New Frontiers in Understanding the Structure of the Sun's Chromosphere II

SPA-Solar and Heliospheric Physics [SH]

SH12A CC:222 Monday 1030h

Presiding: S W McIntosh, Southwest Research Institute; S M Jefferies, University of New Mexico, Maui Scientific; B DePontieu, Lockheed Martin Solar and Astrophysics Laboratory

SH12A-01 INVITED 10:30h

Multi-dimensional Radiation MHD as a Tool to Understanding Waves in Realistic Magnetic Topologies of the Solar Chromosphere

* Carlsson, M (mats.carlsson@astro.uio.no) , Institute of Theoretical Astrophysics, P.O. Box 1029 Blindern, Oslo, 0315 Norway

Advances in computing capabilities have made it possible to perform multi-dimensional radiation MHD simulations with a realistic description of the physics in the photosphere. In the chromosphere non-LTE becomes important and the choice is between realistic physics in one dimension and approximations to the non-local radiation in multi-dimensions. We will here discuss such simulations from a methodological vantage point. We will discuss how we can make such simulations to study how waves are excited in the solar convection zone, how they propagate through the chromosphere and transition region and undergo mode conversion, refraction and reflection in various magnetic field topologies. We will also discuss the limitations of observational diagnostics with respect to wide response functions, non-locality and non-equilibrium effects.

SH12A-02 10:45h

Response functions of chromospheric lines to changes in temperature and magnetic field

* Uitenbroek, H (huitenbroek@nso.edu) , National Solar Observatory Sacramento Peak, P.O. Box 62, Sunspot, NM 88349

Typical densities in the chromosphere are four orders of magnitude smaller than in the underlying photosphere. For this reason the chromosphere is mostly transparent in the optical, aside from wavelengths in the centres of a handful of strong lines. Few viable diagnostics are, therefore, available for routine chromospheric temperature, velocity and magnetic field measurements. Interpretation of these diagnostics is problematic because the low density environment favours radiative line excitation over collisional excitation. As a result, chromospheric lines generally require non-LTE radiative transfer solutions to determine the population of their upper and lower levels, and their formation heights. I will present Non-LTE response functions of several chromospheric lines to investigate the sensitivity of the intensity profile of these lines to changes in temperature and magnetic field. Although these response functions are model dependent they give a first indication of the heights at which we can expect to measure magnetic field strength and geometry in the chromosphere. We will also discuss the sensitivity of the response functions to different solar models

SH12A-03 11:00h

Millimeter-Interferometer Observations of Oscillations in the Solar Chromosphere

* White, S M (white@astro.umd.edu) , Department of Astronomy, University of Maryland, College Park, MD 20742 United States
Loukitcheva, M , Astronomical Institute, St Petersburg University, St Petersburg, 198504 Russian Federation
Loukitcheva, M , MPIS, Max-Planck-Institut fuer Sonnensystemforschung, Katlenburg-Lindau, D-37191 Germany
Solanki, S K , MPIS, Max-Planck-Institut fuer Sonnensystemforschung, Katlenburg-Lindau, D-37191 Germany

The use of millimeter-interferometer data for the study of chromospheric structure and dynamics is tested using 85 GHz observations with the 10-element Berkeley-Illinois-Maryland Array (BIMA). Interferometer data have the advantage over single-dish data that they allow both high spatial resolution and dense temporal sampling simultaneously. However, snapshot imaging of the quiet solar atmosphere with a small number of dishes is challenging. We demonstrate that techniques are available to carry out this task successfully. We compare observations of quiet Sun, active region and coronal hole targets using images with 10 arcsec resolution at 15 second cadence. The brightest features in the images are typically 1500 K above the background level, with a snapshot noise level of order 100 K. We use extensive tests to determine whether oscillation power can be recovered from sequences of snapshot images and show that they can down to quite weak levels. Intensity oscillations with significant power in the frequency range 1.5-8.0 mHz are found in the quiet-Sun and active region targets. For the quiet-Sun region we use the spatially-resolved time series to investigate the properties of network boundaries and cell interiors (internetwork) separately. In agreement with investigations at other wavelengths, the millimeter data show that power in the network tends to be at periods of 5 minutes and longer while power in the internetwork is present also at shorter (3-minute) periods.

SH12A-04 11:15h

MHD Waves Propogation and Heating of Solar Atmosphere

* Bharti, L (lokesh_bharti@yahoo.co.in) , Dept.of Physics, College of Science, Mohanlal Sukhadia University, Dept.of Physics, College of Science, Mohanlal Sukhadia University, Udaipur, Raj 313001 India
Jain, R (rajmal@prl.ernet.in) , Physical Research Laboratory, Physical Research Laboratory, Navrangpura, Ahemdabad, Guj 380009 India
Joshi, C (joshichandan_79@rediffmail.com) , Dept.of Physics, College of Science, Mohanlal Sukhadia University, Dept.of Physics, College of Science, Mohanlal Sukhadia University, Udaipur, Raj 313001 India
Jaaffrey, S N (sna_jaaffrey@yahoo.co.in) , Dept.of Physics, College of Science, Mohanlal Sukhadia University, Dept.of Physics, College of Science, Mohanlal Sukhadia University, Udaipur, Raj 313001 India

We examine oscillations in isolated three bright points co-temporal and co-spatial in photosphere and chromosphere in G-band and Ca II K line. Wavelet analysis was used to study wave packets and identify traveling magnetohydrodynamic waves. In general, it is thought likely that the photosphere and chromosphere oscillates in response to forcing by p-modes and granular buffeting, but they are also influenced strongly by presence of magnetic fields. The observed oscillations reveals evidence for kink-mode waves, traveling up through the chromosphere and coupling with sausage-modes waves. This provides a means for energy depositing in the upper chromosphere.

SH12A-05 11:30h

Structure and Organization of the Upper Chromosphere

* Korendyke, C M (ckorendyke@ssd5.nrl.anvy.mil) , Naval Research Laboratory, 4555 Overlook Ave, Washington, DC 20375
Landi, E , Naval Research Laboratory, 4555 Overlook Ave, Washington, DC 20375
Vourlidas, A , Naval Research Laboratory, 4555 Overlook Ave, Washington, DC 20375

Over its past two flights, the VAULT sounding rocket instrument obtained a series of subarcsecond resolution images of the solar disk. These Lyman alpha images resolve and separate structures in the upper chromosphere. The observed plasmas are concentrated in larger diameter, optically thick loops. The images taken near the limb unambiguously identify the height of the upper chromosphere in the quiet sun. An unexpected level of evolution and activity is present in the "quiet sun" at small spatial scales. The third flight of the payload will investigate the interconnectivity of the observed structures with the photosphere.

http://wwwsolar.nrl.navy.mil/rockets/vault/index.html

SH12A-06 INVITED 11:45h

The Next Generation of Chromospheric Measurements

* Tarbell, T D (tarbell@lmsal.com) , Lockheed Martin Solar & Astrophysics Lab, Dept ADBS, Bldg 252 3251 Hanover St., Palo Alto, CA 94304 United States

I discuss the new measurements which we know will happen, from missions or observatories which are being developed now, as well as the measurements which should happen for further progress. The future is promising, with new missions such as Solar-B, SDO, and SunRise, and new or upgraded observatories, such as SVST, DOT, GREGOR, ATST, and FASR. I also point out significant needs for the future, such as detailed chromospheric spectroscopy of the type which would have been provided by NEXUS or similar instruments.