Author name code: bertello
ADS astronomy entries on 2022-09-14
author:"Bertello, Luca"
------------------------------------------------------------------------
Title: Multi-height Measurements Of The Solar Vector Magnetic Field:
A White Paper Submitted To The Decadal Survey For Solar And Space
Physics (Heliophysics) 2024-2033
Authors: Bertello, L.; Arge, N.; De Wijn, A. G.; Gosain, S.; Henney,
C.; Leka, K. D.; Linker, J.; Liu, Y.; Luhmann, J.; Macniece, P. J.;
Petrie, G.; Pevtsov, A.; Pevtsov, A. A.
Bibcode: 2022arXiv220904453B
Altcode:
This white paper advocates the importance of multi-height measurements
of the vector magnetic field in the solar atmosphere. As briefly
described in this document, these measurements are critical for
addressing some of the most fundamental questions in solar and
heliospheric physics today, including: (1) What is the origin
of the magnetic field observed in the solar atmosphere? (2) What
is the coupling between magnetic fields and flows throughout the
solar atmosphere? Accurate measurements of the photospheric and
chromospheric three-dimensional magnetic fields are required for
a precise determination of the emergence and evolution of active
regions. Newly emerging magnetic flux in pre-existing magnetic regions
causes an increase in the topological complexity of the magnetic field,
which leads to flares and coronal mass ejections. Measurements of the
vector magnetic field constitute also the primary product for space
weather operations, research, and modeling of the solar atmosphere
and heliosphere. The proposed next generation Ground-based solar
Observing Network Group (ngGONG), a coordinated system of multi-platform
instruments, will address these questions and provide large datasets
for statistical investigations of solar feature behavior and evolution
and continuity in monitoring for space-weather focused endeavors
both research and operational. It will also enable sun-as-a-star
investigations, crucial as we look toward understanding other
planet-hosting stars.
Title: The exoplanetary magnetosphere extension in Sun-like stars
based on the solar wind - solar UV relation
Authors: Reda, Raffaele; Giovannelli, Luca; Alberti, Tommaso; Berrilli,
Francesco; Bertello, Luca; Del Moro, Dario; Di Mauro, Maria Pia;
Giobbi, Piermarco; Penza, Valentina
Bibcode: 2022arXiv220301554R
Altcode:
Earth's magnetosphere extension is controlled by solar activity level
via solar wind properties. Understanding such a relation in the Solar
System is useful to predict the condition of exoplanetary magnetosphere
near Sun-like stars. We use measurements of a chromospheric proxy,
the Ca II K index, and solar wind OMNI parameters to connect the
solar activity variations on the decennial time scales to solar
wind properties. The dataset span over the time interval 1965-2021,
which almost entirely covers the last 5 solar cycles. Using both
cross-correlation and mutual information analysis, a 3.2-year
lag of the solar wind speed with respect to the Ca II K index is
found. Analogously, a 3.6-year lag is found with respect to the dynamic
pressure. A correlation between the solar wind dynamic pressure and the
solar UV emission is therefore found and used to derive the Earth's
magnetopause standoff distance. Moreover, the advantage of using a
chromospheric proxy, such as the Ca II K index, opens the possibility
to extend the relation found for the Sun to Sun-like stars, by linking
stellar variability to stellar wind properties. The model is applied
to a sample of Sun-like stars as a case study, where we assume the
presence of an Earth-like exoplanet at 1 AU. Finally, we compare our
results with previous estimates of the magnetosphere extension for
the same set of sun-like stars.
Title: On the Application of the Equal-contrast Technique to Ca-K
Data from Kodaikanal and Other Observatories
Authors: Singh, Jagdev; Priyal, Muthu; Ravindra, Belur; Bertello,
Luca; Pevtsov, Alexei A.
Bibcode: 2022ApJ...927..154S
Altcode:
The "equal-contrast technique" (ECT) methodology, developed by Singh et
al. to generate uniform long time series of Ca-K images obtained during
the 20th century from the Kodaikanal Observatory (KO), improved the
correlation between the plage area and sunspot parameters. The same
methodology can also be used on other observatory data taken with
different instruments. We can combine such ECT-corrected images to
reduce the gaps in the observations and make a long uniform data set
to study short- and long-term variations. We apply this procedure to
Mount Wilson Observatory (MWO) historical Ca-K data and recent Ca-K
filtergrams obtained using narrowband filters at KO and the Mauna Loa
Solar Observatory (MLSO). To determine the success of this method, the
results of the analysis of the ECT images obtained from KO, MWO, and
MLSO are compared. A comparison of the plage and active areas derived
from KO and MWO images before and after the ECT procedure indicates
an improvement in the correlation coefficients (CCs) between all the
data sets after the ECT application. The CC for the combined monthly
mean Ca-K plage area derived from the KO, MWO, and Precision Solar
Photometric Telescope (at the MLSO) data with sunspot numbers is 0.96
for the period 1905-2015. The paper demonstrates that the time series
of Ca-K data obtained from different instruments after applying the
ECT procedure becomes uniform in contrast. The combined time series
of KO and MWO spectroheliograms has 12 hr intervals compared to the
≍24 hr gap for a time series from a single observatory.
Title: AWSoM Magnetohydrodynamic Simulation of a Solar Active Region
with Realistic Spectral Synthesis
Authors: Shi, Tong; Manchester, Ward, IV; Landi, Enrico; van der
Holst, Bart; Szente, Judit; Chen, Yuxi; Tóth, Gábor; Bertello,
Luca; Pevtsov, Alexander
Bibcode: 2022ApJ...928...34S
Altcode:
For the first time, we simulate the detailed spectral line emission
from a solar active region (AR) with the Alfvén Wave Solar Model
(AWSoM). We select an AR appearing near disk center on 2018 July 13
and use the National Solar Observatory's Helioseismic and Magnetic
Imager synoptic magnetogram to specify the magnetic field at the
model's inner boundary. To resolve small-scale magnetic features, we
apply adaptive mesh refinement with a horizontal spatial resolution
of 0°.35 (4.5 Mm), four times higher than the background corona. We
then apply the SPECTRUM code, using CHIANTI spectral emissivities,
to calculate spectral lines forming at temperatures ranging from 0.5
to 3 MK. Comparisons are made between the simulated line intensities
and those observed by Hinode/Extreme-ultraviolet Imaging Spectrometer
where we find close agreement across a wide range of loop sizes and
temperatures (about 20% relative error for both the loop top and
footpoints at a temperature of about 1.5 MK). We also simulate and
compare Doppler velocities and find that simulated flow patterns are
of comparable magnitude to what is observed. Our results demonstrate
the broad applicability of the low-frequency AWSoM for explaining the
heating of coronal loops.
Title: Measurements of the Multi-Height Solar Vector Magnetic Field
Authors: Bertello, L.; Pevtsov, A.; Pevtsov, A. A.
Bibcode: 2022heli.conf.4011B
Altcode:
The development of sophisticated numerical models of the heliosphere
have made measurements of the solar vector magnetic field extremely
relevant today. These measurements and a newly proposed ground-based
global network will be discussed.
Title: Analysis of Solar Hemispheric Chromosphere Properties using
the Kodaikanal Observatory Ca-K Index
Authors: Chowdhury, Partha; Belur, Ravindra; Bertello, Luca; Pevtsov,
Alexei A.
Bibcode: 2022ApJ...925...81C
Altcode:
The Kodaikanal Observatory has provided long-term synoptic observations
of chromospheric activities in the Ca II K line (393.34 nm) since
1907. This article investigates temporal and periodic variations of the
hemispheric Ca-K-index time series in the low-latitude zone (±40°),
utilizing the recently digitized photographic plates of Ca-K images from
the Kodaikanal Observatory for the period of 1907-1980. We find that
the temporal evolution of the Ca-K index differs from one hemisphere to
another, with the solar cycle peaking at different times in the opposite
hemisphere, except for cycles 14, 15, and 21, when the phase difference
between the two hemispheres was not significant. The monthly averaged
data show a higher activity in the northern hemisphere during solar
cycles 15, 16, 18, 19, and 20, and in the southern hemisphere during
cycles 14, 17, and 21. We notice an exponentially decaying distribution
for each hemisphere's Ca-K index and the whole solar disk. We explored
different midterm periodicities of the measured Ca-K index using the
wavelet technique, including Rieger-type and quasi-biennial oscillations
on different timescales present in the time series. We find a clear
manifestation of the Waldmeier effect (stronger cycles rise faster than
the weaker ones) in both the hemispheres separately and the whole disk
in the data. Finally, we have found the presence of the Gnevyshev gap
(time interval between two cycle maxmima) in both the hemispheric data
during cycles 15 to 20. Possible interpretations of our findings are
discussed with the help of existing theoretical models and observations.
Title: AWSoM MHD simulation of a solar active region with realistic
spectral synthesis
Authors: Manchester, Ward; Shi, Tong; Landi, Enrico; Szente, Judit;
van der Holst, Bart; Chen, Yuxi; Toth, Gabor; Bertello, Luca; Pevtsov,
Alexander
Bibcode: 2021AGUFMSH12B..02M
Altcode:
For the first time, we simulate the detailed spectral line emission
from a solar active region (AR) with the Alfven Wave Solar Model
(AWSoM). We select an active region appearing near disk center on
2018 July 13 and use an NSO-HMI synoptic magnetogram to specify the
magnetic field at the model's inner boundary. To resolve smaller-scale
magnetic features, we apply adaptive mesh refinement to resolve the
AR with a spatial resolution of 0.37 degrees, four times higher than
the background corona. We then apply the SPECTRUM code informed with
Chianti spectral emissivities to calculate more than a dozen spectral
lines forming at temperatures ranging from 0.5 to 3+ MK. Comparisons
are made between these simulated line profiles and those observed by
the Hinode/EIS instrument where we find close agreement (within a
20% margin of error of peak intensity) across a wide range of loop
sizes and temperatures. We also compare the differential emission
measure calculated from both the simulation and EIS observation to
further show the model's ability to capture the plasma temperature and
density. Finally, we simulate and compare Doppler velocities and find
that simulated flow patterns to be of comparable magnitude to what
is observed. Our results demonstrate the broad applicability of the
low-frequency Alfven wave balanced turbulence theory for explaining
the heating of coronal loops.
Title: Prediction of Sunspot and Plage Coverage for Solar Cycle 25
Authors: Penza, Valentina; Berrilli, Francesco; Bertello, Luca;
Cantoresi, Matteo; Criscuoli, Serena
Bibcode: 2021ApJ...922L..12P
Altcode: 2021arXiv211102928P
Solar variability occurs over a broad range of spatial and temporal
scales, from the Sun's brightening over its lifetime to the fluctuations
commonly associated with magnetic activity over minutes to years. The
latter activity includes most prominently the 11 yr sunspot solar
cycle and its modulations. Space weather events, in the form of
solar flares, solar energetic particles, coronal mass ejections,
and geomagnetic storms, have long been known to approximately follow
the solar cycle occurring more frequently at solar maximum than solar
minimum. These events can significantly impact our advanced technologies
and critical infrastructures, making the prediction for the strength of
future solar cycles particularly important. Several methods have been
proposed to predict the strength of the next solar cycle, cycle 25,
with results that are generally not always consistent. Most of these
methods are based on the international sunspot number time series,
or other indicators of solar activity. We present here a new approach
that uses more than 100 yr of measured fractional areas of the visible
solar disk covered by sunspots and plages and an empirical relationship
for each of these two indices of solar activity in even-odd cycles. We
anticipate that cycle 25 will peak in 2024 and will last for about 12
yr, slightly longer than cycle 24. We also found that, in terms of
sunspot and plage areas coverage, the amplitude of cycle 25 will be
substantially similar or slightly higher than cycle 24.
Title: Solar Magnetism and Radiation
Authors: Petrie, Gordon; Criscuoli, Serena; Bertello, Luca
Bibcode: 2021GMS...258...83P
Altcode:
No abstract at ADS
Title: On a limitation of Zeeman polarimetry and imperfect
instrumentation in representing solar magnetic fields with weaker
polarization signal
Authors: Pevtsov, A. A.; Liu, Y.; Virtanen, I.; Bertello, L.; Mursula,
K.; Leka, K. D.; Hughes, A. L. H.
Bibcode: 2021JSWSC..11...14P
Altcode: 2021arXiv210107204P
Full disk vector magnetic fields are used widely for developing better
understanding of large-scale structure, morphology, and patterns of
the solar magnetic field. The data are also important for modeling
various solar phenomena. However, observations of vector magnetic
fields have one important limitation that may affect the determination
of the true magnetic field orientation. This limitation stems from
our ability to interpret the differing character of the Zeeman
polarization signals which arise from the photospheric line-of-sight
vs. the transverse components of the solar vector magnetic field,
and is likely exacerbated by unresolved structure (non-unity fill
fraction) as well as the disambiguation of the 180° degeneracy in
the transverse-field azimuth. Here we provide a description of this
phenomenon, and discuss issues, which require additional investigation.
Title: Long-term studies of photospheric magnetic fields on the Sun
Authors: Pevtsov, Alexei A.; Bertello, Luca; Nagovitsyn, Yury A.;
Tlatov, Andrey G.; Pipin, Valery V.
Bibcode: 2021JSWSC..11....4P
Altcode:
We briefly review the history of observations of magnetic fields on the
Sun, and describe early magnetograps for full disk measurements. Changes
in instruments and detectors, the cohort of observers, the knowledge
base etc may result in non-uniformity of the long-term synoptic
datasets. Still, such data are critical for detecting and understanding
the long-term trends in solar activity. We demonstrate the value of
historical data using studies of active region tilt (Joy's law) and the
evolution of polar field and its reversal. Using the longest dataset
of sunspot field strength measurements from Mount Wilson Observatory
(1917-present) supplemented by shorter datasets from Pulkovo (1956-1997)
and Crimean (1956-present) observatories we demonstrate that the
magnetic properties of sunspots did not change over the last hundred
years. We also show that the relationship between the sunspot area and
its magnetic flux can be used to extend the studies of magnetic field in
sunspots to periods with no direct magnetic field measurements. Finally,
we show how more recent full disk observations of the vector magnetic
field can be used to study the long-term (solar cycle) variations in
magnetic helicity on the Sun.
Title: Analysis of Atmospheric Seeing Measurements
Authors: Dulaney, J.; Bertello, L.; Lecinski, A. R.
Bibcode: 2020AGUFMSY0030013D
Altcode:
Atmospheric seeing refers to the blurring and steadiness in the
image of astronomical objects caused by the Earth atmospheric
turbulence when observed through a telescope. Thermal convection in
the atmosphere produces turbulence cells having different optical
refraction indexes, leading to perturbations and distortions of the
incoming light wave fronts. Atmospheric seeing quality affects almost
all ground-based optical astronomy, from choice of site to telescope
design to interpretation of data. Although adaptive optics systems
are designed to improve observations, atmospheric seeing causes the
image quality to degrade the further you look from the location of
target. This is particularly relevant for the new and future generation
of telescopes, making quantitative seeing measurements increasingly
more important. The team has been given access to time series of
atmospheric seeing measurements taken at different locations worldwide,
covering multiple years of observations from GONG . We are expected to
perform some very basic statistical analysis on those time series to
characterize the overall quality of the different sites. Some general
knowledge of statistics is desirable, although not required. The project
involves data manipulation . We use IDL (Interactive Data Language)
as a primary computer language . The results from this project is
relevant in planning for future sites survey.
Title: Uncertainty Estimates of Solar Wind Prediction Using HMI
Photospheric Vector and Spatial Standard Deviation Synoptic Maps
Authors: Poduval, B.; Petrie, G.; Bertello, L.
Bibcode: 2020SoPh..295..138P
Altcode: 2020arXiv200806538P
The solar wind prediction is based on the Wang and Sheeley
(Astrophys. J.365, 372, 1990) empirical relationship between the solar
wind speed observed at 1 AU and the rate of magnetic flux tube expansion
(FTE) between the photosphere and the inner corona, where the FTE is
computed using coronal models (e.g. the current sheet source surface
(CSSS) and the potential field source surface models). These models
take the photospheric flux density synoptic maps as their inner boundary
conditions to extrapolate the photospheric magnetic fields and to deduce
the coronal and the heliospheric magnetic field configuration. These
synoptic maps are among the most widely-used of all solar magnetic
data products and therefore, the uncertainties in the model predictions
that are caused by the uncertainties in the synoptic maps are worthy of
study. However, an estimate of the uncertainties in the construction of
these synoptic maps was not available until recently when Bertello et
al. (Solar Phys.289, 2419, 2014) obtained the spatial standard deviation
synoptic maps. For each photospheric synoptic map, they obtained 98
Monte Carlo realizations of the spatial standard deviation maps.
Title: 70 Years of Chromospheric Solar Activity and Dynamics
Authors: Bertello, Luca; Pevtsov, Alexei A.; Ulrich, Roger K.
Bibcode: 2020ApJ...897..181B
Altcode:
From 1915 to 1985 the monitoring program of the Mount Wilson
Observatory, one of the Observatories of the Carnegie Institution of
Washington, has taken over 35,000 daily images (spectroheliograms)
of the Sun in the chromospheric resonance line of Ca II K. This
important database constitutes a unique resource for a variety of
retrospective analyses of the state of solar magnetism on multidecadal
timescales. These observations may also hold the key for untangling
some of the mysteries behind the solar dynamo, which in turn could
result in a better predictive capability for current dynamo models. We
describe here a procedure to calibrate and rescale these images so
that homogeneous Carrington synoptic maps can be derived for the
whole period covered by these observations. Temporal variations
in full-disk chromospheric activity clearly show the signature of
the 11 yr solar cycle, but no evidence is found for a statistically
significant north/south hemispheric asymmetry. Using a feature-tracking
technique we were also able to obtain the average solar rotation
profile. We find no indication of any detectable periodicity in the
temporal behavior of the orthogonalized rotation rate coefficients,
suggesting the global chromospheric dynamics has not changed during
the 70 years investigated in this work. We found also no significant
evidence in our analysis for a hemispheric asymmetry in rotation rates.
Title: Solar Cycle-Related Variability of Sun-as-a-Star Spectral
Line Profiles
Authors: Kalscheur, M.; Criscuoli, S.; Bertello, L.; Pevtsov, A. A.
Bibcode: 2019AGUFMSH11D3390K
Altcode:
We use daily observations of the Sun-as-a-star by the high resolution
Integrated Sunlight Spectrometer (ISS), one of three instruments
which comprise the Synoptic Optical Long-term Investigations of the
Sun (SOLIS) facility, to investigate solar cycle-related variability
in line profiles from three ISS spectral bands. Preliminary results
show an anti-correlation between the magnitude of the CN band-head
jump and total unsigned magnetic flux through the decline phase of
Solar Cycle 23 and the rise and fall of Solar Cycle 24, consistent
with magnetohydrodynamic simulations. Additional line parameters
(core intensity, full width at half maximum and equivalent width)
show correlations with the solar cycle, but may require correction
for stray light. We investigate two such corrections. Varied line
parameter responses to thermodynamic and magnetic structures in the
solar atmosphere may provide a means of disentangling thermal and
magnetic effects in disk-integrated solar spectra. These line parameter
responses could in turn inform spectroscopic observations of other
stars. Ultimately, this work is a step towards a better understanding
of magnetic activity cycles in other Sun-like stars.
Title: Reconstructing solar magnetic fields from historical
observations. V. Sunspot magnetic field measurements at Mount Wilson
Observatory
Authors: Pevtsov, Alexei A.; Tlatova, Kseniya A.; Pevtsov, Alexander
A.; Heikkinen, Elina; Virtanen, Ilpo; Karachik, Nina V.; Bertello,
Luca; Tlatov, Andrey G.; Ulrich, Roger; Mursula, Kalevi
Bibcode: 2019A&A...628A.103P
Altcode: 2019arXiv190706492P
Context. Systematic observations of magnetic field strength and polarity
in sunspots began at Mount Wilson Observatory (MWO), USA in early
1917. Except for a few brief interruptions, this historical dataset has
continued until the present.
Aims: Sunspot field strength and
polarity observations are critical in our project of reconstructing
the solar magnetic field over the last hundred years. We provide a
detailed description of the newly digitized dataset of drawings of
sunspot magnetic field observations.
Methods: The digitization
of MWO drawings is based on a software package that we developed. It
includes a semiautomatic selection of solar limbs and other features of
the drawing, and a manual entry of the time of observations, measured
field strength, and other notes handwritten on each drawing. The data
are preserved in an MySQL database.
Results: We provide a brief
history of the project and describe the results from digitizing this
historical dataset. We also provide a summary of the final dataset
and describe its known limitations. Finally, we compare the sunspot
magnetic field measurements with those from other instruments, and
demonstrate that, if needed, the dataset could be continued using modern
observations such as, for example, the Vector Stokes Magnetograph on the
Synoptic Optical Long-term Investigations of the Sun platform. The
digitized drawings are also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A103
Title: VizieR Online Data Catalog: Mt Wilson sunspot magnetic field
measurements (Pevtsov+, 2019)
Authors: Pevtsov, A. A.; Tlatova, K. A.; Pevtsov, A. A.; Heikkinen,
E.; Virtanen, I.; Karachik, N. V.; Bertello, L.; Tlatov, A. G.;
Ulrich, R.; Mursula, K.
Bibcode: 2019yCat..36280103P
Altcode:
MOUNT WILSON OBSERVATORY 150-foot solar tower, SUNSPOT DRAWINGS,
1917-2016. File: figs3_5.dat (Contains data shown in Figures
3-5). Three columns contain information on date of observations (Years),
measured Field strength (gauss), and radius of solar disk on drawings
(pixels). For measurements on drawings that only have information
about polarity, but not amplitude, we assigned a fixed value of
"4900". Files: fig6a.dat and fig6b.dat (Contain data shown
in Figure 6). Entries correspond to same-day measurements of field
strengths (in units of Hundreds of gauss) at Mount Wilson Observatory
(MWO, left column) and Crimean Astrophysical Observatory (CrAO, right
column). In Figure 6, observations from 1994-2003 are shown by black
squares, and data for 2004-2014 are shown as filled red circles. File: fig7.dat (Contain data for Figure 7). Field strengths of 50
sunspots observed at Mount Wilson Observatory (MWO) and and by Vector
Stokes Magnetograph (VSM) on Synoptic Optical Long-term Investigations
of the Sun (SOLIS) platform. SOLIS/VSM data are derived using SOLIS
Zeemanfit code. (5 data files).
Title: Reconstructing solar magnetic fields from historical
observations. IV. Testing the reconstruction method
Authors: Virtanen, I. O. I.; Virtanen, I. I.; Pevtsov, A. A.; Bertello,
L.; Yeates, A.; Mursula, K.
Bibcode: 2019A&A...627A..11V
Altcode:
Aims: The evolution of the photospheric magnetic field has
only been regularly observed since the 1970s. The absence of earlier
observations severely limits our ability to understand the long-term
evolution of solar magnetic fields, especially the polar fields that
are important drivers of space weather. Here, we test the possibility
to reconstruct the large-scale solar magnetic fields from Ca II K
line observations and sunspot magnetic field observations, and to
create synoptic maps of the photospheric magnetic field for times
before modern-time magnetographic observations.
Methods:
We reconstructed active regions from Ca II K line synoptic maps
and assigned them magnetic polarities using sunspot magnetic field
observations. We used the reconstructed active regions as input in
a surface flux transport simulation to produce synoptic maps of the
photospheric magnetic field. We compared the simulated field with
the observed field in 1975-1985 in order to test and validate our
method.
Results: The reconstruction very accurately reproduces
the long-term evolution of the large-scale field, including the poleward
flux surges and the strength of polar fields. The reconstruction has
slightly less emerging flux because a few weak active regions are
missing, but it includes the large active regions that are the most
important for the large-scale evolution of the field. Although our
reconstruction method is very robust, individual reconstructed active
regions may be slightly inaccurate in terms of area, total flux, or
polarity, which leads to some uncertainty in the simulation. However,
due to the randomness of these inaccuracies and the lack of long-term
memory in the simulation, these problems do not significantly affect
the long-term evolution of the large-scale field.
