Physics – Plasma Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh51e..06l&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH51E-06
Physics
Plasma Physics
[7509] Solar Physics, Astrophysics, And Astronomy / Corona, [7534] Solar Physics, Astrophysics, And Astronomy / Radio Emissions, [7847] Space Plasma Physics / Radiation Processes, [7859] Space Plasma Physics / Transport Processes
Scientific paper
Large-scale kinetic simulations are presented for decimetric type III bursts at the second harmonic of the local electron plasma frequency fp. The simulations show that 2fp radiation can be observed remotely at Earth in two scenarios for the radiation's generation and propagation. In Scenario A, radiation is produced and propagates in warm plasmas in the lower corona that are caused by previous magnetic reconnection outflows and/or chromospheric evaporation. In Scenario B radiation is generated in normal plasmas; then due to its natural directivity pattern and refraction, some radiation propagates into nearby regions, which are hot because of previous reconnection/evaporation. The simulations demonstrate that the profiles of plasma density ne(r) and electron temperature Te(r) in the lower corona (r-R&sun; &l˜ 100~Mm) are crucial to whether radiation can be produced and escape at observable levels against the effects of free-free absorption, where r is the heliocentric distance. Significantly, the observed wide ranges of radiation properties (e.g., drift rates) require density profiles with a large range of scale heights, consistent nonetheless for Scenario B with short observed EUV loops. The simulations suggest the following: (1) Density profiles with small scale heights, such as given by offset power-laws like ne(r) ∝ (r-R&sun; )-2.38 for flaring regions, are unexpectedly common in the lower corona. This result is consistent with recent work that directly constrained ne(r) profiles for r ≈ (1.05-2) R&sun; from observed metric type IIIs. (2) The dominance of reverse-slope bursts over normal bursts sometimes observed may be caused by asymmetric reconnection or acceleration, which favors downgoing beams.
Cairns Iver H.
Li Baowen
Robinson Adam P.
Yan Yiguang
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