Equinoctial and June solstitial F-region irregularities over Sanya

A 47.5 MHz VHF radar with a peak power of 24 kW has been operated at Sanya (18°N, 109°E, dip 13oN) in Hainan Island, China since February 2009. Data from the continuous observations of F-region irregularities by the VHF radar, an ionosonde and a GPS scintillation/TEC receiver during the equinoctial and June solstitial months of 2009-2010 have been analyzed. It is found that the F-region 3-m scale field aligned irregularities (FAIs) appeared frequently at post-sunset hours during equinox but initiated mostly at midnight/post-midnight in June solstice. Comparison of FAIs with GPS scintillations, TEC fluctuations and spread-F shows that the equinoctial FAIs coincided well with GPS scintillations and TEC fast depletions, which are associated with the development of equatorial plasma bubbles (EPBs). However, for the June solstitial FAIs, the simultaneous Communication/Navigation Outage Forecasting System (C/NOFS) satellite in situ density measurements show that some post-midnight FAI structures over Sanya may originate from equatorial F-region and then extend to Sanya latitude along magnetic field lines, but the others could resemble the irregularities of localized origin, not associated with the equatorial process. Both types of post-midnight FAIs during June solstice are not accompanied by GPS scintillations and TEC depletions, but are associated with the occurrence of spread-F. Possible mechanisms responsible for the occurrence of post-midnight FAIs without GPS scintillations over Sanya have been discussed.

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