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Title: Equatorial spread F development and quiet time variability under solar minimum conditions
Authors: Abdu, M A
Keywords: Equatorial spread F (ESF) irregularity
Low-latitude spread F
Solar minimum condition
Gravity wave seed
Pre-reversal enhancement in vertical drift (PRE)
Medium-scale travelling ionospheric disturbance (MSTID)
Issue Date: Apr-2012
Publisher: NISCAIR-CSIR, India
Abstract: This paper provides a brief review of our current understanding of the equatorial spread F irregularity (ESF) development related to the diverse processes that control or influence the spatial-temporal distribution and day-to-day variability in the occurrence of the irregularities during solar minimum conditions. The sunset electrodynamics processes leading to the ESF development are briefly explained highlighting the main ESF driving forces and their relative importance during solar maximum and minimum conditions. Whereas, its post sunset occurrence characterizes the quiet time solar maximum conditions, the ESF occurrence dominates the midnight-post midnight/pre sunrise hours under solar minimum conditions. The role of the evening pre-reversal enhancement in vertical drift (PRE) relative to that of a gravity wave precursor seed, for instability growth in the ESF development, is discussed. Their relative roles vary with the level of solar activity, such that the ESF occurrence pattern tends to have larger dependence on gravity wave distribution during solar minimum conditions (than during solar maximum), which points to the importance of pursuing studies using the immense data base accumulated during the prolonged solar minimum phase that just passed. While the solar minimum spread F irregularities driven by the equatorial electrodynamics processes might be connected to the gravity waves originating from tropical convective sources, the post midnight spread F of the low-latitude region appears to be ruled mainly by the medium-scale travelling ionospheric disturbance (MSTID) of mid-latitude origin
Description: 168-183
ISSN: 0975-105X (Online); 0367-8393 (Print)
Appears in Collections:IJRSP Vol.41(2) [April 2012]

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