Spread F, GPS phase fluctuations, and plasma bubbles near the crest of equatorial ionization anomaly during solar maximum

Abstract

This work is the first attempt to concurrently study the occurrence probabilities of spread F, GPS phase fluctuations, and plasma bubbles near the crest of equatorial ionization anomaly (EIA). The data were observed by an ionosonde, a GPS receiver, and ROCSAT-1 during 2000, the solar maximum year. Results show that the occurrences of the range spread F (RSF) differ from those of the frequency spread F (FSF). For the seasonal variation, the RSF occurrence has the maximum values in March and September, while the FSF occurrence peaks at June. For the nighttime variation, RSF and FSF peak at 2300 and 0300 LT, respectively. Regarding the GPS phase fluctuations, an index Fp is applied to characterize the irregularity strength. The similarity between the 50 < Fp ≤ 200 and RSF occurrences demonstrates that the characteristics of F region irregularities forming 50 < Fp ≤ 200 are mainly related to RSF. The occurrence of 200 < Fp is almost absent. The rare event is also found in the observation of plasma bubbles by ROCSAT-1. Furthermore, the seasonal variations in GPS phase fluctuations at the EIA crest and the dip equator have similar trends. This indicates that the F region irregularities of RSF and 50 < Fp ≤ 200 at the EIA crest are originated from the equatorial ionosphere. On the other hand, the seasonal variation in occurrence probability of FSF at the EIA crest is close to that of spread F at midlatitudes. This suggests that the generation mechanisms of FSF and midlatitude spread F might be same, but the further study is required. Copyright 2009 by the American Geophysical Union.