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BBSO Seminars
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Seminars are to be held at 3:00pm, Back Lodge, unless noted otherwise. Speakers,
please provide the title, and, if possible, abstract of your talk, when you are ready.
For feedback, please direct to Vasyl Yurchyshyn (vayur bbso njit edu)
- Dec 14, 2016: Dr. Yukio Katsukawa, NAOJ, Japan Space-based solar projects at NAOJ: from HINODE to CLASP, SUNRISE, and SOLAR-C
Diagnostics of magnetic fields in the solar atmosphere is common motivation in future solar observations. We achieved precise spectro-polarimetric measurements at the photospheric Fe I 630 nm line with the Solar Optical Telescope (SOT) on HINODE. In order to extend our spectro-polarimetric capability to diagnose chromospheric magnetic fields, we are now running two projects: One is a sounding rocket experiment CLASP (Chromospheric Lyman-Alpha SpectroPolarimeter) aiming to explore a UV polarimetry in spectrum lines such as Lyman-alpha and Mg II h&k. One is a balloon-borne spectro-polarimeter SCIP (SUNRISE Chromospheric Infrared spectroPolarimeter) aiming to pursue precise spectro-polarimetry of multiple photospheric and chromospheric lines. Scientific and engineering demonstration through these project is an important step toward the next space mission SOLAR-C.
- Apr 26, 2016: Dr. Siqing Liu, NSSC, China Operational Space Weather Services and Researches at Space Environment Prediction Center of NSSC
This presentation briefly reviews the Space Environment Prediction Center (SEPC) of National Space Science Center (NSSC), Chinese Academy of Sciences. Operational space weather services of SEPC will be addressed, particularly the products for public and custom-tailored services to special users such as China’s Manned Space Flight Missions. Aimed to improve the capability of space weather services, the space weather researches and system development will be discussed.
- April 16, 2015: Huaning Wang, NAO, Chinese Acad. Sci. Beijing, China: Coronal magnetic field and CME reconstruction.
The solar eruptive activities can lead to space weather events which can produce disastrous impacts on high-tech systems including the communication, aerospace, navigation and power grid systems, etc. The solar magnetic field plays the most crucial role in solar activities. The study on the solar activity by using reconstruction methods has great importance for understanding the physical nature of solar activities, and for improving the ability for space environment monitoring and early warning.
The key to explore the physical nature of solar eruptions is to understand the solar magnetic field. The structure and evolution of solar magnetic fields are the primary reasons for energy accumulations and releases related to solar eruptions. Observing solar magnetic field and understanding its origin and structure evolution constitute the central tasks of the solar physics. For a long time, solar physicists in the world have continually proposed different approaches for the solar magnetic field measurement and developed many type of measuring instruments. The ultimate goal of solar magnetic field measurement is to acquire 3D structure of coronal magnetic fields . Some observational techniques for diagnosing coronal magnetic fields through infrared and radio approaches have been developed, but these techniques need to consider the radiation mechanism and the peculiar physical condition in the corona, and can hardly achieve the same accuracy as that of the photospheric magnetic field measurement. The reliable solar magnetic field data available for quantitative analyses are still confined to the solar photosphere. Thus with appropriate physical model together with the measured photospheric magnetic field as the boundary condition, reconstructing the solar atmosphere magnetic field is still the primary tool to study the three-dimensional structures of the solar atmosphere magnetic field and its evolution. The currently available solar magnetic field reconstruction methods can be classified into following categories: the Grad-Rubin method which solves the transformed potential and flux functions; the finite difference method that directly discretizes the force-free field equation; the numerical simulation method that let the MHD equations evolve to the force-free state; the pseudo-evolution method that demands the norm of the force-free equation residuals asymptotically to be zero; and boundary integral method that solves the equivalent integral equations. However, the observed photospheric magnetic field is non force-free, and a fore-free model in corona can hardly be based on its non force-free boundary. For this reason, some authors modify the observed vector magnetic field on the photosphere, which might results in a false reconstruction. We suggested a data-driven numerical simulation method in which the forced boundary on the photosphere are directly used.
It has been revealed that coronal mass ejections (CMEs) are magnetized plasma ejected from the solar corona. Parameters of CMEs such as central position angle, angular width, speed, acceleration, and mass can be extracted from coronagraphic images. All of these two-dimensional (2D) parameters are not accurate enough to completely depict the three-dimensional (3D) nature of CMEs due to projection effects . Several kinds of reconstruction techniques were established to solve this problem. Geometric techniques using multi-viewpoint observations have been established that benefit from the instrument STEREO/ SECCHI. Regretfully, multi-viewpoint observations are not always feasible and we need some techniques that can be employed in single-viewpoint conditions. The polarimetric technique, one of typical single-viewpoint approach, , has been used to analyze white light images for a long time. In the STEREO era, this technique is applied to derive the 3D directions and speeds of CMEs for space weather forecasts. However, two symmetric reconstructions owing to the ambiguity of Thomson scattering are inevitable. It is obvious that the polarimetric reconstruction suffers from ambiguities arising from Thomson scattering. In order to improve the polarimetric technique, we suggest a classification for these ambiguities and a method to improve CME mass evaluation.
- Nov 20, 2014: Jean-Pierre Rozelot, Universite de Nice, France: Solar quadrupole moment and Purely Relativistic Gravitation Contributions
Of all the solar fundamental parameters (mass, diameter, gravity at surface, angular momentum ...), the gravitational moments have been ignored in the past, mainly due to the great difficulty to get a reliable estimate. Even though the order of magnitude of the solar quadrupole moment J2 is now known to be 10-7, its precise value is still discussed. Furthermore, stellar equations combined with those of the differential rotation in depth are solar model dependent, i.e. implying a minima solar density and rotation laws. Hence the need for dynamical estimates of the solar quadrupole moment based on other methods, such as the motion of spacecrafts, celestial bodies or light in the gravitational field of the Sun. The expansion in multipoles J(l, l = 2, ..), of the gravitational potential of a rotating body affects the orbital motion of planets at a relativistic level. Recent progresses (in 2014) have been made in testing General Relativity through the contribution of the solar quadrupole moment. Using the Eddington-Robertson parameters, we recall the constraints both on a theoretical and experimental point of view. Together with gamma, which encodes the amount of curvature of space-time per unit rest-mass, the post-Newtonian parameter beta contributes to the relativistic precession of planets. The latter parameter encodes the amount of non-linearity in the superposition law of gravitation. We will show why it is still difficult to decorrelate J(l=2), gamma and beta. However, even though all the planetary dynamics-based values are biased by the Lense Thiring effect, which has never been modelled and solved-for so far, but can be estimated to 7%, it is thus possible to get a good estimate of the solar quadrupole moment: 1.82 x 10-7 <= J2 <= 2.16 x 10-7.
- Oct 21, 2014: Vyacheslav Sadykov (Big Bear Solar Observatory) Analysis of the IRIS Observations of the June 12th, 2014 Flare Event
We present results of observations of a M1.0 class flare event, which occurred on 12 June 2014 (SOL2014-06-12T21:12), with the NASA's Interface Region Imaging Spectrograph (IRIS) mission. IRIS was observing in the coarse raster mode this event and obtained the high-resolution UV spectra and Slit-Jaw (SJ) images for the almost all flaring region. Our analysis of the IRIS data in different lines reveals strong redshifted fluxes of the chromospheric material before the flare. It is also found that most of the chromospheric and transition region lines are redshifted across the flaring region during the flare. Emission of hot (20MK) coronal Fe XXI line is detected 400 seconds after the emission peaks of the lower temperature lines in one of the IRIS windows. However, contrary to previous observations of this line for other flare events no strong blueshift is detected.
