C: Magnetic Field Evolution,
Marc DeRosa (30)

Last Updated Fri Dec 5 16:24:42 2008

1: William Abbett (abbett@ssl.berkeley.edu), UC Berkeley [H]
[soi] My current research interest is to develop an efficient means to numerically model the physics of the solar atmosphere from the upper convection zone to the corona over large, active region spatial scales. My goal is to better understand the magnetic and energetic connection between the corona and the convective interior as active regions emerge and decay.
[]
2: Valentyna Abramenko (avi@bbso.njit.edu), Big Bear Solar Observatory [C]
[soi] WG A: Parameters of the magnetic field in coronal holes and their relationship with the solar wind WG C: The Rate of emergence of magnetic dipoles in coronal holes and adjacent quiet-sun regions
[poster?] (?On the basis of SOHO/MDI full disk observations of coronal holes (CHs) during the declining phase of the 23th solar cycle a comprehensive study of magnetic field distribution was performed in the framework of the LWS/TR&T Heliospheric Magnetic Field Focus Team collaboration. More than 44 low-latitude CHs were analyzed. We found that the average unsigned magnetic flux density varies in an interval of 10-12 G, open flux density is between 1-5 G, and the noise level is about 3-4 G. Considerable part of the total flux in CHs is associated with closed loops: the flux density in loops varies between 1 and 5 G, which is comparable to the open flux density. Solar wind speed, associated with a target coronal hole and measured with ACE instruments, highly correlates with: i) the total unsigned magnetic flux of the CH (the correlation coefficient is CC=0.75), ii) the total open flux (CC=0.71), ii) the total closed (loop) flux (CC=0.73), and iv) the total area of CHs (CC=0.75). Correlations between the solar wind speed and magnetic flux densities are positive, although very low: CC=0.33 for the unsigned flux density and 0.20 for the open flux density. We found that the area of a CH is highly correlated with i) the total unsigned flux (CC=0.997), and the total open flux (CC=0.92). This means that the CH's area, as measured from EUV images, may serve as a reliable proxy for the total unsigned magnetic flux and total open flux. Case studies for CHs observed with MDI in the high resolution mode allowed us to analyze structure characteristics of the magnetic field. The power spectra of the magnetic field (both spatial and temporal spectra) display the power-law with the index between -0.8 and -1.2, which coincides well with the power index of -1 found in the low-frequency part of the spectrum of magnetic oscillations in the solar wind (Bruno et al. 2005). Intermittency analysis showed that the intermittent regime in CHs can be only detected at scales below 1 Mm.?)
3: Nick Arge (nick.arge@kirtland.af.mil), AFRL [C]
[soi] I am interested in the sources and variations of the solar wind and open magnetic flux over the solar cycle.
[none]
4: Stuart Bale (bale@ssl.berkeley.edu), UC Berkeley [J]
[soi] SCIENCE!
[none]
5: Elena Benevolenskaya (elena@sun.stanford.edu), Stanford University [I]
[soi] 'What is a different in the polar magnetic field reversals in cycle 23 compared with cycle 21 and 22? The polar magnetic field is a very important solar penomenon for understanding nature of the solar cycle. The polar field are offen used for the prediction of the next solar cycle under an assumption that it leds to forming of the toroidal field of the next cycle. I am discussing what has been unusual with polar magnetic field in the present cycle 23? And would be it?
[poster] 'Dynamics of the high-mid latitude magnetic field in the cycle 23. Using the SOHO/MDI data covering the period of 1996-2008 years, the dymanics of the small-scale magnetic elements on the Sun are investigated. The results reveal a spid down of magnetic elements close to the poles and a complexity in the behavior of the individual magnetic elements which points out on the effect of the turbulent diffution and subsurface gradients of the plasma velocity rates.
6: Rock Bush (rbush@solar.stanford.edu), Stanford University [I]
[soi] I am involved with both the Michelson Doppler Imager instrument on SOHO and the Helioseismic Magnetic Imager to be launched on the SDO spacecraft. I am interested in solar cycle variation in the Sun's magnetic field, both the MDI measurements of Cycle 23 and the upcoming HMI measurments of Cycle 24.
