Abstract
Abstract The paper studies the relative importance of penetrating eastward electric field (PEEF) and direct effects of equatorward neutral wind in leading to positive ionospheric storms at low-mid latitudes using observations and modeling. The observations show strong positive ionospheric storms in total electron content (TEC) and peak electron density (N max) at low-mid latitudes in Japan longitudes (≈125°E–145°E) during the first main phase (started at sunrise on 08 November) of a super double geomagnetic storm during 07–11 November 2004. The model results obtained using the Sheffield University Plasmashpere Ionosphere Model (SUPIM) show that the direct effects of storm-time equatorward neutral wind (that reduce poleward plasma flow and raise the ionosphere to high altitudes of reduced chemical loss) can be the main driver of positive ionospheric storms at low-mid latitudes except in N max around the equator. The equatorward wind without PEEF can also result in stronger positive ionospheric storms than with PEEF. Though PEEF on its own is unlikely to cause positive ionospheric storms, it can lead to positive ionospheric storms in the presence of an equatorward wind.
Highlights
Following geomagnetic storms, the ionospheric peak electron density (Nmax) and total electron content (TEC) often increase/decrease very much from their quiet-time levels
In this paper we present the relative importance of the penetrating eastward electric field (PEEF) and equatorward neutral wind on positive ionospheric storms at low-mid latitudes
The results presented above have shown that the direct effects of the equatorward neutral wind can be the main driver of positive ionospheric storms in Nmax and TEC at low-mid latitudes except in Nmax around the equator
Summary
The ionospheric peak electron density (Nmax) and total electron content (TEC) often increase/decrease very much from their quiet-time levels. These increase/decrease are known as positive/negative ionospheric storms (e.g., Matsushita, 1959; Matuura, 1972), which are found to depend on time of the day, longitude and season (e.g., Balan and Rao, 1990). The negative ionospheric storms at mid latitudes are more or less understood in terms of the upwelling (indirect) effect of the storm-time equatorward neutral wind (e.g., Richmond and Roble, 1979) that makes the thermosphere richer in molecular [N2] concentration and poorer in atomic [O] concentration so that chemical recombination becomes faster than normal (e.g., Rishbeth, 1991; Fuller-Rowell et al, 1994; Prolss, 1995). The causes of positive ionospheric storms are beginning to be understood (e.g., Reddy et al, 1990; Werner et al, 1999; Namgaladze et al, 2000; Basu et al, 2001; Balan et al, 2003).
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