- Oct 20, 2014: Serge Koutchmy (Institut d'Astrophysique de Paris- CNRS & UPMC) The Solar Diameter, the Solar Edge, the Spectral Irradiance and the Moon !?
During the last decades, considerable efforts have been devoted to the analysis of possible effects of the irregular activity cycles of the Sun, through solar forcing effects. Why such interest and how to reach this goal? Long term variations of the Solar Diameter could be a significant factor and more than 1.5 century long efforts will be summarized. The solar diameter is still measured at Ground-based and in Space without a definite answer. Using the Moon as a cosmic etalon, many attempts were made at past Solar Total eclipses. We show how indeed the solar edge is not even well calibrated, showing the result of an experiment aimed at looking at the spectrum of the edge of the Sun, for different distances near the extreme-limb. The importance of faint low FIP lines is discussed. Finally the calibration of the relief the Moon is an ultimate limitation that is not yet reached and similarities exist with the calibration of instrumental effects in large telescopes, including the amount of smearing.
- Sept 22, 2014: Oskar von der Luhe (KISIP) Current Status of GREGOR
- Sept 2, 2014: Leif Svalgaard (Stanford University)
- July 24, 2014: Illa R. Losad
- May 9, 2014: Choudhary, Debi Prasad (CSU, Northridge) Three Dimensional Chromospheric Structure of Sunspot
We have observed sunspots using the Spectropolarimeter for infrared and optical wavelength ranges at the Dunn Solar Telescope during 29 July to 4 August 2013. The data consists of full Stokes profiles in the Ca II 854.2 nm and Fe I 1.56 micron lines. The inversion of these Stokes spectra provides the magnetic, thermal and velocity structure at photospheric and chromospheric heights of sunspots. In this contribution, we present the first results on the 3D thermal structure in the super-penumbral canopy of a well rounded sunspot, derived by a novel approach for the inversion of Ca II IR spectra. Tracing individual fibrils in the super-penumbral canopy, we find that about half of them form only short loops of a a few Mm length that return to the photosphere in the close surroundings of the sunspot instead of connecting to more remote magnetic network at the outer end of the moat flow.
- May 5, 2014: Friedrich Woeger (NSO) Adaptive Optics supported Speckle Imaging
In the recent past, two new 1.5 meter class solar telescopes were commissioned to advance our knowledge of the very details of plasma motion in the solar atmosphere: the New Solar Telescope at the Big Bear Solar Observatory, and the German GREGOR telescope located on Tenerife. In order to achieve diffraction limited performance, often post-facto image reconstruction techniques that can be combined with Adaptive Optics systems are required. In this presentation, the principles of one particular reconstruction technique are presented: adaptive optics supported speckle image reconstruction. The history and details of the method are explained, as well as its current implementation in the program package called KISIP. The future of this software will be discussed in the light of instrumentation for the Daniel K. Inouye Solar Telescope (DKIST, formerly the Advanced Technology Solar Telescope) currently under construction.
- April 17, 2014: Dr. Leif Svalgaard (Stanford) The Effects of Solar Activity on Our Earth and Our Technological Infrastructure.
The talk is focused on how the Sun's magnetic activity influences our environment, for better and for worse, how we predict and possibly mitigate those influences.
- April 16, 2014: Prof. Jan Stenflo (Institute of Astronomy, ETH, Zurich)Nature of quiet-sun magnetic fields
Since the magnetic structuring continues to scales of order 10-100 m, far smaller than can possibly be resolved, and since the polarization signals are weak on the quiet Sun, one needs to apply robust diagnostic techniques that do not get biased by measurement noise, are independent of telescope resolution, and have minimal model dependence, in order to reliably determine the intrinsic properties of quiet-sun magnetic fields. Such techniques make use of ensemble averages as the observable signatures of the spatially unresolved domain. I will outline how such concepts are applied to derive the field strengths, sizes, and angular distributions from the observed Hanle depolarization and from the symmetry properties of the transverse Zeeman effect.
- Jan 16, 2014: Prof. Jay Pasachoff,Williams College.Coronal temperature and motions from recent eclipse observations
Abstract:We have a series of images and spectra from the total solar eclipses of 2006 (Greece), 2008 (Siberia), 2009 (China), 2010 (Easter Island), 2012 (Australia), and 2013 (Gabon). They cover the solar-activity cycle from sunspot minimum through the current maximum, and our series of flash spectra show the overall change in coronal temperature through the variation of the [5303:6374 [Fe XIV]:[Fe X] line ratio. Further, our high-resolution composite imaging of coronal streamers and CMEs allows measurement of their motions over time intervals between our eclipse sites and others'. We also report on Fabry-Perot observations of motions in a coronal streamer at an eclipse. In addition, we report on our joint work with Dale Gary on Jansky Very Large Array observations of the 2012 annular eclipse. Our research on the annular and total eclipses of 2012 was supported by a grant from the Solar Terrestrial Research Program of the Atmospheric and Geospace Sciences Division of NSF, and on the 2006 eclipse from its predecessor Solar Research Program at NSF. Our research at the 2009 eclipse in China and the 2013 eclipse in Gabon was supported by a grant from the Committee for Research and Exploration of the National Geographic Society.
- July 15, 2013: Deng Yuanyong, National Astronomical Observatoires, Chinese Academy of Sciences.Observational solar physics in China: present and future
- Jan 8, 2013: Rajmal Jain, Physical Research Laboratory,(Dept. of Space, Govt. of India) Ahmedabad, India. Energetic relationship among geo-effective solar flares, associated CMEs and SEPs
Abstract: Firstly, I will briefly introduce our institute. Next, I will briefly discuss the Solar X-ray Spectrometer (SOXS), the first space-borne solar astronomy experiment of India. Then I will move to my main seminar topic where I present energetic relationship among flares, CMEs and SEPs. Major solar eruptions viz. flares, CMEs and SEPs, highly influence geospace and space weather. Currently, the mechanism of their influence on space weather is not well understood, which requires a detailed study of the energetic relationship among these eruptive phenomena. In this view, we investigate 30 flares (observed by RHESSI), followed by weak to strong geomagnetic storms. Flare spectral analysis suggests a new power-law relationship (r ~ 0:79) between the HXR spectral index (before flare-peak) and linear speed of the associated CME observed by LASCO/ SOHO. For 12 flares which were followed by SEP enhancement near Earth, HXR and SEP spectral analysis reveals a new scaling law (r ~ 0:9) between the hardest X-ray flare spectrum and hardest SEP spectrum. Further, a strong correlation is obtained between the CME linear speed and the hardest spectrum of the corresponding SEP event (r ~ 0:96). We propose that the potentially geoeffective flare and associated CME and SEP are well-connected through a possible feedback mechanism, and should be regarded within the framework of a solar eruption. Owing to their space weather effects, these new results will help to improve our current understanding of Sun-Earth relationship, which is a major goal of research programs in Heliophysics.
- Jun 5, 2013: Udaipur Solar Observatory:
An Introduction to Multi Application Solar Telescope and Research
Highlights of Udaipur Solar Observatory
Abstract:
The Udaipur Solar Observatory is currently installing a state-of-the-art 50 cm aperture solar telescope with thermal control of all mirrors and backed by an adaptive optics system. I will briefly summarize the steps leading to the installation. I will then follow this with research highlights of the Udaipur Solar Observatory scientists. I will conclude with some ideas on collaboration with BBSO.
