explanation blue bibcodes open ADS page with paths to full text
Author name code: imada
ADS astronomy entries on 2022-09-14
author:"Imada, Shinsuke"
---------------------------------------------------------
Title: Inference of magnetic field during the Dalton minimum: Case
study with recorded sunspot areas
Authors: Uneme, Shoma; Imada, Shinsuke; Lee, Harim; Park, Eunsu;
Hayakawa, Hisashi; Iju, Tomoya; Moon, Yong-Jae
2022PASJ...74..767U Altcode:
The Dalton minimum is considered to be one of the unique solar activity
periods that have been captured in direct sunspot observations since
1610. Specifically, the solar magnetic field in this period is of great
interest. Derfflinger and Prantner's sunspot observations of 1802-1824
and 1800-1844 are the most important references for this period. To
understand the solar magnetic activity in the Dalton minimum, it
is important to estimate the latitude/longitude distribution of the
sunspots and the sunspot areas for that duration. In this study, we
analyze Derfflinger and Prantner's sunspot drawings to determine the
sunspot parameters, particularly the sunspot area. We find that the
sunspot areas obtained from Derfflinger's drawings are overemphasized by
a factor of eight relative to those derived from modern observations. We
also analyze Prantner's sunspot drawings to validate our analysis of
Derfflinger's drawings. Further, we generate solar magnetograms from
Derfflinger's sunspot drawings using a deep-learning model based on
conditional generative adversarial networks. Our analysis of these
sunspot areas will provide important information for restoring the
magnetograms during the Dalton minimum.
---------------------------------------------------------
Title: A spectral solar irradiance monitor (SoSpIM) on the JAXA
Solar-C (EUVST) space mission
Authors: Harra, Louise K.; Watanabe, Kyoko; Haberreiter, Margit;
Hori, Tomoaki; Hara, Hirohisa; Kretzschmar, Matthieu; Woods, Thomas;
Shimizu, Toshifumi; Krucker, Samuel; Berghmans, David; Jin, Hidekatsu;
Dominique, Marie; Eparvier, Francis G.; Gissot, Samuel; Leng Yeo, Kok;
Pfiffner, Dany; Milligan, Ryan; Thiemann, Edward; Miyoshi, Yoshizumi;
Imada, Shinsuke; Kawate, Tomoko; Chamberlin, Phillip; Rozanov, Eugene;
Silvio Koller, -.; Barczynski, Krzysztof; Nozomu; Nishitani; Ieda,
Akimasa; Langer, Patrick; Meier, Leandro; Tye, Daniel; Alberti, Andrea
2022cosp...44..834H Altcode:
The JAXA Solar-C (EUVST) mission (Shimizu et al., 2020) is designed
to comprehensively understand how mass and energy are transferred
throughout the solar atmosphere. The EUV High-Throughput Spectroscopic
Telescope (EUVST) onboard does this by observing all the temperature
regimes of the atmosphere from the chromosphere to the corona
simultaneously. To enhance the EUVST scientific capabilities,
there will be a Solar Spectral Irradiance Monitor (SoSpIM). SoSpIM
will work hand-in-hand scientifically with EUVST, by providing the
full Sun irradiance at sub-second time cadence combined with the
spatially resolved spectroscopy from EUVST. The SoSPIM instrument
will specifically address two aspects. These are: · Understand how
the solar atmosphere becomes unstable, releasing the energy that
drives solar flares - achieved through probing fast time cadence
solar flare variations. · Measuring solar irradiance that impacts
the Earth's thermosphere and the mesosphere, linking to spatially
resolved measurements of the solar atmosphere with EUVST. SoSpIM will
provide high time resolution measurements in 2 channels (a) in the
corona through channel 1 (EUV) and (b) in the lower atmosphere through
channel 2 (Lyman alpha). Each channel impacts different layers of the
Earth's atmosphere.
---------------------------------------------------------
Title: How Can Solar-C/SOSPIM Contribute to the Understanding of
Quasi-Periodic Pulsations in Solar Flares?
Authors: Dominique, Marie; Harra, Louise K.; Watanabe, Kyoko; Hara,
Hirohisa; Zhukov, Andrei; Shimizu, Toshifumi; Berghmans, David;
Dolla, Laurent; Gissot, Samuel; Pfiffner, Dany; Imada, Shinsuke;
Silvio Koller, -.; Meier, Leandro; Tye, Daniel; Alberti, Andrea
2022cosp...44.2524D Altcode:
Quasi-periodic pulsations (QPPs) refer to nearly-periodic oscillations
that are often observed in irradiance time series during solar flares
and have also been reported in several stellar flares. In the last
years, several statistical studies based on Soft X-ray measurements
have reached the conclusion that QPPs are present in most solar
flares of class M and above. Still, as of today, we are still unsure
of what causes QPPs. Several models could explain the presence of
QPPs with periods matching the ones observed. More detailed analysis
of the observational signatures of QPPs might help determine which
of those models are actually playing a role in the generation of
QPPs. However, as QPPs is a small timescale process (the period of
QPPs is often reported to be less than a minute), such an analysis
requires instruments with a good signal-to-noise and high sampling
rate. In this context, the spectral solar irradiance monitor SOSPIM,
that will be part of the JAXA SOLAR C mission and that will complement
the EUVST spectrograph measurements, could be a valuable asset. SOSPIM
will observe the solar chromosphere and corona in the Lyman-alpha
and EUV spectral ranges at high cadence. In this presentation, we
review the current knowledge of QPPs and describe what could be the
contribution of SOSPIM to push their understanding one step forward.
---------------------------------------------------------
Title: Long-term variation in the solar terrestrial enviroment
related to solar cycle
Authors: Imada, Shinsuke; Tsujimura, Hodaka; Iijima, Haruhisa
2022cosp...44.1549I Altcode:
It is known that the solar activity fluctuates in a cycle of about 11
years, and the global magnetic field structure of the sun changes with
the fluctuation. This change in the magnetic field structure has a
great effect on the solar wind from the sun into the interplanetary
space, and as a result, the solar terrestrial environment also
fluctuates in a cycle of about 11 years. In this research, we will
stochastically discuss what the solar wind will look like in about
10 years by combining the following solar cycle activity prediction
model and the solar wind model that we have developed so far. In this
research, we will combine the next solar cycle activity prediction
model and the solar wind model that we have been developing so far,
and probabilistically discuss what the solar wind will look like about
10 years from now. In addition, we will verify whether the coronal
hole generation, transportation, and disappearance on a time scale of
several tens of days and the solar wind in the earth's orbit can be
reproduced by our method using past observation results.
---------------------------------------------------------
Title: Magnetic Reconnection in the Solar Atmosphere: Future Plans
for Reconnection Observations
Authors: Imada, Shinsuke
2022cosp...44.1496I Altcode:
Magnetic reconnection has been recognized as one of the key mechanisms
for heating and bulk acceleration of space plasmas. To date, many
observations have been made on the solar corona to confirm the presence
of high-temperature and high-speed plasma flows produced by magnetic
reconnection above flare arcades. In this talk, I will introduce
the study on plasma heating considers the time-dependent ionization
process during a large solar flare on 2017 September 10, observed by
Hinode/EUV Imaging Spectrometer (EIS). The observed Fe XXIV/Fe XXIII
ratios increase downstream of the reconnection outflow, and they are
consistent with the time-dependent ionization effect at a constant
electron temperature Te = 25 MK. Moreover, this study also shows that
the nonthermal velocity, which can be related to the turbulent velocity,
reduces significantly along the downstream of the reconnection outflow,
even when considering the time-dependent ionization process. The
number of high-temperature lines observed by Hinode/EIS is limited,
so it is difficult to make a sufficient diagnosis of the reconnection
region. Recently, the next generation solar observation satellite
Solar-C (EUVST) has been discussed intensively. An ultraviolet
imaging spectrometer with dramatically improved spatial and temporal
resolution is planned for this satellite. In the Solar-C era, thermal
nonequilibrium plasma will be extensively discussed. I expect that
Solar-C (EUVST) will reveal the reconnection region in detail.
---------------------------------------------------------
Title: Factors That Determine the Power-law Index of an Energy
Distribution of Solar Flares
Authors: Kawai, Toshiki; Imada, Shinsuke
2022ApJ...931..113K Altcode:
The power-law index of an occurrence frequency distribution of flares
as a function of energy is one of the most important indicators to
evaluate the contribution of small-scale flares to coronal heating. For
a few decades, many studies tried to derive the power-law index using
various instruments and methods. However, these results are various
and the cause of this uncertainty is unknown due to the variety of
observation conditions. Therefore, we investigated the dependence of
the index on the solar activity, coronal features, released energy
range, and active region properties such as magnetic flux, twist, and
size. Our findings are (1) annual power-law index derived from time
series of total solar irradiance (Sun-as-a-star observation analysis)
has a negative correlation with sunspot number; (2) power-law index
in active region is smaller than that of the quiet Sun and coronal
holes; (3) power-law index is almost constant in the energy range of
10<SUP>25</SUP> ≲ E ≲ 10<SUP>30</SUP> erg; and (4) active regions
that have more magnetic free energy density, unsigned magnetic flux,
and shear angle tend to have smaller power-law indices. Based on the
results and energy-scaling law of Petschek-type reconnection, we suggest
that the power-law index of sunspot-scale events is smaller than that
of granule-scale events. Moreover, we indicated that sunspot-scale
events follow CSHKP flare model whereas granule-scale events follow
Parker's nanoflare model.
---------------------------------------------------------
Title: Reproduction of the Earth's ionospheric response to solar
flare emission spectra using physical-based models
Authors: Nishimoto, Shohei; Watanabe, Kyoko; Jin, Hidekatsu; Kawai,
Toshiki; Imada, Shinsuke; Kawate, Tomoko
2021AGUFMSH55C1855N Altcode:
The X-rays and extreme ultraviolet (EUV) emitted during solar flares
can rapidly change the physical composition of the Earth's ionosphere,
causing sudden ionospheric disturbances and other space weather
phenomena. (Dellinger 1937). Therefore, to understand how solar flare
emission spectra affects the ionosphere, it is important to have an
accurate understanding of the solar flare emission spectra. Solar
flares with a long duration have a large effect on ionosphere because
they have a large energy (Qian et al., 2010). The physics-based
model is useful for accurately estimate the profile of solar flare
emission. We verify the extent of reproducing the flare emission
spectra using a newly proposed method based on the physical process
of the flare loop (Kawai et al., 2020). In this method, we convert
the soft X-ray light-curves observed during flare events into EUV
emission spectra using a one-dimensional hydrodynamic calculation and
the CHIANTI atomic database (Dere et al., 2019). We examined the EUV
flare time-integrated irradiance and EUV flare line rise time for 21
flare events by comparing the calculation results of the proposed
method and observed EUV spectral data. Proposed method succeeded
in reproducing the EUV flare time-integrated irradiance of Fe lines
which have relatively higher formation temperature. For the EUV flare
line rise time, there was acceptable correlation between the proposed
method estimations and observations for all Fe flare emission lines. We
used the solar flare emission spectral models and the Earth's whole
atmospheric model to study the effect of X-rays and EUV emissions from
flares on the ionosphere. For the solar flare emission spectral models,
we used the physical model described above and an empirical model, the
Flare Irradiance Spectral Model (FISM; Chamberlin et al., 2020). For
the Earth's whole atmospheric model, we used the Ground-to-Topside Model
of Atmosphere and Ionosphere for Aeronomy (GAIA; Jin et al., 2011). We
compared the total electron content (TEC) variations corresponding to
various solar flare emission spectra for 6 X-class flare events that
occurred from 2010 to the 2021. The results show that the wavelengths
of solar flare emissions that mainly affect TEC variations are soft
X-rays (<10 nm) and EUV emissions (especially 28-30, 32-34 nm).
---------------------------------------------------------
Title: How Can Solar-C/SOSPIM Contribute to the Understanding of
Quasi-Periodic Pulsations in Solar Flares?
Authors: Dominique, Marie; Dolla, Laurent; Zhukov, Andrei; Alberti,
Andrea; Berghmans, David; Gissot, Samuel; Hara, Hirohisa; Harra,
Louise; Imada, Shinsuke; Koller, Silvio; Meier, Leandro; Pfiffner,
Daniel; Shimizu, Toshifumi; Tye, Daniel; Watanabe, Kyoko
2021AGUFMSH25E2124D Altcode:
Quasi-periodic pulsations (QPPs) refer to nearly-periodic oscillations
that are often observed in irradiance time series during solar flares
and have also been reported in several stellar flares. In the last
years, several statistical studies based on Soft X-ray measurements
have reached the conclusion that QPPs are present in most solar flares
of class M and above. Still, the mechanism at the origin of QPPs is
under debate. Are they caused by waves or periodic fluctuations of the
magnetic reconnection driving the flare? Analyzing the characteristics
of QPPs and their evolution during the flare could help identifying
their origin. However, QPPs sometimes exhibit very different
periodicities, and do not always happen during the same phase of the
flare. All this could point to the coexistence of QPPs with different
origin mechanism, and indicates the need for more observations. In this
context, the spectral solar irradiance monitor SOSPIM, that will be
part of the JAXA SOLAR C mission and that will complement the EUVST
spectrograph measurements, could be a valuable asset. SOSPIM will
observe the solar chromosphere and corona in the Lyman-alpha and EUV
spectral ranges at high cadence. In this presentation, we review the
current knowledge of QPPs and describe what could be the contribution
of SOSPIM to push their understanding one step forward.
---------------------------------------------------------
Title: Validation of computed extreme ultraviolet emission spectra
during solar flares
Authors: Nishimoto, Shohei; Watanabe, Kyoko; Kawai, Toshiki; Imada,
Shinsuke; Kawate, Tomoko
2021EP&S...73...79N Altcode:
X-rays and extreme ultraviolet (EUV) emissions from solar flares
rapidly change the physical composition of the Earth's thermosphere
and ionosphere, thereby causing space weather phenomena such as
communication failures. Numerous empirical and physical models have been
developed to estimate the effects of flare emissions on the Earth's
upper atmosphere. We verified the reproduction of the flare emission
spectra using a one-dimensional hydrodynamic calculation and the CHIANTI
atomic database. To validate the proposed model, we used the observed
EUV spectra obtained by the Extreme ultraviolet variability experiment
(EVE) on board the Solar Dynamics Observatory (SDO). We examined the
"EUV flare time-integrated irradiance" and "EUV flare line rise time"
of the EUV emissions for 21 events by comparing the calculation
results of the proposed model and observed EUV spectral data. The
proposed model successfully reproduced the EUV flare time-integrated
irradiance of the Fe VIII 131 Å, Fe XVIII 94 Å, and Fe XX133 Å, as
well as the 55-355 Å and 55-135 Å bands. For the EUV flare line rise
time, there was an acceptable correlation between the proposed model
estimations and observations for all Fe flare emission lines. These
results demonstrate that the proposed model can reproduce the EUV
flare emission spectra from the emitting plasma with a relatively high
formation temperature. This indicates that the physics-based model is
effective for the accurate reproduction of the EUV spectral irradiance.
---------------------------------------------------------
Title: Model-based reproduction and validation of the total spectra
of a solar flare and their impact on the global environment at the
X9.3 event of September 6, 2017
Authors: Watanabe, Kyoko; Jin, Hidekatsu; Nishimoto, Shohei; Imada,
Shinsuke; Kawai, Toshiki; Kawate, Tomoko; Otsuka, Yuichi; Shinbori,
Atsuki; Tsugawa, Takuya; Nishioka, Michi
2021EP&S...73...96W Altcode:
We attempted to reproduce the total electron content (TEC) variation
in the Earth's atmosphere from the temporal variation of the solar
flare spectrum of the X9.3 flare on September 6, 2017. The flare
spectrum from the Flare Irradiance Spectral Model (FISM), and the
flare spectrum from the 1D hydrodynamic model, which considers the
physics of plasma in the flare loop, are used in the GAIA model,
which is a simulation model of the Earth's whole atmosphere and
ionosphere, to calculate the TEC difference. We then compared these
results with the observed TEC. When we used the FISM flare spectrum,
the difference in TEC from the background was in a good agreement with
the observation. However, when the flare spectrum of the 1D-hydrodynamic
model was used, the result varied depending on the presence or absence
of the background. This difference depending on the models is considered
to represent which extreme ultraviolet (EUV) radiation is primarily
responsible for increasing TEC. From the flare spectrum obtained from
these models and the calculation result of TEC fluctuation using GAIA,
it is considered that the enhancement in EUV emission by approximately
15-35 nm mainly contributes in increasing TEC rather than that of
X-ray emission, which is thought to be mainly responsible for sudden
ionospheric disturbance. In addition, from the altitude/wavelength
distribution of the ionization rate of Earth's atmosphere by GAIA
(Ground-to-topside Atmosphere and Ionosphere model for Aeronomy), it
was found that EUV radiation of approximately 15-35 nm affects a wide
altitude range of 120-300 km, and TEC enhancement is mainly caused by
the ionization of nitrogen molecules.
---------------------------------------------------------
Title: PSTEP: project for solar-terrestrial environment prediction
Authors: Kusano, Kanya; Ichimoto, Kiyoshi; Ishii, Mamoru; Miyoshi,
Yoshizumi; Yoden, Shigeo; Akiyoshi, Hideharu; Asai, Ayumi; Ebihara,
Yusuke; Fujiwara, Hitoshi; Goto, Tada-Nori; Hanaoka, Yoichiro;
Hayakawa, Hisashi; Hosokawa, Keisuke; Hotta, Hideyuki; Hozumi,
Kornyanat; Imada, Shinsuke; Iwai, Kazumasa; Iyemori, Toshihiko; Jin,
Hidekatsu; Kataoka, Ryuho; Katoh, Yuto; Kikuchi, Takashi; Kubo, Yûki;
Kurita, Satoshi; Matsumoto, Haruhisa; Mitani, Takefumi; Miyahara,
Hiroko; Miyoshi, Yasunobu; Nagatsuma, Tsutomu; Nakamizo, Aoi; Nakamura,
Satoko; Nakata, Hiroyuki; Nishizuka, Naoto; Otsuka, Yuichi; Saito,
Shinji; Saito, Susumu; Sakurai, Takashi; Sato, Tatsuhiko; Shimizu,
Toshifumi; Shinagawa, Hiroyuki; Shiokawa, Kazuo; Shiota, Daikou;
Takashima, Takeshi; Tao, Chihiro; Toriumi, Shin; Ueno, Satoru;
Watanabe, Kyoko; Watari, Shinichi; Yashiro, Seiji; Yoshida, Kohei;
Yoshikawa, Akimasa
2021EP&S...73..159K Altcode:
Although solar activity may significantly impact the global environment
and socioeconomic systems, the mechanisms for solar eruptions and
the subsequent processes have not yet been fully understood. Thus,
modern society supported by advanced information systems is at risk
from severe space weather disturbances. Project for solar-terrestrial
environment prediction (PSTEP) was launched to improve this situation
through synergy between basic science research and operational
forecast. The PSTEP is a nationwide research collaboration in Japan
and was conducted from April 2015 to March 2020, supported by a
Grant-in-Aid for Scientific Research on Innovative Areas from the
Ministry of Education, Culture, Sports, Science and Technology of
Japan. By this project, we sought to answer the fundamental questions
concerning the solar-terrestrial environment and aimed to build a
next-generation space weather forecast system to prepare for severe
space weather disasters. The PSTEP consists of four research groups and
proposal-based research units. It has made a significant progress in
space weather research and operational forecasts, publishing over 500
refereed journal papers and organizing four international symposiums,
various workshops and seminars, and summer school for graduate students
at Rikubetsu in 2017. This paper is a summary report of the PSTEP and
describes the major research achievements it produced.
---------------------------------------------------------
Title: Johann Christoph Müller's Sunspot Observations in 1719 -
1720: Snapshots of the Immediate Aftermath of the Maunder Minimum
Authors: Hayakawa, Hisashi; Iju, Tomoya; Kuroyanagi, Chiaki; Carrasco,
Víctor M. S.; Besser, Bruno P.; Uneme, Shoma; Imada, Shinsuke
2021SoPh..296..154H Altcode:
The Maunder Minimum (1645 - 1715) was unique in terms of solar-cycle
amplitudes and sunspot-position distributions registered in the last
four centuries; however, little is known for its recovery and transition
to the regular solar cycles until 1749 and the existing reconstructions
vary from one to another here. This article presents a snapshot of Solar
Cycle −3 including sunspot observations by Johann Christoph Müller
(hereafter, JCM) in 1719 - 1720. We identified his sunspot drawings
in the manuscript department of the National Library of Russia in
St. Petersburg and compiled his biographical profile and observational
expertise. Subsequently, we analysed his sunspot drawings and derived
the group number and positions of the observed sunspots. The results
and comparative analyses with contemporary observations revealed
that JCM reported up to five sunspot groups, corresponding well with
Sebastian Alischer's records but contrasting with Johann Rost's records
in the existing databases. These comparisons indicated that Rost's
extremely large values recorded in 1719 - 1720 probably represented
individual sunspot numbers instead of sunspot group numbers, unlike
the understanding in the existing databases. Accordingly, JCM's group
number forms a robust reference for representing the solar activity
in 1719 - 1720 and exhibits relatively moderate solar cycle amplitude
in the immediate aftermath of the Maunder Minimum. Moreover, JCM's
sunspot drawings provide significantly detailed information on sunspot
positions. Our analyses could locate the reported sunspot groups in
both solar hemispheres, unlike those in the Maunder Minimum, which
support the suggested transition between Solar Cycles −4 and −3.
---------------------------------------------------------
Title: Stephan Prantner's Sunspot Observations during the Dalton
Minimum
Authors: Hayakawa, Hisashi; Uneme, Shoma; Besser, Bruno P.; Iju,
Tomoya; Imada, Shinsuke
2021ApJ...919....1H Altcode: 2021arXiv210505405H
In addition to regular Schwabe cycles (≍11 yr), solar variability
also shows longer periods of enhanced or reduced activity. Of these,
reconstructions of the Dalton Minimum provide controversial sunspot
group numbers and limited sunspot positions, partially due to limited
source record accessibility. In this context, we analyzed Stephan
Prantner's sunspot observations spanning from 1804 to 1844, the values
of which had only been known through estimates despite their notable
chronological coverage during the Dalton Minimum. We identified his
original manuscript in Stiftsarchiv Wilten, near Innsbruck (Austria). We
reviewed his biography (1782-1873) and located his observational sites
at Wilten and Waidring, which housed the principal telescopes for his
early and late observations: a 3.5 inch astronomical telescope and
a Reichenbach 4 foot achromatic erecting telescope, respectively. We
identified 215 days of datable sunspot observations, which is almost
twice as much data as his estimated data in the existing databases
(=115 days). In Prantner's records, we counted up to seven to nine
sunspot groups per day and measured sunspot positions, which show their
distributions in both solar hemispheres. These results strikingly
emphasize the difference between the Dalton Minimum and the Maunder
Minimum as well as the similarity between the Dalton Minimum and the
weak solar cycles in the modern observations.
---------------------------------------------------------
Title: Reanalyses of the sunspot observations of Fogelius and Siverus:
two 'long-term' observers during the Maunder minimum
Authors: Hayakawa, Hisashi; Iju, Tomoya; Uneme, Shoma; Besser, Bruno
P.; Kosaka, Shunsuke; Imada, Shinsuke
2021MNRAS.506..650H Altcode: 2020MNRAS.tmp.2883H; 2020arXiv200914369H
The solar activity during the Maunder minimum (MM; 1645-1715) has
been considered significantly different from the one captured in
modern observations, in terms of sunspot group number and sunspot
positions, whereas its actual amplitudes and distributions are still
under active discussions. In its core period (1650/1660-1700), Martin
Fogelius and Heinrich Siverus have formed significant long-term series
in the existing data bases. With numerous spotless days, they have been
considered as the 13th and 7th most active observers before the end of
the MM. In this study, we have analysed their original archival records,
revised their data, have removed significant contaminations of the
apparent 'spotless days' in the existing data bases, and cast caveats on
the potential underestimation of the solar-cycle amplitude in the core
MM. Still, they reported at best one sunspot group throughout their
observational period and confirm the significantly suppressed solar
cycles during the MM. This is also supported from the contemporary
observations of Hook and Willoughby, analysed in this study. Based
on their revised data, we have also derived positions of notable
sunspot groups, which Siverus recorded in 1671 (≍N7.5° ± 2.5°),
in comparison with those of Cassini's drawings (≍N10° ± 1°). Their
coincidence in position and chronology in corrected dates indicates
these sunspot groups were probably the same recurrent active region (AR)
and its lifespan was significantly long (≥35 d) even during the MM.
---------------------------------------------------------
Title: The Energy Conversion Rate of an Active Region Transient
Brightening Estimated by Hinode Spectroscopic Observations
Authors: Kawai, Toshiki; Imada, Shinsuke
2021ApJ...918...51K Altcode: 2021arXiv210606208K
We statistically estimate the conversion rate of the energy released
during an active region transient brightening to Doppler motion and
thermal and nonthermal energies. We used two types of data sets for the
energy estimation and detection of transient brightenings. One includes
spectroscopic images of Fe XIV, Fe XV, and Fe XVI lines observed by
the Hinode/EUV Imaging Spectrometer. The other includes images obtained
from the 211 Å channel of the Solar Dynamics Observatory/Atmospheric
Imaging Assembly (AIA). The observed active region was NOAA 11890 on
2013 November 9 and 10. As a result, the released Doppler motion and
nonthermal energies were found to be approximately 0.1%-1% and 10%-100%
of the change in the amount of thermal energy in each enhancement,
respectively. Using this conversion rate, we estimated the contribution
of the total energy flux of AIA transient brightenings to the active
region heating to be at most 2% of the conduction and radiative losses.
---------------------------------------------------------
Title: A New Broadening Technique of the Numerically Unresolved
Solar Transition Region and Its Effect on the Spectroscopic Synthesis
Using Coronal Approximation
Authors: Iijima, Haruhisa; Imada, Shinsuke
2021ApJ...917...65I Altcode: 2021arXiv210600864I
The transition region is a thin layer of the solar atmosphere that
controls the energy loss from the solar corona. Large numbers of
grid points are required to resolve this thin transition region
fully in numerical modeling. In this study, we propose a new
numerical treatment, called LTRAC, which can be easily extended to
the multidimensional domains. We have tested the proposed method
using a one-dimensional hydrodynamic model of a coronal loop in an
active region. The LTRAC method enables modeling of the transition
region with a numerical grid size of 50-100 km, which is about 1000
times larger than the physically required value. We used the velocity
differential emission measure to evaluate the possible effects on
the optically thin emission. Lower-temperature emissions were better
reproduced by the LTRAC method than by previous methods. Doppler shift
and nonthermal width of the synthesized line emission agree with
those from a high-resolution reference simulation within an error
of several kilometers per second above the formation temperature of
10<SUP>5</SUP> K.
---------------------------------------------------------
Title: Nonequilibrium Ionization Plasma during a Large Solar Limb
Flare Observed by Hinode/EIS
Authors: Imada, S.
2021ApJ...914L..28I Altcode: 2021arXiv210514660I
This study on plasma heating considers the time-dependent ionization
process during a large solar flare on 2017 September 10, observed
by Hinode/EUV Imaging Spectrometer (EIS). The observed Fe XXIV/Fe
XXIII ratios increase downstream of the reconnection outflow, and
they are consistent with the time-dependent ionization effect at a
constant electron temperature T<SUB>e</SUB> 25 MK. Moreover, this
study also shows that the nonthermal velocity, which can be related
to the turbulent velocity, reduces significantly along the downstream
of the reconnection outflow, even when considering the time-dependent
ionization process.
---------------------------------------------------------
Title: Instrumental design of the Solar Observing Satellite:
solar-C_EUVST
Authors: Suematsu, Yoshinori; Shimizu, Toshifumi; Hara, Hirohisa;
Kawate, Tomoko; Katsukawa, Yukio; Ichimoto, Kiyoshi; Imada, Shinsuke
2021SPIE11852E..3KS Altcode:
The EUV High-Throughput Spectroscopic Telescope (EUVST) of Solar-C
mission is a revolutionary spectrometer that is designed to provide
high-quality and high cadence spectroscopic data covering a wide
temperature range of the chromosphere to flaring corona to investigate
the energetics and dynamics of the solar atmosphere. The EUVST consists
of only two imaging optical components; a 28-cm clear aperture off-axis
parabolic primary mirror and a two-split ellipsoidal grating without a
blocking filter for visible light before the primary mirror to achieve
unprecedented high spatial and temporal resolution in EUV-UV imaging
spectroscopic observations. For this reason, about 53 W of sunlight
is absorbed by the multilayer coating on the mirror. We present an
instrumental design of the telescope, particularly, primary mirror
assembly which enables slit-scan observations for imaging spectroscopy,
an image stabilizing tip-tilt control, and a focus adjustment on
orbit, together with an optomechanical design of the primary mirror
and its supporting system which gives optically tolerant wavefront
error against a large temperature increase due to an absorption of
visible and IR lights.
