Simultaneous Observations of Equatorial Plasma Depletion by IMAGE and ROCSAT-1 
Satellites

C.S. Lin, T. Immel, H. Yeh, S.B. Mende, J.L. Burch


Simultaneous observations of the equatorial ionosphere by ROCSAT-1 and IMAGE
satellites have been used to study plasma characteristics of equatorial plasma
bubbles. IMAGE Far-ultraviolet (FUV) nighttime images have indicated signatures
of depression in the brightness of equatorial airglow arcs. Using the list of
airglow brightness depression events observed by IMAGE, we surveyed ROCSAT-1
IPEI data for simultaneous plasma observations in the same local time. Our
preliminary investigation has indicated that features of brightness depression
seen in FUV images were correlated with equatorial plasma bubbles detected by
ROCSAT-1 at 600 km altitude. Successive FUV images are averaged to produce a
keogram with UT versus longitude, which is then used to deduce drift velocity
for plasma density depletions. For the simultaneous observation events of plasma
density depletion, we compare the ion drift velocities measured by ROCSAT-1 with
the drift speed determined from the FUV keogram. We examine the relationship
among the drifting speed of airglow brightness depression, the ion velocity
inside equatorial plasma bubbles, and the ion velocity of the background plasma.
The analysis results are used to answer questions about whether the bubbles are
drifting faster than the ambient plasma, and how equatorial plasma bubbles
evolve as they drift.

_______________ 
Presentation, Fall Meeting, American Geophysical Union, San Francisco, USA, 
8-12 December 2003