Photosphere/Chromosphere Posters
Presiding: B De Pontieu, Lockheed Martin Solar and Astrophysics Laboratory; S Walton, San Fernando Observatory, CSUN
SP41B-01 0830h
Searching for Moving Magnetic Features at 1565 nm
Spectropolarimetric data of the active region 10663 was taken with the CSUN-NSO IR camera and the McMath-Pierce telescope on August 26, 2004 from 16:35 to 21:02 UT. Utilizing the Zeeman split Fe I line near 1565 nm, the data is processed to remove instrumental polarization and a Milne-Eddington inversion technique is applied. The results of the inversion are used to examine the physical properties and radial motions of moving magnetic features which appear to originate in the sunspot penumbra.
SP41B-02 0830h
Destruction Mechanisms of Quiet-Sun Magnetic Flux
We use SWAMIS, a freely available magnetic feature tracking suite, to analyze the destruction of solar small-scale magnetic flux. We track a sequence of high resolution MDI magnetograms to find the destruction rates in a patch of quiet sun. We state criteria for defining the individual magnetochemical destruction mechanisms of merging, cancellation, and disappearance, and determine the contribution of each process to the removal of detected flux from the photosphere. Destruction mechanisms are important to determine because, together with formation mechanisms, they provide information as to the nature of the small-scale dynamo. We present preliminary results and discuss the implications of these rates on models of quiet-sun magnetic flux generation.
SP41B-03 0830h
Spectro-polarimetry of the G band
Narrow-band filter imaging in the G band at 430 nm has been used to track the evolution of small-scale magnetic field elements for more than two decades. Because of the presence of many lines of the CH molecule, and the relatively high contrast at this short wavelength the G-band region is exceptionally suitable for this task. However, despite the frequent use of G-band brightness as magnetic field proxy it has not yet been well established what the precise mechanism is that makes the small scale magnetic elements appear bright. In particular, it is unclear why there is no one-to-one correlation between G-band brightness and magnetic field, as established from co-spatial magnetograms in atomic lines. To obtain a better understanding of the elusive G-band brightening mechanism we obtained high spatial- and spectral resolution spectra of the G-band region in Stokes I and V at the Dunn Solar Telescope on Sacramento Peak. We use the molecular Zeeman effect to determine line-of-sight magnetic field strength directly in the CH lines that provide most of the opacity in the G band, avoiding difficulties with co-aligning images and magnetograms taken seperately. We compare our observations with radiative transfer modeling of the Stokes profiles in snapshots of a magneto-hydrodynamic simulation of solar convection.
SP41B-04 0830h
Multi-scale analysis of solar structures: flatness functions of magnetograms
The fine small-scale structure of the solar surface becomes more pronounced as the observational techniques improve. Complex filigree structures of solar granulation, sunspots, photospheric magnetic and velocity fields can not be described adequately by a single parameter (e.g., filling factor, fractal dimension, or power law index, etc.). Methods which incorporate parameters that are a function of scale (multi-scale methods) to describe the complexity of a field under study should be involved. The multifractal approach offers such a possibility. Multifractality can manifest itself through the shape of a flatness function defined as a ratio of the sixth structure function to the cube of the second structure function (Frisch 1995). For monofractal structures, the flatness is constant with a scale, whereas for multifractal structures the flatness grows as a power-law when the scale decreases. Calculating the flatness functions for SOHO/ MDI high resolution magnetograms of active regions from the catalog available at http://www.bbso.njit.edu/~avi/MDI_catalog.htm we found that the flatness function is unique for each active region. The power-law index, as well as the range of the flatness growth (the scale interval of multifractality), vary for different active regions that indicates the difference in mutlifractality. We found that flare-quiet active regions tend to possess lower degree of multifractality than flaring active regions do. The increase in multifractality is a signal that a magnetic structure is driven to a critical state, thus gaining tangential discontinuities of various length scales. The above suggestion about the relation between the degree of multifractality and level of flare productivity seems to be reasonable and deserves further investigations.