Title: Signature of Extended Solar Cycles as Detected from Ca II K
Synoptic Maps of Kodaikanal and Mount Wilson Observatory
Authors: Chatterjee, Subhamoy; Banerjee, Dipankar; McIntosh, Scott
W.; Leamon, Robert J.; Dikpati, Mausumi; Srivastava, Abhishek K.;
Bertello, Luca
Bibcode: 2019ApJ...874L...4C
Altcode: 2019arXiv190303598C
In recent years there has been a resurgence of the study of extended
solar cycles (ESCs) through observational proxies mainly in extreme
ultraviolet. But most of them are limited only to the space-based era
covering only about two solar cycles. Long-term historical data sets
are worth examining for the consistency of ESCs. The Kodaikanal Solar
Observatory (KSO) and the Mount Wilson Observatory (MWO) are two major
sources of long-term Ca II K digitized spectroheliograms covering the
temporal spans of 1907-2007 and 1915-1985 respectively. In this study,
we detected supergranule boundaries, commonly known as networks, using
the Carrington maps from both KSO and MWO data sets. Subsequently
we excluded the plage areas to consider only the quiet Sun (QS) and
detected small-scale bright features through intensity thresholding
over the QS network. Latitudinal density of those features, which we
named “Network Bright Elements,” could clearly depict the existence
of overlapping cycles with equatorward branches starting at latitude
≈55° and taking about 15 ± 1 yr to reach the equator. We performed
a superposed epoch analysis to depict the similarity of those extended
cycles. Knowledge of such equatorward band interaction, for several
cycles, may provide critical constraints on solar dynamo models.
Title: Tilt of Sunspot Bipoles in Solar Cycles 15 to 24
Authors: Tlatova, Ksenia; Tlatov, Andrey; Pevtsov, Alexei; Mursula,
Kalevi; Vasil'eva, Valeria; Heikkinen, Elina; Bertello, Luca; Pevtsov,
Alexander; Virtanen, Ilpo; Karachik, Nina
Bibcode: 2018SoPh..293..118T
Altcode: 2018arXiv180707913T
We use recently digitized sunspot drawings from Mount Wilson
Observatory to investigate the latitudinal dependence of tilt angles
of active regions and its change with solar cycle. The drawings cover
the period from 1917 to present and contain information as regards
polarity and strength of magnetic field in sunspots. We identified
clusters of sunspots of same polarity, and used these clusters to
form "bipole pairs". The orientation of these bipole pairs was used
to measure their tilts. We find that the latitudinal profile of tilts
does not monotonically increase with latitude as most previous studies
assumed, but instead, it shows a clear maximum at about 25 - 30 degree
latitudes. Functional dependence of tilt (γ ) on latitude (φ ) was
found to be γ =(0.20 ±0.08 )sin(2.80 φ )+(−0.00 ±0.06 ). We also
find that latitudinal dependence of tilts varies from one solar cycle
to another, but larger tilts do not seem to result in stronger solar
cycles. Finally, we find the presence of a systematic offset in tilt
of active regions (non-zero tilts at the equator), with odd cycles
exhibiting negative offset and even cycles showing the positive offset.
Title: Current Efforts to Preserve Mt. Wilson Historical Observations
Authors: Pevtsov, Alexander; Pevtsov, Alexei; Virtanen, Ilpo;
Bertello, Luca
Bibcode: 2018cosp...42E2653P
Altcode:
Mount Wilson Observatory (MWO) located in the San Gabriel Mountains
near Pasadena, California, has been taking solar observations since the
early 1900s. The earliest of which include the nearly unbroken record
of daily sunspot activity from 1917 through the present day. Full disk
spectroheliograms in Ca K spectral line were taken from 1915 through
1985. Starting from the 1950s synoptic magnetograms were also taken
utilizing the full disk longitudinal magnetograph at MWO. However,
working with historical long-term dataset presents unique challenges. To
be useful, data from hand drawings needed to be digitized. Furthermore,
data server failures in the past have led to a loss of public access
to parts of these historical data sets. Over the past several years
we have worked to process and extract metadata from MWO sunspot
drawings. Recently, a new project on the preservation of historical
magnetograms has been started. These efforts have provided insight
into dealing with issues presented by historical datasets. In this
presentation we provide an overview of current efforts in preserving the
historical (solar) datasets from MWO. We discuss some of these issues
and the application of these insights with regard to the recovery and
processing of early magnetogram data along with the current plans to
transfer this data to the public domain.
Title: Composite Photospheric Synoptic Magnetic Maps
Authors: Bertello, Luca; Pevtsov, Alexei A.; Petrie, Gordon J. D.
Bibcode: 2018tess.conf11502B
Altcode:
Photospheric synoptic maps of the Sun's magnetic field are the primary
drivers of both coronal and heliospheric
Title: Photospheric activity of the Sun with VIRGO and
GOLF. Comparison with standard activity proxies
Authors: Salabert, D.; García, R. A.; Jiménez, A.; Bertello, L.;
Corsaro, E.; Pallé, P. L.
Bibcode: 2017A&A...608A..87S
Altcode: 2017arXiv170905110S
We study the variability of solar activity using new photospheric
proxies originally developed for the analysis of stellar magnetism
with the CoRoT and Kepler photometric observations. These proxies
were obtained by tracking the temporal modulations in the observations
associated with the spots and magnetic features as the Sun rotates. We
analyzed 21 yr of observations, spanning solar cycles 23 and 24,
collected by the space-based photometric VIRGO and radial velocity
GOLF instruments on board the SoHO satellite. We then calculated
the photospheric activity proxy Sph is for each of the
three VIRGO photometers and the associated Svel proxy
from the radial velocity GOLF observations. Comparisons with several
standard solar activity proxies sensitive to different layers of the
Sun demonstrate that these new activity proxies, Sph and
Svel, provide a new manner to monitor solar activity. We show
that both the long- and short-term magnetic variabilities respectively
associated with the 11-yr cycle and the quasi-biennial oscillation
are well monitored, and that the magnetic field interaction between
the subsurface, photosphere, and chromosphere of the Sun was modified
between Cycle 24 and Cycle 23. Furthermore, the photometric proxies
show a wavelength dependence of the response function of the solar
photosphere among the three channels of the VIRGO photometers, providing
inputs for the study of the stellar magnetism of Sun-like stars.
Title: VizieR Online Data Catalog: Calibrated solar S-index time
series (Egeland+, 2017)
Authors: Egeland, R.; Soon, W.; Baliunas, S.; Hall, J. C.; Pevtsov,
A. A.; Bertello, L.
Bibcode: 2017yCat..18350025E
Altcode:
The Mount Wilson HK Program observed the Moon with both the HKP-1
and HKP-2 instruments. After removing 11 obvious outliers, there
are 162 HKP-1 observations taken from 1966 September 2 to 1977 June
4 with the Mount Wilson 100 inch reflector, covering the maximum
of cycle 20 and the cycle 20-21 minimum. As mentioned in Baliunas+
(1995ApJ...438..269B), observations of the Moon resumed in 1993 with
the HKP-2 instrument. After removing 10 obvious outliers, there are 75
HKP-2 observations taken from 1994 March 27 to 2002 November 23 with
the Mount Wilson 60 inch reflector, covering the end of cycle 22 and
the cycle 23 minimum, extending just past the cycle 23 maximum. The
end of observations coincides with the unfortunate termination of
the HK Project in 2003. We seek to extend our time series of
solar variability beyond cycle 23 by establishing a proxy to the
NSO Sacramento Peak (NSO/SP) observations taken from 1976 to 2016,
covering cycles 21 to 24. The spectral intensity scale is set by
integrating a 0.53Å band centered at 3934.869Å in the K-line wing
and setting it to the fixed value of 0.162. We extend the S-index
record back to cycle 20 using the composite K time series of Bertello+
(2016SoPh..291.2967B). See section 3 for further explanations. (1
data file).
Title: Ca II K 1-A Emission Index Composites
Authors: Bertello, Luca; Marble, Andrew R.; Pevtsov, Alexei A.
Bibcode: 2017arXiv170200838B
Altcode:
We describe here a procedure to combine measurements in the 393.37 nm Ca
II K spectral line taken at different observatories. Measurements from
the National Solar Observatory (NSO) Integrated Sunlight Spectrometer
(ISS) on the Synoptic Optical Long-term Investigations of the Sun
(SOLIS) telescope, the NSO/Sac Peak Ca II K-Line Monitoring Program,
and Ca II K filtergrams from Kodaikanal Solar Observatory (KKL) are
merged together to create a pair of composites of the Ca II K 1-A
emission index. These composites are publicly available from the SOLIS
website at http://solis.nso.edu/0/iss/.
Title: The Mount Wilson Observatory S-index of the Sun
Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall,
Jeffrey C.; Pevtsov, Alexei A.; Bertello, Luca
Bibcode: 2017ApJ...835...25E
Altcode: 2016arXiv161104540E
The most commonly used index of stellar magnetic activity is the
instrumental flux scale of singly ionized calcium H & K line
core emission, S, developed by the Mount Wilson Observatory (MWO)
HK Project, or the derivative index {R}{HK}\prime
. Accurately placing the Sun on the S scale is important for
comparing solar activity to that of the Sun-like stars. We present
previously unpublished measurements of the reflected sunlight from
the Moon using the second-generation MWO HK photometer during solar
cycle 23 and determine cycle minimum {S}23,\min =0.1634+/-
0.0008, amplitude {{Δ }}{S}23=0.0143+/- 0.0012, and mean
< {S}23> =0.1701+/- 0.0005. By establishing a proxy
relationship with the closely related National Solar Observatory
Sacramento Peak calcium K emission index, itself well correlated with
the Kodaikanal Observatory plage index, we extend the MWO S time series
to cover cycles 15-24 and find on average < {S}\min >
=0.1621+/- 0.0008, < {{Δ }}{S}{cyc}> =0.0145+/-
0.0012, < {S}{cyc}> =0.1694+/- 0.0005. Our measurements
represent an improvement over previous estimates that relied on stellar
measurements or solar proxies with non-overlapping time series. We
find good agreement from these results with measurements by the
Solar-Stellar Spectrograph at Lowell Observatory, an independently
calibrated instrument, which gives us additional confidence that we
have accurately placed the Sun on the S-index flux scale.
Title: Sub-Pixel Magnetic Field Dynamics Derived from Photospheric
Spectral Line Profiles
Authors: Rasca, A.; Chen, J.; Pevtsov, A. A.; Yurchyshyn, V.;
Bertello, L.
Bibcode: 2016AGUFMSH13C2308R
Altcode:
Current high-resolution observations of the photosphere show
small dynamic features at the resolving limit during emerging flux
events. However, line-of-sight (LOS) magnetogram pixels only contain
the net uncanceled magnetic flux, which is expected to increase
for fixed regions as resolution limits improve. Using a new method
with spectrographic images, we quantify distortions in photospheric
absorption (or emission) lines caused by sub-pixel magnetic field and
plasma dynamics in the vicinity of active regions and emerging flux
events. Absorption lines—quantified by their displacement, width,
asymmetry, and peakedness—have previously been used with Stokes
I images from SOLIS/VSM to relate line distortions with sub-pixel
plasma dynamics driven by solar flares or small-scale flux ropes. The
method is extended to include the full Stokes parameters and relate
inferred sub-pixel dynamics with small-scale magnetic fields. Our
analysis is performed on several sets of spectrographic images taken
by SOLIS/VSM and NST/NIRIS while observing eruptive and non-eruptive
active regions. We discuss the results of this application and their
relevance for understanding magnetic fields signatures and coupled
plasma properties on sub-pixel scales.
Title: Short-Term Variations in the Equatorial Rotation Rate of
Sunspot Groups
Authors: Javaraiah, J.; Bertello, L.
Bibcode: 2016SoPh..291.3485J
Altcode: 2016SoPh..tmp..168J; 2016arXiv161006710J
We have detected several periodicities in the solar equatorial rotation
rate of sunspot groups in the catalog Greenwich Photoheliographic
Results (GPR) during the period 1931 - 1976, the Solar Optical
Observing Network (SOON) during the period 1977 - 2014, and the
Debrecen Photoheliographic Data (DPD) during the period 1974 -
2014. We have compared the results from the fast Fourier transform
(FFT), the maximum entropy method (MEM), and the Morlet wavelet
power-spectra of the equatorial rotation rates determined from SOON and
DPD sunspot-group data during the period 1986 - 2007 with those of the
Mount Wilson Doppler-velocity data during the same period determined
by Javaraiah et al. (Solar Phys.257, 61, 2009). We have also compared
the power-spectra computed from the DPD and the combined GPR and SOON
sunspot-group data during the period 1974 - 2014 to those from the GPR
sunspot-group data during the period 1931 - 1973. Our results suggest a
∼ 250-day period in the equatorial rotation rate determined from both
the Mt. Wilson Doppler-velocity data and the sunspot-group data during
1986 - 2007. However, a wavelet analysis reveals that this periodicity
appears mostly around 1991 in the velocity data, while it is present in
most of the solar cycles covered by the sunspot-group data, mainly near
the minimum epochs of the solar cycles. We also found the signature of a
period of ∼ 1.4 years in the velocity data during 1990 - 1995, and in
the equatorial rotation rate of sunspot groups mostly around the year
1956. The equatorial rotation rate of sunspot groups reveals a strong
∼ 1.6-year periodicity around 1933 and 1955, a weaker one around 1976,
and a strong ∼ 1.8-year periodicity around 1943. Our analysis also
suggests periodicities of ∼ 5 years, ∼ 7 years, and ∼ 17 years,
as well as some other short-term periodicities. However, short-term
periodicities are mostly present at the time of solar minima. Hence,
short-term periodicities cannot be confirmed because of the larger
uncertainty in the data.
Title: Modeling the Global Coronal Field with Simulated Synoptic
Magnetograms from L1 and L5
Authors: Petrie, G. J. D.; Bertello, L.; Pevtsov, A. A.
Bibcode: 2016AGUFMSH11C2242P
Altcode:
In solar physics and space weather research, full-disk photospheric
magnetograms are routinely used to map the full solar surface in
near-real-time, and coronal field models are extrapolated from these
data. One major shortcoming of this approach is that, at present,
the magnetograms can only be taken from the Earth's direction. Thus
data immediately eastward of the sub-Earth point in synoptic maps
are around three weeks old, missing much active-region evolution and
leading to inaccuracies in the models. A new magnetograph at L5 would
update the synoptic maps at this critical location east of central
meridian and would provide a more accurate, up-to-date picture of the
global photospheric and coronal field. We demonstrate the value of L5
observations by simulating the construction of synoptic magnetograms
from both L1 and L5 directions using past near-real-time data from two
observatories: the Synoptic Optical Long-term Investigations of the
Sun (SOLIS) Vector Spectromagnetograph (VSM) and Global Oscillation
Network Group (GONG). We extrapolate potential-field source-surface
(PFSS) coronal field models and compare their open-field and streamer
distributions to coronal observations from the Solar Terrestrial
Relations Observatory (STEREO) and the Solar Dynamics Observatory
(SDO) Atmospheric Imaging Assembly (AIA).
Title: Blending of Ground- and Space-Based Magnetograms: Application
to L1-L5 Solar Wind and Coronal Hole Predictions
Authors: Berger, T. E.; Pevtsov, A. A.; Martinez-Pillet, V.; Bertello,
L.; Petrie, G. J. D.; Arge, C. N.; Henney, C. J.; Biesecker, D. A.
Bibcode: 2016AGUFMSH11C2241B
Altcode:
We examine the effect of blending ground-based Global Oscillations
Network Group (GONG) line-of-sight solar magnetic flux maps
("magnetograms") with space-based magnetograms from the Solar Dynamics
Observatory (SDO) Helioseismic and Magnetic Imager (HMI) instrument on
solar wind and coronal hole model-based forecasts. The longitudinally
blended maps are used to "reforecast" solar wind conditions using the
Wang-Sheeley-Arge (WSA) solar wind model during historical periods
of coronal hole High Speed Streams (HSS) and Corotating Interaction
Regions (CIRs) and compared to Advanced Composition Explorer (ACE)
data at the L1 Lagrangian point. The same WSA runs are repeated using
GONG and HMI data alone to determine the effect of data blending. The
blended maps are also used to create Potential Field Source Surface
(PFSS) maps of open coronal field lines and compared with historical
coronal hole data from SDO Atmospheric Imaging Assembly (AIA)
images. The study addresses the feasibility of combining ground- and
space-based data from instruments with widely disparate and varying
spatiotemporal resolution and flux sensitivity levels for use as inputs
to solar wind and coronal hole forecasting models. The results are
relevant to mission studies considering blended data inputs from,
e.g., L5 Lagrangian point satellite instruments with ground-based
measurements on the Sun-Earth line, as well as to expected magnetogram
data from the Solar Orbiter Polarimetric and Helioseismic Imager (PHI)
instrument. This study complements others that examine the utility
of having multiple viewpoint (e.g. L1 and L5) magnetogram inputs to
solar wind models by exploring data blending from disparate instruments.
Title: Correlation Between Sunspot Number and Ca II K Emission Index
Authors: Bertello, Luca; Pevtsov, Alexei; Tlatov, Andrey; Singh, Jagdev
Bibcode: 2016SoPh..291.2967B
Altcode: 2016arXiv160601092B; 2016SoPh..tmp..121B
Long-term synoptic observations in the resonance line of Ca II K
constitute a fundamental database for a variety of retrospective
analyses of the state of the solar magnetism. Synoptic Ca II K
observations began in late 1904 at the Kodaikanal Observatory in
India. In the early 1970s, the National Solar Observatory (NSO) at
Sacramento Peak (USA) started a new program of daily Sun-as-a-star
observations in the Ca II K line. Today the NSO is continuing these
observations through its Synoptic Optical Long-term Investigations
of the Sun (SOLIS) facility. These different data sets can be
combined into a single disk-integrated Ca II K index time series
that describes the average properties of the chromospheric emission
over several solar cycles. We present such a Ca II K composite and
discuss its correlation with the new entirely revised sunspot number
data series. For this preliminary investigation, the scaling factor
between pairs of time series was determined assuming a simple linear
model for the relationship between the monthly mean values during the
duration of overlapping observations.
Title: Impact of Magnetic Carrington Synoptic and Spatial Variance
Maps in Modeling of the Corona and Solar Wind
Authors: Bertello, Luca; Pevtsov, Alexie A.; Petrie, Gordon J. D.;
Hughes, Anna L. H.; Macniece, Peter J.
Bibcode: 2016usc..confE..42B
Altcode:
Synoptic maps derived from the measured photospheric solar longitudinal
magnetic field are routinely used to drive coronal and heliospheric
models. The recent development of spatial variance maps has provided
an additional resource to better understanding the limitation of these
models. In addition, measurements of the vector magnetic field are now
available from different instruments (e.g. SDO/HMI, SOLIS/VSM) and can
be used to compute synoptic maps of the true radial field. However,
due to the low sensitivity of these measurements in regions of weak
magnetic field, the adoption of these maps has been very limited. An
effort is underway at NSO to merge both longitudinal and vector
measurements together and derive more reliable synoptic maps of the
radial field. An even more ambitious project is ongoing to produce also
the first radial synoptic maps derived from SOLIS/VSM chromospheric
measurements. Validation and diagnostic capability of these products
will be discussed.
Title: Solar Ca II K Observations
Authors: Bertello, Luca; Pevtsov, Alexei A.; Tlatov, Andrey; Singh,
Jagdev
Bibcode: 2016AsJPh..25..295B
Altcode:
Some of the most important archives of past and current long-term solar
synoptic observations in the resonance line of Ca II K are described
here. These observations are very important for understanding the
state of the solar magnetism on time scales up to several decades. The
first observations of this kind began in 1904 at the Kodaikanal
Observatory (India), followed by similar programs at different other
locations. Regular full-disk Ca II K monitoring programs started in 1915
at the Mount Wilson Observatory (USA) and in 1917 at the National Solar
Observatory of Japan. Beginning in 1919 and in 1926 regular observations
were taken also at the Paris-Meudon Observatory (France) and at the
"Donati solar tower telescope of the Arcetri Astrophysical Observatory
in Italy, respectively. In 1926 the the Astronomical Observatory of
the Coimbra University in Portugal started its own program of Ca II
K observations. Although some of these programs have been terminated
over the years, their data archives constitute a unique resource for
studies of solar variability. In the early 1970s, the National Solar
Observatory (NSO) at Sacramento Peak (USA) started a new program of
daily Sun-as-a-star observations in the Ca II K line. Today the NSO is
continuing these observations through its Synoptic Optical Long-term
Investigations of the Sun (SOLIS) facility.
Title: Full-Disk Chromospheric Vector Magnetograms with Ca II 854.2
nm line: Some Promising Applications
Authors: Gosain, Sanjay; Harvey, J. W.; Harker, Brian; Pillet, V. M.;
Pevtsov, Alexei A.; Marble, Andrew R.; Bertello, Luca; + SOLIS-Team
Bibcode: 2016SPD....47.0103G
Altcode:
Over the last decade, the focus of solar magnetometry has shifted
outward from the photosphere to the chromospheric layers. The reasons
for this are many. With regards to instrumentation faster detectors
with more sensitivity have become available, as have fast electro-optic
modulators. Also, there are several potential benefits of observing
vector fields in the chromospheric layer as the magnetic field is
more force-free in this layer as compared to the photosphere. Coronal
force-free field extrapolations are more reliable using chromospheric
fields as the lower boundary condition and free magnetic energy is
readily computed using the magnetic virial theorem. Recently, a full
Stokes polarimeter for the chromospheric Ca II 854.2 nm spectral line
was developed and installed in the Vector Spectromagnetograph (VSM)
instrument on the Synoptic Optical Long-term Investigations of the
Sun (SOLIS) telescope. We present details of this new polarimeter,
full disk spectropolarimetric observations and vector magnetograms
of the chromosphere, and examples of some promising applications
(e.g., maps of normal component of electric current density in the
chromosphere, free magnetic energy estimated using virial theorem,
and non-potentiality parameter magnetic shear angle).This work
utilizes SOLIS data obtained by the NSO Integrated Synoptic Program
(NISP), managed by the National Solar Observatory, which is operated
by the Association of Universities for Research in Astronomy (AURA),
Inc. under a cooperative agreement with the National Science Foundation
Title: HMI Synoptic Maps Produced by NSO/NISP
Authors: Hughes, Anna L. H.; Bertello, Luca; Marble, Andrew R.; Oien,
Niles A.; Petrie, Gordon; Pevtsov, Alexei A.
Bibcode: 2016arXiv160503500H
Altcode:
Recently, the National Solar Observatory (NSO) Solar-atmosphere Pipeline
Working Group has undertaken the production of synoptic maps from
Helioseismic and Magnetic Imager (HMI) magnetograms. A set of maps has
been processed spanning the data available for 2010-2015 using twice
daily images (taken at UT midnight and noon) and running them through
the same algorithms used to produce SOLIS/VSM 6302l mean-magnetic
and spatial-variance maps. The contents of this document provide an
overview of what these maps look like, and the processing steps used
to generate them from the original HMI input data.
Title: Current Status of the SOLIS Program: Improved and New Data
Products
Authors: Bertello, Luca; Britanik, John; Callahan, Lorraine; Gosain,
Sanjay; Harker, Brian; Harvey, J. W.; Hughes, A.; Marble, A.; Pevtsov,
Alexei A.; Wentzel, Thomas
Bibcode: 2016SPD....47.1002B
Altcode:
Over the past year the Synoptic Optical Long-term Investigations of the
Sun (SOLIS) team has made significant improvements to the data products
provided to the solar and heliospheric community. In particular,
a considerable effort has been dedicated to reprocess the archive of
vector and longitudinal photospheric magnetograms, from 2003 to present,
using the latest production code. This endeavor is now near completion
and will assure that all derived magnetic products, such as synoptic
maps and flux time series, are consistently calibrated. In addition,
new products have been recently developed. For example, time series of
daily averages of the Sun's polar magnetic field derived from full-disk
photospheric FeI 630.15 nm longitudinal magnetograms are now available
from the SOLIS website at solis.nso.edu/0/vsm/vsm_plrfield.html.New
intensity calibration of high resolution Ca II K & H spectra from
the Integrated Sunlight Spectrometer (ISS) led to significant reduction
in daily variations of parameters derived from these spectra. The
SOLIS team will soon also release Carrington synoptic maps for the
three components of the photospheric magnetic field derived from vector
measurements taken in the Fe I 630.15 nm spectral line. The addition,
in late 2015, of a new Ca II 854.2 nm full-Stokes polarimeter into
the SOLIS core program of magnetic observations will make available to
the community daily chromospheric measurements of the complete Stokes
polarization vector.We present here a summary of these improvements,
with particular emphasis on the new products that can be accessed
from the SOLIS data page at solis.nso.edu/0/solis_data.html. For
a description of the diagnostic capability of the new Ca II 854.2
nm spectro-polarimeter and preliminary results we refer to other
presentations by SOLIS team members at this meeting.This work utilizes
SOLIS data obtained by the NSO Integrated Synoptic Program (NISP),
managed by the National Solar Observatory, which is operated by
the Association of Universities for Research in Astronomy (AURA),
Inc. under a cooperative agreement with the National Science Foundation.
