Vertical E × B drift velocity variations and associated low-latitude ionospheric irregularities investigated with the TOPEX and GPS satellite data

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 H_equator-H_non-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)