Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm72d..06d&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM72D-06
Physics
2451 Particle Acceleration, 2455 Particle Precipitation, 2704 Auroral Phenomena (2407), 2740 Magnetospheric Configuration And Dynamics, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
Sudden increases in the solar wind dynamic pressure compress the magnetopuase, leading to significantly enhanced Chapman-Ferraro currents, and a corresponding increase in the magnetic field strength throughout most of the magnetosphere. This is the dominant magnetic effect during the initial phase of storms, particularly so when the IMF is northward at the time of the solar wind dynamic pressure increase. At least four times during the past decade, a sudden, significant step in solar wind pressure occurred when the viewing conditions at Gillam (Canada) were good enough to allow for observations of the proton aurora, and the CANOPUS Gillam Meridian Scanning Photometer was operating. In each case, a virtually instantaneous increase in the proton auroral brightness occurred simultaneously with the ground magnetic signature of the dynamic pressure increase. Here, we focus on one of these three events, for which there is excellent supporting in situ and ground-based observations. Based on FAST satellite transits of the auroral oval before and after the pressure step, it is clear that the enhanced proton auroral intensity results from adiabatic energization, and not an increased effectiveness of the pitch angle scattering process that causes the precipitation. The sudden step in dynamic pressure leads to a sudden change in the magnetospheric topology. This change is communicated to the ionosphere by a transient Alfven wave, the passage of which is clearly detected by the magnetic and electric field instruments on Polar. This Alfven wave causes a brief burst of electron precipitation that results in a transient (3 min.) enhancement of the electron aurora. This "shock aurora'' was recorded by the CANOPUS All-Sky Imager and MSP at Gillam. Events such as this provide us with an excellent opportunity to quantify one way that the solar wind provides energy to the magnetosphere, and to elucidate some important aspects of auroral electron acceleration, and auroral proton pitch angle scattering.
Cogger Leroy L.
Creutzberg F.
Donovan Eric
Ergun Robert
Henderson Matthew
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