Title: Ca II 854.2 nm Spectromagnetograms: A Powerful Chromospheric
Diagnostic
Authors: Harvey, J. W.; Bertello, Luca; Branston, D.; Britanik, J.;
Bulau, S.; Cole, L.; Gosain, Sanjay; Harker, Brian; Jones, Harrison P.;
Marble, A.; Martinez Pillet, V.; Pevtsov, A.; Schramm, K.; Streander,
Kim; Villegas, H.
Bibcode: 2016SPD....4710106H
Altcode:
The transition from physical dominance by plasma flows in the
photosphere to magnetic pressure in the solar chromosphere motivates
as many diagnostic observations as possible across this important
region. Among the few ground-accessible spectral lines formed within
the chromosphere, the Ca II 854.2 nm line has the desirable properties
of presence everywhere on the solar disk, Zeeman sensitivity, and
narrow line width. Mapped observations of circular polarization within
this line (spectromagnetograms) have been made at NSO infrequently
since 1974, with regular daily full-disk observations starting in
August 1996. Full-disk spectral observations of the complete Stokes
polarization vector are now being made regularly since November
2015. It is not easy to estimate chromospheric magnetic field
properties from the 854.2 nm line profile polarization. To provide
rough quick-look vector field maps we found that the weak-field
approximation provides a fair first estimate of the line-of-sight
component but appears to be too simple to interpret the transverse
magnetic field from frequently asymmetric, linearly-polarized line
profiles. More realistic estimates of the chromospheric vector field,
short of extremely lengthy, full 3D, non-local radiative transfer
inversions, are being investigated. We briefly introduce recent
instrumental modifications and observational characteristics, sample
observations, and results concerning the expansion of the chromospheric
field with increasing height, the presence of large areas of weak,
nearly horizontal fields, and field estimates in plages, sunspots,
flares, filaments, and filament channels. The Stokes spectra will be
freely available to the community.This work utilizes SOLIS data obtained
by the NSO Integrated Synoptic Program (NISP), managed by the National
Solar Observatory, which is operated by the Association of Universities
for Research in Astronomy (AURA), Inc. under a cooperative agreement
with the National Science Foundation.
Title: HMI Vector and Uncertainty Carrington Synoptic Maps
Authors: Bertello, Luca; Hughes, A.; Gosain, Sanjay; Harker, Brian;
Harvey, J. W.; Marble, Andrew R.; Pevtsov, Alexei A.
Bibcode: 2016SPD....47.1001B
Altcode:
Based on our experience with data from the Vector Spectromagnetograph
(VSM) instrument, which is part of the Synoptic Optical Long-term
Investigations of the Sun (SOLIS)facility, we have produced HMI vector
and uncertainty synoptic maps for all Carrington rotations from May
2010 through December 2015. HMI observations provide 12-minute cadence
magnetograms, both for longitudinal and full-Stokes measurements. For
this investigation we have used only two magnetograms per day, 12
hours apart, which are sufficient to produce accurate maps in the
longitude-sine(latitude) projection with 1x1 square-degree resolution
at the equator. From both the HMI longitudinal and vector magnetograms
we have computed radial-flux and spatial-variance synoptic maps. For
the longitudinal data, we have included pole-filled radial-flux maps,
and for the vector data, we have included synoptic maps of the poloidal
and toroidal magnetic flux.We describe here the procedure to generate
those maps and discuss some of their main features. A comparison with
similar products from the SOLIS/VSM is also addressed. The HMI data
used are courtesy of NASA/SDO and HMI science teams.
Title: Long-term Synoptic Observations of Ca II K and Magnetic Flux
Authors: Bertello, L.; Pevtsov, A. A.; Tlatov, A. G.
Bibcode: 2016ASPC..504..213B
Altcode:
Long-term synoptic observations in the resonance line of Ca II K and
measurements of the solar magnetic flux over several decades constitute
a fundamental database for a variety of retrospective analyzes of the
state of the solar magnetism. These data archives may also hold the key
for untangling some of the mysteries behind the solar dynamo, which in
turn could result in a better predictive capability of current dynamo
models. Synoptic Ca II K observations began in 1907 at the Kodaikanal
observatory (India) and in 1915 at the Mt Wilson (California, USA)
solar observatory. By the early 1970s a number of synoptic programs
for solar magnetic observations were established that provided full
disk magnetograms. These programs include measurements carried out at
the Mt Wilson 150-foot solar tower, Wilcox observatory (California,
USA), and by the National Solar Observatory (NSO, USA). Today the
NSO is continuing these observations through its Synoptic Optical
Long-term Investigations of the Sun (SOLIS) facility. We will review
some of these historical observations, their properties, and their
importance for understanding the behavior of the solar magnetic field
over multidecadal time scales. We will also show recent results about
using Ca II K spectroheliograms and sunspot magnetic field measurements
to reconstruct homogeneous series of pseudo-magnetograms prior the
magnetograph era.
Title: Reconstructing solar magnetic fields from historical
observations. I. Renormalized Ca K spectroheliograms and
pseudo-magnetograms
Authors: Pevtsov, Alexei A.; Virtanen, Ilpo; Mursula, Kalevi; Tlatov,
Andrey; Bertello, Luca
Bibcode: 2016A&A...585A..40P
Altcode:
Aims: The present work is the first in a series of articles that
develop a new proxy to represent the evolution of magnetic activity in
past solar cycles by combining the information from historical Ca II
K line spectroheliograms and sunspot magnetic field measurements.
Methods: We use synoptic (Carrington) maps from 1915-1985 that
were derived from daily Ca K line observations at Mount Wilson
Observatory to identify the chromospheric plages and to create synoptic
pseudo-magnetograms. We use historical observations of sunspot magnetic
fields from 1917 to the present to assign polarity to pixels situated
within plages. The original Ca K spectroheliograms are nonuniform in
their brightness, and we develop a novel approach to re-normalize their
intensities.
Results: We show that a homogeneous long-term series
of pseudo-magnetograms can be successfully constructed by combining
sunspot field measurements and plages with renormalized intensities. In
our tests, about 80% of pixels situated within plages showed the same
magnetic polarity as the synoptic magnetograms taken with the Kitt
Peak Vacuum Telescope. Finally, we discuss possible approaches to
further improve the agreement between observed and pseudo-magnetograms.
Title: Effect of uncertainties in solar synoptic magnetic flux maps
in modeling of solar wind
Authors: Pevtsov, Alexei A.; Bertello, Luca; MacNeice, Peter
Bibcode: 2015AdSpR..56.2719P
Altcode:
Recently, the NSO/SOLIS team developed variance (error) maps that
represent uncertainties in magnetic flux synoptic charts. These
uncertainties are determined by the spatial variances of the magnetic
flux distribution from full disk magnetograms that contribute to each
bin in the synoptic chart. Here we present a study of the effects of
variances on solar wind parameters (wind speed, density, magnetic field,
and temperature) derived using the WSA-ENLIL model and ensemble modeling
approach. We compare the results of the modeling with near-Earth solar
wind magnetic field and plasma data as extracted from NASA/GSFC's OMNI
data set. We show that analysis of uncertainties may be useful for
understanding the sensitivity of the model predictions to short-term
evolution of magnetic field and noise in the synoptic magnetograms.
Title: H-alpha Off-limb Carrington Synoptic Charts
Authors: Bertello, L.; Hughes, A.; Pevtsov, A. A.
Bibcode: 2015AGUFMSH43B2459B
Altcode:
Observations of solar prominences (and filaments) reveal complex
structures, with significant differences inmorphology, lifetime, and
complexity of their magnetic field environment. Studies of thesesolar
features are important for understanding not only their origin but
also their role as precursors ofenergetic events such as flares and
coronal mass ejections.The Global Oscillation Network Group (GONG)
operated by the National Solar Observatory provides, amongother
products, high-cadence broad-band intensity measurements centered
in the core ofH-alpha spectral line. Prominences and filaments are
quite visible in these 2Kx2K images, that havebeen obtained since
2010. We recentlystarted a project to produce an archive of H-alpha
off-limb Carrington Synoptic Charts to be usedfor systematic studies
of prominences. Charts are produced to show both spatial and temporal
variabilityof these features in four radius zones covering 1.01 to
1.11 solar radii. Here we describe the applied methodologyand show
some preliminary results. Potential applications of interest to the
solar and heliospheric communitiesare also briefly discussed.
Title: Digital tabulation of historical sunspot field strength
measurements from the Mount Wilson Observatory
Authors: Pevtsov, Alexei; Tlatov, Andrey; Bertello, Luca; Ulrich, Roger
Bibcode: 2015IAUGA..2236421P
Altcode:
Direct (manual) measurements of magnetic fields in sunspots based on
Zeeman effect represent the longest magnetic observations pertinent to
the Sun. Regular (daily) observations started in about 1917 and continue
till present. The data consist of daily drawings of sunspots with the
corresponding field strength and polarity measurements handwritten on
these drawings. All the drawings are now scanned to digital images
(JPEG format). However, the lack of tabulated data severely limits
the use of this unique data set. Here we report on status and the
results of several recent projects aimed at the digital tabulation of
MWO drawings. While the individual projects are funded independently by
the American (USA) and Russian funding agencies, the groups collaborate
closely with each other to achieve a common goal - creation of tabulated
data set contacting magnetic field and sunspot position information
derived from the drawings. The collaboration is coordinated by the
IAU working group on Coordination of Synoptic Observations of the Sun.
Title: SOLIS/VSM Polar Magnetic Field Data
Authors: Bertello, Luca; Marble, Andrew R.
Bibcode: 2015arXiv150707976B
Altcode:
The Vector Spectromagnetograph (VSM) instrument on the Synoptic Optical
Long-term Investigations of the Sun (SOLIS) telescope is designed to
obtain high-quality magnetic field observations in both the photosphere
and chromosphere by measuring the Zeeman-induced polarization
of spectral lines. With 1$^{\prime \prime}$ spatial resolution
(1.14$^{\prime \prime}$ before 2010) and 0.05Å spectral resolution, the
VSM provides, among other products, chromospheric full-disk magnetograms
using the CaII 854.2 nm spectral line and both photospheric full-disk
vector and longitudinal magnetograms using the FeI 630.15 nm line. Here
we describe the procedure used to compute daily weighted averages of
the photospheric radial polar magnetic field at different latitude
bands from SOLIS/VSM longitudinal full-disk observations. Time series
of these measurements are publicly available from the SOLIS website at
http://solis.nso.edu/0/vsm/vsm\_plrfield.html. Future plans include
the calculation of the mean polar field strength from SOLIS/VSM
chromospheric observations and the determination of the {\it true}
radial polar field from SOLIS/VSM full-Stokes measurements.
Title: The Diagnostic Value of Photospheric Fraunhofer Lines in
Sun-as-a-Star Observations
Authors: Bertello, Luca; Pevtsov, Alexei A.; Marble, Andrew R.
Bibcode: 2015TESS....140311B
Altcode:
The distinctive sensitivity of photospheric Fraunhofer lines to
variations in the thermodynamic and magnetic structures of the solar
atmosphere provides an excellent tool to investigate these variations
at different time scales.We used daily Sun-as-a-star spectra taken
with the Integrated Sunlight Spectrometer (ISS) and longitudinal
magnetograms from the Vector SpectroMagnetograph (VSM) to study the
correlation between the global magnetic flux and changes in the line
shape of several photospheric spectral lines during different phases of
the solar cycle. ISS and VSM are two of three instruments comprising
the Synoptic Optical Long-term Investigations of the Sun (SOLIS)
facility operated by the National Solar Observatory. We find a clear
signature of temporal global magnetic flux variations in several of
these photospheric spectral lines, suggesting that the results of our
analysis can be used to develop a better understanding of the magnetic
cycle of activity in other solar-type stars.
Title: Uncertainties Associated to Near Real-Time Synoptic Magnetic
maps and Implications for Solar Wind Models
Authors: Bertello, Luca; Pevtsov, Alexei A.; Macniece, Peter
Bibcode: 2015TESS....111003B
Altcode:
Beginning with May 2006 data, the National Solar Observatory is
providing uncertainty (spatial-variance) maps to accompany its
database of magnetic flux synoptic charts. Early studies using few
selected integral Carrington rotation maps have shown the impact of
these uncertainty maps on the outcome numerical models of the coronal
magnetic field and the solar wind (e.g., Bertello et al. 2014, Solar
Physics, 289 (7), 2419). Here we discuss the evolution of solar
wind parameters at Earth computed from the WSA-ENLIL model using
the more suitable near real-time magnetic flux synoptic charts and
their corresponding uncertainty maps. We investigated the short-term
variations in these parameters during periods of low and high levels
of solar activity to determine the predictive capabilities of these
maps at different phases of the solar cycle. Our preliminary analysis
based on integral synoptic maps suggests that during the period of
low solar activity the short-term variations in solar wind parameters
are within the scatter of the ensemble modeling. When the activity is
high, the short-term variations in the observed parameters are larger
than the scatter from the modeling. The results of this investigation
will help to get a better understanding about some aspects of existing
models of the solar wind that may require further improvements.
Title: SOLIS: Reconciling Disk-integrated and Disk-resolved Spectra
from the Sun
Authors: Pevtsov, Alexei A.; Bertello, Luca; Harker, Brian; Giampapa,
Mark; Marble, Andrew R.
Bibcode: 2015csss...18..887P
Altcode: 2014arXiv1411.7266P
Unlike other stars, the surface of the Sun can be spatially resolved
to a high degree of detail . But the Sun can also be observed as if
it was a distant star. The availability of solar disk-resolved and
disk-integrated spectra offers an opportunity to devise methods to
derive information about the spatial distribution of solar features
from Sun-as-a-star measurements. Here, we present an update on work
done at the National Solar Observatory to reconcile disk-integrated
and disk-resolved solar spectra from the Synoptic Optical Long-term
Investigation of the Sun (SOLIS) station. The results of this work
will lead to a new approach to infer the information about the spatial
distribution of features on other stars, from the overall filling factor
of active regions to, possibly, the latitude/longitude distribution
of features.
Title: Line Bisector Variability in the Sun as a Star
Authors: Giampapa, Mark; Bertello, Luca
Bibcode: 2015csss...18..495G
Altcode:
We utilize spectra obtained with the Integrated Sunlight Spectrometer
(ISS) instrument of the NSO SOLIS facility on Kitt Peak, AZ to perform
a preliminary study of the variability of line asymmetries in the Mn I
line at 539.5 nm and the nearby Fe I line at 539.3 nm, respectively. We
derive the line bisector for these photospheric features from
daily spectra of the Sun as a star acquired since January 2007, and
characterize the variability of a measure of bisector amplitude with
the solar cycle. A simple two-component model of the solar magnetic
field is investigated as a possible origin for the variation in line
depth with time of the magnetically sensitive Mn I feature.
Title: Solar Cycle Dependency of Sun-as-a-Star Photospheric Spectral
Line Profiles
Authors: Bertello, Luca; Pevtsov, Alexei A.; Giampapa, Mark S.;
Marble, Andrew R.
Bibcode: 2015csss...18..693B
Altcode:
We investigate solar-cycle related changes in the profile of several
photospheric spectral lines taken with the Integrated Sunlight
Spectrometer (ISS) operating at the National Solar Observatory at Kitt
Peak (Arizona). ISS, which is one of three instruments comprising
the Synoptic Optical Long-term Investigations of the Sun (SOLIS)
facility, is designed to obtain high spectral resolution (R = 300,000)
observations of the Sun-as-a-star in a broad range of wavelengths
(350 nm - 1100 nm). Daily measurements were obtained since December
2006, covering the decline of solar cycle 23 and the rising phase of
cycle 24. We present time series of line parameters and discuss their
correlation to indices of solar magnetic activity. Because of their
different response to variations in the thermodynamic and magnetic
structures of the solar atmosphere, the measured line shape parameters
provide an excellent tool for disentangling thermal and magnetic effects
occurring during different phases of the solar cycle. The results of
this analysis may also help with developing a better understanding of
magnetic cycles of activity in other solar-like stars.
Title: Uncertainties in Solar Synoptic Magnetic Flux Maps
Authors: Bertello, L.; Pevtsov, A. A.; Petrie, G. J. D.; Keys, D.
Bibcode: 2014SoPh..289.2419B
Altcode: 2013arXiv1312.0509B; 2014SoPh..tmp....7B
Magnetic flux synoptic charts are critical for a reliable modeling
of the corona and heliosphere. Until now, however, these charts were
provided without uncertainty estimates. The uncertainties are due to
instrumental noise in the measurements and to the spatial variance
of the magnetic flux distribution that contributes to each bin in the
synoptic chart. We describe here a simple method to compute synoptic
magnetic flux maps and their corresponding magnetic flux spatial
variance charts that can be used to estimate the uncertainty in the
results of coronal models. We have tested this approach by computing a
potential-field source-surface model of the coronal field for a Monte
Carlo simulation of Carrington synoptic magnetic flux maps generated
from the variance map. We show that these uncertainties affect both
the locations of source-surface neutral lines and the distributions
of coronal holes in the models.
Title: Effect of Uncertainties in Solar Synoptic Magnetic Flux Maps
in Modeling of Solar Wind
Authors: Pevtsov, Alexei; Bertello, Luca; Petrie, Gordon
Bibcode: 2014shin.confE.159P
Altcode:
Recently, the NSO/SOLIS team developed variance (error) maps that
represent uncertainties in magnetic flux synoptic charts. These
uncertainties are determined by the spatial variance of the magnetic
flux distribution from full disk magnetograms that contributes to each
bin in the synoptic chart. The algorithm for the creation of these
maps is described in Bertello, L., Pevtsov, A.A., Petrie, G.J.D.,
Keys, D.: 2014
Title: Temporal Variation of Photospheric Spectral Lines Profiles
with the Solar Cycle of Activity
Authors: Bertello, Luca; Pevtsov, Alexei A.; Marble, Andrew R.
Bibcode: 2014AAS...22421831B
Altcode:
We investigated the variations in the sun-as-a-star profiles of
several photospheric spectral lines observed during the decline of
solar cycle 23 and the rising phase of cycle 24. Daily measurements
were taken with the Integrated Sunlight Spectrometer (ISS) operating at
the National Solar Observatory at Kitt Peak (Arizona) since December
2006. ISS, which is one of three instruments comprising the Solar
Optical Investigations of the Sun (SOLIS) facility, is designed to
obtain high spectral resolution (R = 300,000) observations of the Sun
as a star in a broad range of wavelengths (350 nm - 1100 nm). Recent
improvements in the spectral calibration of SOLIS/ISS measurements have
significantly enhanced the diagnostic capabilities of these data.We will
present time series of line parameters and discuss their correlation
to the global magnetic flux. Because of their different response to
variations in the thermodynamic and magnetic structures of the solar
atmosphere, the measured line shape parameters provide an excellent
tool to disentangle thermal and magnetic effects occurring during
different phases of the solar cycle. The results of this analysis may
also help with developing a better understanding of magnetic cycle of
activity in other solar-like stars.
Title: A Multi-Observatory Inter-Comparison of Line-of-Sight Synoptic
Solar Magnetograms
Authors: Riley, P.; Ben-Nun, M.; Linker, J. A.; Mikic, Z.; Svalgaard,
L.; Harvey, J.; Bertello, L.; Hoeksema, T.; Liu, Y.; Ulrich, R.
Bibcode: 2014SoPh..289..769R
Altcode:
The observed photospheric magnetic field is a crucial parameter
for understanding a range of fundamental solar and heliospheric
phenomena. Synoptic maps, in particular, which are derived from
the observed line-of-sight photospheric magnetic field and built up
over a period of 27 days, are the main driver for global numerical
models of the solar corona and inner heliosphere. Yet, in spite of 60
years of measurements, quantitative estimates remain elusive. In this
study, we compare maps from seven solar observatories (Stanford/WSO,
NSO/KPVT, NSO/SOLIS, NSO/GONG, SOHO/MDI, UCLA/MWO, and SDO /HMI)
to identify consistencies and differences among them. We find that
while there is a general qualitative consensus, there are also some
significant differences. We compute conversion factors that relate
measurements made by one observatory to another using both synoptic
map pixel-by-pixel and histogram-equating techniques, and we also
estimate the correlation between datasets. For example, Wilcox Solar
Observatory (WSO) synoptic maps must be multiplied by a factor of 3 -
4 to match Mount Wilson Observatory (MWO) estimates. Additionally, we
find no evidence that the MWO saturation correction factor should be
applied to WSO data, as has been done in previous studies. Finally,
we explore the relationship between these datasets over more than
a solar cycle, demonstrating that, with a few notable exceptions,
the conversion factors remain relatively constant. While our study
was able to quantitatively describe the relationship between the
datasets, it did not uncover any obvious "ground truth." We offer
several suggestions for how this may be addressed in the future.
Title: Cyclic and Long-Term Variation of Sunspot Magnetic Fields
Authors: Pevtsov, Alexei A.; Bertello, Luca; Tlatov, Andrey G.;
Kilcik, Ali; Nagovitsyn, Yury A.; Cliver, Edward W.
Bibcode: 2014SoPh..289..593P
Altcode: 2013arXiv1301.5935P
Measurements from the Mount Wilson Observatory (MWO) were used to
study the long-term variations of sunspot field strengths from 1920 to
1958. Following a modified approach similar to that presented in Pevtsov
et al. (Astrophys. J. Lett.742, L36, 2011), we selected the sunspot
with the strongest measured field strength for each observing week and
computed monthly averages of these weekly maximum field strengths. The
data show the solar cycle variation of the peak field strengths
with an amplitude of about 500 - 700 gauss (G), but no statistically
significant long-term trends. Next, we used the sunspot observations
from the Royal Greenwich Observatory (RGO) to establish a relationship
between the sunspot areas and the sunspot field strengths for cycles 15
- 19. This relationship was used to create a proxy of the peak magnetic
field strength based on sunspot areas from the RGO and the USAF/NOAA
network for the period from 1874 to early 2012. Over this interval,
the magnetic field proxy shows a clear solar cycle variation with an
amplitude of 500 - 700 G and a weaker long-term trend. From 1874 to
around 1920, the mean value of magnetic field proxy increases by about
300 - 350 G, and, following a broad maximum in 1920 - 1960, it decreases
by about 300 G. Using the proxy for the magnetic field strength as the
reference, we scaled the MWO field measurements to the measurements of
the magnetic fields in Pevtsov et al. (2011) to construct a combined
data set of maximum sunspot field strengths extending from 1920 to early
2012. This combined data set shows strong solar cycle variations and no
significant long-term trend (the linear fit to the data yields a slope
of − 0.2±0.8 G year−1). On the other hand, the peak
sunspot field strengths observed at the minimum of the solar cycle show
a gradual decline over the last three minima (corresponding to cycles
21 - 23) with a mean downward trend of ≈ 15 G year−1.
Title: The sun-as-a-star solar spectrum
Authors: Pevtsov, A. A.; Bertello, L.; Marble, A. R.
Bibcode: 2014AN....335...21P
Altcode:
The Sun is the only star for which individual surface features can
be observed directly. For other stars, the properties of starspots,
stellar rotation, stellar flares, etc, are derived indirectly via
variation of star-integrated spectral line profiles or their luminosity
measurements. Solar disk-integrated and disk-resolved observations allow
for investigations of the contribution of individual solar disk features
to sun-as-a-star spectra. Here, we provide a brief overview of three
sun-as-a-star programs, currently in operation, and describe recent
improvements in observations and data reduction for the Integrated
Sunlight Spectrometer (ISS), one of three instruments comprising
the Synoptic Optical Long-term Investigations of the Sun (SOLIS)
system. Next, we discuss studies employing sun-as-a-star observations
(including Ca II K line as proxy for total unsigned magnetic flux
and 2800 MHz radio flux) as well as the effects of flares on solar
disk-integrated spectra.