---------------------------------------------------------
Title: Sunspot Observations at the Eimmart Observatory and in Its
Neighborhood during the Late Maunder Minimum (1681-1718)
Authors: Hayakawa, Hisashi; Kuroyanagi, Chiaki; Carrasco, Víctor
M. S.; Uneme, Shoma; Besser, Bruno P.; Sôma, Mitsuru; Imada, Shinsuke
2021ApJ...909..166H Altcode:
The Maunder Minimum (1645-1715; hereafter MM) is generally considered
as the only grand minimum in the chronological coverage of telescopic
sunspot observations. Characterized by scarce sunspot occurrences and
their asymmetric concentrations in the southern solar hemisphere, the
MM has frequently been associated with a special state of solar dynamo
activity. As such, it is important to analyze contemporary observational
records and improve our understanding of this peculiar interval,
whereas the original records are frequently preserved in historical
archives and can be difficult to access. In this study, we consult
historical archives in the National Library of Russia, St. Petersburg,
and analyze a series of sunspot observations conducted at the Eimmart
Observatory from 1681 to 1709, which is the second-richest sunspot
data set produced during the MM, following La Hire's series, among
existing data sets. We have further extended our analyses to neighboring
observations to extend our investigations up to 1718. We first analyze
source documents and descriptions of observational instruments. Our
analyses have significantly revised the existing data set, removed
contaminations, and updated and labeled them as Eimmart Observatory (78
days), Altdorf Observatory (4 days), Hoffmann (22 days), and Wideburg
(25 days). The revisions have updated the temporal coverage of the
contemporary sunspot observations from 73.4% to 66.9% from 1677 to
1709. We have also derived the positions of the observed sunspot groups
in comparison with contemporary observations. Our results indicate
hemispheric asymmetry in the MM and recovery of sunspot groups in both
hemispheres after 1716, supporting the common paradigm of the MM.
---------------------------------------------------------
Title: Derfflinger's Sunspot Observations: Primary Dataset to
Understand the Dalton Minimum
Authors: Hayakawa, Hisashi; Besser, Bruno P.; Imada, Shinsuke; Arlt,
Rainer; Iju, Tomoya; Bourdin, Philippe; Kraml, Amand; Uneme, Shoma
2021cosp...43E.915H Altcode:
As various predictions indicate possible arrival of depressed solar
cycles or even a secular/grand solar minimum, it is increasingly
important to understand the actual solar activity during the existing
solar secular/grand minima. The Dalton Minimum is arguably one of such
solar secular/grand minima within the coverage of telescopic sunspot
observations, while its sunspot group number has been differently
reconstructed by various studies and its butterfly diagram has not been
reconstructed. Here, we examine the original observational records
of Derfflinger in Krememünster Observatory, spanning from 1802 to
1824, covering the core period of the Dalton Minimum. We revise his
sunspot group number and reconstruct the butterfly diagram. These
reconstructions show that the Dalton Minimum was significantly different
from the Maunder Minimum, both in terms of amplitude of its solar
cycles and sunspot distributions.
---------------------------------------------------------
Title: Science Objectives and Current Status of Solar-C_EUVST
Authors: Imada, Shinsuke
2021cosp...43E1790I Altcode:
SolarC EUVST is designed to comprehensively understand the energy
and mass transfer from the solar surface to the solar corona and
interplanetary space, and to investigate the elementary processes
that take place universally in cosmic plasmas. The proposed mission
is a fundamental step for answering how the plasma universe is created
and evolves, and how the Sun influences the Earth and other planets in
our solar system. The two primary science objectives for SolarC EUVST
are : I) Understand how fundamental processes lead to the formation of
the solar atmosphere and the solar wind, II) Understand how the solar
atmosphere becomes unstable, releasing the energy that drives solar
flares and eruptions. SolarC EUVST will, A) seamlessly observe all
the temperature regimes of the solar atmosphere from the chromosphere
to the corona at the same time, B) resolve elemental structures of the
solar atmosphere with high spatial resolution and cadence to track their
evolution, and C) obtain spectroscopic information on the dynamics of
elementary processes taking place in the solar atmosphere. In this
talk, we will first discuss the science target of the SolarC EUVST,
and discuss the science topic associated flare in detail. Photospheric
motions lead to the accumulation of free magnetic energy in the
corona. This system eventually becomes unstable, releasing the energy
through magnetic reconnection. This process of energy conversion
heats the plasma to high temperatures and drives coronal mass ejections
(CMEs). By measuring the properties of multi-temperature flaring plasma,
SolarC EUVST will investigate why the reconnection is fast despite
the high magnetic Reynolds number. It will also monitor the temporal
evolution of solar active regions and identify the triggering mechanism
for the flare and eruption. We will discuss the science objectives
"Understand the Fast Magnetic Reconnection Process" and "Identify the
Signatures of Global Energy Buildup and the Local Triggering of the
Flare and Eruption". We also report the current status of SolarC EUVST.
---------------------------------------------------------
Title: Energy Distribution of Small-scale Flares Derived Using a
Genetic Algorithm
Authors: Kawai, Toshiki; Imada, Shinsuke
2021ApJ...906....2K Altcode: 2020arXiv201106390K
To understand the mechanism of coronal heating, it is crucial to derive
the contribution of small-scale flares, the so-called nanoflares,
to the heating up of the solar corona. To date, several studies have
tried to derive the occurrence frequency distribution of flares
as a function of energy to reveal the contribution of small-scale
flares. However, there are no studies that derive the distribution with
considering the following conditions: (1) evolution of the coronal
loop plasma heated by small-scale flares, (2) loops smaller than the
spatial resolution of the observed image, and (3) multiwavelength
observation. To take into account these conditions, we introduce
a new method to analyze small-scale flares statistically based on
a one-dimensional loop simulation and a machine-learning technique,
that is, the genetic algorithm. First, we obtain six channels of Solar
Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) light
curves of the active-region coronal loops. Second, we carry out many
coronal loop simulations and obtain the SDO/AIA light curves for each
simulation in a pseudo-manner. Third, using the genetic algorithm, we
estimate the best combination of simulated light curves that reproduce
the observation. Consequently, the observed coronal loops are heated by
small-scale flares with energy flux larger than that typically required
to heat up an active region intermittently. Moreover, we derive the
occurrence frequency distribution which has various power-law indices
in the range from 1-3, which partially supports the nanoflare heating
model. In contrast, we find that 90% of the coronal heating is done
by flares that have energy larger than 10<SUP>25</SUP> erg.
---------------------------------------------------------
Title: Estimation of solar flare loop length by machine learning
Authors: Nishimoto, S.; Kawai, T.; Watanabe, K.; Imada, S.
2020AGUFMNG0040014N Altcode:
X-rays and extreme ultraviolet (EUV) emissions from solar flares
rapidly change the physical composition of the Earth's thermosphere
and ionosphere, thereby causing space weather phenomena such as
communication failures. To predict the effects of flare emissions
on the Earth's upper atmosphere and the occurrence of communication
failures, numerous empirical and physical models have been developed
which derive the flare spectral changes. <P />We have established
a method to reproduce the flare loop emission using one-dimensional
hydrodynamic calculation and the CHIANTI atomic database (Kawai et al.,
2020). This method has successfully reproduced the time-integrated
irradiance and time evolution of flare EUV lines. An important input
parameter when using this method is the flare loop length. If the
flare loop length can be estimated from the information of the Sun
before flare, flare emissions can be estimated before the occurrence
of flare by this method. <P />In this study, we attempted to estimate
the flare ribbon distance related to the flare loop length from the
observed images before flare using some machine learning techniques
such as Convolutional Neural Network (CNN). We used active region
images by Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics
Observatory (SDO) and loop images before flare by Atmospheric Imaging
Assembly (AIA) onboard SDO as input to machine learning method. We
obtained the ribbon distance from the observations of SDO/AIA 1600 Å
as teacher data. <P />we tried to construct a CNN model using all flare
events greater than M class observed by SDO. The CNN model, which uses
the active area image as input, can estimate the ribbon distance with
error within 45% for majority events. This result indicates that it is
possible to estimate the ribbon distance from the active region image
with a certain level accuracy. <P />In this presentation, we report
the accuracy and latest results of the models for estimating the flare
loop length from solar multi-wavelength real-time observations.
---------------------------------------------------------
Title: Reproduction and validation of flare spectra and their impact
on the global environment
Authors: Watanabe, K.; Jin, H.; Nishimoto, S.; Imada, S.; Kawai, T.;
Kawate, T.
2020AGUFMSM050..02W Altcode:
It is well known that sudden increase of flare emissions accelerates the
ionization and molecular dissociation of atmospheric components in the
ionosphere and thermosphere, and it may cause the sudden ionospheric
disturbance (SID). And then, communication failure also caused by
the absorption of the short-wave by the SID is known as the Dellinger
phenomenon (Dellinger 1937). In order to predict the occurrence of the
Dellinger phenomenon, we must know the relationship with the flare
emission which causes the Dellinger phenomenon. Therefore, in order
to verify which wavelength of the solar flare spectrum influence the
occurrence of the Dellinger phenomenon, we have developed a method
to calculate the solar flare radiation spectrum and its effect on the
Earth's atmosphere. For the flare emission, we constructed new model
with physical processes (Imada et al. 2015, Kawai et al. 2020). In
our model, the physical process of the plasma in the flare loop is
reproduced by combining the one-dimensional hydrodynamic calculation
using CANS (Coordinated Astronomical Numerical Software) 1D package
with the CHIANTI atomic database (Dere et al. 2019). Then, in order to
examine the effect of flare emission on the Earth's atmosphere, we put
our calculated flare spectra into the Earth's atmospheric model GAIA
(Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy; Jin
et al., 2011). Finally, we tried to reproduce the total electron content
(TEC) variation for some flare events, then we compared calculated
results with the observed TEC amount. Especially when we investigated
about the X9.3 flare on September 6, 2017, it is considered that the
EUV emission about 15-40 nm is mainly affected increasing TEC. This
result was also confirmed from the altitude/wavelength distribution
of the ionization rate of Earth's atmosphere by GAIA.
---------------------------------------------------------
Title: Solar cycle-related variation in solar differential rotation
and meridional flow in solar cycle 24
Authors: Imada, Shinsuke; Matoba, Kengo; Fujiyama, Masashi; Iijima,
Haruhisa
2020EP&S...72..182I Altcode:
We studied temporal variation of the differential rotation and poleward
meridional circulation during solar cycle 24 using the magnetic element
feature tracking technique. We used line-of-sight magnetograms obtained
using the helioseismic and magnetic imager aboard the Solar Dynamics
Observatory from May 01, 2010 to March 26, 2020 (for almost the entire
period of solar cycle 24, Carrington rotation from 2096 to 2229) and
tracked the magnetic element features every 1 h. We also estimated
the differential rotation and poleward meridional flow velocity
profiles. The observed profiles are consistent with those of previous
studies on different cycles. Typical properties resulting from torsional
oscillations can also be observed from solar cycle 24. The amplitude of
the variation was approximately ±10 m s-<SUP>1</SUP>. Interestingly,
we found that the average meridional flow observed in solar cycle 24 is
faster than that observed in solar cycle 23. In particular, during the
declining phase of the cycle, the meridional flow of the middle latitude
is accelerated from 10 to 17 m s-<SUP>1</SUP>, which is almost half of
the meridional flow itself. The faster meridional flow in solar cycle
24 might be the result of the weakest cycle during the last 100 years.
---------------------------------------------------------
Title: The Solar-C (EUVST) mission: the latest status
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko; Suematsu,
Yoshinori; Hara, Hirohisa; Tsuzuki, Toshihiro; Katsukawa, Yukio; Kubo,
Masahito; Ishikawa, Ryoko; Watanabe, Tetsuya; Toriumi, Shin; Ichimoto,
Kiyoshi; Nagata, Shin'ichi; Hasegawa, Takahiro; Yokoyama, Takaaki;
Watanabe, Kyoko; Tsuno, Katsuhiko; Korendyke, Clarence M.; Warren,
Harry; De Pontieu, Bart; Boerner, Paul; Solanki, Sami K.; Teriaca,
Luca; Schuehle, Udo; Matthews, Sarah; Long, David; Thomas, William;
Hancock, Barry; Reid, Hamish; Fludra, Andrzej; Auchère, Frederic;
Andretta, Vincenzo; Naletto, Giampiero; Poletto, Luca; Harra, Louise
2020SPIE11444E..0NS Altcode:
Solar-C (EUVST) is the next Japanese solar physics mission to
be developed with significant contributions from US and European
countries. The mission carries an EUV imaging spectrometer with
slit-jaw imaging system called EUVST (EUV High-Throughput Spectroscopic
Telescope) as the mission payload, to take a fundamental step towards
answering how the plasma universe is created and evolves and how the
Sun influences the Earth and other planets in our solar system. In
April 2020, ISAS (Institute of Space and Astronautical Science) of JAXA
(Japan Aerospace Exploration Agency) has made the final down-selection
for this mission as the 4th in the series of competitively chosen
M-class mission to be launched with an Epsilon launch vehicle in mid
2020s. NASA (National Aeronautics and Space Administration) has selected
this mission concept for Phase A concept study in September 2019 and
is in the process leading to final selection. For European countries,
the team has (or is in the process of confirming) confirmed endorsement
for hardware contributions to the EUVST from the national agencies. A
recent update to the mission instrumentation is to add a UV spectral
irradiance monitor capability for EUVST calibration and scientific
purpose. This presentation provides the latest status of the mission
with an overall description of the mission concept emphasizing on key
roles of the mission in heliophysics research from mid 2020s.
---------------------------------------------------------
Title: Current Status of the Solar-C_EUVST Mission
Authors: Imada, S.; Shimizu, T.; Kawate, T.; Toriumi, S.; Katsukawa,
Y.; Kubo, M.; Hara, H.; Suematsu, Y.; Ichimoto, K.; Watanabe, T.;
Watanabe, K.; Yokoyama, T.; Warren, H.; Long, D.; Harra, L. K.;
Teriaca, L.
2020AGUFMSH056..05I Altcode:
Solar-C_EUVST (EUV High-Throughput Spectroscopic Telescope) is designed
to comprehensively understand the energy and mass transfer from the
solar surface to the solar corona and interplanetary space, and to
investigate the elementary processes that take place universally
in cosmic plasmas. As a fundamental step towards answering how the
plasma universe is created and evolves, and how the Sun influences
the Earth and other planets in our solar system, the proposed mission
is designed to comprehensively understand how mass and energy are
transferred throughout the solar atmosphere. Understanding the solar
atmosphere, which connects to the heliosphere via radiation, the solar
wind and coronal mass ejections, and energetic particles is pivotal
for establishing the conditions for life and habitability in the solar
system. <P />The two primary science objectives for Solar-C_EUVST are :
I) Understand how fundamental processes lead to the formation of the
solar atmosphere and the solar wind, II) Understand how the solar
atmosphere becomes unstable, releasing the energy that drives solar
flares and eruptions. Solar-C_EUVST will, A) seamlessly observe all
the temperature regimes of the solar atmosphere from the chromosphere
to the corona at the same time, B) resolve elemental structures of the
solar atmosphere with high spatial resolution and cadence to track their
evolution, and C) obtain spectroscopic information on the dynamics of
elementary processes taking place in the solar atmosphere. <P />In this
talk, we will first discuss the science target of the Solar-C_EUVST,
and then discuss the current status of the Solar-C_EUVST mission.
---------------------------------------------------------
Title: Thermal design of the Solar-C (EUVST) telescope
Authors: Suematsu, Yoshinori; Shimizu, Toshifumi; Hara, Hirohisa;
Kawate, Tomoko; Katsukawa, Yukio; Ichimoto, Kiyoshi; Imada, Shinsuke;
Nagae, Kazuhiro; Yamazaki, Atsumu; Hattori, Tomoya
2020SPIE11444E..3KS Altcode:
The EUV High-Throughput Spectroscopic Telescope (EUVST) of Solar-C
mission consists of only two imaging optical components; a 28-cm clear
aperture off-axis parabolic primary mirror and a two-split ellipsoidal
grating without a blocking filter for visible light before the primary
mirror to achieve unprecedented high spatial and temporal resolution in
EUV-UV imaging spectroscopic observations. For this reason, about 60
W of sunlight is absorbed by the multilayer coating on the mirror. We
report a thermal design of telescope in which the temperature of the
primary mirror bonding part and underlying tip-tilt and slit-scanning
mechanisms is well lower than a glass transition temperature of adhesive
(about 60°C) and thermal deformation of the primary mirror is small,
although it is non-negligibly small.
---------------------------------------------------------
Title: A sensitivity analysis of the updated optical design for
EUVST on the Solar-C mission
Authors: Kawate, Tomoko; Tsuzuki, Toshihiro; Shimizu, Toshifumi;
Imada, Shinsuke; Katsukawa, Yukio; Hara, Hirohisa; Suematsu, Yoshinori;
Ichimoto, Kiyoshi; Hattori, Tomoya; Narasaki, Shota; Warren, Harry P.;
Teriaca, Luca; Korendyke, Clarence M.; Brown, Charles M.; Auchere,
Frederic
2020SPIE11444E..3JK Altcode:
The EUV high-throughput spectroscopic telescope (EUVST) onboard the
Solar-C mission has the high spatial (0.4”) resolution over a wide
wavelength range in the vacuum ultraviolet. To achieve high spatial
resolution under a design constraint given by the JAXA Epsilon launch
vehicle, we further update the optical design to secure margins
needed to realize 0.4” spatial resolution over a field of view of
100”×100”. To estimate the error budgets of spatial and spectral
resolutions due to installation and fabrication errors, we perform a
sensitivity analysis for the position and orientation of each optical
element and for the grating parameters by ray tracing with the Zemax
software. We obtain point spread functions (PSF) for rays from 9
fields and at 9 wavelengths on each detector by changing each parameter
slightly. A full width at half maximum (FWHM) of the PSF is derived at
each field and wavelength position as a function of the perturbation
of each optical parameter. Assuming a mount system of each optical
element and an error of each optical parameter, we estimate spatial
and spectral resolutions by taking installation and fabrication errors
into account. The results of the sensitivity analysis suggest that
budgets of the total of optical design and the assembly errors account
for 15% and 5.8% of our budgets of the spatial resolution in the long
wavelength and short wavelength bands, respectively. On the other hand,
the grating fabrication errors give a large degradation of spatial and
spectral resolutions, and investigations of compensators are needed
to relax the fabrication tolerance of the grating surface parameters.
---------------------------------------------------------
Title: Statistical Analysis of Asymmetric Sunspot Decay Observed
by Hinode
Authors: Imada, Shinsuke; Kato, Shota; Fujiyama, Masashi
2020SoPh..295..154I Altcode:
We statistically studied the transport of magnetic flux in and around
sunspots using a magnetic-element tracking technique to investigate
whether sunspot-decay processes are isotropic. Using this method,
we detected moving magnetic features (MMFs). The observed radius
of an MMFs region was approximately 1.7 times the sunspot radius;
furthermore, the average apparent velocity of MMFs was statistically
estimated to be approximately 350 ms−<SUP>1</SUP>. We determined that
the leading sunspots transport approximately 5% more magnetic flux to
the Equator side than to the Pole side of the sunspots. In addition,
the leading sunspots transport approximately 3% more magnetic flux to
the back (East) than to the front (West) of the sunspots. On the other
hand, the following sunspots do not show the magnetic-flux transport
asymmetry. The statistics might not be sufficient for the analysis of
the following sunspots. These asymmetries of magnetic flux transport
might contribute to the cross-equatorial transport of net magnetic
flux, which is an important physical quantity of polar magnetic-field
reversal.
---------------------------------------------------------
Title: Statistical and Observational Research on Solar Flare EUV
Spectra and Geometrical Features
Authors: Nishimoto, Shohei; Watanabe, Kyoko; Imada, Shinsuke; Kawate,
Tomoko; Lee, Kyoung-Sun
2020ApJ...904...31N Altcode:
We performed statistical analysis on the flare emission data to
examine parameters related to the flare extreme-ultraviolet (EUV)
spectra. This study used the data from the Geostationary Operational
Environmental Satellite X-ray Sensors to determine the fundamental flare
parameters. The relationship between soft X-ray data and EUV emission
data observed by the Extreme Ultraviolet Variability Experiment on
board the Solar Dynamics Observatory (SDO) MEGS-A was investigated
for 50 events. The results showed the hotter Fe line emissions have
strong correlation with soft X-ray data in many cases. However, our
statistical study revealed that EUV flare peak flux of Fe XV, Fe XVI
and He II lines have weak correlation with soft X-ray peak flux. In EUV
line light curves, there was time difference in peak time, however the
tendency to reach the peak in order from the hotter line to cooler line
was not so clear. These results indicate that the temporal evolution
of EUV emission can be roughly explained by soft X-ray data. However,
the time changes of temperature and density distributions in the flare
loop must be needed for accurate reproduction. Moreover, we compared the
geometrical features of solar flares observed by the Atmospheric Imaging
Assembly on board the SDO with the fundamental flare parameters for 32
events. The ribbon distance strongly correlated with both soft X-ray
flare rise and decay times. This results indicate that the geometrical
feature is essential parameter for predicting flare emission duration.
---------------------------------------------------------
Title: Nowcast of an EUV dynamic spectrum during solar flares
Authors: Kawai, Toshiki; Imada, Shinsuke; Nishimoto, Shohei; Watanabe,
Kyoko; Kawate, Tomoko
2020JASTP.20505302K Altcode: 2020arXiv200506099K
In addition to X-rays, extreme ultraviolet (EUV) rays radiated
from solar flares can cause serious problems, such as communication
failures and satellite drag. Therefore, methods for forecasting EUV
dynamic spectra during flares are urgently required. Recently, however,
owing to the lack of instruments, EUV dynamic spectra have rarely been
observed. Hence, we develop a new method that converts the soft X-ray
light curve observed during large flare events into an EUV dynamic
spectrum by using the Solar Dynamics Observatory/Atmospheric Imaging
Assembly images, a numerical simulation, and atomic database. The
simulation provides the solution for a coronal loop that is heated by a
strong flare, and the atomic database calculates its dynamic spectrum,
including X-ray and EUV irradiances. The coefficients needed for the
conversion can be calculated by comparing the observed soft X-ray
light curve with that of the simulation. We apply our new method to
three flares that occurred in the active region 12673 on September 06,
2017. The results show similarities to those of the Flare Irradiance
Spectral Model, and reconstruct some of the EUV peaks observed by the
EUV Variability Experiment onboard the Solar Dynamics Observatory.
---------------------------------------------------------
Title: Intrusion of Magnetic Peninsula toward the Neighboring
Opposite-polarity Region That Triggers the Largest Solar Flare in
Solar Cycle 24
Authors: Bamba, Yumi; Inoue, Satoshi; Imada, Shinsuke
2020ApJ...894...29B Altcode: 2020arXiv200500688B
The largest X9.3 solar flare in solar cycle 24 and the preceding
X2.2 flare occurred on 2017 September 6, in the solar active region
NOAA 12673. This study aims to understand the onset mechanism of these
flares via analysis of multiple observational data sets from the Hinode
and Solar Dynamics Observatory and results from a nonlinear force-free
field extrapolation. The most noticeable feature is the intrusion of
a major negative-polarity region, appearing similar to a peninsula,
oriented northwest into a neighboring opposite-polarity region. We also
observe proxies of magnetic reconnection related to the intrusion of
the negative peninsula: rapid changes of the magnetic field around
the intruding negative peninsula; precursor brightening at the tip
of the negative peninsula, including a cusp-shaped brightening that
shows a transient but significant downflow (∼100 km s<SUP>-1</SUP>)
at a leg of the cusp; a dark tube-like structure that appears to be
a magnetic flux rope that erupted with the X9.3 flare; and coronal
brightening along the dark tube-like structure that appears to
represent the electric current generated under the flux rope. Based
on these observational features, we propose that (1) the intrusion
of the negative peninsula was critical in promoting the push-mode
magnetic reconnection that forms and grows a twisted magnetic flux
rope that erupted with the X2.2 flare, and (2) the continuing intrusion
progressing even beyond the X2.2 flare is further promoted to disrupt
the equilibrium that leads the reinforcement of the magnetic flux rope
that erupted with the X9.3 flare.
---------------------------------------------------------
Title: A Solar Magnetic-fan Flaring Arch Heated by Nonthermal
Particles and Hot Plasma from an X-Ray Jet Eruption
Authors: Lee, Kyoung-Sun; Hara, Hirohisa; Watanabe, Kyoko; Joshi,
Anand D.; Brooks, David H.; Imada, Shinsuke; Prasad, Avijeet; Dang,
Phillip; Shimizu, Toshifumi; Savage, Sabrina L.; Moore, Ronald;
Panesar, Navdeep K.; Reep, Jeffrey W.
2020ApJ...895...42L Altcode: 2020arXiv200509875L
We have investigated an M1.3 limb flare, which develops as a magnetic
loop/arch that fans out from an X-ray jet. Using Hinode/EIS, we
found that the temperature increases with height to a value of over
10<SUP>7</SUP> K at the loop top during the flare. The measured Doppler
velocity (redshifts of 100-500 km s<SUP>-1</SUP>) and the nonthermal
velocity (≥100 km s<SUP>-1</SUP>) from Fe XXIV also increase with
loop height. The electron density increases from 0.3 × 10<SUP>9</SUP>
cm<SUP>-3</SUP> early in the flare rise to 1.3 × 10<SUP>9</SUP>
cm<SUP>-3</SUP> after the flare peak. The 3D structure of the loop
derived with Solar TErrestrial RElations Observatory/EUV Imager
indicates that the strong redshift in the loop-top region is due to
upflowing plasma originating from the jet. Both hard X-ray and soft
X-ray emission from the Reuven Ramaty High Energy Solar Spectroscopic
Imager were only seen as footpoint brightenings during the impulsive
phase of the flare, then, soft X-ray emission moved to the loop top in
the decay phase. Based on the temperature and density measurements and
theoretical cooling models, the temperature evolution of the flare arch
is consistent with impulsive heating during the jet eruption followed
by conductive cooling via evaporation and minor prolonged heating in
the top of the fan loop. Investigating the magnetic field topology and
squashing factor map from Solar Dynamics Observatory/HMI, we conclude
that the observed magnetic-fan flaring arch is mostly heated from low
atmospheric reconnection accompanying the jet ejection, instead of from
reconnection above the arch as expected in the standard flare model.
---------------------------------------------------------
Title: White-light Emission and Chromospheric Response by an
X1.8-class Flare on 2012 October 23
Authors: Watanabe, Kyoko; Imada, Shinsuke
2020ApJ...891...88W Altcode:
On 2012 October 23, a strong white-light emission, associated with
an X1.8-class flare, was observed by the Solar Optical Telescope on
board the Hinode satellite. White-light kernels were clearly observed
along the Ca II H ribbons. RHESSI also observed hard X-ray emissions
that were almost located on the white-light kernels. The total energy
of the white-light emission was ∼ 10<SUP>27-28</SUP> erg, s-1 and
the total energy of the accelerated electrons was almost of the same
order when we used 40 keV as the lower energy cutoff. The white-light
emission appears to have originated from nonthermal electrons in these
energies. Moreover, the EUV imaging spectrometer on board the Hinode
satellite performed a raster scan over this flaring active region and
the flare occurred during the scan. Over the white-light kernels, we
observed redshifts of a few tens of km s<SUP>-1</SUP> in Fe XII. It
appears that these EUV responses originated from some accelerated
electrons due to the solar flare and they are considered to be the
source of the white-light emission. In fact, the electron density of
the white-light kernels was less than 10<SUP>12</SUP> cm<SUP>-3</SUP>,
which is sufficiently low for nonthermal electrons to penetrate into
the photosphere.
