HR: 0800h
AN: SA31A-06    [Abstracts]
TI: Recent Results on Bottomside Sinusoidal Irregularities
AU: * Valladares, C E
EM: valladar@bc.edu
AF: Boston College, 140 Commonwealth Ave., Chestnut Hill, MA 02467, United States
AB: We have used TEC data collected by a set of 12 GPS receivers located in South America, a UHF scintillation receiver system from Ancon, and bottomside profiles from the Jicamarca digisonde to investigate the ionospheric conditions that lead to the onset of BSS plasma irregularities. We have examined 20 months of observations extending between September 2001 and April 2003 to find 18 events that contain BSS-type irregularities. To qualify as a possible BSS event, the following 3 conditions were required to occur simultaneously: (1) strong or moderate levels of UHF scintillations, (2) absence of TEC depletions, and (3) ionograms containing frequency- type spreading. On December 21, 2002 the digisonde reported that the F-layer peak was higher than 600 km altitude between 03 and 06 UT. The high altitude of the F-layer was accompanied by a large latitudinal displacement of the anomaly that remained away from the magnetic equator for many hours after sunset. The ROCSAT satellite passed south of Jicamarca at 0528 UT observing density structures with 1 km-scale oscillations that are the prominent characteristic of BSS structures. The ROCSAT measurements imply that BSS irregularities are associated with frequency-type ionograms. Prior to the initiation and during the BSS irregularities, the drift meter on-board ROCSAT detected an upward drift equal to 50 m/s. This paper also reports the results of 2 ionospheric models that have been conducted to explain the formation of BSS-type irregularities.
DE: 2400 IONOSPHERE (6929)
DE: 2411 Electric fields (2712)
DE: 2415 Equatorial ionosphere
DE: 2439 Ionospheric irregularities
DE: 2494 Instruments and techniques
SC: SPA-Aeronomy [SA]
MN: 2007 Joint Assembly