On blanketing sporadic E and polarization effects near the equatorial electrojet

Abstract

[1] A number of puzzling features have been observed that occur during the day in the vicinity of the equatorial electrojet (EEJ). They include (1) an equatorial belt, essentially collocated with the EEJ, that is virtually devoid of blanketing sporadic E (E sb ); (2) appearances of E sb within that ''forbidden'' belt but only when the EEJ is weak or reversed (i.e., a counterelectrojet); (3) occasional appearances of a secondary current layer above the EEJ; and (4) observations at 4.3°N dip latitude of a latitudinal tilt in the bottomside E layer on one occasion and an unexpectedly large electron drift velocity on another. These features are shown to be accountable if the usual framework for electrodynamics in this region is modified to include the following: (1) transport of E sb that is controlled by a shear in the neutral wind with a crucial contribution from the polarization electric field of the EEJ; (2) the formation of an equatorward boundary for E sb by a dynamical balance between the neutral wind and the polarization electric field; (3) a buildup in conductivity within a band-like region, just poleward of the E sb boundary, from an accumulation of metallic ions; and (4) the appearance of a secondary polarization electric field across the band of enhanced conductivity and current flow throughout the region pervaded by that secondary electric field.

Occurrence of blanketing E<sub>s</sub> layer (E<sub>sb</sub>) over the equatorial region during the peculiar minimum of solar cycle 24

“…In view of the theories summarized above, we understand that the E sb observed at the equatorial region is either formed locally (Reddy and Devasia, 1973) or transported from the off-equatorial region (Chandra and Rastogi, 1975;Tsunoda, 2008). However, the contribution from each of the abovementioned processes to E sb occurrence observed in the different seasons is not known.…”

“…For the formation of E sb at the equator, the authors have also suggested the transport mechanism of ionized E sb layer from off-equatorial latitudes to equatorial latitudes in the presence of horizontal wind with a significant north-south component. However, they could not establish the link between weak EEJ and E sb occurrence, which is addressed by Tsunoda (2008) for the first time.…”

“…Recently, Tsunoda (2008) suggested that E sb is transported to the equator from an off-equatorial station where they are formed due to wind shear mechanism. The author has shown that such a transport occurs only when the neutral wind speed at the off-equatorial station is greater than a certain threshold speed (Tsunoda, 2008, see Eq. 2), which is determined by the vertical polarization electric field linked with EEJ.…”

“…Reddy and Devasia (1973) proposed theories to explain the formation of E sb at equatorial latitudes, which are based on the horizontal convergence of ions. The most widely observed features of E sb are its seasonal occurrence, which indicates a peak during the local summer (Bhargava and Subrahmanyan, 1964;Oyinloye, 1969;Chandra and Rastogi, 1975;Devasia, 1976;Devasia et al, 2006), and its anti-correlation with equatorial electrojet (EEJ) intensity (Tsunoda, 2008). The theories proposed for the formation of E sb do not explain its seasonal dependence and the role of EEJ.…”

“…Based on long-term observations of meteors from 554 V. Yadav et al: Peculiar solar minimum and E sb occurrence mid-latitude stations, it is shown that the strength and occurrence of E s layer are closely related to the meteor influx (Haldoupis et al, 2007;Haldoupis, 2011). Tsunoda (2008) suggested the transport mechanism for the formation of E sb at the equator and established the dependence of EEJ for the first time.…”