---------------------------------------------------------
Title: Thaddäus Derfflinger's Sunspot Observations during 1802-1824:
A Primary Reference to Understand the Dalton Minimum
Authors: Hayakawa, Hisashi; Besser, Bruno P.; Iju, Tomoya; Arlt,
Rainer; Uneme, Shoma; Imada, Shinsuke; Bourdin, Philippe-A.; Kraml,
Amand
2020ApJ...890...98H Altcode: 2020arXiv200102367H
As we are heading toward the next solar cycle, presumably with
a relatively small amplitude, it is of significant interest to
reconstruct and describe the past secular minima on the basis of actual
observations at the time. The Dalton Minimum is often considered
one of the secular minima captured in the coverage of telescopic
observations. Nevertheless, the reconstructions of the sunspot group
number vary significantly, and the existing butterfly diagrams have
a large data gap during the period. This is partially because most
long-term observations at that time have remained unexplored in
historical archives. Therefore, to improve our understanding on the
Dalton Minimum, we have located two series of Thaddäus Derfflinger's
observational records spanning 1802-1824 (a summary manuscript
and logbooks), as well as his Brander's 5.5 feet azimuthal quadrant
preserved in the Kremsmünster Observatory. We have revised the existing
Derfflinger's sunspot group number with Waldmeier classification, and
eliminated all the existing "spotless days" to remove contaminations
from solar elevation observations. We have reconstructed the butterfly
diagram on the basis of his observations and illustrated sunspot
distributions in both solar hemispheres. Our article aims to revise
the trend of Derfflinger's sunspot group number and to bridge a data
gap of the existing butterfly diagrams around the Dalton Minimum. Our
results confirm that the Dalton Minimum is significantly different
from the Maunder Minimum, both in terms of cycle amplitudes and sunspot
distributions. Therefore, the Dalton Minimum is more likely a secular
minimum in the long-term solar activity, while further investigations
for the observations at that time are required.
---------------------------------------------------------
Title: Statistical and Observational Research of Solar Flare EUV
Spectra and Geometrical Features for Predicting Total Flare Emission
Spectra
Authors: Nishimoto, S.; Watanabe, K.; Imada, S.; Kawai, T.; Kawate,
T.; Lee, K. S.
2019AGUFMSH34A..04N Altcode:
We are performing statistical analysis of observed flare emissions for
making the total flare emission spectra prediction model. The Flare
Irradiance Spectral Model (FISM) (Chamberlin et al. 2006, 2007, 2008)
is one of the total flare spectra prediction model which is currently
most widely used. However, since FISM is empirical model, there are
problems such as the uncertain physical process. In order to solve
FISM's problems, we are trying to make new prediction model of total
flare spectra. For this purpose, we searched for which flare parameter
affect to the flare emission. We used the soft X-ray data (intensity
& duration) as fundamental parameter, and compared with EUV data
observed by SDO/EVE MEGS-A statistically. We have 53 events which were
MEGS-A observed with >M3 class flare, and especially analyzed for 6
EUV lines. We found the soft X-ray peak intensity was well correlated
with EUV line peak intensity. The EUV rising time also well correlated
with soft X-ray rising time, and hotter lines peaked earlier than cooler
lines. Moreover, we also searched for the relationship with geometrical
features (ribbon length & width) of solar flare observed by SDO/AIA
1600 Å for 32 events. We found the ribbon distance is related to the
rising time of soft X-ray, and the ribbon length is related to the
decay time of soft X-ray. From these results, we can say that the Fe
line emissions can be explain by the soft X-ray emissions. Moreover,
the soft X-ray light curve also can be estimated by the flare loop
length. Then, we performed numerical simulations (Imada et al., 2015)
using observational parameters obtained above results. In this paper,
we show some results of numerical simulations, and will discuss which
parameters strongly control the solar flare EUV emission spectra by
comparing with observed data.
---------------------------------------------------------
Title: The International Heliophysics Data Environment Alliance and
its possible role in ISWAT
Authors: Masson, A.; Roberts, D. A.; Fung, S. F.; Miyoshi, Y.; Imada,
S.; Malapert, J. C.; Arviset, C.
2019AGUFMSM31C3549M Altcode:
The IHDEA was formed as a result of the first International Heliophysics
Data Environment (IHDE) meeting held at the European Space and Astronomy
Centre (ESAC), Madrid, Spain, on October 17-18, 2018. Meeting attendees
representing NASA, ESA, JAXA, and CNES have all agreed that increasing
collaboration and coordination through the use of standard formats
(for both data and metadata) and community-based data tools are
critical for enabling interoperability of data systems and services
while improving sharing of space-based, ground-based, and model-based
heliophysics data sets. The newly created International Heliophysics
Data Environment Alliance (IHDEA) is a collaborative organization
whose goal is to guide the development of a data environment in
which the international heliophysics and space weather research
community can seamlessly find, access, and use all electronically
accessible, heliophysics relevant data sets. The specific mission
of the IHDEA is to facilitate global access to, and exchange of,
high quality scientific data products managed across international
boundaries. This will be achieved by adhering to, and promote the
use of, a set of governing data standards, data exchange protocols,
visualization and data analysis tools. The role of the IHDEA is to
serve as the focal point to engage the heliophysics data centres and the
scientific community, foster communication, and identify the standards
and services that will best serve the heliophysics and space weather
science needs. Practical examples will be provided, illustrating the
mutual interest to foster collaboration between key heliophysics data
providers. How IHDEA could support ISWAT information architecture will
be discussed and in particular how IHDEA could facilitate information
sharing and interconnection between ISWAT teams and Clusters.
---------------------------------------------------------
Title: Hybrid Simulation for the Solar Modulation of the Galactic
Cosmic Rays During Recent Solar Cycle
Authors: Miyake, S.; Matsumoto, T.; Kataoka, R.; Sato, T.; Shiota,
D.; Miyahara, H.; Imada, S.; Ueno, H.
2019AGUFMSM31E3197M Altcode:
In the current and next weak solar cycles, we expect higher flux of
galactic cosmic rays (GCRs) than that in the previous solar cycles
because of the decreasing trend of the solar activity. It is important
to quantitatively evaluate the high flux of galactic cosmic rays because
it leads to the increase in the radiation exposure of aircrews and the
increasing rates of single event upset events at spacecraft. However,
reliable prediction of the increasing galactic cosmic rays in upcoming
weak solar cycles is a challenges topic in the field of space weather
forecast. Grand Minimum 7 (Gm7) is a new project for understanding of
heliospheric environments during extremely weak solar cycle, such as
past grand minima and current solar cycle. The purposes of Gm7 consists
of revealing fundamental structure of the solar wind during extremely
weak solar cycle, explaining a mechanism of unique solar modulation
of the GCRs [1], and clarifying extreme space weather conditions
on the resultant radiation exposure [2]. In order to achieve these
objectives, we have developed a hybrid simulation model for the solar
modulation of the GCRs in such a weak solar conditions, which solves
the stochastic differential equations of energetic particles in the MHD
solar wind resolved by adaptive mesh refinement technique [3]. In this
presentation, we will show a first result of our hybrid simulation for
the solar modulation of the GCRs during recent solar cycle. <P />[1]
Kataoka, R., H. Miyahara, and F. Steinhilber, Space Weather, 10, S11001,
2012. <P />[2] Miyake, S., R. Kataoka, and T. Sato, Space Weather,
15(4), 589-605, 2017. <P />[3] Matsumoto, T., D. Shiota, R. Kataoka,
H. Miyahara, and S. Miyake, Journal of Physics: Conference Series,
1225, 012008, 2019.
---------------------------------------------------------
Title: Estimation of temporal evolution of coronal hole by surface
flux transport model and potential field source surface extrapolation
method
Authors: Watanabe, Y.; Imada, S.; Iijima, H.; Shiota, D.; Miyoshi, Y.
2019AGUFMSH43E3387W Altcode:
In this study, we will estimate the temporal evolution of coronal holes
by the surface flux transport (SFT) model and the potential field source
surface (PFSS) extrapolation method. Estimating the temporal evolution
of coronal hole, especially low latitude coronal hole, is crucial for
space weather study. So far, we have developed the SFT model calculation
to predict the next solar cycle activity and construct the forecast
scheme. The possible relationship between the polar magnetic fields
in the solar minimum and the solar activity in the maximum of the next
cycle has been intensively discussed. Iijima et al. (2017) calculated
the polar magnetic field at the solar minimum with the SFT model and
concluded that the polar magnetic field of the next cycle is weaker
than the current solar cycle. This is because polar magnetic fields are
well reproduced by the SFT model. On the other hand, it is not clear
whether the middle latitude magnetic fields can be well reproduced or
not by the SFT model calculation. The middle latitude magnetic fields
estimation is crucial for estimating the temporal evolution of coronal
hole. With regard to the September 2017 X9.3 flared active region
(NOAA12673), we focused on the transport of the magnetic field and
the associated time evolutions in the polar coronal holes and open
field lines. We compare the temporal evolution of the solar surface
magnetic field by the SFT model calculations and observations. Further,
we also calculated a three-dimensional coronal magnetic field using the
PFSS extrapolation method with the calculated surface magnetic field
distribution as a boundary condition and traced the open magnetic field
lines derived from the foot point of the coronal hole. Although with
the case where coronal holes are generated for the active region that
appeared behind the Sun, we estimated whether we can predict coronal
holes by comparing the coronal hole temporal evolution estimated by
the SFT/PFSS model and AIA observation.
---------------------------------------------------------
Title: Prediction of Extreme Ultraviolet Dynamic Spectrum during
Large Flare using Convolutional Neural Network
Authors: Kawai, T.; Imada, S.; Nishimoto, S.; Watanabe, K.; Kawate, T.
2019AGUFMSH31D3337K Altcode:
To forecast the influences of large flares on the earth, it is important
to predict the time series of Extreme Ultraviolet (EUV) spectrum
during flares. This is because an enhancement of EUVs can increase the
density of the upper atmosphere and it can crash satellites in the low
earth orbit by atmospheric drag forces. Therefore, the development of
methods to nowcast/forecast EUV dynamic spectra is required. We have
developed two methods. The first one is to nowcast the EUV spectrum
by using 1D hydrodynamic simulation and CHIANTI atomic database. We
calculate the light curve of GOES/XRS-B when a flare occurs in the
simulation. We convert it to observed one by stacking it with matching
these peaks. The EUV dynamic spectrum can be calculated by converting
it as same as XRS-B. The another one is to forecast the EUV spectrum
by using a Convolutional Neural Network (CNN) and 1D hydrodynamic
simulation. We train a CNN to predict GOES/XRS-B light curves during
flares as a response to the input of the past EUV maps and magnetograms
observed by SDO/AIA. After that, we adjust the flare parameters in the
simulation such as heating rate and duration to reconstruct predicted
GOES/XRS-B light curves well. We applied these methods to M- and X-class
flares occurred between 8:00 - 14:00 UT on 6 September 2017. We evaluate
the accuracy of the prediction by comparing observed and predicted
GOES/XRS-A light curves and total irradiance of SDO/AIA EUV maps.
---------------------------------------------------------
Title: Achievements of Hinode in the first eleven years
Authors: Hinode Review Team; Al-Janabi, Khalid; Antolin, Patrick;
Baker, Deborah; Bellot Rubio, Luis R.; Bradley, Louisa; Brooks,
David H.; Centeno, Rebecca; Culhane, J. Leonard; Del Zanna, Giulio;
Doschek, George A.; Fletcher, Lyndsay; Hara, Hirohisa; Harra,
Louise K.; Hillier, Andrew S.; Imada, Shinsuke; Klimchuk, James A.;
Mariska, John T.; Pereira, Tiago M. D.; Reeves, Katharine K.; Sakao,
Taro; Sakurai, Takashi; Shimizu, Toshifumi; Shimojo, Masumi; Shiota,
Daikou; Solanki, Sami K.; Sterling, Alphonse C.; Su, Yingna; Suematsu,
Yoshinori; Tarbell, Theodore D.; Tiwari, Sanjiv K.; Toriumi, Shin;
Ugarte-Urra, Ignacio; Warren, Harry P.; Watanabe, Tetsuya; Young,
Peter R.
2019PASJ...71R...1H Altcode:
Hinode is Japan's third solar mission following Hinotori (1981-1982)
and Yohkoh (1991-2001): it was launched on 2006 September 22 and is in
operation currently. Hinode carries three instruments: the Solar Optical
Telescope, the X-Ray Telescope, and the EUV Imaging Spectrometer. These
instruments were built under international collaboration with the
National Aeronautics and Space Administration and the UK Science and
Technology Facilities Council, and its operation has been contributed
to by the European Space Agency and the Norwegian Space Center. After
describing the satellite operations and giving a performance evaluation
of the three instruments, reviews are presented on major scientific
discoveries by Hinode in the first eleven years (one solar cycle long)
of its operation. This review article concludes with future prospects
for solar physics research based on the achievements of Hinode.
---------------------------------------------------------
Title: Effect of Morphological Asymmetry between Leading and Following
Sunspots on the Prediction of Solar Cycle Activity
Authors: Iijima, H.; Hotta, H.; Imada, S.
2019ApJ...883...24I Altcode: 2019arXiv190804474I
The morphological asymmetry of leading and following sunspots is a
well-known characteristic of the solar surface. In the context of the
large-scale evolution of the surface magnetic field, the asymmetry
has been assumed to have only a negligible effect. Using the surface
flux transport (SFT) model, we show that the morphological asymmetry of
leading and following sunspots has a significant impact on the evolution
of the large-scale magnetic field on the solar surface. By evaluating
the effect of the morphological asymmetry of each bipolar magnetic
region (BMR), we observe that the introduction of asymmetry to the
BMR model significantly reduces the contribution to the polar magnetic
field, especially for large and high-latitude BMRs. Strongly asymmetric
BMRs can even reverse regular polar field formation. The SFT simulations
based on the observed sunspot record show that the introduction of
morphological asymmetry reduces the root-mean-square difference from
the observed axial dipole strength by 30%-40%. These results indicate
that the morphological asymmetry of leading and following sunspots
has a significant effect on the solar cycle prediction.
---------------------------------------------------------
Title: A Transit of Venus Possibly Misinterpreted as an Unaided-Eye
Sunspot Observation in China on 9 December 1874
Authors: Hayakawa, Hisashi; Sôma, Mitsuru; Tanikawa, Kiyotaka;
Willis, David M.; Wild, Matthew N.; Macdonald, Lee T.; Imada, Shinsuke;
Hattori, Kentaro; Richard Stephenson, F.
2019SoPh..294..119H Altcode: 2019arXiv190802452H
Large sunspots can be observed with the unaided eye under suitable
atmospheric seeing conditions. Such observations are of particular
value because the frequency of their appearance provides an approximate
indication of the prevailing level of solar activity. Unaided-eye
sunspot observations can be traced back well before the start of
telescopic observations of the Sun, especially in the East Asian
historical records. It is therefore important to compare more modern,
unaided-eye sunspot observations with the results of telescopic
sunspot observations, to gain a better understanding of the nature
of the unaided-eye sunspot records. A previous comparison of Chinese
unaided-eye sunspot records and Greenwich photo-heliographic results
between 1874 and 1918 indicated that a few of the unaided-eye
observations were apparently not supported by direct photographic
evidence of at least one sunspot with a large area. This article
reveals that one of such Chinese unaided-eye observations had possibly
captured the transit of Venus on 9 December 1874. The Chinese sunspot
records on this date are compared with Western sunspot observations
on the same day. It is concluded that sunspots on the solar disk were
quite small and the transit of Venus was probably misinterpreted as
a sunspot (black spot) by the Chinese local intellectuals. This case
indicates that sunspots or comparable "obscuring" objects with an area
as large as 1000 millionths of the solar disk could reasonably have
been seen with the unaided eye under suitable seeing conditions. It
also confirms the visibility of sunspots near the solar limb with
the unaided eye. This study provides an explanation of the apparent
discrepancy between the Chinese unaided-eye sunspot observation on 9
December 1874 and the Western sunspot observations using telescopes,
as well as a basis for further discussion on the negative pairs in
1900 and 1911, apparently without sufficiently large area.
---------------------------------------------------------
Title: Development of Solar-C_EUVST structural design
Authors: Suematsu, Yoshinori; Shimizu, Toshifumi; Hara, Hirohisa;
Katsukawa, Yukio; Kawate, Tomoko; Ichimoto, Kiyoshi; Imada, Shinsuke
2019SPIE11118E..1OS Altcode:
The Solar-C_EUVST is a mission designed to provide high-quality solar
spectroscopic data covering a wide temperature range of the chromosphere
to flaring corona. To fulfill a high throughput requirement, the
instrument consists of only two optical components; a 28-cm primary
mirror and a segmented toroidal grating which have high reflective
coatings in EUV-UV range. We present a mission payload structural
design which accommodates long focal length optical components and
a launcher condition/launch environment (JAXA Epsilon). We also
present a mechanical design of primary mirror assembly which enables
slit-scan observations, an image stabilizing tip-tilt control, and a
focus adjustment on orbit, together with an optomechanical design of
the primary mirror and its supporting system which gives optically
tolerant wavefront error against a large temperature increase due to
an absorption of visible and IR lights.
---------------------------------------------------------
Title: Concept study of Solar-C_EUVST optical design
Authors: Kawate, Tomoko; Shimizu, Toshifumi; Imada, Shinsuke; Tsuzuki,
Toshihiro; Katsukawa, Yukio; Hara, Hirohisa; Suematsu, Yoshinori;
Ichimoto, Kiyoshi; Warren, Harry; Teriaca, Luca; Korendyke, Clarence
M.; Brown, Charles
2019SPIE11118E..1NK Altcode:
The main characteristics of Solar-C_EUVST are the high temporal and
high spatial resolutions over a wide temperature coverage. In order
to realize the instrument for meeting these scientific requirements
under size constraints given by the JAXA Epsilon vehicle, we examined
four-dimensional optical parameter space of possible solutions of
geometrical optical parameters such as mirror diameter, focal length,
grating magnification, and so on. As a result, we have identified
the solution space that meets the EUVST science objectives and rocket
envelope requirements. A single solution was selected and used to define
the initial optical parameters for the concept study of the baseline
architecture for defining the mission concept. For this solution, we
optimized the grating and geometrical parameters by ray tracing of the
Zemax software. Consequently, we found an optics system that fulfills
the requirement for a 0.4" angular resolution over a field of view of
100" (including margins) covering spectral ranges of 170-215, 463-542,
557-637, 690-850, 925-1085, and 1115-1275 A. This design achieves an
effective area 10 times larger than the Extreme-ultraviolet Imaging
Spectrometer onboard the Hinode satellite, and will provide seamless
observations of 4.2-7.2 log(K) plasmas for the first time. Tolerance
analyses were performed based on the optical design, and the moving
range and step resolution of focus mechanisms were identified. In
the presentation, we describe the derivation of the solution space,
optimization of the optical parameters, and show the results of ray
tracing and tolerance analyses.
---------------------------------------------------------
Title: The Solar-C_EUVST mission
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko;
Ichimoto, Kiyoshi; Suematsu, Yoshinori; Hara, Hirohisa; Katsukawa,
Yukio; Kubo, Masahito; Toriumi, Shin; Watanabe, Tetsuya; Yokoyama,
Takaaki; Korendyke, Clarence M.; Warren, Harry P.; Tarbell, Ted; De
Pontieu, Bart; Teriaca, Luca; Schühle, Udo H.; Solanki, Sami; Harra,
Louise K.; Matthews, Sarah; Fludra, A.; Auchère, F.; Andretta, V.;
Naletto, G.; Zhukov, A.
2019SPIE11118E..07S Altcode:
Solar-C EUVST (EUV High-Throughput Spectroscopic Telescope) is a
solar physics mission concept that was selected as a candidate for
JAXA competitive M-class missions in July 2018. The onboard science
instrument, EUVST, is an EUV spectrometer with slit-jaw imaging
system that will simultaneously observe the solar atmosphere from the
photosphere/chromosphere up to the corona with seamless temperature
coverage, high spatial resolution, and high throughput for the first
time. The mission is designed to provide a conclusive answer to the
most fundamental questions in solar physics: how fundamental processes
lead to the formation of the solar atmosphere and the solar wind, and
how the solar atmosphere becomes unstable, releasing the energy that
drives solar flares and eruptions. The entire instrument structure
and the primary mirror assembly with scanning and tip-tilt fine
pointing capability for the EUVST are being developed in Japan, with
spectrograph and slit-jaw imaging hardware and science contributions
from US and European countries. The mission will be launched and
installed in a sun-synchronous polar orbit by a JAXA Epsilon vehicle in
2025. ISAS/JAXA coordinates the conceptual study activities during the
current mission definition phase in collaboration with NAOJ and other
universities. The team is currently working towards the JAXA final
down-selection expected at the end of 2019, with strong support from
US and European colleagues. The paper provides an overall description
of the mission concept, key technologies, and the latest status.
---------------------------------------------------------
Title: Structure and dynamics of the hot flaring loop-top source
observed by Hinode, SDO, RHESSI, and STEREO
Authors: Lee, Kyoung-Sun; Hara, Hirohisa; Watanabe, Kyoko; Joshi,
Anand D.; Imada, Shinsuke; Brooks, David H.; Dang, Phillip; Shimizu,
Toshifumi; Savage, Sabrina
2019AAS...23421605L Altcode:
We have investigated an M1.3 flare on 2014 January 13 around
21:48 UT observed at the west limb using the Hinode, SDO, RHESSI,
and STEREO. Especially, the Hinode/EIS scanned the flaring loop
covering the loop-top region over the limb, which is a good target to
investigate the dynamics of the flaring loop with their height. Using
the multi-wavelength observations from the Hinode/EIS and SDO/AIA,
we found a very hot emission above the loop-top observed in Fe XXIV
and 131Å channel. Measuring the intensity, Doppler velocity and line
width for the flaring loop, we found that hot emission observed at
the cusp-like shape of the loop-top region which shows strong redshift
about 500 km s<SUP>-1</SUP> in Doppler velocity and strong enhancement
of the non-thermal velocity (line width enhancement) larger than 100
km s<SUP>-1</SUP>. Combining with the STEREO observation, we have
examined the 3D structure with loop tilt angle and have investigated
the velocity distribution of the loop-top region. With the loop tilt
angle, we could identify the strong redshift at the loop-top region
may indicate an up-flow along the loop-top region. From RHESSI hard
X-ray (HXR), and soft X-ray (SXR) emission, we found that the footpoint
brightening region at the beginning of the flare has a both HXR (25-50
keV) and SXR (12-25 keV) emission in which imply that the region has
non-thermal emission or accelerated particles. Then, within 10 minutes
the soft X-ray (SXR) emission observed near the cusp shape region at
loop top. The temporal variation of the HXR and SXR emissions and the
Doppler velocity variation of the hot plasma component at the loop-top
imply that the strong flow in a hot component near loop-top could be
the evaporation flows which detected at the corona along the tilted
loop. Moreover, The temporal evolution of the temperature observed
by SDO/AIA and Hinode/EIS also shows the cooling process of the flare
plasma which is consistent with the impulsively heated flare model.
---------------------------------------------------------
Title: Velocity Structure and Temperature Dependence of an
Extreme-Ultraviolet Jet Observed by Hinode
Authors: Kawai, T.; Kanda, N.; Imada, S.
2019SoPh..294...74K Altcode: 2019arXiv190410271K
The acceleration mechanism of EUV and X-ray jets is still unclear. In
general, there are two candidates for the mechanism. One is magnetic
reconnection, and the other is chromospheric evaporation. We observed
a relatively compact X-ray jet that occurred between 10:50 - 11:10 UT
on 18 February 2011 by using the Solar Dynamics Observatory/Atmospheric
Imaging Assembly, and the X-ray Telescope, Solar Optical Telescope, and
EUV Imaging Spectrometer onboard Hinode. Our results are as follows:
i) The EUV and X-ray observations show the general characteristics of
X-ray jets, such as an arcade straddling a polarity inversion line, a
jet bright point shown at one leg of the arcade, and a spire above the
arcade. ii) The multi-wavelength observations and Ca II H line image
show the existence of a low-temperature (≈ 10 000 K) plasma (i.e.,
filament) at the center of the jet. iii) In the magnetogram and Ca II
H line image, the filament exists over the polarity inversion line and
arcade is also straddling it. In addition, magnetic cancellation occurs
around the jet a few hours before and after the jet is observed. iv) The
temperature distribution of the accelerated plasma, which was estimated
from Doppler velocity maps, the calculated differential emission
measure, and synthetic spectra show that there is no clear dependence
between the plasma velocity and its temperature. For our third result,
observations indicate that magnetic cancellation is probably related
to the occurrence of the jet and filament formation. This suggests
that the trigger of the jet is magnetic cancellation rather than
flux emergence. The fourth result indicates that plasma acceleration
accompanied by an X-ray jet seems to be caused by magnetic reconnection
rather than chromospheric evaporation.
---------------------------------------------------------
Title: Revisiting Kunitomo's Sunspot Drawings During 1835 - 1836
in Japan
Authors: Fujiyama, Masashi; Hayakawa, Hisashi; Iju, Tomoya; Kawai,
Toshiki; Toriumi, Shin; Otsuji, Kenichi; Kondo, Katsuya; Watanabe,
Yusaku; Nozawa, Satoshi; Imada, Shinsuke
2019SoPh..294...43F Altcode: 2019arXiv190303092F
We revisit the sunspot drawings made by the Japanese astronomer Kunitomo
Toubei during 1835 - 1836 and recount the sunspot group number for each
image. There are two series of drawings, preliminary (P , containing
17 days with observations) and summary (S , covering 156 days with
observations), all made using brush and ink. S is a compilation of
drawings for the period from February 1835, to March 1836. Presently,
the P drawings are available only for one month, September 1835;
those of other periods have presumably been lost. Another drawing
(I ) lets us recover the raw group count (RGC) for 25 September 1836,
on which the RGC has not been registered in the existing catalogs. We
also revise the RGCs from P and S using the Zürich classification and
determine that Kunitomo's results tend to yield smaller RGCs than those
of other contemporary observers. In addition, we find that Kunitomo's
RGCs and spot areas have a correlation (0.71) that is not very different
from the contemporary observer Schwabe (0.82). Although Kunitomo's spot
areas are much larger than those determined by Schwabe due to skill and
instrument limitations, Kunitomo at least captured the growing trend
of the spot activity in the early phase of Solar Cycle 8. We also
determine the solar rotation axis to estimate the accurate position
(latitude and longitude) of the sunspot groups in Kunitomo's drawings.
---------------------------------------------------------
Title: Semiconservative reduced speed of sound technique for low
Mach number flows with large density variations
Authors: Iijima, H.; Hotta, H.; Imada, S.
2019A&A...622A.157I Altcode: 2018arXiv181204135I
Context. The reduced speed of sound technique (RSST) has been
used for efficient simulation of low Mach number flows in solar
and stellar convection zones. The basic RSST equations are
hyperbolic and are suitable for parallel computation by domain
decomposition. The application of RSST is limited to cases in which
density perturbations are much smaller than the background density. In
addition, nonconservative variables are required to be evolved using
this method, which is not suitable in cases where discontinuities such
as shock waves coexist in a single numerical domain. <BR /> Aims:
In this study, we suggest a new semiconservative formulation of the
RSST that can be applied to low Mach number flows with large density
variations. <BR /> Methods: We derive the wave speed of the original
and newly suggested methods to clarify that these methods can reduce
the speed of sound without affecting the entropy wave. The equations
are implemented using the finite volume method. Several numerical
tests are carried out to verify the suggested methods. <BR /> Results:
The analysis and numerical results show that the original RSST is not
applicable when mass density variations are large. In contrast, the
newly suggested methods are found to be efficient in such cases. We
also suggest variants of the RSST that conserve momentum in the
machine precision. The newly suggested variants are formulated as
semiconservative equations, which reduce to the conservative form of the
Euler equations when the speed of sound is not reduced. This property
is advantageous when both high and low Mach number regions are included
in the numerical domain. <BR /> Conclusions: The newly suggested forms
of RSST can be applied to a wider range of low Mach number flows.
---------------------------------------------------------
Title: Effect of Magnetic Field Strength on Solar Differential
Rotation and Meridional Circulation
Authors: Imada, S.; Fujiyama, M.
