Ionosphere disturbances observed throughout Southeast Asia of the superstorm of 20--22 November 2003

Ionospheric disturbances in the Southeast Asian region during the super magnetic storm of 20–22 November 2003 were investigated through an ionosonde chain and a GPS network assisted by the space-borne instruments. At early stage of the storm in the postsunset sector, large enhancements in the critical frequency of F2 layer and total electron content were observed at northern crest region of the equatorial ionization anomaly (EIA), which might be produced by both the storm meridional wind superimposed with traveling atmospheric disturbances and prompt penetration electric field (PPE). During the main phase of the storm when interplanetary magnetic field started a 12-h southward turning, equatorial ionosphere was elevated to a very high level which should be most probably caused by a long-duration PPE event. Meanwhile, at mid-low latitudes, ionosphere witnessed an initial simultaneous decrease then followed by drastic increases, which is very different from the past observations in this region (Reddy and Nishida, 1992). Combined analysis of the data from the ionosonde and other space-based measurement shows that for the present case the penetration efficiency of the interplanetary electric field (IEF) to the equatorial ionosphere was larger at night than in the daytime, which agrees with the results of Fejer et al. (2007) showing the ratios of PPE and IEF changes were highly variable with the local time. During the recovery phase, EIA was severely inhibited owing to a wind convergence and possibly because of the westward disturbance dynamo electric field.