending an unknown depth beneath the
photosphere. Simulations by Moradi & Cally of waves skipping across
sunspots with photospheric magnetic fields of order 3 kG show travel
times that respond strongly to the magnetic field and relatively
weakly to the thermal anomaly by itself. We understand that waves
propagating vertically in a vertical magnetic field are insensitive
to the magnetic field and highly responsive to an attendant thermal
anomaly. We therefore recognize travel-time measurements for waves with
large skip distances into the centers of axially symmetric sunspots
as an important resource for discrimination of the thermal anomaly
beneath sunspot umbrae. Helioseismic observations of the response of
sunspot umbrae to low-degree waves impinging into them from beneath
their photospheres invariably show strongly reduced travel times,
the reduction increasing sharply with frequency. These profiles
agree nicely by 1-D simulations of the acoustics of a strong thermal
deficit in the upper few hundred km beneath the sunspot photosphere
with no significant anomaly below 2.2 Mm. This thermal structure is
characteristic of sunspot simulations by Rempel, Schuessler &
Knoelker. We understand the reduced travel times for these models
to be substantially the result of a 450-km Wilson depression caused
by the foregoing thermal deficit. According to this understanding,
the travel-time reduction due to the Wilson depression significantly
outweighs the effect of a reduced sound speed in the cool gas.
Title: Understanding and forecasting solar EUV and UV irradiance
variations
Authors: Haberreiter, M.; Fontenla, J.; Gonzalez-Hernandez, I.;
Lindsey, C.; Quemerais, E.
Bibcode: 2008AGUFMSA24A..02H
Altcode:
We describe the application and current status of the Solar Radiation
Physical Modeling (SRPM) project for understanding the nature of the
solar EUV and UV irradiance variations and building tools to forecast
short and medium term variations of the solar irradiance spectrum at
any location in the Heliosphere. These methods can be used for very
detailed estimates of the EUV solar irradiance changes on the Earth and
planetary atmospheres. Reliable EUV estimates are an important input
for the modeling of the physical parameters of the thermosphere. In
the presentation we show the current status, the solar atmospheric
models, the synthetic EUV and UV spectra and the performance of the
forecasting tool.
Title: Mechanics of Seismic Emission from Solar Flares
Authors: Lindsey, C.; Donea, A. -C.
Bibcode: 2008SoPh..251..627L
Altcode: 2008SoPh..tmp...49L
Instances of seismic transients emitted into the solar interior
in the impulsive phases of some solar flares offer a promising
diagnostic tool, both for understanding the physics of solar flares
and for the general development of local helioseismology. Among
the prospective contributors to flare acoustic emission that have
been considered are: i) chromospheric shocks propelled by pressure
transients caused by impulsive thick-target heating of the upper
and middle chromosphere by high-energy particles, ii) heating of the
photosphere by continuum radiation from the chromosphere or possibly
by high-energy protons, and iii) magnetic-force transients caused by
magnetic reconnection. Hydrodynamic modeling of chromospheric shocks
suggests that radiative losses deplete all but a small fraction of
the energy initially deposited into them before they penetrate the
photosphere. Comparisons between the spatial distribution of acoustic
sources, derived from seismic holography of the surface signatures of
flare acoustic emission, and the spatial distributions of sudden changes
both in visible-light emission and in magnetic signatures offer a
possible means of discriminating between contributions to flare acoustic
emission from photospheric heating and magnetic-force transients. In
this study we develop and test a means for estimating the seismic
intensity and spatial distribution of flare acoustic emission from
photospheric heating associated with visible-light emission and compare
this with the helioseismic signatures of seismic emission. Similar
techniques are applicable to transient magnetic signatures.
Title: Physical Properties of Wave Motion in Inclined Magnetic Fields
within Sunspot Penumbrae
Authors: Schunker, H.; Braun, D. C.; Lindsey, C.; Cally, P. S.
Bibcode: 2008SoPh..251..341S
Altcode: 2008arXiv0801.4448S; 2008SoPh..tmp...41S
At the surface of the Sun, acoustic waves appear to be affected by the
presence of strong magnetic fields in active regions. We explore the
possibility that the inclined magnetic field in sunspot penumbrae may
convert primarily vertically-propagating acoustic waves into elliptical
motion. We use helioseismic holography to measure the modulus and phase
of the correlation between incoming acoustic waves and the local surface
motion within two sunspots. These correlations are modeled by assuming
the surface motion to be elliptical, and we explore the properties
of the elliptical motion on the magnetic-field inclination. We also
demonstrate that the phase shift of the outward-propagating waves is
opposite to the phase shift of the inward-propagating waves in stronger,
more vertical fields, but similar to the inward phase shifts in weaker,
more-inclined fields.
Title: Combining far-side maps from MDI and GONG to improve the
prediction capability
Authors: Gonzalez Hernandez, I.; Scherrer, P.; Lindsey, C.; Braun,
D.; Hill, F.
Bibcode: 2008AGUSMSP41A..04G
Altcode:
Both the Michaelson Doppler Imager (MDI) and the Global Oscillation
Network Group (GONG) projects produce daily seismic maps of surface
magnetic activity at the non-visible hemisphere the Sun. The technique
has proven useful in order to detect and follow large active regions
before they appear to face the Earth. This work explores the possibility
of improving the detection capability of the technique by combining
the results from both instruments. The research should lead to a better
understanding of the spurious, non persistent seismic signal associated
with the far-side images and better discrimination between solar and
instrumental noise.
Title: Recent Developments in Solar Quakes Studies
Authors: Bešliu-Ionescu, D.; Donea, A. -C.; Cally, P.; Lindsey, C.
Bibcode: 2008ASPC..383..297B
Altcode:
Observations in hard and soft X-rays, chromospheric lines, and the
visible continuum, together with helioseismic observations, make
it possible to model the 3-dimensional profile of a sunquake from
the corona into the subphotosphere of the active region that hosts
the flare. Chromospheric line observations show us the part of the
solar atmosphere where high-energy electrons are thought to cause
thick-target heating that causes intense white-light emission and
drives seismic waves into the active region subphotosphere. We have
made a preliminary analysis of observations for some of the strongest
acoustically noisy flares, including spectral observations in line
NaD1 (586.9 nm) and line-center observations in Hα. Hα line-center
observations will be shown for other sunquakes in Solar Cycle 23. Hinode
will give us especially high-resolution chromospheric-line observations
of acoustically active flares in Solar Cycle 24.
Title: Signatures of Seismic Absorption in Magnetic Regions
Authors: Lindsey, C.; Cally, P. S.
Bibcode: 2008ASPC..383..141L
Altcode:
One of the major developments in local helioseismology of the late
1980s was the discovery by Braun, Duvall, & LaBonte that magnetic
regions strongly absorb p modes that the quiet Sun itself efficiently
reflects. A second major development, in the mid 1990s with the advent
of the {Solar and Heliospheric Observatory}, was the discovery by
Duvall et al. that phase travel times for waves propagating into sunspot
photospheres are significantly longer than for waves propagating away
from them along identical paths, a phenomenon to which we refer in
this review as ``the phase asymmetry.'' Theoretical work by Cally et
al. proposes to explain absorption of p modes by coupling of p modes to
Alfvén modes. Recent work by Schunker et al. shows compelling evidence
that this coupling contributes strongly to the phase asymmetry. More
recent work by Rajaguru et al. suggests that radiative transfer effects
in magnetic photospheres with upward-propagating waves contribute
significantly to the phase asymmetry. Both of these contributions
depend on strong absorption of p modes in magnetic photospheres. We
will comment on the physics that relates phase shifts that underlie
phenomena such as the phase asymmetry to irreversible processes such
as p-mode absorption in magnetic regions. Magnetic contributions to
the phase asymmetry have significant implications respecting seismic
diagnostics of flows in active region subphotospheres.
Title: Calibration of the Far Side Seismic-Holography Signature of
Active Regions
Authors: González Hernández, I.; Hill, F.; Lindsey, C.
Bibcode: 2008ASPC..383..155G
Altcode:
We compare helioseismic maps of large active regions on the far side
of the Sun, calculated from Global Oscillation Network Group (GONG)
data, with magnetic and visible-continuum images of the same active
regions on the visible hemisphere before and after their passage
across the far hemisphere. We find a significant correlation between
the far-side signature and both the total area of the active region as
viewed on the near hemisphere and the total area of sunspots within
the active region. We have also studied the relationship between the
magnetic field strength and the phase shift for six of the larger,
more stable active regions.
Title: Calibration of Seismic Signatures of Active Regions on the
Far Side of the Sun
Authors: González Hernández, I.; Hill, F.; Lindsey, C.
Bibcode: 2007ApJ...669.1382G
Altcode:
Synoptic maps of the far hemisphere of the Sun calculated from seismic
holography have proven to be very reliable in localizing large active
regions before they rotate onto the visible hemisphere. We show here
the first results toward a calibration of the far-side signatures
of active regions in terms of active region size and magnetic field
strength. We compare helioseismic maps of large active regions on the
far side of the Sun, calculated from Global Oscillation Network Group
(GONG) Doppler observations, with magnetic and visible-continuum images
of the same active regions on the visible hemisphere before and after
their far-side passage. The far-side seismic signature is expressed as a
phase shift that a far-side active region introduces to waves from the
near hemisphere as they are reflected into the solar interior on their
way back to the near hemisphere. There is a significant correlation
between this far-side signature and both the total area of the active
region, as viewed on the near hemisphere, and the area of the sunspots
contained in the active region. We have studied the relationship
between the magnetic field strength and the phase signature for six
of the larger, more stable active regions. We find an approximately
logarithmic increase in the seismic phase signature with increasing
magnetic field strengths above a critical field of ~10 G. This is
roughly consistent with similar helioseismic signatures measured on
the near solar hemisphere concurrent with associated magnetic fields.
Title: From Gigahertz to Millihertz: A Multiwavelength Study of the
Acoustically Active 14 August 2004 M7.4 Solar Flare
Authors: Martínez-Oliveros, J. C.; Moradi, H.; Besliu-Ionescu, D.;
Donea, A. -C.; Cally, P. S.; Lindsey, C.
Bibcode: 2007SoPh..245..121M
Altcode: 2007arXiv0707.2019M
We carried out an electromagnetic acoustic analysis of the solar
flare of 14 August 2004 in active region AR10656 from the radio to the
hard X-ray spectrum. The flare was a GOES soft X-ray class M7.4 and
produced a detectable sun quake, confirming earlier inferences that
relatively low energy flares may be able to generate sun quakes. We
introduce the hypothesis that the seismicity of the active region is
closely related to the heights of coronal magnetic loops that conduct
high-energy particles from the flare. In the case of relatively short
magnetic loops, chromospheric evaporation populates the loop interior
with ionised gas relatively rapidly, expediting the scattering of
remaining trapped high-energy electrons into the magnetic loss cone and
their rapid precipitation into the chromosphere. This increases both
the intensity and suddenness of the chromospheric heating, satisfying
the basic conditions for an acoustic emission that penetrates into
the solar interior.
Title: Chromospheric Line Emission Analysis of the July 16, 2004
Sun Quake
Authors: Beşliu-Ionescu, Diana; Donea, Alina; Cally, Paul; Lindsey,
Charles
Bibcode: 2007AIPC..934...38B
Altcode:
Observations in chromospheric lines and the visible continuum together
with photospheric helioseismic measurements make possible to image a
3-dimensional profile of a sun quake in a flaring region. Chromospheric
line observations show us the part of the solar atmosphere where
high-energy electrons are thought to cause thick target heating that
then could also cause intense white-light emission and could drive
seismic waves into the active region subphotosphere, we present here
the preliminary results of the sun quake of July 16, 2004.
Title: Far-side Helioseismic Holography: Calibrating The Signature
Of Active Regions.
Authors: Gonzalez-Hernandez, Irene; Lindsey, C.; Hill, F.
Bibcode: 2007AAS...210.2212G
Altcode: 2007BAAS...39..126G
Synoptic maps of the far hemisphere of the Sun calculated from seismic
holography have proven to be very reliable in localizing large active
regions before they rotate onto the visible hemisphere. Both the
Michelson Doppler Imager (MDI) and the Global Oscillation Network Group
(GONG) provide daily far-side maps of magnetic activity using this
technique. We show here the first results towards a calibration
of the far-side signatures of active regions in terms of active
region size and magnetic field strength. We compare helioseismic
maps of large active regions on the far side of the Sun, calculated
from GONG Doppler observations, with magnetic and visible-continuum
images of the same active regions on the visible hemisphere before
and after their far-side passage. We find a significant correlation
between the far-side signature and both the total area of the active
region, as viewed on the near hemisphere, and the area of the sunspots
contained in the active region. We have studied the relationship
between the magnetic field strength and the phase signature for six
of the larger, more stable active regions. We find an approximately
logarithmic increase in the seismic phase signature with increasing
magnetic field strengths above a critical field of 10 Gauss.
Title: Anisotropy in Helioseismic Emission
Authors: Lindsey, Charles A.
Bibcode: 2007AAS...210.2210L
Altcode: 2007BAAS...39..126L
Theoretical research by Nigam, Rast, and Skartlien suggest that seismic
emission from the quiet Sun can be significantly characterized in terms
of sequences of monopole, dipole and quadrupole transients associated
with down-flowing plumes in intergranular lanes. This would result in
a significant phase relationship between seismic radiation emitted
downward, into the solar interior, and seismic radiation emitted
directly upward, into the overlying quiet photosphere. One major result,
if the composite monopole and quadrupole transient were generally
comparable in power to the dipole component, would be a significant
difference in the seismic radiation emitted directly upward from that
emitted downward, into the solar interior. I will discuss what the
analysis of numerical simulations of seismic emission as a result of
turbulence can tell us about this hypothetical anisotropy. Comparisons
between high-frequency seismic emission from the quiet Sun and from
magnetic regions offer a promising diagnostic role in the investigation
of seismic emission anisotropy.
Title: Magnetoseismic signatures and flow diagnostics beneath
magnetic regions
Authors: Lindsey, C.; Schunker, H.; Cally, P. S.
Bibcode: 2007AN....328..298L
Altcode:
% One of the major, important developments in local helioseismology was
the discovery by Duvall et al. (1996) that the travel times of seismic
waves into sunspots from the surrounding quiet Sun significantly exceed
the same in the reverse direction, a behavior they suggested was the
result of rapid downflows directly beneath the sunspot photosphere. This
led to the need for rapid near-surface horizontal inflows to replace the
mass evacuated from the sunspot subphotosphere by such downflows. The
lack of independent evidence for such inflows led to the suggestion
that the travel-time asymmetry could be explained by a relative phase
delay in the response of the sunspot photosphere to incoming waves with
respect to that of the quiet Sun. In the succeeding ten years major
progress has been made in our understanding of how magnetic photospheres
respond to incoming waves, at the instigation of theoretical work by
Spruit, Cally and Bogdan. This has led to the recognition of inclined
penumbral magnetic fields as a major avenue for control work on the
subject of the travel-time asymmetry and its relation to the absorption
of p-modes by magnetic regions. A major recent development has been
the discovery by Schunker et al. (2005) that the phase of this response
in Doppler observations of penumbral photospheres depends strongly on
the vantage of the Doppler measurements projected into the vertical
plane of the magnetic field. This discovery heavily reinforces the
proposition that the travel-time asymmetry is largely the signature of
the same irreversible damping processes that are responsible for the
strong absorption of p-modes in magnetic regions. We will elaborate
on the implications of the foregoing developments respecting the
diagnostics of subphotospheric flows based on seismic observations in
which magnetic regions cannot be avoided.
Title: Helioseismic analysis of the solar flare-induced sunquake of
2005 January 15
Authors: Moradi, H.; Donea, A. -C.; Lindsey, C.; Besliu-Ionescu, D.;
Cally, P. S.
Bibcode: 2007MNRAS.374.1155M
Altcode: 2007arXiv0704.3472M; 2006MNRAS.tmp.1369M
We report the discovery of one of the most powerful sunquakes
detected to date, produced by an X1.2-class solar flare in active
region AR10720 on 2005 January 15. We used helioseismic holography
to image the source of seismic waves emitted into the solar interior
from the site of the flare. Acoustic egression power maps at 3 and 6
mHz with a 2-mHz bandpass reveal a compact acoustic source strongly
correlated with impulsive hard X-ray and visible-continuum emission
along the penumbral neutral line separating the two major opposing
umbrae in the δ-configuration sunspot that predominates AR10720. At 6
mHz the seismic source has two components, an intense, compact kernel
located on the penumbral neutral line of the δ-configuration sunspot
that predominates AR10720, and a significantly more diffuse signature
distributed along the neutral line up to ~15 Mm east and ~30 Mm west
of the kernel. The acoustic emission signatures were directly aligned
with both hard X-ray and visible continuum emission that emanated
during the flare. The visible continuum emission is estimated at 2.0
× 1023 J, approximately 500 times the seismic emission
of ~4 × 1020 J. The flare of 2005 January 15 exhibits
the same close spatial alignment between the sources of the seismic
emission and impulsive visible continuum emission as previous flares,
reinforcing the hypothesis that the acoustic emission may be driven
by heating of the low photosphere. However, it is a major exception
in that there was no signature to indicate the inclusion of protons
in the particle beams thought to supply the energy radiated by the
flare. The continued strong coincidence between the sources of seismic
emission and impulsive visible continuum emission in the case of a
proton-deficient white-lightflare lends substantial support to the
`back-warming' hypothesis, that the low photosphere is significantly
heated by intense Balmer and Paschen continuum-edge radiation from
the overlying chromosphere in white-light flares.
Title: Study of the Seismically Active Flare of July 16, 2004
Authors: Besliu-Ionescu, D.; Donea, A. C.; Cally, P.; Lindsey, C.
Bibcode: 2007RoAJ...17S..83B
Altcode:
Sunquakes have proven to be the most powerful events occurring at the
solar surface. They are triggered by the impulsive flares produced
in the corona, just above the acoustically active regions. Not
every impulsive flare produces seismic waves emanating from the
highly depressed photosphere, just beneath the flare. So far, we
have identified a few mechanisms which can deliver acoustic energy
into the photosphere: 1) the back-warming radiation suddenly heating
the photosphere; 2) a strong shock-like compression wave propagating
downwards into the chromosphere; 3) relativistic particles delivering
directly the energy and momentum into the photosphere; and, 4)
probably the magnetic tension at the feet of the loops. In order to
discriminate which of these is the most efficient or dominated during a
particular acoustically active flare, we have analysed the coronal and
chromospheric emission of the regions just above the seismic source. We
have performed a multiwavelength analysis of the active region 10649
that hosted the acoustically active solar flare of July 16, 2004. The
spatial coincidence between the emissions at different layers of the
sun, from the photosphere to the corona, suggests that high-energy
particles travel through the coronal layers from the reconnection
site, hit the solar chromosphere warming it up, which then, responds
by sending further into the photosphere enough energy (carried either
by the shock wave or by the Balmer and Pachen radiation) to produce
a seismic event.
Title: Chromospheric line emission in seismically active flares
Authors: Beşliu-Ionescu, D.; Donea, A. -C.; Lindsey, C.; Cally, P.;
Mariş, G.