- Sept 4, 2012: Ram Ajor Maurya, Seoul National University:
Chromospheric Oscillations in Sunspot Observed by NST/FISS
- Aug 29, 2012: Ram Ajor Maurya, Seoul National University:
Seismology of Solar Active Regions
- May 15, 2012: W. Uddin, N. Joshi, ARIES, India:
Reasearch at Aryabhatta Research Institute of Observational Sciences in India
- Apr 5, 2012: S. Goasin, NSO/SOLIS:
Dissection of currents in a twisted sunspot
Abstract:
The high resolution vector magnetograms from Hinode show strong localized currents in the umbra and penumbra due to its intricate fine structure. These currents show a mixed pattern of currents specially an alternating positive and negative behavior in penumbra. This pattern of strong localized currents however masks the more general global twist in the solar magnetic structures. A decomposition of the vertical current density into the twist and shear component seems to help in isolating the broader twist component from localized current patterns. We use this decomposition method to study the currents in a unipolar twisted sunspot and the properties of twist and shear currents in a flaring region.
- Jan 23, 2012: J.P.Rozelot, Universite de Nice, France :
History of solar oblatness and relationship to gravitational theories
Abstract:
Exact measurements of the shape of the Sun have a history extending back into the 19th century and dedicated observations such as those of SDT (Princeton and Mount Wilson, USA), SDS (Yale, US) or Pic du Midi (F) were playing a role in this continuing history. Previous observations are serendipitous, such as those of SOHO/MDI or RHESSI. Other space observatories are being actually designed or recently in space for determining solar global parameters, sucha s SDO, and we expect that these will make definitive oblateness measurements over the next few years.
The purpose of this lecture is to show off some of the historical overview for the solar oblateness, and to remind assistance of the basic physics of the oblateness measurement. For instance, RHESSI has just completed its observations through the remarkable recent solar minimum and there is no particular reason why its data should not continue well into the operational lifetimes of SDO and latter on from Dynamiccs. We will conclude by emphasizing the rich history of solar oblateness measurements which have some profound implications touching on the determination of the planetary orbits, on the core rotation, on relativity theory or even up to shear effects in the leptocline region. The shape of the Sun is one of the ways we have now for peering into its interior and learning empirically about flows and motions there that would otherwise only be guessed from theoretical considerations.
- Jan 17, 2012: Irina Kitiashvili, Stanford Univ.:
MHD Modeling of Plasma Vortices
- Nov 9, 2011: Vladimir Obridko, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation (IZMIRAN), Russia:
The unusual sunspot minimum: challenge to the solar dynamo theory
Abstract:
During the recent decades, much progress was achieved in the development of the solar dynamo theory. The beginning solar cycle 24 is the first one attempted to be predicted not only from extrapolation or precursor methods,but also based on physically consistent dynamo models. However, the predictions for the next sunspot maximum, based on virtually the same dynamo models, range from the lowest one in the last 150 years to the highest one during the whole sunspot observational period. Furthermore, the unusually low and prolonged minimum between cycles 23 and 24 was not expected, not explained, and with unclear consequences for the future solar activity. In the present talk we summarize the solar, heliospheric and geospace observations during this unusual minimum, and their implications for the solar dynamo theory.
- Sept 21, 2011: Irina Kitiashvili, Stanford Univ:
MHD Modeling of Pore Formation
- June 9, 2011: Jiong Qiu, Montana SU:
Heating of Flare Loops During Two-ribbon Flares
Abstract:
Many eruptive flares exhibit two extended ribbons in the lower-atmosphere
outlining the feet of the post-flare coronal arcade. High-cadence and
high-resolution UV observations by TRACE reveal that the flare ribbon
consists of small patches sequentially brightened along the ribbon,
suggesting that reconnection takes place sequentially forming individual
post-flare loops along the arcade, as often seen in coronal observations
in the EUV wavelengths. These reconnection events and formation of new
loops continue well into the decay phase. Our recent study (Qiu et al.
2010) further shows that the spatially resolved UV brightness at the
foot-points of individual loops grows rapidly on timescales of a few
minutes, followed by a long decay on timescales of more than 10 minutes. The
rapid rise of UV radiation is correlated with the hard X-ray light curve during
the impulsive phase, hence is most likely a direct response of
instantaneous heating in the reconnection formed flux tubes. In this
study, we utilize the spatially resolved UV brightness time profiles to
reconstruct instantaneous heating functions of individual flux tubes, and
compute evolution of each flux tube using the EBTEL model (Klimchuk et al.
2008). To build the heating function, we take into account the scaling
between the total UV peak count rate, the hard X-ray energy flux derived
from RHESSI spectral analysis during the impulsive phase, and as well the
reconnection rate that persists from the pre-impulsive phase to the decay
phase. The sum of the computed coronal radiation in all the flux tubes
compares favorably with the gross coronal radiation observed by GOES. This
study presents the first effort to constrain heating functions of flare
loops directly using all available observables, and provides a method to
examine physics of heating discrete flux tubes formed by reconnection
events throughout the flare.
- Nov 16, 2010: Valentyna Abramenko, BBSO:
Statistical Distribution of Size and Lifetime of Bright Points
Observed with the NST
Abstract:
We present results of two-hour non-interrupted observations of solar
granulation obtained under excellent seeing conditions with the largest aperture
ground-based solar telescope (the NST) of Big Bear Solar Observatory.
Observations were performed with adaptive optics correction using a broad-band
TiO filter in the 705.7 nm spectral line with a time cadence of 10 s and a pixel
size of 0.0375''. Photospheric bright points (BPs) were detected and tracked.
We find that the BPs detected in NST images are co-spatial with those visible in
Hinode/SOT G-band images. In cases where Hinode/SOT detects one large BP, NST
detects several separated BPs. Extended filigree features are clearly
fragmented into separate BPs in NST images. The distribution function of BP sizes extends
to the diffraction limit of NST (77 km) without saturation and corresponds to a
log-normal distribution. The lifetime distribution function follows a log-
normal approximation for all BPs with lifetime exceeding 100 s. A majority of BPs are
transient events reflecting the strong dynamics of the quiet sun: 98.6\% of
BPs live less than 120 s. The longest registered life time was 44 minutes. The
size and maximum intensity of BPs were found to be proportional to their life
times.
- Sept 29, 2010: Eun-Kyung Lim, Seoul National University, BBSO:
Magnetic Helicity of Active Regions and Filaments
Abstract:
Magnetic helicity quantifies the self and the mutual linking of magnetic field
lines. Since twisted or wound magnetic fields are often observed in associated
with explosive events such as flares, coronal mass ejections, and prominence
eruptions, solar activities may be better understood in terms of magnetic
helicity. I will present what I have done related to magnetic helicity of an
coronal active region, filaments and the formation of a helical structure called
magnetic channel in an active region. Firstly, we measured the temporal
variation of the coronal magnetic helicity of AR 10696 based on the linear
force-free field assumption and confirmed the reliability of the linear
force-free field method with an error less than 17%. Secondly, we studied the
relationship between the active region helicity and the chirality of
intermediate filaments. From the statistical analysis, we obtained results
supporting that the chirality of intermediate filaments may originated from
magnetic helicity of their associated active regions. We also studied the
formation process of magnetic channel in AR 10930 by analyzing both photospheric
vector magnetograms and the nonlinear force-free field reconstructed coronal
magnetic fields. As a result, we obtained some observational evidence that
suggests that the magnetic channel structure forms due to the emergence of the
twisted flux tube.