2018ApJ...864L...5I Altcode: 2018arXiv180803005I
We studied the solar surface flows (differential rotation and meridional
circulation) using a magnetic element feature tracking technique by
which the surface velocity is obtained using magnetic field data. We
used the line-of-sight magnetograms obtained by the Helioseismic
and Magnetic Imager on board the Solar Dynamics Observatory from
2010 May 01 to 2017 August 16 (Carrington rotations 2096 to 2193) and
tracked the magnetic element features every hour. Using our method, we
estimated the differential rotation velocity profile. We found rotation
velocities of ∼30 and -170 m s<SUP>-1</SUP> at latitudes of 0° and
60° in the Carrington rotation frame, respectively. Our results are
consistent with previous results obtained by other methods, such as
direct Doppler, time-distance helioseismology, or cross-correlation
analyses. We also estimated the meridional circulation velocity profile
and found that it peaked at ∼12 m s<SUP>-1</SUP> at a latitude of
45°, which is also consistent with previous results. The dependence
of the surface flow velocity on the magnetic field strength was also
studied. In our analysis, the magnetic elements with stronger and
weaker magnetic fields largely represent the characteristics of the
active region remnants and solar magnetic networks, respectively. We
found that magnetic elements with a strong (weak) magnetic field show
a faster (slower) rotation speed. On the other hand, magnetic elements
with a strong (weak) magnetic field show slower (faster) meridional
circulation velocity. These results might be related to the Sun’s
internal dynamics.
---------------------------------------------------------
Title: Electron Power-Law Spectra in Solar and Space Plasmas
Authors: Oka, M.; Birn, J.; Battaglia, M.; Chaston, C. C.; Hatch,
S. M.; Livadiotis, G.; Imada, S.; Miyoshi, Y.; Kuhar, M.; Effenberger,
F.; Eriksson, E.; Khotyaintsev, Y. V.; Retinò, A.
2018SSRv..214...82O Altcode: 2018arXiv180509278O
Particles are accelerated to very high, non-thermal energies in solar
and space plasma environments. While energy spectra of accelerated
electrons often exhibit a power law, it remains unclear how electrons
are accelerated to high energies and what processes determine the
power-law index δ . Here, we review previous observations of the
power-law index δ in a variety of different plasma environments with
a particular focus on sub-relativistic electrons. It appears that in
regions more closely related to magnetic reconnection (such as the
`above-the-looptop' solar hard X-ray source and the plasma sheet in
Earth's magnetotail), the spectra are typically soft (δ ≳4). This
is in contrast to the typically hard spectra (δ ≲4) that are
observed in coincidence with shocks. The difference implies that
shocks are more efficient in producing a larger non-thermal fraction
of electron energies when compared to magnetic reconnection. A caveat
is that during active times in Earth's magnetotail, δ values seem
spatially uniform in the plasma sheet, while power-law distributions
still exist even in quiet times. The role of magnetotail reconnection
in the electron power-law formation could therefore be confounded
with these background conditions. Because different regions have been
studied with different instrumentations and methodologies, we point
out a need for more systematic and coordinated studies of power-law
distributions for a better understanding of possible scaling laws in
particle acceleration as well as their universality.
---------------------------------------------------------
Title: Sunspot drawings by Japanese official astronomers in 1749-1750
Authors: Hayakawa, Hisashi; Iwahashi, Kiyomi; Fujiyama, Masashi;
Kawai, Toshiki; Toriumi, Shin; Hotta, Hideyuki; Iijima, Haruhisa;
Imada, Shinsuke; Tamazawa, Harufumi; Shibata, Kazunari
2018PASJ...70...63H Altcode: 2018arXiv180408614H; 2018PASJ..tmp...87H
Sunspot observations with telescopes in the 18<SUP>th</SUP> century
were carried out in Japan as well as elsewhere. One of these sunspot
observations is recorded in an account called Sansaizusetsu narabini
Kansei irai Jissoku Zusetsu (Charts of Three Worlds and Diagrams of
Actual Observations since Kansei Era). We have analyzed manuscripts
of this account to show a total of 15 sunspot drawings during
1749-1750. These observations are considered to be carried out by
contemporary official astronomers in Japan, with telescopes covered
by zongurasus (< zonglas in Dutch, corresponding to "sunglass"
in English). We counted their group number of sunspots to locate
them in long-term solar activity and show that their observations
were situated near the solar maximum in 1750. We also computed their
locations and areas, while we have to admit differences of the variant
manuscripts with one another. These observational records show the
spread of sunspot observations not only in Europe, but also in Japan,
and hence may contribute to crosscheck, or possibly to improve the
known sunspot indices.
---------------------------------------------------------
Title: Science Objectives of the Solar-C_EUVST
Authors: Imada, Shinsuke; Suematsu, Yoshinori
2018cosp...42E1542I Altcode:
Solar-C EUVST (EUV High-Throughput Spectroscopic Telescope) is
designed to comprehensively understand the energy and mass transfer
from the solar surface to the solar corona and interplanetary
space, and to investigate the elementary processes that take place
universally in cosmic plasmas. The proposed mission is a fundamental
step for answering how the plasma universe is created and evolves,
and how the Sun influences the Earth and other planets in our solar
system. The two primary science objectives for Solar-C EUVST are : I)
Understand how fundamental processes lead to the formation of the solar
atmosphere and the solar wind, II) Understand how the solar atmosphere
becomes unstable, releasing the energy that drives solar flares and
eruptions. Solar-C EUVST will, A) seamlessly observe all the temperature
regimes of the solar atmosphere from the chromosphere to the corona at
the same time, B) resolve elemental structures of the solar atmosphere
with high spatial resolution and cadence to track their evolution,
and C) obtain spectroscopic information on the dynamics of elementary
processes taking place in the solar atmosphere. In this talk, we will
first discuss the science target of the Solar-C EUVST, and discuss the
science topic associated flare in detail. Photospheric motions lead to
the accumulation of free magnetic energy in the corona. This system
eventually becomes unstable, releasing the energy through magnetic
reconnection. This process of energy conversion heats the plasma to
high temperatures and drives coronal mass ejections (CMEs). By measuring
the properties of multi-temperature flaring plasma, Solar-C EUVST will
investigate why the reconnection is fast despite the high magnetic
Reynolds number. It will also monitor the temporal evolution of solar
active regions and identify the triggering mechanism for the flare
and eruption. Therefore two important science objectives are defined
for the flare physics. The first objective is "Understand the Fast
Magnetic Reconnection Process". Magnetic reconnection is one of the
fundamental processes for converting magnetic energy into the thermal
and kinetic energy of the plasma. This process occurs much faster
than is predicted by classical theory. Solar-C EUVST will observe the
dynamics of magnetic structures to understand the mechanisms that lead
to fast magnetic reconnection in partially or fully ionized plasmas. The
second objective is "Identify the Signatures of Global Energy Buildup
and the Local Triggering of the Flare and Eruption". Understanding the
accumulation and release of free magnetic energy in the corona is a
fundamental problem. Solar-C EUVST will perform long-term monitoring
of active regions to identify the signatures of energy buildup and
high-resolution observations to understand the triggers of energy
release.
---------------------------------------------------------
Title: First Ten Years of Hinode Solar On-Orbit Observatory
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kubo, Masahito
2018ASSL..449.....S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Origin of the Solar Wind
Authors: Lee, Kyoung-Sun; Brooks, David H.; Imada, Shinsuke
2018ASSL..449...95L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Thermal Non-equilibrium Plasma Observed by Hinode
Authors: Imada, Shinsuke
2018ASSL..449..221I Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Statistical and observational research of solar flare for
total spectra and geometrical features
Authors: Nishimoto, S.; Watanabe, K.; Imada, S.; Kawate, T.; Lee, K. S.
2017AGUFMSH41A2749N Altcode:
Impulsive energy release phenomena such as solar flares, sometimes
affect to the solar-terrestrial environment. Usually, we use soft X-ray
flux (GOES class) as the index of flare scale. However, the magnitude of
effect to the solar-terrestrial environment is not proportional to that
scale. To identify the relationship between solar flare phenomena and
influence to the solar-terrestrial environment, we need to understand
the full spectrum of solar flares. There is the solar flare irradiance
model named the Flare Irradiance Spectral Model (FISM) (Chamberlin et
al., 2006, 2007, 2008). The FISM can estimate solar flare spectra with
high wavelength resolution. However, this model can not express the
time evolution of emitted plasma during the solar flare, and has low
accuracy on short wavelength that strongly effects and/or controls the
total flare spectra. For the purpose of obtaining the time evolution
of total solar flare spectra, we are performing statistical analysis
of the electromagnetic data of solar flares. In this study, we select
solar flare events larger than M-class from the Hinode flare catalogue
(Watanabe et al., 2012). First, we focus on the EUV emission observed
by the SDO/EVE. We examined the intensities and time evolutions of
five EUV lines of 55 flare events. As a result, we found positive
correlation between the "soft X-ray flux" and the "EUV peak flux" for
all EVU lines. Moreover, we found that hot lines peaked earlier than
cool lines of the EUV light curves. We also examined the hard X-ray
data obtained by RHESSI. When we analyzed 163 events, we found good
correlation between the "hard X-ray intensity" and the "soft X-ray
flux". Because it seems that the geometrical features of solar flares
effect to those time evolutions, we also looked into flare ribbons
observed by SDO/AIA. We examined 21 flare events, and found positive
correlation between the "GOES duration" and the "ribbon length". We
also found positive correlation between the "ribbon length" and the
"ribbon distance", however, there was no remarkable correlation of
the "ribbon width". To understand physical process of flare emission,
we performed numerical simulation (Imada et al., 2015), and compared
with the observational flare model. We also discuss the flare numerical
model which can be fitted to the observational flare model.
---------------------------------------------------------
Title: Investigation of the magnetic neutral line region with the
frame of two-fluid equations: A possibility of anomalous resistivity
inferred from MMS observations
Authors: Kobayashi, Y.; Kitamura, N.; Ieda, A.; Yoshizumi, M.; Imada,
S.; Tsugawa, Y.; Burch, J. L.; Russell, C. T.; Moore, T. E.; Giles,
B. L.; Paterson, W.; Torbert, R. B.; Ergun, R.; Saito, Y.; Yokota,
S.; Machida, S.
2017AGUFMSM13B2355K Altcode:
Magnetic reconnection is a basic physical process by which energy of
magnetic field is converted into the kinetic energy of plasmas. In
recent years, MMS missionconsisting of four spacecraft has been
conducted aiming at elucidating the physical mechanism of merging
themagnetic fields in the vicinity of the magnetic neutral linethat
exists in the central part of the structure. In this paper, we examine
the magnetic field frozen-in relation near the magnetic neutral line
as well as the causal relationship between electron and ion dynamics
in the frame of two fluid equations.Theoretically, it is shown that
electrons are frozen-in to the magnetic fields while ion's frozen-in
relation is broken in the ion dissipation region. However, when we
examined the observational data around 1307 UT on October 16, 2015 when
MMS spacecraft passed through the vicinity of the magnetic neutral line
[Burch et al., Science 2016] , it was confirmed that the frozen-ion
relation was not established for electrons in the ion dissipation
region. In addition, we found that intense wave electric fields in
this region. From the spectral analysis of the waves, it turned out
that their characteristic frequencies are the lower-hybrid and electron
cyclotron frequencies.In the framework of the two-fluid equation, we can
evaluate the values of each term of the equations of motion for both
ions and electrons except for the collision term from MMS spacecraft
data. Therefore, it is possible to obtain collision terms for both
species. Since magnetospheric plasma is basically collisionless, it
is considered that the collision term is due to anomalous resistivity
associated with the excited waves . On the other hand, in the two-fluid
equation system, the two vectors corresponding to the collision terms
of ions and electrons have the same absolute value. Because the force
exerted between the two is the internal force, they should face in
the opposite direction. However, the vectors corresponding to the
collision terms obtained by using the actual data did not satisfy
such a condition. One of the possible reasons is that the momentum
carried by the waves cannot be neglected. After careful examination,
we conclude that the effect of the anomalous resistivity in the ion
dissipation region acts to some degree that cannot be ignored in the
equation of motion of the two-fluid system.
---------------------------------------------------------
Title: Non-thermal Power-Law Distributions in Solar and Space Plasmas
Authors: Oka, M.; Battaglia, M.; Birn, J.; Chaston, C. C.; Effenberger,
F.; Eriksson, E.; Fletcher, L.; Hatch, S.; Imada, S.; Khotyaintsev,
Y. V.; Kuhar, M.; Livadiotis, G.; Miyoshi, Y.; Retino, A.
2017AGUFMSH51C2518O Altcode:
Particles are accelerated to very high, non-thermal energies in solar
and space plasma environments. While energy spectra of accelerated
particles often exhibit a power-law and are characterized by the
power-law index δ, it remains unclear how particles are accelerated
to high energies and how δ is determined. Here, we review previous
observations of the power-law index δ in a variety of different plasma
environments with a particular focus on sub-relativistic electrons. It
appears that in regions more closely related to magnetic reconnection
(such as the "above-the-looptop" solar hard X-ray source and the plasma
sheet in Earth's magnetotail), the spectra are typically soft (δ>
4). This is in contrast to the typically hard spectra (δ< 4)
that are observed in coincidence with shocks. The difference implies
that shocks are more efficient in producing a larger fraction of
non-thermal electron energies than magnetic reconnection. A caveat
is that during active times in Earth's magnetotail, δ values seem
spatially uniform in the plasma sheet, while power-law distributions
still exist even in quiet times. The role of magnetotail reconnection
in the electron power-law formation could therefore be confounded
with these background conditions. Because different regions have been
studied with different instrumentations and methodologies, we point
out a need for more systematic and coordinated studies of power-law
distributions for a better understanding of possible scaling laws in
particle acceleration as well as their universality.
---------------------------------------------------------
Title: Cosmic Ray Modulation and Radiation Dose of Aircrews During
Possible Grand Minimum
Authors: Miyake, S.; Kataoka, R.; Sato, T.; Imada, S.; Miyahara, H.;
Shiota, D.; Matsumoto, T.; Ueno, H.
2017AGUFMSH53A2556M Altcode:
The Sun is exhibiting low solar activity levels since the descending
phase of the last solar cycle, and it is likely to be continued as
well as in the case of the past grand solar minima. The cosmic-ray
modulation, which is the variation of the galactic cosmic ray (GCR)
spectrum caused by the heliospheric environmental change, is basically
anti-correlated with the solar activity. In the recent weak solar cycle,
we thus expect that the flux of GCRs is getting higher than that in
the previous solar cycles, leading to the increase in the radiation
exposure in the space and atmosphere. In order to quantitatively
evaluate the possible solar modulation of GCRs and resultant radiation
exposure at flight altitude, we have developed the time-dependent and
three-dimensional model of the cosmic-ray modulation. Our model can give
the flux of GCRs anywhere in the heliosphere by assuming the variation
of the solar wind speed, the strength of the heliospheric magnetic field
(HMF), and its tilt angle. We solve the gradient-curvature drift motion
of GCRs in the HMF, and therefore reproduce the 22-year variation
of the cosmic-ray modulation. We also calculate the neutron monitor
counting rate and the radiation dose of aircrews at flight altitude,
by the air-shower simulation performed by PHITS (Particle and Heavy
Ion Transport code System). In our previous study [1], we calculated
the radiation dose at a flight altitude during the coming solar cycle
by assuming the variation of the solar wind speed and the strength of
the HMF expressed by sinusoidal curve, and obtained that an annual
radiation dose of aircrews in 5 years around the next solar minimum
will be up to 19% higher than that at the last cycle. In this study, we
predict the new model of the heliospheric environmental change on the
basis of a prediction model for the sunspot number. The quantitative
predictions of the cosmic-ray modulation and the radiation dose at
a flight altitude during possible Grand Minimum considering the new
model for the heliospheric environmental change will be presented at
the meeting. [1] S. Miyake, R. Kataoka, and T. Sato, Space Weather,
15, 589-605, 2017.
---------------------------------------------------------
Title: Solar Surface Velocity in the Large Scale estimated by Magnetic
Element Tracking Method
Authors: Fujiyama, M.; Imada, S.; Iijima, H.; Machida, S.
2017AGUFMSH13A2474F Altcode:
The 11years variation in the solar activity is one of the
important sources of decadal variation in the solar-terrestrial
environment. Therefore, predicting the solar cycle activity is crucial
for the space weather. To build the prediction schemes for the next
solar cycle is a key for the long-term space weather study. Recently,
the relationship between polar magnetic field at the solar minimum
and next solar cycle activity is intensively discussed. Nowadays,
many people believe that the polar magnetic field at the solar minimum
is one of the best predictor for the next solar cycle. To estimate
polar magnetic field, Surface Flux Transport (SFT) model have been
often used. On the other hand, SFT model needs several parameters,
for example Meridional circulation, differential rotation, turbulent
diffusion etc.. So far, those parameters have not been fully understood,
and their uncertainties may affect the accuracy of the prediction. In
this study, we try to discuss the parameters which are used in
SFT model. We focus on two kinds of the solar surface motions,
Differential rotation and Meridional circulation. First, we have
developed Magnetic Element Tracking (MET) module, which is able to
obtain the surface velocity by using the magnetic field data. We have
used SOHO/MDI and SDO/HMI for the magnetic field data. By using MET,
we study the solar surface motion over 2 cycle (nearly 24 years), and
we found that the velocity variation is related to the active region
belt. This result is consistent with [Hathaway et al., 2011]. Further,
we apply our module to the Hinode/SOT data which spatial resolution
is high. Because of its high resolution, we can discuss the surface
motion close to the pole which has not been discussed enough. Further,
we discuss the relationship between the surface motion and the magnetic
field strength and the location of longitude.
---------------------------------------------------------
Title: Improvement of solar-cycle prediction: Plateau of solar axial
dipole moment
Authors: Iijima, H.; Hotta, H.; Imada, S.; Kusano, K.; Shiota, D.
2017A&A...607L...2I Altcode: 2017arXiv171006528I
<BR /> Aims: We report the small temporal variation of the axial dipole
moment near the solar minimum and its application to the solar-cycle
prediction by the surface flux transport (SFT) model. <BR /> Methods:
We measure the axial dipole moment using the photospheric synoptic
magnetogram observed by the Wilcox Solar Observatory (WSO), the ESA/NASA
Solar and Heliospheric Observatory Michelson Doppler Imager (MDI), and
the NASA Solar Dynamics Observatory Helioseismic and Magnetic Imager
(HMI). We also use the SFT model for the interpretation and prediction
of the observed axial dipole moment. <BR /> Results: We find that the
observed axial dipole moment becomes approximately constant during
the period of several years before each cycle minimum, which we call
the axial dipole moment plateau. The cross-equatorial magnetic flux
transport is found to be small during the period, although a significant
number of sunspots are still emerging. The results indicate that the
newly emerged magnetic flux does not contribute to the build up of
the axial dipole moment near the end of each cycle. This is confirmed
by showing that the time variation of the observed axial dipole moment
agrees well with that predicted by the SFT model without introducing new
emergence of magnetic flux. These results allow us to predict the axial
dipole moment at the Cycle 24/25 minimum using the SFT model without
introducing new flux emergence. The predicted axial dipole moment at
the Cycle 24/25 minimum is 60-80 percent of Cycle 23/24 minimum, which
suggests the amplitude of Cycle 25 is even weaker than the current
Cycle 24. <BR /> Conclusions: The plateau of the solar axial dipole
moment is an important feature for the longer-term prediction of the
solar cycle based on the SFT model.
---------------------------------------------------------
Title: Multi-Wavelength Spectroscopic Observations of a White Light
Flare Produced Directly by Non-thermal Electrons
Authors: Lee, Kyoung-Sun; Imada, Shinsuke; Watanabe, Kyoko; Bamba,
Yumi; Brooks, David
2017SPD....4810806L Altcode:
An X1.6 flare on 2014 October 22 was observed by multiple
spectrometers in UV, EUV and X-ray (Hinode/EIS, IRIS, and RHESSI),
and multi-wavelength imaging observations (SDO/AIA and HMI). We
analyze a bright kernel that produces a white light (WL) flare with
continuum enhancement and a hard X-ray (HXR) peak. Taking advantage of
the spectroscopic observations of IRIS and Hinode/EIS, we measure the
temporal variation of the plasma properties in the bright kernel in
the chromosphere and corona. We find that explosive evaporation was
observed when the WL emission occurred. The temporal correlation of
the WL emission, HXR peak, and evaporation flows indicates that the
WL emission was produced by accelerated electrons. We calculated the
energy flux deposited by non-thermal electrons (observed by RHESSI) and
compared it to the dissipated energy estimated from a chromospheric
line (Mg II triplet) observed by IRIS. The deposited energy flux
from the non-thermal electrons is about (3-7.7)x10<SUP>10</SUP> erg
cm<SUP>-2</SUP> s<SUP>-1</SUP> for a given low-energy cutoff of 30-40
keV, assuming the thick-target model. The energy flux estimated from
the changes in temperature in the chromosphere measured using the Mg II
subordinate line is about (4.6-6.7)×10<SUP>9</SUP> erg cm<SUP>-2</SUP>
s<SUP>-1</SUP>: ∼6%-22% of the deposited energy. This comparison
of estimated energy fluxes implies that the continuum enhancement was
directly produced by the non-thermal electrons.
---------------------------------------------------------
Title: Detection of Heating Processes in Coronal Loops by Soft
X-ray Spectroscopy
Authors: Kawate, Tomoko; Narukage, Noriyuki; Ishikawa, Shin-nosuke;
Imada, Shinsuke
2017SPD....4810615K Altcode:
Imaging and Spectroscopic observations in the soft X-ray band will open
a new window of the heating/acceleration/transport processes in the
solar corona. The soft X-ray spectrum between 0.5 and 10 keV consists
of the electron thermal free-free continuum and hot coronal lines such
as O VIII, Fe XVII, Mg XI, Si XVII. Intensity of free-free continuum
emission is not affected by the population of ions, whereas line
intensities especially from highly ionized species have a sensitivity of
the timescale of ionization/recombination processes. Thus, spectroscopic
observations of both continuum and line intensities have a capability of
diagnostics of heating/cooling timescales. We perform a 1D hydrodynamic
simulation coupled with the time-dependent ionization, and calculate
continuum and line intensities under different heat input conditions
in a coronal loop. We also examine the differential emission measure
of the coronal loop from the time-integrated soft x-ray spectra. As a
result, line intensity shows a departure from the ionization equilibrium
and shows different responses depending on the frequency of the heat
input. Solar soft X-ray spectroscopic imager will be mounted in the
sounding rocket experiment of the Focusing Optics X-ray Solar Imager
(FOXSI). This observation will deepen our understanding of heating
processes to solve the “coronal heating problem”.
---------------------------------------------------------
Title: Predicting Solar Cycle 25 using Surface Flux Transport Model
Authors: Imada, Shinsuke; Iijima, Haruhisa; Hotta, Hideyuki; Shiota,
Daiko; Kusano, Kanya
2017SPD....4811106I Altcode:
It is thought that the longer-term variations of the solar activity
may affect the Earth’s climate. Therefore, predicting the next
solar cycle is crucial for the forecast of the “solar-terrestrial
environment”. To build prediction schemes for the next solar
cycle is a key for the long-term space weather study. Recently, the
relationship between polar magnetic field at the solar minimum and
next solar activity is intensively discussed. Because we can determine
the polar magnetic field at the solar minimum roughly 3 years before
the next solar maximum, we may discuss the next solar cycle 3years
before. Further, the longer term (~5 years) prediction might be
achieved by estimating the polar magnetic field with the Surface Flux
Transport (SFT) model. Now, we are developing a prediction scheme
by SFT model as a part of the PSTEP (Project for Solar-Terrestrial
Environment Prediction) and adapting to the Cycle 25 prediction. The
predicted polar field strength of Cycle 24/25 minimum is several
tens of percent smaller than Cycle 23/24 minimum. The result suggests
that the amplitude of Cycle 25 is weaker than the current cycle. We
also try to obtain the meridional flow, differential rotation,
and turbulent diffusivity from recent modern observations (Hinode
and Solar Dynamics Observatory). These parameters will be used in
the SFT models to predict the polar magnetic fields strength at the
solar minimum. In this presentation, we will explain the outline of
our strategy to predict the next solar cycle and discuss the initial
results for Cycle 25 prediction.
---------------------------------------------------------
Title: White paper of the "soft X-ray imaging spectroscopy"
Authors: Narukage, Noriyuki; Ishikawa, Shin-nosuke; Kawate, Tomoko;
Imada, Shinsuke; Sakao, Taro
2017arXiv170604536N Altcode:
The solar corona is full of dynamic phenomena, e.g., solar flares,
micro flares in active regions, jets in coronal holes and in the polar
regions, X-ray bright points in quiet regions, etc. They are accompanied
by interesting physical processes, namely, magnetic reconnection,
particle acceleration, shocks, waves, flows, evaporation, heating,
cooling, and so on. The understandings of these phenomena and processes
have been progressing step-by-step with the evolution of the observation
technology in EUV and X-rays from the space. But, there are fundamental
questions remain unanswered, or haven't even addressed so far. Our
scientific objective is to understand underlying physics of dynamic
phenomena in the solar corona, covering some of the long-standing
questions in solar physics such as particle acceleration in flares
and coronal heating. In order to achieve these science objectives,
we identify the imaging spectroscopy (the observations with spatial,
temporal and energy resolutions) in the soft X-ray range (from ~0.5
keV to ~10 keV) is a powerful approach for the detection and analysis
of energetic events.
---------------------------------------------------------
Title: Study on Precursor Activity of the X1.6 Flare in the Great
AR 12192 with SDO, IRIS, and Hinode
Authors: Bamba, Yumi; Lee, Kyoung-Sun; Imada, Shinsuke; Kusano, Kanya
2017ApJ...840..116B Altcode: 2017arXiv170405158B
The physical properties and their contribution to the onset of a solar
flare are still uncleare even though chromospheric brightening is
considered a precursor phenomenon of a flare. Many studies suggested
that photospheric magnetic field changes cause destabilization of
large-scale coronal structure. We aim to understand how a small
photospheric change contributes to a flare and to reveal how the
intermediary chromosphere behaves in the precursor phase. We analyzed
the precursor brightening of the X1.6 flare on 2014 October 22 in
the AR 12192 using the Interface Region Imaging Spectrograph (IRIS)
and Hinode/EUV Imaging Spectrometer (EIS) data. We investigated a
localized jet with the strong precursor brightening, and compared the
intensity, Doppler velocity, and line width in C II, Mg II k, and Si
IV lines by IRIS and He II, Fe xii, and Fe xv lines by Hinode/EIS. We
also analyzed the photospheric magnetic field and chromospheric/coronal
structures using the Solar Dynamics Observatory (SDO)/Helioseismic and
Magnetic Imager and Atmospheric Imaging Assembly. We found a significant
blueshift (∼100 km s<SUP>-1</SUP>), which is related to the strong
precursor brightening over a characteristic magnetic field structure,
and the blueshift was observed at all of the temperatures. This might
indicate that the flow is accelerated by Lorentz force. Moreover, the
large-scale coronal loop that connects the foot points of the flare
ribbons was destabilized just after the precursor brightening with the
blueshift. It suggests that magnetic reconnection locally occurred in
the lower chromosphere and it triggered magnetic reconnection of the
X1.6 flare in the corona.
---------------------------------------------------------
Title: IRIS, Hinode, SDO, and RHESSI Observations of a White Light
Flare Produced Directly by Nonthermal Electrons
Authors: Lee, Kyoung-Sun; Imada, Shinsuke; Watanabe, Kyoko; Bamba,
Yumi; Brooks, David H.
2017ApJ...836..150L Altcode: 2017arXiv170106286L
An X1.6 flare occurred in active region AR 12192 on 2014 October 22
at 14:02 UT and was observed by Hinode, IRIS, SDO, and RHESSI. We
analyze a bright kernel that produces a white light (WL) flare with
continuum enhancement and a hard X-ray (HXR) peak. Taking advantage
of the spectroscopic observations of IRIS and Hinode/EIS, we measure
the temporal variation of the plasma properties in the bright kernel
in the chromosphere and corona. We find that explosive evaporation
was observed when the WL emission occurred, even though the intensity
enhancement in hotter lines is quite weak. The temporal correlation of
the WL emission, HXR peak, and evaporation flows indicates that the WL
emission was produced by accelerated electrons. To understand the WL
emission process, we calculated the energy flux deposited by non-thermal
electrons (observed by RHESSI) and compared it to the dissipated
energy estimated from a chromospheric line (Mg II triplet) observed
by IRIS. The deposited energy flux from the non-thermal electrons is
about (3-7.7) × 10<SUP>10</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>
for a given low-energy cutoff of 30-40 keV, assuming the thick-target
model. The energy flux estimated from the changes in temperature in
the chromosphere measured using the Mg II subordinate line is about
(4.6-6.7) × 10<SUP>9</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>:
∼6%-22% of the deposited energy. This comparison of estimated energy
fluxes implies that the continuum enhancement was directly produced
by the non-thermal electrons.
