New Frontiers in Understanding the Structure of the Sun's Chromosphere III Posters
Presiding: S W McIntosh, Southwest Research Institute; S M Jefferies, University of New Mexico, Maui Scientific; B DePontieu, Lockheed Martin Solar and Astrophysics Laboratory
SH13C-01 1330h
Magnetic Topology and Wave Propagation in the Solar Atmosphere
We analyze a 9 hr sequence of simultaneous, high resolution, 21 s cadence SVST G-band and K-line solar filtergrams plus magnetograms of lower cadence and resolution. The data include both network and internetwork areas (Berger and Title 2001, Cadavid, et al. 2003, Lawrence, et al. 2003). Time series of the G-band and K-line data are compared after filtering by a Morlet wavelet transform of period 2.5 min. On the average, the K-line signal is delayed by several seconds after the G-band signal Δ T = 8.6 ± 0.1 s for weak (|BZ| < 50 G) magnetic field in internetwork but Δ T = 7.2 ± 0.1 s for weak field in an area including network. The internetwork has no strong fields, but in network (|BZ| > 80 G) the mean delay time drops to Δ T = 3.4 ± 0.3 s. This is consistent with results by McIntosh, Fleck and Tarbell (2004) using TRACE 1600Ã… and 1700Ã… UV image series. Our principal result is that the time delay is greater in the internetwork than in the network by 1.4 ± 0.1 s, even for the same local magnetic field strength. This suggests that the difference must be an effect of the field topology. Spatial maps of time delays, in comparison to maps of such topological quantities as the height in the solar atmosphere at which the plasma β = 1, offer additional details of the relationship between wave propagation and the magnetic fields in the solar atmosphere. This work was supported in part by grants NSF-ATM 9987305 and NASA-NAG5-10880. The SVST is operated by the Swedish Royal Academy of Sciences at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Berger, T.E. and Title, A.M. 2001, ApJ, 553, 449. Cadavid, A.C., et al. 2003, ApJ, 586, 1409. Lawrence, J.K., et al. 2003, ApJ, 597, 1178. McIntosh, S.W., Fleck, B. and Tarbell, T.D. 2004, ApJ, 609, L95.
SH13C-02 1330h
Spicules, mass transfer, oscillations, and the heating of the corona
The mass moving in chromospheric spicules is enough to replace the corona in a brief time, so understanding the dynamics of spicules is important for understanding the support and heating of the solar corona. We have undertaken a program involving simultaneous high-resolution observations in various chromospheric visible lines (H-alpha, Ca II H, and G-band, as well as Dopplergrams) using the Swedish Solar Telescope on La Palma, ultraviolet chromospheric, transition-region, and coronal lines (Fe IX/X 171 A, Lyman-alpha 1216 A, and continuum/C I/C IV 1600 A) using NASA's TRACE, and ultraviolet chromospheric and transition-region lines (Si II 1533, C IV 1548, and Ne VIII 770) using SUMER on SOHO. Our first coordinated observing run, in May 2004, yielded a variety of images that are under study, especially for the morphological statistics and dynamics of spicules. The energy transfer through the chromosphere is relevant to the overlapping investigation of coronal heating through rapid (1Hz range) oscillations of coronal loops as observed at total eclipses by Williams College expeditions. This research is supported by NASA grant number NNG04GK44G to Williams College. TRACE analysis at SAO is supported by a contract from Lockheed Martin. SOHO is a project of international cooperation between ESA and NASA.
SH13C-03 1330h
Active Region Oscillations and Their Relation to the Magnetic Field Topology
In this contribution we present an analysis of time sequences of MDI intensity and Doppler velocity together with simultaneous filtergrams taken by TRACE at 1700A in an active region. The high frequency halos found in MDI velocity and the deficiency of high frequency power sampled at the height of the TRACE UV filter around the active region can be explained by an interaction of the acoustic wave field with the magnetic field of the active region. From a magnetic field extrapolation we calculate the plasma β for the complete TRACE FOV up to the base of the corona. The contours giving the location of β approximately 1 where h=500 km agree very well with the decrease in 1700A high frequency power.
SH13C-04 1330h
Travel Time and Phase Analysis of Waves in the Lower Solar Chromosphere
In an effort to better understand how the chromospheric plasma and magnetic fields are guiding, converting and dissipating acoustic waves, we analyze high-cadence time series taken in Na I D2 589.0 nm and K I 769.9 nm that were obtained with the Magneto Optical Filters at Two Heights (MOTH) experiment at the South Pole in January 2003. These data are complemented by a very high spatial resolution time series taken in Na D with the Swedish Vacuum Solar Telescope in June 1992. The travel time maps, power maps, and phase diagrams show some unexpected behaviour, in particular in and around active regions.