Bibcode: 2007AdSpR..40.1921B
Altcode:
Some flares are known to drive seismic transients into the solar
interior. The effects of these seismic transients are seen in
helioseismic observations of the Sun's surface thousands of km
from their sources in the hour succeeding the impulsive phase of
the flare. Energetic particles impinging from the corona into the
chromosphere are known to drive strong, downward-propagating shocks in
active region chromospheres during the impulsive phases of flares. Hα
observations have served as an important diagnostic of these shocks,
showing intense emission with characteristic transient redshifts. In
most flares no detectable transients penetrate beneath the active region
photosphere. In those that do, there is a strong correlation between
compact white-light emission and the signature of seismic emission. This
study introduces the first known Hα observations of acoustically active
flares, centered in the core of the line. The morphology of line-core
emission Hα in the impulsive phase of the flare is similar to that
of co-spatial line-core emission in NaD 1, encompassing
the site of seismic emission but more extended. The latter shows a
compact red shift in the region of seismic emission, but a similar
feature is known to appear in a conjugate magnetic footpoint from
which no seismic emission emanates. Radiative MHD modelling based
on the profiles of chromospheric line emission during the impulsive
phases of flares can contribute significantly to our understanding of
the mechanics of flare acoustic emission penetrating into the solar
interior and the conditions under which it occurs.
Title: New Detection of Acoustic Signatures from Solar Flares
Authors: Donea, A. C.; Besliu-Ionescu, D.; Cally, P.; Lindsey, C.
Bibcode: 2006ASPC..354..204D
Altcode:
With the advancement of local helioseismic techniques such as
helioseismic holography we have now detected numerous seismic sources
of varying size and intensity produced by solar flares. We have
performed a systematic survey of the SOHO-MDI database in search for
seismic waves from X-class flares produced during 1996 -- 2005. The
detection of acoustically active flares has opened a new and
promising connection between helioseismology and flare physics. The
main question we ask is: why are some large flares acoustically active
while most are acoustically inactive? We also address questions
such as: Is photospheric heating by high-energy protons a major factor
in seismic emission from flares? What is the effect of magnetic fields
in the acoustics of a flare?
Title: Simulations of Acoustic Excitation
Authors: Lindsey, C.; Birch, A. C.; Donea, A. -C.
Bibcode: 2006ASPC..354..174L
Altcode:
Acoustic emission from solar granulation is thought to be relatively
localized and episodic, emanating largely as relatively discrete
wavepackets emitted from convective plumes falling into the solar
interior from near-surface layers at which granular convection
takes place. We devise preliminary simulated sound computations to
characterize the range of acoustic signatures that can be expected
from random localized emission for a range of surface densities and
mean episodic frequencies. In the simple models studied here wave
excitation is represented by dipole emitters at a depth of one~Mm
randomly distributed in time and location over the surface of a standard
solar model. We apply holographic regressions to the resulting surface
acoustic fields and compile acoustic power statistics on the resulting
helioseismic signatures. Acoustic power statistics of random, stationary
Gaussian noise are characterized by an exponential distribution. The
relatively localized and episodic nature of acoustic emission expected
from downfalling plumes should be distinguishable from Gaussian noise
by a characteristic deviation from the exponential distribution. If the
episodes are relatively dense and frequent compared to the temporal and
spatial discrimination of the helioseismic diagnostics, the deviation
from Gaussian statistics becomes small. Simulations of acoustic
emission, then, allow us to assess the potential of local helioseismic
diagnostics for recognizing episodic excitation of acoustic waves.
Title: Seismic Emission from A M9.5-Class Solar Flare
Authors: Donea, A. -C.; Besliu-Ionescu, D.; Cally, P. S.; Lindsey,
C.; Zharkova, V. V.
Bibcode: 2006SoPh..239..113D
Altcode: 2006SoPh..tmp...65D
Following the discovery of a few significant seismic sources at
6.0 mHz from the large solar flares of October 28 and 29, 2003, we
have extended SOHO/MDI helioseismic observations to moderate M-class
flares. We report the detection of seismic waves emitted from the β
γ δ active region NOAA 9608 on September 9, 2001. A quite impulsive
solar flare of type M9.5 occurred from 20:40 to 20:48 UT. We used
helioseismic holography to image seismic emission from this flare into
the solar interior and computed time series of egression power maps
in 2.0 mHz bands centered at 3.0 and 6.0 mHz. The 6.0 mHz images show
an acoustic source associated with the flare some 30 Mm across in the
East - West direction and 15 Mm in the North - South direction nestled
in the southern penumbra of the main sunspot of AR 9608. This coincides
closely with three white-light flare kernels that appear in the sunspot
penumbra. The close spatial correspondence between white-light and
acoustic emission adds considerable weight to the hypothesis that the
acoustic emission is driven by heating of the lower photosphere. This
is further supported by a rough hydromechanical model of an acoustic
transient driven by sudden heating of the low photosphere. Where direct
heating of the low photosphere by protons or high-energy electrons is
unrealistic, the strong association between the acoustic source and
co-spatial continuum emission can be regarded as evidence supporting
the back-warming hypothesis, in which the low photosphere is heated
by radiation from the overlying chromosphere. This is to say that a
seismic source coincident with strong, sudden radiative emission in the
visible continuum spectrum indicates a photosphere sufficiently heated
so as to contribute significantly to the continuum emission observed.
Title: Behaviour of Acoustic Waves in Sunspots
Authors: Schunker, H.; Braun, D. C.; Cally, P. S.; Lindsey, C.
Bibcode: 2006ASPC..354..244S
Altcode:
Because helioseismology uses surface signals to calculate subsurface
characteristics the behaviour of surface acoustic oscillations in
sunspots is important in interpreting helioseismic results. SOHO-MDI
Doppler velocity analysis of AR9026 and AR9033 at 3, 4, and 5 mHz,
using helioseismic holography, show that the amplitude and the phase
in the correlation of the acoustic ingression with the observed surface
velocity are found to be sensitive to the relative line-of-sight angle
in the penumbra of both sunspots. This is consistent with a conversion
of vertically propagating acoustic waves into magneto-acoustic waves
with motion described by ellipses.
Title: Magnetohelioseismic Analysis of AR10720 Using Helioseismic
Holography
Authors: Moradi, H.; Donea, A.; Besliu-Ionescu, D.; Cally, P.; Lindsey,
C.; Leka, K.
Bibcode: 2006ASPC..354..168M
Altcode:
We report on the recent discovery of one of the most powerful sunquakes
detected to date produced by the January 15, 2005 X1.2 solar flare
in active region 10720. We used helioseismic holography to image the
acoustic source of the seismic waves produced by the flare. Egression
power maps at 6 mHz with a 2 mHz bandwidth reveal a strong, compact
acoustic source correlated with the footpoints of a coronal loop
that hosted the flare. Using data from various solar observatories,
we present a comprehensive analysis of the acoustic properties of
the sunquake and investigate the role played by the configuration of
the photospehric magnetic field in the production of flare generated
sunquakes.
Title: Magnetoseismic signatures of active regions and the question
of rapid downflows beneath sunspots
Authors: Lindsey, C.
Bibcode: 2006ESASP.624E...4L
Altcode: 2006soho...18E...4L
No abstract at ADS
Title: Farside helioseismic holography: recent advances
Authors: González Hernández, I.; Hill, F.; Lindsey, C.; Braun, D.;
Scherrer, P.; Hanasoge, S. M.
Bibcode: 2006ESASP.624E...3G
Altcode: 2006soho...18E...3G
No abstract at ADS
Title: Seismic emission from M-class solar flares
Authors: Besliu-Ionescu, D.; Donea, A. -C.; Cally, P.; Lindsey, C.
Bibcode: 2006ESASP.624E..67B
Altcode: 2006soho...18E..67B
No abstract at ADS
Title: The acoustically active solar flare of 2005 January 15
Authors: Moradi, H.; Donea, A. -C.; Lindsey, C.; Besliu-Ionescu, D.;
Cally, P. S.
Bibcode: 2006ESASP.624E..66M
Altcode: 2006soho...18E..66M
No abstract at ADS
Title: The interaction between acoustic waves and inclined magnetic
fields near the β~1 layer
Authors: Schunker, H.; Braun, D. C.; Cally, P. S.; Lindsey, C.
Bibcode: 2006IAUJD..17E..16S
Altcode:
The acoustic showerglass effect may be hindering our helioseismic
renditions of the solar subsurface. We present the results of near
-surface wave conversion of acoustic waves in a model polytropic
atmosphere by a uniform, inclined magnetic field. The upcoming fast,
acoustic wave undergoes conversion to a slow, magnetic wave at the β
~ 1 layer where the sound speed and Alfven speed are comparable. The
conversion is dependent upon the " attack angle" between the ray path
and the magnetic field. The angle of the wave vectors at the polytropic
" surface" is compared to observations of surface velocity vectors in
sunspot penumbrae. AR9026 and AR9057 both have well- defined, static
penumbrae and their Doppler velocities are viewed from different
angles by SOHO-MDI as they cross the solar disk. The phase of the
correlation between the ingression and surface velocity, determined by
helioseismic holography, is used to assess the effect the penumbral
magnetic field has on incoming acoustic waves. The phase is found to
be dependent upon the line-of-sight of observation indicating that
this is a surface phenomenon, which could otherwise be interpreted as
subsurface travel-time perturbations of up to one minute. Furthermore,
using vector magnetograms from the IVM at the Mees Observatory, the
phase of the correlation is found to be dependent on the magnetic
field tilt from vertical, and the dependence is consistent across the
two sunspots. Comparing the results from the polytropic model with the
observations show strong support for the near-surface wave conversion
theory, although many questions still remain.
Title: Farside Helioseismic Holography: Recent Advances
Authors: Gonzalez-Hernandez, Irene; Braun, D. C.; Hanasoge, S. M.;
Hill, F.; Lindsey, C. A.; Scherrer, P. H.
Bibcode: 2006SPD....37.0502G
Altcode: 2006BAAS...38Q.223G
Both MDI and GONG have been calculating partial farside maps for some
time, showing a high degree of agreement in detecting large active
regions within approximately 45 degrees around the antipode of disk
center.Recently, the full-hemisphere capability has been added to the
farside pipelines of both instruments. We show here the capability of
detecting large active regions and tracking them through out the full
farside hemisphere by applying the technique to active region 10808.We
also report on efforts underway to calibrate the farside signal in
terms of equivalent magnetic field, including some preliminary maps
obtained from artificial helioseismic data.
Title: Seismology of Magnetic Photospheres
Authors: Lindsey, Charles A.
Bibcode: 2006SPD....37.0504L
Altcode: 2006BAAS...38..223L
In the early 1990s various techniques in local helioseismology showed
that the travel times of waves from magnetic regions to the surrounding
quiet Sun were consistently shorter than for waves traveling the same
distance between points on the quiet Sun. Time-distance correlation
measurements also indicated that the travel times for waves traveling
from magnetic to quiet photospheres were shorter than for waves
traveling the same distance in the opposite direction, suggesting rapid
downflows beneath sunspots. I will review evidence that an interaction
between waves and magnetic photospheres that manifests itself in strong
absorption of p-modes contributes significantly, possibly predominantly,
to the apparent ingoing-vs-outgoing travel-time inequality. Central
to the hypothesis of a magnetically induced phase asymmetry is the
physics of coupling between fast and slow magneto-acoustic gravity
waves in a relatively narrow layer in the upper few hundred km of
magnetic photospheres. A clear understanding of the physics of this
interaction is essential for further progress in seismic diagnostics
of active region subphotospheres.
Title: Seismic Radiation from M-class Solar Flares
Authors: Besliu-Ionescu, Diana; Donea, Alina-C.; Cally, Paul; Lindsey,
Charles
Bibcode: 2006IAUS..233..385B
Altcode:
Helioseismic holography is a technique used to image the sources
of seismic disturbances observed at the solar surface. It has been
used to detect acoustic emission, known as sun quakes, radiated from
X-class solar flares. Since the seismic power emitted by the X-class
flares has proved to be independent of the strength of the flare,
we have undertaking a systematic search for seismic signatures from
M-class solar flares, observed by SOHO-MDI.We have detected significant
acoustic emission from a few M-class solar flares. Preliminary results
of the survey of M-type solar flares studied so far is available at:
aira.astro.ro/~deanna/M.html.
Title: Significant Acoustic Activity in AR10720 on January 15, 2005
Authors: Beşliu-Ionescu, D.; Donea, A. -C.; Cally, P.; Lindsey, C.
Bibcode: 2006RoAJ...16S.203B
Altcode: 2006RoAJS..16..203B
We report the recent discovery of one of the most acoustically powerful
flare detected to date produced by the January 2005 2005, X1.2 solar
flare in AR10720. We used helioseismic holography to image the acoustic
source of the seismic waves produced by the flare. Egression Power maps
at 6 mHz show a strong, extended acoustic signature which is the focus
of the solar quake. At approximately 20 minutes after the appearance
of the flare signature, we could also see the seismic response of
the photosphere to the energy deposited by the flare in the form of
"ripples" on the solar surface.
Title: a Survey of X-Class Solar Flares during 2001 and 2002 IN
Search for Seismic Radiation
Authors: Besliu-Ionescu, D.; Donea, A. -C.; Cally, P.; Lindsey, C.
Bibcode: 2005ESASP.600E.111B
Altcode: 2005ESPM...11..111B; 2005dysu.confE.111B
No abstract at ADS
Title: Seismic Emission from the Solar Flares of 2003 October 28
and 29
Authors: Donea, A. -C.; Lindsey, C.
Bibcode: 2005ApJ...630.1168D
Altcode:
We report the detection of seismic waves emitted from powerful solar
flares that occurred in NOAA Active Region 10486 on 2003 October 28 and
29. We used helioseismic holography to image the seismic sources of
the waves. This technique was previously used to image the source of
seismic emission from the large solar flare of 1996 July 9. Egression
power maps at 6 mHz with a 2 mHz bandwidth reveal multiple compact
acoustic sources strongly associated with the footpoints of a coronal
loop that hosted the flares. The total acoustic energy in the flare
signatures is a very small fraction of the total energy radiated by
the flares. The acoustic signatures are co-aligned with hard X-ray
signatures, suggesting a direct link between energetic particles
accelerated during the flare and the acoustic waves as a hydrodynamic
response of the chromosphere, or possibly the underlying photosphere,
to these particles at the footpoints of the loop. There is also
evidence of high-energy protons impinging onto the chromosphere in
the neighborhoods of the acoustic sources. Observations of emission
in the D1 line of neutral sodium at the onset of the October 29 flare
show evidence of a downward-propagating shock/condensation at the
onset of the flare. Concurrent Global Oscillation Network Group (GONG)
intensity observations show significant radiative emission with a sudden
onset in the compact region encompassing the acoustic signature. Most
flares appear to be acoustically inactive. Photospheric heating by
high-energy protons is likely to be a major factor in seismic emission
from acoustically active flares.
Title: The GONG Farside Project
Authors: Leibacher, J. W.; Braun, D.; González Hernández, I.;
Goodrich, J.; Kholikov, S.; Lindsey, C.; Malanushenko, A.; Scherrer, P.
Bibcode: 2005AGUSMSP11B..14L
Altcode:
The GONG program is currently providing near-real-time helioseismic
images of the farside of the Sun. The continuous stream of low
resolution images, obtained from the 6 earth based GONG stations, are
merged into a single data series that are the input to the farside
pipeline. In order to validate the farside images, it is crucial
to compare the results obtained from different instruments. We show
comparisons between the farside images provided by the MDI instrument
and the GONG ones. New aditions to the pipeline will allow us to create
full-hemisphere farside images, examples of the latest are shown in
this poster. Our efforts are now concentrated in calibrating the
farside signal so it became a reliable solar activity forecasting
tool. We are also testing single-skip acoustic power holography
at 5-7 mHz as a prospective means of reinforcing the signatures of
active regions crossing the the east and west limb and monitoring
acoustic emission in the neighborhoods of Sun's the poles. This work
utilizes data obtained by the Global Oscillation Network Group (GONG)
Program, managed by the National Solar Observatory, which is operated
by AURA, Inc. under a cooperative agreement with the National Science
Foundation. The data were acquired by instruments operated by the Big
Bear Solar Observatory, High Altitude Observatory, Learmonth Solar
Observatory, Udaipur Solar Observatory, Instituto de Astrofisico de
Canarias, and Cerro Tololo Interamerican Observatory, as well as
the Michaelson Doppler Imager on SoHO, a mission of international
cooperation between ESA and NASA. This work has been supported by the
NASA Living with a Star - Targeted Research and Technology program.
Title: Seismic Emission From Solar Flares
Authors: Lindsey, C. A.; Donea, A.
Bibcode: 2005AGUSMSP24A..06L
Altcode:
Local helioseismic diagnostics applied to helioseismic observations from
the Michelson Doppler Imager (MDI) on the Solar Heliospheric Observatory
(SOHO) have shown the clear signature of seismic emission from three
flares during the advent of SOHO. All three of these flares showed the
signatures of γ-ray emission indicating the involvement of accelerated
protons. Two of the acoustically active flares were recent, October 28
and 29 of 2003, and were observed by RHESSI. In both of these instances,
the sources of the acoustic emission acoustic source, determined by
computational seismic holography, coincided closely with compact γ -ray
signatures of protons. Elementary considerations ofenergy and momentum
transfer appear to make chromospheric and photospheric heating by
protons favorable for seismic emission from flares. If this is actually
the case, proton diagnostics of flares from RHESSI would be useful for
identifying acoustically active flares for the Helioseismic Magnetic
Imager (HMI) on the Solar Dynamics Observatory (SDO), and possibly for
the SOHO/MDI. Given a clear understanding of the effects of flares on
Doppler signatures in active regions, acoustic emission from flares can
give us a powerful control utility for seismic diagnostics of active
regions subphotospheres. This research has benefitted greatly from
the keen insights of Valentina Zharkova, Gerald Share, Hugh Hudson,
and Sam Krucker. It has been supported by grants from the Living with
a Star and Supporting Research and Technology programs of the National
Aeronautics and Space Administration and the Stellar Astronomy and
Astrophysics branch of the National Science Foundation.
Title: Modeling Seismic Emission in the Quiet Sun
Authors: Lindsey, C. A.; Birch, A. C.; Donea, A.; Rast, M. P.
Bibcode: 2005AGUSMSP13A..06L
Altcode:
A major issue in the physics of seismic emission in the quiet Sun
is the degree to which the emission from any particular location is
episodic. Given our present understanding, this question is equivalent
to that of how localized the sources of emission are at any particular
moment. A variety of statistical tools are available to address
this issue. For example, if seismic emission can be characterized
in terms of relatively infrequent episodes sparsely distributed,
then the distribution in amplitude of the source terms over space and
time should be non-Gaussian. If the episodes of emission are densely
disseminenated in space and time such that many phase-independent
episodes would be expected in a space-time resolution element,then
the distribution in amplitude approaches Gaussian statistics, and
the distribution in power becomes exponential. Computational seismic
holography focused at the solar surface from a subjacent vantage
makes it possible to image acoustic sources and do statistics on the
seismic source term. Earlier work by Donea, Lindsey and Braun, based on
holographic imaging of acoustic sources, failed to detect a departure of
source amplitudes from Gaussian statistics. This suggests that seismic
sources are relatively dense on a spatial scale of 3~Mm and a temporal
scale of 10~min. What this means in terms of the physics of acoustic
excitation requires modeling. We will describe beginning efforts to
model seismic emission in a standard model of the solar subphotosphere
in terms of randomly distributed dipoles located close to the solar
surface. A significant departute of the source amplitude distribution
from Gaussian statistics is of fundamental importance to the utility
of local helioseismic diagnostics to seismic emission in the quiet Sun.