[none]
7: Steven Chapman (sachapman@uclan.ac.uk), University of Central Lancashire [C]
[soi] I have been investigating the variation of open flux from solar minimum to solar minimum. I've used data obtained from daily coronal hole areas derived from the SOHO/CDS synoptic study and the Kitt-Peak/SOLIS-VSM magnetograms to derive the open flux measurements using the relationship I(open) = A(CH) * B(CH). This appears to show a steady increase in open flux from solar minimum and peaks a few years after solar maximum. This shows that there is a global process slowly generating the open field lines on the rise to solar maximum, and that shortly after solar maximum, whilst the sun in returning to a low activity state the number of open field lines decreases.
[poster] Variation in Coronal Hole Temperature with Solar Cycle, The temperature of coronal holes has been determined using temperature maps of the solar corona derived from the Mg X/Mg IX intensity ratio. This has been developed into an automated procedure with the use of the coronal hole maps from our CDS Synoptic Atlas. The coronal hole temperature was found to vary in phase with the solar cycle from 1.02+/-0.02MK (solar maximum) down to 0.90+/-0.02MK (solar minimum).
8: Cilia Damiani (damiani@obspm.fr), OBS-Meudon [F]
[soi] We will first introduce the concept of oblateness (n=2) in slowly, non rigid rotating stars. For the Sun, the differential rotation, anchored not only on the surface, but also deeper, contributes to distort (through higher orders, n) the free surface of the body. Then, we will review measurements of solar oblateness since the first ones made by Brans and Dicke in Princeton in 1996. It will be shown how inaccurate measurements can be useful. We will extend the subject to our own measurements made from 1996 to 2008 by means of the scanning heliometer at the Pic du Midi Observatory. We will describe solar asphericities whose departures from sphericity should certainly not exceed a few milliseconds of arc. These rather faint values allows to constrain helioseismic models. We will show the physical properties of the sub-surface layer, the leptocline, recognized at the last International Astronomical Union General Assembly in Praha (2006). Incidentally, we will give the latest values of the solar gravitational moments as deduced from models of rotation, using for the first time a radial gradient of rotation. A few words on related alternative theories on General Relativity will be said also. Lastly, we will conclude by showing the contribution of some space experiments or balloon flights, like the French mission DYNAMICCS or the US one, SDO.
[poster] A general survey of solar radius variations will be presented, using different techniques, including eclipses and space observations. It will be show why the amplitude of such radius variations cannot exceed a few second of arc over the solar cycle. Such physical grounds, leading to astrophysical consequences, are the input in new space dedicatred missions such as DYNAMICCS, scheduled within the ESA road map.
9: Marc DeRosa (derosa@lmsal.com), LMSAL [C]
[soi]
[none]
10: George Fisher (fisher@ssl.berkeley.edu), UC Berkeley [I]
[soi] I am interested in how observations of the vector magnetic field can be used to constrain velocity and electric fields in the solar atmosphere.
[poster] A New Technique for Finding Electric Fields from Sequences of Vector Magnetograms The advent of extensive ground-based and space-based vector magnetogram data will greatly improve our quantitative understanding of how magnetic fields evolve in the solar atmosphere. A problem of great interest is the derivation of electric fields from vector magnetogram data, as this is the crucial link between observation and future physics-based time-dependent models of the solar atmosphere. Most previous techniques for deriving E have used only the normal component of the magnetic induction equation, as it is generally believed that depth derivatives contained in the magnetic induction equation cannot be derived from vector measurements taken within a single layer. I will show that in fact, sufficient information exists within a sequence of vector magnetograms to determine a 3-dimensional electric field whose curl reproduces the observed changes in all 3 components of B. While this is certainly a major step forward, it is still true that the electric field E itself, as opposed to its curl, is under-constrained by the data. I will discuss how additional considerations may be used to uniquely determine all 3 components of the electric field.