- Aug 12, 2010: Aglae Kellerer, Institute for Astronomy, Hilo, Hawaii:
Observations on Seeing
Abstract: The first question most astronomers ask about an observatory site is:
"How is the seeing"? This, however, will generally yield an incomplete
answer. During this talk, I will therefore discuss some additional relevant
questions:
1. How are the coherence time, the isoplanatic angle and the outer scale?
Unduly simplified, the seeing determines the minimum required number of
actuators of an adaptive optics (AO) systems, the coherence time sets the
necessary correction frequency and the outer scale specifies the required
actuator-stroke. The isoplanatic angle then specifies the sky-coverage.
I will indicate the different monitoring instruments that measure these
parameters, and will note their advantages and shortcomings.
2. What is the height-distribution of the turbulent intensity?
At most sites the ground-layer turbulence is dominant. Its effects can be
mitigated by installing the telescopes on tall structures, or it may be
remedied by an AO system, as this is now envisaged with the IMAKA project -- a
ground-layer adaptive optics system (GLAO) for the Canada-France-Hawaii
telescope on Mauna Kea.
Higher turbulent layers are somewhat more frustrating because they will not be
conciliated by venting the dome or elevating the telescope. Instead one
requires techniques such as multi-conjugated adaptive optics (MCAO) or multi-
object adaptive optics (MOAO). I will present some experience with a
prototype MOAO system called Canary.
3. How about the temporal variations of the seeing?
Seeing fluctuations on a given site are often larger than differences in seeing
between sites. The widely used Shack-Hartmann wavefront sensor, can not be
adjusted for seeing variations. It can merely be designed to be optimally
sensitive to the average seeing expected to prevail during the instrument's
lifetime. In curvature wavefront sensors, however, the dynamic range varies
with the distance of the detector from the focal plane. Accordingly, curvature
sensors can be tuned to be optimally sensitive to the wavefront aberrations
that prevail during a particular observation. I will propose methods to
automatically adjust the dynamic range of a curvature sensor and will analyze
the resultant performance increase of the AO system.
- July 20, 2010: Aaron Coulter (BBSO/NJIT): Preliminary Thermal
Modeling for the NST Primary Mirror
Abstract: The New Solar Telescope (NST) was to be equipped with a forced air
heat ex-changer designed to flow air, cooled slightly below ambient, across the
upper and lower surfaces of the primary mirror (PM) in a closed loop, fan
driven system. Production and installation issues forced the NST team to
abandon plans to implement this system and all imaging, to this point, has been
accomplished with no thermal control system at all. Despite general
expectations and the existing conventional wisdom on large aperture solar
telescope design, the NST is producing good images, even performing at the
diffraction limit, with suitable real-time and post-fact image correction. Why
is this the case? We will present Computational Fluid Dynamics (CFD) modeling
that illustrates how this may be occurring, discuss various measurements of air
flows and telescope performance related to this phenomenon, and look at CFD
analysis of possible thermal control systems that could be implemented with the
current NST PM cell configuration.
- July 15, 2010: Luke Johnson (UC Santa Cruz): Wind-predictive control:
Applications to single and multiple conjugate adaptive optics
systems
Abstract: The frozen-flow hypothesis suggests that, on short timescales,
atmospheric temporal dynamics are dominated by translational shifts of a
frozen Kolmogorov spatial pattern. On-sky studies have detected frozen
flow in a large fraction (>90%) of datasets from Mauna Kea over varying
atmospheric conditions. We propose a way to exploit frozen flow dynamics
by adding a time update step to the standard adaptive optics control
loop in order to estimate and predict this translational motion. I will
present results from computer simulations of single-conjugate,
visible-light adaptive optics systems and from the UCO/Lick
Multi-Conjugate and Multi-Object Adaptive Optics testbed that
quantitatively demonstrate the potential performance improvements due to
wind-predictive control. I will also discuss the impact of predictive
control on adaptive optics error budgets and identify next-generation
systems that would reap significant benefits from incorporating
predictive models into their design.
- July 6, 2010: Kenichi Otsuji (Kyoto University): "Cooperative observation
between Hida observatory and Hinode/SOT"
Abstract: Cooperative observation with Hida observatory and Hinode satellite
was performed in Aug. 2007. Doppler velocity of Ca II K spectra at uprising
arch filament in small EFR were measured by Hida observatory Domeless Solar
Telescope. There is time delay between the appearance of horizontal magnetic
signal and detection of rising motion, which is indicating that the emerged
flux on the solar surface stayed until the instability grew.
- Apr 22, 2010: Ali Kilcik (BBSO): "Statistical srudy of the relationship
between the sunspot number, maximum of CME speeds and Ap Index"
- Mar 31, 2010: Nina Karachik (NSO) "Formation of Coronal Holes on the
Ashes of Active Regions"
- Mar 16, 2010: Haisheng Ji (Purple Mountain Observatory)
- Jan 18, 2009: Vadim Uritsky (University of Calgary)
- Nov 15, 2009: Kwangsu Ahn (BBSO, KASI): PhD Thesis Presentation
- Nov 12, 2009: Zong-Jun Ning (Purple Mountain Observatory):
"Prominence oscillations seen by Hinode/SOT on 2008 January 15"
- Tue., Oct 28, 2009: Yeon-Han Kim, Korea Astronomy and Space Science
Institute: The small-scale X-ray/EUV jets and the evidence of
propagating waves observed by Hinode
- Tue., August 11, 2009: Jiong Qiu (Montana SU): Analysis of Magnetic
Reconnection Sequence: from 2D to 3D
- Wed., March 18, 2009: Kwangsu Ahn (BBSO, KASI): Fine Structures of Solar Filaments/Prominences : Their Dynamics and Magnetic Structures
- Wed., April 8, 2009: Prof. Kiyoshi Ichimoto (Kyoto Univ): Introduction to Hida Observatory; Evershed flows in sunspots as seen in Hinode data
- November 5, 2008: Alex Pevtsov (NSO): Helicity on the Sun: what is it good for
anyway?
- October 30, 2008: Oskar Von Der Lühe (KIS): High resolution observations at KIS
- August 5, 2008: Friedrich Woeger (NSO): Specle Imaging and Adaptive Optics Correction
- May 7, 2008: Vadim M. Uritsky (Univ. Calgary): Spatiotemporal Event Decomposition (STED) for Solar
and Magnetospheric Physics
- November 13, 2007: Franco Rappazzo and Marco Velli (Caltech): Coronal heating
- August 23, 2007: Serge Koutchmy (Institut d'Astrophysique de Paris): Chromospheric prolatenes variations, spicules,
marco-spicules and SXR jets
- Apil 25, 2007: Olya Panasenco (Helioresearch): Topological analyses of eruptive filaments
- April 12, 2007: Wenda Cao (NJIT): IR Observations at BBSO
- April 11, 2007: Sridharan Rengaswamy: Crowded Field Astrometry with SIM
- February 14, 2007: Patricia Jibben: The X-ray Telescope (XRT) aboard the Hinode Observatory
- January 24, 2007: Na Deng: Spectral and Multi-wavelength Studies of
Active Regions and Flares
- January 24, 2007: Haisheng Ji: The relaxation of sheared magnetic field - a process
of contraction
- January 24, 2007: Chang Liu: Multiwavelength and Multiscale
Study of Magnetic Fields Involved with Flares/CMEs
- January 24, 2007: Changyi Tan: Statistical Correlations between
Parameters of Photospheric Magnetic Field and Coronal Soft X-ray Brightness
- January 24, 2007: Valentyna Abramenko: Solar photospheric fields
and their connection with the heliosphere
- January 24, 2007: Ju Jing: Progress in Setting up Data Processing
Tools for BBSO Vector Magnetogram Data
- January 24, 2007: Hui Song: Prediction of Imminent Solar Flares
with Ordinal Logistic Model
- January 24, 2007: Vasyl Yurchyshyn: Observed
Elongation of LASCO Halo CMEs and its Connection to the Structure of
Magnetic Clouds
January
16, 2007: Pilar Montanes-Rodriguez Earthshine
applications in the search for distant worlds
December
12, 2006: Enric Palle Bago: Ocean-cloud-albedo
interactions at decadal time scales
(
abstract)
November
14, 2006: Haisheng Ji: Contracting
flaring loops suggests the relaxation of sheared magnetic field
(abstract)
February
6, 2006: Jongchul Chae: The
Optical Design for the Fast Imaging Solar Spectrograph
January
28, 2006: Jongchul Chae: Study
of magnetic structures of chromospheric filaments.