Title: Towards Assessing, Understanding, and Correcting the Influence
of Surface Magnetism in Local Helioseismology
Authors: Braun, D. C.; Schunker, H.; Lindsey, C.; Cally, P. S.
Bibcode: 2005AGUSMSP23C..03B
Altcode:
Efforts to probe subsurface wave-speed variations and mass flows
near and under solar active regions are complicated and potentially
compromised by strong phase and amplitude perturbations introduced in
the photosphere by magnetic fields. Recently it has been shown that
the phase distortions correlate with surface magnetic field strength
and may be corrected to image wave-speed variations underlying active
regions. A strong phase asymmetry between waves arriving into and
departing from a magnetic region is also shown to produce spurious
signatures of horizontal outflows below active regions. Further
evidence of the photospheric origin of these phase distortions, as
well as a key to their physical origin, is also presented. Using MDI
observations, from the SOHO spacecraft, we perform ingression control
correlations in the inclined magnetic fields of sunspot penumbra and
demonstrate that incoming acoustic waves produce photospheric motion
that describes an ellipse tilted towards the inclination of the magnetic
field. A consequence is that the phase of the correlation varies with
the viewing angle with respect to the field direction. Observations
of the vector components of the photospheric fields could be used to
correct these phase perturbations analogous to the procedures already
developed using line-of-sight magnetograms. A physical understanding
of surface distortions will come through MHD modeling, including
simulations of the interaction of acoustic and magneto-acoustic-gravity
waves with prescribed magnetic and sound-speed perturbations and flows
(artificial data). The development of appropriate tools for assessing
and correcting the effects of the surface magnetism will be vital for
the interpretation of helioseismic data from the upcoming HMI mission
on SDO. DCB and CL gratefully acknowledge support from the NSF (SAA/AST)
and NASA (LWS, SR&T).
Title: The Local Helioseismology of Inclined Magnetic Fields and
the Showerglass Effect
Authors: Schunker, H.; Braun, D. C.; Cally, P. S.; Lindsey, C.
Bibcode: 2005ApJ...621L.149S
Altcode:
We present evidence for the dependence of helioseismic Doppler
signatures in active regions on the line-of-sight angle in inclined
magnetic fields. Using data from the Michelson Doppler Imager
(MDI) on board the Solar and Heliospheric Observatory, we performed
phase-sensitive holography in the penumbrae of sunspots over the
course of several days as the spots traversed the solar disk. Control
correlations, which comprise a correlation of the surface wave amplitude
with the incoming acoustic wave amplitude from a surrounding region,
were mapped. There is a direct dependence of control-correlation phase
signatures on the line-of-sight angle in the plane defined by the
vertical and magnetic field vectors. The phase shift of waves observed
along directions close to the orientation of the magnetic field is
smaller than the phase shift observed when the line of sight is at a
significant angle with respect to the field orientation. These findings
have important implications for local helioseismology. The variation
in phase shift (or the equivalent acoustic travel-time perturbations)
with line-of-sight direction suggests that a substantial portion of the
phase shift occurs in the photospheric magnetic field. Observations of
the vector components of the field may be used to develop a proxy to
correct these phase perturbations (known as the acoustic showerglass)
that introduce uncertainties in the signatures of acoustic perturbations
below the surface.
Title: The Acoustic Showerglass. I. Seismic Diagnostics of
Photospheric Magnetic Fields
Authors: Lindsey, Charles; Braun, D. C.
Bibcode: 2005ApJ...620.1107L
Altcode:
A problem of major interest in the helioseismology of active
regions is the acoustics of magnetic photospheres and shallow
subphotospheres. Magnetic fields suppress the photospheric signatures
of acoustic waves impinging onto them from the underlying solar
interior and shift their phases. The phase shifts function as a
sort of acoustic showerglass that impairs the coherence of seismic
waves arriving from below, degrading images of subsurface anomalies
derived by mechanical reconstruction of phase-coherent waves. The
purpose of this study is to characterize the ``acoustic showerglass''
in general optical terms and make a rough practical assessment of its
impact on local seismic diagnostics of the shallow subphotospheres of
active regions. We compile statistics comparing the acoustic field in
magnetic photospheres with holographic projections of waves arriving
from distant surrounding pupils. These ``local control correlations''
are consistent with an acoustic anomaly in the shallow subphotosphere
of the active region that is strong but predominantly superficial;
we call this the ``acoustic Wilson depression.'' The local control
correlations also exhibit a phenomenon we call the ``penumbral acoustic
anomaly,'' characterized by a conspicuous phase shift in regions of
inclined magnetic field. This appears to be consistent with a fairly
straightforward hydromechanical interpretation of the interaction of
acoustic waves with photospheric magnetic forces. Detailed numerical
simulations of the interaction of acoustic waves with magnetic forces
can greatly facilitate our understanding of the acoustic showerglass
and the thermal structure of the top few hundred kilometers of active
region subphotospheres.
Title: The Acoustic Showerglass. II. Imaging Active Region
Subphotospheres
Authors: Lindsey, Charles; Braun, D. C.
Bibcode: 2005ApJ...620.1118L
Altcode:
Seismic diagnostics of the shallow subphotospheres of strong active
regions are substantially impacted by large amplitude and phase
perturbations introduced by overlying surface magnetic fields. These
function as an ``acoustic showerglass'' that impairs the coherence
of acoustic waves impinging onto the solar surface from below,
degrading images of subsurface anomalies derived by phase-coherent
seismic reconstruction. In an independent study we have developed a
rough proxy to characterize showerglass phase errors based on maps of
the square magnitude of the vector magnetic field at the surface. In
this study we apply the proxy to correct helioseismic observations of
active region photospheres from the Michelson Doppler Imager aboard the
Solar and Heliospheric Observatory. We apply phase-correlation seismic
holography to the corrected observations to image the underlying 5-10
Mm subphotosphere. The corrected phase maps show no consistent evidence
for sound-speed anomalies more than 5 Mm beneath a moderately large,
isolated sunspot. Forward-modeling computations applied to simple
models suggest sound-speed anomalies limited to approximately +/-250 m
s-1 for depths from 5 to 10 Mm, averaged over the horizontal
extent of the sunspot. For complex active regions, uncertainties are
considerably greater. However, results of this study suggest that more
careful modeling of the acoustic showerglass will lead to substantially
improved seismic diagnostics of active region subphotospheres. Detailed
hydromechanical computations of acoustics models of active region
photospheres and subphotospheres are needed to facilitate the
interpretation of showerglass-corrected holographic signatures.
Title: Principles of Seismic Holography for Diagnostics of the
Shallow Subphotosphere
Authors: Lindsey, Charles; Braun, D. C.
Bibcode: 2004ApJS..155..209L
Altcode:
We develop the wave-mechanical formalism for phase-correlation
computational seismic holography of the shallow subphotosphere under
the plane-parallel approximation and apply it to helioseismic Doppler
observations from the Michelson Doppler Imager on the SOHO spacecraft
of both the quiet Sun and active regions. We compare holographic
signatures computed wave-mechanically with similar signatures
computed under the widely used eikonal approximation. The major
difference between the hydromechanical and eikonal computations can
be expressed in terms of acoustic dispersion effects within a few
Mm of the solar surface. With an appropriate account for dispersion,
the eikonal computations are remarkably accurate over a broad range
of practical applications. A major imposition that confronts local
diagnostics of the shallow subphotosphere is a phenomenon we call
``ghost signatures,'' artifacts introduced by a local ambiguity in
the origin of the waves that give rise to the helioseismic signatures
observed in the photosphere. Phase-correlation holographic signatures
of the shallow subphotospheres of active regions are predominated by
strong, stochastic phase shifts associated with magnetic fields at the
solar surface. These introduce effects similar to those of an optical
showerglass, significantly impairing the coherence of waves impinging
into the magnetic photosphere from beneath, smearing the holographic
signatures of possible subphotospheric anomalies.
Title: Local Helioseismology of Inclined Magnetic Fields and the
Showerglass Effect
Authors: Schunker, H.; Braun, D. C.; Lindsey, C.; Cally, P. S.
Bibcode: 2004ESASP.559..227S
Altcode: 2004soho...14..227S
No abstract at ADS
Title: Local Helioseismology of Near-Surface Flows
Authors: Braun, D. C.; Birch, A. C.; Lindsey, C.
Bibcode: 2004ESASP.559..337B
Altcode: 2004soho...14..337B
No abstract at ADS
Title: Seismic Waves from the Solar Flares of 2003 October 28 and 29
Authors: Donea, A. -C.; Lindsey, C.
Bibcode: 2004ESASP.559..152D
Altcode: 2004soho...14..152D
No abstract at ADS
Title: The Penumbral Acoustic Anomaly
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 2004ESASP.559..552L
Altcode: 2004soho...14..552L
No abstract at ADS
Title: Remote distributed pipeline processing of GONG helioseismic
data: experience and lessons learned
Authors: Goodrich, Jean N.; Kholikov, Shukur; Lindsey, Charles;
Malanushenko, Anna; Shroff, Chirag; Toner, Clifford
Bibcode: 2004SPIE.5493..538G
Altcode:
The Global Oscillation Network Group (GONG) helioseismic network
can create images of the farside of the Sun which frequently show the
presence of large active regions that would be otherwise invisible. This
ability to "see" through the sun is of potential benefit to the
prediction of solar influences on the Earth, provided that the data can
be obtained and reduced in a timely fashion. Thus, GONG is developing a
system to A) perform initial data analysis steps at six geographically
distributed sites, B) transmit the reduced data to a home station, C)
perform the final steps in the analysis, and D) distribute the science
products to space weather forecasters. The essential requirements are
that the system operate automatically around the clock with little human
intervention, and that the science products be available no more than 48
hours after the observations are obtained. We will discuss the design,
implementation, testing, and current status of the system.
Title: Local Helioseismology of Solar Dynamics
Authors: Braun, D. C.; Lindsey, C.; Birch, A. C.
Bibcode: 2004AAS...204.5309B
Altcode: 2004BAAS...36..757B
We have initiated a systematic exploration of the dynamics of the
solar interior, applying Doppler-sensitive seismic holography to data
from the MDI instrument onboard the SOHO spacecraft and the Global
Oscillations Network Group (GONG). Goals of this comprehensive project
include understanding the nature of supergranulation, monitoring the
subsurface variations of the meridional circulation, and understanding
other subsurface flows and their relation to solar activity. We
present initial results on our inference of subsurface flows due with
an emphasis on control work, including comparisons between MDI and GONG
datasets and other local seismic procedures such as ring diagrams. The
project will develop and test data analysis tools and a forward
(and inverse) modeling formalism based on the Born approximation,
in preparation for their routine application to the next generation
of helioseismic data from the Helioseismic and Magnetic Imager (HMI)
on the Solar Dynamics Observer. This work is supported by funding
from NASA SR&T and Living With a Star programs and the NSF Stellar
Astronomy and Astrophysics program.
Title: The Acoustic Showerglass and Diagnostics of Active Region
Subphotospheres
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 2004AAS...204.5310L
Altcode: 2004BAAS...36..757L
Magnetic fields introduce large phase shifts into acoustic waves
passing through the upper 400 km of an active region subphotosphere,
impairing the phase coherence of time-distance correlation measurements,
including seismic images of the underlying subphotosphere. We call
this the "acoustic showerglass" effect. Reliable diagnostics of active
region subphotospheres require a careful account of the interaction of
acoustic waves with showerglass magnetic fields. A clear understanding
of the acoustics of shallow magnetic fields offers the facility for
detailed thermal modeling of the showerglass layer. It also opens the
possibility of a high-quality magnetic proxy to correct showerglass
phase errors, greatly improving our view of the underlying magnetic
subphotosphere. The research reported in this poster is supported by
grants from the National Aeronautics and Space Administration and the
National Science Foundation.
Title: Acoustic Holographic Studies of Solar Active Regions
Authors: Malanushenko, A.; Braun, D.; Kholikov, S.; Leibacher, J.;
Lindsey, C.
Bibcode: 2004IAUS..223..283M
Altcode: 2005IAUS..223..283M
We present results of a study of the morphology and evolution of
active regions using solar acoustic holography. These include acoustic
signatures of large far-side active regions and their relationship to
near-side activity indices a half rotation before and after the farside
image, and the direct comparison of near-side acoustic signatures with
the standard activity indicators, not only in their own right but also
to calibrate the farside acoustic signature.
Title: Two days in the life of AR10486
Authors: Donea, A. -C.; Maris, G.; Lindsey, C. A.
Bibcode: 2004IAUS..223..241D
Altcode: 2005IAUS..223..241D
Magnetic and acoustic properties of the complex active region AR 486
are analyzed for two consecutive days: October 28 and October 29,
2003 when two large flares of magnitude X17.2 and X10 were produced,
respectively. Using the technique of helioseismic holography we detected
seismic waves emitted from these flares at 6 mHz. SOHO-MDI white light
images, magnetograms, and Dopplergrams are used to study the physics
of the acoustic sources.
Title: Computational Seismic Holography of Active Region
Subphotospheres
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 2003SPD....34.0808L
Altcode: 2003BAAS...35Q.823L
We apply phase-correlation seismic holography to SOHO/MDI observations
of large sunspots to render signatures of local sound-speed anomalies
in their shallow subphotospheres. In the computations reported
here, a magnetic proxy we call the ``showerglass correction'' was
applied to correct large phase errors introduced by surface magnetic
fields. Preliminary results suggest a general sound speed enhancement
in the range 1--4% up to depths of 10 Mm over horizontally extended
regions surrounding large sunspots. These regions cover diameters
roughly in the range 30--50 Mm. Phase maps of large active region
complexes show signatures that tend to blanket most of the active
region. The correlation between the phase shift and the magnetic
field strength is generally high, but there are localized regions in
which the phase signature departs significantly from the magnetic. The
signature of the sunspot itself tends to be subtle with a maximum that
may be significantly displaced towards the periphery of the active
region. The research reported here is supported by funding from the
Supporting Research and Technology and the Living with a Star Programs
of the National Aeronautics and Space Administration, and from the
Astronomical Sciences Division of the National Science Foundation.
Title: The showerglass effect in seismic diagnostics of active
region subphotospehres
Authors: Lindsey, Charles; Braun, D. C.
Bibcode: 2003ESASP.517...23L
Altcode: 2003soho...12...23L
A major obstacle that encumbers local seismic diagnostics of the shallow
subphotospheres of strong active regions is phase errors introduced by
overlying surface magnetic fields. These errors function as a sort of
"acoustic showerglass" that obscures subphotospheric acoustic anomalies,
scrambling computational images of these derived by phase-coherent
seismic reconstruction. We develop a proxy based on the surface magnetic
field to correct the showerglass phase errors and image acoustic
scatterers beneath it. Preliminary applications of this correction give
us signatures that appear to signify strong, sharply outlined acoustic
anomalies 3-9 Mm beneath large growing active regions. Correction of
the showerglass correction appears to be important, if not essential,
for diffraction-limited diagnostics of acoustic anomalies in the
shallow subphotospheres of strong active regions.
Title: Helioseismic probing of the solar dynamo
Authors: Ruzmaikin, Alexander; Lindsey, Charles
Bibcode: 2003ESASP.517...71R
Altcode: 2003soho...12...71R
According to theoretical predictions, the solar dynamo operating in
the convection zone generates maximal magnetic fields near the base
of the convection zone. Detection of this field is a challenging task
for helioseismology. We discuss the ways of probing the magnetic field
in the solar interior and estimate the magnitude of the field that can
be detected with presently achievable accuracy. It is easier, however,
to detect the flows that drive the dynamo. We describe the major flow
parameters related to the dynamo flows and present the requirements
for measurement of these parameters with local helioseismic techniques.
Title: Helioseismic imaging of the farside and the interior
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 2003ESASP.517...15B
Altcode: 2003soho...12...15B
Helioseismic holography is a highly efficient and flexible procedure
with a wide range of utility, from mapping sound wave travel times over
the entire far solar hemisphere to imaging small scale scatterers and
flows beneath solar active regions. Seismic images covering the entire
far hemisphere of the Sun have been constructed using data from the
recently upgraded Global Oscillation Network Group (GONG+) network
and compare favorably with those made using simultaneous data from
the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric
Observer (SOHO). We are also continuing our comprehensive exploration
of diffraction-limited seismic imaging of active regions. We have
recently extended our applications of helioseismic holography to include
Doppler diagnostics of active regions and quiet Sun. A major finding
presented here is that the horizontal velocity field in supergranules
and sunspot moats appears to be concentrated at the surface. Another
recent, but vital, contribution to local helioseismology has been a
study of what is termed the "showerglass effect". Magnetic fields in
the photosphere produce large, local amplitude and phase perturbations
to the observed acoustic wave field which may be quantified and removed
prior to the holographic computations. Removal of the showerglass from
local helioseismic images of active regions is proving to be a crucial
step in the detection of compact subsurface scatterers.
Title: MDI and GONG inferences of the changing solar interior
Authors: Barban, C.; Howe, R.; Hill, F.; Komm, R. W.; Leibacher, J.;
Toner, C.; Bogart, R.; Braun, D.; Haber, D.; Hindman, B.; Lindsey, C.
Bibcode: 2002ESASP.508...55B
Altcode: 2002soho...11...55B
The Global Oscillation Network Group (GONG) and the Solar Oscillations
Investigation (SOI) using the Michelson Doppler Imager (MDI) instrument
aboard the SOHO spacecraft provide combined data sets that now cover
more than six years and allow us to probe the changing dynamics of the
convection zone in unprecedented detail. Here we present the latest
combined results from both projects, showing the evolution of the
migrating zonal flows close to the surface and also changes close to
and below the base of the convection zone, as well as changes in the
mode parameters related to surface magnetic activity variation in time
and latitude.
Title: The First Seismic Images of the Solar Interior and Far Side
from the GONG+ Network
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 2002AAS...200.8906B
Altcode: 2002BAAS...34..791B
Since mid-2001, the upgraded GONG+ network has been providing
high-resolution Doppler images of the Sun. We are now analyzing GONG+
data as part of our program in local helioseismology and acoustic
holography. The bulk of the results shown here are derived from data
obtained during a 24-hour period in 2001 September, when simultaneous
full-disk observations from the MDI instrument onboard the SOHO
spacecraft were available for comparison. Images showing the acoustic
travel-time perturbations over the entire far hemisphere obtained from
GONG+ and MDI data are essentially identical. This demonstrates that
the GONG+ network may be used as the basis of a synoptic far-side
imaging program of comparable quality to that now provided by
MDI. Holographic depth-diagnostics of travel-time perturbations below
several active regions on the solar front side are also presented. These
phase-sensitive holographic images from GONG+ and MDI have similar
noise characteristics when computed using acoustic modes with degree
(wavenumber) below about 300, which implies that the r.m.s. fluctuations
in these images are solar in nature. At higher wavenumbers, atmospheric
seeing introduces an excess r.m.s., which increases with mode degree,
to the images derived from GONG+ data. However, acceptable images are
possible using modes with degrees up to at least 700. We will discuss
how GONG+ data may be advantageously utilized in detailed, continuous,
and long-term local-helioseismic analyses of the far side and deep
interior of the Sun. This work is supported by awards AST-9987286 from
NSF, and awards NASW-01007 and NAG5-10984 from NASA.