http://www.bbso.njit.edu/~avi/
SP41B-05 0830h
Calcium Circumfacules: New Findings About a Neglected Phenomenon
In 1903, Hale and Ellerman noted faint, elliptical dark regions surrounding CaII K232 plages. Deslandres in 1910 showed these features to be more prominent in CaII K3 spectroheliograms and named them circumfacules. In 1930, d'Azambuja found them to be strikingly prominent in CaII 8542 Å spectroheliograms. Bumba and Howard in 1965 suggested that the calcium circumfacules are composed of broad dark features corresponding to dark Hα fibrils. They noted that the visibility is greatest at the time of maximum K plage brightness. The small handful of available descriptions of this phenomenon leave one with the impression that the calcium circumfacules are manifestations of dark fibrils fanning out from the edges of plages to form the outermost chromospheric boundaries of active regions. Many questions remain: Why are they most prominent in 8542 Å? Are they really fuzzy dark fibrils or something different? Are they associated with the diffuse, mainly horizontal chromospheric magnetic field surrounding some plages? What is their effect on sun-as-a-star spectral irradiance measurements? Daily full disk observations of the 8542 Å line have been made at NSO since 1996. Using these data, and new SOLIS vector spectromagnetograph 8542 Å observations of Stokes I and V line profiles, these and other questions are addressed. The National Solar Observatory is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under cooperative agreement with the National Science Foundation.
SP41B-06 0830h
The correlation between features in the solar spectrum near Mg II and photospheric magnetic fields
During the HRTS-9 flight, spectrograms and spectroheliograms where obtained of the quiet sun, quiet limb, plage, and sunspots. Previous analysis of these observations required the correction of a small set of spectra for instrumental distortions and the absolute intensity calibration. We have applied these corrections to a larger portion of the HRTS-9 observations where the spectrograph slit was rastered across a small region of the sun along the solar equator. This set of corrected spectrograms has allowed us to generate high spatial and spectral resolution spectroheliograms of the observed quiet and active portions of the sun. In addition, with use of a magnetogram taken while the flight was in progress we have examined the relationship between the photospheric magnetic field and both Mg II emission at 280 nm and absorption features in the nearby solar spectrum due to both neutral and singly ionized species. In this presentation we will present our high resolution spectroheliograms as well as results showing the relationship between the magnetic field and several specific spectral features.
SP41B-07 0830h
Solar Magnetic Flux as a Function of Disk Position over the Solar Cycle
A novel analysis of a SOHO/MDI full-disk magnetogram time series from March 1996 to November 2004 is presented. Each of the 26,052 magnetograms in the series are segmented into sectors of constant Μ = cos θ, each sector having a width of ΔΜ = 0.05. Within each sector, a histogram of signed magnetic flux density, corrected for the line-of-sight angle θ, is compiled. For each magnetogram we thus obtain a distribution of signed magnetic flux density as a function of Μ. Summing the signed flux in each Μ bin gives the total signed flux as a function of Μ. Plotting these totals for each Μ-sector as a function of time over the course of Solar Cycle 22 reveals that cycle minimum and maximum are differentiated only by the magnitude of the flux distributions. In other words, in contrast to analogous plots of flux versus heliocentric latitude, there is no discernible pattern, or "Butterfly Diagram", of flux seen on the solar disk from Earth. The finding is relevant to investigations of total solar irradiance (TSI) since it is known that the primary cause of the ~ 0.1% TSI variation over the solar cycle is the distribution of non-sunspot magnetic flux at smaller Μ-values (so-called "faculae").