January
23, 2006: Hongqi Zhang: Magnetic
properties of flare-CME productive active regions
September
13, 2004: Nancy King: Vegetation
Albedoes for Life on Other Planets
(abstract)
August
2, 2004: Jongchul Chae: Fast
Imaging Solar Spectrograph (FISS) for New Solar Telescope: The First
Idea
July
26, 2004: Thomas H. Zurbuchen (): The
Structure and Sources of the Solar Wind During the Solar Cycle
(videoconference) (abstract)
April
15, 2004: Valentyna Abramenko: Distribution
of the magnetic flux in elements of the magnetic field in an active
region
(abstract)
April
5, 2004: Prof. Cheng Fang: Spectral
Diagnostics Of Non-Thermal Particles In The Solar Chromosphere
(abstract)
February
10, 2004: Enric Palle Bago: A
review on the Earthshine Project. Changes in the earth's reflectance
over the past two decades
(abstract)
Valentyna
Abramenko: Changes
in the Spectral Line Profiles During a Solar Flare
(abstract)
Reiner
Volkmer: Actual
Status and Design of the 1.5 m Solar Telescope GREGOR
K.D.
Leka: What
makes a flare? Determining the magnetic signature of a flaring
photosphere.
(abstract)
Klaus
Hartkorn: Application
Of Adaptive Optics To The Spectroscopic Investigation Of Small-Scale
Solar Structures.
(abstract)
Haisheng
Ji: Report
On My Work at BBSO
Ayumi
Asai: Flare
Evolution and Energy Release
(abstract)
Valentyna
Abramenko: Signature
of Avalanche in Solar Flares as Measured by Photospheric Magnetic
Fields
(abstract)
Vasyl
Yurchyshyn: How
Directions And Helicity Of The Magnetic Field In Erupted Solar
Filaments Define Geoeffectiveness Of Coronal Mass Ejections
(abstract)
Yong-Jae
Moon: Magnetic
Helicity and X-Ray Fluxes of Homologous Flares
(abstract)
Martin
Woodard: Seismic
Imaging of Solar Convection
(abstract)
Guo
Yang: The
introduction to Coronal Mass Ejection and the work I am doing
Abramenko,
Magnetic
Power Spectra in the Solar Photosphere Derived from Ground and Space
Based Observations
Carsten
Denker, Center-to-Limb
Variation of Small-Scale Magnetic Features
Leonid
Didkovsky, Proper
Motion of Sunspots Observed with MDI
Michael
Steinegger, The
H-alpha Network: Overview - Status - Outlook
Louis
Strous, THE
DYNAMICS OF THE EXCITATION OF SOLAR OSCILLATIONS
(abstract)
Jongchul
Chae, High
Resolution H alpha Observations of Proper Motions in NOAA 8668:
Evidence for Filament Mass Injection by Chromospheric Reconnection
(abstract,
H
alpha movie)
Peter
Gallagher, Observing
the Sun at Radio Wavelengths
(abstract)
Jung-Hoon
Kim, A
Rapid Magnetic Connectivity Change Observed Before a Filament
Eruption
Sangwoo
Lee, Observational
Evidence for Magnetic Dips in Solar Prominences
ABSTRACTS
Title,
Name
Abstract
[Top]
Topological
analyses of eruptive filaments by Olya Panasenco
Erupting
filaments (prominences) that we have analyzed from H" Doppler
data at Helio Research and from SOHO/EIT 304 D show several different
motions along the main axis and legs. Our simple geometrical analyses
of these motions reveal strong coherency in some filaments between
their chirality, and the direction of the vertical motions of the top
of the filaments, and the directions of twisting of their legs.
Viewed from the positive network side, dextral filaments develop
rolling motion toward the observer along with right-hand helicity in
the left leg (clockwise streaming for downward motion) and left-hand
helicity in the right leg. Sinistral filaments, also viewed from the
positive network field side, have the opposite pattern: rolling
motion at the top away from the observer, left-hand helical twist in
the left leg (counterclockwise for downward motion) and right-hand
twist in the right leg. We find consistency between our analyses of
these motions and forms determined from our Ha Doppler observations
and twists or bending deduced from the properties of erupting
filaments observed in EIT images at 304 D. We cannot reconcile these
findings with filaments modeled as magnetic flux ropes that by
definition only have one sign of helicity. In addition, the popular
hypothetical configuration of an eruptive filament as a twisted flux
rope does not account for the complete range of observed shapes in
the erupting filaments. However, we find that a simple flat ribbon or
sheet satisfactorily reproduces nearly all of the observed forms. The
flat ribbon is the most logical beginning topology because filament
spines already have this topology prior to eruption and an initial
long flat sheet with parallel, non twisted threads, as a basic form,
can be bent into many more and different geometrical forms than a
flux rope. To date, we have been able to identify three common
patterns of motion. All are consistent with the ribbon topology and
characterize the helicity of many erupting filaments: (1) Roll of the
top of the filament with horizontal and vertical components, (2)
Twist of the legs consistent in sign with the rolling motion along
the top of the filament, and (3) rotation (writhe) of the whole
filament as it moves and expands outward. Considering that erupting
filament dynamics have large-scale coherency and always occur beneath
CMEs, we suggest that it is reasonable for the top of an erupting
filament to be first in responding to relatively unknown, changing,
coronal forces in its environment. For morphological analyses of
eruptive filaments we used the ratio h/l, where h - is the height of
filament, l - is distance between its legs, and also " - the
angle in degrees of twist or roll during increments of time, t. We
consider three general cases: 1) h/l - 0; 2) h/l > 1, legs close
together; 3) h/l # 1, legs far apart. We also describe the
relationship between the direction of twists in the legs and the roll
direction at the top of the filament using the geometrical terms: l,
h, and ". Starting with our finding that filaments are thin
sheets after their eruption, as known before their eruption, we apply
our geometrical analyses to determinate of the sign of magnetic
helicity and estimate the degree of twisting or bending in different
parts of the top and legs of erupting filaments.
[Top]
The
X-ray Telescope (XRT) aboard the Hinode Observatory by Patricia
Jibben
XRT is a high resolution grazing incidence telescope
capable of observing coronal temperatures from 700,000 to 10,000,000
Kelvin. It has a 34x34 arcmin full field of view and 2" spatial
resolution capable of studying global coronal structures as well as
resolving active region loops. The unique combination of high spatial
resolution and broad temperature range allows observations of energy
buildup, storage and the release process in the corona for any
transient event. XRT was launched on September 22, 2006 and has been
actively observing the sun since November 2006. Recent observations
include transient polar jets within polar coronal hole, C-class
flares, loop evolution, and the so-called coronal 'doughnut'. A
sample of these observations will be presented.
