Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm51a0805w&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM51A-0805
Physics
2704 Auroral Phenomena (2407), 2712 Electric Fields (2411), 2748 Magnetotail Boundary Layers, 2752 Mhd Waves And Instabilities
Scientific paper
We present observations from the EFI and MFE instruments on the Polar spacecraft obtained during several major geomagnetic storms (Dst<-100 nT)of intense electric field (> 40 mV/m, ptp) and magnetic field fluctuations (40-80 nT, ptp). . These spatially extensive field wave fields are observed at altitudes of 4-6 Re and last for 10-30 minutes in the spacecraft frame and can exist over a large fraction of the spatial extent of the plasma sheet. The fields map to a latitudinal extent on the ground of 4-6 degrees. This is a much larger spatial extent than the previously reported observations of intense Poynting flux due to Alfven wave at the outer boundary of the plasma sheet which were observed to last in the spacecraft frame a period of about 3 minutes and occurred durilng the expansion phase of substorms. The Poynting flux associated with the fields presented herein is directed along the magnetic field direction towards the Earth and exceeds 0.25 erg/cm2 s. If mapped to 100 km altitude along converging magnetic field lines, the Poynting flux peak values can exceed 30 ergs/cm2 s. This is sufficient to power some of the most intense aurora in the UVI data set. Preliminary analysis indicates that the ratio of E/B for these waves is consistent with a mixture of Alfvenic fluctuations interspersed with steady state electric fields closing in the ionosphere through field aligned currents. We will compare these observations of intense Poynting flux to simultaneously obtained images of the aurora obtained from Polar and IMAGE spacecraft Ultravioltet Imagers and the associated estimates of the electron energy flux . The data from the four Cluster spacecraft will be analyzed to provide estimates of the spatial scale sizes of the waves from similar kinds of events.
André Martial
Cattell Cynthia A.
Elphic Richard C.
Frey Harald
Keiling Andreas
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