Title: Computational Seismic Holography of the Deep Interior and
Far Surface of the Sun
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 2002AAS...200.7903L
Altcode: 2002BAAS...34..780L
Computational seismic holography has given us a remarkably flexible and
powerful new utility for local diagnostics of the solar interior. Major
results to date include the following: - Seismic signatures
surrounding sunspots up to 100 Mm in diameter, called ``acoustic
moats.'' - Enhancements of locally stochastic seismic emission, called
``acoustic glories,'' surrounding complex active regions. - Chromatic
siesmic emission maps of a solar flare. - Signatures suggesting compact
thermal enhancements in the shallow subphotospheres of surface magnetic
regions. - Synoptic phase-correlation maps of active regions on the
far surface of the Sun. Prospects for deep interior diagnostics of the
solar interior are highly encouraging. Seismic holography applied to the
database we expect from the Solar Dynamics Observatory is nearly certain
to give us a synoptic view of the local structure of flows and torsional
oscillations down to the base of the convection zone. Cooperative
seismic observations of both near and far surfaces of the Sun offer
high quality holographic diagnostics of the solar core. Holographic
diagnostics promise deep insight into the operation of the solar dynamo,
and may give us indications of emerging magnetic fields significantly
in advance of their appearance at the solar surface. This research
has been supported by funding from the National Science Foundation
and the National Aeronautics and Space Administration.
Title: Seismic forecasting of solar activity
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 2002HiA....12..378B
Altcode:
No abstract at ADS
Title: Seismic Imaging of the Far Hemisphere of the Sun
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 2001ApJ...560L.189B
Altcode:
We apply phase-sensitive helioseismic holography to Solar and
Heliospheric Observatory/Michelson Dopper Imager data to demonstrate
how acoustic travel-time perturbations may be mapped over the entire
portion of the Sun facing away from the Earth, including the polar
regions. In addition to offering significant improvements to ongoing
space weather forecasting efforts, the procedure offers the possibility
of local seismic monitoring of both the temporal and spatial variations
in the acoustic properties of the Sun over all of the far surface.
Title: Helioseismic Holography and a Study of the Process of Magnetic
Flux Disappearance in Canceling Bipoles
Authors: Lindsey, Charles; Harvey, Karen L.; Braun, D.; Jones, H. P.;
Penn, M.; Hassler, D.
Bibcode: 2001STIN...0156300L
Altcode:
Project 1: We have developed and applied a technique of helioseismic
holography along the lines of originally set out in our proposal. The
result of the application of this diagnostic technique to solar activity
and the quiet Sun has produced a number of important discoveries:
(1) acoustic moats surrounding sunspots; (2) acoustic glories
surround large active regions; (3) acoustic condensations beneath
active regions; and (4) temporally-resolve acoustic images of a solar
flare. These results have been published in a series of papers in the
Astrophysical Journal. We think that helioseismic holography is now
established as the most powerful and discriminating diagnostic in local
helioseismology. Project 2: We conducted a collaborative observational
program to define the physical character and magnetic geometry of
canceling magnetic bipoles aimed at determining if the cancellation
process is the result of submergence of magnetic fields. This assessment
is based on ground-based observations combining photospheric and
chromospheric magnetograms from NSO/KP, BBSO, and SOHO-MDI, and EUV
and X-ray images from SOHO EIT/CDS, Yohkoh/SXT, and TRACE. Our study
involves the analysis of data taken during three observing campaigns to
define the height structure of canceling bipoles inferred from magnetic
field and intensity images, and how this varies with time. We find
that some canceling bipoles can be explained by the submerge of their
magnetic flux. A paper on the results of this analysis will be presented
at an upcoming scientific meeting and be written up for publication.
Title: Prospects for Helioseismic Holography in the Deep Solar
Interior
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 2001AGUSM..SP21C08L
Altcode:
Holographic seismic imaging of low-degree acoustic noise
opens new prospects for solar interior diagnostics that are most
encouraging. Seismic imaging of the near solar interior has given us the
discoveries of ``acoustic moats,'' surrounding sunspots, of anomalous
emission from ``acoustic glories'' surrounding large active regions,
acoustic images of solar flares, and the signatures of apparent acoustic
perturbations up to 20~Mm beneath active region photospheres. Low-degree
seismic holography is now giving us images of large magnetic regions
on the far surface of the Sun, a utility with valuable space-weather
forecasting and general synoptic applications. Extensions of the
foregoing applications promise insight into the deep solar interior,
to the base of the convection zone and into the Sun's nuclear-burning
core. Diffraction-limited imaging of low-degree noise over pupils
covering most of the near solar hemisphere offer the most discriminating
probe of the deep solar interior. Earth-based helioseismic observations
coordinated with seismic observations of the far side of the Sun at
frequencies in the range 6--7 mHz would allow us to resolve local
thermal and Doppler structure in the solar core with a resolution of
75~Mm. Coordinated seismic observations of both near and far sides
of the Sun are essential to take advantage of the superior spatial
resolution offered by high-frequency waves.
Title: Seismic Holography of the Solar Interior and Far Side
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 2001IAUS..203..167B
Altcode:
The development of solar acoustic holography has opened a major
new diagnostic avenue in local helioseismology. Its application to
SOI-MDI data from SOHO has revealed ``acoustic moats'' surrounding
sunspots, ``acoustic glories'' surrounding complex active-regions,
and ``acoustic condensations'' suggesting the existence of significant
seismic anomalies up to 20 Mm beneath active-region photospheres. It has
given us the first seismic images of a solar flare, and has uncovered a
remarkable anomaly in the statistical distribution of seismic emission
from acoustic glories. Phase-sensitive seismic holography is now
producing high-resolution maps of sound travel-time anomalies caused
by magnetic forces in the immediate subphotosphere, apparent thermal
enhancements in acoustic moats, and Doppler signatures of subsurface
flows. It has also produced the first seismic images of active regions
on the far-side of the Sun, giving us a powerful tool for forecasting
more than a week in advance their arrival at the east limb. This
diagnostic now promises a new insight into the hydromechanical and
thermal environments of the solar interior in the local perspective.
Title: Seismic Holography of the Deep Solar Interior
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 2000SPD....31.0503L
Altcode: 2000BAAS...32R.836L
The first images of magnetic regions on the far solar surface
were recently secured by applying seismic holography to five-minute
oscillations with spherical harmonic degrees roughly in the range 20 to
40 in SOHO-MDI observations. These waves penetrate up to half way to the
sun's center, and can therefore sample the base of the convection zone
with a resolution similar to that of the aforementioned far-side images,
approximately 10o in longitude at the solar equator. However,
by far the best seismic diagnostics are invariably offered by the
highest possible frequencies, 6 mHz and above, if possible. Because
these waves are efficiently absorbed by the solar surface, helioseismic
observations that can compare the far side of the sun with earth-based
observations of the near side are needed for coherent phase-sensitive
imaging of the deep solar interior. Coordinated near- and far-side
seismic observations of the sun at frequencies in the range 6--7
mHz would allow us to examine the thermal and Doppler profile of the
solar core with a resolution of 75 Mm. This presentation is based on
research supported by grants NAG5-7236 from NASA and AST-9528249 from
NSF, and by a contract, PY-0184, with Stanford University.
Title: Seismic Imaging of the Far Side and Interior of the Sun
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 2000SPD....3102112B
Altcode: 2000BAAS...32Q.831B
Images of active regions on the far side of the Sun were derived
by applying seismic holography to observations from the SOI-MDI
instrument on the SOHO spacecraft. Synoptic seismic imaging of
far-side solar activity will allow anticipation of the appearance of
large active regions more than a week ahead of their arrival on the
east limb. The technical requirements for a synoptic monitor appear
to be quite modest, given real time access to observations from the
Global Oscillations Network Group, for example. Currently, seismic
images of the solar far side are easily computed in less than a day
using a single-processor Pentium-based PC running Linux. In addition to
providing new applications for space weather prediction, the development
of solar acoustic holography is opening major new diagnostic avenues in
the study of the solar interior. Phase-sensitive seismic holography is
producing high-resolution maps of sound travel-time anomalies caused
by magnetic forces in the immediate subphotosphere, apparent thermal
enhancements in acoustic moats around sunspots, and Doppler signatures
of subsurface flows. Seismic holography applied to global modes, such
as those used to image the far side, has directly demonstrated the
influence of active regions on these modes. This reinforces a growing
consensus that reduced sound travel times in magnetic regions explain
the entirety of the frequency shifts of global modes with the solar
cycle. Phase-sensitive holography will also be used to probe thermal
and Doppler perturbations deep in the solar convection zone and the
tachocline. This work is supported by grants NAG5-7236 from NASA
and AST-9528249 from NSF, and by a contract, PY-0184, from Stanford
University.
Title: Stochastic Seismic Emission from Acoustic Glories and the
Quiet Sun
Authors: Donea, A. -C.; Lindsey, C.; Braun, D. C.
Bibcode: 2000SoPh..192..321D
Altcode:
Helioseismic images of multipolar active regions show enhanced seismic
emission in 5-mHz oscillations in a halo surrounding the active region
called the `acoustic glory'. The acoustic glories contain elements
that sustain an average seismic emission 50% greater than similar
elements in the quiet Sun. The most intense seismic emitters tend to
form strings in non-magnetic regions, sometimes marking the borders of
weak magnetic regions and the separation between weak magnetic regions
of opposite polarity. This study compares the temporal character
of seismic emission from acoustic glories with that from the quiet
Sun. The power distribution of quiet-Sun seismic emission far from solar
activity is exponential, as for random Gaussian noise, and therefore
not perceivably episodic. The distribution of seismic power emanating
from the most intense elements that comprise the acoustic glories is
exponential out to approximately 4 times the average power emitted
by the quiet Sun. Above this threshold the latter distribution shows
significant saturation, suggesting the operation of a hydromechanical
non-linearity that sets limits on the acoustic power generated by
the convection zone. This could give us considerable insight into the
physical mechanism of seismic emission from the near subphotosphere.
Title: Helioseismic Holography of Active-Region Subphotospheres -
(Invited Review)
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 2000SoPh..192..285B
Altcode:
The development of solar acoustic holography has opened a major new
diagnostic avenue in local helioseismology. It has revealed `acoustic
moats' surrounding sunspots, `acoustic glories' surrounding complex
active regions, and `acoustic condensations' suggesting the existence
of significant seismic anomalies up to 20 Mm beneath active-region
photospheres. Phase-sensitive seismic holography is now yielding
high-resolution maps of sound travel-time anomalies caused by magnetic
forces in the immediate subphotosphere, apparent thermal enhancements
in acoustic moats, and Doppler signatures of subsurface flows. It has
given us the first seismic images of a solar flare, and has uncovered a
remarkable anomaly in the statistical distribution of seismic emission
from acoustic glories. Seismic holography will probably give us the
means for early detection of large active regions on the far-surface
of the Sun, and possibly of deep subsurface activity as well. This
powerful diagnostic now promises a new insight into the hydromechanical
and thermal environments of the solar interior in the local perspective.
Title: Seismic Images of the Far Side of the Sun
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 2000Sci...287.1799L
Altcode:
Images of an active region on the far side of the sun were derived by
applying seismic holography to recent helioseismic observations from
space. Active regions are the centers of energetic phenomena such as
solar flares and coronal mass ejections, whose resulting electromagnetic
and particle radiation interfere with telecommunications and power
transmissions on Earth and can pose significant hazards to astronauts
and spacecraft. Synoptic seismic imaging of far-side solar activity
will now allow anticipation of the appearance of large active regions
more than a week ahead of their arrival on the east solar limb.
Title: Phase-sensitive Holography of Solar Activity
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 2000SoPh..192..307B
Altcode:
Phase-correlation statistics comparing acoustic radiation coming
out of a particular point on the solar photosphere with acoustic
radiation going into it show considerably reduced sound travel times
through the subphotospheres of active regions. We have now applied
techniques in phase-sensitive seismic holography to data from the Solar
Oscillations Investigation - Michelson Doppler Imager (SOI-MDI) on the
Solar and Heliospheric Observatory (SOHO) spacecraft to obtain high
resolution phase-correlation maps of a large, complex active region
and the `acoustic moat' which surrounds it. We report the following
new results: First, the reduced sound travel-time perturbations in
sunspots, acoustic moats, and isolated plages increase approximately in
proportion to the logarithm of the surface magnetic flux density, for
flux densities above 10 G. This is consistent with an interpretation
of the travel-time anomalies, observed with holographic and other
local-helioseismic procedures, as caused by acoustic Wilson-like
depressions in photospheres of magnetic regions. Second, we find that,
compared with isolated plages, the acoustic moats have an additional
sound travel-time reduction on the order of 3-5 s which may be
explained by a thermal excess due to the blockage of convective
transport by the sunspot photosphere. Third, the combined effect of
the Wilson depression in plages, acoustic moats, and sunspots may
explain the observed variation of global p-mode frequencies with the
solar cycle. Fourth, we find that active regions, including sunspots,
acoustic moats, and plages, significantly reflect p modes above the
acoustic cut-off frequency, where the surface of the quiet Sun acts
as a nearly perfect absorber of incident acoustic radiation.
Title: Basic Principles of Solar Acoustic Holography - (Invited
Review)
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 2000SoPh..192..261L
Altcode:
We summarize the basic principles of holographic seismic imaging of
the solar interior, drawing on familiar principles in optics and
parallels with standard optical holography. Computational seismic
holography is accomplished by the phase-coherent wave-mechanical
reconstruction of the p-mode acoustic field into the solar interior
based on helioseismic observations at the solar surface. It treats the
acoustic field at the solar surface in a way broadly analogous to how
the eye treats electromagnetic radiation at the surface of the cornea,
wave-mechanically refocusing radiation from submerged sources to render
stigmatic images that can be sampled over focal surfaces at any desired
depth. Holographic diagnostics offer a straight-forward assessment of
the informational content of the observed p-mode spectrum independent
of prospective physical models of the local interior anomalies that
it represents. Computational holography was proposed as the optimum
approach whereby to address the severe diffraction effects that
confront standard tomography in the solar p-mode environment. It has
given us a number of remarkable discoveries in the last two years
and now promises a new insight into solar interior structure and
dynamics in the local perspective. We compare the diagnostic roles of
simple acoustic-power holography and phase-sensitive holography, and
anticipate approaches to solar interior modeling based on holographic
signatures. We identify simple computational principles that, applied to
high-quality helioseismic observations, make it easy for prospective
analysts to produce high-quality holographic images for practical
applications in local helioseismology.
Title: Seismic Forecasting of Solar Activity
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 2000IAUJD...7E...4L
Altcode:
from SOHO, has recently given us the first images of an active region on
the far side of the Sun. The advent of phase-coherent seismic imaging is
now allowing us quite literally to look into the solar interior from a
local perspective, indeed to see through the solar interior acoustically
to its far surface. Space and ground-based helioseismic observatories
will soon have the capability for ``real-time helioseismology,'' and
will be routinely monitoring the far surface of the Sun. This will
greatly facilitate medium-range forecasts important to space weather,
allowing us to anticipate more than a week in advance the arrival
of large far-side active regions at the Sun's east limb to within a
few hours.
Title: Phase-Sensitive Holography of Acoustic Moats
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 1999AAS...194.5610B
Altcode: 1999BAAS...31..913B
Phase-correlation statistics comparing acoustic radiation coming out
of a particular point on the solar photosphere with acoustic radiation
going into it show considerably reduced sound travel times through the
subphotospheres of active regions. This is already well established by
time-distance correlations measured by Duvall et al., and is consistent
with earlier measurements of scattering phase shifts of single sunspots
by Braun and Fan. We have now applied techniques in phase-sensitive
seismic holography to obtain high resolution phase-correlation maps
of active regions and the ``acoustic moats'' that surround them. The
important new result which the holographic correlation maps give us
is that the seismic perturbation manifested by the acoustic moats
is generally quite significant and in large active-region complexes
predominant. Indeed, the acoustic moat surrounding the large active
region complex NOAA AR 8179 (1998 March 16) manifests a one-way
travel-time reduction of ~ 30s over an area of some 10(4) Mm(2) ,
encompassing all of the significant sunspots in the region. Onto
this phase perturbation the major sunspots impose an additional
localized contribution of ~ 30s. These results strongly reinforce an
interpretation of the acoustic moat as a well integrated convection
cell driven by the thermal perturbation that results from the local
blockage of convective heat transport by the sunspot photosphere. The
remarkable lateral extent of the acoustic moat, some 100 Mm in latitude
and more than 150 Mm in longitude, suggests a convective flow that
undertakes to spread the thermal perturbation into a relatively thin
layer, such that the excess heat contained therein can access the
solar surface through normal supergranular and granular diffusion. We
expect holographic Doppler diagnostics, now under development, to shed
considerable light very soon on the flows that are needed to explain
the extended dimensions of the thermal perturbations that surround
large active regions. This research is supported by NSF Grants AST
9521637 and AST 9528249, and NASA Grants NAGW-97029 and NAG5-7236.
Title: Seismic Images of a Solar Flare
Authors: Donea, A. -C.; Braun, D. C.; Lindsey, C.
Bibcode: 1999ApJ...513L.143D
Altcode:
We have used helioseismic holography to render seismic images of
the solar flare of 1996 July 9, whose helioseismic signature was
recently reported by Kosovichev & Zharkova. We computed time
series of ``egression power maps'' in 2 mHz bands centered at 3.5 and
6 mHz. These images suggest an oblong acoustic source associated with
the flare some 18 Mm in the north-south direction and approximately 15
Mm in the east-west direction. The considerable preponderance of the
flare acoustic power emanates in the 3.5 mHz band. However, because
the ambient noise in the 6 mHz band is much lower and the diffraction
limit for 6 mHz waves is much finer, the flare is rendered far more
clearly in the 6 mHz band. The 6 mHz flare signature lags the 3.5 mHz
by approximately 4 minutes.
Title: Helioseismic Images of an Active Region Complex
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 1999ApJ...513L..79B
Altcode:
Helioseismic images of a large active region complex at a frequency
of 5 mHz show a prominent halo of acoustic emission, which we
call the ``acoustic glory,'' surrounding the active region. This
feature is remarkably intense and contains small-scale elements of
concentrated seismic emission which cluster in strings in nonmagnetic
regions. Subsurface images show condensations of acoustic deficit
that appear to represent acoustic perturbations located in excess of
10 Mm beneath the photosphere. The analysis of this complex active
region suggests that these features are common in the neighborhoods of
large active regions and can appear tens of megameters horizontally
separated from sunspots. We propose that acoustic condensations are
the result of refraction or scattering by subsurface thermal or Doppler
perturbations below active regions. The appearance of acoustic glories
and condensations strongly suggests that complex active regions have
acoustic properties that are fundamentally different from those of
single isolated sunspots.