Title: Uncertainties in Solar Synoptic Maps and their Effect on
Models.
Authors: Pevtsov, Alexei; Petrie, Gordon; Bertello, Luca
Bibcode: 2014cosp...40E2524P
Altcode:
Synoptic charts of the photospheric magnetic flux are used widely in
modeling the magnetic field in the corona and the heliosphere. Recently,
the National Solar Observatory began producing accompanying maps of
uncertainties (http://solis.nso.edu/0/ermaps/6302l_er2138-2157.html),
which can be used to estimate the uncertainty in the results of coronal
models. These maps of uncertainties represent the spatial variance
of the magnetic flux distribution that contributes to each bin in
the synoptic chart. We will describe a method to compute synoptic
magnetic flux spatial variance charts, and discuss the effects of
these uncertainties on models of the coronal magnetic field and the
solar wind speed.
Title: Synoptic Magnetic Variance Maps and Their Effects on
Field-extrapolation Coronal Models
Authors: Bertello, Luca; Pevtsov, A. A.; Keys, D.; Petrie, G.
Bibcode: 2013SPD....44..113B
Altcode:
The prediction and description of the conditions throughout the
heliosphere relies today mostly on potential field source surface (PFSS)
and magnetohydrodynamics coronal and heliospheric models. Carrington
synoptic maps are produced from individual magnetograms and used as
the primary drivers for these models. However, the uncertainties on the
flux distribution across synoptic maps have never been included in the
models. As the measure of uncertainties, we produced synoptic spatial
variance (1-sigma standard deviation) maps derived from the distribution
of pixel values in the sky magnetograms that contribute the to average
flux in each bin of the final Carrington map. Each variance-map is then
used to generate a series of Carrington maps where the value of each
bin differs, randomly, from the original value by up to 3-sigma. We
discuss here how the uncertainty in the Carrington map affects the
location of neutral lines and the footpoint locations of the open-field,
the model coronal holes, determined from a standard PFSS model. In this
preliminary investigation we studied two distinct periods, corresponding
to minimum and maximum of solar activity. We show that the variance
in the derived synoptic maps does not affect significantly the shape
of neutral line or general location of coronal holes. The position of
neutral lines and boundaries of coronal holes can be shifted by as much
as 5 degrees in some locations.Abstract (2,250 Maximum Characters):
The prediction and description of the conditions throughout the
heliosphere relies today mostly on potential field source surface (PFSS)
and magnetohydrodynamics coronal and heliospheric models. Carrington
synoptic maps are produced from individual magnetograms and used as
the primary drivers for these models. However, the uncertainties on
the flux distribution across synoptic maps have never been included
in the models. As the measure of uncertainties, we produced synoptic
spatial variance (1-sigma standard deviation) maps derived from the
distribution of pixel values in the sky magnetograms that contribute
the to average flux in each bin of the final Carrington map. Each
variance-map is then used to generate a series of Carrington maps where
the value of each bin differs, randomly, from the original value by
up to 3-sigma. We discuss here how the uncertainty in the Carrington
map affects the location of neutral lines and the footpoint locations
of the open-field, the model coronal holes, determined from a standard
PFSS model. In this preliminary investigation we studied two distinct
periods, corresponding to minimum and maximum of solar activity. We
show that the variance in the derived synoptic maps does not affect
significantly the shape of neutral line or general location of coronal
holes. The position of neutral lines and boundaries of coronal holes
can be shifted by as much as 5 degrees in some locations.
Title: Improvements to the SOLIS Program: New Data Products and
Recent Science Results
Authors: Bertello, Luca; Callahan, L.; Gusain, S.; Harker, B.; Harvey,
J. W.; Hughes, A.; Marble, A. R.; Pevtsov, A. A.; SOLIS
Bibcode: 2013SPD....44..135B
Altcode:
Over the past two years the Synoptic Optical Long-term Investigations
of the Sun (SOLIS) Team made significant improvements to the data
products provided to the solar and heliospheric community. Longitudinal
photospheric magnetograms were consistently calibrated to form a
uniform magnetic flux series from 2003-present. Improvements in image
geometric corrections enabled providing the high spectral resolution
spectra for each pixel in full disk images taken in Fe 630.2 nm and
Ca II 854.2 nm. New treatment of high resolution spectra from the
Integrated Sunlight Spectrometer (ISS), led to significant reduction
in daily variations of parameters derived from these spectra. Several
new data products were developed, including simultaneous photospheric
and chromospheric longitudinal magnetograms derived from the core and
wings of Ca II 854.2 nm line, and derivation of field strength via
fitting non-polarized I-profiles of Fe I 630.2 nm. We present here a
summary of recent changes to this database, with particular emphasis on
chromospheric longitudinal magnetic field and intensity measurements,
photospheric vector magnetic field products, and high-spectral
resolution integrated sunlight data. Some significant results derived
from the analysis of these data sets will also be presented, while
more detailed descriptions about specific topics will be referred to
other SOLIS-related studies presented at this meeting.
Title: On Possible Variations of Basal Ca II K Chromospheric Line
Profiles with the Solar Cycle
Authors: Pevtsov, Alexei A.; Bertello, Luca; Uitenbroek, Han
Bibcode: 2013ApJ...767...56P
Altcode:
We use daily observations of the Ca II K line profiles of the
Sun-as-a-star taken with the Integrated Sunlight Spectrometer from 2006
December through 2011 July to deconvolve the contributions from the
quiet (basal) chromosphere and with magnetic network/plage areas. The
0.5 Å emission index computed from basal profiles shows a significantly
reduced modulation (as compared with one derived from the observed
profiles) corresponding to the Sun's rotation. For basal contribution
of the Ca II K line, the peak in power spectrum corresponding to solar
rotation is broad and not well defined. Power spectra for the plage
contribution show two narrow well-defined peaks corresponding to solar
rotation at two distinct latitudes, in agreement with the latitudinal
distribution of activity on the Sun at the end of Cycle 23 and beginning
of Cycle 24. We use the lack of a signature of solar rotation in the
basal (quiet Sun) component as an indication of a successful removal
of the active Sun (plage) component. Even though the contribution
from solar activity is removed from the basal line profiles, we find
a weak dependency of intensity in the line core (K3) of basal profiles
with the phase of the solar cycle. Such dependency could be the result
of changes in thermal properties of basal chromosphere with the solar
cycle. As an alternative explanation, we also discuss a possibility that
the basal component does not change with the phase of the solar cycle.
Title: An analysis of apparent r-mode oscillations in solar activity,
the solar diameter, the solar neutrino flux, and nuclear decay
rates, with implications concerning the Sun's internal structure
and rotation, and neutrino processes
Authors: Sturrock, P. A.; Bertello, L.; Fischbach, E.; Javorsek, D.;
Jenkins, J. H.; Kosovichev, A.; Parkhomov, A. G.
Bibcode: 2013APh....42...62S
Altcode: 2012arXiv1211.6352S
This article presents a comparative analysis of solar activity data, Mt
Wilson diameter data, Super-Kamiokande solar neutrino data, and nuclear
decay data acquired at the Lomonosov Moscow State University (LMSU). We
propose that salient periodicities in all of these datasets may be
attributed to r-mode oscillations. Periodicities in the solar activity
data and in Super-Kamiokande solar neutrino data may be attributed to
r-mode oscillations in the known tachocline, with normalized radius
in the range 0.66-0.74, where the sidereal rotation rate is in the
range 13.7-14.6 year-1. We propose that periodicities
in the Mt Wilson and LMSU data may be attributed to similar r-mode
oscillations where the sidereal rotation rate is approximately
12.0 year-1, which we attribute to a hypothetical "inner"
tachocline separating a slowly rotating core from the radiative zone. We
also discuss the possible role of the Resonant Spin Flavor Precession
(RSFP) process, which leads to estimates of the neutrino magnetic
moment and of the magnetic field strength in or near the solar core.
Title: Comparison of Ground-Based and Space-Based Longitudinal
Magnetograms
Authors: Pietarila, A.; Bertello, L.; Harvey, J. W.; Pevtsov, A. A.
Bibcode: 2013SoPh..282...91P
Altcode: 2012arXiv1209.6390P; 2012SoPh..tmp..274P
We compare photospheric line-of-sight magnetograms from the
Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector
Spectro-Magnetograph (VSM) instrument with observations from the
150-foot Solar Tower at Mt. Wilson Observatory (MWO), the Helioseismic
and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO),
and the Michelson Doppler Imager (MDI) on the Solar and Heliospheric
Observatory (SOHO). We find very good agreement between VSM and
the other data sources for both disk-averaged flux densities and
pixel-by-pixel measurements. We show that the VSM mean flux density
time series is of consistently high signal-to-noise ratio with no
significant zero offsets. We discuss in detail some of the factors -
spatial resolution, flux dependence, and position on the solar disk -
affecting the determination of scaling between VSM and SOHO/MDI or
SDO/HMI magnetograms. The VSM flux densities agree well with spatially
smoothed data from MDI and HMI, although the scaling factors show a
clear dependence on flux density. The factor to convert VSM to HMI
increases with increasing flux density (from ≈1 to ≈1.5). The
nonlinearity is smaller for the VSM vs. SOHO/MDI scaling factor (from
≈1 to ≈1.2).
Title: Signature of Differential Rotation in Sun-as-a-star Ca II
K Measurements
Authors: Bertello, L.; Pevtsov, A. A.; Pietarila, A.
Bibcode: 2012ApJ...761...11B
Altcode: 2012arXiv1210.5556B
The characterization of solar surface differential rotation (SDR) from
disk-integrated chromospheric measurements has important implications
for the study of differential rotation and dynamo processes in other
stars. Some chromospheric lines, such as Ca II K, are very sensitive
to the presence of activity on the disk and are an ideal choice
for investigating SDR in Sun-as-a-star observations. Past studies
indicate that when the activity is low, the determination of Sun's
differential rotation from integrated-sunlight measurements becomes
uncertain. However, our study shows that using the proper technique, SDR
can be detected from these type of measurements even during periods of
extended solar minima. This paper describes results from the analysis
of the temporal variations of Ca II K line profiles observed by the
Integrated Sunlight Spectrometer during the declining phase of Cycle 23
and the rising phase of Cycle 24, and discusses the signature of SDR
in the power spectra computed from time series of parameters derived
from these profiles. The methodology described is quite general, and
could be applied to photometric time series of other main-sequence
stars for detecting differential rotation.
Title: Detection of Solar Differential Rotation in Disk-Integrated
Ca II K Measurements
Authors: Bertello, Luca; Pietarila, A.; Pevtsov, A. A.
Bibcode: 2012AAS...22020311B
Altcode:
The characterization of solar differential rotation (SDR) from
disk-integrated chromospheric measurements has important implications
for the study of differential rotation and dynamo processes in other
stars. Chromospheric lines, such as Ca II K, are very sensitive
to the presence of activity on the disk and are an ideal choice for
investigating SDR in Sun-as-a star obervations. Here we use daily
observations from the SOLIS Integrated Sunlight Spectrometer (ISS) to
study the temporal variations of the Ca II K line profiles from 2006
to 2012. We discuss the signature of SDR in the power spectra
computed from time series of parameters derived from these profiles,
and the implications for detecting differential rotation in other
Main-Sequence stars.
Title: Ca II K And H Spectral Line Profiles From “Basal” And
“Magnetic” Chromospheres
Authors: Pevtsov, Alexei A.; Bertello, L.
Bibcode: 2012AAS...22020309P
Altcode:
We use observations from the SOLIS’ Integrated Sunlight Spectrometer
(ISS) to investigate properties of the Ca II K and H disk-integrated
spectral line profiles. The ISS daily observations cover the period
of declining phase of cycle 23 and rising phase of cycle 24. The
contributions of “basal” and “magnetic” chromospheres were
extracted from the observed profiles in order to investigate their
solar-cycle dependency. Our analysis suggests that the properties of
the "basal" chromosphere may change slightly with the cycle of activity.
Title: Solar Cycle Variations of Sunspot Magnetic Field Strengths
from the Mount Wilson Observatory
Authors: Pevtsov, Alexei A.; Bertello, L.; Tlatov, A.; Nagovitsyn,
Y.; Kilcik, A.
Bibcode: 2012AAS...22011003P
Altcode:
We used historical synoptic data the Mount Wilson Observatory (MWO)
to study long-term changes in sunspot magnetic field strengths over
the period of 1920-1959. By selecting sunspots with the strongest
field strength for each observing day, we find that the average
field strengths in sunspots vary with solar cycle with amplitude
of a few hundred Gauss. The data show no statistically significant
long-term trend over the period of about 40 years covered by these
observations. We also find that the fractional distribution of sunspots
changes from cycle to cycle. From Cycle 15 to Cycle 19, MWO data show
a steady increase in fraction of sunspots with weaker field strengths
(<1000 G), while the fraction of sunspots with strongest field
strengths (>3000 G) steadily decreases. The fraction of sunspots
with field strengths between 1000-3000 Gauss does not change in any
systematic way. In contract, the fractional distribution of sunspots
by their area (i.e., small, intermediate, and large) taken from the
Greenwich observatory data set does not change during the same period
of time. The different behavior in these two fractional distributions
might indicate some physical changes in the properties of sunspots
(e.g., sunspots of about the same area show progressively smaller
field strengths), or it could be the result of some systematic
instrumental/observational effects. We discuss our findings in the
framework of these two possible explanations.
Title: The Solar Cycle
Authors: Javaraiah, J.; Rozelot, J. P.; Bertello, Luca
Bibcode: 2012AdAst2012E..35J
Altcode:
No abstract at ADS
Title: Evidence from Helioradiology of an Inner Tachocline in the Sun
Authors: Sturrock, P. A.; Bertello, L.; Fischbach, E.; Jenkins, J. H.
Bibcode: 2011AGUFMSH13B1931S
Altcode:
One can make a good case that the Rieger and related solar oscillations
may be understood as r-mode oscillations. The frequencies of these
oscillations fit the formula 2*m*nu/(l*(l+1)), where l and m (two
of the three spherical harmonic indices) take the values m = 1, l =
2,3,4,..., (the third index n does not affect the mode frequency),
and the sidereal rotation frequency nu = 13.7 year-1. This value of
the rotation frequency indicates that these oscillations occur in the
tachocline, which separates the radiative zone from the convection
zone. There is now strong evidence that beta decay rates are not
constant, and there is a persuasive case that the Sun is responsible
for variations in these rates. This new source of solar observational
data, for which we propose the name "helioradiology," yields evidence
that the solar core rotates more slowly than the radiative zone. This
raises the possibility that there is a second, "inner," tachocline
that separates the core from the radiative zone. This possibility
in turn suggests that there may be a second group of "Rieger-like"
oscillations that have their origin in this inner tachocline. We present
evidence for such oscillations, derived from helioradiology data and
also from the long-term diameter measurements acquired at the Mount
Wilson Observatory.
Title: The Longitudinal Solar Magnetic Field Measured by SOLIS
Authors: Bertello, L.; Pevtsov, A. A.; Harvey, J. W.; Pietarila, A.
Bibcode: 2011AGUFMSH13B1934B
Altcode:
The SOLIS (Synoptic Optical Long-term Investigations of the Sun) Vector
SpectroMagnetograph (VSM) instrument operating at the National Solar
Observatory at Kitt Peak (Arizona) measures the full-disk longitudinal
solar magnetic field in the neutral iron spectral lines at 630.15-630.25
nm (photosphere) and ionized calcium spectral line at 854.2 nm (lower
chromosphere). Over the past two years a considerable effort has
been made to improve the quality of the computed magnetograms. Major
modifications to the original data reduction pipeline include a
new determination of the instrumental magnetic bias and an improved
calibration of the computed solar magnetic flux density. As a result of
these changes SOLIS-VSM is now able to provide, among other products,
more reliable values of the full-disk mean magnetic flux measured in
the photosphere and low chromosphere. In addition, these improvements
open the possibility to extend the current SOLIS-VSM catalog with new
products of interest to the solar and heliospheric communities. We
describe some of these changes and their impact on the quality of the
derived SOLIS-VSM data.
Title: Improvements in the Determination of ISS Ca II K Parameters
Authors: Bertello, L.; Pevtsov, A. A.; Harvey, J. W.; Toussaint, R. M.
Bibcode: 2011SoPh..272..229B
Altcode: 2011arXiv1106.4265B
Measurements of the ionized Ca II K line are one of the major resources
for long-term studies of solar and stellar activity. They also play a
critical role in many studies related to solar irradiance variability,
particularly as a ground-based proxy to model the solar ultraviolet flux
variation that may influence the Earth's climate. Full disk images of
the Sun in Ca II K have been available from various observatories for
more than 100 years and latter synoptic Sun-as-a-star observations
in Ca II K began in the early 1970s. One of these instruments, the
Integrated Sunlight Spectrometer (ISS) has been in operation at Kitt
Peak (Arizona) since late 2006. The ISS takes daily observations
of solar spectra in nine spectra bands, including the Ca II K and H
lines. We describe recent improvements in data reduction of Ca II K
observations, and present time variations of nine parameters derived
from the profile of this spectral line.
Title: Ca Ii K and H Measurements from the SOLIS ISS Instrument
Authors: Bertello, Luca; Pevtsov, A. A.; Pietarila, A.; Harvey, J. W.;
Toussaint, R. M.; SOLIS Team
Bibcode: 2011SPD....42.1744B
Altcode: 2011BAAS..43S.1744B
Precise measurements of the disk integrated solar Ca II K and H
lines play a critical role in many investigations of solar activity
and studies related to solar irradiance variability. The Integrated
Sunlight Spectrometer(ISS) operating at the National Solar Observatory
at Kitt Peak (Arizona) since December 2006 is designed to obtain
high spectral resolution (R = 300,000) observations of the Sun as
a star in a broad range of wavelengths (350 nm -1100 nm). The ISS
is one of three instruments, with the Vector Spectro-Magnetograph
(VSM) and the Full Disk Patrol (FDP), comprising the Synoptic Optical
Long-term Investigations of the Sun (SOLIS) - a synoptic facility for
solar observations operating at NSO/Kitt Peak. The ISS takes daily
observations of solar spectra in nine spectral bands, including the Ca
II K and H lines. We describe recent improvements in data reduction of
Ca II K and H observations, and present time variations of parameters
derived from the profiles of these spectral lines. Some properties of
these time series are also discussed.
Title: Solar Magnetic Fields As Observed By Solis
Authors: Pietarila, Anna; Bertello, L.; Callahan, L.; Harker, B.;
Harvey, J.; Marble, A.; Pevtsov, A.; Toussaint, R.
Bibcode: 2011SPD....42.1746P
Altcode: 2011BAAS..43S.1746P
The Vector Spectromagnetograph (VSM), part of the Synoptic Optical
Long-term Investigations of the Sun (SOLIS), makes spectropolarimetric
observations of the full-disk of the Sun in the photospheric Fe I lines
around 630 nm (Stokes I, Q, U and V) and the chromospheric Ca II 854.2
nm (Stokes I and V) line. We present some of the updated SOLIS VSM data
products and show how they compare with data from other instruments,
e.g., SDO/HMI and Hinode/SP. We also illustrate some of the differences
between the photospheric and chromospheric magnetograms, and how they
can be used to study the height variation of the magnetic field.
Title: Status of Synoptic Optical Long-term Investigation of the Sun
(SOLIS) Project.
Authors: Pevtsov, Alexei A.; Streander, K.; Harvey, J.; Bertello,
L.; Branston, D.; Britanik, J.; Callahan, L.; Cole, L.; Galayda, E.;
Harker, B.; Hauth, D.; Jaksha, D.; Leiker, C.; Marble, A.; Mills, N.;
Pietarila, A.; Schramm, K.; Stover, E.; Suarez-Sola, I.; Toussaint, R.
Bibcode: 2011SPD....42.1747P
Altcode: 2011BAAS..43S.1747P
Synoptic Optical Long-term Investigation of the Sun (SOLIS) is a suite
of three instruments to study various aspects of solar activity. Vector
Stokes Magnetograph (VSM) takes full disk longitudinal magnetograms in
the photosphere (Fe I 6301 A-6302 A) and the chromosphere (Ca II 8542A),
the photospheric vector magnetograms, and the full disk images of
equivalent width for He I 10830A. The VSM data set goes back to August
2003. Integrated Sunlight Spectrometer (ISS) provides high-resolution
spectra of sun-as-a-star for nine selected spectral bands (starting
from December 2006). Full-Disk Patrol (FDP) observes full disk images
of the Sun at high cadence in several selected wavelengths (starting
from June 2011). In the last two years, the SOLIS instruments and
data reduction went through a series of upgrades resulting in higher
data quality. These upgrades include new CCD cameras, photo guider,
and improved magbias calculations and data reduction of ISS line
profiles. We will present the current status of SOLIS, and show the
comparison between SOLIS observations with other instruments.
Title: Power Spectrum Analysis of Mount Wilson Solar Diameter
Measurements: Evidence for Solar Internal r-mode Oscillations
Authors: Sturrock, P. A.; Bertello, L.
Bibcode: 2010ApJ...725..492S
Altcode: 2010arXiv1010.0261S
This paper presents a power-spectrum analysis of 39,024 measurements of
the solar diameter made at the Mount Wilson Observatory from 1968.670 to
1997.965. This power spectrum contains a number of very strong peaks. We
find that eight of these peaks agree closely with the frequencies of
r-mode oscillations for a region of the Sun where the sidereal rotation
frequency is 12.08 year-1. We estimate that there is less
than one chance in 106 of finding this pattern by chance.
Title: Photospheric synoptic magnetograms, potential-field models
and observed global coronal structure
Authors: Petrie, G. J.; Bertello, L.; Tran, T.
Bibcode: 2010AGUFMSH31B1798P
Altcode:
The standard method for modeling the global coronal field is to
calculate a potential-field source-surface (PFSS) solution based on
a photospheric synoptic map, a full-surface map of the photospheric
radial field component based on observations taken throughout a solar
rotation. At the spherical source surface in the model the field is
forced to be radial, modeling the coronal field being forced open by the
solar wind. The radius of the source surface is a free parameter. Using
synoptic maps from NSO's GONG and SOLIS programs and from Wilcox Solar
Observatory for a set of approximately 30 rotations we generate PFSS
models and compare them to NASA STEREO observations of coronal holes
and streamer structures. The SOLIS maps are constructed converting
line-of-sight field measurements to radial field maps in two different
ways, (1) a standard diachronic approach where the photospheric field
is assumed to be approximately radial, and (2) a synchronic approach
that doesn't assume a radial photospheric field. The GONG and Wilcox
maps are constructed the first way only. Differences between the modeled
and observed coronal structures are calculated quantitatively for each
permutation of data source, map construction method and source-surface
radius and the implications for synoptic map construction and PFSS
modeling are discussed. We also test models based on 5 rotations of
GONG zero-point-corrected data.
Title: The Impact of Different Global Photospheric Magnetic Field
Maps on Coronal Models
Authors: Bertello, L.; Petrie, G. J.; Tran, T.
Bibcode: 2010AGUFMSH31B1796B
Altcode:
A primary objective of current and future solar magnetic field
observations is to provide an accurate description of the spatial
and temporal distribution of the photospheric magnetic field. These
observations are usually merged together over an extended period of
time, typically a solar rotation, to produce 360-degree surface maps
of the magnetic flux distribution that are regularly used today in
several space weather programs. As the main drivers for coronal and
heliospheric models, the quality of the maps will ultimately test the
diagnostic capabilities of these models and our ability to model the
state of the inner heliosphere. Different techniques have been used to
construct global magnetic maps of the solar surface from selected set
of magnetograms. In our study we have compared the impact of using
either diachronic or synchronic maps for predicting the background
solar wind speed at Earth. For this purpose we used a potential field
source surface model driven by 1-degree resolution full Carrington
rotation (CR) radial maps, combined with the Wang-Sheeley-Arge
model. The radial maps were produced for CR 2055 to CR 2087 using SOLIS
longitudinal magnetic field observations in the spectral line of Fe
I at 630.15nm. The quality of each of these maps is then validated by
comparing the predicted background solar wind speeds to the observed
values as measured by ACE.
