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Ann. Geophys., 21, 1017-1030, 2003
www.ann-geophys.net/21/1017/2003/
© European Geosciences Union 2003
Vertical E × B drift velocity variations and associated low-latitude ionospheric irregularities investigated with the TOPEX and GPS satellite data
I. Horvath and E. A. Essex
Department of Physics, La Trobe University Cooperative Research Centre for Satellite Systems, Bundoora, Victoria, 3086, Australia
Abstract. With a well-selected data
set, the various events of the vertical E × B drift velocity
variations at magnetic-equator-latitudes, the resultant ionospheric features at
low-and mid-latitudes, and the practical consequences of these E × B
events on the equatorial radio signal propagation are demonstrated. On a global
scale, the development of a equatorial anomaly is illustrated with a series of
1995 global TOPEX TEC (total electron content) maps. Locally, in the Australian
longitude region, some field-aligned TOPEX TEC cross sections are combined with
the matching Guam (144.86° E; 13.59° N, geographic) GPS (Global Positioning
System) TEC data, covering the northern crest of the equatorial anomaly.
Together, the 1998 TOPEX and GPS TEC data are utilized to show the three main
events of vertical E × B drift velocity variations: (1) the
pre-reversal enhancement, (2) the reversal and (3) the downward maximum. Their
effects on the dual-frequency GPS recordings are documented with the raw Guam
GPS TEC data and with the filtered Guam GPS dTEC/min or 1-min GPS TEC data
after Aarons et al. (1997). During these E × B drift velocity
events, the Port Moresby (147.10° E; - 9.40° N, geographic) virtual height or
h'F ionosonde data (km), which cover the southern crest of the equatorial
anomaly in the Australian longitude region, show the effects of plasma drift on
the equatorial ionosphere. With the net (D)
horizontal (H) magnetic field intensity parameter, introduced and called DH
or Hequator-Hnon-equator (nT) by Chandra and Rastogi
(1974), the daily E × B drift velocity variations are
illustrated at 121° E (geographic) in the Australian longitude region. The
results obtained with the various data show very clearly that the development
of mid-latitude night-time TEC increases is triggered by the westward electric
field as the appearance of such night-time TEC increases coincides with the E
× B drift velocity reversal. An explanation is offered with the
F-region dynamo theory and electrodynamics, and with the
ionospheric-plasmaspheric coupling. A comparison is made with the published
model results of SUPIM (Sheffield University Plasmasphere-Ionosphere Model;
Balan and Bailey, 1995) and experimental results of Park (1971), and the good
agreement found is highlighted.
Key words. Ionosphere (electric
fields; equatorial ionosphere; mid-latitude ionosphere)
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