Spacecraft Observations of Intense
Electric and Magnetic Field Fluctuations and Associated Earthward Magnetic
Field -aligned Poynting Flux Throughout the Plasma Sheet at 4-6 Re Altitudes
during Major Geomagnetic Storms
Wygant, J
R
wygant@ham.space.umn.edu
School of Physics and
Astronomy, Unviersity of Minnesota, Minneapolis, MN 55455 United States
Way, P
School of Physics and
Astronomy, Unviersity of Minnesota, Minneapolis, MN 55455 United States
Keiling, A
School of Physics and
Astronomy, Unviersity of Minnesota, Minneapolis, MN 55455 United States
Cattell, C A
School of Physics and
Astronomy, Unviersity of Minnesota, Minneapolis, MN 55455 United States
Lysak, R L
School of Physics and
Astronomy, Unviersity of Minnesota, Minneapolis, MN 55455 United States
Temerin, M A
Space Science
Laboratory, University of California, Berkeley, CA United States
Mozer, F S
Space Science
Laboratory, University of California, Berkeley, CA United States
Mende, S
Space Science
Laboratory, University of California, Berkeley, CA United States
Parks, G
Space Science
Laboratory, University of California, Berkeley, CA United States
Brittnacher, M
Geophysics Program,
University of Washington, Seattle, WA United States
Kletzing, C A
Department of Physics
and Astronomy, University of Iowa, Souix City, IA United States
Scudder, J D
Department of Physics
and Astronomy, University of Iowa, Souix City, IA United States
Petersen, W K
Laboratory for
Atmospheric and Space Physics, University of Colorado, Boulder, CO United
States
Russell, C T
IGPP, University of
California, Los Angeles, CA United States
Spann, J
NASA, Headquarters,
Washington, DC United States
Andre, M
Swedish Institute of
Space Physics, Uppsala Division, Uppsala, Sweden
Toivanen, P
Laboratory for Atmospheric
and Space Physics, University of Colorado, Boulder, CO United States
Lotko, W
Thayer School of
Engineering, Dartmouth College, NH United States
Streltsov, A
Thayer School of
Engineering, Dartmouth College, NH United States
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). The
fluctuations have periods ranging from 0.25 to 600 seconds. These spatially
extensive field fluctuations are observed at altitudes of 4-6 Re and last for
10-30 minutes in the spacecraft frame and can exist over the entire 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 (Wygant et al., 2000;Keiling et al., 2000) observations of intense
Poynting flux due to Alfven wave at the outer boundary of the plasma sheet. The
Poynting flux associated with the fields presented herein is directed along the
magnetic field direction towards the Earth and exceeds .25 erg/cm2 . If mapped
to 100 km altitude along converging magnetic field lines, the Poynting flux
peak values can exceed 30 ergs/cm2s. This is sufficient to power some of the
most intense aurora in the Polar 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. Spacecraft potential measurements
indicate the presence of a strong density depletion (<0.1 cm**-3)during
these electric field fluctuations. We will compare these observations of
intense Poynting flux to simultaneously obtained images of the aurora obtained
from Polar and IMAGE spacecraft UVI images . We will also use data from the
four CLUSTER spacecraft obtained during similar plasmsheet crossings to analyze
the spatial-temporal structure of these electric field fluctuations.