Occurrence and onset conditions of postsunset equatorial spread F at Jicamarca during solar minimum and maximum

Abstract

The data of digisonde and the NRLMSISE‐00 model on the occurrence of postsunset equatorial spread F (ESF) at Jicamarca during solar minimum and maximum years are used in a detailed statistical analysis. The onset conditions chosen in this study are the prereversal enhancement velocity (dhF80/dt), minimum virtual height of F‐layer (h′F), gradient density scale length (L), and local linear growth rate (γ) of collisional Rayleigh‐Taylor instability. The monthly variation in ESF occurrence during solar minimum generally agrees with that during maximum. This agreement indicates that the ESF occurrence does not depend on solar activity. For the onset conditions, the differences between solar minimum and maximum exists in the monthly variations in dhF80/dt, h′F, and L, but not in γ. This consistence in monthly γ variation between two solar epochs mainly account for the solar cycle independence of ESF occurrence. Furthermore, the variations in collision frequency and recombination rate are principally responsible to the consistence in γ.