[Top]
Earthshine
applications in the search for distant worlds by Pilar
Montanes-Rodriguez
Since
the discovery of the first planet outside the solar system, the
number of planet detections is increasing exponentially. Although we
have not been capable of detecting and exploring planets like our own
yet, challenging space missions are already being planned for the
next decades, and the discovery of earth-like planets is only a
matter of time. When the time arrives, one of our main concerns will
be to determine their degree of similarity with our own planet, and
to answer a more intriguing question for the humankind: if there is
life on them. Using real cloud cover observations from satellite, we
have unequivocally detected the vegetation's signature in the Earth's
globally averaged spectrum. The signature is stronger when larger
vegetated regions of the Earth are seen free of clouds. Our results
show that, considering the real cloud cover present in our planet,
previous estimates of the vegetation signal strength were
overoptimistic. Vegetation can be detected on Earth when it is
observed as a distant planet, and although its signal is going to be
much weaker than what we previously though, when detected, it will be
an unquestionable indication of extraterrestrial complex life. Future
applications of earthshine spectroscopy will also be introduced.[Top]
Ocean-cloud-albedo
interactions at decadal time scales by Enric Palle Bago
Over
the past century, our planet has experienced a global warming
generally associated to an increase in anthropogenic greenhouse
gases, superimposed to an unknown intrinsic climate variability. To
understand this warming, it is essential to know the response of the
climate system to external forcing, and the decadal-scale energy
exchange between the oceans and the atmosphere. Presently, two of the
most uncertain elements in the climate are the role of clouds and the
heat storage of the Earth's oceans. Especially intriguing are the
cloud feedback mechanisms, which strongly affect the ability of
global circulation models to predict future climate change. Here, we
compare 20 years of global ocean thermal properties and cloud amount
data to derive their large-scale inter-annual relationships. Despite
some restriction in our conclusions due to the nature of the
datasets, we find significant correlations whose strength and sign
vary with cloud type and latitude. At decadal timescales, we find an
anti-correlation between the global mean cloud amount and the ocean's
heat content, with the clouds leading in the correlation by about 1
year. Our results suggest that cloud changes, whether natural or
anthropogenic in origin, might have a direct influence in the decadal
variability of ocean temperatures and heat content. [Top]
Contracting
flaring loops suggests the relaxation of sheared magnetic field by
Haisheng Ji
In recent years, a new kind of solar flare
phenomenon has been discovered in many flares by different authors.
That is, during the early rising phase of solar flares, hard X-ray
loop top sources or radio/extreme-ultraviolet flaring loops have a
shrinkage motion and, at the same time, flaring ribbons or hard X-ray
footpoints have a converging motion. Only after the rising phase,
there begin to appear an upward expansion for loop top sources and
flaring loops and, also, an outward motion (separation motion) for
flare ribbons or footpoints. So far, the shrinkage motion can not be
fully explained with a 2D flare model. We propose that the new solar
flare phenomenon suggests the relaxation of sheared force-free
magnetic field. [Top]
Vegetation
Albedoes for Life on Other Planets by Nancy King
Scientists
are fast approaching the capability to detect Earth-size planets and
to resolve them spectrally. How can we tell if there is life on
another planet through astronomical observations? Life abounds in
extreme environments and in hidden places of the Earth and could
likewise on other planets. However, on Earth, only photosynthetic
organisms produce unequivocal signs of life that we can detect from
space. These signs are the vegetation "red edge" (the
strong contrast in absorbance by vegetation in the visible light
range and high reflectance in he near-infrared) and the presence of
oxygen in our atmosphere (due to water photolysis by photosynthesis).
In addition, the seasonal cycles of atmospheric carbon dioxide and
methane concentrations are due to the seasonal growth and respiration
of the biosphere. These "biosignatures" are the result of
short-term biophysical processes, which have arisen through long-term
coevolution of the biosphere with the atmosphere, and perhaps due to
evolutionary accidents in the origin of photosynthesis. Could
photosynthesis arise on another planet, and would such organisms
produce the same biosignatures as those on Earth? This talk will
review the state of knowledge on the vegetation red edge and
predicting plant canopy albedoes, the environmental constraints on
photosynthesis, and present potential biosignatures for life around
M-stars, with discussion about their detectability. [Top]
The
Structure and Sources of the Solar Wind During the Solar Cycle
The
solar corona and hence the structure of the heliosphere change
dramatically during the solar cycle. At solar minimum, solar wind
predominantly emerges from polar coronal holes and propagates close
to equatorial regions. Associated with streamers, an intermittent
stream of solar wind is emerging and forming slow solar wind. As
solar activity progresses, this bimodal distribution of the solar
wind becomes much more complicated. Fast and slow solar wind can be
found at all latitudes. We will discuss this transition from low to
high solar activity focusing on solar wind composition data that
provide a new way of observing the evolution of the solar corona over
time. These data show interesting compositional anomalies that
distinguish different sources of solar wind and mark hot ejecta in
the heliosphere. [Top]
Distribution
of the magnetic flux in elements of the magnetic field in an active
region by Valentyna Abramenko
Probability distribution
functions (PDFs) of the unsigned magnetic flux content in flux
concentrations in a mature active region NOAA 9077 were calculated by
using a set of 248 high resolution SOHO/MDI magnetograms. Two
independent routines to outline magnetic flux concentrations were
elaborated. The analysis was performed with 4 different values of the
threshold, p, of the magnetic flux density (p=25, 50, 75, 100 G). We
have found that: i) the best analytical approximation of the observed
PDFs in the range of low flux (F < 100 x 10^18 Mx) is a lognormal
distribution, LN(m, sigma^2), with the expected value m=(0.7 to 5) x
10^18 Mx and the standard deviation sigma = (10 to 45) x 10^18 Mx.
The peak of the lognormal distribution tends to shift toward the
lower flux as the threshold p decreases. This tendency suggests that
the real expected value may be even smaller than 0.7 x 10^18 Mx; ii)
for the flux F > 100 x 10^18 Mx the observed PDFs fall off slower
than the lognormal approximation predicts. In this flux range, the
power law is found to be the best analytical approximation with the
power law index, alpha, approximately equal to 2. The above findings
are consistent with the concept of highly intermittent nature of the
cluster of magnetic flux concentrations in the active region. [Top]
Spectral
Diagnostics Of Non-Thermal Particles In The Solar Chromosphere by
Prof. Cheng Fang
There are at least three effects of the
non-thermal particle bombardment on the solar atmosphere: (1)
non-thermal ionization and excitation; (2) proton-hydrogen charge
exchange; (3) impact line polarization. Due to the non-thermal
ionization and excitation effects of electron bombardments in flares,
H? line is widely broadened and shows a obvious central reversal.
Significant enhancements at the line wings of Ly?and Ly?are also
predicted. In the case of proton bombardment, less strong broadening
and no large central reversal are expected. Based on theoretical
calculations, we proposed a method to estimate the total flux of
electron beam by the measurement of integrated flux in H? line
profiles. Due to the proton-hydrogen charge exchange, the
enhancements at the red wings of Ly? and especially of Ly?lines at
the early impulsive phase of flares are significant. Electron beam
can also in some cases produces visible and UV continuum emission in
white-light flares. However, at the onset phase, a negative "black"
flare may appear in several seconds, due to the increase of the H?
opacity. The impact polarization of atomic lines can provide
complementary information on the energetic particles, the energy
transport and deposit in the solar chromosphere. New results of
spectropolarimetric analysis for the major flare on are also given.