SH13C-05 1330h
The TRACE Inter-Network Oscillations (INO) Program I: Probing Chromospheric Topography
We will present results of the TRACE Inter-Network Oscillations (INO) observing program from 2003 to the present. The INO program uses near-simultaneous observations in the 1600Ã… and 1700Ã… UV continuum pass bands as an acoustic probe of chromospheric structure. In the two years of INO observations we have studied a large number of quiet chromosphere and active regions as well as regions of the chromosphere under coronal holes. In this poster we will discuss the diagnostic methods applied to analyze the INO observations and the key results found, thus far. These diagnostic methods offer us a remote means to study the complex plasma topography of the solar chromosphere.
SH13C-06 1330h
The TRACE Inter-Network Oscillations (INO) Program II: Observations of Limb and Coronal Hole Regions
We will present results of the TRACE Inter-Network Oscillations (INO) observing program from 2003 to the present. The INO program uses near-simultaneous observations in the 1600Ã… and 1700Ã… UV continuum pass bands as an acoustic probe of chromospheric structure. In this poster we will discuss the INO observations of limb, polar and coronal hole regions and show the key results found, thus far. These observations offer us a remote means to study the structure and behavior of the chromopsheric plasma topography at a potential driving base for the heliospheric plasma system.
SH13C-07 1330h
Wavelet Analysis Methods of Oscillatory Power in Chromospheric Lightcurves
The symbiotic relationship between time-series oscillatory power and waves in the chromosphere is studied using several novel wavelet techniques. Theses include automated wave-packet searching routines for large datasets, correlation of wave-packets at multiple heights in the atmosphere, and a full multi-wavelength wavelet-phase analysis (including the cross transform, phase difference and phase coherence). In each study we interpret oscillatory power as a signature of waves in the quiet-Sun chromosphere and relate these wave modes to the underlying photospheric magnetic field.
SH13C-08 1330h
Dynamics of the Magnetic Network on the Sun
Observations have revealed the presence of a rich spectrum of waves with different periods in regions of the solar atmosphere called the "magnetic network" that are dominated by strong magnetic fields. This network is believed to be heated by dissipation of magnetohydrodynamic (MHD) waves, but the MHD processes involved in wave generation, propagation and dissipation are poorly understood. In this work we attempt to identify some of the processes that occur in the network and which contribute to its dynamics and heating. We model the network as consisting of individual magnetic elements or flux tubes, rooted in intergranular lanes, with a typical horizontal size of 100 km. They expand upward and merge with their neighbors at a height of about 600 km. Above this height the magnetic field becomes uniform. An equilibrium configuration based on the above model is constructed by solving the magnetostatic equations in 2-D. Waves are generated in this medium by means of motions at the lower boundary. We focus on transverse driving which generates fast waves within the flux tubes and acoustic waves at the interface of the tubes and the field-free medium, but not otherwise in the field-free gas. The acoustic waves at the interface are due to compression of the gas on one side of the flux tube and expansion on the other. These waves travel upward along the two sides of the (2D) flux tube and enter it, where they become longitudinal waves. For impulsive excitation with a time constant of 120 s, we find that a dominant feature is the creation of vortical motions that propagate upwards. We have identified a new and efficient mechanism for the generation of longitudinal waves and shock formation in the chromosphere. We examine the observational implications of our results and their broad applications to chromospheric heating and activity.
SH13C-09 1330h
Energy Transfer and the Acoustic Wave Packets in Randomly Magnetized Solar Atmosphere
Energy transfer from the acoustic waves and unsteady wave packets to overlying atmosphere strongly depends on the 'magnetic status' of the photosphere and chromosphere regions (Ryutova & Priest, 1993 ApJ, 419, 349; 419, 371 ). Here we concentrate on the magnetic network outside sunspots and active regions, where we distinguish several types of magnetic field topography, determined by the distribution of flux tubes in space and over their physical parameters, non-collinearity of flux tubes, predominance of one polarity elements or balanced distribution of mixed polarities. Magnetic structures in the chromosphere are as well very different and span from different kinds of compact magnetic arcades to "tall" magnetic structures typical to regions underlying the coronal holes. Interaction of waves and wave packets with the ensembles of magnetic flux tubes is accompanied by frequency shift and clear morphological effects in the enhanced emission at chromosphere/transition region level that are different for different regions. For example, over the regions with wide distribution function of non-collinear flux tubes, variation of physical parameters of flux tubes (radius, magnetic field strength, etc.) and their inclinations lead to the spreading of the energy deposition region and its dislocation from the expected site, i.e. site which is directly above the studied magnetic region. The energy density, frequency range, specific properties and location of the enhanced emission ("magneto-acoustic halos") are given in terms of the observable parameters for differently magnetized regions. Obtained results allow quantitative analysis of magnetic effects in the seismology of upper layers of atmosphere.