Title: Chromatic Holography of the Sunspot Acoustic Environment
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 1999ApJ...510..494L
Altcode:
We use helioseismic holography to obtain seismic images of a sunspot
and its local environment over the 3-8 mHz acoustic spectrum. We
are particularly interested in the acoustic deficit brought about by
strong acoustic absorption by the sunspot itself in the 3-4 mHz range
and in the helioseismic character of the ``acoustic moat'' recently
discovered by Braun et al. The holographic images computed here clearly
show that over a broad range in frequency the sunspot replaces the
acoustic radiation impinging into it from the ambient solar interior
with an outgoing acoustic flux that is only a fraction of that which
it receives. This acoustic deficit persists uniformly over the 3-7
mHz spectrum, even as the reflectivity of the quiet-Sun photosphere
goes from being an almost perfect, specular reflector at 4 mHz to an
almost perfect absorber at 5 mHz. As far as we can judge, the acoustic
moat surrounding the sunspot need not require a helioseismic absorption
mechanism of its own. Its signature in 3-4 mHz images could arise from
simple scattering of an acoustic deficit that originates in the nearby
sunspot. Such scattering may be the result of a thermal perturbation
resulting from the blockage of convective heat transport through the
sunspot photosphere. Alternatively, it could be the signature of a
Doppler perturbation attendant to the rapid convective outflow that
might be driven by such a thermal accumulation. While the results
presented here do not rule out the possibility that the acoustic moat
has its own absorption mechanism, they show little independent evidence
to indicate that the acoustic moat otherwise behaves very differently
from the quiet Sun where absorption and reemission of acoustic flux
are concerned. Helioseismic images of conspicuous halos that
appear in 6 mHz acoustic power maps show no significant enhancement of
acoustic emission from these regions. A fairly broad region surrounding
the sunspot appears to render a weak enhancement, ~2.5%, in the local
generation of 5 mHz acoustic power. This seems to explain peculiarities
in the spectrum of acoustic flux balance measurements based on Hankel
analysis. The distribution of the 5 mHz ``acoustic egression'' excess
is fairly diffuse and does not seem to be spatially correlated with
the strong acoustic power halos seen in 6 mHz acoustic power maps.
Title: Basic Principles of Seismic Holography
Authors: Lindsey, C.
Bibcode: 1999soho....9E..10L
Altcode:
Seismic imaging of the near solar interior using the basic principles of
computational holography has given us a number of remarkable discoveries
in the last two years. Seismic holography is accomplished by the
phase-coherent wave-mechanical reconstruction of the p-mode acoustic
field into the solar interior based on helioseismic observations at the
solar surface. Seismic holography treats the acoustic field at the solar
surface in a way broadly analogous to how the eye treats electromagnetic
radiation at the surface of the cornea, wave-mechanically regressing
radiation from distant sources to render stigmatic images that can
sampled over any desired focal plane. Holographic diagnostics are
designed to give us a straight-forward assessment of the information
content of the observed p-mode spectrum independent of a physical model
of the acoustic perturbations that give rise to the seismic signature
observed at the solar surface. Computational holography was initially
proposed as the optimum approach to the severe diffraction effects that
confront standard tomography in the solar p-mode environment. The more
general term "acoustic imaging" has recently been introduced to refer
to this diagnostic concept. I will summarize the basic principles of
the diagnostic in its broad generality as intuitively as possible,
drawing on familiar principles in optics and the parallel with
standard optical holography. I will discuss the diagnostic role of
phase-sensitive holography and point out the parallels between this
and time-distance- correlation measurements. Keeping in mind the
critical distinction between holography and physical modeling, I will
speculate into concepts that may offer us convenient avenues whereby
to model solar interior acoustic perturbations based on a holographic
presentation of solar interior acoustics.
Title: Seismic Images of a Solar Flare
Authors: Donea, Alina-C.; Braun, Doug C.; Lindsey, Charles A.
Bibcode: 1999soho....9E..13D
Altcode:
Helioseismic holography has given us remarkable images of the solar
flare of 1996 July 9. We computed time series of "egression power"
images in 2 mHz bands centered at 3.5 mHz and 6 mHz. These images show
an acoustic source associated with the flare some 18 Mm in the N-S
direction and approximately 15 Mm in the E-W. The flare is rendered
considerably more clearly in the 6 mHz band. The 6 mHz flare signature
lags the 3.5 mHz by approximately 4 min. The results offer a highly
encouraging assessment of the general diagnostic utility of seismic
holography for understanding the physics of solar flares.
Title: Stochastic Seismic Emission from Acoustic Glories and the
Quiet Sun
Authors: Donea, Alina-C.; Lindsey, Charles A.; Braun, Doug C.
Bibcode: 1999soho....9E..52D
Altcode:
Helioseismic images of multipolar active regions show enhanced seismic
emission in 5 mHz oscillations in a halo surrounding the active region
called the "acoustic glory." The acoustic glories contain seismic
elements that sustain an average seismic emission 50% greater than a
similar element of the quiet Sun. The most intense seismic emitters
tend to form strings in non-magnetic regions, sometimes marking the
borders of weak magnetic regions and even the separation between weak
magnetic regions of opposite polarity. This study compares the temporal
character of seismic emission from acoustic glories with that from the
quiet Sun. The distribution of quiet-Sun seismic power far from solar
activity is exponential, as for random Gaussian noise. The distribution
of seismic power emanating from the most intense elements that comprise
the acoustic glories is likewise exponential out to approximately 6
times the average power emitted by the quiet Sun. Above this threshold
the latter distribution shows significant saturation, suggesting the
operation of a hydromechanical non-linearity that sets limits on the
acoustic power generated by the convection zone. This could give us
considerable insight into the physical mechanism of seismic emission
from the near subphotosphere.
Title: Seismic images of the solar flare of July 9, 1996.
Authors: Donea, A. -C.; Braun, D. C.; Lindsey, C.
Bibcode: 1999joso.proc..124D
Altcode:
The helioseismic holography is a new method useful for rendering
seismic images of the solar flare of July 9, 1996. Time series of the
"egression power map" are computed in 2 mHz bands centered at 3.5
mHz and 6 mHz. The images show an acoustic source associated with the
flare some 18 mm in the N-S direction and approximately 15 mm in the
E-W. The flare is rendered far more clearly in the 6 mHz band. The 6
mHz flare signature lags the 3.5 mHz by approximately 6 minutes.
Title: Phase-Sensitive Seismic Holography of the Photospheres and
Near Subphotospheres of Active Regions
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 1999soho....9E..71L
Altcode:
The discovery of acoustic power halos surrounding active regions by
Braun, et al., Brown et al., and Toner and LaBonte, suggested that
surface regions with weak magnetic fields were enhanced emitters of
high-frequency seismic noise. Seismic holography of these regions
by Lindsey and Braun showed clearly that this was not generally the
case. Phase-sensitive holography of these features shows that these are
regions in which the Doppler signatures of seismic waves from distant
sources are locally enhanced, but the local seismic emission is not
enhanced. On the other hand, acoustic glories are regions of strongly
enhanced seismic emission from the quiet Sun just outside of magnetic
regions. Moreover, regions of strong magnetic field show suppressed
seismic emission. We examine the phase relation between the acoustic
ingressions, acoustic egressions, and local acoustic amplitudes of
these regions and consider how these can be treated as diagnostic of
the photospheres and near subphotospheres of active regions.
Title: Helioseismic Holography - a Technique for Understanding
Solar Flares
Authors: Donea, A. C.; Lindsey, C.; Braun, D.
Bibcode: 1999RoAJ....9S..71D
Altcode:
The helioseismic holography is a technique which allows the analysis of
the photosphere of the Sun from the point of view of the acoustics. In
this paper we shall discuss mainly the seismic image of the flare of
July 9, 1996 which produced the largest sunquake observed by MDI-SOHO
instrument. We emphasize the fact that the kernel-like structure
observed in the seismic signature at both 3.5 mHz and 6 mHz egression
power maps are not side lobes effect. The seismic signature reveals
the presence of an extended acoustic source, much larger than the
Doppler redshift motion observed in the MDI-SOHO Dopplergrams.
Title: Seismic Imaging of Acoustic Moats around Active Regions
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 1999soho....9E..46B
Altcode:
Phase-correlation statistics comparing acoustic radiation coming out
of a particular point on the solar photosphere with acoustic radiation
going into it show considerably reduced sound travel times through the
subphotospheres of active regions. This is already well established
by scattering phase shifts of single sunspots by Braun and Fan, and
by time-distance correlations measured by Duvall et al. We have now
applied techniques in phase-sensitive seismic holography to obtain high
resolution phase-correlation maps of active regions and the "acoustic
moats" that surround them. Correlation maps obtained for several active
regions show that the seismic perturbation manifested by the acoustic
moats extends 30 Mm or so beyond the visible sunspots, and in large
active-region complexes is quite predominate. Indeed, the acoustic moat
surrounding the large active region complex NOAA AR 8179 (1998 March 15)
manifests a one-way travel-time reduction of approximately 30s over an
area of some 10,000 sq. Mm, encompassing all of the significant sunspots
in the region. Onto this phase perturbation the major sunspots impose an
additional localized contribution of about 30s. These results strongly
reinforce an interpretation of the acoustic moat as a well integrated
convection cell driven by the thermal perturbation that results from the
local blockage of convective heat transport by the sunspot photosphere.
Title: Acoustic Signatures of Subphotospheric Structure Underlying
Sunspots
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 1998ApJ...509L.129L
Altcode:
Helioseismic holography of active regions at frequencies in the
range of 5-6 mHz renders acoustic signatures that we think signify
acoustic perturbations several megameters beneath the photosphere. The
application of holographic diagnostics at 5-6 mHz gives us images
with considerably finer horizontal spatial resolution, and likewise
much finer depth resolution with respect to focus, than the 3 mHz
diagnostics we have recently published. This Letter reports comparative
results of standard focus-defocus diagnostics of a single sunspot at 3
and 6 mHz. Images of the ``acoustic egression power'' at 6 mHz show a
remarkable, compact acoustic deficit that persists in acoustic focal
planes submerged up to 11.2 Mm beneath the solar surface. We propose
that this and other similar features associated with other active
regions are the result of refraction or scattering by submerged thermal
or Doppler perturbations of an acoustic deficit that is caused by strong
wave absorption in the overlying photosphere of the active region.
Title: Seismic Holography of Solar Activity
Authors: Braun, D. C.; Lindsey, C.; Fan, Y.; Fagan, M.
Bibcode: 1998ApJ...502..968B
Altcode:
Helioseismic images of sunspots show a remarkable acoustic anomaly
surrounding the sunspot. We applied the computational formalism of
``helioseismic holography'' to SOHO-MDI observations to render
acoustic images of NOAA AR 7973, an active region containing a
moderately large sunspot. The results of this study are based on
simple ``acoustic power holography,'' to image the absorption of
p-mode waves by the sunspot. These images clearly show a strong,
compact acoustic deficit representing the sunspot, as well as plages
in the neighborhood of the sunspot, consistent with earlier results of
``Hankel analysis.'' However, they also show surrounding the sunspot
a conspicuous acoustic halo extending out to a radius of approximately
35,000 km. We propose that this ``acoustic moat'' is the helioseismic
manifestation of a single convection eddy that is driven by the thermal
disturbance resulting from the local blockage of convective transport
in the sunspot subphotosphere. Depth diagnostics based on acoustic
focus show a rapidly defocusing sunspot image as the focal plane is
submerged. Acoustic noise models in which absorption by the sunspot
is entirely superficial yield images that defocus significantly more
slowly with increasing focal-plane depth than the SOHO-MDI images of
NOAA AR 7973. Extending the absorption significantly beneath the model
photosphere enhances the discrepancy. More recent tests tentatively
suggest that this ``focus anomaly'' is the result of neglect of image
smearing introduced into the MDI instrument to suppress aliasing,
and that a proper account of the instrumental MTF will render
defocus profiles roughly consistent with superficial absorption. Our
holographic images roughly indicate that the sunspot in NOAA AR 7973
absorbs low-l waves with approximately the same efficiency as it does
high-l waves. Contrary to widely held opinion, this result is entirely
consistent with that of the Hankel analysis, given that the absorption
of waves by magnetic regions is indeed superficial. We expect that the
efficient absorption of low-l waves will make it possible to image large
active regions on the far side of the Sun by the acoustic-absorption
signatures they render at their antipodes.
Title: The Acoustic Moat and Thermal Transport in the Neighborhoods
of Sunspots
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 1998ApJ...499L..99L
Altcode:
Helioseismic holography of sunspots shows a remarkable acoustic anomaly
surrounding the sunspot, which we call an ``acoustic moat.'' We used
Solar and Heliospheric Observatory (SOHO) Michelson Doppler Imager
observations of NOAA Active Region 7973 to render acoustic images
of a typical sunspot. These images show a conspicuous halo, 70,000
km in diameter, surrounding the sunspot, in which there appears a
predominant acoustic deficit. This ``acoustic moat'' may be terminated
by a sharp outer boundary, which appears to circumscribe the sunspot
completely in some instances. The outer boundary of the acoustic
moat coincides conspicuously with plages in the neighborhood of the
sunspot. Depth diagnostics based on acoustic focus suggest that the
acoustic perturbations characterizing both the sunspot and the acoustic
are predominantly superficial, within a few thousand kilometers of
the solar surface. Following work by Meyer et al., we propose that
the acoustic moat is the helioseismic manifestation of a single,
integrated convection eddy that is driven by heat accumulation
resulting from the local blockage of convective transport from the
solar interior into the sunspot subphotosphere. We propose that the
acoustic deficit predominantly characterizing the halo is the result
of thermal refraction or Doppler scattering by the eddy outflow of an
acoustic deficit originating in the helioseismic absorption by the
nearby sunspot and possibly neighboring plages. With the advent of
SOHO and the Global Oscillation Network Group, helioseismic holography
promises considerable insight into the general subject of convective
flows surrounding sunspots, an issue that is certain to be critical
to the long-standing problem of thermal transport in the neighborhoods
of sunspots.
Title: Helioseismic Signatures of Subphotospheric Structure Beneath
Active Regions
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 1998ESASP.418..641L
Altcode: 1998soho....6..641L
No abstract at ADS
Title: Helioseismic Holography
Authors: Lindsey, C.; Braun, D. C.
Bibcode: 1997ApJ...485..895L
Altcode:
We describe the basic principles of ``helioseismic holography,'' an
analytic technique intended for local helioseismology of subsurface
structure. The purpose of this technique is to provide depth
discrimination of subsurface structure that manifests a surface
signature in acoustic waves. It is based on the computational
application of spatially resolved helioseismic observations to the
surface of an acoustic model of the solar interior that contains no
local structure. The observed surface oscillations are applied to
the model in time reverse, and the model is then computationally
sampled at various depths in its interior. This technique takes
advantage of the coherence retained by waves in a smooth acoustic
medium following an interaction with subsurface structure, allowing
us to extrapolate the acoustic field with high accuracy to the depth
where the structure lies. Depth discrimination is then accomplished by
focus-defocus diagnostics. We describe computational approaches
to the technique from two different perspectives, the ``spectral''
and the ``spatial.'' For rigorous models of the solar interior,
the computational demands of the spectral and spatial approaches are
approximately the same. For diagnostics of relatively shallow structure,
the plane-parallel approximation of the model is useful. In this case
the spectral approach reduces computational holography essentially to
Fourier transforms, which can be performed rapidly with very modest
hardware. We illustrate the technique in this case, using artificial
data characterizing waves in an idealized plane-parallel medium
with acoustic absorbers located at various depths. At present,
we prefer to maintain a secure distinction between holography and
modeling. While we do not discuss modeling in this paper, we think
that it is important to develop an approach to modeling that takes
advantage of holographic reconstruction. The prospect of viewing local
subsurface magnetic regions and flows opens an entirely new dimension
to helioseismology and to solar and stellar physics in general. It may
make it possible to anticipate solar activity far in advance of its
emergence to the surface. Local acoustic diagnostics could revolutionize
our understanding of the solar dynamo and the 22 yr activity cycle.
Title: A Stochastic Model of the Solar Atmosphere
Authors: Gu, Yeming; Jefferies, John T.; Lindsey, Charles; Avrett,
E. H.
Bibcode: 1997ApJ...484..960G
Altcode:
We present a model for the lower solar atmosphere based on continuum
observations of the Sun spanning the 2-1200 μm wavelength range. We
have shown that the data, in particular the center-to-limb brightness
profiles at 50-350 μm, cannot be accounted for by any model which
is plane-parallel and homogeneous in the height range in which this
radiation is formed. We accordingly set out to develop a two-component
model as the natural generalization. Making use of a theory for
radiation transfer in a stochastic multi-component atmosphere, we find
that one can indeed obtain an inhomogeneous model which satisfies
center-to-limb data over the 2-1200 μm range. This composite model
is made up of hot ``flux tubes'' randomly embedded in a cool medium,
the flux tubes expanding to occupy an increasing proportion of the
atmosphere as we move up in height. The cool ambient component
shows a monotonic decrease in temperature in the range defined by the
data. The temperature in the hot component is constant at about 6500 K
up to about 400 km and increases monotonically above that height. The
center-to-limb observations demand that the gas in the interiors of
the flux tubes be recessed downward with respect to a hydrostatic
equilibrium distribution of density. This appears to constitute a
chromospheric Wilson depression consistent with a magnetic field
of about 120 G in the flux-tube interior at a height of about 600
km. The new model is shown to be consistent with other spectral
measurements independent of those used to define it. It gives a
very good fit to the 0.5 μm continuum intensities across the disk,
and provides an excellent accounting for the disk-center brightness
temperature in the center of the 3-2 R14 CO line at 4.667 μm. A
boundary temperature of less than about 3000 K in the cold component
is suggested from the limb-darkening data available for this line. In an appendix we mention a procedure for an analogous study based on
the intensities of multiplet lines, which may hold promise for modeling
over a wider range of heights that can be spanned by the IR data.
Title: Doppler Acoustic Diagnostics of Subsurface Solar Magnetic
Structure
Authors: Lindsey, C.; Braun, D. C.; Jefferies, S. M.; Woodard, M. F.;
Fan, Y.; Gu, Y.; Redfield, S.
Bibcode: 1996ApJ...470..636L
Altcode:
We used the Bartol-NSO-NASA South Pole helioseismic observations of 1991
January to probe the subsurface structure of active regions to depths
of ∼15,000 km. The helioseismic signature we particularly examine is
intended to register acoustic Doppler effects caused by horizontal flows
associated with the active region. We propose to show that the Doppler
acoustic signature of horizontal flows is particularly well suited
for deep subsurface diagnostics in terms of vertical discrimination
of the structure. This study is based primarily on observations of
NOAA Active Regions 6431, 6432, 6440, and 6442 between 1991 January
1 and January 8. We interpret the acoustic signatures we find in
terms of a general outflow of the solar medium surrounding the active
region. The acoustic signatures are strongly dependent on wavenumber,
which suggests an outflow that is quite weak near the surface, the upper
4000 km of the subphotosphere, but which increases strongly with depth
to velocities of several hundred meters per second at 15,000 km. This
depth profile evolves rapidly as the active region matures. Young
active regions show a strong outflow signature for waves that explore
depths between 4000 and 8000 km. As the active region matures, the
outflow vacates these intermediate layers and submerges to depths
mostly below 8000 km. We examine the location of AR 6442 for a
possible preemergence signature. We also show evidence for extended,
relatively superficial flows in the quiet Sun between the active region
bands directed roughly into the active region bands.
