Low latitude ionospheric variations during geomagnetic storms measured using ROCSAT-1 satellite observations

171-179In the present paper the response of ionospheric parameters- ion densities and ion temperature (H+, O+ and Ti) to a weak (30 July 1999) and a moderate (13 November 1999) geomagnetic storm (GS) at low latitude Indian region using observed and modelled values has been analyzed. The study has been carried out by using ROCSAT-1 satellite data over the region encompassed between 5-35º geog N and 65-95º geog E at an average altitude ~ 600 km. A comparative study has also been done with the IRI-2016 modelled values. The ionospheric plasma parameters have shown anomalous behaviour during disturbed days in comparison to the quiet days. For the weak GS, both the average O+ and H+ density have been increased by a factor of around 1.8 during disturbed and quiet days respectively as calculated by ROCSAT-1. For the moderate GS, the average O+ and H+ density has been increased by a factor of around 2.7 and 6.3 respectively during disturbed and quiet days respectively, as calculated by ROCSAT-1. And the least or negligible variation has been observed in Ti for both measured and modelled values during weak and moderate GS

Low latitude ionospheric variations during geomagnetic storms measured using ROCSAT-1 satellite observations

This paper studies the response of ionospheric parameters- ion densities (O+ and H+) and ion temperature (Ti) to a moderate (30 July 1999) and a strong (13 November 1999)  geomagnetic storm (GS) at low latitude Indian region using observations and modelling. The analysis has been carried out by using ROCSAT-1 satellite data over the region encompassed between 5-35º geog N and 65-95º geog E at an average altitude ~ 600 km. This study of the effect of these geomagnetic storms over the low-latitude F2 region ionosphere has been compared with the estimated values of IRI-2016 model. The ionospheric plasma parameters show anomalous behaviour during disturbed days compared to the quiet days. For the moderate GS, both the average O+ and H+ density are found to increase by a factor of around1.8 during disturbed and quiet days respectively as calculated by ROCSAT-1. For the strong GS, the average O+/H+ density is found to increase by a factor of around 2.7/ 6.3 respectively during disturbed/quiet days as calculated by ROCSAT-1. And the Ti is observed showing the least or negligible variation both by measured and modelled values during moderate and strong GS

Variability of ion density due to solar flares as measured by SROSS-C2 satellite

The ion densities have been measured from year 1995-1998, using RPA payload of SROSSC2 satellite to study the effect of solar flares on ion density. Solar flare data has been obtained from National Geophysical Data Center (NGDC) Boulder, Colorado (USA). Study indicates considerable decrease in total ion density during flare time compared to normal time. This decrease varies from 1.2 to 2.8 times. Out of four ion species – O+, O2+, H+ and He+ as measured by SROSS – C2, O+ ion density is most affected by the effects of the flare. There is considerable decrease in O+ ion density while O2 +, H+ and He+ density show negligible change during flare time compared to normal time. Furthermore relation between change in ion density (ΔN) as a response to change in ion temperature (ΔT) during flare time and normal days has been estimated. A comparison with O+ density obtained from IRI – 2012 during the flare time underestimates the density value

Low latitude, topside ionosphere composition and its variation with changeable solar activity

The ions composition and their densities have been studied for different solar activity periods - along with their diurnal, seasonal and annual variations - for half of the 23rd solar cycle, covering solar minima (1995) to solar maxima (2000) over Indian sector (65–95ᵒE and 5–35ᵒN) at an average altitude of ~500 km. The study has been done by processing the data obtained from in situ measurement made by separate Retarding Potential Analyser (RPA) for electrons and ions, aboard Indian satellite SROSS C2. The plasma density has been found to be rich in O+ ion for all instances of time and showed a direct increase with solar activity. H+ has been observed to be in plenty during night time, especially from moderate to high solar activity period. The difference between H+ and O+ densities widens with increasing value of F10.7. He+ always constitutes a small part of plasma but its density exceeds H+ - during moderate to high solar activity period. O2+ has beenfound to be a minor constituent, even 3-4 folds lesser than He+ density. A positive correlation with solar activity has been found for O2+

Variability of ion density due to solar flares as measured by SROSS–C2 satellite

88-95In the present paper the effect of solar flares on ion density has been studied. The ion densities have been measured for the period 1995-1998 using RPA payload of SROSS-C2 satellite. Solar flare data has been obtained from National Geophysical Data Center (NGDC) Boulder, Colorado (USA). The study indicates considerable decrease (1.2 to 2.8 times) in total ion density during flare time as compared to normal time. Out of four ion species, i.e. O+, O2+, H+ and He+, the O+ ion density is most affected by the effects of the flare as measured by SROSS–C2. There is considerable decrease in O+ ion density while O2+, H+ and He+ density show negligible change during flare time as compared to normal time. Furthermore, relation between change in ion density (∆N) as a response to change in ion temperature (∆T) during flare time and normal days has been estimated. A comparison of ion density obtained from SROSS-C2 with IRI–2012 during the flare time indicates an overestimation by IRI-2012

Equinoctial asymmetry in low latitude ionosphere as observed by SROSS-C2 satellite

International audienceThe ionospheric plasma parameters (electron, ion temperatures and ion composition-Te, Ti, O+ and H+) measured by SROSS-C2 satellite at an average altitude of ~500 km has been investigated to study the behaviour of the ionosphere in equinoxes during half a solar cycle (year 1995-2000, F10.7 ~70-195). The region under study spans over 5-35°N geog. latitude and 65-95°E geog. longitude in the Indian sector. We found an equinoctial asymmetry in the diurnal behaviour of Te, Ti, O+ and H+ varying with increase in solar activity. The strength of equinoctial asymmetry in Te and Ti is strong during early morning and daytime and strength decreases with increase in solar activity whereas during night time no asymmetry/weaker is observed in low/high solar activity respectively. During the day time, a very strong equinoctial asymmetry in O+ is observed during solar minimum which diminishes with increase in solar activity. The similar diurnal behaviour of H+ as that of O+ is observed during low solar activity but no clear equinoctial asymmetry is observed during solar maximum, as H+ being highly dynamic. The transition height (O+/H+) is the lowest in early morning during solar minimum, which increases during local day-time. The rate of increase in transition height is different in both the equinoxes (higher in vernal than autumn) with respect to dependence on the solar activity, during daytime. Hence equinoctial asymmetry is stronger during solar minimum period than maximum, with higher/lower transition height in vernal during daytime/nighttime respectively