11: Martin Fivian (mfivian@ssl.berkeley.edu), Space Sciences Lab - UC Berkeley [E]
[soi] Solar oblateness. Recent RHESSI/SAS measurements show a large excess in apparent solar oblateness. Correlations of the optical radius measurements with EUV data from SOHO/EIT let us relate those larger radius values to magnetic elements in the enhanced network. While a corrected value for the oblateness is consistent with solar rotation, the observed excess can very well be variable and positively correlated with the solar cycle and its global evolution of magnetic elements at the surface.
[none]
12: Mandy Hagenaar (hagenaar@lmsal.com), Lockheed Martin Solar and Astrophysics Labs [C]
[soi] We investigated the distribution and evolution of existing and emerging magnetic network elements in the quiet-Sun photosphere. The ephemeral region emergence rate is found to depend primarily on the imbalance of magnetic flux in the area surrounding its emergence location, such that the rate of flux emergence is lower within strongly unipolar regions by at least a factor of three relative to flux-balanced quiet Sun. As coronal holes occur over unipolar regions, this also means that ephemeral regions occur less frequently there, but we show that this is an indirect effect - independent of whether the region is located within an open-field coronal hole or a closed-field quiet region. We discuss the implications of this finding for near-photospheric dynamo action and for the coupling between closed coronal and open heliospheric fields.
[none]
13: David Hathaway (david.hathaway@msfc.nasa.gov), [C]
[soi] Solar Activity Cycles - Past and Future
[none]
14: Todd Hoeksema (todd@sun.stanford.edu), Stanford University [C]
[soi]
[none]
15: Kirill Kuzanyan (kuzanyan@gmail.com), IZMIRAN, Russian Academy of Sciences, 142190 Moscow region RUSSIA [D]
[soi] We are interested in long term prediction of the solar cycle with the use of the dynamo theory and observational proxies
[poster] K. Kuzanyan, S. Zharkov, V. Zharkova Probing the forthcoming solar cycle 24 with the thin shell solar dynamo and additional observational proxies. We present our study on revealing regularities and prediction of the magnitude and duration of the solar cycle by the use of basic properties of the dynamo wave and, added on time series methods. Consideration of the nonlinear Parker dynamo waves in a thin shell enables us links between amplitude and phase of the solar magnetic activity. Furthermore, the sunspot index series have been analysed using time series methods, and predictions on the magnitude of this activity has been produced. Our results indicate that the two forthcoming solar cycles will be somehow lower than the previous ones, namely the maximum of 12-month averaged Wolf number for cycle 24 is expected in 2011-2012 as approximately 106, and for cycle 25 in 2021-2022 about 99.
16: Christina Lee (clee@ssl.berkeley.edu), Space Sciences Lab [C]
[soi] I am interested in the sources of the solar wind during the onset of Solar Cycle 24. I have been investigating how the sources have differed between the current minimum period and the period from the previous solar min cycle, and whether this plays a direct role with regards to the low IMF that we are seeing at L1 for this current min period.
[none]
17: Yan Li (yanli@ssl.berkeley.edu), SSL UCB [F]
[soi] Magnetic field evolution of AR8038 and sequential CMEs Yan Li, Ben Lynch, Brian Welsch, Janet Luhmann, George Fisher SSL UCB A sequence of three Coronal Mass Ejections (CMEs) initiated from the same magnetic neutral line of a classic bipolar magnetic region AR8038 at the east limb, near CMD (Halo) and near west limb. The three CMEs were associated with small flares and EIT double dimming. The Halo CME was accompanied with an EIT wave having near circular wave front. The CMEs have all arisen from the same magnetic neutral line and active region configuration within dipolar global coronal geometry, supported by photospheric and coronal imaging and PFSS modeling. Given the three CMEs can be considered homologous to some extend, and had comparable initiation condition and process, we investigate the possible free magnetic energy storage mechanisms and discuss the implications to understanding and predicting CME initiations. The unsigned magnetic flux (MDI) of the entire AR8038 decreased monotonically by ~20% about 66 hrs prior to the C1.3 flare, whereas the unsigned magnetic flux of a sub-region at the erupting neutral line was mostly increasing and up by about 16 during ~36 hrs prior to the C1.3 flare. Within the AR we found converging flow, but no shear motion. Energy build up by surface flows after each release is not evident. We discuss the possible energy source for the repeated eruptions.
