Low-latitude ionospheric scintillations and total electron content obtained with the CITRIS instrument on STPSat1 using radio transmissions from DORIS ground beacons

The primary objective of the Scintillation and Tomography Receiver in Space (CITRIS) is to detect ionospheric irregularities from space at low latitude. For this purpose, the satellite receiver uses the UHF and S-Band transmissions of the ground network of Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) beacons. CITRIS, developed at the Naval Research Laboratory, differs from the normal DORIS receiver by being able to capture and store the complex amplitude of the 401.25 and 2036.25 MHz transmissions at 200 Hz sample rate. Ground processing of the CITRIS data yields total electron content (TEC) and both phase and amplitude scintillations. With CITRIS flying on the US Space Test Program (STP) satellite STPSat1, 2 years of data were collected and processed to determine the fluctuations in ionospheric TEC and radio scintillations associated with equatorial irregularities. CITRIS flights over DORIS transmitters yield direct measurements of the horizontal plasma density fluctuations associated with equatorial plasma bubbles. Future flights of CITRIS can provide valuable complements to other satellite instruments such as GPS occultation receivers used to estimate vertical electron density profiles in the ionosphere.     

Response of the ionospheric F-region in the Brazilian sector during the super geomagnetic storm in April 2000 observed by GPS

The response of the ionospheric F-region in the equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm on 06–07 April 2000 has been studied in the present investigation. The geomagnetic storm reached a minimum D_st of −288 nT at 0100 UT on 07 April. In this paper, we present vertical total electron content (VTEC) and phase fluctuations (in TECU/min) from GPS observations obtained at Imperatriz (5.5°S, 47.5°W; IMPZ), Brasília (15.9°S, 47.9°W; BRAZ), Presidente Prudente (22.12°S, 51.4°W; UEPP), and Porto Alegre (30.1°S, 51.1°W; POAL) during the period 05–08 April. Also, several GPS-based TEC maps are presented from the global GPS network, showing widespread and drastic TEC changes during the different phases of the geomagnetic storm. In addition, ion density measurements on-board the satellite Defense Meteorological Satellite Program (DMSP) F15 orbiting at an altitude of 840 km and the first Republic of China satellite (ROCSAT-1) orbiting at an altitude of 600 km are presented. The observations indicate that one of the orbits of the DMSP satellite is fairly close to the 4 GPS stations and both the DMSP F15 ion-density plots and the phase fluctuations from GPS observations show no ionospheric irregularities in the Brazilian sector before 2358 UT on the night of 06–07 April 2000. During the fast decrease of D_st on 06 April, there is a prompt penetration of electric field of magnetospheric origin resulting in decrease of VTEC at IMPZ, an equatorial station and large increase in VTEC at POAL, a low latitude station. This resulted in strong phase fluctuations on the night of 06–07 April, up to POAL. During the daytime on 07 April during the recovery phase, the VTEC observations show positive ionospheric storm at all the GPS stations, from IMPZ to POAL, and the effect increasing from IMPZ to POAL. This is possibly linked to the equatorward directed meridional wind. During the daytime on 08 April (the recovery phase continues), the VTEC observations show very small negative ionospheric storm at IMPZ but the positive ionospheric storm effect is observed from BRAZ to POAL possibly linked to enhancement of the equatorial ionospheric anomaly.