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Decimetric Type III Bursts: Generation and Propagation  

Bo Li   Submitted: 2011-08-11 19:53

Simulations are presented for decimetric type III radio bursts at 2fp , where fp is the local electron plasma frequency. The simulations show that 2fp radiation can be observed 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, radiation partly propagates into nearby regions, which are hot because of previous reconnection/evaporation. The profiles of plasma density ne (r) and electron temperature Te (r) in the lower corona (r – R ? lsim 100 Mm) are found to be 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 ne (r) with a large range of scale heights hs , consistent nonetheless for Scenario B with short observed EUV loops. This is relevant to problems with large hs inferred from tall EUV loops. The simulations suggest: (1) ne (r) with small hs , such as ne (r)vprop(r – R ?)–2.38 for flaring regions, are unexpectedly common deep in the corona. This result is consistent with recent work on ne (r) for r ? (1.05-2)R ? extracted from observed metric type IIIs. (2) The dominance of reverse-slope bursts over normal bursts sometimes observed may originate from asymmetric reconnection/acceleration, which favors downgoing beams.

Authors: B. Li, Iver H. Cairns, Y.H. Yan, P.A. Robinson
Projects: None

Publication Status: ApJ Letts, vol 738, L9
Last Modified: 2011-08-12 16:49
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Effects of spatial variations in coronal temperatures on type III bursts  

Bo Li   Submitted: 2011-03-23 15:57

The electron temperature Te and ion temperature Ti in the coronavary with time and location, due to transient and persistent activityon the Sun. A method is developed for include spatial variations ofcoronal temperatures into our quasilinear-nonlinear simulation forcoronal type III bursts. The effects on type III bursts are simulatedfor monotonic temperature variations, and/or for spatially localizeddisturbances in the temperatures. Localized temperature disturbancesare found to have stronger effects than monotonic variations.Importantly, distinct signatures of the Te or Ti disturbancesare found in the dependence on frequency of the 2fp radio spectralcharacteristics, e.g., the maximum flux. The results thus indicatethat coronal type III bursts provide a new tool to probe anddistinguish localized disturbances in Ti or Te in the corona. Inaddition, the presence of localized Te or Ti disturbances may beresponsible for some fine structures in type IIIs, e.g., the fluxmodulations in type IIIb bursts.

Authors: B. Li, Iver H. Cairns, and P.A. Robinson
Projects: None

Publication Status: published on ApJ: Vol 730 (2011) 20; Vol 730 (2011) 21
Last Modified: 2011-03-24 02:58
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Decimetric Type III Bursts: Generation and Propagation
Effects of spatial variations in coronal temperatures on type III bursts

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