Abstract:
Topside ionospheric parameters-total ion density (Ni) and ion temperature(Ti) have
12 been analysed at low latitude region with changing solar activity (years 1999 to 2003).The Ni and Ti data collected from ROCSAT-1 satellite has been compared with the estimated values of IRI-2016 model. The annual diurnal features observed for Ni (measured by ROCSAT-1) are: a minimum value just before local sunrise (~04:00/05:00 LT), a day-time peak (~13:00/14:00 LT) and then a gradual decrement throughout the evening and nighttime. The annual diurnal variation of Ti (measured by ROCSAT-1) shows that Ti exhibits a morning peak (morning overshoot, ~07:00 LT), a day-time trough, a secondary peak (evening enhancement) followed by nighttime minima and a minimum value before the sunrise. The distinct annual diurnal feature observed by the IRI model is the presence of a secondary evening peak in Ni which is absent in Ti, which is exactly opposite to the trend measured by ROCSAT-1. Some other discrepancies observed in the
model are:overestimation of Ni during all the years, specifically in the morning and evening time; overestimation of Ti, during the entire day except in the morning peak hours of the year 1999, 2000 and 2003.For each year, the hourly averaged ROCSAT-1 measured value of Ni and Ti has been correlated with the estimated value of IRI-2016 model. The correlation coefficient factor R2 is ~ 0.8 for Ni and ~ 0.9 for Ti respectively. The variations of Ni and Ti with changing solar flux have also been studied. The ionospheric parameters are found positively and linearly correlated with solar-flux (F10.7). The correlation coefficient factor R2 for Ni and Ti with F10.7 is ~ 0.8 and ~ 0.9 respectively.