[poster] STEREO ICMEs and Solar Origins during Solar Minimum Y. Li (UCB), E. Kilpua (UHF), B. J. Lynch (UCB), J. G. Luhmann (UCB), V. Toy (UCB), A. Vourlidas (NRL), L. Jian (UCLA), C. T. Russell (UCLA), A. B. Galvin(UNH), M. Acuna (GSFC), J-A. Sauvaud (CESR), R. Skoug (LANL), P. Schroeder (UCB), G. Petrie (NSO) The separation of the twin spacecraft of STEREO A (STA) and B (STB) was between 0.05 deg to 58.4 deg helio-longitude from 2007 Jan 01 to 2008 June 30. During this solar minimum period, we identified about ten ICME events using in-situ IMF and solar wind observations by IMPACT and PLASTIC on board STEREO and by ACE or Wind at L1 point. Before STA and STB separated further than ~40.8 deg (or ~0.7AU) on 2007 Nov 19, the two spacecraft intersected a few of the same ICMEs, but beyond that distance, no ICMEs were encountered by both STA and STB, indicating these ICMEs had small spatial dimensions. These solar minimum ICMEs had slow to moderate speed between ~300 km/s and ~500 km/s. CME driven shocks were weak or unidentifiable. The transit times of these ICMEs range from ~4hrs to ~47hrs. The peak magnitude of the enhanced magnetic field within the transients ranges from ~8 nT to ~18 nT. Counter streaming electrons are observed for a few cases, indicating closed field within those ICMEs. Both magnetic fields and electron flux can behave very differently at each spacecraft within some of the same ICMEs. Most of these ICMEs were followed with a high speed solar wind stream. The ICME characteristics are discussed in comparison with events at the previous solar minimum. In contrary to expectations for solar minimum time, it is difficult to determine the solar origins of these ICMEs, partly because most CMEs during this period are faint in coronagraph images, and have no association with intense flares and other obvious on-disk activity. We describe possible source CMEs during 5 days prior to the ICMEs. The coronal structure of the current solar minimum is significantly different from the dipolar structure that prevailed for the previous solar minimum, but has low latitude coronal holes and highly warped coronal streamer arcades. We discuss coronal and solar wind context for and the likely influence of the coronal structure on solar minimum time ICMEs.
18: Janet Luhmann (jgluhman@ssl.berkeley.edu), SSL, University of California, Berkeley [B]
[soi] am interested in origin and properties of different solar wind sources (fast and slow), and their relationship to the solar magnetic field
[none]
19: Kalevi Mursula (kalevi.mursula@oulu.fi), University of Oulu, Finland [C]
[soi] Long-term observations of the heliospheric magnetic field (HMF) at 1 AU have depicted interesting systematic hemispheric and longitudinal asymmetries that have far-reaching implications for the understanding of solar magnetism. Based on HMF observations during solar cycles 20-22, it was found that the HMF sector of the northern solar hemisphere dominates in the observed HMF sector occurrence for about three years during the late declining to minimum phase of each solar cycle. This dominance leads to a southward shift or coning of the heliospheric current sheet at these times, which has been described by the concept of the bashful ballerina. Measurements of the photospheric magnetic field have verified that the average field intensity is smaller and the area larger in the northern than in the southern solar hemisphere at these times. Also, long-term observations of the geomagnetic field yielding information on the HMF sector structure in the pre-satellite era show that the ballerina was bashful at least since 1930s. These results suggested for a new, general rule for the behaviour of the solar/heliospheric magnetic fields. We show that, despite some exceptional features of the solar magnetic field during the declining phase of solar cycle 23, the bashful ballerina appeared even during this cycle. This further underlines the significance and fundamental nature of this rule. However, some arguments exist that the asymmetry may reverse during one of the next few solar cycles.