Title: Photospheric Magnetic Field Maps and Their Impact on Coronal
Models
Authors: Bertello, Luca; Petrie, Gordon; Tran, Tham
Bibcode: 2010shin.confE..49B
Altcode:
A primary objective of current and future solar magnetic field
observations is to provide an accurate description of the spatial
and temporal distribution of the photosperic magnetic field. These
observations are usually merged together over a significant period
of time, typically a solar rotation, to produce 360-degree surface
maps of the magnetic flux distribution that are regularly used today
in several space weather programs. As the main drivers for coronal and
heliospheric models, the quality of these maps will ultimately test the
diagnostic capabilities of these models and our ability to model the
state of the inner heliosphere. Maps of the solar surface magnetic
field are routinely produced by different observatories, using different
techniques. We have compared the impact of using different combinations
of data/techniques into a potential field source surface model combined
with the Wang-Sheeley-Arge model to predict the background solar wind
speed at Earth. Some of the results are presented and discussed.
Title: On the Radial Assumption of the Solar Surface Magnetic Field
Authors: Tran, Tham Vinh; Bertello, Luca; Ulrich, Roger K.
Bibcode: 2010shin.confE..58T
Altcode:
Global photospheric magnetic maps are currently used as primary inner
boundary conditions in solar and space weather models. The quality
of these maps strongly affects the capability of these models to
simulate the solar corona and inner heliospheric magnetic fields as
well as to predict the ambient solar wind. Presently, these maps are
built using the observed line-of-sight (LOS) magnetograms. The radial
component of the magnetic field, which is widely used in the models,
is normally deduced from the LOS observations by assuming that the
magnetic field on the solar surface is nearly radial. This assumption
is based on the study showing that the average LOS magnetic field of
selected magnetic features crossing the solar surface varies linearly
with the cosine of the central meridian angle (Svalgaard et. al. 1978,
Solar Physics, 58, 225). We show in our poster that this relationship
may simply be due to a combination of the LOS projection effects and
the magnetic filling factor.
Title: Photospheric synoptic magnetograms, potential-field models
and observed global coronal structure
Authors: Petrie, Gordon; Bertello, Luca; Tran, Tham
Bibcode: 2010shin.confE..51P
Altcode:
The standard method for modeling the global coronal field is to
calculate a potential-field source-surface (PFSS) model based on
a photospheric synoptic magnetogram, a full-surface map of the
photospheric radial field component based on observations taken
throughout a solar rotation. At the spherical source surface in the
model the field is forced to be radial, modeling the coronal field
being forced open by the solar wind. The radius of the source surface
is a free parameter. Using synoptic magnetograms from NSO's GONG and
SOLIS programs for a set of approximately 30 rotations we generate PFSS
models and compare them to NASA STEREO observations of coronal holes
and streamer structures. The SOLIS maps are constructed converting
line-of-sight field measurements to radial field maps in two different
ways, (1) assuming that the photospheric field is approximately radial
and (2) by tracking features across the solar disk. The GONG maps are
constructed the first way only at present. Differences between the
predicted and observed coronal structures are calculated quantitatively
for each permutation of data source, radial field correction and
source-surface radius and the implications of results for synoptic
map construction and PFSS modeling are discussed.
Title: The Mount Wilson Ca II K Plage Index Time Series
Authors: Bertello, L.; Ulrich, R. K.; Boyden, J. E.
Bibcode: 2010SoPh..264...31B
Altcode: 2010SoPh..tmp...91B
It is well established that both total and spectral solar irradiance are
modulated by variable magnetic activity on the solar surface. However,
there is still disagreement about the contribution of individual solar
features for changes in the solar output, in particular over decadal
time scales. Ionized Ca II K line spectroheliograms are one of the
major resources for these long-term trend studies, mainly because such
measurements have been available now for more than 100 years. In this
paper we introduce a new Ca II K plage and active network index time
series derived from the digitization of almost 40 000 photographic
solar images that were obtained at the 60-foot solar tower, between
1915 and 1985, as a part of the monitoring program of the Mount Wilson
Observatory. We describe here the procedure we applied to calibrate the
images and the properties of our new defined index, which is strongly
correlated to the average fractional area of the visible solar disk
occupied by plages and active network. We show that the long-term
variation of this index is in an excellent agreement with the 11-year
solar-cycle trend determined from the annual international sunspot
numbers series. Our time series agrees also very well with similar
indicators derived from a different reduction of the same data base
and other Ca II K spectroheliograms long-term synoptic programs, such
as those at Kodaikanal Observatory (India), and at the National Solar
Observatory at Sacramento Peak (USA). Finally, we show that using
appropriate proxies it is possible to extend this time series up to
date, making this data set one of the longest Ca II K index series
currently available.
Title: The Mount Wilson Ca II K index
Authors: Bertello, Luca; Ulrich, Roger K.; Boyden, John E.
Bibcode: 2010arXiv1005.5402B
Altcode:
It is well established that both total and spectral solar irradiance are
modulated by variable magnetic activity on the solar surface. However,
there is still disagreement about the contribution of individual solar
features for changes in the solar output, in particular over decadal
time scales. Ionized Ca II K line spectroheliograms are one of the
major resources for these long-term trend studies, mainly because such
measurements have been available now for more than 100 years. In this
paper we introduce a new Ca II K plage and active network index time
series derived from the digitization of almost 40,000 photographic
solar images that were obtained at the 60-foot solar tower, between
1915 and 1985, as a part of the monitoring program of the Mount Wilson
Observatory. We describe here the procedure we applied to calibrate the
images and the properties of our new defined index, which is strongly
correlated to the average fractional area of the visible solar disk
occupied by plages and active network. We show that the long-term
variation of this index is in an excellent agreement with the 11-year
solar cycle trend determined from the annual international sunspot
numbers series. Our time series agrees also very well with similar
indicators derived from a different reduction of the same data base
and other \caii K spectroheliograms long-term synoptic programs, such
as those at Kodaikanal Observatory (India), and at the National Solar
Observatory at Sacramento Peak (USA). Finally, we show that using
appropriate proxies it is possible to extend this time series up to
date, making this data set one of the longest Ca II K index series
currently available.
Title: Modeling Total Solar Irradiance Variations Using Automated
Classification Software on Mount Wilson Data
Authors: Ulrich, R. K.; Parker, D.; Bertello, L.; Boyden, J.
Bibcode: 2010SoPh..261...11U
Altcode: 2009arXiv0909.2392U
We present the results using the AutoClass analysis application
available at NASA/Ames Intelligent Systems Div. (2002) which is a
Bayesian, finite mixture model classification system developed by
Cheeseman and Stutz (1996). We apply this system to Mount Wilson
Solar Observatory (MWO) intensity and magnetogram images and classify
individual pixels on the solar surface to calculate daily indices
that are then correlated with total solar irradiance (TSI) to yield
a set of regression coefficients. This approach allows us to model
the TSI with a correlation of better than 0.96 for the period 1996 to
2007. These regression coefficients applied to classified pixels on
the observed solar surface allow the construction of images of the
Sun as it would be seen by TSI measuring instruments like the Solar
Bolometric Imager recently flown by Foukal et al. (Astrophys. J. 611,
L57, 2004). As a consequence of the very high correlation we achieve in
reproducing the TSI record, our approach holds out the possibility of
creating an on-going, accurate, independent estimate of TSI variations
from ground-based observations which could be used to compare, and
identify the sources of disagreement among, TSI observations from the
various satellite instruments and to fill in gaps in the satellite
record. Further, our spatially-resolved images should assist in
characterizing the particular solar surface regions associated with
TSI variations. Also, since the particular set of MWO data on which
this analysis is based is available on a daily basis back to at least
1985, and on an intermittent basis before then, it will be possible
to estimate the TSI emission due to identified solar surface features
at several solar minima to constrain the role surface magnetic effects
have on long-term trends in solar energy output.
Title: Comparison of Independent Feature Recognition Method for
Time Series Analysis of Irradiance Variations Based on Statistical
Feature Recognition
Authors: Pap, Judit M.; Bertello, L.; Chapman, G.; Floyd, L. E.;
Jones, H.; Malanushenko, E.; Preminger, D.; Turmon, M.
Bibcode: 2009SPD....41.0934P
Altcode:
Solar total and UV irradiances have been observed over three decades,
and recently spectral irradiance data are available from the Solar
Irradiance Monitor (SIM) on the SORCE Mission. Results of these
measurements show that irradiance varies on various time scales from
minutes to decades. To better understand the origin of irradiance
changes, we need to use spatially resolved data rather than full
disk indices. For this purpose various automated image processing
and analyses techniques have been developed. Using these image
processing techniques, we separated quiet-sun, network, faculae and
sunspots. On one hand, we compare the area data of these features
derived from various images to validate results and discuss future
efforts needed to coordinate efforts between various groups working
on image analysis. Another goal is to compare the variations of the
identified features with total solar and UV irradiances to establish
to what degree the identified images explain short and long-term
irradiance variations.
Title: Search for Short-Term Periodicities in the Sun's Surface
Rotation: A Revisit
Authors: Javaraiah, J.; Ulrich, R. K.; Bertello, L.; Boyden, J. E.
Bibcode: 2009SoPh..257...61J
Altcode: 2009arXiv0903.4031J
We have used the daily values of the equatorial rotation rate determined
from the Mt. Wilson daily Doppler-velocity measurements during the
period 3 December 1985 - 5 March 2007 to search for periodicities
in the solar equatorial rotation rate on time scales shorter than 11
years. After the daily values have been binned into 61-day intervals,
a cosine fit with a period of one year was applied to the sequence to
remove any seasonal trend. The spectral properties of this sequence were
then investigated by using standard Fourier analysis, maximum-entropy
methods, and a Morlet-wavelet analysis. From the analysis of the Fourier
power spectrum we detected peaks with periodicities around 7.6, 2.8,
and 1.47 years and 245, 182, and 158 days, but none of them were at
a statistically significant level. In the Morlet-wavelet analysis
the ≈1.47-year periodicity is detected only for 1990 (i.e., near
the maximum of cycle 22) and near the end of cycle 22 in 1995. From
the same wavelet analysis we found some evidence for the existence
of a 2.8-year periodicity and a 245-day periodicity in the equatorial
rotation rate around the years 1990 and 1992, respectively. In the data
taken during the period 1996 - 2007, when the Mt. Wilson spectrograph
instrumentation was more stable, we were unable to detect any signal
from the wavelet analysis. Thus, the detected periodicities during
the period before 1996 could be artifacts of frequent changes in
the Mt. Wilson spectrograph instrumentation. However, the temporal
behavior of most of the activity phenomena during cycles 22 (1986 -
1996) and 23 (after 1997) is considerably different. Therefore, the
presence of the aforementioned short-term periodicities during the
last cycle and absence of them in the current cycle may, in principle,
be real temporal behavior of the solar rotation during these cycles.
Title: Recalibration of Zurich Sunspot Number
Authors: Svalgaard, Leif; Bertello, L.
Bibcode: 2009SPD....40.1513S
Altcode:
Three independent datasets support the finding that a discontinuous
change of 20% was introduced in the Zurich Sunspot Number, Rz, when
Max Waldmeier took over the production of Rz in 1946. The range of
the diurnal variation of the geomagnetic field (the East-component) is
controlled by the EUV-induced conductivity of the day-side ionosphere
and indicates a 23% increase of Rz from 1946 on. The Greenwich Sunspot
Areas (and the Group Sunspot Number derived from the Greenwich data
since 1874) indicate a 17.5% increase of Rz. A CaII K-line index derived
from recently digitized Mount Wilson Observatory spectroheliograms
(since 1915) indicates a 21% increase in Rz. Friedli [2005] notes that
"The new observer-team in Zurich was thus relatively inexperienced
and Waldmeier himself feared that his scale factor could vary". We
suggest that his fear was not unfounded and that the Zurich Sunspot
Number be increased by 20% before 1946 to match the modern record.
Title: Modeling Total Solar Irradiance Variations Using Automated
Classification Software on Mount Wilson Data
Authors: Ulrich, Roger K.; Parker, D.; Bertello, L.; Boyden, J.
Bibcode: 2009SPD....40.1520U
Altcode:
We present the results of using the AutoClass software, a Bayesian
finite mixture model based pattern recognition program developed by
Cheeseman and Stutz(1996), on Mount Wilson Solar Observatory (MWO)
intensity and magnetogram images to identify spatially resolved areas on
the solar surface associated with Total Solar Irradiance (TSI). Using
indices based on the resolved solar surface patterns identified by
AutoClass from MWO magnetogram and intensity ratio images, and a linear
regression fit of those indices to satellite observations of TSI from
the Virgo satellite, we are able to model the TSI data from the MWO
images with a correlation of better than 0.96 for the period 1996
to 2007. The association of the spatially resolved surface patterns
identified by AutoClass with the indices developed from them also allows
construction of spatially resolved images of the Sun as it would be
"seen" by TSI measuring instruments like Virgo if they were able to
capture resolved images. The spatial resolution of these "images"
should assist in identifying with greater accuracy the particular
solar surface regions associated with TSI variations. Also, since the
particular set of MWO data on which this analysis is based is available
on a daily basis back to at least 1985, and on an intermittent basis
before then, it may be possible to construct an independent estimate
of TSI emission at several solar minima.
Title: Comparison Of Solar Surface Features Identified By The
Autoclass Pattern Recognition Software From Mount Wilson Observatory
Data To Solar Surface Feature Areas Measured By The San Fernando
Observatory
Authors: Parker, Daryl; Preminger, D.; Ulrich, R.; Bertello, L.;
Cookson, A.; Chapman, G.
Bibcode: 2009SPD....40.1607P
Altcode:
In previous work, the AutoClass software, a Bayesian pattern recognition
program based on a finite mixture model, developed by Cheeseman and
Stutz (1996), has been used on Mount Wilson Solar Observatory (MWO)
intensity and magnetogram images to identify spatially resolved areas on
the solar surface associated with Total Solar Irradiance (TSI) and to
classify the identified areas in terms of traditional categories-spot,
plage, quiet, etc. Those results, were in turn used to (1) model TSI
variations as measured by satellite and composite TSI observations,
with a correlation of better than 0.96, for the period 1996-2008-most
of Cycle 23, and (2) create solar images as they would be seen by a
hypothetical TSI instrument able to capture resolved images. Here,
we compare the same regions identified by AutoClass which were found
to be associated with TSI, and the indices derived from them, with the
following areas measured by the San Fernando Observatory (SFO): (1)
sunspot area in red continuum; (2) facular area in red continuum; (3)
sunspot area in wide Ca K-line (WK-line); (4) plage area in WK-line;
and (5) plage plus network area in WK-line. The correlations of
the AutoClass-MWO indices with the different SFO area measurements
varies from better than 0.91 to over 0.98, depending on the type
of feature. The comparison of the spatially resolved surface areas
identified by AutoClass in the MWO images to the areas of the different
feature observed at SFO, and the creation of spatially resolved images
depicting those areas, should enable better identification of the
types of surface features associated with TSI measurements and their
evolution over a solar cycle. The comparison should also assist in
validating the automated categorization of solar features found using
the AutoClass automated pattern recognition software.
Title: Results from the Mt. Wilson Solar Photographic Archive
Digitization Project
Authors: Bertello, Luca; Ulrich, R.; Boyden, J.
Bibcode: 2009SPD....40.1516B
Altcode:
We have digitized almost 40,000 ionized CaK line spectroheliograms that
were obtained at the 60-foot solar tower, between 1915 and 1985, as a
part of the monitoring program of the Mount Wilson Observatory. From
the analysis of these photographic solar images we have derived a Ca II
K index, defined as the average fractional area of the visible solar
disk occupied by plages and active network. Our time series agrees
very well with a different reduction of the same data base and other
Ca K spectroheliograms long-term synoptic programs, such as those at
Kodaikanal Observatory (India), and at the National Solar Observatory
at Sacramento Peak (USA). We show that using appropriate proxies it is
possible to extend this time series up to date, making this data set
one of the longest Ca II K index series currently available. The rate
of solar rotation over the whole solar surface can also be determined
as a function of time using the day-to day motions of features visible
on these CaK images. We present here preliminary results about the
rotation rate pattern determined by cross-correlating observations taken
on successive days for separate latitude zones spanning the solar disk.
Title: A Century of Solar Ca II Measurements and Their Implication
for Solar UV Driving of Climate
Authors: Foukal, Peter; Bertello, Luca; Livingston, William C.;
Pevtsov, Alexei A.; Singh, Jagdev; Tlatov, Andrey G.; Ulrich, Roger K.
Bibcode: 2009SoPh..255..229F
Altcode:
Spectroheliograms and disk-integrated flux monitoring in the strong
resonance line of Ca II (K line) provide the longest record of
chromospheric magnetic plages. We compare recent reductions of the Ca II
K spectroheliograms obtained since 1907 at the Kodaikanal, Mt. Wilson,
and US National Solar Observatories. Certain differences between the
individual plage indices appear to be caused mainly by differences
in the spectral passbands used. Our main finding is that the indices
show remarkably consistent behavior on the multidecadal time scales of
greatest interest to global warming studies. The reconstruction of solar
ultraviolet flux variation from these indices differs significantly
from the 20th-century global temperature record. This difference is
consistent with other findings that, although solar UV irradiance
variation may affect climate through influence on precipitation and
storm tracks, its significance in global temperature remains elusive.
Title: Interpretation of Solar Magnetic Field Strength Observations
Authors: Ulrich, R. K.; Bertello, L.; Boyden, J. E.; Webster, L.
Bibcode: 2009SoPh..255...53U
Altcode: 2008arXiv0812.2294U
This study based on longitudinal Zeeman effect magnetograms and spectral
line scans investigates the dependence of solar surface magnetic fields
on the spectral line used and the way the line is sampled to estimate
the magnetic flux emerging above the solar atmosphere and penetrating to
the corona from magnetograms of the Mt. Wilson 150-foot tower synoptic
program (MWO). We have compared the synoptic program λ5250 Å line
of Fe I to the line of Fe I at λ5233 Å since this latter line has a
broad shape with a profile that is nearly linear over a large portion of
its wings. The present study uses five pairs of sampling points on the
λ5233 Å line. Line profile observations show that the determination of
the field strength from the Stokes V parameter or from line bisectors in
the circularly polarized line profiles lead to similar dependencies on
the spectral sampling of the lines, with the bisector method being the
less sensitive. We recommend adoption of the field determined with the
line bisector method as the best estimate of the emergent photospheric
flux and further recommend the use of a sampling point as close to
the line core as is practical. The combination of the line profile
measurements and the cross-correlation of fields measured simultaneously
with λ5250 Å and λ5233 Å yields a formula for the scale factor
δ−1 that multiplies the MWO synoptic magnetic fields. By
using ρ as the center-to-limb angle (CLA), a fit to this scale factor
is δ−1=4.15−2.82sin 2(ρ). Previously
δ−1=4.5−2.5sin 2(ρ) had been used. The new
calibration shows that magnetic fields measured by the MDI system on
the SOHO spacecraft are equal to 0.619±0.018 times the true value at a
center-to-limb position 30°. Berger and Lites (2003, Solar Phys.213,
213) found this factor to be 0.64±0.013 based on a comparison using
the Advanced Stokes Polarimeter.
Title: Spectral Irradiance Variations and Magnetic Field Changes
During Solar Cycle 23.
Authors: Pap, J. M.; Bertello, L.; Chapman, G.; Floyd, L. E.; Harder,
J.; Jones, H.; Malanuskenko, O.; Preminger, D.; Turmon, M.
Bibcode: 2008AGUFMSH13A1504P
Altcode:
Both total irradiance and the Mg core-to-wing ratio was high at the
maximum of weak solar cycle 23. However, photometric observations
from the San Fernando Observatory show that both the number and size
of active regions (spots and faculae) were low at the maximum of
solar cycle 23 which points to the importance of the role of weak
magnetic fields in irradiance variations. The purpose of this paper
is to use new SOLIS spectromagnetograph observations in conjunction
with a newly developed image analysis technique to compare irradiance
time series as function of wavelengths with various surface magnetic
features. One major goal is to compare features derived from the
SOLIS images using the new technique with well-established features
from SFO. Another important goal is to determine the contribution
of active regions/weak fields to irradiance variations at various
wavelengths, using the SOHO/VIRGO and SORCE/SIM data. A third goal
is to determine the extent of irradiance variations not explained by
magnetic structures. To do this, we use a new analysis technique to
evaluate SOLIS spectromagnetograph observations.
Title: The Solar Rotation Rate Profile from 1915 to 1985
Authors: Bertello, L.; Ulrich, R. K.; Boyden, J. E.; Javaraiah, J.
Bibcode: 2008AGUFMSH13A1503B
Altcode:
The Mount Wilson solar photographic archive digitization project makes
available to the scientific community in digital form a selection of
the solar images in the archives of the Carnegie Observatories. This
archive contains over 150,000 images of the Sun which were acquired
over a time span in excess of 100 years. The images include broad-band
images called White Light Directs, ionized CaK line spectroheliograms
and Hydrogen Balmer alpha spectroheliograms. This project will digitize
essentially all of the CaK and broad-band direct images out of the
archive with 12 bits of significant precision and up to 3000 by 3000
spatial pixels. This project has already completed the digitization
of essentially all of the CaK and about 50% of the broad-band direct
images out of the archive with 12 bits of significant precision and
up to 3000 by 3000 spatial pixels. Solar images have been extracted
and identified with original logbook parameters of observation time
and scan format, and they are available from the project web site at
www.astro.ucla.edu/~ulrich/MW_SPADP. The rate of solar rotation over
the whole solar surface can be determined as a function of time using
the day-to day motions of features on these CaK images. We present here
preliminary results for the period 1915 to 1975. The pattern of rotation
rate is determined by cross-correlating observations taken on successive
days for 11 separate latitude zones spanning the solar disk between
+/- 50 degrees in latitude. We found that the average rotation rate of
the Sun during the 20th century was higher during periods of minimum
activity than it was during periods of maximum activity. The difference
in the rotation rate at the equator can be estimated at about 0.01
microrad/s. We also found that the orthogonalized rotation coefficients
calculated from the northern and southern hemispheres separately show
an asymmetry between the two hemispheres, with the northern hemisphere
rotating slightly faster than the southern hemisphere.
Title: Modeling Tsi Variations Using Automated Pattern Recognition
Software On Mount Wilson Data
Authors: Parker, D. G.; Ulrich, R. K.; Bertello, L.; Boyden, J. E.;
Pap, J. M.
Bibcode: 2008AGUFMSH23A1631P
Altcode:
This poster presents the results of using the AutoClass software,
a Bayesian finite mixture model based pattern recognition program
developed by Cheeseman and Stutz (1996), on Mount Wilson Solar
Observatory (MWO) intensity and magnetogram images to identify
spatially resolved areas on the solar surface associated with TSI
emissions. Using indices based on the resolved patterns identified
by AutoClass from MWO images, and a linear regression fit of those
indices to satellite observations of TSI, we were able to model the
satellite observations from the MWO data with a correlation of better
than 0.96 for the period 1996 to 2007. The association of the spatial
surface regional patterns identified by AutoClass with the indices
developed from them also allows construction of spatially resolved
images of the Sun as it would be "seen" by TSI measuring instruments
like Virgo if they were able to capture resolved images. This approach
holds out the possibility of creating an on-going, accurate, independent
estimate of TSI variations from ground based observations which could
be used to compare, and identify the sources of disagreement among,
TSI observations from the various satellite instruments and to fill
in gaps in the satellite record. Further, the spatial resolution of
these "images" should assist in identifying with greater accuracy the
particular solar surface regions associated with TSI variations. Also,
since the particular set of MWO data on which this analysis is based is
available on a daily basis back to at least 1985, and on an intermittent
basis before then, it may be possible to construct an independent
estimate of TSI emission at several solar minima to ascertain if there
has been any significant increase or decrease, a topic of significance
to determining what part, if any, solar TSI variations play in global
warming. Cheeseman, P. & Stutz, J.,1996, in Advances in Knowledge
Discovery and Data Mining, U.M. Fayyad, G. Piatetsky-Shapiro, P. Smyth,
and R. Uthurusamny (Eds.). (AAAI Press), p.61
Title: A Determination of the Value and Variability of the Sun's
Open Magnetic Flux using a Global MHD Model
Authors: Riley, P.; Mikic, Z.; Linker, J.; Harvey, J. W.; Hoeksema,
T.; Liu, Y.; Bertello, L.
