LSWS linked with the low-latitude E-s and its implications for the growth of the R-T instability

摘要

abstract_textpA comprehensive investigation of spread F irregularities over the Indian sector has been carried out using VHF radar and ionosonde observations. Two different categories of spread F observations, one where the onset of the range spread F (RSF) was concurrent with the peak hF (category 1) and another where the RSF onset happened similar to 90min after the peak hF time (category 2), are presented. RSF in category 2 was preceded by the presence of oblique echoes in ionograms, indicating the irregularity genesis westward of Sriharikota. The average peak hF in category 1 was similar to 30km higher than that in category 2 indicating the presence of standing large-scale wave structure (LSWS). Occurrence of the blanketing E-s during 19:30 to 20:30Indian Standard Time in category 1 (category 2) was 0 (50). Model computation is also carried out to further substantiate the observational results. Model computation indicates that zonal variation of low-latitude E-s can generate zonal modulation in the F layer height rise. It is found that the modulation of the F layer height, linked with the low-latitude E-s, assists the equatorial spread F onset by modifying both the growth rate of the collisional Rayleigh-Taylor (R-T) instability and also its efficiency. A predominant presence of low-latitude E-s has been observed, but the increase in the F layer height and the R-T instability growth in the evening hours will maximize with complete absence of low-latitude E-s. A new mechanism for the generation of LSWS and its implications on R-T instability is discussed./p/abstract_text