Type II Solar Radio Bursts : Extraction of Shock Parameters and Detailed Comparison of Theory with Observations

Details Type II Solar Radio Bursts : Extraction of Shock Parameters and Detailed Comparison of Theory with Observations Type II Solar Radio Bursts : Extraction of Shock Parameters and Detailed Comparison of Theory with Observations

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh54c..07h&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SH54C-07

Physics

Plasma Physics

[7534] Solar Physics, Astrophysics, And Astronomy / Radio Emissions, [7847] Space Plasma Physics / Radiation Processes, [7924] Space Weather / Forecasting

Scientific paper

We use the current interplanetary type II theory and a data-driven solar wind model to simulate dynamic spectra of type II bursts. We start by developing techniques and performance metrics for extraction of shock parameters from artificial data sets. An iterative downhill simplex method is used, which compares two dynamic spectra and quantitatively assesses and then improves the agreement using two performance metrics; the first is based on the correlation function and the second is based on a normalized difference. By maximizing the agreement we are able to extract the input model shock parameters to within 30% or better when using model solar winds of increasing complexity. When using a realistic solar wind model, the parameters are recovered very accurately, generally to within a few percent of the correct solution. We then quantitatively compare the theory with observations and extract the parameters of the shocks for three well observed type II events. We first obtain good qualitative and semi-quantitative agreement (40-50% correlations) between the predicted and observed dynamic spectra using estimates of shock parameters from LASCO/SOHO coronal mass ejections (CME) observations. The iterative downhill simplex method with the two assessment parameters then extracts model shock parameters that increase the agreement between theory and observation in terms of relative flux levels, spectral intensifications, and drift rates. The shock parameters agree qualitatively and semi-quantitatively with those estimated from CME observations (speed, size and expansion index) for two events. Quantitatively, the simulated radio emission is typically overpredicted for each event by around 5 dB. Analysis of the third event leads to improved agreement for only a range of times and frequencies in the dynamic spectra, and leads to an implausible shock size. The theory and methods show great potential for space weather prediction and remote inference of CME-driven shock parameters.

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