SH13C-10 1330h
Another Piece of the Elephant: Chromospheric Vector Field Observations
As with most solar observational questions, investigating the structure and role of the chromosphere is one of remote sensing: many investigations describing their "piece of the elephant". The goal is, of course, to form a coherent picture of the state of the magnetized plasma which resides there (or passes through). In this presentation, recent efforts to understand the chromospheric magnetic field structure via direct observation, i.e. chromospheric vector magnetograms, will be presented. Since late 2003, the U. Hawai`i/Mees Solar Observatory's Imaging Vector Magnetograph has routinely acquired spectropolarimetry measurements of active regions across the Na-I 589.6nm line; from the polarization at the line's near-wings approximately 0.007nm from line center we deduce the vector magnetic field. The data are specific to active regions, with the focus being the structure, free energy storage and evolution at that low-chromospheric layer. I will present salient aspects of the observed chromospheric magnetic field structure, to compare and contrast with the picture formed by the other methods in this session.
SH13C-11 1330h
Acoustic Mapping of the Magnetic Canopy in the Solar Chromosphere
We show that high-frequency acoustic waves can be used to map the location where the gas and magnetic pressures of the plasma in the solar chromosphere are comparable. This transition region, which can be considered as a "magnetic canopy" where MHD waves can transform from one type into another, is believe to play a key role in the flow of mass and energy through the chromosphere. Results will be presented from the analysis of 18 (uninterrupted) hours of simultaneous, full-disk, velocity observations using the Ni (676 nm), K (770 nm) and Na (589 nm) Fraunhofer lines (with the SOHO/MDI and MOTH/South Pole instruments), and 106 (uninterrupted) hours of K and Na data (from the MOTH/South Pole instrument). The MOTH data were acquired every 10 seconds and the MDI data every 60 seconds. This work was funded by awards OPP-0087541 and OPP-0338251 from the National Science Foundation.
SH13C-12 1330h
A new Instrument for High-cadence, Multi-height Observations of the Velocity and Magnetic Fields of the Full Solar Disk
We will describe a new instrument that is being built to measure the velocity, intensity and line-of-sight magnetic fields of the full solar disk, simultaneously at four heights in the solar atmosphere with a resolution of 4 arc-seconds and a cadence of 10 seconds. The heart of the instrument is the magneto-optical filter [1] that can be operated using vapor cells containing K, Na, Ca and He. The instrument is also designed to have a high-resolution imaging mode that will provide 1 arc-second resolution over a FOV of 450x450 square arc-seconds. The instrument is scheduled for deployment to South Pole during the Austral summer of 2005/2006. This work is funded by award OPP-0338251 from the National Science Foundation. [1] Cacciani & Fofi, Solar Phys 59, 179 (1978)
SH13C-13 1330h
A Calcium-Based Magneto-Optical Filter
The magneto-optical filter, MOF [1], has been used for imaged Doppler and magnetic field observations of the Sun for nearly three decades. The strengths of the MOF lie in its wavelength stability, its narrow pass-band (approx. 0.005nm) and high throughput. Until recently, its main limitation has been that it has only been available for use with the Na I (sodium) and K I (potassium) D-lines. We will discuss some developments in the technology for building the vapor cells for the MOF and will show preliminary results for a calcium-based MOF. The Ca I line at 422nm is formed in the mid-chromosphere and can thus provide a probe for velocity and magnetic field information for this region. [1] Cacciani and Fofi, Solar Phys. 59, 1978
SH13C-14 1330h
Chromospheric observations in the He 1083nm line - a new instrument.
Photometric, spectroscopic and polarimetric observations in the He 1083 nm line provide important diagnostic information on the structure and dynamics of the chromosphere and the overlying corona. We will describe an imaging instrument, designed to observe the chromospheric He 1083 line, based on a helium magneto-optical filter. The narrow pass-bands and high throughput of the filter make it ideal for making high cadence observations in support of studies of wave propagation in the chromosphere. We will describe the operation of the instrument and present preliminary photometric observations.