Characterization of seasonal and longitudinal variability of EEJ in the Indian region

Abstract

This paper presents the seasonal and longitudinal variability of the equatorial electrojet (EEJ) based on geomagnetic variation data from two electrojet stations in the northern Indian Ocean at a longitudinal separation of~15°: i.e., at 77°E and at 93°E. One complete year of data is used (i.e., from November 2011 to October 2012) at the two longitudes and compared with the climatological model of the equatorial electrojet (EEJM-2.0). The results of our analysis show that (i) the monthly averaged hourly values of EEJ strength at 77°E and 93°E are overall in agreement with global characteristics of EEJ with significant departures over the year of study, (ii) the monthly average hourly daytime values at Campbell Bay and Vencode show poor correlation (r < 0.7) for 5 out of 10 months, (iii) comparison of observed EEJ strength at respective longitudes and the current densities derived from EEJM-2.0 show overall agreement with significant differences for monthly mean hourly daytime values at respective longitudes, and (iv) day-to-day variability in noontime EEJ amplitudes between the two longitudes is >10 nT, >20 nT for 30% of quiet days, sorted by planetary index (Kp) <1 and <2. This variability is reflected in monthly average values (V) mechanisms for persistent differences in EEJ on day-to-day basis are sought from perturbation of westward ion drifts by neutral winds caused by the upward propagation of gravity waves from troposphere/stratosphere into the mesosphere. These mechanisms have been identified theoretically and experimentally. The four-wave structure of ionospheric current densities obtained by EEJM-2.0 and other contemporary models closely resembles atmospheric tidal signatures and has a common origin. The magnitude and persistence of these differences, at short spatial scales (15°), are significant observation. These effects are reflected in the monthly and seasonal signatures of EEJ and contribute to the contemporary models.

Effect of Disturbance Electric Fields on Equatorial Electrojet Over Indian Longitudes

“…It has been established earlier that the eastward electric field ( E region) at equator shows a four‐wave longitudinal structure with a crest at 100°E and a trough at 60°E longitude, attributed to DE3 nonmigrating tide (Lühr et al, ). Similar trend was noted in comparison of CBY and VEN and EEJ and CEJ strengths (Chandrasekhar et al, , , )(from 93–77°). Additionally, using a year's concurrent data with MNC (72°), the westward decrease in EEJ strength as well as increase strength of westward currents demonstrated in a separate analysis (Archana R. K., personal communication, June 25, 2018).…”

Solar quiet current response in the African sector due to a 2009 sudden stratospheric warming event

“…[], Doumouya and Cohen [], and Chandrasekhar et al . [] when there is no influence due to SSW. Doumouya et al .…”

“…Chandrasekhar et al . [] showed that EEJ current is strongest in South America sector (western axis) and weakest in India sector (eastern axis). In the worldwide context summary, magnetic field variations are stronger in the western than the eastern axis.…”

“…This indicates that during SSW peak phases, reduction of upward propagating tides at the lower thermosphere from the middle atmosphere is on worldwide scale. One obvious longitudinal feature found in all the phases with SSW ascending phase as an exception that further clarifies the controversial western and eastern axes issues [ Doumouya et al ., ; Doumouya and Cohen , ; Chandrasekhar et al ., ] is that S q H variability is highest, higher, and high at the South America, Africa, and Pacific Ocean sectors, respectively. Also, the S q H variability is relatively weaker over the Asian sector.…”

On the variation in the ionospheric response to geomagnetic storms with time of onset

“…Numerical and observational studies of the variability of ionospheric features in the middle and low latitudes have been conducted over the years; however, there are limited studies focused exclusively on longitudinal variability due to the univeral time (UT) onset time in the low latitudes. Explorations of the longitude sector differences of equatorial spread F have been conducted by several groups[ Aarons , ; Fejer et al , ; Abdu et al , ; Oladipo et al , ], and several studies have found an impact of longitudinal effects on the equatorial electroject (EEJ) [ England et al , ; Klimenko and Klimenko , ; Yizengaw et al , ; Phani Chandrasekhar et al , ]. It has also been recognized that the neutral atmosphere plays a critical role through nonmigrating tidal influences [ Immel et al , ; Forbes et al , ; Maute et al , ] and longitudinally dependent thermospheric winds [ Fuller‐Rowell et al , ; Sojka et al , ] in the distribution of plasma.…”