Spectral characteristics of magnetic storm-induced F-region scintillations extending into daytime

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

“…This plays a significant role in the generation and growth of F-region irregularities and explains the magnetic storm-induced post-midnight scintillations extending into the daytime (Chandra et al, 1995;Chakraborty et al, 1999;Basu et al, 2001a;Bhattacharya et al, 2002). The equatorial dynamo electric field is also disturbed during a magnetic storm and this also affects the irregularities (Basu et al, 2001a;Bhattacharya et al, 2002).…”

Geomagnetic storms and their ionospheric effects observed at the equatorial anomaly crest in the Indian Region

“…During disturbed conditions only high latitude current systems may produce significant perturbations, or reversals, of equatorial electric fields (Nopper and Carovillano, 1978) and such reversals are most pronounced from midnight to dawn sectors. Chandra et al (1995), from positive dH/dt in the post-midnight period and the oscillating changes in the geomagnetic H component at Alibag (19.01N, 73.01E) and Trivendrum (8.31N, 76.91E) for the storm of 11 November 1991, reported that it is the highlatitude electric field which during severe magnetic storm events, penetrates to low and equatorial latitudes and leads to generation of new F-region irregularities. F-region irregularities thus generated cause intense scintillations in the post-midnight period, which can persist into the morning or daytime.…”

“…Aarons (1991) studied F-layer irregularities during a number of magnetic storms in the American and Eastern sectors, during 1971-1981, a period of high solar activity and found that if minimum Dst occurs during the midnight to post-midnight period, equatorial electron density irregularities are generated in the post-midnight period, and if minimum Dst occurs in early afternoon the nighttime irregularities are inhibited. Chandra et al (1995) have reported F-region scintillations extending into daytime at Bombay near the anomaly crest and at Trivendrum near the dip equator in the Indian region during the severe magnetic storm of 11 November, 1991 in which Dst of À230 nT occurred in the post-midnight sector. We report here that magnetic storms with DstoÀ100 nT are most effective in producing post-midnight scintillations which can extent into the daytime sectors.…”

“…Radio wave signals transmitted from geostationary satellites and recorded by ground based receivers yield information about the ionospheric irregularities producing the scintillations. Several workers have reported geomagnetic control over the occurrence of scintillations at equatorial and low latitudes (Aarons et al, 1980;Rastogi et al, 1981;Aarons and DasGupta, 1984;DasGupta et al, 1985;Dabas et al, 1989;Aarons, 1991;Chandra et al, 1995;Kumar and Gwal, 2000;Basu et al, 2002). Nevertheless, it is not yet possible to forecast the response of scintillations to geomagnetic storms, due to complexity and unique character of each particular geomagnetic storm.…”

Fuzzy mathematical model for the analysis of geomagnetic field data

“…India has a unique set of geomagnetic observatories spanning the magnetic equator and the S q focus in a region of the world where the geomagnetic and geographic meridian planes are least separated. A number of geomagnetic storms have been analyzed in terms of their (1) solar flare effects and sudden commencement (Rastogi et al, 1997), (2) the H amplitude of sudden commencement at Sabhawala (Jain, 1978), (3) spectral characteristics (Chandra et al, 1995), (4) effects on the ionosphere total electron content and evidence of electro-jet control (Jain, 1978), (5) multi-dimensional scaling (Sridharan and Ramasamy, 2002), (6) extreme behavior (magnetic storm of 1-2 September 1859; Tsurutani et al, 2002), and (6) fractal behavior (29-31 October 2003;Sridharan and Gururajan, 2006). Although no two storms are identical, most storms have certain features in common (Parkinson, 1983).…”