Plasma blob observed by ground-based radio and optical techniques in the F-region — A case study on 27–28 August 1987

An interesting case of plasma blob event was observed on August 27-28, 1987 over Cachoeira Paulista (22.7°S, 45.0°W; magnetic latitude 13.25°S, declination 20°W) showing localized plasma density enhanced by a factor of, approximately, 2 above the background level. The F-region parameters were obtained from a Digisonde 256, which provide a good idea of the ionospheric behavior during the event. On this night, geomagnetic activity was moderately disturbed with Dst >; -70 nT. Complementary data was obtained from an all-sky imager operating on a routine basis at the same site. All-sky images were used to map the spatial extension and temporal location of plasma blob that showed, typically, east-west and north-south extensions of 320-350km and of 360-380km, respectively. In this paper, important features from this observation is presented and discussed.