---------------------------------------------------------
Title: UV/EUV High-Throughput Spectroscopic Telescope: A Next
Generation Solar Physics Mission white paper
Authors: Imada, S.; Shimizu, T.; Kawate, T.; Hara, H.; Watanabe, T.
2017arXiv170104972I Altcode:
The origin of the activity in the solar corona is a long-standing
problem in solar physics. Recent satellite observations, such as Hinode,
Solar Dynamics Observatory (SDO), Interface Region Imaging Spectrograph
(IRIS), show the detail characteristics of the solar atmosphere and
try to reveal the energy transfer from the photosphere to the corona
through the magnetic fields and its energy conversion by various
processes. However, quantitative estimation of energy transfer along
the magnetic field is not enough. There are mainly two reason why it is
difficult to observe the energy transfer from photosphere to corona; 1)
spatial resolution gap between photosphere (a few 0.1 arcsec) and corona
(a few arcsec), 2) lack in temperature coverage. Furthermore, there
is not enough observational knowledge of the physical parameters in
the energy dissipation region. There are mainly three reason why it is
difficult to observe in the vicinity of the energy dissipation region;
1) small spatial scale, 2) short time scale, 3) low emission. It is
generally believed that the energy dissipation occurs in the very small
scale and its duration is very short (10 second). Further, the density
in the dissipation region might be very low. Therefore, the high spatial
and temporal resolution UV/EUV spectroscopic observation with wide
temperature coverage is crucial to estimate the energy transport from
photosphere to corona quantitatively and diagnose the plasma dynamics
in the vicinity of the energy dissipation region. Main Science Target
for the telescope is quantitative estimation for the energy transfer
from the photosphere to the corona, and clarification of the plasma
dynamics in the vicinity of the energy dissipation region, where is the
key region for coronal heating, solar wind acceleration, and/or solar
flare, by the high spatial and temporal resolution UV/EUV spectroscopy.
---------------------------------------------------------
Title: Structures of the Hall magnetic field in the dayside magnetic
reconnection inferred from Geotail data
Authors: Tanaka, R.; Machida, S.; Uchino, H.; Imada, S.; Miyoshi,
Y.; Seki, K.; Ieda, A.; Miyashita, Y.; Keika, K.; Saito, Y.
2016AGUFMSM13A2184T Altcode:
Using Geotail data, we have investigated the magnetic reconnection
structure at the dayside magnetopause. In the magnetotail, symmetric
reconnection generally occurs, since upstream conditions are almost
the same on the northern and southern sides. On the other hand, at the
dayside magnetopause, asymmetric reconnection tends to occurs, since
magnetospheric and solar wind plasmas have different conditions. In
addition, while magnetotail reconnection has a quadrupole structure of
the magnetic field produced by the Hall effect, dayside reconnection
has basically a dipole structure. In the present study we selected
26 dayside reconnection events, based on simultaneous sign reversals
of the ion outflow velocity and the magnetic field observed by Geotail
from year 1994 to 2014. We find that the reconnection events have either
quadrupole or dipole structure in the duskward magnetic field component
(By). We further investigated the magnetic field structure near the
neutral line by analyzing changes in the ion density and magnetic field
when Geotail passed near the neutral line. In the quadrupole-structure
cases, the ratio of the ion density in the magnetosheath to that
at the magnetopause is 7.5 on average, and the ratio of Bz at the
magnetopause to |Bz| in the magnetosheath is 1.5. On the other hand,
in the dipole-structure cases, the average ion density ratio is 36.1,
and the average magnetic field intensity ratio is 2.7. These values
are greater than those for the quadrupole structure. These results
indicate that dayside reconnection has the dipole structure in the
Hall magnetic field when density asymmetry is large and the electron
flux from the magnetosheath is much larger than that from the dayside
magnetosphere. In the dipole structure, the Hall current flows along
the separatrix toward and away from the diffusion region on the
magnetosheath and magnetospheric sides, respectively.
---------------------------------------------------------
Title: Hinode and IRIS Observations of the Magnetohydrodynamic Waves
Propagating from the Photosphere to the Chromosphere in a Sunspot
Authors: Kanoh, Ryuichi; Shimizu, Toshifumi; Imada, Shinsuke
2016ApJ...831...24K Altcode: 2016arXiv160803910K
Magnetohydrodynamic (MHD) waves have been considered as energy
sources for heating the solar chromosphere and the corona. Although
MHD waves have been observed in the solar atmosphere, there are a
lack of quantitative estimates on the energy transfer and dissipation
in the atmosphere. We performed simultaneous Hinode and Interface
Region Imaging Spectrograph observations of a sunspot umbra to
derive the upward energy fluxes at two different atmospheric layers
(photosphere and lower transition region) and estimate the energy
dissipation. The observations revealed some properties of the observed
periodic oscillations in physical quantities, such as their phase
relations, temporal behaviors, and power spectra, making a conclusion
that standing slow-mode waves are dominant at the photosphere with
their high-frequency leakage, which is observed as upward waves at
the chromosphere and the lower transition region. Our estimates of
upward energy fluxes are 2.0× {10}<SUP>7</SUP> erg cm<SUP>-2</SUP>
s<SUP>-1</SUP> at the photospheric level and 8.3× {10}<SUP>4</SUP>
erg cm<SUP>-2</SUP> s<SUP>-1</SUP> at the lower transition region
level. The difference between the energy fluxes is larger than the
energy required to maintain the chromosphere in the sunspot umbrae,
suggesting that the observed waves can make a crucial contribution to
the heating of the chromosphere in the sunspot umbrae. In contrast,
the upward energy flux derived at the lower transition region level is
smaller than the energy flux required for heating the corona, implying
that we may need another heating mechanism. We should, however, note
a possibility that the energy dissipated at the chromosphere might be
overestimated because of the opacity effect.
---------------------------------------------------------
Title: Quantitative estimation of the energy flux during an explosive
chromospheric evaporation in a white light flare kernel observed by
Hinode, IRIS, SDO, and RHESSI
Authors: Lee, Kyoung-Sun; Imada, Shinsuke; Kyoko, Watanabe; Bamba,
Yumi; Brooks, David H.
2016usc..confE..77L Altcode:
An X1.6 flare occurred at the AR 12192 on 2014 October 22 at14:02 UT was
observed by Hinode, IRIS, SDO, and RHESSI. We analyze a bright kernel
which produces a white light (WL) flare with continuum enhancement
and a hard X-ray (HXR) peak. Taking advantage of the spectroscopic
observations of IRIS and Hinode/EIS, we measure the temporal variation
of the plasma properties in the bright kernel in the chromosphere and
corona. We found that explosive evaporation was observed when the WL
emission occurred, even though the intensity enhancement in hotter lines
is quite weak. The temporal correlation of the WL emission, HXR peak,
and evaporation flows indicate that the WL emission was produced by
accelerated electrons. To understand the white light emission processes,
we calculated the deposited energy flux from the non-thermal electrons
observed by RHESSI and compared it to the dissipated energy estimated
from the chromospheric line (Mg II triplet) observed by IRIS. The
deposited energy flux from the non-thermal electrons is about 3.1 ×
1010erg cm-2 s-1 when we consider a cut-off energy 20 keV. The estimated
energy flux from the temperature changes in the chromosphere measured
from the Mg II subordinate line is about 4.6-6.7×109erg cm-2 s-1,
∼ 15-22% of the deposited energy. By comparison of these estimated
energy fluxes we conclude that the continuum enhancement was directly
produced by the non-thermal electrons.
---------------------------------------------------------
Title: Project for Solar-Terrestrial Environment Prediction (PSTEP):
Towards Predicting Next Solar Cycle
Authors: Imada, S.; Iijima, H.; Hotta, H.; Shiota, D.; Kanou, O.;
Fujiyama, M.; Kusano, K.
2016usc..confE..83I Altcode:
It is believed that the longer-term variations of the solar activity can
affect the Earth's climate. Therefore, predicting the next solar cycle
is crucial for the forecast of the "solar-terrestrial environment". To
build prediction schemes for the activity level of the next solar cycle
is a key for the long-term space weather study. Although three-years
prediction can be almost achieved, the prediction of next solar cycle
is very limited, so far. We are developing a five-years prediction
scheme by combining the Surface Flux Transport (SFT) model and the
most accurate measurements of solar magnetic fields as a part of the
PSTEP (Project for Solar-Terrestrial Environment Prediction),. We
estimate the meridional flow, differential rotation, and turbulent
diffusivity from recent modern observations (Hinode and Solar Dynamics
Observatory). These parameters are used in the SFT models to predict
the polar magnetic fields strength at the solar minimum. In this
presentation, we will explain the outline of our strategy to predict
the next solar cycle. We also report the present status and the future
perspective of our project.
---------------------------------------------------------
Title: Boosting magnetic reconnection by viscosity and thermal
conduction
Authors: Minoshima, Takashi; Miyoshi, Takahiro; Imada, Shinsuke
2016PhPl...23g2122M Altcode: 2016arXiv160702839M
Nonlinear evolution of magnetic reconnection is investigated by means of
magnetohydrodynamic simulations including uniform resistivity, uniform
viscosity, and anisotropic thermal conduction. When viscosity exceeds
resistivity (the magnetic Prandtl number P <SUB>r m</SUB> > 1 ), the
viscous dissipation dominates outflow dynamics and leads to the decrease
in the plasma density inside a current sheet. The low-density current
sheet supports the excitation of the vortex. The thickness of the vortex
is broader than that of the current for P <SUB>r m</SUB> > 1 . The
broader vortex flow more efficiently carries the upstream magnetic
flux toward the reconnection region, and consequently, boosts the
reconnection. The reconnection rate increases with viscosity provided
that thermal conduction is fast enough to take away the thermal energy
increased by the viscous dissipation (the fluid Prandtl number Pr <
1). The result suggests the need to control the Prandtl numbers for
the reconnection against the conventional resistive model.
---------------------------------------------------------
Title: A Comparative Study of Confined and Eruptive Solar Flares
using Microwave Observations
Authors: Yashiro, S.; Akiyama, S.; Masuda, S.; Shimojo, M.; Asai,
A.; Imada, S.; Gopalswamy, N.
2015AGUFMSH43B2447Y Altcode:
It is well known that about 10% X-class solar flares are not associated
with coronal mass ejections (CMEs). These flares are referred to
as confined flares, which are not associated with mass or energetic
particles leaving the Sun. However, electrons are accelerated to MeV
energies as indicated by the presence of microwave emission with a
turnover frequency of ~15 GHz (Gopalswamy et al. 2009, IAU Symposium
257, p. 283). In this paper, we extend the study of confined flares to
lower soft X-ray flare sizes (M and above) that occurred in the time
window of the Nobeyama Radioheliograph (NoRH). We also make use of the
microwave spectral information from the Nobeyama Radio Polarimeters
(NoRP). During 1996 - 2014, NoRH and NoRP observed 663 flares with
size M1.0 or larger. Using the CME observations made by SOHO/LASCO
and STEREO/SECCHI, we found 215 flares with definite CME association
(eruptive flares) and 202 flares that definitely lacked CMEs (confined
flares). The remaining 146 flares whose CME association is unclear are
excluded from the analysis. We examined the peak brightness temperature
and the spatial size obtained by NoRH. Although there is a large
overlap between the two populations in these properties, we found
that microwave sources with the largest spatial extent and highest
brightness temperature are associated with eruptive flares. Spectral
analysis using NoRP data showed a tendency that more confined flares
had higher turnover frequency (≥17 GHz). We also compare the NoRH
images with the photospheric magnetograms to understand the difference
in the magnetic structure of the two types of flare sources.
---------------------------------------------------------
Title: Modeling of magnetically confined plasma in hot coronal loops
Authors: Asgari-Targhi, M.; Imada, S.; Schmelz, J. T.
2015AGUFMSH13C2452A Altcode:
In this talk, we present results of three-dimensional MHD modeling
for the Alfvén wave turbulence within loops with high temperatures
⩾ 5 MK. One of our findings is that for the Alfvén waves to create
enough turbulence to heat the loops in the core of the active region,
the footpoint velocity must be 5-6 km/s. We also present the results of
the non-thermal line broadenings in these loops and draw a comparison
between the observations and modeling.
---------------------------------------------------------
Title: Energetic ion acceleration during magnetic reconnection in
the Earth's magnetotail
Authors: Imada, Shinsuke; Hirai, Mariko; Hoshino, Masahiro
2015EP&S...67..203I Altcode:
In this paper, we present a comprehensive study of the energetic ion
acceleration during magnetic reconnection in the Earth's magnetosphere
using the Geotail data. A clear example of the energetic ion
acceleration up to 1 MeV around an X-type neutral line is shown. We
find that the energetic ions are localized at far downstream
of reconnection outflow. The time variation of energetic ion and
electron is almost the same. We observe ∼100 keV ions over the entire
observation period. We study ten events in which the Geotail satellite
observed in the vicinity of diffusion region in order to understand
the reconnection characteristics that determine the energetic ion
acceleration efficiency. We find that the reconnection electric field,
total amount of reduced magnetic energy, reconnection rate, satellite
location in the Earth's magnetosphere (both X <SUB>GSM</SUB> and Y
<SUB>GSM</SUB>) show high correlation with energetic ion acceleration
efficiency. Also, ion temperature, electron temperature, ion/electron
temperature ratio, current sheet thickness, and electric field normal to
the neutral sheet show low correlation. We do not find any correlation
with absolute value of outflow velocity and current density parallel
to magnetic field. The energetic ion acceleration efficiency is well
correlated with large-scale parameters (e.g., total amount of reduced
magnetic energy and satellite location), whereas the energetic electron
acceleration efficiency is correlated with small-scale parameters
(e.g., current sheet thickness and electric field normal to the neutral
sheet). We conclude that the spatial size of magnetic reconnection is
important for energetic ion acceleration in the Earth's magnetotail.
---------------------------------------------------------
Title: High-energy ions produced by two approaching flow fronts in
the magnetotail
Authors: Uchino, H.; Ieda, A.; Machida, S.; Imada, S.
2015AGUFMSM13D2549U Altcode:
During a substorm event in 2009, THEMIS probes observed high-energy
(≲ 1MeV) ions and characteristic time evolution of the differential
flux. The high-energy ions seem to be produced in the magnetotail,
but existing acceleration theories cannot explain the production
of such high-energy ions due to the limitation of dawn-dusk (DD)
flow scale. We propose that if two approaching flow fronts exist
simultaneously in the magnetotail, the production of high-energy ions
can be achieved. Namely, some ideal ions are repeatedly reflected by the
two fronts and accelerated to high energies, exceeding the energy-limit
given by the product of the duskward electric field and DD scale
length of the flows. In addition, this acceleration model similar to
"first-order Fermi acceleration" can produce the observed differential
flux change. We have analytically calculated the energy-gain of each
ion between two approaching flow fronts, and roughly estimated the
efficiency of the acceleration and the spectrum change. In order to
include the DD flow scale, we have further performed a spatially 1-D
(2-D in velocity) test particle simulation where a couple of flow
fronts approach each other. Using the simulation, we have confirmed
the production of high-energy ions as well as the change of the energy
spectrum of ions associated with the acceleration. The simulation
result shows that high-energy ions can be produced with shorter DD
scale length compared to that of the simple acceleration for trapped
particles in the flow front. If we assume that the DD scale length
of the flow is 10Re, the simulated ion maximum energy near 1MeV and
differential flux change are similar to those of the observation. This
scale length is less than half of the length needed for the product
with the duskward electric field to produce 1MeV ions. This estimated
10Re flow scale in that event does not contradict previous studies.
---------------------------------------------------------
Title: Observation and numerical modeling of chromospheric evaporation
during the impulsive phase of a solar flare
Authors: Imada, Shinsuke; Murakami, Izumi; Watanabe, Tetsuya
2015PhPl...22j1206I Altcode: 2015arXiv150604674I
We have studied the chromospheric evaporation flow during the impulsive
phase of the flare by using the Hinode/EUV Imaging Spectrometer
observation and 1D hydrodynamic numerical simulation coupled to the
time-dependent ionization. The observation clearly shows that the strong
redshift can be observed at the base of the flaring loop only during the
impulsive phase. We performed two different numerical simulations to
reproduce the strong downflows in FeXII and FeXV during the impulsive
phase. By changing the thermal conduction coefficient, we carried out
the numerical calculation of chromospheric evaporation in the thermal
conduction dominant regime (conductivity coefficient κ<SUB>0</SUB> =
classical value) and the enthalpy flux dominant regime (κ<SUB>0</SUB>
= 0.1 × classical value). The chromospheric evaporation calculation in
the enthalpy flux dominant regime could reproduce the strong redshift
at the base of the flare during the impulsive phase. This result might
indicate that the thermal conduction can be strongly suppressed in some
cases of flare. We also find that time-dependent ionization effect is
important to reproduce the strong downflows in Fe XII and Fe XV.
---------------------------------------------------------
Title: Photospheric Abundances of Polar Jets on the Sun Observed
by Hinode
Authors: Lee, Kyoung-Sun; Brooks, David H.; Imada, Shinsuke
2015ApJ...809..114L Altcode: 2015arXiv150704075L
Many jets are detected at X-ray wavelengths in the Sun's polar
regions, and the ejected plasma along the jets has been suggested to
contribute mass to the fast solar wind. From in situ measurements
in the magnetosphere, it has been found that the fast solar wind
has photospheric abundances while the slow solar wind has coronal
abundances. Therefore, we investigated the abundances of polar jets
to determine whether they are the same as that of the fast solar
wind. For this study, we selected 22 jets in the polar region observed
by Hinode/EUV Imaging Spectroscopy (EIS) and X-ray Telescope (XRT)
simultaneously on 2007 November 1-3. We calculated the First Ionization
Potential (FIP) bias factor from the ratio of the intensity between high
(S) and low (Si, Fe) FIP elements using the EIS spectra. The values of
the FIP bias factors for the polar jets are around 0.7-1.9, and 75% of
the values are in the range of 0.7-1.5, which indicates that they have
photospheric abundances similar to the fast solar wind. The results
are consistent with the reconnection jet model where photospheric
plasma emerges and is rapidly ejected into the fast wind.
---------------------------------------------------------
Title: Modeling of Hot Plasma in the Solar Active Region Core
Authors: Asgari-Targhi, M.; Schmelz, J. T.; Imada, S.; Pathak, S.;
Christian, G. M.
2015ApJ...807..146A Altcode:
Magnetically confined plasma with temperatures ≥slant 5 {MK} are a
feature of hot coronal loops observed in the core of active regions. In
this paper, using observations and MHD modeling of coronal loops,
we investigate whether wave heating (Alternating Current) models can
describe the high temperature loops observed in the active region
of 2012 September 7. We construct three-dimensional MHD models for
the Alfvén wave turbulence within loops with high temperature. We
find that for the Alfvén waves to create enough turbulence to
heat the corona, the rms velocity at the footpoints must be 5-6 {km}
{{{s}}}<SUP>-1</SUP>. We conclude that the Alfvén wave turbulence model
may be a candidate for explaining how the hot loops are heated, provided
the loops have a high velocity at their photospheric footpoints.
---------------------------------------------------------
Title: Coronal behavior before the large flare onset
Authors: Imada, Shinsuke; Bamba, Yumi; Kusano, Kanya
2014PASJ...66S..17I Altcode: 2014PASJ..tmp..103I; 2014arXiv1408.2585I
Flares are a major explosive event in our solar system. They are
often followed by a coronal mass ejection that has the potential
to trigger geomagnetic storms. There are various studies aiming to
predict when and where the flares are likely to occur. Most of these
studies mainly discuss the photospheric and chromospheric activity
before the flare onset. In this paper we study the coronal features
before the famous large flare occurrence on 2006 December 13. Using the
data from Hinode/Extreme ultraviolet Imaging Spectrometer (EIS), X-Ray
Telescope (XRT), and Solar and Heliospheric Observatory (SOHO)/Extreme
ultraviolet Imaging Telescope (EIT), we discuss the coronal features
in the large scale (a few 100″) before the flare onset. Our findings
are as follows. (1) The upflows in and around the active region start
growing from ∼ 10 to 30 km s<SUP>-1</SUP> a day before the flare. (2)
The expanding coronal loops are clearly observed a few hours before the
flare. (3) Soft X-ray and extreme ultraviolet intensity are gradually
reduced. (4) The upflows are further enhanced after the flare. From
these observed signatures, we conclude that the outer part of active
region loops with low density was expanding a day before the flare
onset, and the inner part with high density was expanding a few hours
before the onset.
---------------------------------------------------------
Title: Comparison between Hinode/SOT and SDO/HMI, AIA data for the
study of the solar flare trigger process
Authors: Bamba, Yumi; Kusano, Kanya; Imada, Shinsuke; Iida, Yusuke
2014PASJ...66S..16B Altcode: 2014arXiv1407.1887B; 2014PASJ..tmp..124B
Understanding the mechanism that produces solar flares is important
not only from the scientific point of view but also for improving
space weather predictability. There are numerous observational and
computational studies that have attempted to reveal the onset mechanism
of solar flares. However, the underlying mechanism of flare onset
remains elusive. To elucidate the flare trigger mechanism, we analyzed
several flare events which were observed by Hinode/Solar Optical
Telescope (SOT) in our previous study. Because of the limitation of
the SOT field of view, however, only four events in the Hinode data
sets have been usable. Therefore, increasing the number of events is
required for evaluating the flare trigger models. We investigated the
applicability of data obtained by the Solar Dynamics Observatory (SDO)
to increase the data sample for a statistical analysis of the flare
trigger process. SDO regularly observes the full disk of the sun and all
flares, although its spatial resolution is lower than that of Hinode. We
investigated the M6.6 flare which occurred on 2011 February 13, and
compared the analyzed data of SDO with the results of our previous study
using Hinode/SOT data. Filter and vector magnetograms obtained by the
Helioseismic and Magnetic Imager and filtergrams from the Atmospheric
Imaging Assembly (AIA) 1600 Å were employed. From the comparison of
small-scale magnetic configurations and chromospheric emission prior to
the flare onset, we confirmed that the trigger region is detectable with
the SDO data. We also measured the magnetic shear angles of the active
region and the azimuth and strength of the flare trigger field. The
results were consistent with our previous study. We concluded that
statistical studies of the flare trigger process are feasible with SDO
as well as Hinode data. We also investigated the temporal evolution
of the magnetic field before the flare onset with SDO.
---------------------------------------------------------
Title: Investigation of solar wind dependence of the plasma sheet
based on long-term Geotail/LEP data evaluation
Authors: Saeki, R.; Seki, K.; Saito, Y.; Shinohara, I.; Miyashita,
Y.; Imada, S.; Machida, S.
2014AGUFMSM53A..08S Altcode:
It is observationally known that the plasma density and temperature
in plasma sheet are significantly changed by solar wind conditions
[e.g., Terasawa et al., 1997]. Thus it is considered that the plasma
sheet plasma is originated from the solar wind, and several entry
mechanisms have been suggested. When the interplanetary magnetic field
(IMF) is southward, the solar wind plasma enters the plasma sheet mainly
through magnetic reconnection at the dayside magnetopause. In contrast,
for the northward IMF, the double-lobe reconnection [Song et al.,
1999], abnormal diffusion [Johnson and Cheng., 1997], and plasma mixing
through the Kelvin-Helmholtz instability caused by viscous interaction
[Hasegawa et al., 2004] have been proposed. Relative contribution
of each process is, however, far from understood. In the present
study, we use magnetotail observations by the Geotail spacecraft
at radial distances of 10-32 Re during 12-year period from 1995 to
2006 to investigate properties of the plasma sheet. We conducted a
statistical analysis with calibrated LEP-EA [Mukai et al., 1994] ion
and electron data. We selected central plasma sheet observations and
derived electron and ion temperature and density using the same method
and criteria as Terasawa et al. [1997]. In addition, OMNI solar-wind
data are used. The results show that the plasma sheet density (both
ion and electron temperatures) has a good correlation with the solar
wind density (kinetic energy) over the whole solar cycle. We find
clear dawn-dusk asymmetry in the temperature ratio Ti/Te, i.e., the
average Ti/Te is higher on the duskside than the dawn. The density
also shows the dawn-dusk asymmetry and higher on the duskside than
on the dawnside. A previous study by Wang et al. [2012] showed that
Ti/Te is high (typically 5-10) in the magnetosheath. The statistical
results, therefore, suggest that the shocked solar wind plasma can
easily enter the duskside plasma sheet rather than the dawnside. We
will discuss the possible mechanisms of the entry of the cold plasma
into the duskside plasma sheet.
---------------------------------------------------------
Title: Investigating Alfven Wave Turbulence in Chromosphere and
Corona Using Extreme Ultraviolet Imaging Spectrometer (EIS)
Authors: Asgari-Targhi, M.; Imada, S.; DeLuca, E. E.
2014AGUFMSH53D..07A Altcode:
The solar corona is known to be very dynamic. Mass motions due to
Alfven wave turbulence are one of the main causes of plasma flows
within the coronal loops. Using observations from EIS we analyze the
structure of active region loops observed on 2012 September 7. We
study the spectral line profiles of Fe XII, Fe XIII, Fe XV and Fe
XVI and compare the non-thermal line broadening from this region to
line-of-sight velocity from our Alfven wave turbulence modeling of the
loops. In our computations, the relationship between the width of the
coronal emission lines and the orientation of the coronal loops with
respect to the line-of-sight direction is taken in to account. We
predict that in coronal loops, the transverse component of plasma
flows with respect to the loop axis move at the speed of 15-40 km/s. In
conclusion, Alfven waves are a strong candidate in explaining the flows
within the coronal loops and play an important role in the heating of
the chromosphere and corona.
---------------------------------------------------------
Title: Formation of a Flare-Productive Active Region: Observation
and Numerical Simulation of NOAA AR 11158
Authors: Toriumi, S.; Iida, Y.; Kusano, K.; Bamba, Y.; Imada, S.
2014SoPh..289.3351T Altcode: 2014SoPh..tmp...40T; 2014arXiv1403.4029T
We present a comparison of the Solar Dynamics Observatory (SDO)
analysis of NOAA Active Region (AR) 11158 and numerical simulations
of flux-tube emergence, aiming to investigate the formation process of
this flare-productive AR. First, we use SDO/Helioseismic and Magnetic
Imager (HMI) magnetograms to investigate the photospheric evolution and
Atmospheric Imaging Assembly (AIA) data to analyze the relevant coronal
structures. Key features of this quadrupolar region are a long sheared
polarity inversion line (PIL) in the central δ-sunspots and a coronal
arcade above the PIL. We find that these features are responsible for
the production of intense flares, including an X2.2-class event. Based
on the observations, we then propose two possible models for the
creation of AR 11158 and conduct flux-emergence simulations of the two
cases to reproduce this AR. Case 1 is the emergence of a single flux
tube, which is split into two in the convection zone and emerges at two
locations, while Case 2 is the emergence of two isolated but neighboring
tubes. We find that, in Case 1, a sheared PIL and a coronal arcade are
created in the middle of the region, which agrees with the AR 11158
observation. However, Case 2 never builds a clear PIL, which deviates
from the observation. Therefore, we conclude that the flare-productive
AR 11158 is, between the two cases, more likely to be created from a
single split emerging flux than from two independent flux bundles.
---------------------------------------------------------
Title: The soft x-ray photon-counting telescope for solar observations
Authors: Sakao, Taro; Narukage, Noriyuki; Suematsu, Yoshinori;
Watanabe, Kyoko; Shimojo, Masumi; Imada, Shinsuke; Ishikawa,
Shin-nosuke; DeLuca, Edward E.
2014SPIE.9144E..3DS Altcode:
We present overview and development activities of a soft X-ray
photon-counting spectroscopic imager for the solar corona that
we conceive as a possible scientific payload for future space
solar missions including Japanese Solar-C. The soft X-ray imager
will employ a Wolter I grazing-incidence sector mirror with which
images of the corona (1 MK to beyond 10 MK) will be taken with
the highest-ever angular resolution (0.5"/pixel for a focal length
of 4 m) as a solar Xray telescope. In addition to high-resolution
imagery, we attempt to implement photon-counting capability for the
imager by employing a backside-illuminated CMOS image sensor as the
focal-plane device. Imaging-spectroscopy of the X-ray corona will be
performed for the first time in the energy range from ~0.5 keV up to
10 keV. The imaging-spectroscopic observations with the soft X-ray
imager will provide a noble probe for investigating mechanism(s) of
magnetic reconnection and generation of supra-thermal (non-thermal)
electrons associated with flares. Ongoing development activities in
Japan towards the photon-counting imager is described with emphasis
on that for sub-arcsecond-resolution grazing-incidence mirrors.