SP41B-08 0830h
Transport of Poloidal Flux Along Subphotospheric Flux Ropes: Photospheric Signatures
We consider the transport of poloidal (locally azimuthal) magnetic flux along a subphotospheric flux rope, which is anchored in the convection zone. We perform 3-D MHD simulations, in which a straight cylinder is initialized using a number of different model flux ropes. We use two distinct electric current profiles, one with zero and the other with nonzero net toroidal (axial) current. The poloidal flux is increased by increasing the toroidal current at the lower footpoint, and the subsequent dynamics are studied. Simulations are carried out for uniform and nonuniform background plasmas. We discuss results with the emphasis on the expected observable signatures of the transport of poloidal flux or equivalently, magnetic helicity, across the photosphere. Work supported by ONR.
SP41B-09 0830h
The Solar Oxygen Abundance, and the Rare Isotopes of C and O, Derived from Infrared Spectra of Carbon Monoxide
A detailed abundance analysis is presented for solar oxygen based on the ΔV=1 fundamental (4.6~Îœm) and ΔV=2 (2.3~Îœm) first-overtone rovibrational bands of carbon monoxide observed above the Earth's atmosphere at very high spectral resolution and high signal-to-noise by the Shuttle-borne ATMOS Fourier transform spectrometer (FTS). Additional observations to define the reference photospheric thermal structure were taken of the CO fundamental bands in an atmospheric window at 2145~cm-1 (4.6~Îœm) using the 1~m FTS of the McMath-Pierce telescope at Kitt Peak and a fast tip/tilt image stabilization system. The latter allowed measurements at the extreme limb where the highly slanted rays probe into the outer layers of the photosphere. High spatial resolution "movies" of weak CO lines at disk center taken under excellent seeing conditions with the Infrared Imaging Spectrometer (IRIS), also on the McMath-Pierce telescope, further constrained thermal and velocity fluctuations in the layers in which the abundance-sensitive CO lines form. This work is meant to complement a series of recent studies which have revised the previously recommended solar oxygen abundance downward by nearly a factor of two; although in fact our conclusions do not support such a revision. The oxygen abundance recovered in the present work is 700±70~ppm (parts per million relative to hydrogen) compared with the proposed downward revision to 460±60~ppm, and the recommended value of 650±100~ppm of a decade ago. In our analysis, a fixed C/O ratio of 0.5, derived in independent work, was assumed; so the associated carbon abundance is 350~ppm. New accurate values for the solar abundance ratios of the rare isotopes of C and O also are reported: 12C/13C= 70, 16O/17O= 400, and 16O/18O= 2000. All three ratios are lower than terrestrial or meteoritic values (indicating higher isotopic abundances). We find no evidence in the ATMOS3 spectra for measurable 14C16O lines.
SP41B-10 0830h
A "Toy" Simulation of Total Solar Irradiance Variations
Recently, we have developed a method for deducing the total solar irradiance S from sunspot area AS using a finite impulse response FIR which, when convolved with AS, produces S (Preminger & Walton 2005, JGR, submitted). In an effort to gain physical insight into the meaning of the FIR, we have produced a simple model of the solar cycle with the following characteristics: (1) nd sunspots per day are generated, each with a fixed area AS = 500 millionths of the solar hemisphere; (2) sunspots decay exponentially with time constant Ï„S = 10 days; (3) decayed sunspot area becomes faculae, which in turn decay with a time constant Ï„F = 45 days. These parameters were deduced from various characteristics of the actual solar cycle. Each sunspot is generated at a random solar longitude, and the faculae remain at the same longitude as the sunspots. Latitude variation is not modeled; that is, they are always zero. We allow nd to vary as a simple cosine bell from 0 up to nd,max. Simple models of sunspot and facular contrast are used to compute a pseudo-TSI. When nd,max=1, the resulting model reproduces a few of the observed characteristics of the solar activity cycle; e.g., the projected sunspot and facular area peak at about 1500 and 45,000 parts per million of the solar disk. If we use this simple model to compute a FIR, it has a very similar shape to the one found empirically from the actual measured S and AS. The model FIR is also independent of nd,max over the range 0.1 to 10. It is missing some qualitatively important characteristics, however, in particular the fact that S actually begins to rise some time before AS; we are investigating refinements to our model which might reproduce this property of the empirical FIR.