An investication into geomagnetic and atmospheric response associated with the storm of April 12-14, 1981
An investigation is made of the intense storms of April 12- 14, 1981(Dst =-311nT) in an attempt to contribute to the current understanding of solar wind structures and magnetospheric processes that generate intense magnetic storms, as well as explain the F2 region response associated with these interplanetary structures and magnetospheric processes. The interplanetary and geomagnetic data used in this study consists of hourly values of proton density, solar wind flow speed, interplanetary magnetic field B component, and the low-latitude magnetic index, Dst. The ionospheric data are hourly values of foF2 obtained from a network of ionosonde stations located in the East Asian sector: Yakutsk, Magadan, Khabarovsk, Wakkanai, Akita, Kokubunji, Okinawa and Manila. The study shows that the present storm is double step, and the leading single magnetospheric process that was responsible for both the first and second Dst decrease is the enhancement of the plasma sheet. An enhanced solar wind density drove, under southward B conditions, the plasma sheet density leading to the injection of the ring current. In regards to the F2-region response, it appears the ionosphere in the East Asian zone is characterized by the occurrence of strong negative phase at the low latitude station of Manila before the beginning of the geomagnetic storm, absence of positive ionospheric storm effects at high and mid latitudes on the dayside during the initial phase of the magnetic storm, and simultaneous intense depletion of foF2 at all latitudes at ~ 20:00 UT, April 12. The simultaneous depletion of foF2 at all latitudes does not appear to support the previously held notion that the depletion of F2-region plasma density is due to changes in neutral composition resulting from neutral wind produced predominantly by Joule heating in the aurora zone, but rather suggests that particle precipitation does contribute to depletion of foF2 at all latitudes during intense magnetic storms.
Keywords: Geomagneticstorm, ionospheric Fz region, negative storm, plasma sheet density and ring current
Nigerian Journal of Physics Vol. 18 (2) 2006: pp. 171-180