Bibcode: 2008AGUSMSH44A..03R
Altcode:
The underlying value and variation of the Sun's open, unsigned magnetic
flux is of fundamental scientific importance, yet its properties remain
poorly known. For example, do long term (on the time-scale of ~ 100
years) changes in the strength of the solar magnetic field exist and
do they persist through the heliosphere? If present, they may have
a direct impact on space climate, including implications for the
transport of cosmic rays (CRs), and as such, may affect technology,
space, and even terrestrial climate. Global MHD models are capable of
reproducing the structure of the large-scale solar and interplanetary
magnetic field (at least in the absence of transient phenomena such as
Coronal Mass Ejections), and should, in principle, be able to address
this topic. However, they rely - and depend crucially - on boundary
conditions derived from observations of the photospheric magnetic
field. In spite of ~ 40 years of measurements, accurate estimates of the
radial component of the photospheric magnetic field remain difficult
to make. In this study, we attempt to find a "ground truth" estimate
of the photospheric magnetic field by carefully comparing both disk
magnetograms and diachronic (previously known as synoptic) maps from
6 different observatories (KPVT, SOLIS, GONG, MDI, WSO, and MWO). We
find that although there is a general consensus between several of
them, there are also some significant discrepancies. Using data from
these observatories, we compute global heliospheric solutions for a
selection of epochs during the last 3 solar cycles and compare the
results with in situ observations. We apply these results to several
topics related to the Sun's open flux.
Title: The Mount Wilson CaK Plage Index Time Series
Authors: Bertello, L.; Ulrich, R. K.; Boyden, J. E.; Javaraiah, J.
Bibcode: 2008AGUSMSP53B..01B
Altcode:
The Mount Wilson solar photographic archive digitization project makes
available to the scientific community in digital form a selection of
the solar images in the archives of the Carnegie Observatories. This
archive contains over 150,000 images of the Sun which were acquired
over a time span in excess of 100 years. The images include broad-band
images called White Light Directs, ionized CaK line spectroheliograms
and Hydrogen Balmer alpha spectroheliograms. This project will digitize
essentially all of the CaK and broad-band direct images out of the
archive with 12 bits of significant precision and up to 3000 by 3000
spatial pixels. The analysis of this data set will permit a variety of
retrospective analyzes of the state of the solar magnetism and provide
a temporal baseline of about 100 years for many solar properties. We
have already completed the digitization of the CaK series and we
are currently working on the broad-band direct images. Solar images
have been extracted and identified with original logbook parameters
of observation time and scan format, and they are available from the
project web site at www.astro.ucla.edu/~ulrich/MW_SPADP. We present
preliminary results on a CaK plage index time series derived from the
analysis of 70 years of CaK observations, from 1915 to 1985. One of
the main problem we encountered during the calibration process of these
images is the presence of a vignetting function. This function is linked
to the relative position between the pupil and the grating. As a result
of this effect the intensity and its gradient are highly variable from
one image to another. We currently remove this effect by using a running
median filter to determine the background of the image and divide the
image by this background to obtain a flat image. A plage index value is
then computed from the intensity distribution of this flat image. We
show that the temporal variability of our CaK plage index agrees very
well with the behavior of the international sunspot number series.
Title: Solar Radius Measurements at Mount Wilson Observatory
Authors: Lefebvre, S.; Bertello, L.; Ulrich, R. K.; Boyden, J. E.;
Rozelot, J. P.
Bibcode: 2006ApJ...649..444L
Altcode:
Possible temporal variations of the solar radius are important
as an indicator of internal energy storage and as a mechanism for
changes in the total solar irradiance. Variations in the total solar
irradiance with an amplitude of 0.1% have been observed from space
for more than two decades. Although the variability of this solar
output has been definitely established, the detailed dependence of
the rate of energy output on the level of solar magnetic activity
has not yet been measured with enough continuity and precision to
determine the correlation throughout the full solar cycle. While a
large fraction of the irradiance variability can be explained by the
distribution of solar magnetic activity at the surface, small changes
in the solar radius (i.e., contributing to the global variability of
the solar envelope) could account for a significant fraction of the
remaining variations. Studies of the apparent solar radius variation
have reported contradictory results, in the form of both correlations
and anticorrelations between the solar radius and, for example, the
cycle of sunspot numbers. We present results from more than 30 yr of
solar radius measurements obtained from the Mount Wilson synoptic
program of solar magnetic observations carried out at the 150 foot
(45.72 m) tower. We have used an improved definition of the solar
radius that also allows us to study the heliolatitude dependence of
the radius measurements. We find that the variations of the average
radius are not significantly correlated with the solar cycle over the
last three decades. We also compare the heliolatitude dependence of
these radius measurements with recent results obtained at the Pic du
Midi Observatory in France.
Title: Long-Term Variations in Solar Differential Rotation and
Sunspot Activity
Authors: Javaraiah, J.; Bertello, L.; Ulrich, R. K.
Bibcode: 2005SoPh..232...25J
Altcode:
The solar equatorial rotation rate, determined from sunspot group data
during the period 1879-2004, decreased over the last century, whereas
the level of activity has increased considerably. The latitude gradient
term of the solar rotation shows a significant modulation of about 79
year, which is consistent with what is expected for the existence of
the Gleissberg cycle. Our analysis indicates that the level of activity
will remain almost the same as the present cycle during the next few
solar cycles (i.e., during the current double Hale cycle), while the
length of the next double Hale cycle in sunspot activity is predicted
to be longer than the current one. We find evidence for the existence
of a weak linear relationship between the equatorial rotation rate and
the length of sunspot cycle. Finally, we find that the length of the
current cycle will be as short as that of cycle 22, indicating that
the present Hale cycle may be a combination of two shorter cycles.
Title: Global solar Doppler velocity determination with the GOLF/SoHO
instrument
Authors: García, R. A.; Turck-Chièze, S.; Boumier, P.; Robillot,
J. M.; Bertello, L.; Charra, J.; Dzitko, H.; Gabriel, A. H.;
Jiménez-Reyes, S. J.; Pallé, P. L.; Renaud, C.; Roca Cortés, T.;
Ulrich, R. K.
Bibcode: 2005A&A...442..385G
Altcode:
The Global Oscillation at Low Frequencies (GOLF) experiment is
a resonant scattering spectrophotometer on board the Solar and
Heliospheric Observatory (SoHO) mission, originally designed to measure
the disk-integrated solar oscillations of the Sun. This instrument was
designed in a relative photometric mode involving both wings of the
neutral sodium doublet (D1 at λ 5896 and D2 at
λ 5890 Å). However, a "one-wing" photometric mode has been selected
to ensure 100% continuity in the measurements after a problem in the
polarization mechanisms. Thus the velocity is obtained from only two
points on the same wing of the lines. This operating configuration
imposes tighter constraints on the stability of the instrument with a
higher sensitivity to instrumental variations. In this paper we discuss
the evolution of the instrument during the last 8 years in space and
the corrections applied to the measured counting rates due to known
instrumental effects. We also describe a scaling procedure to obtain
the variation of the Doppler velocity based on our knowledge of the
sodium profile slope and we compare it to previous velocity estimations.
Title: An Interpretation of the Differences in the Solar Differential
Rotation during Even and Odd Sunspot Cycles
Authors: Javaraiah, J.; Bertello, L.; Ulrich, R. K.
Bibcode: 2005ApJ...626..579J
Altcode:
Using the data on sunspot groups during the period 1879-2004, we have
found that the solar equatorial rotation rate during the odd-numbered
sunspot cycles is well correlated with the equatorial rotation rate
of the preceding even-numbered sunspot cycles, which is similar to the
well-known Gnevyshev & Ohl rule (G-O rule) in sunspot activity. This
indicates that a 22 yr cycle in the equatorial rotation rate begins in
an even-numbered cycle and ends in the following odd-numbered cycle, the
same as a solar magnetic cycle (Hale cycle), as inferred from the G-O
rule. On the other hand, the latitudinal gradient of the solar rotation
during the even-numbered cycles is found to be well correlated with that
of the preceding odd-numbered cycles. This result indicates that a 22
yr cycle in the latitudinal gradient begins in an odd-numbered cycle
and ends in the following even-numbered cycle. That is, the phase of
the beginning of a 22 yr cycle in the latitudinal gradient is different
by about 180° relative to the beginning of a 22 yr magnetic cycle.
Title: Potential Field Source Surface analysis from high resolution
synoptic and heliographic maps
Authors: Tran, T. V.; Bertello, L.; Ulrich, R. K.; Boyden, J. E.
Bibcode: 2005AGUSMSH13A..11T
Altcode:
The well established existence of an inverse correlation between the
solar magnetic flux tube expansion factor (FTE) and the solar wind
speed (SWS) at the Earth allows for the possibility to predict the SWS
using observed solar photosphere magnetograms. A widely used method
to compute the FTE is the potential field source surface (PFSS)
model. Current PFSS models, however, do not always produce good
agreement between the observed and predicted SWS. One complication
is that traditional synoptic maps, used as input in the PFSS models,
use the Carrington coordinates as the horizontal and vertical axes
of the synoptic chart. Unfortunately, this choice leads to a mix
of the time and space coordinates unless differential rotation is
included in the tracking of magnetic features. We show here that the
heliographic maps (longitude vs latitude or sine latitude) may be
a better choice for the PFSS models. An additional problem is that
the photospheric foot points and the FTE calculated from the PFSS
models depend on Nmax, the number of multipole components used in
the analysis. Current analyses use a combination of low resolution
maps and small values of Nmax, typically around 30. We find that
using a small Nmax produces fringing patterns in the reconstructed
photospheric magnetic map. These fringing patterns alter the locations
of the computed foot prints and the computed magnetic values on the
photosphere as well as the predicted FTE. Increasing the Nmax value
will then improve the reconstructed map and reveal more detail. In
our analysis, we use high resolution synoptic and heliographic maps,
which are 512 by 256, and Nmax up to 255. A typical simplification in
previous analyses is to assume that the line-of-sight component of the
solar magnetic field in the observed photospheric maps does not have
a north-south contribution. This assumption may not be correct if one
wants to reconstruct the north-south component map from the calculated
coefficients using PFSS model. We use the Shrauner-Scherrer method to
create both line-of-sight component and transverse component from the
same observations. With the assumption (∇ × ěc{B}) = 0, we aim
to obtain the north-south map from the transverse map and remove the
north-south component from the line-of- sight component.
Title: Magnetic Fields from SOHO MDI Converted to the Mount Wilson
150 Foot Solar Tower Scale
Authors: Tran, Tham; Bertello, Luca; Ulrich, Roger K.; Evans, Scott
Bibcode: 2005ApJS..156..295T
Altcode:
In order to permit the construction of long-duration time series
dependent on the Sun's magnetic field, this paper presents a detailed
cross-correlation between sets of simultaneous magnetograms from
the Mount Wilson Observatory (MWO) and the Michelson Doppler Imager
(MDI) aboard the SOHO spacecraft. The MWO 150 foot (45.72 m) solar
tower telescope magnetogram data are for the Fe I 525.0 nm and Ni
I 676.8 nm lines, and the MDI data are level 1.8 magnetograms also
for the Ni I 676.8 nm spectral line. In these comparisons, we apply
a saturation correction factor to the MWO 525.0 nm fields prior
to the derivation of the MDI scale factor. Data from 1997 March to
2002 August are used for this work. We have found that the ratio of
MWO Fe I 525.0 nm magnetograms over MDI magnetograms is about 1.7,
and it is a function of the center-to-limb angle. Moreover, there are
differences between the west-side and the east-side ratios, and these
differences may come from the angle dependence of the Michelson filters
in the MDI instrument. The MDI tuning changes, on the other hand,
are not associated with significant jumps in the derived scale factor
ratio. The average scale factors should be adequate for the construction
of MDI images closely comparable to those of the saturation-corrected
long-duration MWO 525.0 nm sequence.
Title: The solar photograph archive of the Mount Wilson Observatory. A
resource for a century of digital data
Authors: Lefebvre, S.; Ulrich, R. K.; Webster, L. S.; Varadi, F.;
Javaraiah, J.; Bertello, L.; Werden, L.; Boyden, J. E.; Gilman, P.
Bibcode: 2005MmSAI..76..862L
Altcode:
The solar telescopes and spectroheliographs of the Mount Wilson
Observatory were among the earliest modern facilities for the study of
the solar surface. The photographic collection of the solar program
at Mt. Wilson begins in 1894 and continues to the present day. A
program to digitize and distribute the images in this collection
was begun at UCLA in 2003 and is now making available the first of
the catalogued and catagorized images from the CaK sequence. Most
of the instrumentation with which the images were obtained is still
available although in a disassembled form. Original log books have
been digitized and associated with the images so that a maximum of
scientific return can be obtained from the data base. The present range
of images available from www.astro.ucla.edu/~ulrich extends from late
1915 to 1952. Each image has been digitized with 12-bit precision and
represented in a 16-bit format. These images are each 13 Mbytes in size
and larger than will be the final product images since not all image
defects have been mitigated at this time. The radii and centers of the
solar images have been determined and are included in the available data
files. Optical vignetting by the system introduces an intensity gradient
of known magnitude that can be used to help characterize the photograph
plates. The roll angle of the images has yet to be determined.
Title: Solar Radius Measurements at Mount Wilson
Authors: Lefebvre, S.; Bertello, L.; Ulrich, R. K.; Boyden, J. E.;
Rozelot, J.
Bibcode: 2004AGUFMSH53B0314L
Altcode:
Variations of the solar radius are not only important for solar physics
but they also play a fundamental role in the research of terrestrial
climate. In fact, changes in the apparent size of the Sun could account
for a significant fraction of the total irradiance variations, and
solar irradiance is known to be a primary force in driving atmospheric
circulation. While the MDI instrument aboard SOHO is likely to provide
the most accurate constraint on possible solar radius variations, the
radius measurements obtained from ground base observations represent
a unique resource due to their long temporal coverage. Since 1970, the
Mount Wilson synoptic programme of solar magnetic observations carried
out at the 150-foot tower scans the solar disk using the radiation in
the neutral iron line at 525.0 nm. For these images, the radius has
been determined and results are presented on this paper. We show first
the temporal behavior of these measurements. Secondly, if data are
gathered by heliolatitude, the shape of the Sun differs from a perfect
ellipsoid and shows solar distortions. We compare these results with
others obtained with the heliometer at the Pic du Midi observatory
in France. The comparison show a similitude in the shape with a bulge
near the equator extending on 20-30 degrees followed by a depression
at higher latitude near 60-70 degrees. These solar distortions needs
to be confirmed by future space measurements (PICARD microsatellite)
but it already raises the problem of a better understanding of the
physics in the sub-surface layers.
Title: Solar Radius Measurements at Mount Wilson
Authors: Lefebvre, S.; Bertello, L.; Ulrich, R. K.; Boyden, J. E.;
Rozelot, J. -P.
Bibcode: 2004ESASP.559..532L
Altcode: 2004soho...14..532L
No abstract at ADS
Title: Acoustic Modes and the Structure of the Solar Interior
Authors: Bertello, L.; Varadi, F.; Ulrich, R. K.; Basu, S.
Bibcode: 2004ESASP.559..321B
Altcode: 2004soho...14..321B
No abstract at ADS
Title: Erratum: ``Looking for Gravity-Mode Multiplets with the GOLF
Experiment aboard SOHO'' (ApJ,
604, 455 [2004])
Authors: Turck-Chièze, S.; García, R. A.; Couvidat, S.; Ulrich,
R. K.; Bertello, L.; Varadi, F.; Kosovichev, A. G.; Gabriel, A. H.;
Berthomieu, G.; Brun, A. S.; Lopes, I.; Pallé, P.; Provost, J.;
Robillot, J. M.; Roca Cortés, T.
Bibcode: 2004ApJ...608..610T
Altcode:
As a result of an error at the Press, the second panel of Figure 9
was repeated twice in the top row of the printed, black-and-white
version of this figure, and the first panel was omitted. This error
appears in the print edition and the PDF and postscript (PS) versions
available with the electronic edition of the journal, although the
panels of the color figure displayed in the electronic article itself
are correct. Please see below for the corrected print version of Figure
9. The Press sincerely regrets the error.
Title: Looking for Gravity-Mode Multiplets with the GOLF Experiment
aboard SOHO
Authors: Turck-Chièze, S.; García, R. A.; Couvidat, S.; Ulrich,
R. K.; Bertello, L.; Varadi, F.; Kosovichev, A. G.; Gabriel, A. H.;
Berthomieu, G.; Brun, A. S.; Lopes, I.; Pallé, P.; Provost, J.;
Robillot, J. M.; Roca Cortés, T.
Bibcode: 2004ApJ...604..455T
Altcode:
This paper is focused on the search for low-amplitude solar gravity
modes between 150 and 400 μHz, corresponding to low-degree, low-order
modes. It presents results based on an original strategy that looks
for multiplets instead of single peaks, taking into consideration
our knowledge of the solar interior from acoustic modes. Five years
of quasi-continuous measurements collected with the helioseismic GOLF
experiment aboard the SOHO spacecraft are analyzed. We use different
power spectrum estimators and calculate confidence levels for the
most significant peaks. This approach allows us to look for signals
with velocities down to 2 mm s-1, not far from the limit
of existing instruments aboard SOHO, amplitudes that have never been
investigated up to now. We apply the method to series of 1290 days,
beginning in 1996 April, near the solar cycle minimum. An automatic
detection algorithm lists those peaks and multiplets that have a
probability of more than 90% of not being pure noise. The detected
patterns are then followed in time, considering also series of 1768 and
2034 days, partly covering the solar cycle maximum. In the analyzed
frequency range, the probability of detection of the multiplets
does not increase with time as for very long lifetime modes. This is
partly due to the observational conditions after 1998 October and the
degradation of these observational conditions near the solar maximum,
since these modes have a ``mixed'' character and probably behave as
acoustic modes. Several structures retain our attention because of
the presence of persistent peaks along the whole time span. These
features may support the idea of an increase of the rotation in the
inner core. There are good arguments for thinking that complementary
observations up to the solar activity minimum in 2007 will be decisive
for drawing conclusions on the presence or absence of gravity modes
detected aboard the SOHO satellite.
Title: Variability of the Solar Radius
Authors: Bertello, L.; Ulrich, R. K.
Bibcode: 2003SPD....34.2602B
Altcode: 2003BAAS...35..854B
Possible temporal variability of the solar radius is important as an
indicator of internal energy storage and as a mechanism for changes
in the total solar irradiance (TSI). Variations in the TSI with an
amplitude of 0.1% have been observed from space for more than two
decades. Although the variability of this solar output is definitely
established, the detailed dependence of the rate of energy output on
the level of solar magnetic activity has not yet been measured with
enough continuity and precision to establish the correlation throughout
the full solar cycle. Changes in the solar radius could account for
a significant fraction of the total irradiance variations. However,
studies of the solar radius variation have reported contradictory
results in the form of both correlations and anticorrelations between
the solar radius and, for example, the cycle of sunspot numbers. Most
of these studies however, are affected by the highly inhomogeneous
data used in the analysis. This factor becomes particularly critical
in the case of measurements that cover a very long period of time. We present consistent solar radius measurements obtained from the
Mt Wilson synoptic programme of solar magnetic observations carried
out at the 150-foot tower. Two definitions of the solar radius are
used: the longest reduced record beginning in 1975 is derived from
the fit of a circle to the isophote having an intensity equal to
40%\ of the central intensity and more recently we have developed a
definition based on intensity fits within 16 sectors around the solar
circumference. Ulrich and Bertello (Nature, 1995, 377, 214) have
made a re-analysis of an older database correcting for such effects
as scattered light and atmospheric refraction. The older database is
brought up to date and compared to results based on the new radius
definition as well as other published radius variations. This
work was supported by NASA through grants NAG5-10905 and NAG5-11708
as well as by NSF through grant ATM-0101350.
Title: A two color pupil imaging method to detect stellar oscillations
Authors: Cacciani, A.; Dolci, M.; Jefferies, S. M.; Finsterle, W.;
Fossat, E.; Sigismondi, C.; Cesario, L.; Bertello, L.; Varadi, F.
Bibcode: 2003MSAIS...2..172C
Altcode:
Observations of stellar intensity oscillations from the ground are
strongly affected by intensity fluctuations caused by the atmosphere
(scintillation). However, by using a differential observational method
that images the pupil of the telescope in two colors at the same
time on a single CCD, we can partially compensate for this source of
atmospheric noise (which is color dependant) as well as other problems,
such as guiding and saturation. Moreover, by placing instruments at
different locations (eg. Dome C and South Pole) we can further reduce
the atmospheric noise contribution by using cross-spectral methods,
such as Random Lag Singular Cross-Spectrum Analysis (RLSCA). (We
also decrease the likelihood of gaps in the data string due to
bad weather). The RLSCA method is well suited for extracting common
oscillatory components from two or more observations, including their
relative phases. We have evaluated the performance of our method
using real data from SOHO. We find that our differential algorithm can
recover the absolute amplitudes of the solar intensity oscillations
with an efficiency of 70%. We are currently carrying out tests using a
number of telescopes, including Big Bear, Mt. Wilson, Teramo and Milano,
while waiting for the South Pole and Dome C sites to become available.
Title: A search for solar g modes in the GOLF data
Authors: Gabriel, A. H.; Baudin, F.; Boumier, P.; García, R. A.;
Turck-Chièze, S.; Appourchaux, T.; Bertello, L.; Berthomieu, G.;
Charra, J.; Gough, D. O.; Pallé, P. L.; Provost, J.; Renaud, C.;
Robillot, J. -M.; Roca Cortés, T.; Thiery, S.; Ulrich, R. K.
Bibcode: 2002A&A...390.1119G
Altcode:
With over 5 years of GOLF data having some 90% continuity, a new
attempt has been made to search for possible solar g modes. Statistical
methods are used, based on the minimum of assumptions regarding the
solar physics; namely that mode line-widths are small compared with
the inverse of the observing time, and that modes are sought in the
frequency interval 150 to 400 mu Hz. A number of simulations are carried
out in order to understand the expected behaviour of a system consisting
principally of a solar noise continuum overlaid with some weak sharp
resonances. The method adopted is based on the FFT analysis of a time
series with zero-padding by a factor of 5. One prominent resonance at
284.666 mu Hz coincides with a previous tentative assignment as one
member of an n=1, l=1, p-mode multiplet. Components of two multiplets,
previously tentatively identified as possible g-mode candidates from
the GOLF data in 1998, continue to be found, although their statistical
significance is shown to be insufficient, within the present assumption
regarding the nature of the signal. An upper limit to the amplitude
of any g mode present is calculated using two different statistical
approaches, according to either the assumed absence (H0 hypothesis)
or the assumed presence (H1 hypothesis) of a signal. The former yields
a slightly lower limit of around 6 mm/s.
Title: Global low frequency acoustic modes after half a solar cycle
aboard SOHO: an improved view of the nuclear core
Authors: Turck-Chièze, S.; Garcí, R. A.; Couvidat, S.; Kosovichev,
A. G.; Bertello, L.; Corbad, T.; Berthomieu, G.; Provost, J.;
Eff-Darwich, A.
Bibcode: 2002ESASP.508..593T
Altcode: 2002soho...11..593T
Solar global oscillations have now been measured for more than 20
years. The study of these modes has contributed to improve, along
time, the description of the solar core. We have now a proper access
to this part of the Sun, with ground networks observing for more than
10 years and the three instruments aboard SOHO in a quasi continuous
mode for now half a cycle. In this talk, we show the advantages of
the global acoustic modes measured at low frequency. They are due to
their longer lifetime and the reduced influence of the turbulent and
variable surface effects. As a consequence, we have converged last
year, after 30 years of unsuccess, to a boron-8 emitted neutrino flux
in perfect agreement with the better understood detection of these
neutrinos on earth. The splitting at low frequency is also now properly
determined but the extracted rotation information is still limited in
the core. It contains nevertheless the first dynamical vision of this
part of the radiative zone. We will focus on it up to the end of the
SOHO mission, together with the gravity mode region and the possible
internal signature of the magnetic field. Some limits are given on
these observables. Further improvements of their detectability are
under study and will be mentioned.
