Latitudinal Differences in Spread F Characteristics at Asian Longitude Sector during the Descending Phase of the 24th Solar Cycle

Abstract

By using ionosonde data recorded at Chiang Mai (18.8° N, 98.9° E, magnetic latitude is 9.1° N), Puer (22.7° N, 101.1° E, magnetic latitude is 12.9° N), and Leshan (29.6° N, 103.7° E, magnetic latitude is 19.8° N), the statistical features of different types of spread F (SF) occurrence at low and middle latitudes were analyzed in this study. The results showed that the SF occurrence had obvious local time, latitude, and SF-type variations. The range spread F (RSF) occurrence in equinox months decreased with the increase in latitude, while the frequency spread F’s (FSF) occurrence rate in the summer months increased and the onset time of FSF became earlier when the latitude increased. The generation of SF depends on the SF type. A plasma bubble excited by the generalized Rayleigh–Taylor instability (GRT) at the equator is more likely to produce RSF, while nighttime medium-scale traveling ionospheric disturbances (MSTIDs) induced by Perkins instability at middle latitudes is the main reason for the generation of FSF.

Keywords

• spread F
• longitudinal difference
• ionogram