[none]
20: Aimee Norton (Aimee.Norton@gmail.com), National Solar Observatory [H]
[soi] I am interested in large-scale flux emergence and migration patterns and the effects on the global coronal geometry. In a recent paper (Norton at al., 2008, ApJ, 682, 1306 ), we examined the tilt of the solar magnetic dipole away from the rotational axis near solar minimum. A persistent tilted dipole may result from an MHD instability acting upon the toroidal magnetic bands in the solar interior. Non-axisymmetric eruption of sunspots, the decay of the follower spots and migration of flux poleward could create polar caps that are slightly misaligned with the N-S rotational axis. To investigate this, we analyzed the coronal streamer geometry, the center-of-gravity of the polar caps and we modeled the coronal hole boundaries and the neutral line locations by potential field source surface modeling. Our results are consistent with an observed tilt of 5-10 degrees in the heliospheric current sheet at solar minimum and the idea of stubborn, persistently off-axis magnetic polar caps for certain Carrington Rotations. I will use these results as a launching off point to discuss other aspects of flux emergence and evolution.
[none]
21: Kala Perkins (quasar9@mac.com), UCSB [I]
[soi]
[none]
22: Alexei Pevtsov (apevtsov@nso.edu), National Solar Observatory [J]
[soi]
[none]
23: Jean-Pierre Rozelot (rozelot@obs-azur.fr), Nice Univeristy, Fizeau Dpt [C]
[soi] Solar oblateness. A full story on the question. Up to date developements, including oblateness dependence with solar activity, observations (ground and space) and physical basis
[talk] In this talk I will first introduce the concept of oblateness (n=2) in slowly, non rigid rotating stars. For the Sun, the differential rotation, anchored not only on the surface, but also deeper, contributes to distort (through higher orders, n) the free surface of the body. Then, I will review measurements of solar oblateness since the first ones made by Brans and Dicke in Princeton in 1996. It will be shown how inaccurate measurements can be useful. We will extend the subject to our own measurements made from 1996 to 2008 by means of the scanning heliometer at the Pic du Midi Observatory. I will describe solar asphericities whose departures from sphericity should certainly not exceed a few milliseconds of arc. These rather faint values allows to constrain helioseismic models (including the leptocline). Incidentally, I will give the latest values of the solar gravitational moments as deduced from models of rotation, using for the first time a radial gradient of rotation. A few words on related alternative theories on General Relativity will be said also. The dependence with the solar cycle will be tackled and physical interpretations given. Lastly, I will conclude by showing the contribution of some space experiments or balloon flights, like the French mission DYNAMICCS or the US one, SDO, without excluding RHESSI.
24: Leif Svalgaard (leif@leif.org), SELF [F]
[soi] The prediction of solar cycles is a key goal of solar physics. Knowledge of past solar cycles is important for assessing the future. I will discuss that possibly the sunspot number series is not correctly calibrated and therefore inhomogeneous and propose a remedy
[none]
25: Ted Tarbell (tarbell@lmsal.com), LMSAL [H]
[soi] The mixed success of coronal field extrapolations from the best available photospheric observations is a serious concern and a challenge. What other observations can we use to make more accurate extrapolations, or to choose among the various competing field models? A few ideas which come to mind are using the flux emergence history, H-alpha or He II 304 fibril geometry, connectivity hints from micro-flares as a region evolves, and inversions for magnetic field gradients in addition to photspheric values. I am interested in how to optimize Hinode and eventually AIA observations to address most effectively the outstanding questions in these areas.
[none]
26: Adriaan Van Ballegooijen (vanballe@cfa.harvard.edu), SAO [J]
[soi] I'm interested in modeling the evolution of solar magnetic fields in response to the emergence of bipolar active regions (Omega loops). Where does the helicity of active regions come from? How does the helicity spread through the corona to form filaments and prominences on the quiet Sun? What effect do decaying active regions have on the underlying toroidal field? I'm also interested in learning more about the fine structure of prominences.
