Effect of geomagnetic activity on equatorial radio VHF scintillations and spread F

Abstract

The paper discusses the occurrence of scintillations of ATS 3 (137 MHz) beacons recorded at Huancayo on geomagnetically quiet and disturbed days during the years 1969–1976 and compares the results with the corresponding occurrence of range and frequency spread F at Huancayo. During the equinoctial months and the December solsticial months the geomagnetic activity reduces the equatorial scintillations during premidnight hours but increases their occurrence during the postmidnight hours. These features are very similar to the effect of geomagnetic activity on the occurrence of the range type of equatorial spread F rather than on the occurrence of frequency spread, which decreases for any hour of the night during geomagnetic active periods. During the June solsticial months, the occurrence of both scintillations and spread F is very much reduced; however, both the phenomena are more frequent on disturbed than on quiet days for any of the hours of the night. These effects are consistently the same for any of the years within the solar cycle. It is suggested that the equatorial radio scintillations at 137 MHz during the nighttime are produced primarily by the occurrence of the range type of spread F. The geomagnetic effects are due to the modifications of the equatorial electric field by the geomagnetic disturbance and thereby affect the development of F region irregularities causing scintillations.

Seasonal and solar cycle variations of spread F at the equatorial anomaly crest zone.

“…In low latitude regions, no significant delayed peak or dip in the occurrence of spread Fis found with respect to geomagnetic activity. At Huancayo, RASTOGI et al (1981) reported that on disturbed days during the equinoctial and December solstitial months, the occurrence of range spread F reduced during the pre-midnight hours but increased during the post-midnight hours, while the occurrence of frequency spread F decreased at any hours of the night. However, on June solstitial months, both range spread F and frequency spread F are more frequent on disturbed days than on quiet days at any hour of the night.…”

Occurrence of Equatorial Plasma Bubbles during Intense Magnetic Storms

“…In earlier studies, some investigators suggested that magnetic storms suppressed equatorial spread F (ESF) in the evening sector. Rastogi et al [33] reported that the enhanced magnetic activity reduced the occurrence of equatorial radio scintillations and spread F during premidnight hours. Watanabe and Oya [34] found that the occurrence probability of plasma bubbles decreased during magnetically active periods for the local time in premidnight.…”

Effect of solar and magnetic activity on VHF scintillations near the equatorial anomaly crest

“…Any change in the electric field influences the occurrence of low-latitude scintillations. With increasing interest in understanding the behavior of ionospheric irregularities near the magnetic equator, efforts have been made to examine the influence of solar and magnetic activity over the occurrence of scintillations associated with ionospheric irregularities (Aarons et al, 1980;Rastogi et al, 1981;DasGupta et al, 1985;Dabas et al, 1989;Pathak et al, 1995;Chakraborty et al, 1999;Kumar and Gwal, 2000;Banola et al, 2001;Basu et al, 2001a, b;Bhattacharya et al, 2002). Analysis of the role of magnetic storms on low-latitude scintillations has shown that for most of the storms for which the recovery phase starts after midnight, the probability of occurrence of scintillation activity is enhanced during the post-midnight period (Aarons and Das Gupta, 1984;Kumar and Gwal, 2000).…”