---------------------------------------------------------
Title: New developments in rotating and linear motion mechanisms
used in contamination sensitive space telescopes
Authors: Shimizu, Toshifumi; Watanabe, Kyoko; Nakayama, Satoshi;
Tajima, Takao; Obara, Shingo; Imada, Shinsuke; Nishizuka, Naoto;
Ishikawa, Shin-nosuke; Hara, Hirohisa
2014SPIE.9151E..38S Altcode:
We have been developing a rotating mechanism and a linear motion
mechanism for their usage in contamination sensitive space
telescopes. They both are needed for ~1.4 meter optical telescope
and its focal plane instrument onboard SOLAR-C, the next-generation
spaceborne solar observatory following Hinode. Highly reliable long life
performance, low outgassing properties, and low level of micro-vibration
are required along with their scientific performance. With the
proto-type mechanisms, the long life performance and outgassing
properties of the mechanisms have been evaluated in vacuum chambers. The
level of micro-vibration excited during the operations of the rotating
mechanism was measured by operating it on the Kestler table. This
paper provides the overall descriptions of our mechanism developments.
---------------------------------------------------------
Title: Observational Signatures of Alfven Wave Turbulence in Solar
Coronal Loops
Authors: Asgari-Targhi, Mahboubeh; Imada, Shinsuke; DeLuca, Edward E.
2014AAS...22432325A Altcode:
The non-thermal width in coronal emission lines could be due to
the Alfven wave turbulence. In order to find observational evidence
of the Alfven waves that result in coronal heating, we examine and
analyze the dynamics of an active region observed on 2012 September
7. We use spectral line profiles of Fe XII, Fe XIII, Fe XV and Fe
XVI obtained by Extreme-ultraviolet Imaging Spectrometer (EIS) on
Hinode spacecraft. Line profile observations from EIS were generated
and compared with our computations of line of sight Alfven wave
amplitude. We show non-thermal velocities, Doppler outflows, and
intensities for loops in this active region and derive comparisons
between our numerical results and observations from EIS. In our modeling
we take into account the relationship between the width of the coronal
emission lines and the orientation of the coronal loops with respect
to the line-of-sight direction. We conclude that the Alfven wave
turbulence model is a strong candidate for explaining how the observed
loops are heated.
---------------------------------------------------------
Title: Comparison of Extreme Ultraviolet Imaging Spectrometer
Observations of Solar Coronal Loops with Alfvén Wave Turbulence
Models
Authors: Asgari-Targhi, M.; van Ballegooijen, A. A.; Imada, S.
2014ApJ...786...28A Altcode:
The observed non-thermal widths of coronal emission lines could be
due to Alfvén wave turbulence. To test this idea, we examine and
analyze the dynamics of an active region observed on 2012 September
7. We use spectral line profiles of Fe XII, Fe XIII, Fe XV, and Fe
XVI obtained by the Extreme-ultraviolet Imaging Spectrometer on the
it Hinode spacecraft. The observations show non-thermal velocities,
Doppler outflows, and intensities for loops in this active region. The
observed non-thermal velocities are compared with predictions from
models for Alfvén wave turbulence in the observed coronal loops. This
modeling takes into account the relationship between the width of the
coronal emission lines and the orientation of the coronal loops with
respect to the line-of-sight direction. We find that in order to produce
the observed line widths we need to introduce a random parallel-flow
component in addition to the perpendicular velocity due to Alfvén
waves. The observed widths are consistent with photospheric footpoint
velocities in the range 0.3-1.5 km s<SUP>-1</SUP>. We conclude that
the Alfvén wave turbulence model is a strong candidate for explaining
how the observed loops are heated.
---------------------------------------------------------
Title: Flux emergence and formation of a flare-productive active
region
Authors: Toriumi, Shin; Kusano, Kanya; Bamba, Yumi; Imada, Shinsuke;
Iida, Yusuke
2014cosp...40E3375T Altcode:
We present a comparison of the SDO observation of NOAA Active Region
(AR) 11158 and numerical simulations, aiming to investigate the flux
emergence and the resultant formation of a flare-productive AR. First,
we use SDO/HMI magnetograms to investigate the emerging flux events
in the photosphere and AIA data to analyze the corresponding coronal
EUV evolutions. Key features of this quadrupolar region are a long
sheared polarity inversion line (PIL) in the central delta-sunspots
and a coronal arcade. We find that these features are responsible
for the production of a series of intense flares including X-
and M-class events. Based on the observations, we then propose two
possible scenarios for the creation of AR 11158 and conduct flux
emergence simulations of the two cases to reproduce this AR. Case
1 is the emergence of a single flux tube, which is split into two
in the convection zone and emerges at two locations, while Case 2
is the emergence of two isolated, but neighboring, flux tubes. We
find that, in Case 1, a sheared PIL and a coronal arcade are created
in the middle of the region, which agrees well with the AR 11158
observation. However, Case 2 never build a clear PIL, which deviates
from the observation. Therefore, we conclude that the flare-productive
AR 11158 is, between the two models, more likely to be created from
a single split emerging flux than two independent flux bundles.
---------------------------------------------------------
Title: Spectroscopic Study of a Dark Lane and a Cool Loop in a Solar
Limb Active Region by Hinode/EIS
Authors: Lee, Kyoung-Sun; Imada, S.; Moon, Y. -J.; Lee, Jin-Yi
2014ApJ...780..177L Altcode:
We investigated a cool loop and a dark lane over a limb active region
on 2007 March 14 using the Hinode/EUV Imaging Spectrometer. The cool
loop is clearly seen in the spectral lines formed at the transition
region temperature. The dark lane is characterized by an elongated
faint structure in the coronal spectral lines and is rooted on a
bright point. We examined their electron densities, Doppler velocities,
and nonthermal velocities as a function of distance from the limb. We
derived electron densities using the density sensitive line pairs of
Mg VII, Si X, Fe XII, Fe XIII, and Fe XIV spectra. We also compared
the observed density scale heights with the calculated scale heights
from each peak formation temperatures of the spectral lines under
the hydrostatic equilibrium. We noted that the observed density scale
heights of the cool loop are consistent with the calculated heights,
with the exception of one observed cooler temperature; we also found
that the observed scale heights of the dark lane are much lower than
their calculated scale heights. The nonthermal velocity in the cool loop
slightly decreases along the loop, while nonthermal velocity in the dark
lane sharply falls off with height. Such a decrease in the nonthermal
velocity may be explained by wave damping near the solar surface or
by turbulence due to magnetic reconnection near the bright point.
---------------------------------------------------------
Title: Velocity structure of solar flare plasmas
Authors: Watanabe, Tetsuya; Watanabe, Kyoko; Hara, Hirohisa; Imada,
Shinsuke
2014cosp...40E3606W Altcode:
Thanks to its increased sensitivity and spectral resolution, EIS
enabled emission line profile analysis for the first time in solar
EUV spectroscopy, and it found detailed structures in velocity and
temperature in solar flares. A widely accepted model for solar flares
incorporates magnetic reconnection in the corona which results
in local heating as well as acceleration of nonthermal particle
beams. The standard model of solar flares is called the CSHKP model,
arranging the initials of model proposers. We find loop-top hot source,
fast outflows nearby, inflow structure flowing to the hot source that
appeared in the impulsive phase of long-duration eruptive flares. From
the geometrical relationships of these phenomena, we conclude that
they provide evidence for magnetic reconnection that occurs near the
loop-top region. The reconnection rate is estimated to 0.05 - 0.1,
which supports the Petschek-type magnetic reconnection. The nonthermal
particle beams will travel unimpeded until they reach the cold, dense
chromosphere, where the energy of the beam is predominantly used to
heat the chromosphere at the foot points of flaring loops. Explosive
chromospheric evaporation happens when the beam energy is high enough
that the chromosphere cannot radiate away energy fast enough and
hence expands at high velocities into the corona. Spatially resolved
observations of chromopheric evaporation during the initial phases of
impulsive flares, a few bright points of Fexxiii and Fexxiv emission
lines at the footpoints of flaring loops present dominated blue-shifted
components of 300 - 400 kms (-1) , while Fexv/xvi lines are nearly
stationary, and Feviii and Sivii lines present +50 kms (-1) red
shifts. We will review these new views on dynamical structure in flares.
---------------------------------------------------------
Title: White-Light Emission and related Chromospheric Response in
an X1.8-class Flare on 2012 October 23
Authors: Watanabe, Kyoko; Shimizu, Toshifumi; Imada, Shinsuke
2014cosp...40E3604W Altcode:
In association with strong solar flares, we sometimes observe
enhancements of visible continuum radiation, which is known as a
”white-light flare”. Because many observed events show a close
correlation between the time profiles and locations of white-light
emission, and the hard X-rays and/or radio emission, there is some
consensus that the origin of white-light emission is non-thermal
electrons. Generally, white-light emission is emitted from near the
photosphere, however, non-thermal electrons are almost thermalized
by the time they reach the lower chromosphere - and cannot reach
the photosphere. So, still there is a problem concerning how the
energy of non-thermal electrons propagates to the photosphere,
and produces white-light emission. On October 23, 2012, white-light
emission was observed by Hinode/SOT in association with the X1.8 class
flare. Although the main phenomena of this solar flare occurred in a
very compact region and the two Ca II H ribbons are separated by less
than only 5 arcseconds, the white-light kernels are clearly observed
along the Ca II H ribbons. Moreover, hard X-ray, and gamma-ray emission
is present up to about 1 MeV, observed by the RHESSI satellite, and
most of this emission is associated with the white-light kernels. The
Hinode/EIS was also scanning over this flaring active region before the
flare, and the flare occurred during the scan. Over the white-light
kernel, strong red shifts were observed in FeXII etc. before the
flare. In this paper, we will report the observed white-light emission,
and chromospheric response obtained by the EUV observations. We also
discuss the relationship between the downflows over the white-light
kernel and the strength of the white-light emission, and try to show
a possible prediction of how white-light emission can be produced by
the transportation of non-thermal electrons.
---------------------------------------------------------
Title: A quantitative study of ionospheric disturbance characteristics
during solar flare events using the SuperDARN Hokkaido radar and
solar radiation data
Authors: Watanabe, D.; Nishitani, N.; Imada, S.
2013AGUFMSA41B2106W Altcode:
Ionospheric disturbances during solar flare events have been studied by
various kinds of observation instrument in the last few decades. Kikuchi
et al. (1985) reported on the positive Doppler shift in the HF Doppler
system data during solar flare events, and indicated that there are two
possible factors of Doppler shift, i.e., (1) apparent ray path decrease
by changing refraction index due to increasing electron densities in
the D-region ionosphere, and (2) ray path decrease due to descending
reflection point associated with increasing electron density in the
F-region ionosphere. In this study, we use the SuperDARN Hokkaido
Radar to investigate the detailed characteristics of solar flare
effects on ionospheric disturbances. We focus on the positive Doppler
shift of ground / sea scatter echoes just before sudden fade-out of
echoes. Davies et al. (1962) showed that if the factor (1) is dominant,
the Doppler shift should have positive correlation with slant range
and negative correlation with elevation angle and frequency. On the
other hand, if the factor (2) is dominant, the Doppler shift should
have negative correlation with slant range and positive correlation with
elevation angle and frequency. While Kikuchi et al. (1985) studied solar
flare events and mainly discussed frequency dependence of Doppler shift,
we study mainly slant range and elevation angle dependence, for the
first time to the best of our knowledge. We found that the factor (1),
in other words, increase of electron densities at D-region ionosphere,
is dominant during solar flare events. This result is consistent
with that of Kikuchi et al. In order to study characteristics of
ionospheric disturbance in more detail, we are studying relationship
between timing / amplitude of ionospheric disturbance and that of the
solar irradiation changes, by comparing the HF radar data with high
wavelength resolution irradiation data for X-ray and EUV from RHESSI
and SDO satellites. Generally, X-ray radiation becomes more important
for the changes in the D-region during solar flare events. Therefore we
investigate relationship between X-ray flux changes and electron density
variation in the D-region ionosphere intensively. Further, we estimated
electron density changes in the ionsosphere by analyzing elevation
angle dependence of Doppler shift in radar echoes quantitatively. We
are estimating electron density by considering chemical reaction
and photoreaction caused by solar radiation. We will compare the two
electron density changes deduced from different two ways and evaluate
the amplitude of ionospheric disturbance observed by the HF radar. More
detailed analysis result will be reported.
---------------------------------------------------------
Title: The Relationship between Extreme Ultraviolet Non-thermal Line
Broadening and High-energy Particles during Solar Flares
Authors: Kawate, T.; Imada, S.
2013ApJ...775..122K Altcode: 2013arXiv1308.3415K
We have studied the relationship between the location of EUV non-thermal
broadening and high-energy particles during large flares using the EUV
Imaging Spectrometer on board Hinode, the Nobeyama Radio Polarimeter,
the Nobeyama Radioheliograph, and the Atmospheric Imaging Assembly
on board the Solar Dynamic Observatory. We have analyzed five large
flare events that contain thermal-rich, intermediate, and thermal-poor
flares classified by the definition discussed in the paper. We found
that, in the case of thermal-rich flares, the non-thermal broadening
of Fe XXIV occurred at the top of the flaring loop at the beginning
of the flares. The source of 17 GHz microwaves is located at the
footpoint of the flare loop. On the other hand, in the case of
intermediate/thermal-poor flares, the non-thermal broadening of Fe
XXIV occurred at the footpoint of the flare loop at the beginning of
the flares. The source of 17 GHz microwaves is located at the top of
the flaring loop. We discussed the difference between thermal-rich and
intermediate/thermal-poor flares based on the spatial information of
non-thermal broadening, which may provide clues that the presence of
turbulence plays an important role in the pitch angle scattering of
high-energy electrons.
---------------------------------------------------------
Title: Saturation of Stellar Winds from Young Suns
Authors: Suzuki, Takeru K.; Imada, Shinsuke; Kataoka, Ryuho; Kato,
Yoshiaki; Matsumoto, Takuma; Miyahara, Hiroko; Tsuneta, Saku
2013PASJ...65...98S Altcode: 2012arXiv1212.6713S
We investigated mass losses via stellar winds from Sun-like
main-sequence stars with a wide range of activity levels. We performed
forward-type magnetohydrodynamical numerical experiments for Alfvén
wave-driven stellar winds with a wide range of input Poynting flux
from the photosphere. Increasing the magnetic field strength and
the turbulent velocity at the stellar photosphere from the current
solar level, the mass-loss rate rapidly at first increases, owing
to suppression of the reflection of the Alfvén waves. The surface
materials are lifted up by the magnetic pressure associated with
the Alfvén waves, and the cool dense chromosphere is intermittently
extended to 10%#8211;20% of the stellar radius. The dense atmospheres
enhance the radiative losses, and eventually most of the input Poynting
energy from the stellar surface escapes by radiation. As a result, there
is no more sufficient energy remaining for the kinetic energy of the
wind; the stellar wind saturates in very active stars, as observed in
Wood et al. (2002, ApJ, 574, 412; 2005, ApJ, 628, L143). The saturation
level is positively correlated with B<SUB>r,</SUB><SUB>0</SUB>
f<SUB>0</SUB>, where B<SUB>r,</SUB><SUB>0</SUB> and f<SUB>0</SUB>
are the magnetic field strength and the filling factor of open flux
tubes at the photosphere. If B<SUB>r,</SUB><SUB>0</SUB> f<SUB>0</SUB>
is relatively large gtrsim 5 G, the mass-loss rate could be as high as
1000 times. If such a strong mass loss lasts for ∼ 1 billion years,
the stellar mass itself would be affected, which could be a solution to
the faint young Sun paradox. We derived a Reimers-type scaling relation
that estimates the mass-loss rate from an energetics consideration of
our simulations. Finally, we derived the evolution of the mass-loss
rates, dot;{M} ∝ t<SUP>-1.23</SUP>, of our simulations, combining
with an observed time evolution of X-ray flux from Sun-like stars,
which are shallower than dot;{M} ∝ t<SUP>-2.33±0.55</SUP> in Wood
et al. (2005).
---------------------------------------------------------
Title: Evidence for Hot Fast Flow above a Solar Flare Arcade
Authors: Imada, S.; Aoki, K.; Hara, H.; Watanabe, T.; Harra, L. K.;
Shimizu, T.
2013ApJ...776L..11I Altcode: 2013arXiv1309.3401I
Solar flares are one of the main forces behind space weather
events. However, the mechanism that drives such energetic phenomena is
not fully understood. The standard eruptive flare model predicts that
magnetic reconnection occurs high in the corona where hot fast flows are
created. Some imaging or spectroscopic observations have indicated the
presence of these hot fast flows, but there have been no spectroscopic
scanning observations to date to measure the two-dimensional structure
quantitatively. We analyzed a flare that occurred on the west solar
limb on 2012 January 27 observed by the Hinode EUV Imaging Spectrometer
(EIS) and found that the hot (~30MK) fast (>500 km s<SUP>-1</SUP>)
component was located above the flare loop. This is consistent with
magnetic reconnection taking place above the flare loop.
---------------------------------------------------------
Title: The Magnetic Systems Triggering the M6.6 Class Solar Flare
in NOAA Active Region 11158
Authors: Toriumi, Shin; Iida, Yusuke; Bamba, Yumi; Kusano, Kanya;
Imada, Shinsuke; Inoue, Satoshi
2013ApJ...773..128T Altcode: 2013arXiv1306.2451T
We report a detailed event analysis of the M6.6 class flare in the
active region (AR) NOAA 11158 on 2011 February 13. AR 11158, which
consisted of two major emerging bipoles, showed prominent activity
including one X- and several M-class flares. In order to investigate
the magnetic structures related to the M6.6 event, particularly the
formation process of a flare-triggering magnetic region, we analyzed
multiple spacecraft observations and numerical results of a flare
simulation. We observed that, in the center of this quadrupolar AR,
a highly sheared polarity inversion line (PIL) was formed through
proper motions of the major magnetic elements, which built a sheared
coronal arcade lying over the PIL. The observations lend support
to the interpretation that the target flare was triggered by a
localized magnetic region that had an intrusive structure, namely,
a positive polarity penetrating into a negative counterpart. The
geometrical relationship between the sheared coronal arcade and the
triggering region is consistent with the theoretical flare model based
on the previous numerical study. We found that the formation of the
trigger region was due to the continuous accumulation of small-scale
magnetic patches. A few hours before the flare occurred, the series of
emerged/advected patches reconnected with a pre-existing field. Finally,
the abrupt flare eruption of the M6.6 event started around 17:30 UT. Our
analysis suggests that in the process of triggering flare activity,
all magnetic systems on multiple scales are included, not only the
entire AR evolution but also the fine magnetic elements.
---------------------------------------------------------
Title: Hinode observations of the Venus corona during the 2012
transit of Venus
Authors: Kanao, M.; Yamazaki, A.; Imada, S.; Shimizu, T.; Sakao, T.;
Kasaba, Y.; Sakanoi, T.; Kagitani, M.; Nakamura, M.
2012AGUFM.P11D1851K Altcode:
The Hinode satellite successfully observed the transit of Venus on
5th June 2012 with the highest spatial resolution. This presentation
will focus on UV and soft X-ray data acquired with the EUV Imaging
Spectrometer (EIS) and the X-ray Telescope (XRT) onboard Hinode. We
expected the EUV and X-ray emissions from the charge exchange reaction
by the solar wind impacting on the neutral particles in Venus upper
atmosphere. The neutral particles escape through the photoreaction, the
solar wind pick-up process, and so on, in connection with the solar wind
and the solar radiation. However, there are few precedent observations
of the escaping hydrogen and oxygen, ranging from a few eV to a few keV
because of difficulty in the groundbased observations. The atmosphere
loss can be estimated based on the two-dimensional image of the neutral
particle density. Our estimation was made for 18.4nm (OVI), 19.3nm (OV)
and 25.6nm (HII), which intensity and line profiles can be recorded with
EIS, and 1.72-2.18nm (OVII), 1.60-1.90nm(OVIII), 2.85-3.37nm (CVI),
3.50-4.03 nm (CV), which are located in XRT's broadband range. Multi
wavelength observation could clarify the collision velocities between
the solar wind and Venus neutral particles. Before the transit of Venus,
for science planning purpose, we estimated the EUV and X-ray emission
intensities by using typical solar wind parameters (the proton density
10/cc and the solar wind velocity 400 km/sec) with a Venus atmosphere
model. The photon production rate of the X-ray emission is estimated
to be 1.1 x 10^25 photons/s, and that of the OVI emission line (18.4nm)
is 6.9 x 10^23 photons/s. These values are much lower than the emissions
from the solar corona, but unexpected signals may be observed dureing
the transit. In this presentation, we will present the calculation
results on intensity distribution of the Venus corona and some X-ray
and EUV data acquired during the transit. Also we briefly compare
the observed intensities in dark Venus feature with the calculation
results and discuss the signification of the difference.
---------------------------------------------------------
Title: Spectroscopic Study of a Dark Lane and a Cool Loop in a Solar
Limb Active Region by Hinode/EIS
Authors: Lee, K.; Imada, S.; Moon, Y.; Lee, J.
2012AGUFMSH13A2241L Altcode:
We investigate a cool loop and a dark lane over a limb active region
on 2007 March 14 by the Hinode/EUV Imaging Spectrometer (EIS). The cool
loop is clearly seen in the EIS spectral lines formed at the transition
region temperature (log T = 5.8). The dark lane is characterized by
an elongated faint structure in coronal spectral lines (log T = 5.8 -
6.1) and rooted on a bright point. We examine their electron densities,
Doppler velocities, and non-thermal velocities as a function of distance
from the limb using the spectral lines formed at different temperatures
(log T = 5.4 - 6.4). The electron densities of the cool loop and the
dark lane are derived from the density sensitive line pairs of Mg
VII, Fe XII, and Fe XIV spectra. Under the hydrostatic equilibrium
and isothermal assumption, we determine their temperatures from the
density scale height. Comparing the scale height temperatures to the
peak formation temperatures of the spectral lines, we note that the
scale height temperature of the cool loop is consistent with a peak
formation temperature of the Mg VII (log T = 5.8) and the scale height
temperature of the dark lane is close to a peak formation temperature
of the Fe XII and Fe XIII (log T = 6.1 - 6.2). It is interesting to
note that the structures of the cool loop and the dark lane are most
visible in these temperature lines. While the non-thermal velocity
in the cool loop slightly decreases (less than 7 km {s<SUP>-1}</SUP>)
along the loop, that in the dark lane sharply falls off with height. The
variation of non-thermal velocity with height in the cool loop and the
dark lane is contrast to that in off-limb polar coronal holes which
are considered as source of the fast solar wind. Such a decrease in
the non-thermal velocity may be explained by wave damping near the
solar surface or turbulence due to magnetic reconnection near the
bright point.
---------------------------------------------------------
Title: Multi-wavelength Spectroscopic Observation of
Extreme-ultraviolet Jet in AR 10960
Authors: Matsui, Y.; Yokoyama, T.; Kitagawa, N.; Imada, S.
2012ApJ...759...15M Altcode: 2012arXiv1209.0867M
We have studied the relationship between the velocity and temperature
of a solar EUV jet. The highly accelerated jet occurred in the active
region NOAA 10960 on 2007 June 5. Multi-wavelength spectral observations
with EIS/Hinode allow us to investigate Doppler velocities at a wide
temperature range. We analyzed the three-dimensional angle of the jet
from stereoscopic analysis with STEREO. Using this angle and Doppler
velocity, we derived the true velocity of the jet. As a result, we
found that the cool jet observed with He II 256 Å log<SUB>10</SUB>
T<SUB>e</SUB> [K] = 4.9 is accelerated to around 220 km s<SUP>-1</SUP>,
which is over the upper limit of the chromospheric evaporation. The
velocities observed with the other lines are below the upper limit
of the chromospheric evaporation, while most of the velocities of
the hot lines are higher than those of cool lines. We interpret
that the chromospheric evaporation and magnetic acceleration occur
simultaneously. A morphological interpretation of this event based on
the reconnection model is given by utilizing the multi-instrumental
observations.
---------------------------------------------------------
Title: LEMUR: Large European module for solar Ultraviolet
Research. European contribution to JAXA's Solar-C mission
Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric;
Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len;
Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George
A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green,
Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem,
Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet,
Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto,
Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu,
Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele;
Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas;
Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann,
Thomas; Winter, Berend; Young, Peter
2012ExA....34..273T Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T
The solar outer atmosphere is an extremely dynamic environment
characterized by the continuous interplay between the plasma and the
magnetic field that generates and permeates it. Such interactions play a
fundamental role in hugely diverse astrophysical systems, but occur at
scales that cannot be studied outside the solar system. Understanding
this complex system requires concerted, simultaneous solar observations
from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at
high spatial resolution (between 0.1” and 0.3”), at high temporal
resolution (on the order of 10 s, i.e., the time scale of chromospheric
dynamics), with a wide temperature coverage (0.01 MK to 20 MK,
from the chromosphere to the flaring corona), and the capability of
measuring magnetic fields through spectropolarimetry at visible and
near-infrared wavelengths. Simultaneous spectroscopic measurements
sampling the entire temperature range are particularly important. These
requirements are fulfilled by the Japanese Solar-C mission (Plan B),
composed of a spacecraft in a geosynchronous orbit with a payload
providing a significant improvement of imaging and spectropolarimetric
capabilities in the UV, visible, and near-infrared with respect to
what is available today and foreseen in the near future. The Large
European Module for solar Ultraviolet Research (LEMUR), described
in this paper, is a large VUV telescope feeding a scientific payload
of high-resolution imaging spectrographs and cameras. LEMUR consists
of two major components: a VUV solar telescope with a 30 cm diameter
mirror and a focal length of 3.6 m, and a focal-plane package composed
of VUV spectrometers covering six carefully chosen wavelength ranges
between 170 Å and 1270 Å. The LEMUR slit covers 280” on the Sun with
0.14” per pixel sampling. In addition, LEMUR is capable of measuring
mass flows velocities (line shifts) down to 2 km s<SUP> - 1</SUP> or
better. LEMUR has been proposed to ESA as the European contribution
to the Solar C mission.
---------------------------------------------------------
Title: Chromospheric Lyman-alpha spectro-polarimeter (CLASP)
Authors: Kano, Ryouhei; Bando, Takamasa; Narukage, Noriyuki; Ishikawa,
Ryoko; Tsuneta, Saku; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
Shin-nosuke; Hara, Hirohisa; Shimizu, Toshifumi; Suematsu, Yoshinori;
Ichimoto, Kiyoshi; Sakao, Taro; Goto, Motoshi; Kato, Yoshiaki; Imada,
Shinsuke; Kobayashi, Ken; Holloway, Todd; Winebarger, Amy; Cirtain,
Jonathan; De Pontieu, Bart; Casini, Roberto; Trujillo Bueno, Javier;
Štepán, Jiří; Manso Sainz, Rafael; Belluzzi, Luca; Asensio Ramos,
Andres; Auchère, Frédéric; Carlsson, Mats
2012SPIE.8443E..4FK Altcode:
One of the biggest challenges in heliophysics is to decipher the
magnetic structure of the solar chromosphere. The importance of
measuring the chromospheric magnetic field is due to both the key role
the chromosphere plays in energizing and structuring the outer solar
atmosphere and the inability of extrapolation of photospheric fields to
adequately describe this key boundary region. Over the last few years,
significant progress has been made in the spectral line formation
of UV lines as well as the MHD modeling of the solar atmosphere. It
is found that the Hanle effect in the Lyman-alpha line (121.567 nm)
is a most promising diagnostic tool for weaker magnetic fields in
the chromosphere and transition region. Based on this groundbreaking
research, we propose the Chromospheric Lyman-Alpha Spectro-Polarimeter
(CLASP) to NASA as a sounding rocket experiment, for making the first
measurement of the linear polarization produced by scattering processes
and the Hanle effect in the Lyman-alpha line (121.567 nm), and making
the first exploration of the magnetic field in the upper chromosphere
and transition region of the Sun. The CLASP instrument consists
of a Cassegrain telescope, a rotating 1/2-wave plate, a dual-beam
spectrograph assembly with a grating working as a beam splitter, and
an identical pair of reflective polarization analyzers each equipped
with a CCD camera. We propose to launch CLASP in December 2014.
