Polar spacecraft measured evolution of large scale and Alfvenic Poynting flux during major geomagnetic storms in the inner magnetosphere

Details Polar spacecraft measured evolution of large scale and Alfvenic Poynting flux during major geomagnetic storms in the inner magnetosphere Polar spacecraft measured evolution of large scale and Alfvenic Poynting flux during major geomagnetic storms in the inner magnetosphere

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm21a1672t&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SM21A-1672

Physics

2730 Magnetosphere: Inner, 2764 Plasma Sheet, 2774 Radiation Belts, 7836 Mhd Waves And Instabilities (2149, 2752, 6050), 7846 Plasma Energization

Scientific paper

In this poster we present the first study of the time evolution of the field aligned Poynting flux as determined from spacecraft observation over the onset, main phase and recovery phase of major geomagnetic storms as determined by the DST index. This study uses electric and magnetic field data from the Polar spacecraft taken from April 27 though May 9, 1998 and October 17 through October 27, 2001 while Polar was on the night side of the Earth positioned at a radial distance of 2.5 to 6 Earth radii This study is concerned with two kinds of Poynting flux. The first is Alfvenic Poynting flux ( <3 minutes duration) . The second kind is large scale Poynting flux associated with the convection electric and field aligned current system ( 3 - 40 min.). The peak intensity for large scale Poynting flux shows a moderate increase during active conditions: from ~0.1 mW/m2 during quiet times to ~0.15 mW/m2 during active times. The intensity for Alfvenic Poynting flux shows 1-2 orders of magnitude increase from the lowest values observed during quiet times to the largest values observed during the main phase and recovery phases of the storm. There is significant Alfvenic pointing flux observed preceeding the storm possibly in association with substorm activity. The maximum value of the Alfvenic Poynting flux observed during the storm periods was -0. 1- 0.5 mW/m2. If mapped along converging magnetic field lines to 100 km altitude, these peak Poynting flux values correspond to 10- 50 mW/m2. This value is about a factor of two larger than the typical energy fluxes associated with broad band magnetic field-aligned electrons observed by low altitude spacecraft at low latitudes. This work provides evidence that both Alfvenic and large scale Poynting flux are significant energy inputs into low altitudes at low latitudes. It also provides evidence that Poynting flux in the inner magnetosphere can provide enough energy to power the low altitude acceleration of broad band electrons. We will present particle data from the FAST spacecraft in order to provide measurements of electron energy flux during these storm periods.

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