| || || Prasad, Ramendra|
| || || Ionospheric electron content and L band scintillation study in the South Pacific region using GPS |
Institution: University of the South Pacific.
Subject: Ionospheric electron density -- Oceania , Global Positioning System
Call No.: pac QC 879 .P73 2012
Copyright:Under 10% of this thesis may be copied without the authors written permission
Abstract: The total electron content (TEC) and L1-band ionospheric scintillations recorded using GSV 4004B GPS Ionospheric Scintillation and TEC monitor (GISTM) data acquisition system during 2010-11 have been analyzed to accomplish the scientific objectives of this work. The TEC recorded by the receiver at different elevation angles of the GPS satellites were slant TEC (STEC) values which were then converted to vertical TEC (VTEC) to remove the biases induced by different elevation angles. The diurnal, monthly, seasonal and annual TEC variations as well as day-to-day TEC variability on magnetically quiet and disturbed days were studied. The diurnal variation revealed TEC maximum at around 14:00 LT and minimum between 02:00-06:00 LT. Monthly variation showed maximum VTEC in the months of December and minimum in June and August. The day-to-day variability study in TEC showed maximum variability in the daytime between 12:00-15:00 LT followed by pre-midnight and least variability during post-midnight period between 04:00-06:00 LT. The day-to-day variability in VTEC could have been due to various factors such as EUV flux, geomagnetic activity, local temporal conditions in the thermosphere, variation in thermospheric neutral composition, variation in neutral winds, influence of solar dynamic processes, atmosphere-ionosphere coupling, vertical coupling resulting from atmospheric waves like gravity waves and tides or planetary waves, the equatorial electrojet (EEJ) generated by atmospheric tides and meteorological factors. Seasonal analysis showed higher TEC during the hot and wet season as compared to the cold and dry season. The cold and dry seasonal average, showed a diurnal plateau from 09:00 to 16:30 LT whereas during hot and wet season, no significant plateau was observed, but a distinct crest occurred at around 14:45 LT. L-band amplitude scintillations were examined for their morphological study at Suva. The GSV 4004B receiver records scintillation index S4, on L1 signal and the correction to S4 (S4 Cor) due to multipath effects. The final S4 (S4 FIN) values were computed by subtracting the S4 Cor from the recorded S4 in a Random Sum Spectrum (RSS) sense. This S4 FIN has been used to categorize weak (0.2 ≤ S4 < 0.3), moderate (0.3 ≤ S4 < 0.45) and strong (0.45 ≤ S4) scintillation events and then the monthly and seasonal percentage occurrences of different category of scintillation events were ii studied. Out of a total of 480 events, 84.4% were weak, 14.6% were moderate and 1% were strong, according to the above category. The amplitude scintillations were most pronounced in the daytime with January showing the highest number of events. Seasonal analysis revealed that scintillation events were more often during the hot and wet season as compared to the cold and dry season. Annually, scintillations occurred mostly in the daytime with peak occurrence at around 05:00-09:00 LT. Daytime strong scintillation events were not associated with TEC depletions and phase scintillations, but the signal to noise ratio during the scintillation events decreased with increase in S4. However, post-midnight strong amplitude scintillations were associated with TEC depletion and phase scintillations indicative of large scale irregularities.