[Top]
A
review on the Earthshine Project. Changes in the earth's
reflectance over the past two decades by Enric Palle Bago
We
correlate an overlapping period of earthshine measurements of the
earth's reflectance (1999 through mid-2001) with satellite
observations of global cloud properties to construct from the latter
a proxy measure of the earth's global shortwave reflectance. This
proxy shows a steady decrease in the earth's reflectance from 1984 to
2000, with a strong drop during the 1990's. During 2001-2003 only
earthshine data are available, and they indicate a complete reversal
of the decline. The radiative forcing implied by either of these
decadal changes in reflectance is climatologically significant.
Understanding how these changes are apportioned between natural
variability, direct forcing, and feedbacks, is fundamental to
confidently assessing and predicting climate change. [Top]
Changes
in the Spectral Line by Profiles During a Solar Flare by Valentyna
Abramenko
The profiles of six photospheric absorption
spectral lines (Fe I 5250A, Fe I 5324A, Fe I 5576A, Ca I 5590A, Ca I
6103A, and Fe I 6165A) measured in the kernel of a 2N solar flare and
in a quiet-sun area, were compared. The observations were carried out
with an echelle spectrograph of Crimean Astrophysical Observatory. It
was shown that compared to the quiet-sun profiles, the flare profiles
are shallower in the line core and are less steep in the wings.
Therefore, measurements of the longitudinal magnetic field made with
a magnetograph system which use the Ca 6103\AA~ spectral line, can be
underestimated by 18-25\% in the areas of bright H$\alpha$ ribbons of
a moderate solar flare of importance 2N. The modeling of the solar
photosphere performed by using a synthesis method, showed that in a
solar flare, the enhanced core emission seems to be related to
heating of the photosphere by the flare, whereas the decrease of the
wings slope was presumably caused by the inhomogeneity of the
photospheric magnetic field. [Top]
What
makes a flare? Determining the magnetic signature of a flaring
photosphere by K.D. Leka.
Big Bear Solar Observatory have
searched for and in many cases, found, changes in photospheric
magnetic fields associated with solar flares; this is demonstrated
with the recent work of Wang et al (2002) which found variations in
magnetic flux temporally associated with six X-Class solar flares. In
this talk I will outline an approach we have developed to distinguish
what may be unique to a flare-imminent solar atmosphere as determined
by the photospheric magnetic field. Using archive data from the
Imaging Vector Magnetograph from U. Hawai`i/Mees Solar Observatory,
we perform statistical evaluations of the state of the photospheric
magnetic field as well as on measures of the inferred coronal
topological complexity (Leka & Barnes 2003; Barnes et al 2003). I
will describe our method which, when applied to the minimal dataset
so far acquired, has indeed been able to distinguish that atmosphere
which is flare-imminent, but only by simultaneously considering six
or more parameters derived from the photospheric magnetic field
vector.[Top]
Application
Of Adaptive Optics To The Spectroscopic Investigation Of Small-Scale
Solar Structures by Klaus Hartkorn.
We study bright
points, umbral dots and the G-band using a two-dimensional
spectrometer and an Adaptive Optics system, which allows us to record
high-resolution dopplergrams and residual intensity images. We find
evidence that bright points are smaller than 120 km in diameter.
Bright points are situated exclusively in regions of enhanced G-band
brightness and do not show a change in their shape or a displacement
in their position of more than 120 km horizontally over a height
range from 0 km to 320 km above photospheric level $\tau =1$. We do
not find velocity differences of more than 100 m/s and a size of 120
km at the locations of bright points compared to the surroundings.
Bright points have a higher contrast in the G-band as well as in the
atomic spectral lines. We suspect the existence of two contrast
enhancement mechanisms for bright points one exclusively for the
G-band, one independent of specific spectral lines. We perform
calculations using the results of a three-dimensional
magneto-hydrodynamical model as input for a radiative transfer
calculation, but find little agreement with our observations. The
core intensity of the G-band CH lines is significantly influenced by
the atmospheric conditions in heights of 160 km and 320 km, but not
heights of 40 km. The velocity investigation of a sunspot shows that
umbral dots seem to consist of two different types. The first type is
the bright part of an intensity pattern of 1000-2000 km size with a
corresponding negatively correlated velocity pattern which is
probably related to umbral oscillations. The second type consists of
localized brightening of a size of not more than 300 km that are
associated with down-flowing plasma. Furthermore, we find penumbral
grains that have penetrated the umbra and appear as brightenings. We
study the velocity signature of penumbral grains and find strong
up-flows of solar plasma associated with the inner, bright parts of
penumbral grains, where as the general correlation between intensity
and velocity within the penumbra is weak.
[Top]
Flare
Evolution and Energy Release by Ayumi Asai.
Studies of
solar flares by using optical (mainly H-alpha) data, combined with
EUV (TRACE), X-rays (Yohkoh & RHESSI), and microwave (Nobeyama)
data. The main results are as follows: 1) We found a good correlation
between motions of H-alpha flare kernels and HXR foot point source
time history. It was shown that the HXR temporal variation can be
explained by a combination between the magnetic field strength and
the separation speed of the H-alpha kernels. 2) Down flow motions
above the EUV arcade correlate with HXR bursts in the impulsive
phase. [Top]
Signature
of Avalanche in Solar Flares as Measured by Photospheric Magnetic
Fields by Valentyna Abramenko.
Turbulent/fractal
parameters of the longitudinal magnetic field, B_z, for four powerful
solar flares were analyzed utilizing the correlation length, \lambda,
of the magnetic energy dissipation field and the scaling exponent,
\beta, which characterizes the measure of intermittency of the B_z
structure. We select a set of four two-ribbon flares, which were
followed by coronal mass ejections, for the study of magnetic
structure. During the course of each flare, we found a peak in \beta
which was followed by a peak in \lambda in all of the cases studied
in this paper. These two peaks were separated by the time interval
\tau_{\lambda} during which a rapid growth of the soft X-ray and
H\alpha flux occurred. The peak in \beta was preceded by a time
period \tau_{\beta} during which \beta increased gradually. For all
of the flares \tau_{\beta} was longer than the time interval
\tau_{\lambda}. The maximum of \lambda occurred nearly
simultaneously, within an accuracy of about 2-5 minutes, with the
maximum of the hard X-ray emission. For the four flares considered in
this paper, we concluded that the more impulsive and/or more powerful
a flare is, the shorter the \beta growth time, \tau_{\beta}, and the
\lambda growth time, \tau_{\lambda}, are. In the framework of the
theory of non-linear dissipative processes, these results may be
interpreted as follows. Before a solar flare occurs there is a
significant increase in the number of magnetic field discontinuities
(\beta increasing), which is followed by an avalanche (increase of
the correlation length) of magnetic energy dissipation events. The
avalanche event occupies the entire active region from the corona to
the photosphere. Our study indicates that the more abrupt is the
avalanche, the stronger and/or more impulsive a flare is. The time
profiles of an avalanche is either Gaussian, which satisfies the
logistic avalanche model, or exponential with an abrupt drop, which
satisfies the exponential avalanche model. The driving time,
\tau_{\beta}, was longer than the avalanching time, \tau_{\lambda},
for all of the events. This qualitatively agrees with the
requirements of the self-organized criticality theory. [Top]
HOW
DIRECTIONS AND HELICITY OF THE MAGNETIC FIELD IN ERUPTED SOLAR
FILAMENTS DEFINE GEOEFFECTIVENESS OF CORONAL MASS EJECTIONS by Vasyl
Yerchyshyn.