Title: Helioseismic Measurements of Subsurface Outflows From Sunspots
Authors: Braun, D. C.; Fan, Y.; Lindsey, C.; Jefferies, S. M.
Bibcode: 1996AAS...188.6911B
Altcode: 1996BAAS...28Q.937B
We measure the mean frequencies of acoustic waves propagating toward
and away from sunspots employing a spot-centered Fourier-Hankel
decomposition of p-mode amplitudes as measured from observations made at
the South Pole in 1988 and 1991. There is a significant frequency shift
between the inward and outward traveling waves which is consistent with
the Doppler effect of a radial outflow from the sunspots. For p-modes
of temporal frequencies of 3 mHz it is observed that the frequency
shift decreases slightly with spatial frequency, for modes with degree
l between 160 to 600. From the l dependence of the frequency shift, we
infer that the mean radial outflow within the observed annular region
(which extends between 30 and 137 Mm from the spots) increases nearly
linearly with depth, reaching a magnitude of about 200 m/s at a depth
of 20 Mm. This outflow exhibits properties similar to flows recently
reported by Lindsey, et al. (1996 ApJ submitted) using spatially
sensitive local helioseismic techniques. This work is supported by
NSF Grant AST 9496171 and NASA Grant NAGW-4143.
Title: Doppler Acoustic Diagnostics of Subsurface Solar Magnetic
Structure
Authors: Lindsey, C.; Braun, D.; Jefferies, S.; Fan, Y.; Gu, Y.;
Redfield, S.
Bibcode: 1996AAS...188.7903L
Altcode: 1996BAAS...28R.955L
We used the Bartol-NSO-NASA South Pole helioseismic observations of 1991
January to study the subsurface structure of active regions to depths of
~ 15,000 km. The helioseismic signature we particularly examine is based
on acoustic Doppler effects caused by horizontal flows associated with
the active region. We demonstrate that the Doppler-acoustic signature
of horizontal flows is particularly well suited for deep subsurface
diagnostics in terms of vertical discrimination of the structure. This
study is based primarily on observations of NOAA active regions 6431,
6432, 6440 and 6442 between 1991 January 1 and January 8. We interpret
the Doppler signatures we find in terms of a general outflow of the
solar medium surrounding the active region. The existence of deep
subsurface structure is indicated by the strong dependence of the
Doppler signature on horizontal wavelength. The outflows in surface
layers, the upper 4,000 km of the subphotosphere, are quite weak but
increase strongly with depth to velocities of several hundred m/s at
15,000 km. This depth profile evolves rapidly as the active region
matures. Young active regions show strong outflows at depths between
4,000 and 8,000 km. As the active region matures, the outflow vacates
these intermediate layers and submerges to depths mostly below 8,000
km. We examine the location of Region 6442 for a possible pre-emergence
signature. We also show strong evidence for extended, relatively
superficial flows in the quiet Sun between the active-region bands
directed roughly into the active region bands.
Title: Diagnostics of a Subsurface Radial Outflow From a Sunspot
Authors: Braun, D. C.; Fan, Y.; Lindsey, C.; Jefferies, S. M.
Bibcode: 1996astro.ph..3078B
Altcode:
We measure the mean frequencies of acoustic waves propagating toward
and away from a sunspot employing a spot-centered Fourier-Hankel
decomposition of p-mode amplitudes as measured from a set of
observations made at the South Pole in 1991. We demonstrate that
there is a significant frequency shift between the inward and outward
traveling waves which is consistent with the Doppler effect of a radial
outflow from the sunspot. For p-modes of temporal frequencies of 3
mHz it is observed that the frequency shift decreases slightly with
spatial frequency, for modes with degree l between 160 to 600. From
the l dependence of the frequency shift, we infer that the mean radial
outflow within the observed annular region (which extends between 30 and
137 Mm from the spot) increases nearly linearly with depth, reaching a
magnitude of about 200 m/s at a depth of 20 Mm. This outflow exhibits
properties similar to flows recently reported by Lindsey, et al. (1996)
using spatially sensitive local helioseismic techniques.
Title: Submillimeter Radiometry of Sunspots
Authors: Lindsey, C.; Kopp, G.
Bibcode: 1995ApJ...453..517L
Altcode:
We use observations of sunspots by the 15 m James Clerk Maxwell
Telescope (JCMT) for radiometry of sunspot umbrae and penumbrae The
observations reported here, taking account of the effects of the far
wings of the JCMT's beam, show that sunspot umbrae and penumbrae vary
considerably in brightness between one another. The sunspot umbra is
typically considerably dimmer than the quiet Sun but surrounded by a
penumbra that may be fully as bright as surrounding plage. Moreover,
the vertical brightness temperature gradients of sunspot umbrae and
penumbrae appear to be uniformly positive, roughly equivalent to
that of the quiet Sun. This gradient substantiates the operation of
nonradiative heating in the low chromospheres of the strongest magnetic
regions visible on the Sun's surface, i.e., sunspot umbrae.
Title: The Sun in Submillimeter and Near-Millimeter Radiation
Authors: Lindsey, C.; Kopp, G.; Clark, T. A.; Watt, G.
Bibcode: 1995ApJ...453..511L
Altcode:
We examine the best solar submillimeter observations made on the James
Clerk Maxwell Telescope in 1991 and 1992. In these observations, the
solar disk was observed concurrently in pairs of wavelengths chosen
from 350, 850, and 1200 μm. Images at all of these wavelengths show
clear limb brightening of the quiet Sun. The observations clearly
resolve the chromospheric supergranular network in active and quiet
regions. The quiet Sun is characterized by large-scale variations in
brightness, particularly the occasion of anomalously dark regions that
tend to surround active regions. Sunspots are clearly resolved, with
large dark umbrae clearly distinguished from sometimes particularly
bright penumbrae.
Title: Radiative Transfer in Stochastic Media
Authors: Gu, Yeming; Lindsey, Charles; Jefferies, John T.
Bibcode: 1995ApJ...450..318G
Altcode:
We review some basic concepts arising in the study of radiative
transfer in a stochastic atmosphere and consider their application
to realistic atmospheric models. In particular, we examine the theory
of Lindsey and Jefferies which deals with multicomponent atmospheres
whose stochastic nature is entailed in the morphology of a network of
boundaries separating different atmospheric components. This theory
is based on the Markov assumption, that the probability, per unit path
length along a ray, for transition into another component 15 independent
of the distance already traveled in the current component. We examine
the applicability of the theory to models that are non-Markovian,
paying particular attention to the assignment of transition rates
of such atmospheres. We consider in detail transition probabilities
for spherical, tubular, conical, and other fluted structures, and
show how the effects of overlap are to be incorporated for the case
of a two-component atmosphere. Comparisons of results obtained from
the theory of Lindsey and Jefferies with those found from Monte Carlo
calculations, for models based on identical structures randomly embedded
into an ambient medium, show that the Markov assumption promises to
be a good approximation for the determination of the statistics of
radiative transfer in a wide variety of stochastic atmospheres, even
when they are markedly non-Markovian.
Title: Eclipse Measurements of the Distribution of CO Emission Above
the Solar Limb
Authors: Clark, T. A.; Lindsey, C.; Rabin, D. M.; Livingston, W. C.
Bibcode: 1995itsa.conf..133C
Altcode:
No abstract at ADS
Title: Submillimeter solar research with the KAO.
Authors: Becklin, Eric E.; Lindsey, C.
Bibcode: 1995ASPC...73..329B
Altcode: 1995fgts.symp..329B
From 1981 to 1988 the KAO was used to measure the 30 to 670 μm
continuum radiation from the Sun. The most significant result was
the measurement of the limb brightness and extent during two total
solar eclipses. The results clearly indicate a solar limb at 50 to
670 μm which is extended beyond that expected for an atmosphere in
hydrostatic equilibrium. Unique measurements of far infrared solar
oscillations and the brightness of active regions were also carried out.
Title: Infrared Applications for Radiative Transport in Stochastic
Media
Authors: Lindsey, C.; Gu, Y.; Jefferies, J. T.
Bibcode: 1995itsa.conf..313L
Altcode:
No abstract at ADS
Title: Radiative Transfer in Stochastic Atmospheres
Authors: Gu, Y.; Lindsey, C.; Jefferies, J. T.
Bibcode: 1994AAS...185.0702G
Altcode: 1994BAAS...26Q1316G
We describe a general statistical perspective for the study of
radiative transfer through inhomogeneous media and apply it to
simple stochastic atmospheric models. The particular context for our
applications considers a stochastic atmosphere to be a multi-component
medium in which any individual component of the medium is locally
smooth. The stochastic nature of the atmosphere resides in the
statistical character of the complex network of boundaries that
separate various species of media one from another. We illustrate the
theory with simple atmospheric models based on an ambient medium into
which are randomly embedded structural elements containing alternative
species of medium. We consider structures of various shapes and sizes,
ranging from simple spheres to elongated or fluted structures with
preferred orientation. An important distinctive quality of a stochastic
atmosphere is whether the medium contains structures that individually
may be optically thick. Atmospheres containing only optically thin
structures tend to be statistically amenable to representation by
equivalent smooth atmospheres. The theory we have developed is fully
applicable to atmospheres that contain optically thick elements as
well as optically thin ones. Such conditions apply to a broad variety
of radiative transfer problems in astrophysics and stellar physics,
for example, to emission from interstellar gas clouds, from solar
or stellar chromospheres or from photospheres that contain heated
magnetic flux tubes. In this work we concentrate on a formalism that
rests on the Markov assumption, which states that the probability of
encountering a transition from one type of medium, A, to another,
B, is independent of the cumulative distance since the transition
into medium A, as one proceeds along the optical path. We examine the
importance of this assumption and its utility as a first approximation
by illustrating the consequences of its application to atmospheric
models that are non-Markovian.
Title: Eclipse Observations of the Extreme Solar Limb Profile of HI
Pfund beta Emission.
Authors: Clark, T. A.; Lindsey, C. A.; Rabin, D. M.; Livingston, W. C.
Bibcode: 1994AAS...185.4412C
Altcode: 1994BAAS...26.1378C
A region of the infrared solar spectrum (2147.7 - 2150.1 cm(-1)
) around the HI Pfund beta line (2148.79 cm(-1) ) was monitored
through 3 eclipse "contacts" with the Amber InSb array on the Main
spectrograph on the McMath-Pierce telescope during the 10 May 1994
partial solar eclipse over Kitt Peak National Observatory to produce
limb profiles of intensity and line width to an angular resolution
of 0.15 arc second. This line is broad (FWHM = 0.9 cm(-1) and shallow
(5.7%) in absorption at disk center but shows a narrow emission core
above the continuum envelope at 2 arc seconds inside the limb which
remains visible out to 4.5 arc seconds beyond the continuum limb. The
Pfund beta peak intensity appears to follow the continuum profile at
the limb but then intensifies again to reach a peak at about 1000 km
above the limb in a manner similar to that of the HeI D3 line. The line
width becomes narrower with height above the limb, reaching a FWHM of
0.22 cm(-1) at several arc seconds above the limb. These profiles will
be discussed in relation to those of other HI lines above the solar
limb. This work was supported by NSERC of Canada and by NSO, Tucson.
Title: The Sun in Submillimeter Radiation
Authors: Lindsey, C.
Bibcode: 1994IAUS..154...85L
Altcode:
No abstract at ADS
Title: Infrared solar physics: proceedings of the 154th Symposium
of the International Astronomical Union, held in Tucson, Arizona,
U.S.A., March 2-6, 1992.
Authors: Rabin, D. M.; Jefferies, John T.; Lindsey, C.
Bibcode: 1994IAUS..154.....R
Altcode:
No abstract at ADS
Title: Near IR Observations of the 11 July 1991 Total Solar Eclipse
from Mauna Kea; Hawaii
Authors: Clark, T. A.; Naylor, D. A.; Tompkins, G. J.; Lindsey, C.
Bibcode: 1994IAUS..154..173C
Altcode:
No abstract at ADS
Title: An active solar prominence in 1.3 MM radiation
Authors: Harrison, R. A.; Carter, M. K.; Clark, T. A.; Lindsey, C.;
Jefferies, J. T.; Sime, D. G.; Watt, G.; Roellig, T. L.; Becklin,
E. E.; Naylor, D. A.; Tompkins, G. J.; Braun, D.
Bibcode: 1993A&A...274L...9H
Altcode:
We present new millimetre-wavelength observations of an active solar
prominence. Observations made over a two-day period with the James
Clerk Maxwell Telescope on Manna Kea, Hawaii, give a unique view in
1.3 mm radiation of the spectacular prominence that appeared on the
west solar limb in the total solar eclipse of 11 July 1991.
Title: Imaging Solar Bolometric and Spectral Intensity Using Thermal
Detector Arrays
Authors: Deming, D.; Glenar, D.; Kostiuk, T.; Bly, V.; Forrest, K.;
Nadler, D.; Hudson, H.; Lindsey, C.; Kopp, G.; Avrett, E.; Terrill,
C. W.
Bibcode: 1993BAAS...25R1221D
Altcode:
No abstract at ADS
Title: Sunspot and Active Region Chromospheres from Submillimeter
JCMT Observations
Authors: Kopp, G.; Lindsey, C.
Bibcode: 1993BAAS...25.1181K
Altcode:
No abstract at ADS
Title: Prospects in Helioseismic Holography
Authors: Lindsey, C. A.; Braun, D. C.; Jefferies, S. M.
Bibcode: 1993BAAS...25.1220L
Altcode:
No abstract at ADS
Title: Local Helioseismology of Subsurface Structure
Authors: Lindsey, C.; Braun, D. C.; Jefferies, S. M.
Bibcode: 1993ASPC...42...81L
Altcode: 1993gong.conf...81L
No abstract at ADS
Title: Submillimeter Solar Images from the JCMT
Authors: Kopp, G.; Lindsey, C.
Bibcode: 1992AAS...181.9406K
Altcode: 1992BAAS...24.1270K
We present nearly full-disk, diffraction-limited solar images made at
350 and 850 microns and at 1.3 mm from the 15 m James Clerk Maxwell
Telescope on Mauna Kea. These wavelengths sample the thermal structure
of the solar chromosphere at altitudes from 500 to about 1500 km,
providing a height-dependent diagnostic of the atmosphere. Filament
channels and neutral lines are apparent in the submillimeter images,
although filaments themselves are not clearly visible. The submillimeter
images show plage approximately 20% brighter than the surrounding
quiet Sun, while sunspot intensities are comparable to the quiet
Sun. ``Circumfacules,'' dark areas surrounding active regions,
are observed in the submillimeter images and are similar to those
seen in Ca 8542; comparison with Ca H and K may give estimates of the
temperature and filling factor of the hot gas present in these probably
bifurcated regions.
Title: Measurement of the Height of the Solar CO Layer During the
11 July 1991 Eclipse
Authors: Clark, T. A.; Naylor, D. A.; Tompkins, G. J.; Lindsey, C. A.;
Becklin, E. E.; Jefferies, J. T.; Harrison, R. A.; Roellig, T. L.;
Carter, M.; Braun, D. C.; Watt, G.
Bibcode: 1992AAS...181.8108C
Altcode: 1992BAAS...24.1253C
No abstract at ADS
Title: Extreme-infrared brightness profile of the solar chromosphere
obtained during the total eclipse of 1991
Authors: Lindsey, C.; Jefferies, J. T.; Clark, T. A.; Harrison, R. A.;
Carter, M. K.; Watt, G.; Becklin, E. E.; Roellig, T. L.; Braun, D. C.;
Naylor, D. A.
Bibcode: 1992Natur.358..308L
Altcode:
THE solar chromosphere is a thin layer of gas that is several thousand
degrees hotter than the underlying photosphere, and responsible for
most of the Sun's ultraviolet emission. The mechanism by which it is
heated to temperatures exceeding 10,000 K is not understood. Millimetre
and submillimetre radiometry can be used to obtain the chromospheric
temperature profile, but the diffraction-limited resolution for the
largest telescopes is at best 17 arcsec, or ~12,500 km at the Sun's
distance. This is greater than the thickness of the quiet chromosphere
itself. The total eclipse of July 1991, which passed over the Mauna
Kea Observatory in Hawaii, provided a rare opportunity to make limb
occultation observations with a large submillimetrewavelength telescope,
the 15-m James Clerk Maxwell Telescope, and in this way we obtained a
temperature profile in 1.3-mm radiation with ~300 km resolution at the
Sun. Our observations indicate that spicules (magnetically entrained
funnels of gas) reach a temperature of 8,000 K at 3,000-4,000 km above
the photosphere, a temperature lower than those of many spicule models.
Title: Local Acoustic Diagnostics of the Solar Interior
Authors: Braun, D. C.; Lindsey, C.; Fan, Y.; Jefferies, S. M.
Bibcode: 1992ApJ...392..739B
Altcode:
Two diagnostic utilities, acoustic power maps, and surface acoustic
flux maps are used to explore the local diagnostics of magnetic field
structure in the solar interior. The acoustic power maps, constructed
from 50 hr of continuous K-line intensity images, show three general
features: acoustic power deficits at 3 mHz corresponding to surface
magnetic flux, acoustic power enhancements at 6 mHz surrounding the
exterior of magnetic regions, and occasional power deficits at 3 mHz
which extend beyond magnetic regions visible on the surface to regions
of quiet-sun. Surface acoustic flux vector maps of two active regions
were constructed for two 6-hr time-series of Dopplergrams. Both maps
show the divergence of 3-mHz acoustic flux into surface magnetic
structures and also sources and sinks of wave energy which are not
associated with surface features.
Title: Prospects in Acoustic Holography of the Solar Interior
Authors: Lindsey, C.; Braun, D. C.; Fan, Y.; Jefferies, S. M.
Bibcode: 1992AAS...180.1703L
Altcode: 1992BAAS...24..753L
Acoustic power maps of the solar surface show strong evidence
of magnetic structure crossing the solar equator not far beneath
the photosphere to connect the active latitude bands. These maps,
generated using the Bartol-NSO-NASA South Pole Observations show long
finger-like acoustic shadows we think are caused by absorption of
acoustic energy by the submerged magnetic structure. These features
suggest a solar interior magnetic structure quite different from any
previously expected. These new results open the prospect of a new and
powerful solar interior diagnostic based on acoustic holography.
