Escape Altitude of Ionospheric Photoelectrons in the Low Latitude Region

Abstract

In the present work theoretical calculations are made to estimate the escape altitude of photoelectrons in the F-region of the ionosphere as a function of latitude in the low latitudes for different photoelectron energies. It is found that at the equator, the escape altitude for 1 eV photoelectrons is about 454 km for solar minimum conditions. This value decreases with increasing dip angle, falling to about 318km for a magnetic dip angle of 9°. Beyond this, the escape altitude varies rather slowly with latitude becoming about 268 km at a magnetic dip angle of 45°. At the equator, the escape altitude for 10 eV photoelectrons is about 550km for solar minimum conditions. This value decreases to 334 km at a magnetic dip angle of 45°. Below about 4 eV photoelectron energy, the escape altitude is energy-dependent whereas above 4 eV and up to about 12 eV, the escape altitude is insensitive to the photoelectron energy. The observed maximum in the escape altitude at 3 eV is explained as due to the maximum in inelastic collision cross-section of molecular nitrogen at that energy. Above 12 eV, it increases slowly with energy.