EE 350 RADIOSCIENCE SEMINAR

Professor Umran S. Inan

Winter 1997-98



Date: Wednesday, March 4, 1998

Time: 4:15 PM Refreshments at 4:00

Location: Gesb 124 (Green Earth Sciences Bldg.)

Optical Observations of High Latitude Auroras in Antarctica

UC Berkeley

Abstract

The Automatic Geophysical Observatory (AGO) sites provide excellent data sets for studying the behavior of the dayside and night side auroras and their response to solar wind and substorm influences. Dynamic changes of the magnetopause that map to the dayside aurora were studied from coordinated observations between South Pole station and the AMPTE/CCE satellite when it was at 9 Re apogee in the midday sector. An example of a local event shows rotation of the magnetic field and the sudden appearance of low energy electrons indicating the satellite entering the magnetosheath or LLBL. Although the magnetic field signatures are not characteristics of an FTE localized at the satellite, the event could be a magnetic field change produced be a distant flux erosion event, which propagated to the vicinity of the satellite. In another example a clear case of (local) field erosion is discussed during which the satellite entered the magnetosheath characterized by a reduction in energetic electrons, increase in soft electrons and a decrease in the magnetic field. An accompanying strong equatorward movement of the aurora showed that flux erosion took place. In another event in the afternoon sector showed similar changes in the electron fluxes associated with an increase in the magnetic field at the satellite suggesting that the fringing fields of the region 1 current system, which normally cause field depression at the sub solar region, created an increase in the field at the CCE satellite near the late afternoon side. The equatorward movements of the aurora for all three events were strongly correlated with the global Ae index which was determined mainly by dawn dusk stations signifying that the correlation exists with the dayside region 1 currents only and not with the nightside substorm components. The extended latitude region covered by the station array data permitted the observation of substorm expansions into the polar cap. A typical substorm event (June 3, 1994 0400-0500 UT) started equatorward from South Pole and propagated to the high latitude limit of the field of view the high latitude stations P1 and P4. The morphological appearance of these high latitude auroral substorm features was similar to substorm auroras observed at lower latitude. Statistical analysis of the 1995 AGO optical data shows that over 20% of substorms that are seen by these stations to penetrate to regions greater than 80 degrees latitude. This shows that during such substorms the dipolarization frequently extends into regions located quite deeply in the earth's magnetic tail.