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Earth Planets Space, Vol. 57 (No. 5), pp. 385-392, 2005

Simultaneous ground- and satellite-based airglow observations of geomagnetic conjugate plasma bubbles in the equatorial anomaly

Tadahiko Ogawa1, Eiichi Sagawa2, Yuichi Otsuka1, Kazuo Shiokawa1, Thomas I. Immel3, Stephen B. Mende3, and Phil Wilkinson4

1Solar-Terrestrial Environment Laboratory, Nagoya University, Honohara, Toyokawa, Aichi 442-8507, Japan
2National Institute of Information and Communications Technology, Koganei, Tokyo 184-8795, Japan
3Space Sciences Laboratory, University of California, Berkeley, CA 94720, U.S.A.
4IPS Radio and Space Services, Haymarket, New South Wales 1240, Australia

(Received December 16, 2004; Revised March 17, 2005; Accepted March 18, 2005)

Abstract: We compare, for the first time, geomagnetically-conjugate plasma bubbles observed by ground-based OI 630.0-nm all-sky imagers at Shigaraki, Japan (34.8°N, 136.1°E; magnetic latitude 25.4°N) and Darwin, Australia (12.4°S, 131.0°E; magnetic latitude 22.0°S), with global-scale plasma structures ( ~10,000 km in longitude) in the equatorial anomaly simultaneously detected with an OI 135.6-nm imager on the IMAGE satellite at ~7 earth radii. As found previously, global-scale plasma structures in both hemisphere imaged by IMAGE consist of an array of geomagnetically-conjugate small- to medium-scale (a few hundreds to 1000 km in longitude) wavy structures that move to the east at ~100 ms-1. We find the following: 1) plasma bubbles detected with the all-sky imagers reach an apex altitude of ~1800 km over the geomagnetic equator while moving to the east at ~100 ms-1 with spacings of 200-250 km. 2) Bubbles observed with the all-sky imagers and IMAGE are embedded within the small- to medium-scale wavy structures, and some of them are located near the crest of an enhanced electron density region associated with the wavy structures. 3) The bubbles and wavy structures that are generated near sunset slant to the west with increasing latitude in both hemispheres, and tilts do not change with longitude (i.e., local time). The results suggest that the generation and evolution of plasma bubbles are closely related to those of the small- to medium-scale plasma structures.
Key words: Equatorial ionosphere, equatorial anomaly, plasma bubble, airglow.


Corresponding author E-mail: ogawa@stelab.nagoya-u.ac.jp


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