Effect of solar cycle on topside ion temperature measured by SROSS C2 and ROCSAT 1 over the Indian equatorial and low latitudes

Abstract

Abstract. The effect of solar activity on the diurnal, seasonal and latitudinal variations of ion temperature T i and its relationship with corresponding ion density N i 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. T i varies between 800 K and 1100 K during nighttime and rises to peak values of ∼1800 K in the post sunrise hours. Daytime T i 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, T i 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 T i is higher at off equatorial latitudes and lower over the Equator, while in the solstices, T i exhibits a north-south gradient during daytime. Nighttime T i is found to be higher over the Equator. Daytime ion temperature exhibits insignificant positive correlation with F 10.7 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 T i does not exhibit any correlation. However, during high solar activity, significant positive correlation of T i with N i has been observed over the Equator, while at 10 • S and 10 • N temperature and density exhibit significant negative correlation. The neutral temperature T n derived from the MSISE 90 model is found to be higher than measured T i during nighttime, while daytime T i is higher than model T n .

Correlations between ion density and temperature in the topside ionosphere measured by ROCSAT‐1

“…The Ti difference between the lower (green) and higher (black) fluxes is about 200–300 K at the magnetic dip equator. Similar solar flux dependence is shown in the result by Borgohain and Bhuyan [].…”

“…The Ti difference between the lower (green) and higher (black) fluxes is about 200-300 K at the magnetic dip equator. Similar solar flux dependence is shown in the result by Borgohain and Bhuyan [2012]. Figure 6 presents magnetic disturbance (Kp) dependences of the correlation between Ni and Ti in MLAT ranges from 10:00 to 16:00 LT.…”

“…Similar latitudinal dependences of the correlation were seen in all longitudes, seasons, solar flux levels, and magnetic disturbance levels, although the minimum Ti clearly varied with solar flux level. These features have not been reported in the previous study [ Borgohain and Bhuyan , ]. Figure presents the distribution of median Ti in Ni‐MLAT space under Kp ≦ 2, for which Ti and Ni were calculated with IRI2007 (International Reference Ionosphere 2007) [ Billiza and Reinisch , ].…”

“…Ion temperature (Ti) is a key parameter that may clarify the issue, because ions act as intermediates of the heat flow between hot electrons and cold neutral atmosphere. Borgohain and Bhuyan [] investigated the correlation between Ni and Ti in the topside ionosphere over India. Although they showed that negative correlations occur in low solar activity and positive correlations occur in high solar activity, the mechanism has not been fully revealed due to lack of a comprehensive study.…”

Seasonal Variations in Ion Density, Ion Temperature, and Migrating Tides in the Topside Ionosphere Revealed by ICON/IVM

“…Our analysis also reveals a relatively lower correlation at latitudes around 18 • N, while the absolute values of the negative correlation coefficients southward from 9 • N are generally higher than 0.6. Zhang et al [51] also reported the anticorrelation between total ion density and ion temperature in local daytime at low latitudes in the northern hemisphere, while a positive correlation is captured southward from 15 • S. Borgohain and Bhuyan [52] suggested that the ion temperature was not related to the total ion density during the nighttime. Kakinami et al [34] analyzed the correlation between ion density and ion temperature based on the ROCSAT-1 plasma data, while both positive and negative relations were observed.…”