The equatorward wall of the subauroral trough in the afternoon/evening sector

Abstract

Abstract. Although ionospheric troughs are a very important feature of the subauroral ionosphere, many of their properties remain incompletely documented and understood. Here Dynamics Explorer-2 satellite data are used to investigate one specific part of this complex phenomenon, namely its equatorward wall. We find that in the afternoon/evening sector of the Northern Hemisphere the location of this density drop depends primarily on the level of geomagnetic activity and magnetic local time. Longitudinal variations are only of secondary importance. A formula is derived which summarizes these variations. The magnitude of the density drop in the trough wall depends primarily on altitude and longitude, and to a lesser degree on local time and geomagnetic activity. These variations are also described quantitatively. Using a superposed epoch type of averaging procedure, a mean latitudinal profile of the trough wall is derived. No anomalous increase in the density at the equatorward edge of the trough is observed. There is, however, a significant increase in the electron temperature at the location of the density drop. Our results are important for the empirical description and numerical simulation of ionospheric troughs. They also may be used to define the boundary between middle and subauroral latitudes.

The main ionospheric trough in the East Asian region: Observation and modeling

“…A depleted region of the F2 layer ionization in the afternoon/evening sector has been observed for many years (Lockwood, 1980;Benkova et al, 1980;Besprozvannaya et al, 1986;Evans et al, 1983b;Holt et al, 1984;Whalen, 1987Whalen, , 1989Vo and Foster, 2001;Prh olss et al, 1991;Prh olss, 2007). In these papers, this region is termed daytime, midday, mid-latitude, and subauroral troughs.…”

Ionospheric altitude profiles in the main ionospheric trough as observed by field-aligned EISCAT incoherent scatter radar observations

“…1 and 6). The trough depth depends on MLT (Prölss, 2007, his figure 8), but as he has shown this dependence is not very pronounced. So the main reason for the difference should be related to E Â B drifts.…”

Ionospheric response to geomagnetic disturbances in the north-eastern region of Asia during the minimum of 23rd cycle of solar activity

“…The fall of the foF2 was more expressed on 25 September in the second recovery phase. It is similar to the sudden density drop on the equatorward wall of the subauroral trough (Prö lss, 2007). At night the foF2 did not stand out above 2 MHz and sometimes the reflections in F2 layer absented because of the low level of ionization.…”