Coronal mass ejections (CMEs) are often
associated with erupted magnetic fields or disappeared chromospheric
filaments. The majority of CMEs headed directly toward the earth
(halo CMEs) are observed at 1AU as magnetic clouds (MC). The 3D
structure of a MC can be represented by a force-free flux rope. When
CMEs reach the earth, they may or may not cause magnetic storms. The
geoeffectiveness of CMEs depends on the orientation of the magnetic
field in them. We show that the direction of the axial field in a MC
and its helicity are consistent with the direction of the axial field
and helicity of the erupted filaments. We also suggest that
geoeffectiveness of a CME can be forecasted by using daily Big Bear
Solar Observatory full disk H$\alpha$ and SOHO EIT 195\AA~ images and
SOHO/MDI magnetograms, as well. We continue to study the orientation
of magnetic fields in CMEs and its correlation with the occurrence of
geomagnetic storms. Here we report on the relationship between the
projected speed of CMEs, measured at 20R$_\odot$ from SOHO/LASCO
images, and the hourly averaged magnitude of the southwardly directed
magnetic field, B$_z$, in interplanetary ejecta, as measured by the
ACE magnetometer. CMEs that origin at the central part of the solar
disk ($r < 0.6R_\odot$) are the most geoeffective and the
instensity of the B$_z$ is an exponential function of the CME's
speeds. We propose that the strength of the southward IMF can be
estimated at least one day in advance, immidiatelly after a CME
started. The predicted value of the B$_z$ component can be then used
to estimate the intensity of a geomagnetic storm caused by the
erupteion. The prediction method is based on the correlation between
the speeds of CMEs and magnitudes of the southward IMF as well as the
fact that the orientaion and chirality of the erupted solar filaments
correspond to the orientation and chirality of interplanetary ejecta.
[Top]
Magnetic
Helicity and X-Ray Fluxes of Homologous Flares by Yong-Jae Moon
We present evidence that the occurrence of a series of homologous
flares in an active region is physically related to the accumulation
of magnetic helicity in the corona by shearing motion in the
photosphere. We have analyzed a set of 6.5 hour 1 minute cadence
magnetograms of NOAA 8100 taken by Michelson Doppler Images (MDI) on
board Solar and Heliospheric Observatory (SOHO). During this period,
seven homologous flares took place in the active region, but there
was no remarkable change of magnetic flux. We have determined the
magnetic helicity transport rate via photospheric footpoint shuffling
motions, and found that magnetic helicity was significantly
increasing during the observing period. It was obvious in the case of
a strong M4.1 flare that magnetic helicity injection rate impulsively
increased to a peak during the flaring time as the X-ray flux did. We
also found that the X-ray flux of a flare integrated over the flaring
time interval was strongly correlated with the magnetic helicity
accumulated during the flaring time, with the integrated flux
logarithmically increasing with the accumulated magnetic helicity.
Our results suggest that photospheric shearing motion is an important
driver of coronal activities and, hence, support Choe Cheng's
homologous flare model in which flares can occur in the same plage
repeatedly by continuous photospheric shearing motions. [Top]
Seismic
Imaging of Solar Convection by Martin Woodard
A new
seismic technique is being developed to image inhomogeneous
structure, such as subsurface convective cells, in the Sun. In the
direct imaging approach, a physical model of the solar interior is
inferred directly from correlations in the observed seismic wave
field. A preliminary map of supergranular convection, inferred from
SOHO/MDI helioseismology images, agrees reasonably well with
simultaneous surface Doppler maps of supergranulation. Further
development of the method is expected to improve the technique
considerably. [Top]
THE
DYNAMICS OF THE EXCITATION OF SOLAR OSCILLATIONS by Louis Strous
We investigate seismic events, bursts of seismic waves that
are generated locally just below the solar surface and that we detect
traveling up through the photosphere. We identify a few thousand
seismic events by their traveling wave character, and find that they
are associated with continuum darkening and downflow, and have an
extent of on average about 10 -- 15 minutes and 1 Mm. Their birth
rate is about 8e-16 m^-2 s^-1. The observed upwardly traveling
seismic flux in the average event (as derived from velocities in the
p-mode region of k-omega space) is followed after about 3 minutes by
some reflected downward flux. Only a small fraction of the energy
generated in the hypocenter of the event below the surface travels
straight up for us to see. The bulk of the generated energy is
directed or reflected downward, and is eventually transformed into
p-modes. The seismic events at the surface contain about 1.5e19 J of
seismic energy each, which corresponds to an average flux level of
about 8.5 kW/m^2 over the whole surface. The total energy flow is
likely more than an order of magnitude greater, and is then in the
same ballpark as the estimate of Libbrecht (1988) for the power
required to sustain the p-mode spectrum. We find a roughly linear
relation between the peak seismic flux and the peak downward
convective velocity associated with each seismic event, which does
not fit the highly non-linear relations found theoretically by
Lighthill (1952) and Goldreich & Kumar (1990) for stochastic
excitation by turbulent convection, but does fit the monopole source
deduced by Nigam & Kosovichev (1999) from a study of the p-mode
spectrum.
Reference: Strous, Goode, & Rimmele (2000),
Ap.J. 535, 1000 [Top]
High
Resolution H$\alpha$ Observations of Proper Motion in NOAA 8668:
Evidence for Filament Mass Injection by Chromospheric Reconnection by
Jongchul Chae
There
have been two different kinds of explanations for the source of cool
material in prominences or filaments: coronal condensations from
above and cool plasma injections from below. In this paper, we
present observational results which support filament mass injection
by chromospheric reconnection. The observations of an active filament
in the active region NOAA~8668 were performed on at a wavelength of
H$\alpha-0.6$ \AA\ using the 65~cm vacuum reflector, a Zeiss
H$\alpha$ birefringent filter, and a 12-bit SMD digital camera of Big
Bear Solar Observatory. The best image was selected every 12~s for an
hour based on a frame selection algorithm. All the images were then
co-aligned and corrected for local distortion due to the seeing. The
time-lapse movie of the data shows that the filament was undergoing
ceaseless motion. The H$\alpha$ flow field has been determined as a
function of time using local correlation tracking. Time-averaged flow
patterns usually trace local magnetic field lines, as inferred from
H$\alpha$ fibrils and line-of-sight magnetograms. An interesting
finding is a transient flow field in a system of small H$\alpha$
loops, some of which merge into the filament. The flow is associated
with a cancelling magnetic feature which is located at one end of the
loop system. Initially a diverging flow with speeds below 10 km
s$^{-1}$ is visible at the flux cancellation site. The flow is soon
directed along the loops and accelerated up to 40 km s$^{-1}$ in a
few minutes. Some part of the plasma flow then merges into and moves
along the filament. This kind of transient flow takes place several
times during the observations. Our results clearly demonstrate that
reconnection in the photosphere and chromosphere is a likely way to
supply cool material to a filament, as well as re-organizing the
magnetic field configuration, and, hence, is important in the
formation of filaments. [Top]
Observing
the Sun at Radio Wavelengths by
Peter T. Gallagher
In this talk, I will give an introduction to observing the
Sun using the Owens Valley Solar Array (OVSA). The basic elements of
the radio telescopes together with the mechanisms responsible for
radio emission will first be reviewed. I will then discuss the recent
upgrade of OVSA, data access and analysis, and how to observe using
the array. Finally, some recent scientific results from high
resolution flare observations will be discussed. [Top]