Spread‐F/sporadic E coupling at Chung‐Li, especially for postsunset periods of sunspot maximum years

Abstract

[1] Using ionogram-recorded data, the coupling between spread-F occurrence and enhanced E s blanketing frequencies ( f b E s ) (indicative of f o E s changes), has been investigated for an equatorial-ionospheric-anomaly crest station, Chung-Li, for the postsunset periods of sunspot-maximum years. Apart from the evidence for coupling from inspections of the f-plots alone, for the years analyzed (1981, 1982, 1988, and 1989), statistical results of more significance were found from superposed-epoch analyses. Isolated spread-F events of duration of 2 hours or less which started at or before 2200 LT were used as controls on time series. These series were made up of comparisons between 15-min f-plot f b E s values and interpolated monthly median f b E s values. Evidence for coupling was found for the analyses which involved 97 controls. The evidence in the f-plots for three events involving E s patches, which investigators have examined in some detail using the VHF radar at Chung-Li, suggests that these events are also coupled to isolated spread-F occurrence.

Planetary wave signatures in the equatorial atmosphere–ionosphere system, and mesosphere- E- and F-region coupling

“…However, observational evidence on the effect of Es-layers on ESF development so far available lead to diverging conclusions. For example, while an isolated case of ESF inhibition in the presence of sporadic E-layer over the equatorial station Jicamarca has been reported by Stephan et al (2002) an exactly opposite effect from the statistical data set of ESF enhancement in the presence of sporadic E-layers over an equatorial anomaly (low latitude) station, Chung-Li, has been shown by Bowman and Mortimer (2003). Such apparently ambiguous/contradictory manifestations of the Es-layer-ESF relationship can be understood in the light of a direct relationship between the PRE development and the evening Es-layer formation conditions that has been recently demonstrated by Abdu et al (2003).…”

The Initial Results of the Chung-Li Dynasonde for RF Environment Surveillance and Ionospheric Observations

“…The foEs of the mid-latitudes has been depicted as being less than that of aurora areas according to earlier research (Davies 1990). However, in the case of sporadic E over Chung-Li, which is near an area where electro-jets descend, something quite distinct appears to be occurring; the results of Mortimer (2002 and2003) support the existence of coupling between isolated spread-F events and sporadic E enhancements for the EIA crest station especially for post-sunset periods of sunspot maximum years from old Chung-Li data. From the initial results of the Chung-Li dynasonde, sporadic E appeared in both the daytime and nighttime.…”

A Statistical Study on The Local Time Dependence of Equatorial Spread F (ESF) Irregularities and Their Relation to Low‐Latitude Es Layers Under Geomagnetic Storms

“…However, the PRE itself depends on longitudinal variation of the flux tube-integrated conductivity (Abdu et al, 1981;Batista et al, 1986;Bowman & Mortimer, 2003). However, the PRE itself depends on longitudinal variation of the flux tube-integrated conductivity (Abdu et al, 1981;Batista et al, 1986;Bowman & Mortimer, 2003).…”

“…It is seen that if Es-layer disruption does not occur, the percentage occurrence of spread F can get reduced. There are several reports that suggest the existence of coupling between the postsunset occurrence and nonoccurrence of spread-F and Es-layer absence/presence at low-latitude crest region (Bowman & Mortimer, 2003). The base height of the Es layer or disruption of the Es layer starts at~05:00 IST, and at the same time, virtual height of the F layer also starts to enhance and reaches its maximum mean value at~370 km at~05:30 IST, and the percentage occurrence of ionospheric irregularities is enhanced to~38%.…”