Title: Low-Degree Low-Order Solar p Modes As Seen By GOLF On
board SOHO
Authors: García, R. A.; Régulo, C.; Turck-Chièze, S.; Bertello,
L.; Kosovichev, A. G.; Brun, A. S.; Couvidat, S.; Henney, C. J.;
Lazrek, M.; Ulrich, R. K.; Varadi, F.
Bibcode: 2001SoPh..200..361G
Altcode:
Data recovered from the GOLF experiment on board the ESA/NASA SOHO
spacecraft have been used to analyze the low-order low-degree
solar velocity acoustic-mode spectrum below ν=1.5 mHz (i.e.,
1≤n≤9,l≤2). Various techniques (periodogram, RLAvCS,
homomorphic-deconvolution and RLSCSA) have been used and compared to
avoid possible biases due to a given analysis method. In this work,
the acoustic resonance modes sensitive to the solar central region
are studied. Comparing results from the different analysis techniques,
10 modes below 1.5 mHz have been identified.
Title: The search for solar low frequency resonant modes
Authors: Bertello, L.; García, R. A.; Varadi, F.; Turck-Chièze,
S.; Ulrich, R. K.; Henney, C. J.; Couvidat, S.
Bibcode: 2001ESASP.464..479B
Altcode: 2001soho...10..479B
We present the results obtained from the analysis of 4-year long GOLF
and MDI time series. The GOLF time series includes the period where the
instrument operated in the blue wing of the doublet Na D lines, and also
the data from the current red-wing photometric mode. Disk-averaged MDI
velocity signals from the calibrated level-1.4 MDI LOI-proxy Doppler
images were obtained using integrated spatially weighted masks. The
analysis was carried out by Random-Lag Singular Cross-Spectrum
Analysis. This technique searches for simultaneous oscillatory
components in two or more time series, and has been proven to be very
effective for the identification of solar acoustic modes of low angular
degree and low radial order. In the present work we have extended our
analysis to the frequency range between 200 and 1500 microHZ, which
includes the region of low radial order gravity modes. Selected cases
are presented and compared with the results obtained using classical
spectral estimations based on Fourier transforms.
Title: Analysis of low frequency signal with the GOLF experiment:
methodology and results
Authors: García, R. A.; Bertello, L.; Turck-Chièze, S.; Couvidat,
S.; Gabriel, A. H.; Henney, C. J.; Régulo, C.; Robillot, J. M.;
Roca Cortés, T.; Ulrich, R. K.; Varadi, F.
Bibcode: 2001ESASP.464..473G
Altcode: 2001soho...10..473G
Four years of GOLF velocity time series have been used to study the
low frequency part of the solar spectrum below 1.5 mHz. This paper
discusses the methods already developed for the research of the
low-degree low-order acoustic modes by Garcia et al. (2000) and for
the gravity modes by Turck-Chieze et al. (2000). These methods are
based on our knowledge of the general theoretical properties of the p
and g modes that lead us to determine the statistical significance of
the structures (multiplets) present in the GOLF spectrum in terms of
p- and g-mode candidates. In addition to the search of single peaks,
we try to detect multiplets (l = 1, 2 and 3) which allows us to lower
the detection threshold while keeping the same confidence level. We
will concentrate the discussion on the limits of this search that only
takes into account those peaks above a selected statistical threshold
giving an estimation of the possible uncertainties due to the solar
noise and the nature of the solar resonances.
Title: Sensitivity of the GOLF signal to combined solar velocity
and intensity variations
Authors: Ulrich, R. K.; García, R. A.; Robillot, J. -M.;
Turck-Chièze, S.; Bertello, L.; Charra, J.; Dzitko, H.; Gabriel,
A. H.; Roca Cortés, T.
Bibcode: 2000A&A...364..799U
Altcode:
The GOLF instrument provides a stable and continuous measurement of
the intensity of spatially integrated sunlight in one wing of the
sodium D lines. Because the detected radiation results from atomic
scattering, the GOLF signal can be traced to an atomic reference
wavelength. The planned operations were to involve a form of relative
photometry through the use of measurements on both the blue and red
wings of the solar D lines of neutral sodium. However, due to the
occasional malfunction of the polarization subsystem a ``one wing
photometric mode" operational alternative has been selected in order
to ensure achievement of a 100% duty cycle. In this case, the signal
observed consists of two photometric measurements at only one wing
of each line of the sodium doublet separated by gx0.43 picometers
(pm). The sodium cell system in GOLF combines photons scattered at
three different wavelengths: one at D_1 and two at D_2. This paper
developes a formalism to describe this system in terms of the solar
spectral line profiles. A method of converting the one wing data to an
effective velocity scale is presented. The method is applied to the
nearly continuous 804 day sequence received from the GOLF instrument
prior to the loss of telecommunications with SOHO on 24-June-1998. The
resulting time sequence is part of the GOLF archive and can be made
available to investigators. This publication describes some properties
of this time series.
Title: Identification of Solar Acoustic Modes of Low Angular Degree
and Low Radial Order
Authors: Bertello, L.; Varadi, F.; Ulrich, R. K.; Henney, C. J.;
Kosovichev, A. G.; García, R. A.; Turck-Chièze, S.
Bibcode: 2000ApJ...537L.143B
Altcode:
We present evidence for the detection of low radial order (n<10)
acoustic modes of low angular degree, l=0-2, in the 759 day long
Global Oscillations at Low Frequency and Michelson Doppler Imager time
series. We used Random-Lag Singular Cross-Spectrum Analysis, which
searches for simultaneous oscillatory components in two or more time
series. We have determined 11 modes in the range n=3-9, of which eight
modes confirm the previous measurements by Toutain et al. and three
modes of l=0 and n=3, 5, and 6 are reliably measured for the first
time. The errors of frequency determination are also significantly
reduced for several previously identified modes. New sound speed
inversion results suggest that the effect of inhomogeneous initial
composition of the Sun should be included in the standard solar model.
Title: Comparison of Frequencies and Rotational Splittings of Solar
Acoustic Modes of Low Angular Degree from Simultaneous MDI and
GOLF Observations
Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.;
Kosovichev, A. G.; Scherrer, P. H.; Roca Cortés, T.; Thiery, S.;
Boumier, P.; Gabriel, A. H.; Turck-Chièze, S.
Bibcode: 2000ApJ...535.1066B
Altcode:
During the years 1996 through 1998 the Michelson Doppler Imager (MDI)
and the Global Oscillations at Low Frequency (GOLF) experiments on the
Solar and Heliospheric Observatory (SOHO) mission have provided unique
and nearly uninterrupted sequences of helioseismic observations. This
paper describes the analysis carried out on power spectra from 759
days of calibrated disk-averaged velocity signals provided by these two
experiments. The period investigated in this work is from 1996 May 25
to 1998 June 22. We report the results of frequency determination of
low-degree (l<=3) acoustic modes in the frequency range between 1.4
mHz and 3.7 mHz. Rotational splittings are also measured for nonradial
modes up to 3.0 mHz. The power spectrum estimation of the signals
is performed using classical Fourier analysis and the line-profile
parameters of the modes are determined by means of a maximum likelihood
method. All parameters have been estimated using both symmetrical and
asymmetrical line profile-fitting formula. The line asymmetry parameter
of all modes with frequency higher than 2.0 mHz is systematically
negative and independent of l. This result is consistent with the
fact that both MDI and GOLF data sets investigated in this paper are
predominantly velocity signals, in agreement with previous results. A
comparison of the results between the symmetric and asymmetric fits
shows that there is a systematic shift in the frequencies for modes
above 2.0 mHz. Below this frequency, the line width of the modes
is very small and the time base of the data does not provide enough
statistics to reveal an asymmetry. In general, the results show that
frequency and rotational splitting values obtained from both the
MDI and GOLF signals are in excellent agreement, and no significant
differences exist between the two data sets within the accuracy of the
measurements. Our results are consistent with a uniform rotation of
the solar core at the rate of about 435 nHz and show only very small
deviations of the core structure from the standard solar model.
Title: Analysis of asymmetric p-mode profiles in GOLF data
Authors: Thiery, S.; Boumier, P.; Gabriel, A. H.; Bertello, L.;
Lazrek, M.; García, R. A.; Grec, G.; Robillot, J. M.; Roca Cortés,
T.; Turck-Chièze, S.; Ulrich, R. K.
Bibcode: 2000A&A...355..743T
Altcode:
We show here evidence for the necessity of an asymmetric form in
modelling the profile of an acoustic mode in the power spectral
density. The analysis was performed on a 805-day series of GOLF data
(l=0 to 3). The assumptions used for the fits are discussed and their
consequences quantified, in particular for the optimum choice of the
fitting spectral window. Values are given for the bias on the mode
parameters (frequency, width, splitting) when using a Lorentzian
fit. The bias depends on the degree l and on the frequency, and when
taken into account leads to variations in the mode parameters with
degree more consistent with theoretical expectations.
Title: Random-Lag Singular Cross-Spectrum Analysis
Authors: Varadi, F.; Ulrich, R. K.; Bertello, L.; Henney, C. J.
Bibcode: 2000ApJ...528L..53V
Altcode: 1999astro.ph.10424V
In a previous paper (Varadi et al.), random-lag singular spectrum
analysis was introduced for finding oscillations in very noisy and long
time series. This work presents a generalization of the technique to
search for common oscillations in two or more time series.
Title: Searching for Signal in Noise by Random-Lag Singular Spectrum
Analysis
Authors: Varadi, F.; Pap, J. M.; Ulrich, R. K.; Bertello, L.; Henney,
C. J.
Bibcode: 1999ApJ...526.1052V
Altcode:
Singular spectrum analysis, a technique to detect oscillations in
short and noisy time series, was first developed for geophysical
applications. This work offers a generalization for long and noisy
time series in astrophysical applications. The motivating problem is
the detection of low-amplitude solar oscillations.
Title: Frequencies and splittings of low-degree acoustic modes:
a comparison between MDI and GOLF observations
Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.;
Kosovichev, A. G.; Roca Cortes, T.; Garcia, R. A.; Scherrer, P. H.
Bibcode: 1999AAS...19410805B
Altcode:
During the years 1996 through 1998 the MDI and GOLF experiments on the
SOHO mission have provided unique and nearly uninterrupted sequences of
helioseismic observations. This paper describes the analysis carried out
on power spectra from 759 days of calibrated velocity signals provided
by these two experiments. The time series investigated in this work are
from 25 May, 1996 to 22 June, 1998. We report the results of frequency
and splitting determination of low-degree (l < 4) acoustic modes
in the frequency range between 1.5 mHz and 4.0 mHz. The power spectrum
estimation of the signals is performed using classical Fourier analysis
and the line-profile parameters of the modes are determined by means of
a maximum likelihood method. All parameters have been estimated using
both symmetrical and asymmetrical line profile-fitting formula. The
line asymmetry parameter of all modes with frequency higher than 2.0
mHz is systematically negative and independent from l. This result is
consistent with the fact that both MDI and GOLF data sets investigated
in this paper are predominantly velocity signals. A comparison of the
results between symmetric fit and asymmetric one shows that there
is a systematic shift in the eigenfrequencies for modes above 2.0
mHz. The results show that eigenfrequency and rotational splitting
values obtained from both the MDI and GOLF signals are in excellent
agreement, and no significant differences exist between the two data
sets within the indetermination of the measurement.
Title: Frequencies and splittings of low-degree acoustic modes:
a comparison between MDI and GOLF observations.
Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Varadi, F.;
Kosovichev, A. G.; Roca Cortes, T.; Garcia, R. A.; Scherrer, P. H.
Bibcode: 1999BAAS...31.1242B
Altcode:
No abstract at ADS
Title: Power spectra comparison between GOLF and MDI velocity
observations
Authors: Henney, C. J.; Ulrich, R. K.; Bertello, L.; Bogart,
R. S.; Bush, R. I.; Scherrer, P. H.; Palle, P. L.; Roca Cortes, T.;
Turck-Chieze, S.
Bibcode: 1999AAS...194.5617H
Altcode: 1999BAAS...31..914H
We present a comparison of the velocity power spectra between the GOLF
and MDI instruments. In addition, this poster outlines work towards
creating a GOLF-simulated signal utilizing MDI velocity images. The
simulation of the GOLF signal is achieved by integrating spatially
weighted masks with MDI LOI-proxy velocity images. The GOLF-simulated
signal and a selection of additional spatially masked MDI velocity
signals are compared with the observed GOLF signal for a 759 day period
from May 25, 1996 through June 22, 1998. Ultimately, a cross-analysis
process between GOLF and MDI signals could lead to an enhancement
of our ability to detect low frequency solar oscillations. The
signal-to-background ratio (S/B) for the GOLF and the spatially masked
MDI velocity data is presented for low degree (l <= 3) and low
frequency p-modes. We find that signals from both MDI and GOLF are
beneficial for detecting low degree (l <= 3) and low frequency
(< 2000 mu Hz) p-modes. For the frequency range and the signals
compared in this poster, the GOLF signal has the highest S/B for l=0
p-modes. The S/B of the GOLF and MDI central region masked signals
is good for detecting l=1 p-modes. For l >= 2 p-modes, the central
region masked signals have the highest S/B of the power spectra compared
here. In addition, the S/B of the preliminary GOLF-simulated signal
is found to be more similar to the GOLF signal than the MDI LOI-proxy
signal without spatial masking for the modes investigated here.
Title: Power spectra comparison between GOLF and spatially masked
MDI velocity signals
Authors: Henney, C. J.; Ulrich, R. K.; Bertello, L.; Bogart, R. S.;
Bush, R. I.; Scherrer, P. H.; Roca Cortés, T.; Turck-Chièze, S.
Bibcode: 1999A&A...348..627H
Altcode:
The Global Oscillations at Low Frequency (GOLF) and the Michelson
Doppler Imager (MDI) instruments aboard the Solar and Heliospheric
Observatory (SOHO) give an excellent opportunity to search for solar
low frequency oscillation modes previously undetected from ground
based experiments. Presented here is a comparison of the velocity power
spectra between the two instruments. In addition, this paper outlines
work towards creating a GOLF-simulated signal utilizing MDI velocity
images. The simulation of the GOLF signal is achieved by integrating
spatially weighted masks with MDI full-disk Doppler images. The
GOLF-simulated signal and a selection of additional spatially masked
MDI velocity signals are compared with the observed GOLF signal for a
759 day period from May 25, 1996 through June 22, 1998. Ultimately,
a cross-analysis process between GOLF and MDI signals could lead
to an enhancement of our ability to detect low frequency solar
oscillations. For low degree (l<= 3) and low frequency acoustic
modes, the signal-to-background ratio between GOLF and the spatially
masked MDI velocity data is compared here.
Title: Results from the GOLF instrument on SOHO
Authors: Gabriel, A. H.; Turck-Chièze, S.; García, R. A.; Pallé,
P. L.; Boumier, P.; Thiery, S.; Baudin, F.; Grec, G.; Ulrich, R. K.;
Bertello, L.; Roca Cortés, T.; Robillot, J. -M.
Bibcode: 1999AdSpR..24..147G
Altcode:
An 800 day series of GOLF velocity data, with uniquely high continuity
and stability, offers the best ever signal to noise ratio obtained
in global Sun observations. Following meticulous efforts to provide
reliable calibration, these data have been used for measurements of
frequencies, line-widths and power in the p-modes, which are used
for inversion to give the internal sound speed, for comparison with
theoretical models. A search for g-modes is at present inconclusive, but
has yielded two possible candidate frequencies. The analysis available
today is regarded as preliminary and more complete methods are currently
in hand. With the resumption of routine observations following the
SOHO recovery, it is hoped that the data can be considerably extended,
enabling changes with the solar cycle to be explored, as well as an
extended g-mode search.
Title: Power spectra comparison between GOLF and MDI velocity
observations.
Authors: Henney, C. J.; Ulrich, R. K.; Bertello, L.; Bogart, R. S.;
Bush, R. I.; Scherrer, P. H.; Pallé, P. L.; Roca Cortés, T.;
Turck-Chièze, S.
Bibcode: 1999BAAS...31Q1237H
Altcode:
No abstract at ADS
Title: Autoregressive analysis of the GOLF velocity time series
Authors: Ulrich, R. K.; Varadi, F.; Bertello, L.; GOLF Team
Bibcode: 1998IAUS..185...57U
Altcode:
The theory of solar oscillations describes the motions in terms of
stochastically excited modes which obey a system of linear partial
differential equations. A natural statistical model for the resulting
time series is the autoregressive stochastic process since it embodies
the same principles as the differential equations but in discrete time
samples. The association of the power spectrum of a time series with
the spectral response of its autoregressive model yields the well-known
Maximum Entropy Method (MEM). The present work uses very high order
autoregressive models to identify solar p-modes in the GOLF velocity
signal. Besides straightforward MEM computations, the characteristic
roots of the autoregressive models are also determined. These roots
provide estimates of both the frequencies and the damping rates of
the modes. In autoregressive models the complexity of the modelled
process is indicated by the order (which is essentially the number of
adjustable model parameters) required to describe the time series. The
results demonstrate that one has to use very high orders, at least
20000, in order to capture the complicated spectral features associated
with rotational mode splitting. The computed frequencies and damping
rates agree well with those obtained by other means such as fitting
Lorentzian line profiles.
Title: The Solar Acoustic Spectrum as Seen by GOLF. IV. Linewidth,
Power and Energy of the Modes
Authors: Roca Cortés, T.; Lazrek, M.; Bertello, L.; Thiery, S.;
GOLF Team
Bibcode: 1998ESASP.418..335R
Altcode: 1998soho....6..335R
The model fitted to the observed spectra also allows the measurement
of the linewidth and power of each mode (see poster II). The linewidths
are related to the damping mechanisms and the energies give information
on the excitation mechanisms. Here the results of these parameters
as well as the relative energy shared by the components of a given
multiplet are presented. The results supports the turbulent convection
as the main mechanism to excite the modes, however their damping also
has to include radiative damping and possibly other sources. Moreover,
results on the relative power of the components of the same multiplet
seem to depart from the standard assumptions derived from a convection
driven excitation mechanism only.
Title: The Solar Acoustic Spectrum as Seen by GOLF. III. Asymmetries,
Resonant Frequencies and Splittings
Authors: Roca Cortés, T.; Lazrek, M.; Bertello, L.; Thiery, S.;
Baudin, F.; Garcia, R. A.; GOLF Team
Bibcode: 1998ESASP.418..329R
Altcode: 1998soho....6..329R
The definition of the model to fit to the observed spectra depends
on the physics we are assuming is present in the phenomena we are
observing. Here we present the results obtained following the fit
of several models (described in poster II). Therefore the effects
of asymmetrical line shapes, a common background for all modes, fixed
relative power in the components of a multiplet and a constant splitting
between the components of each multiplet on the resonant frequencies
(and their errors) of the modes will be evaluated. Finally, a table
of frequencies and splittings will be given.
Title: Calibration of the GOLF Velocity Signal
Authors: Ulrich, R. K.; Bertello, L.; Garcia, R. A.; Robillot, J. -M.;
GOLF Team
Bibcode: 1998ESASP.418..353U
Altcode: 1998soho....6..353U
The GOLF instrument is functioning in a one-wing mode which precludes
calibrating its signal with the classic resonance ratio: R =
(Ib-Ir) / (Ib+Ir). The
instrument performance is otherwise outstanding and the returned
data is free of contaminating periodicities and largely free from
temporal gaps. Full utilization of the signal for some modes of
physical analysis requires knowledge of the relationship between
the intensity variations and solar surface velocities. This
poster describes two methods of deriving such a relationship
based on the onboard magnetic modulation. One method utilizes X =
0.5(I++I-) <I+-I->
where I+ and I- are the counting rates corrected
for stem temperature variations and photomultiplier deadtime at the plus
and minus phases of the magnetic modulation and the <I> notation
denotes a mean of I. The second method corrects the counting rates to
a signal function S by accounting for all known effects and fits the
resulting quantity to a function having only long-time components. By
combining corrected signals from the plus and minus phase of magnetic
modulation and utilizing the orbital velocity variation it is possible
to derive the effective solar line profile as seen by GOLF. This
function provides a means of calculating velocity from the deviations
of signal from the long-time trend. A third method of calibrating the
one-wing GOLF signal utilizes an amplitude comparison to ground-based
experiments and assumes the GOLF and ground-based signals have the
same amplitude in the five-minute band. We do not discuss this method
because we are ultimately interested in comparing signals based on an
absolute independent calibration. Thus we consider three velocities:
vR = (V0)R(R-<R>), vX
= (V0)X(X-<X>) and vS =
(V0)S(S/<S>-1). Each of the V0
parameters can be calculated by calibration against the orbital velocity
and is individually known to a precision of about 2%. During the
commissioning phase of the SOHO project the GOLF instrument provided
data in the two-wing mode. For much of the commissioning phase the
instrument and spacecraft were undergoing tests and adjustments so
the data is of lower quality. We have selected a six-day interval from
March 1 to March 7, 1996 during which relatively quiet two-wing data
are available. The velocities derived from the one-wing in the above
two ways are compared to velocities derived from R for this quiet
period. Correlations between the two forms of one-wing velocity signal
and the two-wing velocity signal are both 0.92. The rms variation
for the three signals after detrending with a gaussian of three hour
width are 1.05, 1.22 and 1.30 m/s for vR; vX
and vS respectively. Spectral distributions for velocities
derived by the two-wing and the two different one-wing methods show
that the power below the five-minute band is enhanced roughly a factor
of 3 in the one-wing methods as compared to the two wing method but
is only enhanced roughly 40% in the five-minute band.
Title: The Solar Acoustic Spectrum as Seen by GOLF. I. The Difficult
Case: Modes With n<10
Authors: Régulo, C.; Roca Cortés, T.; Bertello, L.; Ulrich, R. K.;
GOLF Team
Bibcode: 1998ESASP.418..305R
Altcode: 1998soho....6..305R
Below 1.3 mHz the solar background level increases as well as the
energy of the solar acoustic modes decreases. This situation yields
the detection of low degree p-modes extremely difficult because the
signal to background ratio is very small (S/B ll 1). Yet, these modes
are of paramount importance to be able to infer the structure of the
solar core. On the other hand, the extrapolation of the linewidths
of p-modes of higher frequency seem to tell us that these modes live
for many months thus allowing an improvement of the S/B ratio as the
length of the observations increases; however, not much better of what
we have now will be possible. Therefore techniques to search for small
signals amongst noise have to be used. Here, we present the actual
status of the search and the preliminary results so far obtained.
Title: The Solar Acoustic Spectrum as Seen by GOLF. II. Noise
Statistics Background and Methods of Analysis
Authors: Roca Cortés, T.; Lazrek, M.; Bertello, L.; Thiery, S.;
Baudin, F.; Boumier, P.; Gavryusev, V.; Garcia, R. A.; Regulo, C.;
Ulrich, R. K.; Grec, G.; GOLF Team
Bibcode: 1998ESASP.418..323R
Altcode: 1998soho....6..323R
Data acquired by GOLF experiment onboard SOHO during ~20 months has been
analysed. GOLF is a disk-integrated sunlight experiment therefore biased
to observe very low ell modes (ell < 3). However the excellent ratio
signal to background (S/B) achieved permits also the detection of some
modes with 4 < ell < 6 and those from n >= 8 up to the cut-off
frequency and even beyond with the pseudomodes signal. Due to the nature
of the excitation function of the modes (which we will call noise) the
line shapes look "spiky" rising the possibility (the necessity?) to
use several methods of analysis of such data: a) FFT spectrum and
maximum likelihood fitting technique, b) averaged FFT spectra of
subseries and least squares fitting technique, c) HD spectra and least
squares fit. Moreover, as a consequence of the characteristics of the
spectrum: 1 <= S/B <= 104, linewidths of 0.1 <=
Γ <= 40 muHz and the presence of noise, several fit strategies
have to be defined in order to fit appropriately and accurately the
mode line shapes. In this poster these methods and fit strategies will
be explained and comparative results will be presented.
