Coronal Holes/Solar Wind Posters
Presiding: L Ofman, Catholic University of America; M Laming, Naval Research Laboratory
SP51B-01 0830h
Solar Wind Forecasting with the SOLIS-VSM
A web based solar wind forecasting resource applying a simple empirical model with SOLIS-VSM (Vector Spectromagnetograph) data is presented here. The solar wind empirical model uses the locations of coronal holes on the observed solar disk to forecast an estimated solar wind velocity at Earth. The model coefficients are estimated minimizing the difference between 10+ years of coronal hole images and the corresponding measured solar wind velocities. The coronal hole training data set was derived from Kitt Peak Vacuum Telescope (KPVT) He I 1083 nm images and photospheric magnetograms. The model can forecast up to 8.5 days in advance. The VSM estimated coronal hole images are derived from daily full-disk photospheric magnetograms and He I 1083 nm spectroheliograms using an automated coronal hole detection algorithm. Daily solar wind forecasts are planned to be automated using SOLIS-VSM data and made available publicly during the year 2005. The coronal hole data used here was compiled by K. Harvey and F. Recely using National Solar Observatory (NSO) KPVT observations under a grant from the National Science Foundation (NSF). Solar wind data utilized for this project is provided on the Internet at http://nssdc.gsfc.nasa.gov/omniweb/. This work is carried out through the NSO Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program. This research was supported in part by the Office of Naval Research Grant N00014-91-J-1040. The NSO is operated by AURA, Inc. under a cooperative agreement with the NSF.
SP51B-02 0830h
Study of Small-Scale Dynamics in Coronal Holes and Quiet Regions from TRACE/BBSO Observations
We made high-spatial and temporal resolution TRACE UV/EUV observations of coronal holes and quiet regions in September 2004 jointly with BBSO Hα and magnetogram observations. From the observations, we study the dynamics, structure, and magnetic setting of small-scale explosive events such as microflares, macrospicules, and mini-filament eruptions, both in coronal holes and in quiet regions. These event are of interest because they may play an important role in coronal heating in these regions. These events are thought to result from explosions in fine-scale mixed-polarity magnetic fields in the network. However, even though the fine-scale magnetic structure of the network is expected to be essentially the same in both regions, coronal holes and quiet regions are quite different in that coronal holes show open field magnetic structure and are the source of fast solar wind while quiet regions have closed magnetic fields and are the source of slow solar wind. Study of small-scale dynamic events is important for solving the problem of coronal heating in the regions and for understanding whether the heating process is different in coronal holes than in quiet regions. We report on the time evolution of dynamics of these events in relation to the structure and evolution of the network magnetic flux at their footpoints. We also report whether any differences between the events in coronal holes and quiet regions are seen.
SP51B-03 0830h
Scientific Studies Using MACS: Coronal Reconnection Measurements and Solar Wind Acceleration Diagnostics
We have developed an instrument and an observational technique that exploits the shape of the K-coronal visible spectrum, 380-450 nm, to determine simultaneously both the thermal electron temperature and its bulk flow speed (see Reginald et al poster, this conference). For a given electron density along the line of sight, the shape of the K-coronal visible spectrum is influenced by the thermal electron temperature and its bulk flow speed. The bulk flow speed of the coronal electrons in the solar wind causes a Doppler-shift in the shape of the K-coronal spectrum depending on the magnitude of the speed. The simple reason for the red shift is that the wavelength-independent Thomson scattered coronal electrons observe a red-shifted photosphere as they move away from the Sun at the bulk flow speed. In addition, recent models have shown that identical streamers could be distinguished through their influence on the shape of the K-coronal visible spectrum in different wavelength regions. Modeling efforts have expanded to include a scenario where the observing line of sight passes through a coronal reconnection area. Using realistic parameters for the reconnection, and assuming that it produces bulk electron flows both toward and away from the Sun, our preliminary results indicate that the resulting red and blue-shifted K-coronal spectrum should be detectable with the MACS instrument.
