Abstract

Abstract. The effect of solar activity on the diurnal, seasonal and latitudinal variations of ion temperature Ti and its relationship with corresponding ion density Ni over the Indian low and equatorial topside ionosphere within 17.5° S to 22.5° N magnetic latitudes are being investigated, combining the data from SROSS C2 and ROCSAT 1 for the 9-year period from 1995 to 2003 during solar cycle 23. Ti varies between 800 K and 1100 K during nighttime and rises to peak values of ~1800 K in the post sunrise hours. Daytime Ti varies from 1000 K to 1500 K. The time of occurrence, magnitude and duration of the morning enhancement show distinct seasonal bias. For example, in the June solstice, Ti increases to ~1650 K at ~06:00 h and exhibits a daytime plateau till 17:00 LT. In the equinoxes, enhanced ion temperature is observed for a longer duration in the morning. There is also a latitudinal asymmetry in the ion temperature distribution. In the equinoxes, the daytime Ti is higher at off equatorial latitudes and lower over the Equator, while in the solstices, Ti exhibits a north–south gradient during daytime. Nighttime Ti is found to be higher over the Equator. Daytime ion temperature exhibits insignificant positive correlation with F10.7 cm solar flux, while nighttime ion temperature decreases with increase in solar flux. Daytime ion temperature and ion density are negatively correlated during solar minimum, while nighttime Ti does not exhibit any correlation. However, during high solar activity, significant positive correlation of Ti with Ni has been observed over the Equator, while at 10° S and 10° N temperature and density exhibit significant negative correlation. The neutral temperature Tn derived from the MSISE 90 model is found to be higher than measured Ti during nighttime, while daytime Ti is higher than model Tn.

Highlights

  • In the ionospheric F-region, the photo electrons produced by the solar ionizing radiations are hotter than the neutral atoms

  • The combined data from the two satellites provide a unique opportunity to study the effect of solar activity on the diurnal, seasonal and latitudinal variation of ion temperature during solar cycle 23

  • It is seen from the figure that in low solar activity, equinox enhancement in Ti up to ∼1400 K occurs in the sunrise hours (05:00–07:00 LT) at latitudes away from the Equator

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Summary

Introduction

In the ionospheric F-region, the photo electrons produced by the solar ionizing radiations are hotter than the neutral atoms. The electron temperature, measured by the SROSS C2 satellite over the Indian sector during the low solar activity period of 1995–1996, varied from 800–900 K during nighttime, rose sharply to 3000 K and fell to a daytime average of 1500 K (Bhuyan et al, 2002a) They found Ti to be less than Te in all seasons. Diurnal, seasonal, solar activity and latitudinal variations of ion temperature, and its relationship with corresponding ion density over the Indian low and equatorial topside ionosphere, are being investigated – combining the data from SROSS C2 and ROCSAT 1 for the 9 year period from 1995 to 2003 during solar cycle 23. Borgohain and Bhuyan (2010) have reported the diurnal, seasonal and latitudinal variation of O+, H+, He+, O+2 ion densities for the 1995–2003 period over the Indian low and equatorial latitudes, combining measurements from the SROSS C2 and ROCSAT 1 The combined data from the two satellites provide a unique opportunity to study the effect of solar activity on the diurnal, seasonal and latitudinal variation of ion temperature during solar cycle 23. Borgohain and Bhuyan (2010) have reported the diurnal, seasonal and latitudinal variation of O+, H+, He+, O+2 ion densities for the 1995–2003 period over the Indian low and equatorial latitudes, combining measurements from the SROSS C2 and ROCSAT 1

SROSS C2
ROCSAT-1
Temporal and latitudinal variations
Solar cycle variation of ion temperature
Relationship between ion temperature and ion density
Neutral temperature from the MSIS model
Conclusions
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