Title: Chromospheric Dynamics Based on Infrared Solar Brightness
Variations
Authors: Kopp, G.; Lindsey, C.; Roellig, T. L.; Werner, M. W.; Becklin,
E. E.; Orrall, F. Q.; Jefferies, J. T.
Bibcode: 1992ApJ...388..203K
Altcode:
The NASA Kuiper Airborne Observatory was used to observe far-infrared
continuum brightness fluctuations in the lower chromosphere due to
solar 5 minute oscillations on the quiet sun. Brightness measurements
made at 50, 100, 200, and 400 microns show a strong correlation with
visible-line Doppler measurements from photospheric and chromospheric
altitudes. The motion of the chromosphere is nearly in phase over a
large range of heights, while the infrared brightness lags the Doppler
velocity by phases varying from significantly less than 90 deg at low
altitudes to nearly 90 deg at higher altitudes. It is proposed that
this is the result of a nonadiabatic response of the chromospheric
gas to compression and may indicate an important mechanism for wave
dissipation. Thermal relaxation times ranging from about 40 s at
340 km above the tau(5000) = 1 photosphere to about 300 s at 600 km
are proposed.
Title: The Solar Chromospheric Supergranular Network in 850 Micron
Radiation
Authors: Lindsey, Charles A.; Jefferies, John T.
Bibcode: 1991ApJ...383..443L
Altcode:
The first submillimeter solar observations are examined of the
chromospheric supergranular network, made on the 15-m James Clerk
Maxwell Telescope on Mauna Kea in 850-micron radiation. These
observations are useful for thermal diagnostics of the low and middle
chromospheres of the quiet-sun and magnetic regions, where mechanical
heating of the atmospheric medium first becomes manifest. The models
of Vernazza, Avrett and Loeser appear to be consistent with these
observations.
Title: Submillimeter Solar Limb Profiles Determined from Observations
of the Total Solar Eclipse of 1988 March 18
Authors: Roellig, T. L.; Becklin, E. E.; Jefferies, J. T.; Kopp,
G. A.; Lindsey, C. A.; Orrall, F. Q.; Werner, M. W.
Bibcode: 1991ApJ...381..288R
Altcode:
Observations were made of the extreme solar limb in six far-infrared
wavelength bands ranging from 30 to 670 micron using the Kuiper
Airborne Observatory during the total eclipse of the sun on 1988 March
18. By observations of the occultation of the solar limb by the moon,
it was possible to obtain a spatial resolution of 0.5 arcsec normal
to the limb. The solar limb was found to be extended with respect
to the visible limb at all of these wavelengths, with the extension
increasing with wavelength. Limb brightening was observed to increase
slightly with increasing wavelength, and no sign of a sharp emission
spike at the extreme limb was found at any of these wavelengths. The
observations can be well fitted by a chromospheric model incorporating
cool dense spicules in the lower chromosphere.
Title: Telescope Beam-Profile Diagnostics and the Solar Limb
Authors: Lindsey, Charles A.; Roellig, Thomas L.
Bibcode: 1991ApJ...375..414L
Altcode:
The basic method is described for determining the solar limb brightness
profile properly corrected for spurious limb darkening caused by the
far wings of the resolving beams encountered in large far-infrared and
radio telescopes. When the far wings of the beam can be independently
measured this problem is usually amenable to standard deconvolution
procedures. Under a broad range of well-defined cases, solutions to the
deconvolution problem are unique to within the discrimination provided
by the core of the beam profile. The theory is applied to solar limb
scans made recently on the James Clerk Maxwell Telscope to show solar
limb brightening in 850 micron radiation.
Title: Zeeman Splitting and Continuum Measurements of Sunspots at
1.56 μm
Authors: Kopp, G.; Rabin, D.; Lindsey, C.
Bibcode: 1991BAAS...23.1055K
Altcode:
No abstract at ADS
Title: An Acoustic Poynting Vector for Solar p-mode Oscillations
Authors: Braun, D. C.; Lindsey, C.
Bibcode: 1991BAAS...23.1049B
Altcode:
No abstract at ADS
Title: Ionization Pumping (With 3 Figures)
Authors: Lindsey, C.
Bibcode: 1991mcch.conf..359L
Altcode:
No abstract at ADS
Title: Physics of the infrared spectrum.
Authors: Deming, Drake; Jennings, Donald E.; Jefferies, John; Lindsey,
Charles
Bibcode: 1991sia..book..933D
Altcode:
The authors describe the diagnostic value and principal results
derived from solar studies at wavelengths exceeding 1.6 μm. The
infrared is a favorable region to conduct studies of the solar
magnetic field. The high-n emission lines in the 12-μm spectrum are
of special interest. However, the LTE or NLTE nature of the lines,
and the mechanism of their excitation, remain poorly understood. The
far-infrared continuum is an excellent thermometer for the upper
photosphere and chromosphere, allowing study of the average thermal
state and the compressional effects of wave motions. Observations
of limb brightening at far-infrared wavelengths have shown that the
structure of the chromosphere is spatially inhomogeneous, even at
the lowest chromospheric altitudes. Time-series observations in the
far-infrared show that the chromosphere exhibits a substantial thermal
response to the 5-min oscillations. Further progress in far-infrared
studies will result from the new generation of large-aperture
submillimeter telescopes, and from the development of the theory of
radiative transfer in inhomogeneous media.
Title: Submillimeter Observations of the Sun from the James Clerk
Maxwell Telescope
Authors: Lindsey, Charles A.; Yee, Selwyn; Roellig, Thomas L.; Hills,
Richard; Brock, David; Duncan, William; Watt, Graeme; Webster, Adrian;
Jefferies, John T.
Bibcode: 1990ApJ...353L..53L
Altcode:
The first submillimeter solar observations from the 15 m James
Clerk Maxwell Telescope (JCMT) on Mauna Kea are reported. The JCMT
submillimeter heterodyne receiver is used to observe the sun in 850
micron radiation. These are the first submillimeter observations of
features on the size scale of the chromospheric supergranular network
and of sunspots. A comparison is made between 850 micron images and
calcium K line images of the chromospheric supergranular network in
the quiet sun and in plage. Images of sunspots are given, noting that
their 850 micron brightness is comparable to, or somewhat greater than,
that of the quiet sun.
Title: Helioseismic Imaging of Sunspots at Their Antipodes
Authors: Lindsey, Charles; Braun, Douglas C.
Bibcode: 1990SoPh..126..101L
Altcode:
Recent work by Braun, Duvall, and LaBonte has shown that sunspots absorb
helioseismic waves. We propose that sunspot absorption causes a seismic
deficit that should be imaged at the antipode of the sunspot. If these
images are observable, it should be possible to produce seismic maps
of magnetic regions on the far side of the Sun. This possibility opens
a broad range of synoptic and diagnostic applications. Diagnostic
applications would include lifetimes of higher-frequency modes, and
possibly rotation of the solar interior and detection of subsurface
magnetic structure. We outline elements of the theory of seismic
imaging and consider some applications. We propose the extention of
acoustic holography to solar interior diagnostics in the context of
antipodal imaging.
Title: Far-Infrared Intensity Variations Caused by 5 Minute
Oscillations
Authors: Lindsey, C.; Kopp, G.; Becklin, E. E.; Roellig, T.; Werner,
M. W.; Jefferies, J. T.; Orrall, F. Q.; Braun, D.; Mickey, D. L.
Bibcode: 1990ApJ...350..475L
Altcode:
Observations of solar IR intensity variations at 50, 100, and
200 microns were made simultaneously and cospatially with Doppler
measurements in the sodium D1 line at 5896 A. Brightness temperature
variations of several K in amplitude are highly correlated with five
minute Doppler oscillations. The brightness variations are attributed
to work done on the chromospheric medium by compression, driven by the
five minute oscillations. The Doppler oscillations lead the brightness
variations by about 47 deg in phase at 50 and 100 microns and by about
72 deg in phase at 200 microns.
Title: Statistical Concepts in Radiative Transfer through
Inhomogeneous Media
Authors: Lindsey, C.; Jefferies, J. T.
Bibcode: 1990ApJ...349..286L
Altcode:
The theory of radiative transfer in inhomogeneous media is extended
to handle transfer for scale lengths small compared to the scale
size of the inhomogeneity. This is called the microscopic domain of
inhomogeneous radiative transfer. A concept called the vector intensity
distribution is introduced to characterize the statistical properties
of radiation in various species of medium. Radiative transfer in an
inhomogeneous atmosphere is expressed in terms of the evolution of
this vector intensity distribution and its various moments along the
optical path.
Title: Profiles of the Extreme Solar Limb at Far Infrared and
Submillimeter Wavelengths
Authors: Roellig, T. L.; Werner, M. W.; Kopp, G.; Becklin, E. E.;
Lindsey, C.; Orrall, F. Q.; Jefferies, J. T.
Bibcode: 1989BAAS...21..765R
Altcode:
No abstract at ADS
Title: Radiative Transfer in Inhomogeneous Atmospheres: A Statistical
Approach
Authors: Jefferies, John T.; Lindsey, Charles A.
Bibcode: 1988ApJ...335..372J
Altcode:
A procedure is presented for calculating the statistical properties
of the radiation which emerges from a multicomponent gas when the
absorption and emission coefficients vary statistically along the
direction of propagation. A relation describing the evolution of
the intensity distribution through the gas is derived, and, from
that, a transfer equation for the expected value of the intensity is
obtained which is analogous to the standard transfer equation for a
continuous medium and to which it reduces in the limit of a homogeneous
medium. General solutions for this transfer equation, and the analogous
transfer equation for the variance, are found for a special class of
situations. As a representative example, consideration is given to
the transfer of radiation through a spherical atmosphere consisting of
radial structures, with an exponential height distribution, which are
immersed according to a given probability distribution in an ambium,
itself inhomogeneous, whose properties also vary with height.
Title: Submillimeter Observations of the Extreme Solar Limb by
Occultation in the Total Solar Eclipse of 18 March 1988
Authors: Roellig, T. R.; Werner, M. W.; Kopp, G.; Becklin, E. E.;
Lindsey, C.; Orrall, F. Q.; Jefferies, J. T.
Bibcode: 1988BAAS...20..689R
Altcode:
No abstract at ADS
Title: Simultaneous Observations of Far-Infrared Solar Continuum
Brightness Variations and Five-Minute Oscillations
Authors: Lindsey, C.; Becklin, E. E.; Orrall, F. Q.; Kopp, G.; Werner,
M. W.; Roellig, T. R.
Bibcode: 1988BAAS...20..690L
Altcode:
No abstract at ADS
Title: Observations of the Sun and Corona for the 1988 March 18
Total Solar Eclipse
Authors: Orrall, F. Q.; Lindsey, C. A.; Mickey, D. L.; Dulk, G.;
Rottman, G.; Altrock, R. C.; Fisher, R. R.; Sime, D. G.
Bibcode: 1988BAAS...20..703O
Altcode:
No abstract at ADS
Title: A Solar Chromosphere and Spicule Model Based on Far-Infrared
Limb Observations
Authors: Braun, D.; Lindsey, C.
Bibcode: 1987ApJ...320..898B
Altcode:
Techniques developed for LTE radiative transfer problems in a rough
atmosphere were used to compute a model chromosphere containing spicules
consistent with high-resolution solar limb observations from 100 microns
to 2.6 mm. The model consists of a smooth, plane-parallel temperature
minimum region extending from the photosphere to a height of 1000 km
and randomly distributed cylindrical spicules above this height. It
is found that the observed limb brightness profiles are well fitted
by spicules with electron temperatures on the order of 7000 K.
Title: LTE Modeling of Inhomogeneous Chromospheric Structure Using
High-Resolution Limb Observation
Authors: Lindsey, C.
Bibcode: 1987ApJ...320..893L
Altcode:
The paper discusses considerations relevant to LTE modeling of rough
atmospheres. Particular attention is given to the application of recent
high-resolution observations of the solar limb in the far-infrared
and radio continuum to the modeling of chromospheric spicules. It is
explained how the continuum limb observations can be combined with
morphological knowledge of spicule structure to model the physical
conditions in chromospheric spicules. This discussion forms the basis
for a chromospheric model presented in a parallel publication based
on observations ranging from 100 microns to 2.6 mm.
Title: Modeling the Solar Chromosphere by Airborne Solar Eclipse
Observations
Authors: Orrall, F. Q.; Becklin, E. E.; Lindsey, C.; Roellig, T. R.;
Werner, M. W.; Kopp, G.; Jefferies, J. T.
Bibcode: 1987BAAS...19.1014O
Altcode:
No abstract at ADS
Title: Observations of Far-Infrared Solar Continuum Variations Due
to Compression Waves
Authors: Lindsey, C.; Becklin, E. E.; Orrall, F. Q.; Werner, M. W.;
Roellig, T. R.; Kopp, G.; Jefferies, J. T.
Bibcode: 1987BAAS...19S1014L
Altcode:
No abstract at ADS
Title: Observations of Far-Infrared Solar Continuum Variations Due
to Compression Waves
Authors: Lindsey, C.; Becklin, E. E.; Orrall, F. Q.; Werner, M. W.;
Roellig, T. R.; Kopp, G.
Bibcode: 1987BAAS...19R.933L
Altcode:
No abstract at ADS
Title: Observations of far-infrared solar continuum variations due
to compression waves.
Authors: Lindsey, C.; Becklin, E. E.; Orrall, F. Q.; Werner, M. W.;
Roellig, T. R.; Kopp, G.
Bibcode: 1987BAAS...19..933L
Altcode:
No abstract at ADS
Title: Observations of far-infrared solar continuum variations due
to compression waves.
Authors: Lindsey, C.; Becklin, E. E.; Orrall, F. Q.; Werner, M. W.;
Roellig, T. R.; Kopp, G.
Bibcode: 1987BAAS...19..741L
Altcode:
No abstract at ADS
Title: Observations of Far-Infrared Solar Continuum Variations Due
to Compression Waves
Authors: Lindsey, C.; Becklin, E. E.; Orrall, F. Q.; Werner, M. W.;
Roellig, T. R.; Kopp, G.
Bibcode: 1987BAAS...19R.741L
Altcode:
No abstract at ADS
Title: Submillimeter Diagnostics of the Response of the Solar
Chromosphere to Compressional Waves
Authors: Lindsey, C.; Roellig, T.
Bibcode: 1987ApJ...313..877L
Altcode:
The NASA Infrared Telescope Facility has been used to observe local
continuum brightness variations of the quiet sun in 350 and 800
micron radiation simultaneously. Variations of order 5 K are found
at both wavelengths, with a strong correlation between the two. The
800 micron variations lag behind the 350 micron variations by 25-35
deg in phase. This is similar to unexpected phase shifts reported by
Lites and Chipman in 1979 and Lites, Chipman, and White in 1982 between
velocity and intensity for certain chromospheric lines. It is proposed
that the phase lags observed are the result of nonadiabatic response of
the chromosphere to compression, which could be an important mechanism
for dissipation of mechanical energy.
Title: Solar Chromospheric Modeling Based on Submillimeter Limb
Brightness Profile
Authors: Hermans, L. M.; Lindsey, C.
Bibcode: 1986ApJ...310..907H
Altcode:
A method of modeling the solar chromosphere is developed, based on
submillimeter continuum observations of the solar limb. Submillimeter
radiation from the solar limb emanates from the chromosphere in local
thermodynamic equilibrium, making it an important chromospheric
diagnostic. Also, the use of high-resolution limb profiles allows
for atmospheric modeling independent of gravitational hydrostatic
equilibrium. The chromospheric model is constructed to match
high-resolution solar limb profiles at 30, 50, 100, and 200 microns,
determined by an occultation of the solar limb observed from the
Kuiper Airborne Observatory during the total solar eclipse of July
31, 1981. This matching is achieved by 'stretching' the solar model
atmosphere of Vernazza, Avrett, and Loesser (1981) vertically
out of hydrostatic equilibrium, while maintainingn its vertical
temperature-optical depth profile.
Title: Extreme Limb Profiles of the Sun at Far-Infrared and
Submillimeter Wavelengths
Authors: Lindsey, C.; Becklin, E. E.; Orrall, F. Q.; Werner, M. W.;
Jefferies, J. T.; Gatley, I.
Bibcode: 1986ApJ...308..448L
Altcode:
Thirty, 50, 100, and 200 microns solar limb intensity profiles
determined with arcsecond resolution from airborne observations of
the occultation of the solar limb during the total eclipse of July
31, 1981, are presented. Two points of particular importance emerge:
(1) the longer-wavelength (100 and 200 micron) limbs are significantly
brighter than disk center. At 200 microns the extreme limb is about 1.22
times the brightness of disk center. This is consistent with the 6000 K
temperature-plateau structure of the model chromospheres of Vernazza,
Avrett, and Loeser (1973, Ap. J., 184, 605; 1981; Ap. J. Suppl., 45,
635); and (2) the longer wavelength limbs are extended significantly
further above the visible limb than Vernazza, Avrett, and Loeser
predict. These results provide a strong basis for modeling of the solar
chromosphere free from the assumption of gravitational-hydrostatic
equilibrium.
Title: Extreme limb profiles of the sun at far-infrared and
submillimeter wavelengths
Authors: Lindsey, C.; Becklin, E. E.; Orrall, F. Q.; Werner, M. W.;
Jefferies, J. T.; Gatley, I.
Bibcode: 1986STIN...8632375L
Altcode:
Thirty, 50, 100, and 200 microns solar limb intensity profiles
determined with arcsecond resolution from airborne observations of
the occultation of the solar limb during the total eclipse of 1981
July 31 are presented. Two points of particular importance emerge:
(1) the longer-wavelength (100 and 200 micron) limbs are significantly
brighter than disk center. At 200 microns the extreme limb is about 1.22
times the brightness of disk center. This is consistent with the 6000 K
temperature-plateau structure of the model chromospheres of Vernazza,
Avrett, and Loeser (1973, Ap. J., 184, 605; 1981; Ap. J. Suppl., 45,
635;) and (2) the longer wavelength limbs are extended significantly
further above the visible limb than Vernazza, Avrett, and Loeser
predict. These results provide a strong basis for modeling of the solar
chromosphere free from the assumption of gravitational-hydrostatic
equilibrium.
Title: Submillimeter Diagnostics of the Response of the Solar
Chromosphere to Compressional Waves
Authors: Lindsey, C.; Roellig, T.
Bibcode: 1985BAAS...17..896L
Altcode:
No abstract at ADS
Title: Modeling the Solar Chromosphere With Submillimeter Limb
Brightness Profiles
Authors: Lindsey, C.; Hermans, L.
Bibcode: 1985BAAS...17Q.631L
Altcode:
No abstract at ADS
Title: Extreme limb profiles of the sun at far infrared and
submillimeter wavelengths.
Authors: Becklin, E. E.; Lindsey, C.; Orrall, F. Q.; Jefferies, J. T.;
Werner, M.; Gatley, I.
Bibcode: 1985NASCP2353...58B
Altcode:
The authors present results of analysis of 30 to 200 μm observations
of the occultation of the solar limb during the total solar eclipse
of 1981 July 31. The observations were made from the Kuiper Airborne
Observatory. The 30 to 200 μm continuum radiation from the solar
limb originates in the lower and middle chromosphere. By measuring the
brightness profiles, one is able to fix important constraints on both
the temperature of the material and its density structure.
Title: Extreme limb profiles of the Sun at far infrared and
submillimeter wavelengths
Authors: Becklin, E. E.; Lindsey, C.; Orrall, F. Q.; Jefferies, J. T.;
Werner, M. W.; Gatley, I.