Title: Comparison of the Calibrated MDI and GOLF Signals. V. The
Low Frequency p-Modes
Authors: Varadi, F.; Ulrich, R. K.; Bertello, L.; Henney, C. J.;
Roca Cortés, T.; Bogart, R. S.; Bush, R. I.; GOLF Team
Bibcode: 1998ESASP.418..359V
Altcode: 1998soho....6..359V
Low-frequency p-modes have relatively small amplitudes and are set
against the background of granulation on the solar surface. In this
work, the calibrated signals of both the MDI and GOLF instruments are
processed in the following steps: 1) prewhitening 2) signal extraction
and demodulation in given frequency bands and 3) separation of noise
and signal by singular spectrum analysis. The resulting signals are
compared in both time and frequency domains and mode parameters are
determined by fitting autoregressive models and Lorentzian spectral
profiles. Particular attention is paid to spectral features at very
low frequency among the investigated data sets, which can lead to the
identification of low radial order p-modes.
Title: Comparison of the Calibrated MDI and GOLF Signals. II. Power
Spectra
Authors: Henney, C. J.; Ulrich, R. K.; Bertello, L.; GOLF Team
Bibcode: 1998ESASP.418..219H
Altcode: 1998soho....6..219H
The GOLF and MDI instruments utilize different spectral lines: the
Na D lines for GOLF and the λ676.8nm line of Ni I for MDI. The two
instruments also detect the solar surface motions utilizing different
techniques: an intensity measurement on one wing of the lines for
GOLF and a series of filtergrams with peak transmission tuned to four
wavelengths spanning the Ni line for MDI. These differences cause
the two instruments to respond to solar phenomena with differing
sensitivity. For example the sodium lines are formed near the
temperature minimum where acoustic modes may have a larger amplitude
due to the solar atmospheric density gradient. The supergranulation is
generally confined to the photospheric layers and may contribute less
incoherent velocity variation to an instrument like GOLF deriving
its signal from the temperature minimum. The GOLF instrument in
its current one-wing mode of operation may be more sensitive to
temperature and emmissivity variations than either MDI or GOLF in a
two-wing mode. The GOLF instrument does not detect all parts of the
solar surface with equal sensitivity. A step towards understanding
the nature of the two helioseismology observations can be taken by
comparing the power spectra for identical periods for the data from
the two instruments. This comparison shows that the amplitudes of
oscillations in the five-minute band are enhanced in the GOLF data
compared to the MDI integrated velocity. The utilization of a GOLF
simulation mask function to produce a GOLF simulated velocity from the
MDI data moves the spectrum towards that of the actual GOLF data but
by only a small fraction of the difference. We note that the comparison
by Ulrich et al. (1998) between GOLF in different operating modes shows
that a shift in going from two-wing operations to one-wing operations is
similar to that seen in going from the MDI simulation of GOLF to GOLF
one-wing. Since the GOLF one-wing data is taken from the blue wing,
it is further from the line core than the two-wing data and formed at a
lower altitude. Thus the extra amplitude in the one-wing data probably
results from an intensity component in this GOLF signal. The indirect
comparison of GOLF two-wing data to the MDI simulation of GOLF suggests
that the amplitudes for these two signals are similar. Consequently,
the enhanced amplitude of the GOLF one-wing signal probably results from
an intensity component of the this signal rather than the difference
in altitude of formation of the two spectral lines. Examination of the
structure of individual power spectrum peaks shows that the detailed
match is better between GOLF and the GOLF-simulated velocity from MDI
than between GOLF and a straight average MDI velocity.
Title: Comparison of the Calibrated MDI and GOLF Signals. III. p-Mode
Frequencies and Splittings
Authors: Bertello, L.; Henney, C. J.; Ulrich, R. K.; Bogart, R. S.;
Bush, R. I.; GOLF Team
Bibcode: 1998ESASP.418..115B
Altcode: 1998soho....6..115B
Power spectra of 619-day calibrated velocity signals provided by the
MDI and GOLF experiments on the SOHO mission are compared. All the time
series being investigated in this poster are from 25 May, 1996 through 2
February, 1998. Here we describe the results of the analysis performed
on p-mode frequency and splitting estimations carried out from these
data sets. Only modes with a significant signal to background ratio
present in all data sets have been considered. These are the modes
with 0 <= l <= 3 in the frequency range between 1.5 mHz and 4.0
mHz. The power spectrum of each single mode is calculated by averaging
FFT spectra of subseries in order to achieve the best compromise
between frequency resolution and signal to noise ratio. The modes are
assumed to have a Lorentzian spectral profile and a maximum likelihood
method for estimating the line-profile parameters is used. The data
reduction for each mode has been performed consistently for all the
investigated time series. We present our results as frequency and
splitting differences with respect to the corresponding parameters
as obtained from the reduction of GOLF velocity signal. This poster
includes a breif description of the adopted strategy and some detail
of the fitting procedure used to determine the mode line-profile
parameters. Finally, we discuss the implications of the presented
result from the point of view of the two instruments.
Title: Comparison of the Calibrated MDI and GOLF Signals. I. Time
Series
Authors: Henney, C. J.; Ulrich, R. K.; Bertello, L.; Bogart, R. S.;
Bush, R. I.; GOLF Team
Bibcode: 1998ESASP.418..213H
Altcode: 1998soho....6..213H
The search for low frequency solar coherent oscillations may be enhanced
through the combination of data from the GOLF and MDI instruments on
SOHO since both provide a low noise data stream and their sources of
solar and instrumental noise are expected to be different from each
other. Ideally we want to synthesize a GOLF-simulated velocity signal
from the spatially resolved MDI images and compare that directly to
the observed GOLF signal. Because the GOLF instrument is not uniformly
sensitive to velocity signals as a function of position on the solar
image, we plan to separate the MDI images into a GOLF-like component
and anti-GOLF component. Cross spectra between the actual GOLF signal
and the MDI GOLF-simulated signal will reduce the effects of instrument
and photon noise. In addition, comparison between the GOLF-simulated and
anti-GOLF signals can provide a way of confirming the solar origin of
potential low frequency oscillations. This poster begins the reduction
process which we hope will ultimately lead to an enhancement of out
ability to detect low frequency solar oscillations. In particular a
velocity calibrated GOLF signal will be compared to the MDI velocity
signal and the MDI GOLF-simulated velocity signal derived from observed
MDI LOI-mask velocity images. The calibrated GOLF velocity signal
used in this investigation is discussed in Ulrich et al. (1998). A
description of the GOLF simulated signal along with preliminary
calibration results are presented in this poster. Crosscorrelation
results between the three signals for time scales of seconds to hours
are presented. In addition, crosscorrelations between the MDI continuum
signal and differences between the velocity signals are shown along
with a discussion of the influence of intensity fluctuations on the
GOLF velocity signal.
Title: Comparison of the Calibrated MDI and GOLF Signals. IV. p-Mode
Energy Budget
Authors: Bertello, L.; Ulrich, R. K.; Henney, C. J.; Roca Cortés,
T.; Bogart, R. S.; Bush, R. I.; GOLF Team
Bibcode: 1998ESASP.418..121B
Altcode: 1998soho....6..121B
The energy calculation of the p-modes requires accurate estimates of
both amplitudes and linewidths. These parameters can be derived from a
suitable model used to fit the spectral distribution of the mode. In
this poster we describe the technique used to achieve this goal. The
model chosen to represent the power spectrum of a solar oscillation
is a Lorentzian profile and, for the more general case of multiplets,
a superposition of Lorentzian profiles. We use a maximum likelihood
method to estimate the amplitudes and linewidths from the model
and we calculate the energy from the product between the amplitude
square and the linewidth. In this poster we also describe the adopted
strategy to calculate the power spectrum for reducing the bias in the
estimated amplitudes and linewidth. Artificial data to simulate solar
oscillations are used to test the adopted strategy. We have applied this
technique to three power spectra obtained from 619-day long time series
provided by both MDI and GOLF experiments aboard SOHO. The amplitude,
linewidth and energy are calculated for acoustic modes with l = 0 -
3, in the frequency range between 1.5 mHz and 4.0 mHz. The results
are presented with particular emphasis on the differences among the
investigated data sets.
Title: First Results on it P Modes from GOLF Experiment
Authors: Lazrek, M.; Baudin, F.; Bertello, L.; Boumier, P.; Charra,
J.; Fierry-Fraillon, D.; Fossat, E.; Gabriel, A. H.; García, R. A.;
Gelly, B.; Gouiffes, C.; Grec, G.; Pallé, P. L.; Pérez Hernández,
F.; Régulo, C.; Renaud, C.; Robillot, J. -M.; Roca Cortés, T.;
Turck-Chièze, S.; Ulrich, R. K.
Bibcode: 1997SoPh..175..227L
Altcode:
The GOLF experiment on the SOHO mission aims to study the internal
structure of the Sun by measuring the spectrum of global oscillations
in the frequency range 10-7 to 10-2 Hz. Here
we present the results of the analysis of the first 8 months of
data. Special emphasis is put into the frequency determination of the p
modes, as well as the splitting in the multiplets due to rotation. For
both, we show that the improvement in S/N level with respect to the
ground-based networks and other experiments is essential in achieving
a very low-degree frequency table with small errors ∼ 2 parts in
10-5). On the other hand, the splitting found seems to favour
a solar core which does not rotate slower than its surface. The line
widths do agree with theoretical expectations and other observations.
Title: Performance and Early Results from the GOLF Instrument Flown
on the SOHO Mission
Authors: Gabriel, A. H.; Charra, J.; Grec, G.; Robillot, J. -M.;
Roca Cortés, T.; Turck-Chièze, S.; Ulrich, R.; Basu, S.; Baudin,
F.; Bertello, L.; Boumier, P.; Charra, M.; Christensen-Dalsgaard, J.;
Decaudin, M.; Dzitko, H.; Foglizzo, T.; Fossat, E.; García, R. A.;
Herreros, J. M.; Lazrek, M.; Pallé, P. L.; Pétrou, N.; Renaud, C.;
Régulo, C.
Bibcode: 1997SoPh..175..207G
Altcode:
GOLF in-flight commissioning and calibration was carried out during the
first four months, most of which represented the cruise phase of SOHO
towards its final L1 orbit. The initial performance of GOLF is shown
to be within the design specification, for the entire instrument as
well as for the separate sub-systems. Malfunctioning of the polarising
mechanisms after 3 to 4 months operation has led to the adoption of an
unplanned operating sequence in which these mechanisms are no longer
used. This mode, which measures only the blue wing of the solar sodium
lines, detracts little from the detection and frequency measurements of
global oscillations, but does make more difficult the absolute velocity
calibration, which is currently of the order of 20%. Data continuity
in the new mode is extremely high and the instrument is producing
exceptionally noise-free p-mode spectra. The data set is particularly
well suited to the study of effects due to the excitation mechanism
of the modes, leading to temporal variations in their amplitudes. The
g modes have not yet been detected in this limited data set. In the
present mode of operation, there are no indications of any degradation
which would limit the use of GOLF for up to 6 years or more.
Title: Persistent Convective Structures on the Sun
Authors: Beck, J. G.; Ulrich, R. K.; Hill, F.; Bogart, R.; Bertello,
Luca
Bibcode: 1997BAAS...29R1121B
Altcode:
No abstract at ADS
Title: Performance and first results from the GOLF instrument on SoHO
Authors: Gabriel, A. H.; Charra, J.; Grec, G.; Robillot, J. -M.; Roca
Cortés, T.; Turck-Chièze, S.; Ulrich, R.; Baudin, F.; Bertello,
L.; Boumier, P.; Decaudin, M.; Dzitko, H.; Foglizzo, T.; Fossat, E.;
García, R. A.; Herreros, J. M.; Lazrek, M.; Pallé, P. L.; Pétrou,
N.; Renaud, C.; Régulo, C.
Bibcode: 1997IAUS..181...53G
Altcode:
No abstract at ADS
Title: GOLF results: today's view on the solar modes
Authors: Grec, C.; Turck-Chièze, S.; Lazrek, M.; Roca Cortés, T.;
Bertello, L.; Baudin, F.; Boumier, P.; Charra, J.; Fierry-Fraillon,
D.; Fossat, E.; Gabriel, A. H.; Garcia, R. A.; Gelly, B.; Gouiffes,
C.; Régulo, C.; Renaud, C.; Robillot, J. M.; Ulrich, R. K.
Bibcode: 1997IAUS..181...91G
Altcode:
No abstract at ADS
Title: Solar Rotation Measurements at Mount Wilson over the Period
1990--1995
Authors: Ulrich, Roger K.; Bertello, Luca
Bibcode: 1996ApJ...465L..65U
Altcode:
One of the most fundamental properties of the Sun is its rate of
rotation. Kinetic energy of large-scale circulation might interact
with rotation and cause the surface rate to vary throughout the solar
cycle. The solar wind carries off angular momentum from the Sun, and
the coupling between the outer and inner parts of the heliosphere
might produce effects that are evident in the photosphere and
chromosphere. The quadrapole moment of Sun's gravitational potential
depends on the rotation rate. The interaction between rotation,
convection, and solar magnetic fields forms the solar dynamo which
governs the solar cycle of activity. Although the rate of solar rotation
has been measured for decades, several key questions remain: What is
the rotation rate, and what is the uncertainty in this value? Does
the rotation rate depend on the solar cycle? Can the gradient of
rotation rate as a function of distance from the solar center be
detected within the solar atmosphere? The synoptic program of solar
observations carried out at the 150 foot tower of the Mount Wilson
Observatory has long been a source of measurements which address these
questions. Improvements in the facilities of this program over the past
decade have led to a reduction in the errors of measurement which now
permit a new examination of these questions. Key improvements were:
12/81---installation of a fiber-optic image reformattor to select
the spectral sampling of the absorption lines; 2/86---multiple daily
observations were begun; 12/87---the Cr II line at lambda 5237.3 was
added to the regular program of observation; 9/90---the grating mount
and alignment system were replaced; 7/91---the polarization analysis
optics were placed in a new alignment box and index matching fluid was
introduced around the KDP variable retarder; 11/95---antireflection
optics were installed for the KDP end windows to reduce interference
fringes. Each of these changes resulted in a noticeable reduction in
the rms error in the measured rotation rate which is now at the level
of 7 m s-1. Within this error we find that there is no solar cycle
variation in the rotation rate and the rate is the same for both lambda
5250 and lambda 5237. We find that the synodic rotation rate is 2.84 +/-
0.01 mu rad s-1. This value agrees well with most recent determinations.
Title: Solar-cycle dependence of the Sun's apparent radius in the
neutral iron spectral line at 525 nm
Authors: Ulrich, R. K.; Bertello, L.
Bibcode: 1995Natur.377..214U
Altcode:
SPACE-BASED observations have established that the Sun's irradiance
varies with solar magnetic activityl-4. A fraction of this
variability arises from the increased area of cool gas associated
with sunspots, which decreases irradiance; but on average the blocking
effect of sunspots is more than offset by the increased emission from
photospheric faculae and other effects of magnetic activity5
(although the precise contributions of these opposing effects remain
poorly constrained6,7). Here we show that the apparent radius
of the Sun, when viewed in the spectral line of neutral iron at 525
nm, also varies in phase with solar magnetic activity. This variation
probably results from changes in the temperature profile of the Sun's
atmosphere with the solar cycle. If similar behaviour is found for other
spectral lines, changes in the apparent radius of the Sun could account
for a significant fraction (∼20%) of the total irradiance variations.
Title: Solar Cycle Dependence of the Sun's Radius at λ = 525.0 NM
Authors: Ulrich, R. K.; Bertello, L.
Bibcode: 1995ESASP.376b.107U
Altcode: 1995soho....2..107U; 1995help.confP.107U
The Mt. Wilson synoptic program of solar magnetic observations carried
out at the 150-foot tower scans the solar disk one to twenty times per
day. As part of this program, the radius is determined as an average
distance between the image center and the point where the intensity
in the Fe I line at λ525.0 nm drops to 25% of its value at disk
center. This record extends back to 1967. The authors have carried out a
re-analysis of this data base correcting for such effects as scattered
light and atmospheric refraction. Since 1982 the authors find a peak
to peak change of 0.4″which is correlated with the solar cycle. This
change may play a role in the variations in the total solar irradiance.
Title: Measurements of the Energy Flux of Non-Stationary Acoustic
Waves in the Solar Atmosphere
Authors: Ulrich, R. K.; Bertello, L.
Bibcode: 1995ASPC...76..350U
Altcode: 1995gong.conf..350U
No abstract at ADS
Title: The Heating of the Solar Chromosphere and Corona by
Non-Stationary Acoustic Waves
Authors: Bertello, L.; Ulrich, R. K.
Bibcode: 1995ASPC...76..346B
Altcode: 1995gong.conf..346B
No abstract at ADS
Title: The height dependence of intensity and velocity structures
in the solar photosphere
Authors: Salucci, G.; Bertello, L.; Cavallini, F.; Ceppatelli, G.;
Righini, A.
Bibcode: 1994A&A...285..322S
Altcode:
Results about a statistical analysis of the solar granulation, obtained
by analyzing a series of narrow band (20 mA FWHM) images in the 6162.18
A CaI photospheric line, are presented. The observations have been
performed at the Vacuum Solar Tower of the National Solar Observatory
at Sac. Peak (NM-USA) in 1988, using a Fabry-Perot interferometer and a
Universal Birefringent Filter mounted in tandem. We computed coherence,
phase and power spectra of intensity and velocity fields in a 27"x27"
quiet region at the disk center. Energy spectra, plotted in the usual
log-log coordinates, clearly show a linear shape for wavenumbers between
3 and 10 Mm^-1^. The exponent is -17/3: it does not significatively vary
within the considered photospheric layers and largely differs from both
the theoretical value and the results of previous 1-D observations. This
result indicates that in the photosphere we are in presence of a
redistribution of the convective energy through a cascade from larger
granules to smaller ones, although the size distribution does not follow
the Kolmogorov law. The physical processes involved in the granulation
have been investigated by studying the height dependence of coherence
and phase spectra of Velocity-Velocity (V-V) and Velocity-Intensity
(V-I) fields. We find that the photosphere is divided in two regions:
the velocity structures existing in the lower layers (first region)
are convective and extend up to about 170 km. The decay of these
granular motions generates well correlated velocity structures in the
second region (height range 170-400 km), at spatial frequencies 5-10
Mm^-1^. In this region, moreover, the coherence moderately increases
with height, while the phase is stable around +/-180°. This means
that velocity and intensity fields are predominantly anticorrelated,
as expected for gravity waves.
Title: Some evidence for large-scale motions on the Sun
Authors: Bertello, L.; Restaino, S. R.
Bibcode: 1993A&A...273..260B
Altcode:
The importance of two indicators, the energy density and the
Blue wing/Red wing ratio of the rms wavelength shift, related
to the mechanical energy flux of the 5-minutes oscillations, is
investigated. The goal is to search for the existence of large-scale
motions in the solar convective region. Results obtained by analysing
high- spectral-resolution line profiles (5434.5 Fe I), obtained over
a large spatial area, spanning a solar radius, are also discussed. We
obtained horizontal spatial sequences for both indicators at three
different heights in the solar photosphere (50 Km, 150 Km and 200 Km),
which correspond to regions where the variations of the mechanical
energy flux are larger. The spatial power spectra of these indicators
clearly show the existence of a peak at ∼200 Mm. The physical
identification of this peak, and its relationship to the interaction
between steady waves and large-scale velocity pattern in the solar
convective region are discussed. Finally, the effect of magnetic
features in our data set is briefly clarified.
Title: New Observations of 5 Minute Oscillations in the Opposite
Flanks of Solar Fraunhofer Lines. I. The Effect of Varying the
Spectral and Temporal Resolution
Authors: Bertello, L.; Caccin, B.; Francia, P.; Pietropaolo, E.
Bibcode: 1992ApJ...401..768B
Altcode:
Results of an investigation of the rms wavelength fluctuations in
the 5-min range, at fixed intensity levels, in the opposite flanks
of 15 Fe I and two Fe II lines, selected from the range 6200-6400 A
are presented. Critical values for these quantities are evaluated. The
number of used lines makes it possible to analyze the height dependence
of the oscillations within the photosphere, and a clear correlation
between the formation height of the emergent intensity and the ratio
of the oscillation power in the two flanks of the lines is found. The
existence of a unique relationship, independent of the characteristics
of the single lines, confirms the diagnostic value of this ratio
to investigate the variations of the wave properties throughout the
solar atmosphere. The effect is argued to be due to radiative damping,
which produces a height-dependent phase shift between velocity and
thermodynamic perturbations within the line-forming region.
Title: High resolution granulation spectrophotometry with a UBF and
a FP interferometer in tandem.
Authors: Salucci, G.; Bertello, L.; Righini, A.; Bonaccini, D.;
Cavallini, F.; Ceppatelli, G.
Bibcode: 1992ESASP.344..157S
Altcode: 1992spai.rept..157S
Recent studies have shown that in the solar granulation, granules sizes
lower than 3″may be considered as turbulent eddies. However this
result is in contradiction with morphological studies carried out by
other authors. In this paper the authors analyse in the spatial domain
the autocorrelation and crosscorrelation functions of the velocity
and of the intensity fields at several depths in the solar atmosphere,
using narrow band filtergrams obtained at Sacramento Peak Observatory
Vacuum Tower Telescope with a UBF and a FP interferometer mounted in
tandem. The results show that the granular motion is turbulent for
heights larger than 170 km while at lower heights is convective.
Title: A Search for Existence of Large-Scale Motions on the Sun
Authors: Bertello, Luca; Restaino, Sergio R.
Bibcode: 1992ASPC...27..265B
Altcode: 1992socy.work..265B
No abstract at ADS
Title: 5 Minute Oscillations and Large Scale Spatial Structures
Authors: Restaino, S. R.; Bertello, L.
Bibcode: 1991BAAS...23..938R
Altcode:
No abstract at ADS
Title: Depth dependence of the intensity-velocity phase difference
in the solar '5-min' oscillations
Authors: Alamanni, N.; Bertello, L.; Righini, A.; Cavallini, F.;
Ceppatelli, G.
Bibcode: 1990A&A...231..518A
Altcode:
Previous measurements carried out on four Fe I photospheric lines have
suggested that the different oscillating power observed on the blue and
red line flanks is produced by the intensity-velocity phase lag in the
'5-min' waves. Former measurements and new additional observations on
the 6149.2 A Fe II and 6162.2 A Ca I lines have been used to evaluate
more accurately the dependence of this intensity-velocity phase
difference on the photospheric height. A nonadiabatic and nonisothermal
bidimensional model of the thermodynamic fluctuations induced in the
photosphere by the high degree p-modes suggests that radiative damping
might explain the observed line profile oscillations.
Title: Non-adiabatic modelling of '5-min' oscillations - Effects on
photospheric line profiles
Authors: Bertello, L.; Caccin, B.
Bibcode: 1990A&A...231..509B
Altcode:
A realistic form of the temperature, pressure, and velocity
perturbations representing the '5-min' oscillations with a
monochromatic bidimensional wave in the solar photosphere is derived
and used to compute the oscillations of typical Fe I and Fe II line
profiles. Results demonstrate the role of radiative damping in producing
different amplitudes of the oscillation in the opposite flanks of
the lines, by causing a depth-dependent phase difference between the
thermodynamical and the velocity perturbations. A comparison of results
obtained with wave models with observations showed that an agreement
can be obtained along the whole profile of the Fe I and Fe II lines,
provided that 0th order temperature gradients are taken into acccount.
Title: On the diagnostic of 5m oscillations through
photospheric line profiles.
Authors: Bertello, L.; Caccin, B.
Bibcode: 1988ESASP.286...17B
Altcode: 1988ssls.rept...17B
Recent measurements show that the 5m oscillations have
different amplitudes in the opposite flanks of several photospheric
lines. This effect can be suitably described by giving the (blue
wing)/(red wing) ratio of the r.m.s. wavelength shift at any given
level of residual intensity. The authors suggest that the main
cause is radiative damping, which produces a depth dependent phase
difference between the velocity and the thermodynamical (temperature
and pressure) perturbations within the line forming region. Synthetic
profiles of the Fe I λ6301.5 Å line, obtained by numerical solution
of the time independent radiative transfer equation in the oscillating
atmosphere (quasi static radiation field approximation), show that
agreement between observed and computed profiles can be achieved. The
consequences of this effect (which is also dependent on the magnetic
flux concentration) on the diagnostic properties of line profiles are
briefly discussed.