---------------------------------------------------------
Title: The x-ray/EUV telescope for the Solar-C mission: science and
development activities
Authors: Sakao, Taro; Narukage, Noriyuki; Imada, Shinsuke; Suematsu,
Yoshinori; Shimojo, Masumi; Tsuneta, Saku; DeLuca, Edward E.; Watanabe,
Kyoko; Ishikawa, Shin-nosuke
2012SPIE.8443E..0AS Altcode:
We report science and development activities of the X-ray/EUV telescope
for the Japanese Solar-C mission whose projected launch around 2019. The
telescope consists of a package of (a) a normal-incidence (NI) EUV
telescope and (b) a grazing-incidence (GI) soft X-ray telescope. The NI
telescope chiefly provides images of low corona (whose temperature 1
MK or even lower) with ultra-high angular resolution (0.2-0.3"/pixel)
in 3 wavelength bands (304, 171, and 94 angstroms). On the other
hand, the GI telescope provides images of the corona with a wide
temperature coverage (1 MK to beyond 10 MK) with the highest-ever
angular resolution (~0.5"/pixel) as a soft X-ray coronal imager. The
set of NI and GI telescopes should provide crucial information for
establishing magnetic and gas-dynamic connection between the corona and
the lower atmosphere of the Sun which is essential for understanding
heating of, and plasma activities in, the corona. Moreover, we attempt
to implement photon-counting capability for the GI telescope with
which imaging-spectroscopy of the X-ray corona will be performed for
the first time, in the energy range from ~0.5 keV up to 10 keV. The
imaging-spectroscopic observations will provide totally-new information
on mechanism(s) for the generation of hot coronal plasmas (heated
beyond a few MK), those for magnetic reconnection, and even generation
of supra-thermal electrons associated with flares. An overview of
instrument outline and science for the X-ray photoncounting telescope
are presented, together with ongoing development activities in Japan
towards soft X-ray photoncounting observations, focusing on high-speed
X-ray CMOS detector and sub-arcsecond-resolution GI mirror.
---------------------------------------------------------
Title: Flare Onset Observed with Hinode in the 2006 December 13 Flare
Authors: Asai, A.; Hara, H.; Watanabe, T.; Imada, S.
2012ASPC..454..303A Altcode:
We present a detailed examination of the preflare phenomena of
the X3.4 flare that occurred on 2006 December 13. This flare was
associated with a faint arc-shaped ejection, which is thought to be
an MHD fast-mode shock wave, seen in the soft X-ray images taken
with the Hinode X-Ray Telescope (XRT), just at the start of the
impulsive phase of the flare. Even before the ejection, we found many
preflare features, such as an S-shaped brightening (sigmoid) with XRT,
chromospheric brightening at the footpoints of the sigmoid loops with
the Solar Optical Telescope (SOT), a faint X-ray eruption with XRT,
and so on. The EUV Imaging Spectrometer (EIS) also observed the flare,
and therefore, enabled us to examine the spectroscopic features. We
discuss these phenomena and the energy release prosses.
---------------------------------------------------------
Title: Self-organization of Reconnecting Plasmas to Marginal
Collisionality in the Solar Corona
Authors: Imada, S.; Zweibel, E. G.
2012ApJ...755...93I Altcode: 2012arXiv1206.2706I
We explore the suggestions by Uzdensky and Cassak et al. that coronal
loops heated by magnetic reconnection should self-organize to a state
of marginal collisionality. We discuss their model of coronal loop
dynamics with a one-dimensional hydrodynamic calculation. We assume that
many current sheets are present, with a distribution of thicknesses,
but that only current sheets thinner than the ion skin depth can
rapidly reconnect. This assumption naturally causes a density-dependent
heating rate which is actively regulated by the plasma. We report nine
numerical simulation results of coronal loop hydrodynamics in which
the absolute values of the heating rates are different but their
density dependences are the same. We find two regimes of behavior,
depending on the amplitude of the heating rate. In the case that the
amplitude of heating is below a threshold value, the loop is in stable
equilibrium. Typically, the upper and less dense part of a coronal
loop is collisionlessly heated and conductively cooled. When the
amplitude of heating is above the threshold, the conductive flux to the
lower atmosphere required to balance collisionless heating drives an
evaporative flow which quenches fast reconnection, ultimately cooling
and draining the loop until the cycle begins again. The key elements
of this cycle are gravity and the density dependence of the heating
function. Some additional factors are present, including pressure-driven
flows from the loop top, which carry a large enthalpy flux and play
an important role in reducing the density. We find that on average the
density of the system is close to the marginally collisionless value.
---------------------------------------------------------
Title: Multi-wavelength Observations of an EUV Jet in AR 10960
Authors: Matsui, Y.; Yokoyama, T.; Imada, S.
2012ASPC..456...47M Altcode:
We analyzed the fine structure of a solar EUV jet based on the magnetic
reconnection model. Multi-wavelength spectral observations with EIS
allow us to know Doppler velocities at the wide temperature range. What
we found is as follows: (1) The jet consists of multi-temperature plasma
in a few 10<SUP>4</SUP> rm{K} to a few MK range. (2) The observed
speed of the jet does not have dependence on the plasma temperature
that is expected by the evaporation scenario. We interpret that the
chromospheric evaporation jet have been accelerated by the magnetic
Lorentz force over the speed expected by the evaporation scenario.
---------------------------------------------------------
Title: Clear Detection of Chromospheric Evaporation Upflows with
High Spatial/Temporal Resolution by Hinode XRT
Authors: Nitta, S.; Imada, S.; Yamamoto, T. T.
2012SoPh..276..183N Altcode:
We find clear evidence for typical chromospheric evaporation associated
with small transient brightenings, using the data from the X-ray
Telescope (XRT) onboard Hinode. We found 13 events, each having a pair
of evaporation upflows arising almost symmetrically from both foot
points of a magnetic loop. These facts strongly support the standard
flare model based on the magnetic reconnection. The apparent upflow
velocities of three of the events are ≈ 500 km s<SUP>−1</SUP>,
while those of the other events are ≈ 100 km s<SUP>−1</SUP>. This
is the first clear direct detection of evaporating upflow motion in
soft X-ray images from Hinode/XRT; such images were obtained with high
cadence (≈ 60 s) and high spatial resolution (1 arcsec).
---------------------------------------------------------
Title: Dynamical Behaviors of the Solar Chromosphere Observed with
Hinode Dynamics in Sunspot Light Bridges and Magnetic Reconnection
Processes
Authors: Shimizu, Toshifumi; Imada, Shinsuke
2012ASSP...33...23S Altcode: 2012msdp.book...23S
The Hinode's Solar Optical Telescope has revealed that the solar
chromosphere is full of dynamical nature and much more dynamic than
our thought. Observations of chromospheric dynamics in sunspot light
bridges provides a new insight on the magnetic field topology for
causing magnetic reconnection in the solar atmosphere and the process
to supply and maintain the twisted flux in light bridges.
---------------------------------------------------------
Title: One-dimensional Modeling for Temperature-dependent Upflow in
the Dimming Region Observed by Hinode/EUV Imaging Spectrometer
Authors: Imada, S.; Hara, H.; Watanabe, T.; Murakami, I.; Harra,
L. K.; Shimizu, T.; Zweibel, E. G.
2011ApJ...743...57I Altcode: 2011arXiv1108.5031I
We previously found a temperature-dependent upflow in the dimming region
following a coronal mass ejection observed by the Hinode EUV Imaging
Spectrometer (EIS). In this paper, we reanalyzed the observations along
with previous work on this event and provided boundary conditions for
modeling. We found that the intensity in the dimming region dramatically
drops within 30 minutes from the flare onset, and the dimming region
reaches the equilibrium stage after ~1 hr. The temperature-dependent
upflows were observed during the equilibrium stage by EIS. The
cross-sectional area of the flux tube in the dimming region does not
appear to expand significantly. From the observational constraints,
we reconstructed the temperature-dependent upflow by using a new method
that considers the mass and momentum conservation law and demonstrated
the height variation of plasma conditions in the dimming region. We
found that a super-radial expansion of the cross-sectional area is
required to satisfy the mass conservation and momentum equations. There
is a steep temperature and velocity gradient of around 7 Mm from
the solar surface. This result may suggest that the strong heating
occurred above 7 Mm from the solar surface in the dimming region. We
also showed that the ionization equilibrium assumption in the dimming
region is violated, especially in the higher temperature range.
---------------------------------------------------------
Title: Magnetic Reconnection in Non-equilibrium Ionization Plasma
Authors: Imada, S.; Murakami, I.; Watanabe, T.; Hara, H.; Shimizu, T.
2011ApJ...742...70I Altcode: 2011arXiv1108.5026I
We have studied the effect of time-dependent ionization and
the recombination processes on magnetic reconnection in the solar
corona. Petschek-type steady reconnection, in which the magnetic energy
is mainly converted at the slow-mode shocks, was assumed. We carried out
the time-dependent ionization calculation in the magnetic reconnection
structure. We only calculated the transient ionization of iron;
the other species were assumed to be in ionization equilibrium. The
intensity of line emissions at specific wavelengths was also calculated
for comparison with Hinode or other observations in future. We found
the following: (1) iron is mostly in non-equilibrium ionization in the
reconnection region; (2) the intensity of line emission estimated by
the time-dependent ionization calculation is significantly different
from that determined from the ionization equilibrium assumption;
(3) the effect of time-dependent ionization is sensitive to the
electron density in the case where the electron density is less than
10<SUP>10</SUP> cm<SUP>-3</SUP> (4) the effect of thermal conduction
lessens the time-dependent ionization effect; and (5) the effect of
radiative cooling is negligibly small even if we take into account
time-dependent ionization.
---------------------------------------------------------
Title: Photon-counting soft x-ray telescope for the Solar-C mission
Authors: Sakao, Taro; Narukage, Noriyuki; Shimojo, Masumi; Tsuneta,
Saku; Suematsu, Yoshinori; Miyazaki, Satoshi; Imada, Shinsuke;
Nishizuka, Naoto; Watanabe, Kyoko; Dotani, Tadayasu; DeLuca, Edward
E.; Ishikawa, Shin-nosuke
2011SPIE.8148E..0CS Altcode: 2011SPIE.8148E..11S
We report instrument outline as well as science of the photon-counting
soft X-ray telescope that we have been studying as a possible scientific
payload for the Japanese Solar-C mission whose projected launch around
2019. Soft X-rays (~1- 10 keV) from the solar corona include rich
information on (1) possible mechanism(s) for heating the bright core of
active regions seen in soft X-rays (namely, the hottest portion in the
non-flaring corona), (2) dynamics and magnetohydrodynamic structures
associated with magnetic reconnection processes ongoing in flares,
and even (3) generation of supra-thermal distributions of coronal
plasmas associated with flares. Nevertheless, imaging-spectroscopic
investigation of the soft X-ray corona has so far remained unexplored
due to difficulty in the instrumentation for achieving this aim. With
the advent of recent remarkable progress in CMOS-APS detector
technology, the photon-counting X-ray telescope will be capable
of, in addition to conventional photon-integration type exposures,
performing imaging-spectroscopic investigation on active regions and
flares, thus providing, for example, detailed temperature information
(beyond the sofar- utilized filter-ratio temperature) at each spatial
point of the observing target. The photon-counting X-ray telescope will
emply a Wolter type I optics with a piece of a segmented mirror whose
focal length 4 meters, combined with a focal-plane CMOS-APS detector
(0.4-0.5"/pixel) whose frame read-out rate required to be as high as
1000 fps.
---------------------------------------------------------
Title: Favorable conditions for energetic electron acceleration
during magnetic reconnection in the Earth's magnetotail
Authors: Imada, S.; Hirai, M.; Hoshino, M.; Mukai, T.
2011JGRA..116.8217I Altcode:
We have studied favorable conditions for energetic electron acceleration
during magnetic reconnection in the Earth's magnetosphere using the
Geotail data. We have found the strong energetic electron acceleration
in some reconnection events. On the other hand, the other reconnection
events show weak electron acceleration. To discuss what reconnection
characteristics determine energetic electron acceleration efficiency, we
have studied the reconnection characteristics for 10 events in which the
Geotail satellite observed the vicinity of the diffusion region. We have
classified the relationship between the reconnection characteristics
and the electron acceleration efficiency into three types: (1) good
correlation (absolute value of correlation coefficient ∣r∣ >
0.6); (2) ambiguous correlation (0.6 > ∣r∣ > 0.3); and
(3) no correlation (0.3 > ∣r∣). We found that ion heating,
electron heating, current sheet thickness, reconnection electric field,
and converging normal electric field could be categorized into good
correlation. Ion/electron temperature ratio, total amount of reconnected
magnetic energy, and reconnection rate were classified in ambiguous
correlation. We could not find any correlation between energetic
electron acceleration efficiency and absolute value of outflow velocity,
current density parallel to magnetic field (Hall current system), and
satellite location in the Earth's magnetosphere. From our analysis
we claimed that the electrons are efficiently accelerated in a thin
current sheet during fast reconnection events.
---------------------------------------------------------
Title: Two Types of Extreme-ultraviolet Brightenings In AR 10926
Observed by Hinode/EIS
Authors: Lee, K. -S.; Moon, Y. -J.; Kim, Sujin; Choe, G. S.; Cho,
Kyung-Suk; Imada, S.
2011ApJ...736...15L Altcode:
We have investigated seven extreme-ultraviolet (EUV) brightenings in the
active region AR 10926 on 2006 December 2 observed by the EUV Imaging
Spectrometer on board the Hinode spacecraft. We have determined their
Doppler velocities and non-thermal velocities from 15 EUV spectral
lines (log T = 4.7 - 6.4) by fitting each line profile to a Gaussian
function. The Doppler velocity maps for different temperatures are
presented to show the height dependence of the Doppler shifts. It is
found that the active region brightenings show two distinct Doppler
shift patterns. The type 1 brightening shows a systematic increase
of Doppler velocity from -68 km s<SUP>-1</SUP> (strong blueshift) at
log T = 4.7 to -2 km s<SUP>-1</SUP> (weak blueshift) at log T = 6.4,
while the type 2 brightenings have Doppler velocities in the range from
-20 km s<SUP>-1</SUP> to 20 km s<SUP>-1</SUP>. The type 1 brightening
point is considered to sit in an upward reconnection outflow whose speed
decreases with height. In both types of brightenings, the non-thermal
velocity is found to be significantly enhanced at log T = 5.8 compared
to the background region. We have also determined electron densities
from line ratios and derived temperatures from emission measure loci
using the CHIANTI atomic database. The electron densities of all
brightenings are comparable to typical values in active regions (log
N<SUB>e</SUB> = 9.9-10.4). The emission measure loci plots indicate
that these brightenings should be multi-thermal whereas the background
is isothermal. The differential emission measure as a function of
temperature shows multiple peaks in the EUV brightening regions, while
it has only a single peak (log T = 6.0) in the background region. Using
Michelson Doppler Imager magnetograms, we have found that the type 1
brightening is associated with a canceling magnetic feature with a flux
canceling rate of 2.4 × 10<SUP>18</SUP> Mx hr<SUP>-1</SUP>. We also
found the canceling magnetic feature and chromospheric brightenings
in the type 1 brightening from the Hinode SOT and Transition Region
and Coronal Explorer data. This observation corroborates our argument
that brightening is caused by magnetic reconnection in a low atmosphere.
---------------------------------------------------------
Title: Morphology, dynamics and plasma parameters of plumes and
inter-plume regions in solar coronal holes
Authors: Wilhelm, K.; Abbo, L.; Auchère, F.; Barbey, N.; Feng, L.;
Gabriel, A. H.; Giordano, S.; Imada, S.; Llebaria, A.; Matthaeus,
W. H.; Poletto, G.; Raouafi, N. -E.; Suess, S. T.; Teriaca, L.; Wang,
Y. -M.
2011A&ARv..19...35W Altcode: 2011arXiv1103.4481W
Coronal plumes, which extend from solar coronal holes (CH) into the high
corona and—possibly—into the solar wind (SW), can now continuously
be studied with modern telescopes and spectrometers on spacecraft,
in addition to investigations from the ground, in particular, during
total eclipses. Despite the large amount of data available on these
prominent features and related phenomena, many questions remained
unanswered as to their generation and relative contributions to
the high-speed streams emanating from CHs. An understanding of the
processes of plume formation and evolution requires a better knowledge
of the physical conditions at the base of CHs, in plumes and in the
surrounding inter-plume regions. More specifically, information is
needed on the magnetic field configuration, the electron densities
and temperatures, effective ion temperatures, non-thermal motions,
plume cross sections relative to the size of a CH, the plasma bulk
speeds, as well as any plume signatures in the SW. In spring 2007, the
authors proposed a study on `Structure and dynamics of coronal plumes
and inter-plume regions in solar coronal holes' to the International
Space Science Institute (ISSI) in Bern to clarify some of these aspects
by considering relevant observations and the extensive literature. This
review summarizes the results and conclusions of the study. Stereoscopic
observations allowed us to include three-dimensional reconstructions
of plumes. Multi-instrument investigations carried out during several
campaigns led to progress in some areas, such as plasma densities,
temperatures, plume structure and the relation to other solar phenomena,
but not all questions could be answered concerning the details of
plume generation process(es) and interaction with the SW.
---------------------------------------------------------
Title: Determining the Solar Source of a Magnetic Cloud Using a
Velocity Difference Technique
Authors: Harra, L. K.; Mandrini, C. H.; Dasso, S.; Gulisano, A. M.;
Steed, K.; Imada, S.
2011SoPh..268..213H Altcode: 2010SoPh..tmp..210H; 2010SoPh..tmp..234H
For large eruptions on the Sun, it is often a problem that the core
dimming region cannot be observed due to the bright emission from the
flare itself. However, spectroscopic data can provide the missing
information through the measurement of Doppler velocities. In this
paper we analyse the well-studied flare and coronal mass ejection
that erupted on the Sun on 13 December 2006 and reached the Earth on
14 December 2006. In this example, although the imaging data were
saturated at the flare site itself, by using velocity measurements
we could extract information on the core dimming region, as well as
on remote dimmings. The purpose of this paper is to determine more
accurately the magnetic flux of the solar source region, potentially
involved in the ejection, through a new technique. The results of its
application are compared to the flux in the magnetic cloud observed at
1 AU, as a way to check the reliability of this technique. We analysed
data from the Hinode EUV Imaging Spectrometer to estimate the Doppler
velocity in the active region and its surroundings before and after
the event. This allowed us to determine a Doppler velocity `difference'
image. We used the velocity difference image overlayed on a Michelson
Doppler Imager magnetogram to identify the regions in which the blue
shifts were more prominent after the event; the magnetic flux in these
regions was used as a proxy for the ejected flux and compared to the
magnetic cloud flux. This new method provides a more accurate flux
determination in the solar source region.
---------------------------------------------------------
Title: Magnetic Reconnection in the Solar Atmopshere Observed
by Hinode
Authors: Imada, Shinsuke; Isobe, Hiroaki; Shimizu, Toshifumi
2011sswh.book...63I Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ionization non-equilibrium plasma during magnetic reconnection
in solar corona
Authors: Imada, S.; Murakami, I.; Watanabe, T.; Hara, H.; Shimizu, T.
2010AGUFMSH31A1788I Altcode:
Hinode can provide us both of the stored magnetic field energy in
corona before magnetic reconnection and the most part of energy post
reconnection stage. On the other hand, there is not enough observational
knowledge of the physical parameters in the reconnection region. The
inflow into the reconnection region, the temperature of the plasma in
the reconnection region, and the temperatures and densities of the
plasma jets predicted by reconnection, have not been quantitatively
measured in sufficient. EIS on Hinode may provide some answers if
solar cycle 24 ever produces a solar maximum. But it is important
to answer why the most observation cannot detect the predicted flow
or temperature in the reconnection region. One of the reasons why we
cannot observe inside the magnetic reconnection region is due to its
darkness. Generally we can see the bright cusp-like structure during
solar flare, although the reconnection region is faint/blind. One may
think that the temperature in the reconnection region is enough higher
than that of cusp-like flare loops. Thus the wavelength of emission
from reconnection region is different from flare loops. However, this
is not entirely true. Magnetic reconnection causes rapid heating. Thus
ionization cannot reach to the equilibrium stage. We have calculated
the ionization process in the down stream of Petschek type magnetic
reconnection. From our result, we can clearly see that plasma cannot
reach the ionization equilibrium in the down stream of slow-mode
shock. The typical emissions from magnetic reconnection region are
FeIXX or FeXX, although the plasma temperature is equal to 40MK. The
typical temperature and density of post flare loops are 10 MK and 10^11
/cc, and the dominant emissions from post flare loops are from FeIXX
to FeXXIII. Thus the wavelength of emission from reconnection region
is not so much different from post flare loops. We will discuss how
the emissions from reconnection region looks like by using several
ionization calculations of magnetic reconnection.
---------------------------------------------------------
Title: On the Origin of the Solar Moreton Wave of 2006 December 6
Authors: Balasubramaniam, K. S.; Cliver, E. W.; Pevtsov, A.; Temmer,
M.; Henry, T. W.; Hudson, H. S.; Imada, S.; Ling, A. G.; Moore, R. L.;
Muhr, N.; Neidig, D. F.; Petrie, G. J. D.; Veronig, A. M.; Vršnak,
B.; White, S. M.
2010ApJ...723..587B Altcode:
We analyzed ground- and space-based observations of the eruptive flare
(3B/X6.5) and associated Moreton wave (~850 km s<SUP>-1</SUP> ~270°
azimuthal span) of 2006 December 6 to determine the wave driver—either
flare pressure pulse (blast) or coronal mass ejection (CME). Kinematic
analysis favors a CME driver of the wave, despite key gaps in coronal
data. The CME scenario has a less constrained/smoother velocity versus
time profile than is the case for the flare hypothesis and requires an
acceleration rate more in accord with observations. The CME picture is
based, in part, on the assumption that a strong and impulsive magnetic
field change observed by a GONG magnetograph during the rapid rise phase
of the flare corresponds to the main acceleration phase of the CME. The
Moreton wave evolution tracks the inferred eruption of an extended
coronal arcade, overlying a region of weak magnetic field to the west
of the principal flare in NOAA active region 10930. Observations of
Hα foot point brightenings, disturbance contours in off-band Hα
images, and He I 10830 Å flare ribbons trace the eruption from 18:42
to 18:44 UT as it progressed southwest along the arcade. Hinode EIS
observations show strong blueshifts at foot points of this arcade
during the post-eruption phase, indicating mass outflow. At 18:45
UT, the Moreton wave exhibited two separate arcs (one off each flank
of the tip of the arcade) that merged and coalesced by 18:47 UT to
form a single smooth wave front, having its maximum amplitude in
the southwest direction. We suggest that the erupting arcade (i.e.,
CME) expanded laterally to drive a coronal shock responsible for the
Moreton wave. We attribute a darkening in Hα from a region underlying
the arcade to absorption by faint unresolved post-eruption loops.
---------------------------------------------------------
Title: Experimental Simulation of Magnetic Reconnection in the
Sunspot Light Bridge
Authors: Hayashi, Yoshinori; Tanabe, Hiroshi; Inomoto, Michiaki; Ono,
Yasushi; Shimizu, Toshifumi; Imada, Shinsuke; Nishizuka, Naoto
2010APS..DPPCP9122H Altcode:
Intermittent and recurrent chromospheric plasma ejections were
discovered in the sunspot light bridge (LB) by the Solar Optical
Telescope of the Hinode satellite (Shimizu et al. 2009, ApJ, 696,
L66). Strong current was observed under the jet, suggesting existence
of twisted flux tube in the vertical background field. The magnetic
reconnection between the flux tube and the vertical field is considered
to cause the plasma ejection. It is left unsolved why the intermittent
reconnection continuing more than one day. Note that the magnetic
configuration of LB is similar to the spheromak plasma maintained
by vertical field in the laboratory. We formed spheromak in the TS-4
device and drove magnetic reconnection with center solenoid coil. We
measured 2D magnetic profile of the reconnecting field lines between
the spheromak and the solenoid coil by the magnetic probe array and
local temperature, density and plasma flow at the reconnection point
by the Langmuir probes and ion Doppler spectroscopy. We will discuss
about the LB reconnection by comparing the laboratory experiment with
the satellite observation.
---------------------------------------------------------
Title: Mode Identification of MHD Waves in an Active Region Observed
with Hinode/EIS
Authors: Kitagawa, N.; Yokoyama, T.; Imada, S.; Hara, H.
2010ApJ...721..744K Altcode: 2010arXiv1008.1823K
In order to better understand the possibility of coronal heating
by MHD waves, we analyze Fe XII 195.12Å data observed with the EUV
Imaging Spectrometer on board Hinode. We performed a Fourier analysis
of EUV intensity and Doppler velocity time series data in the active
region corona. Notable intensity and Doppler velocity oscillations were
found for two moss regions out of the five studied, while only small
oscillations were found for five apexes of loops. The amplitudes of the
oscillations were 0.4%-5.7% for intensity and 0.2-1.2 km s<SUP>-1</SUP>
for Doppler velocity. In addition, oscillations of only the Doppler
velocity were seen relatively less often in the data. We compared
the amplitudes of intensity and those of Doppler velocity in order to
identify MHD wave modes and calculated the phase delays between Fourier
components of intensity and those of Doppler velocity. The results
are interpreted in terms of MHD waves as follows: (1) few kink modes
or torsional Alfvén mode waves were seen in both moss regions and the
apexes of loops, (2) upwardly propagating and standing slow mode waves
were found in moss regions, and (3) consistent with previous studies,
estimated values of energy flux of the waves were several orders of
magnitude lower than that required for heating active regions.
---------------------------------------------------------
Title: Accelerating Waves in Polar Coronal Holes as Seen by EIS
and SUMER
Authors: Gupta, G. R.; Banerjee, D.; Teriaca, L.; Imada, S.;
Solanki, S.
2010ApJ...718...11G Altcode: 2010arXiv1005.3453G
We present EIS/Hinode and SUMER/SOHO observations of propagating
disturbances detected in coronal lines in inter-plume and plume
regions of a polar coronal hole. The observation was carried out on
2007 November 13 as part of the JOP196/HOP045 program. The SUMER
spectroscopic observation gives information about fluctuations in
radiance and on both resolved (Doppler shift) and unresolved (Doppler
width) line-of-sight velocities, whereas EIS 40” wide slot images
detect fluctuations only in radiance but maximize the probability
of overlapping field of view between the two instruments. From
distance-time radiance maps, we detect the presence of propagating
waves in a polar inter-plume region with a period of 15-20 minutes
and a propagation speed increasing from 130 ± 14 km s<SUP>-1</SUP>
just above the limb to 330 ± 140 km s<SUP>-1</SUP> around 160” above
the limb. These waves can be traced to originate from a bright region
of the on-disk part of the coronal hole where the propagation speed
is in the range of 25 ± 1.3 to 38 ± 4.5 km s<SUP>-1</SUP>, with the
same periodicity. These on-disk bright regions can be visualized as the
base of the coronal funnels. The adjacent plume region also shows the
presence of propagating disturbances with the same range of periodicity
but with propagation speeds in the range of 135 ± 18 to 165 ± 43 km
s<SUP>-1</SUP> only. A comparison between the distance-time radiance
map of the two regions indicates that the waves within the plumes are
not observable (may be getting dissipated) far off-limb, whereas this
is not the case in the inter-plume region. A correlation analysis was
also performed to find out the time delay between the oscillations at
several heights in the off-limb region, finding results consistent with
those from the analysis of the distance-time maps. To our knowledge,
this result provides first spectroscopic evidence of the acceleration of
propagating disturbances in the polar region close to the Sun (within
1.2 R/R <SUB>sun</SUB>), which provides clues to the understanding of
the origin of these waves. We suggest that the waves are likely either
Alfvénic or fast magnetoacoustic in the inter-plume region and slow
magnetoacoustic in the plume region. This may lead to the conclusion
that inter-plumes are a preferred channel for the acceleration of the
fast solar wind.