SP51B-04 0830h
MACS for global measurements of the thermal electron temperature and its bulk flow speed in the low solar corona through ground based experiments
The determination of the radial and latitudinal temperature and wind profiles of the solar corona is of immense importance in understanding the coronal heating mechanism and the dynamics of the coronal features. We have built MACS-1 (Multi Aperture Coronal Spectrometer); a fiber optic based spectrograph, to study the coronal properties during the total solar eclipses of August 1999 in Elazig, Turkey and June 2001 in Lusaka, Zambia, through the measurement of the K-coronal spectrum. In these experiments we have successfully demonstrated the feasibility of simultaneously measuring both the thermal electron temperature and its bulk flow speed at multiple locations on the solar corona. Measurement of these properties radially in the solar corona could provide valuable information on the solar wind acceleration in the low corona. We are now in the process of conducting a similar experiment on the low solar corona with an advanced spectrograph MACS-2 interfaced with the SolarC coronagraph at the Mees Solar Observatory in Haleakala, Hawaii. This if proven successful would provide an ability to measure simultaneously and globally the above coronal properties on demand.
SP51B-05 0830h
The Complexity of Equatorial Coronal Holes
We will investigate the multi-thermal intensities, flow structures and extrapolated magnetic structures in an massive equatorial coronal holes that crossed the solar disk in early November of 1999. We will use a large suite of observations from the MDI and SUMER instruments on SOHO. We will use the insight developed from our understanding of the multi-thermal coronal hole topography to propose a consistent picture of solar wind structure at the base of the Sun-Earth Connection.
SP51B-06 0830h
Electron Heating in the Solar Wind
We report on progress in modeling the elevated charge states observed in the fast solar wind with respect to the coronal hole source region. Improvements include the incorporation of new atomic data for dielectronic recombination of L-shell ions in our modeling, following the recent work of Badnell and collaborators. A second issue considered will be that of magnetic field inhomogeneity (as opposed to plasma density inhomogeneity) as an agent of instability. High temperature ions gyrating in curved magnetic field produce local anisotropies in their velocity distribution function, which in turn are unstable to the generation of lower hybrid waves. These waves then damp by heating electrons, giving rise to the observed increase in ion charge state. Work supported by NASA LWS NNH05AA05i and by the NRL/ONR Solar Magnetism and the Earth's Environment 6.1 Research Option.
SP51B-07 0830h
Solar Cycle Variations of Coronal Hole Properties
As of early 2005, we have measured with the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) the physical properties of at least 136 large coronal holes that produced a variety of high-speed solar wind conditions at 1 AU. UVCS has been used to observe O VI (103.2 and 103.7 nm) and H I Lyman alpha (121.6 nm) emission lines as a function of heliocentric distance in coronal holes since 1996. The analysis of their spectroscopic parameters allows us to identify similarities and differences among coronal holes at different phases of the solar cycle. From such measurements we can derive plasma parameters (densities, temperatures, velocity distribution anisotropies, and outflow speeds) for O5+ and protons as a function of heliocentric distance in the coronal holes. These properties, combined with other observed quantities such as white-light polarization brightness and the more-or-less unipolar magnetic fluxes measured on-disk, let us map out the "allowed parameter space" of coronal hole plasma properties more fully than ever before. We will present the solar cycle dependence of the above plasma parameters from the last solar minimum in 1996 to present and compare them, where possible, with the in situ solar wind properties. We will also present an update on the pattern that is beginning to emerge, i.e., coronal holes with lower densities at a given heliocentric distance tend to exhibit faster ion outflow and higher ion temperatures. This information will thus be used to set firm empirical constraints on coronal heating and solar wind acceleration in coronal holes. In 2005, the polar coronal holes have not yet evolved to the fully quiescent minimum state seen in 1996-1997, though the next solar minimum is expected to occur in about 1.5 to 2 years. This work is supported by NASA under Grant NNG04GE84G to the Smithsonian Astrophysical Observatory, by the Italian Space Agency, and by PRODEX (Swiss contribution).
SP51B-08 0830h
The He I 1083 nm line in Coronal Holes, a study with high spectral resolution.
The He 1083 nm line (He), formed in the upper chromosphere, is used for observations of coronal holes (CH) near their origins at the solar surface. Weak He 1083 nm profiles in CHs show some peculiarities such as asymmetry, broadening, and a different ratio between the spectral components. These effects are small so that the influence of disturbing noise and approximations in reduction processes are important for the results. In this research we have used low noise and high spectral resolution observations carried out at the Kitt Peak McMath-Pierce telescope to establish the key characteristics of the He profile in CHs. For accurate reduction we corrected the He profile for spectral blending from water vapor and weak solar lines. We confirm our previous result, based on imaging-spectroscopy data from the Kitt Peak Vacuum Telescope, regarding broadening of the He line in CHs and explain previous instability of CH contrast in our procedure for CH recognition as an influence of hidden photospheric lines.