Bibcode: 1984abas.symp...58B
Altcode:
Limb intensity profiles at 30, 50, 100, and 200 microns, determined
from Kuiper airborne observatory (KAO) observations of the occultation
of the solar limb during the total eclipse of July 31, 1981, are
presented. Significant but gradual limb brightening was found at the
longer wavelengths consistent with the 6000 K temperature-plateau
structure of the model chromospheres of Vernazza, Avrett, and
Loeser. The 100 and 200 micrometers limbs are extended significantly
further above the visible limb than the Vernazza, Avrett, and Loeser
model predicts. These results show that the solar chromosphere is
strongly perturbed from gravitational-hydrostatic equilibrium to heights
as low as 1000 km. These profiles can serve as a powerful diagnostic
for modeling the temperature and density of chromospheric structure
free from the assumption of gravitational-hydrostatic equilibrium.
Title: Extreme Limb Profiles of the Sun at Far Infrared and
Submillimeter Wavelengths
Authors: Lindsey, C.; Becklin, E. E.; Orrall, F. Q.; Werner, M. W.;
Jefferies, J. T.; Gatley, I.
Bibcode: 1984BAAS...16..992L
Altcode:
No abstract at ADS
Title: Temporal variations in the solar submillimeter continuum
Authors: Lindsey, C.; Kaminski, C.
Bibcode: 1984ApJ...282L.103L
Altcode:
The authors present observations of local intensity variations in the
300 - 800 μm solar continuum. Two-beam difference observations were
used to determine power spectrum statistics of small temporal variations
over the frequency range 0.1 - 20 mHz. The authors find a significant
enhancement in spectral power (≡5K rms) for frequencies between 3
and 7 mHz. These and higher frequency variations are attributed to
adiabatic response of the chromospheric medium to compression waves.
Title: Observations of the brightness profile of the sun in the
30-200 micron continuum
Authors: Lindsey, C.; Becklin, E. E.; Jefferies, J. T.; Orrall, F. Q.;
Werner, M. W.; Gatley, I.
Bibcode: 1984ApJ...281..862L
Altcode:
The authors observed the brightness profile of the quiet Sun in
broad continuum passbands centered at 30, 50, 100, and 200 μm with
a resolution of 2arcmin. Weak radial darkening was seen at all four
wavelengths near disk center. This reverses to brightening toward the
limb in the 100 and 200 μm continuum. Radial darkening at 100 and
200 μm is not expected from smooth model chromospheres consistent
with absolute brightness measurements. These results do not support
a homogeneous model of the low chromosphere, where the temperature
reversal occurs.
Title: Solar limb brightening at 820 microns
Authors: Lindsey, C.; de Graauw, T.; de Vries, C.; Lidholm, S.
Bibcode: 1984ApJ...277..424L
Altcode:
The sun in 820 micron radiation is mapped, and strong radial brightening
of the intensity profile is found. The east and west limbs show an
intensity excess of about twice that of the quiet north and south
limbs. This may be attributable to active regions near the east and
west limbs. The radial brightening observed is as strong as that
observed by others at 1.3 mm, and much stronger than that observed
at 350 microns by still others. A strong general increase in gradual
radial brightening with wavelength longward of 350 microns is thus
indicated, and this is attributed to variations in the character of
chromospheric fine structure above the temperature minimum region.
Title: Submillimeter extensions of the solar limb determined from
observations of the total eclipse of 1981 July 31
Authors: Lindsey, C.; Becklin, E. E.; Jefferies, J. T.; Orrall, F. Q.;
Werner, M. W.; Gatley, I.
Bibcode: 1983ApJ...264L..25L
Altcode:
The authors present first results of observations of a lunar occultation
of the solar limb made from the Kuiper Airborne Observatory in the
30, 50, 100, and 200 μm continuum during the total solar eclipse
of 1981 July 31. The solar limb is found to be extended at the
longer wavelengths up to 1000 km higher than predicted from smooth
plane-parallel chromospheric models. Results at both second and third
contact show the infrared limb extensions to be approximately 0arcsec.8,
1arcsec.5, 2arcsec.5, and 3arcsec.0 above the visible limb in the 30,
50, 100, and 200 μm bands, respectively.
Title: Submillimeter extensions of the solar limb determined from
observations of the total eclipse of 1981 July 31
Authors: Lindsey, C.; Becklin, E. E.; Jefferies, J. T.; Orrall, F. Q.;
Werner, M. W.; Gatley, I.
Bibcode: 1982STIN...8314047L
Altcode:
First results are presented of observations of a lunar occultation
of the solar limb made from the Kuiper Airborne Observatory in the
30 micrometr, 50 micrometer, 100 micrometer, and 200 micrometer
continuum during the total solar eclipse of 1981 July 31. The solar
limb was extended at the longer wavelengths up to 1000 km higher than
predicted from smooth plane-parallel chromospheric models. Results at
both second and third contact show the infrared limb extensions to
be approximately 0".8, 1"5, 2".5 and 3".0 above the visible limb in
the observed bands, respectively. A possible interpretation proposes
chromospheric fine structure inhomogeneities of greater density than
presently incorporated in models of the middle chromosphere.
Title: Submillimeter observations of solar limb-brightening in the
total solar eclipse of 31 July 1981
Authors: Becklin, E. E.; Jefferies, J. T.; Lindsey, C.; Orrall, F.;
Gatley, I.; Werner, M.
Bibcode: 1981huha.rept.....B
Altcode:
Eight flights of the Kuiper Airborne Observatory (KAO) were devoted to
solar observation. The successful observation of a total solar eclipse
was accomplished. The observations were made simultaneously at 30,
50, 100, and 200 microns. The successful adaptation of the KAO for
solar observations thus provided the most detailed data to date in
this spectral band. The results from a preliminary analysis of the KAO
data are summarized: (1) the 200 micron limb is extended about 3 arc
sec above the 30 micron limb, indicating the prescence of cool dense
material up to the altitudes of spicules; (2) strong radial darkening
of the quiet sun intensity profile appeared at 200 microns, probably an
indication that hot material in the low chromosphere is recessed into
vertical magnetic flux tubes embedded in a cooler nonmagnetic substrate,
which obscures the heated material approaching the limb; (3) active
regions were observed to undergo a strong increase in contrast above the
quiet sun background at wave lengths of 100 microns and longer; and (4)
the moon was mapped for use as a photometric standard for determining
the absolute intensity of the sun in all four wavelength bands.
Title: Solar limb brightening at 350 microns
Authors: Lindsey, C.; Hildebrand, R. H.; Keene, J.; Whitcomb, S. E.
Bibcode: 1981ApJ...248..830L
Altcode:
The NASA Infrared Telescope Facility at Mauna Kea was used to
observe the intensity profile of the quiet solar limb in the 300-400
micron continuum. A significant resolved brightening of several
percent over the outer 60 arcsec of the solar limb in this band is
found. However, the magnitude of the brightening is considerably less
than that indicated by earlier observations of a total solar eclipse
in integrated sun-moon radiation by Beckman, Lesurf, and Ross (1975)
in the 1.2 mm continuum. More recent ground-based observations indicate
that the magnitude of solar limb brightening at 800 microns and at
1.3 mm is stronger than that at 350 microns. This may be regarded as
an indication that the hot material which produces the brightening at
the extreme limb, thought to consist in part of chromospheric spicules,
is optically thin in the 350 micron continuum.
Title: Far-infrared continuum observations of solar faculae
Authors: Lindsey, C.; Heasley, J. N.
Bibcode: 1981ApJ...247..348L
Altcode:
New observations of photospheric faculae in the far-infrared (10-25
micron wavelength) continuum are presented. Two-beam linear scans with
10 arcsec and 20 arcsec resolution were used to compile statistics
on infrared continuum emission from faculae surrounding sunspots. The
infrared facular excess above the quiet sun continuum is found to be
much smaller than that predicted by plane parallel photospheric models
constructed from Mg II h and k line wing observations. It is proposed
that the discrepancy results from unresolved granular structure in
which the facular granules occupy only about 0.1 of the resolved
surface area in the low photosphere.
Title: Submillimeter Continuum Observations of Solar Plages
Authors: Jefferies, J. T.; Becklin, E. E.; Lindsey, C.; Orrall, F. Q.;
Gatley, I.; Werner, M.
Bibcode: 1981BAAS...13Q.881J
Altcode:
No abstract at ADS
Title: Heating of the solar chromosphere by ionization pumping
Authors: Lindsey, C. A.
Bibcode: 1981ApJ...244..659L
Altcode:
A new theory is proposed to explain the heating of the solar
chromosphere, and possibly the corona, by the dissipation of
hydrodynamic compression waves. The basis of the dissipative
mechanism, here referred to as ionization pumping, is hysteresis
caused by irreversible relaxation of the chromospheric medium to
ionization equilibrium following pressure perturbations. In the
middle chromosphere, where hydrogen is partially ionized, it is shown
that ionization pumping will cause strong dissipation of waves whose
periods are 200s or less. This could cause heating of the chromosphere
sufficient to compensate for the radiative losses. The mechanism retains
a high efficiency for waves of arbitrarily small amplitude and, thus,
can be more efficient than shock dissipation for small perturbations
in pressure. The formation of shocks therefore is not required for
the dissipation of waves whose periods are several minutes or less.
Title: Observations of the Center-to-Limb Intensity of the Quiet
Sun at 30-200 μm
Authors: Orrall, F. Q.; Becklin, E. E.; Jefferies, J. T.; Lindsey,
C.; Gatley, I.; Werner, M.
Bibcode: 1981BAAS...13..880O
Altcode:
No abstract at ADS
Title: Submillimeter Observations of the Extreme Solar Limb Obtained
in the Total Eclipse of 1981 July 31
Authors: Lindsey, C.; Becklin, E. E.; Jefferies, J. T.; Orrall, F. Q.;
Gatley, I.; Werner, M.
Bibcode: 1981BAAS...13..880L
Altcode:
No abstract at ADS
Title: A Comprehensive Study of the Sun in the Submillimeter Continuum
Authors: Becklin, E. E.; Jefferies, J. T.; Lindsey, C.; Orrall, F. Q.;
Gatley, I.; Werner, M.
Bibcode: 1981BAAS...13..880B
Altcode:
No abstract at ADS
Title: Effects of granular convection in the response of C I 5380
A to solar luminosity variations
Authors: Lindsey, C. A.; Landman, D. A.
Bibcode: 1980ApJ...237..999L
Altcode:
The response of the weak solar photospheric neutral carbon line at
5380.3 A to percolations of photospheric granulation and the five-minute
solar oscillations is investigated in order to calibrate the sensitivity
of the line to temporal variations in solar luminosity. Line strength
variations and simultaneous continuum variations in two granular regions
were observed at 30 sec intervals using a 25-cm coude spectrograph. The
response of line equivalent width to continuum intensity variations
is found to be essentially uniform at time scales ranging from 5 min
to 2 hr independently of whether the variations arise from granular
convection or velocity field oscillations. The extent to which line
strength varies with luminosity (sensitivity) is observed to be
significantly smaller than estimates based on models of the perturbed
Harvard-Smithsonian Reference Atmosphere of Gingerich et al. (1970), and
it is proposed that the structure of the solar granulation is a major
factor determining local luminosity variations and line sensitivity.
Title: Solar Limb Brightening at Submillimeter Wavelengths
Authors: Lindsey, C.; Hildebrand, R.; de Graauw, Th.
Bibcode: 1980BAAS...12..474L
Altcode:
No abstract at ADS
Title: Far Infrared Continuum Observations of Solar Faculae
Authors: Lindsey, C. A.; Heasley, J. N.
Bibcode: 1980BAAS...12..437L
Altcode:
No abstract at ADS
Title: Polarization of He I 10830 Å Emission in Solar Prominences
Authors: Lindsey, C.; Mickey, D. L.
Bibcode: 1979BAAS...11..409L
Altcode:
No abstract at ADS
Title: Infrared continuum observations of the solar atmosphere
Authors: Hudson, H.; Levan, P.; Lindsey, C.
Bibcode: 1979ucsd.rept.....H
Altcode:
The far-infrared wavelengths (10 microns to 1 mm) were used to study the
spatial and temporal structure of the solar atmosphere. Observational
results were obtained on flares, faculae, sunspots, and on the
center-to-limb intensity distribution, as well as on time variability
within these regions. A program of precise monitoring of slow variations
in the integrated solar luminosity was shown to be feasible, and
initial steps to implement observations were completed.
Title: Photospheric lines in diagnostics of solar luminosity
variations.
Authors: Lindsey, C. A.; Landman, D. A.
Bibcode: 1979BAAS...11Q.611L
Altcode:
No abstract at ADS
Title: Effects of diffraction in multiple-grid telescopes for X-ray
astronomy
Authors: Lindsey, C. A.
Bibcode: 1978JOSA...68.1708L
Altcode: 1978OSAJ...68.1708L
Diffraction effects in modern designs for grid collimator telescopes
(assumed to have roughly a 100-micron grid period) are apparent at
wavelengths longer than 1 A and are dominant at wavelengths longer
than 10 A. In collimators with many grids spaced far apart the effects
of diffracation are to reduce strongly the peak transmission of the
collimator at longer wavelengths and to broaden it by about the amount
expected from Fraunhofer diffraction through a slit the size of the
grid openings. Comparisons between two-collimator measurements and
the present calculations show reasonable agreement; it is therefore
concluded that the present single-collimator calculation gives a good
representation of their diffraction-limited angular response.
Title: Quiet Sun Fluctuations of CI5380Å
Authors: Lindsey, C. A.; Landman, D. A.
Bibcode: 1978BAAS...10R.417L
Altcode:
No abstract at ADS
Title: Effects of Diffraction in Multiple-Grid X-Ray Telescopes.
Authors: Lindsey, C. A.
Bibcode: 1977BAAS....9Q.626L
Altcode:
No abstract at ADS
Title: Infrared continuum observations of five-minute oscillations.
Authors: Lindsey, C. A.
Bibcode: 1977SoPh...52..263L
Altcode:
Infrared continuum observations of the Sun at wavelengths
between 10μ and 30μ show a nonisothermal response of the upper
photosphere to compression waves associated with the five-minute
oscillations. Observations were made with four broad-band filters with
effective transmission wavelengths between 10μ and 26μ and with a
10″ aperture. Further observations at submillimeter wavelengths with
a 2' aperture did not resolve oscillatory fluctuations of five-minute
period.
Title: Study of effects of space power satellites on life support
functions of the earth's magnetosphere
Authors: Douglas, M.; Laquey, R.; Deforest, S. E.; Lindsey, C.;
Warshaw, H.
Bibcode: 1977maya.rept.....D
Altcode:
The effects of the Satellite Solar Power System (SSPS) on the life
support functions of the earth's magnetosphere were investigated. Topics
considered include: (1) thruster effluent effects on the magnetosphere;
(2) biological consequences of SSPS reflected light; (3) impact on earth
bound astronomy; (4) catastrophic failure and debris; (5) satellite
induced processes; and (6) microwave power transmission. Several impacts
are identified and recommendations for further studies are provided.
Title: Solar limb brightening in submillimeter wavelengths.
Authors: Lindsey, C.; Hudson, H. S.
Bibcode: 1976ApJ...203..753L
Altcode:
Differential two-beam scans of the sun in submillimeter wavelengths
(350 microns to 1 millimeter) indicate limb brightening approaching 1
percent when the cosine of the angle from the normal equals 0.60. The
observations also show considerable chromospheric structure, both in
active and quiet regions, but with less relative amplitude than at
millimeter and centimeter wavelengths. The limited angular resolution
of the observing system, together with photometric errors due to
fluctuating atmospheric transparency, make the brightness profile of
the extreme limb uncertain. The observed degree of limb brightening is
considerably less than that consistent with spherically symmetric model
atmospheres based on continuum brightness-temperature measurements. The
suppression of limb brightening suggests the existence of irregular
granular structure with both horizontal and vertical characteristic
sizes of the order of 1500 km. High-resolution images in the wings of
the K-line show granular structure of about this horizontal scale.
Title: Photospheric Thermal Fluctuations in the Quiet Sun.
Authors: Lindsey, C. A.
Bibcode: 1975BAAS....7..406L
Altcode:
No abstract at ADS
Title: Solar Limb Brightening at Submillimeter wavelengths
Authors: Lindsey, C.; Hudson, H. S.
Bibcode: 1975BAAS....7..360L
Altcode:
No abstract at ADS
Title: An infrared continuum study of the solar atmosphere
Authors: Lindsey, Charles Allan
Bibcode: 1975PhDT.......175L
Altcode:
No abstract at ADS
Title: An Infrared Continuum Study of the Solar Atmosphere.
Authors: Lindsey, C. A.
Bibcode: 1975PhDT.........9L
Altcode:
A study of the temperature structure of the solar photosphere using
five broad-band filters in the 10-30 micron region was made with
the UCSD-University of Minnesota 60-inch telescope at Mt. Lemmon,
Arizona. This provided a spatial resolution of approximately 10
arc sec. Results are presented and discussed in detail. The thermal
structure of the chromosphere was also studied. Results of a two beam
scans of the sun at submillimeter wavelengths indicate a small degree
of limb brightening, approaching 1 percent at 0.8 solar radii. This
is considerably smaller than would exist if the chromosphere were as
smoothly stratified at the temperature minimum as the photosphere. The
observations show considerable spatially resolved structure, both in
active and quiet regions, but with less relative amplitude than is seen
in millimeter and centimeter radio observations. The suppression of the
expected limb brightening was studied and the existence of irregular
granular structure with both horizontal and vertical characteristic
sizes of order 1,500 km is suggested. High-resolution images in the
wings of the K-line of ionized calcium show granular structure of
about this horizontal scale.
Title: Submillimeter Observations of Planets
Authors: Hudson, H. S.; Lindsey, C. A.; Soifer, B. T.
Bibcode: 1974Icar...23..374H
Altcode:
A new program of ground-based observations at submillimeter (≈400 μm)
wavelengths has yielded observations of Mercury, Venus, Mars, Jupiter,
and Saturn. We report here observations near planetary conjunctions,
which have minimal corrections for atmospheric extinction: Mercury,
361±65 K; Venus, 231±35 K; and Saturn, 205±15 K (based upon the
area of the planetary disk), using Jupiter (150 K) and Mars (220 K) as
photometric standards. The Mercury observations show that the brightness
temperature does not decrease at the submillimeter wavelengths, relative
to observations at 3 mm; for Venus, however, the brightness temperature
appears appreciably lower than at millimeter wavelengths. The results
for Saturn indicate a strong and possibly optically thick contribution
from the rings. We also gave a description of our instrumentation and
observational techniques, with special emphasis upon the effect of
extinction by atmospheric water vapor.
Title: Direct Observation of Temperature Amplitude of Solar 300-SECOND
Oscillations
Authors: Hudson, H. S.; Lindsey, C. A.
Bibcode: 1974ApJ...187L..35H
Altcode:
The 300-second oscillations form the dominant source of variability
of the solar infrared continuum. We have observed them at 20 with
an amplitude AT, = 3.0 K over an area with an effective diameter of
33". This new mode of observation of the 300-s oscillations should
make possible a fundamental improvement in our knowledge of their
nature and origin. Subject headings: Infrared solar atmospheric motions