---------------------------------------------------------
Title: Accelerating disturbances in polar plume and inter-plume
Authors: Gupta, Girjesh R.; Banerjee, Dipankar; Teriaca, Luca; Imada,
Shinsuke; Solanki, Sami
2010cosp...38.2937G Altcode: 2010cosp.meet.2937G
We present EIS/Hinode & SUMER/SoHO joint observations allowing the
first spectroscopic detection of accelerating disturbances as recorded
with coronal lines in inter-plume and plume regions of a polar coronal
hole. From time-distance radiance maps, we detect the presence of
propagating disturbances in a polar inter-plume region with a period
of 15 to 20 min and a propagation speed increasing from 130±14 km/s
just above the limb, to 330±140 km/s around 160" above the limb. These
disturbances can also be traced to originate from a bright region of
the on-disk part of the coronal hole where the propagation speed was
found to be in the range of 25±1.3 to 38±4.5 km/s, with the same
periodicity. These on-disk bright regions can be vi-sualized as the
base of the coronal funnels. The adjacent plume region also shows the
presence of propagating disturbance with the same range of period but
with propagation speeds in the range of 135±18 to 165±43 km/s only. A
comparison between the time-distance radiance map of both regions,
indicate that the disturbances within the plumes are not observable (may
be getting dissipated) far off-limb whereas this is not the case in the
inter-plume region. Conclu-sions drawn from these observations in terms
of accelerating waves or high speed jets/upflows will be discussed.
---------------------------------------------------------
Title: Comparison of reconnection in magnetosphere and solar corona
Authors: Imada, Shinsuke; Hirai, Mariko; Isobe, Hiroaki; Oka, Mitsuo;
Watanabe, Kyoko; Minoshima, Takashi
2010cosp...38.1940I Altcode: 2010cosp.meet.1940I
One of the most famous rapid energy conversion mechanisms in space is a
magnetic reconnec-tion. The general concept of a magnetic reconnection
is that the rapid energy conversion from magnetic field energy to
thermal energy, kinetic energy or non-thermal particle energy. The
understanding of rapid energy conversion rates from magnetic field
energy to other energy is the fundamental and essential problem in
the space physics. One of the important goals for studying magnetic
reconnection is to answer what plasma condition/parameter controls
the energy conversion rates. Earth's magnetotail has been paid
much attention to discuss a mag-netic reconnection, because we can
discuss magnetic reconnection characteristics in detail with direct
in-situ observation. Recently, solar atmosphere has been focused as a
space laboratory for magnetic reconnection because of its variety in
plasma condition. So far considerable effort has been devoted toward
understanding the energy conversion rates of magnetic reconnection,
and various typical features associated with magnetic reconnection have
been observed in the Earth's magnetotail and the solar corona. In this
talk, we first introduce the variety of plasma condition/parameter in
solar corona and Earth's magnetotail. Later, we discuss what plasma
condition/parameter controls the energy conversion from magnetic field
to especially non-thermal particle. To compare non-thermal electron and
ion acceleration in magnetic reconnection, we used Hard X-ray (electron)
/Neu-tron monitor (ion) for solar corona and Geotail in-situ measurement
(electron and ion) for magnetoatil. We found both of electron and ion
accelerations are roughly controlled by re-connection electric field
(reconnection rate). However, some detail points are different in ion
and electron acceleration. Further, we will discuss what is the major
difference between solar corona and Earth's magnetotail for particle
acceleration.
---------------------------------------------------------
Title: Ion Temperature and Non-Thermal Velocity in a Solar Active
Region: Using Emission Lines of Different Atomic Species
Authors: Imada, S.; Hara, H.; Watanabe, T.
2009ApJ...705L.208I Altcode:
We have studied the characteristics of the ion thermal temperature
and non-thermal velocity in an active region observed by the EUV
Imaging Spectrometer onboard Hinode. We used two emission lines of
different atomic species (Fe XVI 262.98 Å and S XIII 256.69 Å) to
distinguish the ion thermal velocity from the observed full width at
half-maximum. We assumed that the sources of the two emission lines
are the same thermal temperature. We also assumed that they have the
same non-thermal velocity. With these assumptions, we could obtain
the ion thermal temperature, after noting that M <SUB>sulfur</SUB> ~
0.6M <SUB>iron</SUB>. We have carried out the ion thermal temperature
analysis in the active region where the photon counts are sufficient
(>4500). What we found is as follows: (1) the common ion thermal
temperatures obtained by Fe XVI and S XIII are ~2.5 MK, (2) the typical
non-thermal velocities are ~13 km s<SUP>-1</SUP>, (3) the highest
non-thermal velocities (>20 km s<SUP>-1</SUP>) are preferentially
observed between the bright points in Fe XVI, while (4) the hottest
material (>3 MK) is observed relatively inside the bright points
compared with the highest non-thermal velocity region.
---------------------------------------------------------
Title: Coronal Mass Ejection Induced Outflows Observed with Hinode/EIS
Authors: Jin, M.; Ding, M. D.; Chen, P. F.; Fang, C.; Imada, S.
2009ApJ...702...27J Altcode:
We investigate the outflows associated with two halo coronal mass
ejections (CMEs) that occurred on 2006 December 13 and 14 in NOAA
10930, using the Hinode/EIS observations. Each CME was accompanied by
an EIT wave and coronal dimmings. Dopplergrams in the dimming regions
are obtained from the spectra of seven EIS lines. The results show
that strong outflows are visible in the dimming regions during the
CME eruption at different heights from the lower transition region to
the corona. It is found that the velocity is positively correlated
with the photospheric magnetic field, as well as the magnitude of
the dimming. We estimate the mass loss based on height-dependent EUV
dimmings and find it to be smaller than the CME mass derived from
white-light observations. The mass difference is attributed partly to
the uncertain atmospheric model, and partly to the transition region
outflows, which refill the coronal dimmings.
---------------------------------------------------------
Title: Evidence from the Extreme-Ultraviolet Imaging Spectrometer
for Axial Filament Rotation before a Large Flare
Authors: Williams, David R.; Harra, Louise K.; Brooks, David H.;
Imada, Shinsuke; Hansteen, Viggo H.
2009PASJ...61..493W Altcode:
In this article, we present observations made with the
Extreme-ultraviolet Imaging Spectrometer on-board the Hinode solar
satellite, of an active region filament in the HeII emission line at
256.32Å. The host active region AR 10930 produces an X-class flare
during these observations. We measure Doppler shifts with apparent
velocities of up to 20km s<SUP>-1</SUP>, which are antisymmetric about
the filament length and occur several minutes before the flare's
impulsive phase. This is indicative of a rotation of the filament,
which is in turn consistent with expansion of a twisted flux rope due
to the MHD helical kink instability. This is the first time that such
an observation has been possible in this transition-region line, and we
note that the signature observed occurs before the first indications of
pre-flare activity in the GOES solar soft X-ray flux, suggesting that
the filament begins to destabilise in tandem with a reorganization of
the local magnetic field. We suggest that this expansion is triggered
by the decrease of magnetic tension around, and/or total pressure above,
the filament.
---------------------------------------------------------
Title: Propagating waves in polar coronal holes as seen by SUMER
& EIS
Authors: Banerjee, D.; Teriaca, L.; Gupta, G. R.; Imada, S.; Stenborg,
G.; Solanki, S. K.
2009A&A...499L..29B Altcode: 2009arXiv0905.1013B
Context: To study the dynamics of coronal holes and the role of waves in
the acceleration of the solar wind, spectral observations were performed
over polar coronal hole regions with the SUMER spectrometer on SoHO and
the EIS spectrometer on Hinode. <BR />Aims: Using these observations,
we aim to detect the presence of propagating waves in the corona and
to study their properties. <BR />Methods: The observations analysed
here consist of SUMER spectra of the Ne viii 770 Å line (T = 0.6 MK)
and EIS slot images in the Fe xii 195 Å line (T = 1.3 MK). Using the
wavelet technique, we study line radiance oscillations at different
heights from the limb in the polar coronal hole regions. <BR />Results:
We detect the presence of long period oscillations with periods of 10
to 30 min in polar coronal holes. The oscillations have an amplitude
of a few percent in radiance and are not detectable in line-of-sight
velocity. From the time distance maps we find evidence for propagating
velocities from 75 km s<SUP>-1</SUP> (Ne viii) to 125 km s<SUP>-1</SUP>
(Fe xii). These velocities are subsonic and roughly in the same ratio
as the respective sound speeds. <BR />Conclusions: We interpret the
observed propagating oscillations in terms of slow magneto-acoustic
waves. These waves can be important for the acceleration of the fast
solar wind.
---------------------------------------------------------
Title: Multiwavelength Observation of Electron Acceleration in the
2006 December 13 Flare
Authors: Minoshima, T.; Imada, S.; Morimoto, T.; Kawate, T.;
Koshiishi, H.; Kubo, M.; Inoue, S.; Isobe, H.; Masuda, S.; Krucker,
S.; Yokoyama, T.
2009ApJ...697..843M Altcode: 2009arXiv0903.1144M
We present a multiwavelength observation of a solar flare occurring on
2006 December 13 with Hinode, RHESSI, and the Nobeyama Radio Observatory
to study the electron acceleration site and mechanism. The Solar Optical
Telescope (SOT) on board Hinode observed elongated flare ribbons, and
RHESSI observed double-footpoint hard X-ray (HXR) sources appearing
in part of the ribbons. A photospheric vector magnetogram obtained
from SOT reveals that the HXR sources are located at the region where
horizontal magnetic fields change direction. The region is interpreted
as the footpoint of magnetic separatrix. Microwave images taken
with the Nobeyama Radioheliograph show a loop structure connecting
the HXR sources. The brighter parts of the microwave intensity are
located between the top and footpoints of the loop. We consider these
observations as evidence of electron acceleration near the magnetic
separatrix and injection parallel to the field line.
---------------------------------------------------------
Title: Observational Study of Particle Acceleration in the 2006
December 13 Flare
Authors: Minoshima, T.; Morimoto, T.; Kawate, T.; Imada, S.;
Koshiishi, H.; Masuda, S.; Kubo, M.; Inoue, S.; Isobe, H.; Krucker,
S.; Yokoyama, T.
2008AGUFMSH41B1619M Altcode:
We study the particle acceleration in a flare on 2006 December 13,
by using the Hinode, RHESSI, Nobeyama Radio Polarimeters (NoRP) and
Nobeyama Radioheliograph (NoRH) observations. For technical reasons,
both RHESSI and NoRH have a problem in imaging in this flare. Since we
have succeeded in solving the problem, it is now possible to discuss
the particle acceleration mechanism from an image analysis. This flare
shows very long-lasting (1 hour) non-thermal emissions, consisting of
many spikes. We focus on the second major spike at 02:29 UT, because
the RHESSI image is available only in this period. The RHESSI 35-100 keV
HXR image shows double sources located at the footpoints of the western
soft X-ray (SXR) loop seen by the Hinode/XRT. The non-linear force-free
(NLFF) modeling based on a magnetogram data by Inoue et al. shows the
NLFF to potential magnetic transition of the loop, which would induce
the electric field and then accelerate particles. Overlaying the HXR
image on the photospheric three-dimensional magnetic field map taken
by the Hinode Spectro-Polarimeter, we find that the HXR sources are
located at the region where the horizontal magnetic fields invert. The
NoRH 34 GHz microwave images show the loop structure connecting the
HXR sources. The microwave peaks do not located at the top of the
loop but between the loop top and the footpoints. The NoRP microwave
spectrum shows the soft-hard-soft pattern in the period, same as the
HXR spectrum (Ning 2008). From these observational results we suggest
that the electrons were accelerated parallel to the magnetic field
line near the magnetic separatrix.
---------------------------------------------------------
Title: The dawn-dusk asymmetry of energetic electron in the Earth's
magnetotail: Observation and transport models
Authors: Imada, S.; Hoshino, M.; Mukai, T.
2008JGRA..11311201I Altcode:
We have studied the dawn-dusk asymmetry of the energetic/thermal
particle in the plasma sheet using the Geotail data. We found the
species- and energy-dependent dawn-dusk asymmetries in the plasma
sheet. The dawn-dusk asymmetries have some typical structures, and
we used a finite width two-dimensional model of the magnetotail to
explain their characteristics. The characteristics and assumptions
of our model can be summarized as follows: (1) the magnetotail
convection is steady (both of magnetic field and electric field is
steady), (2) the directions of electric fields are duskward, (3) the
directions of magnetic fields are northward, (4) the magnetic field
gradient is constant for earthward (constant for other directions),
(5) the width of the magnetotail is constant in the entire plasma
sheet (40 R<SUB>E</SUB>), (6) the plasma source region is steady at
X<SUB>GSM</SUB> ∼ -100 R<SUB>E</SUB>, (7) the magnetic moment μ is
conserved during transport, and (8) the particle spatial diffusion takes
place only for dawn-dusk direction. In this model, we found that the
energetic electrons cannot be provided sufficiently at the dusk flank
with the simple adiabatic process (no spatial diffusion). Furthermore
we applied the Bohm-type diffusion to the model and found that the
observed asymmetries are well reproduced in the case that the diffusion
coefficient is equal to 0.006/0.03v<SUB>⊥</SUB>r<SUB>g</SUB> for
electron/ion.
---------------------------------------------------------
Title: Strongly Blueshifted Phenomena Observed with Hinode EIS in
the 2006 December 13 Solar Flare
Authors: Asai, Ayumi; Hara, Hirohisa; Watanabe, Tetsuya; Imada,
Shinsuke; Sakao, Taro; Narukage, Noriyuki; Culhane, J. L.; Doschek,
G. A.
2008ApJ...685..622A Altcode: 2008arXiv0805.4468A
We present a detailed examination of strongly blueshifted emission
lines observed with the EUV Imaging Spectrometer on board the Hinode
satellite. We found two kinds of blueshifted phenomenon associated
with the X3.4 flare that occurred on 2006 December 13. One was related
to a plasmoid ejection seen in soft X-rays. It was very bright in all
the lines used for the observations. The other was associated with the
faint arc-shaped ejection seen in soft X-rays. The soft X-ray ejection
is thought to be a magnetohydrodynamic (MHD) fast-mode shock wave. This
is therefore the first spectroscopic observation of an MHD fast-mode
shock wave associated with a flare.
---------------------------------------------------------
Title: Doppler Shifts in the Boundary of the Dimming Region
Authors: Imada, S.; Hara, H.; Watanabe, T.; Asai, A.; Kamio, S.;
Matsuzaki, K.; Harra, L. K.; Mariska, J. T.
2008ASPC..397..102I Altcode:
We present Hinode/EIS raster scan observations of the GOES X3.2
flare that occurred on 2006 December 13. There was a small transient
coronal hole which was located 200 arcsec east of the flare arcade. The
transient coronal hole was strongly affected by the X-class flare, and
the strong upflows were observed in Fe XV line 284.2 Å (log{T/{K}}
= 6.3) at the boundary of dimming region. In this paper, we discuss
how to obtain the velocity map by correcting the instrumental effects.
---------------------------------------------------------
Title: Non-Gaussian Line Profiles in a Large Solar Flare Observed
on 2006 December 13
Authors: Imada, S.; Hara, H.; Watanabe, T.; Asai, A.; Minoshima, T.;
Harra, L. K.; Mariska, J. T.
2008ApJ...679L.155I Altcode:
We have studied the characteristics of the non-Gaussian line profile
of the Fe XIV 274.20 Å line in and around a flare arcade. We found
that broad non-Gaussian line profiles associated with redshifts
are observed in the flare arcade. There were two typical types
of broad line profiles. One was a distorted line profile caused by
multiple flows, and the other was a symmetric line profile without any
additional component. We successfully distinguished those two types
using higher order statistical moments or M—the additional component
contribution—defined in this Letter. The distorted/symmetric broad
line profiles were preferentially observed in new/old flare loops,
respectively.
---------------------------------------------------------
Title: Outflows at the Edges of Active Regions: Contribution to
Solar Wind Formation?
Authors: Harra, L. K.; Sakao, T.; Mandrini, C. H.; Hara, H.; Imada,
S.; Young, P. R.; van Driel-Gesztelyi, L.; Baker, D.
2008ApJ...676L.147H Altcode:
The formation of the slow solar wind has been debated for many years. In
this Letter we show evidence of persistent outflow at the edges of
an active region as measured by the EUV Imaging Spectrometer on board
Hinode. The Doppler velocity ranged between 20 and 50 km s<SUP>-1</SUP>
and was consistent with a steady flow seen in the X-Ray Telescope. The
latter showed steady, pulsing outflowing material and some transverse
motions of the loops. We analyze the magnetic field around the active
region and produce a coronal magnetic field model. We determine from
the latter that the outflow speeds adjusted for line-of-sight effects
can reach over 100 km s<SUP>-1</SUP>. We can interpret this outflow as
expansion of loops that lie over the active region, which may either
reconnect with neighboring large-scale loops or are likely to open to
the interplanetary space. This material constitutes at least part of
the slow solar wind.
---------------------------------------------------------
Title: Erratum: "Outflows at the Edges of Active Regions: Contribution
to Solar Wind Formation?" (ApJ, 676, L147 [2008])
Authors: Harra, L. K.; Sakao, T.; Mandrini, C. H.; Hara, H.; Imada,
S.; Young, P. R.; van Driel-Gesztelyi, L.; Baker, D.
2008ApJ...677L.159H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observation of energetic electrons within magnetic islands
Authors: Chen, L. -J.; Bhattacharjee, A.; Puhl-Quinn, P. A.; Yang,
H.; Bessho, N.; Imada, S.; Mühlbachler, S.; Daly, P. W.; Lefebvre,
B.; Khotyaintsev, Y.; Vaivads, A.; Fazakerley, A.; Georgescu, E.
2008NatPh...4...19C Altcode:
Magnetic reconnection is the underlying process that releases
impulsively an enormous amount of magnetic energy in solar flares
, flares on strongly magnetized neutron stars and substorms in the
Earth's magnetosphere. Studies of energy release during solar flares,
in particular, indicate that up to 50% of the released energy is
carried by accelerated 20-100keV suprathermal electrons. How so
many electrons can gain so much energy during reconnection has been
a long-standing question. A recent theoretical study suggests that
volume-filling contracting magnetic islands formed during reconnection
can produce a large number of energetic electrons. Here we report the
first evidence of the link between energetic electrons and magnetic
islands during reconnection in the Earth's magnetosphere. The results
indicate that energetic electron fluxes peak at sites of compressed
density within islands, which imposes a new constraint on theories of
electron acceleration.
---------------------------------------------------------
Title: Discovery of a Temperature-Dependent Upflow in the Plage
Region During a Gradual Phase of the X-Class Flare
Authors: Imada, Shinsuke; Hara, Hirohisa; Watanabe, Tetsuya; Kamio,
Suguru; Asai, Ayumi; Matsuzaki, Keiichi; Harra, Louise K.; Mariska,
John T.
2007PASJ...59S.793I Altcode:
We present Hinode/EIS raster scan observations of the plage region
taken during the gradual phase of the GOES X3.2 flare that occurred on
2006 December 13. The plage region is located 200" east of the flare
arcade. The plage region has a small transient coronal hole. The
transient coronal hole is strongly affected by an X-class flare,
and upflows are observed at its boundary. Multi-wavelength spectral
observations allow us to determine velocities from the Doppler shifts
at different temperatures. Strong upflows along with stationary plasma
have been observed in the FeXV line 284.2Å (log T / K = 6.3) in the
plage region. The strong upflows reach almost 150kms<SUP>-1</SUP>, which
was estimated by a two-component Gaussian fitting. On the other hand,
at a lower corona/transition region temperature (HeII, 256.3Å, log T /
K = 4.9), very weak upflows, almost stationary, have been observed. We
find that these upflow velocities clearly depend on the temperature
with the hottest line, FeXV, showing the fastest upflow velocity and the
second-highest line, FeXIV, showing the second-highest upflow velocity
(130kms<SUP>-1</SUP>). All velocities are below the sound speed. The
trend of the upflow dependence on temperature dramatically changes
at 1MK. These results suggest that heating may have an important role
for strong upflow.
---------------------------------------------------------
Title: Coronal Dimming Observed with Hinode: Outflows Related to a
Coronal Mass Ejection
Authors: Harra, Louise K.; Hara, Hirohisa; Imada, Shinsuke; Young,
Peter R.; Williams, David R.; Sterling, Alphonse C.; Korendyke,
Clarence; Attrill, Gemma D. R.
2007PASJ...59S.801H Altcode:
Coronal dimming has been a signature used to determine the source
of plasma that forms part of a coronal mass ejection (CME) for many
years. Generally dimming is detected through imaging instruments such
as SOHO EIT by taking difference images. Hinode tracked active region
10930 from which there were a series of flares. We combined dimming
observations from EIT with Hinode data to show the impact of flares
and coronal mass ejections on the region surrounding the flaring
active region, and we discuss evidence that the eruption resulted in
a prolonged steady outflow of material from the corona. The dimming
region shows clear structure with extended loops whose footpoints are
the source of the strongest outflow (≈ 40 kms<SUP>-1</SUP>). This
confirms that the loops that are disrupted during the event do lose
plasma and hence are likely to form part of the CME. This is the
first time the velocity of the coronal plasma has been measured in an
extended dimming region away from the flare core. In addition there
was a weaker steady outflow from extended, faint loops outside the
active region before the eruption, which is also long lasting. These
were disturbed and the velocity increased following the flare. Such
outflows could be the source of the slow solar wind.
---------------------------------------------------------
Title: Cluster observation of magnetic islands and energetic electrons
Authors: Chen, L.; Bhattacharjee, A.; Puhl-Quinn, P. A.; Yang, H.;
Bessho, N.; Imada, S.; Muehlbachler, S.; Daly, P.; Lefebvre, B.;
Fazakerley, A.; Georgescu, E.; Mouikis, C.
2007AGUSMSM53C..06C Altcode:
Magnetic reconnection is widely accepted to be a mechanism for
electron acceleration, but exactly how electrons are accelerated
during reconnection remains a long-standing question. A series of
magnetic islands is observed in the magnetotail current sheet during
active reconnection by multiple spacecraft. Electrons are hot within
islands. The islands move away from the main reconnection sites with
a velocity ~ 500 km/s based on multi-spacecraft timing analysis. The
electric current distribution within an island varies significantly over
a fraction of an ion inertial length in the out-of-plane direction,
necessitating a 3D description. Associated with each island, is a
burst of energetic electrons with energies ~35 to 120 keV. High
time-resolution data reveal that energetic electron fluxes peak
at sites of compressed density within magnetic islands. Within the
islands, the density of O+ is higher than that of H+. The O+ ions are
unmagnetized, and their density exhibits similar compression as the
electron density, indicating that the density compression is not due
to magnetic trapping by contracting islands, but most likely, due to
the continuous injection of the ion and electron jets from the two
reconnection sites bounding an island. The observation establishes a
link between energetic electrons and magnetic islands, and provides
supporting evidence for multiple reconnection sites.
---------------------------------------------------------
Title: Particle Acceleration in the X3 Event on Dec. 13, 2007
Authors: Shibasaki, Kiyoto; Koshiishi, H.; Shimojo, M.; Minoshima,
T.; Imada, S.; Sakao, T.; Hinode Team
2007AAS...210.9435S Altcode: 2007BAAS...39..223S
Even during the solar minimum period, the active region NOAA 10930 had
a complex magnetic configuration especially around the main sunspot
and produced a couple of X-class events. The one on Dec. 13, 2007 was
well observed by Nobeyama Radioheliograph (NoRH) and Polarimeters
(NoRP). Microwave emission associated with this event has several
interesting characteristics: <P />1. Long lasting non-thermal phase <P
/>2. Very large decimetric flux (several thousand times of the quiet
sun flux) and quite different time development of decimetric emission
compared to shorter wavelengths <P />3. Very high turn-over frequency
(around 35 GHz) <P />This event was also well observed by HINODE
satellite and partially by RHESSI satellite. Optical telescope (SOT) and
Soft X-ray telescope (XRT) onboard HINODE showed that the flare started
around the polarity reversal line which divides the main sunspot and
the closely associated small sunspot with opposite polarity. This line
is the interface of the penumbrae of both sunspots. The flare ribbons
started in the penumbrae and entered into umbrae of both sunspots. <P
/>Microwave images of the event at 17 and 34 GHz are synthesized
and compared with optical and soft X-ray images taken by SOT and XRT
respectively. Based on these overlays, frequency spectral information
(NoRP) and RHESSI images in the later phase of the event, we try to
locate particle acceleration site and discuss possible mechanisms of
acceleration. <P />Hinode is an international project supported by JAXA,
NASA, PPARC and ESA. We are grateful to the Hinode team for all their
efforts in the design, development and operation of the mission. NoRH
and NoRP are operated by Nobeyama Solar Radio Observatory, NAOJ. RHESSI
is a NASA project.
---------------------------------------------------------
Title: Energetic electron acceleration in the downstream reconnection
outflow region
Authors: Imada, S.; Nakamura, R.; Daly, P. W.; Hoshino, M.; Baumjohann,
W.; Mühlbachler, S.; Balogh, A.; RèMe, H.
2007JGRA..112.3202I Altcode: 2007JGRA..11203202I
Energetic electrons in an earthward reconnection outflow region have
been observed by Cluster/Research with Adaptive Particle Imaging
Detectors. We found a good correlation between the energetic electron
enhancement and a normal magnetic field (B<SUB>z</SUB>) enhancement
within a 0.25-s time resolution. The large normal magnetic field
is thought to be associated with magnetic reconnection because the
negative/positive B<SUB>z</SUB> reversal observed during the fast
proton tailward/earthward flow reversal is a good indicator of magnetic
reconnection. Using the four-spacecraft Cluster, we can clearly see
that this large positive B<SUB>z</SUB> structure propagates in the
earthward direction. Furthermore, we find that the energy spectrum
of the energetic electrons becomes harder toward the downstream
region. A negative B<SUB>z</SUB> enhancement is also observed. The
intensity of energetic electron enhancement associated with the
negative B<SUB>z</SUB> enhancement is weaker than that associated
with the positive one. To discuss the temporal and spatial profile of
energetic electron acceleration in the magnetic reconnection region,
we determined the spacecraft position in the temporally evolving
magnetic structures of reconnection. Our observation clearly indicates
second-step acceleration, in addition to X line acceleration, of
energetic electrons in the downstream reconnection outflow region.
---------------------------------------------------------
Title: Electron acceleration by impulsive reconnection near
separatrices: Cluster observations
Authors: Mühlbachler, S.; Chen, L.; Imada, S.; Puhl-Quinn, P.;
Lefebvre, B.; Bhattacharjee, A.; Daly, P.; Georgescu, E.
2006AGUFMSM43C..05M Altcode:
Near a magnetotail reconnection site, energetic electron bursts
(50-100 keV) were observed by the Cluster spacecraft. These bursts
correlate closely with spiky electric fields and pulse-like structures
in the magnetic field. The spiky electric fields have DC components
greater than 20 mV/m and AC components reaching 300 mV/m peak to
peak. The pulse-like magnetic structures have Δ B/B ~ 1 and time
durations comparable to one proton gyroperiod. Most of the energetic
electron bursts were observed near the separatrices in the reconnection
exhaust. Our observations are consistent with electron acceleration by
electric fields at the separatrices. The strong correlation between the
electron bursts and sudden commencements of large-amplitude electric
and magnetic structures suggests that the underlying reconnection
dynamics is impulsive and non-steady.
---------------------------------------------------------
Title: Average profiles of energetic and thermal electrons in the
magnetotail reconnection regions
Authors: Imada, S.; Hoshino, M.; Mukai, T.
2005GeoRL..32.9101I Altcode: 2005GeoRL..3209101I
We study plasma heating and acceleration around magnetic reconnection
region by using GEOTAIL data. We carry out the superposed analysis
of thermal temperature and energetic electrons flux as a function
of distance from X-type neutral line, for both the near-Earth and
the distant magnetotail. It is found that the enhanced energetic
flux and high temperature regions are located around reconnection
outflow region downstream away from the center of the X-type neutral
region. Those heated and accelerated regions are symmetric in both
of the tail- and earth-ward flow regions in the distant magnetotail,
while in the near-Earth magnetotail more energetic electrons are
preferentially observed in the earthward flow region. In addition,
we also study electron heating and acceleration during the passage of
plasmoid, which may correspond to O-type neutral line. We find the hot
and energetic electrons behind the core of plasmoid but slightly away
from the central plasma sheet.
---------------------------------------------------------
Title: The Dawn-Dusk Asymmetry in Magnetosheath and the Leakage of
Energetic Electrons: The Geotail Observation
Authors: Imada, S.; Hoshino, M.; Mukai, T.
2005fmpp.conf...34I Altcode:
No abstract at ADS
