Evolution of Freshly Generated Equatorial Spread F (F‐ESF) Irregularities on Quiet and Disturbed Days

• Published in: Journal of geophysical research. Space physics Vol. 123; no. 9; pp. 7710 - 7725
• Main Authors: Gurram, P., Kakad, B., Bhattacharyya, A., Pant, T. K.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-09-2018
• Subjects: Dependence; Electric fields; ESF structuring; ESF‐irregularities; Evolution; Ionosondes; Irregularities; magnetic storm; Perturbation; Plasma bubbles; Solar activity; Solar flux; Solstices; Spread F; VHF scintillation
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2018JA025705

We examined the seasonal and solar flux dependence of the occurrence of freshly generated intermediate scale (100 m to few km) equatorial spread F (ESF) irregularities during magnetically quiet (Q) and disturbed (D) periods. We utilized long‐term (1992–2006 and 2013–2015) amplitude scintillation data on a 251 MHz signal recorded at Tirunelveli (dip lat. 1.5°N ). Also, ionosonde data (1990–2003) recorded at Trivandrum (dip lat. 0.5°N) are used. The presence of fresh ESF (F‐ESF) is identified using the maximum cross‐correlation between intensity variations recorded by two spaced receivers on a magnetic east‐west baseline. We find distinct differences in the seasonal and solar flux dependence of the usual postsunset (<22 LT) generation of F‐ESF on both Q‐ and D‐days. Interesting feature is that F‐ESF linked moderate–strong scintillations are more prevalent on D‐days as compared to Q‐days in both early (18–22 LT) and later (>22 LT) phase of evolution of the irregularities. It directly hints toward the difference in the spatial structuring (spatial scales) of F‐ESF on D‐days as compared to Q‐days. On D‐days, the occurrence of F‐ESF is more likely around midnight and early‐morning hours in all seasons. Whereas on Q‐days, the postmidnight F‐ESF is found to occur mainly during solstices of low solar activity. The possible sources for the generation of F‐ESF around midnight on Q‐days of solstices during low solar activity are examined. We also find that perturbation electric field linked with F‐ESF on D‐days sustains for longer time, which results in longer durations of the active phase of equatorial plasma bubbles.
Key Points
Perturbation electric field linked with fresh ESF is sustained for longer duration on disturbed days
Disturbed time fresh ESF irregularities produce stronger scintillations as compared to quiet time fresh ESF
Theoretical model indicates a smaller altitudinal extent for postmidnight fresh ESF on quiet days as compared to disturbed days