Unique latitudinal shape of ion upper transition height ( H T ) surface during deep solar minimum (2008–2009)

The ionospheric upper transition height ( H T ) is found to increase dramatically by ~100 km from 2008–2009 to 2010 only for a marginal increase in solar activity ( F 10.7 ) by 11.76 solar flux units. The latitudinal variation of H T surface during 2008–2009 period exhibits a local minimum at equatorial latitudes and increase at low latitudes. Further, the H T at equatorial latitudes exhibits slower rate of increase than at low latitudes. These interesting features are new and different from those reported in literature. A quick loss of O + and increase in H + ions are observed around ~550 to 650 km indicating that the charge exchange reaction is responsible for the slower rate of increase and lowered H T at equatorial latitudes. These new aspects of H T are more conspicuously observed during this deep solar minimum period where the resonant charge exchange reaction is taking place at altitudes as low as ~550 km.