[none]
27: Yi-Ming Wang (yi.wang@nrl.navy.mil), NRL [B]
[soi]
[none]
28: Stephen White (white@astro.umd.edu), University of Maryland [F]
[soi]
[none]
29: Anthony Yeates (ayeates@cfa.harvard.edu), Smithsonian Astrophysical Observatory [J]
[soi] I will describe new simulations of the global magnetic field evolution in the solar corona, developed in conjunction with A.A. van Ballegooijen (SAO) and D.H. Mackay (University of St Andrews). Using a coupled surface flux transport and magnetofrictional model, we can follow, for the first time, the build-up of magnetic helicity and shear on a global scale over many solar rotations. The evolution is driven by surface motions and by flux emergence, with properties of new active regions determined from synoptic normal-component photospheric magnetograms from NSO/Kitt Peak. As a first application we have compared the model to observations of sheared magnetic fields in filaments, over a 6-month period. We have unprecedented success in reproducing the chirality of filaments, enabling us to explain how the observed hemispheric pattern in filament chirality comes about. We are currently studying the distribution of current helicity, and of magnetic flux rope ejections. The latter occur when too much twist builds up in filament channels, and may correspond to a class of observed CMEs.
[poster] MODELLING THE GLOBAL SOLAR CORONA A. R. Yeates, D.H. Mackay, & A.A. van Ballegooijen We have developed new simulations of the global magnetic field evolution in the solar corona. Using a coupled surface flux transport and magnetofrictional model, we can follow, for the first time, the build-up of magnetic helicity and shear on a global scale over many solar rotations. The evolution is driven by surface motions and by flux emergence, with properties of new active regions determined from synoptic normal-component photospheric magnetograms from NSO/Kitt Peak. As a first application we have compared the model to observations of sheared magnetic fields in filaments, over a 6-month period. We have unprecedented success in reproducing the chirality of filaments, enabling us to explain how the observed hemispheric pattern in filament chirality comes about. We are currently studying the distribution of current helicity, and of magnetic flux rope ejections. The latter occur when too much twist builds up in filament channels, and may correspond to a class of observed CMEs.
30: Valentina Zharkova (v.v.zharkova@brad.ac.uk), University of Bradford [E]
[soi] Heartbeat of the Sun, or statistical properties of the solar activity deduced from the observations of active region and background magnetic field in the cycle 23 & Diagnostic tools of photon and electron transport from the non-isotropic Fokker-Plank solutions of electron precipitation in flaring atmospheres
[poster] The talk will deal with observed periodicities of sunspots and active regions measured from SFCs, their latitudinal and longitudinal distribution and relation to the background magnetic field. We will reveal the characteristic periods in poloidal and toroidal magnetic field and phase relation between them. Some implications on the dynamo models will be also discussed. & We discuss FP solutions for relativistic electron precipitation into a converging magnetic field with collisional and Ohmic losses and deduce photon intensity and polarization in MW and HXR radiation for different locations of flaring loops on the solar disk and different atmospheric depth. The resulst will be compared with those observed for a few known flares including the flare of 23 July with the sliding HXR emission along the visible location.

Second Choice

Valentyna Abramenko, Nick Arge, Steven Chapman, Bart De Pontieu, Alfred De Wijn, Marc DeRosa, George Doschek, Bernhard Fleck, Mandy Hagenaar, David Hathaway, Todd Hoeksema, Russell Howard, Hugh Hudson, Stuart Jefferies, Christina Lee, Ying Liu, Duncan H Mackay, Sara F. Martin, Helen Mason, James McTiernan, Kalevi Mursula, Jean-Pierre Rozelot, Isroil Sattarov, Toshifumi Shimizu, Han Uitenbroek, Angelos Vourlidas, Vasyl Yurchyshyn,