HR: 0800h
AN: SM51A-0353    [Abstracts]
TI: FAST auroral DC electric field studies using ion data and fields data to provide the full DC E vector
AU: * Hwang, K
EM: kyoung-joo.hwang@dartmouth.edu
AF: Dartmouth College, 6127 Wilder Lab, Dartmouth College, Hanover, NH 03755 United States
AU: Lynch, K A
EM: lynch@birkeland.Dartmouth.EDU
AF: Dartmouth College, 6127 Wilder Lab, Dartmouth College, Hanover, NH 03755 United States
AU: Carlson, C W
EM: cwc@ssl.berkeley.edu
AF: University of California, Space Sciences Laboratory, Berkeley, CA 94720 United States
AU: Peria, W J
EM: peria1@comcast.net
AF: University of Washington, Geophysics Program, Seattle, WA 98195 United States
AB: We present an analysis of auroral FAST perpendicular E data using ion distributions in return current regions to study the full DC E vector and potential structures. While the axial boom measurement is available, its interpretation requires careful use and some assumptions. Our new technique provides an independent measure of this axial component. Our new tool extracts two perpendicular components of electric field, using the electric field data from the field instrument for the spin-plane component of E, and the ion drift measurements for the axial DC E. This allows studies of the full perpendicular DC E vector for the first time with FAST data. In addition the new tool transforms from velocity-based coordinates to north-south, east-west coordinates for analyzing the morphology and structure of the auroral return current region more effectively. With more than fifteen return current region crossings collected at FAST altitudes above 3000 km in either the pre-noon dayside or near midnight sector, three quarters of our data show linearly polarized diverging electric field structures. A significant fraction (almost one quarter) show rotational polarity during large field events. For these rotational events, it is probable that the spacecraft was passing through the edge of elongated quasi-static potential structures. They can also be interpreted as a temporal variation. Generally in many orbits, linear and rotational polarity appear together, one followed by the other, which means the potential structure has a wiggled or droopy shape. Statistical comparison shows several differences between these two different polarizations. (1) When a rotational polarity appears, the correspondence between electron characteristic energy and the potential obtained by integrating E weakens. (2) For linear polarization the electric field vector is likely to be almost perpendicular to the magnetic disturbance, while for rotational polarization the E is not perpendicular to delta-B. (3) Both the absolute scale length of the current signature and its size relative to that of the electric field signature are smaller for the linearly polarized cases. With this full DC E vector, we can study various questions including the morphology of auroral return currents and inconsistencies with static return current models. Our tool for extracting this information will be part of the FAST software library.
DE: 2407 Auroral ionosphere (2704)
DE: 2411 Electric fields (2712)
DE: 2704 Auroral phenomena (2407)
DE: 2712 Electric fields (2411)
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting