摘要:

One‐dimensional resistive MHD and hybrid simulations are carried out to study the manner by which variations of the interplanetary magnetic field (IMF) direction generate dynamic pressure pulses in the magnetosheath. The reaction of the magnetosheath to the temporal IMF variation is modeled as the interaction between the bow shock (BS) and an interplanetary rotational discontinuity (RD), an Alfven wave pulse (AW), or an Alfven wave train. The resistive MHD simulation indicates that the arrival of an RD produces two time‐dependent intermediate shocks (TDISs) and two slow shocks downstream of the bow shock, which propagate through the magnetosheath toward the Earth's magnetopause. An enhancement of plasma density is present throughout the TDISs and slow shocks. A plasma dynamic pressure pulse is formed in this region. In the hybrid simulation, the two TDISs are replaced by rotational discontinuities. For a bow shock with a shock normal angle θBn>45°, the pulse in the dynamic pressure ρV2causes the total pressure (P+B2/2μ0+ ρV2) in the magnetosheath to increases by about 0–100% of the background value. The strength of the pressure pulse increases with the field rotation angle across the incident rotational discontinuity, while it decreases with the Mach number or upstream plasma beta of the bow shock. The pressure pulse propagates toward the magnetopause with nearly a constant amplitude. On the other hand, the BS/AW interaction leads to the generation of Alfven waves downstream of the bow shock, and large‐amplitude dynamic pressure pulses are generated in the downstream Alfven wave. Pressure pulses impinging on the magnetopause may produce magnetic impulse events (MIEs) observed in the high‐latit

ISSN:0148-0227    

DOI:10.1029/95JA02985

年代:1996

数据来源: WILEY

摘要:

Radio wave emission sources in the interplanetary medium (IPM) include type II and type III radio bursts and emission from planetary bow shock regions. The presence of electron beams in a range of energies suggests the possibility of a ring beam‐plasma interaction as a mechanism for the generation of radio waves at both the fundamental and the second harmonic of the background electron plasma frequency. In this paper, ring beam‐plasma interactions are simulated for the conditions of the IPM, ωe/Ωe= 100 to 200. In these simulations, the ring beam‐plasma interaction couples the electrostatic Langmuir waves at the fundamental plasma frequency to electromagnetic waves; harmonic radiation is produced by an electrostatic trapped electron instability. Mode conversion processes permit theZmode radiation generated through these instabilities to be converted to theXmode. Examination of both theory and observations suggests the ring beam‐plasma interaction as a candidate for many of the radio phenomena i

ISSN:0148-0227    

DOI:10.1029/95JA02026

年代:1996

数据来源: WILEY