Abstract
The characteristics of longitudinal variability of equatorial electrojet (EEJ) and counter electrojet (CEJ), presented in this study, are based on concurrent observations from a hitherto unsampled region of the world to examine the (1) degree of correlation between hourly means and monthly averaged hourly means of ground observations with equatorial electrojet climatological model (EEJM-2.0), (2) day-to-day longitudinal variability of EEJ strength between the pairs of sites, and (3) longitudinal variability in occurrences of counter electrojet. The analyses are based on the data obtained from an observatory and three new remote sites in the northern Indian Ocean at a longitudinal separation of approximately 15°: Hyderabad (HYB) and Vencode (VEN) at 77° E and Port Blair (PBR) and Campbell Bay (CBY) at 93° E, for a period of 4 months during Lloyd's D-season (November 2011 to February 2012) and comparison with the EEJM-2.0 based on CHAMP satellite data. At both longitudes, the overall correlation of monthly mean hourly values (i.e., from 05:00 to 19:00 LT) between the observed EEJ strength and modeled current density from EEJM-2.0 is good (r > 0.8). However, a significant lack of correlation is witnessed on day-to-day peak values (i.e., 12:00 LT) between the observed variations and the model at both sites. Further, a comparison of noontime peaks between the two sites shows a considerable day-to-day variability. A large number of CEJs (43 events) are recorded during the study: at CBY (15 events) and VEN (28 events). Analyses of the CEJ events highlight the variability of CEJ phenomena in terms of amplitude, dates, and time of occurrence over 15° longitude separation. The local nature of perturbations causing CEJ is evident; the possible factors are being non-migrating eastward and westward propagating diurnal tides and local meteorological phenomena associated with upper mesospheric temperature, wind, and density variations.
Highlights
The equatorial electrojet The two or three fold enhancement in the daily variation of the horizontal component of the earth's magnetic field (H), within a narrow belt of latitudes (±3°) over the dip equator (Egedal 1947), is caused by an eastward current in the E-region of the ionosphere, called the equatorial electrojet (EEJ) (Chapman 1951)
New data at closely spaced EEJ sites and comparison with EEJM-2.0 A new set of electrojet pairs used in the present study (VEN-HYB and Campbell Bay (CBY)-Port Blair (PBR)) formed the first such set of observations of magnetic variations, separated by 15° longitude and were compared with the monthly averaged values of current densities over the northern Indian
The current study presents for the first time observations that document the variability in EEJ at separation of 15° longitude with two new remote electrojet sites in India
Summary
The equatorial electrojet The two or three fold enhancement in the daily variation of the horizontal component of the earth's magnetic field (H), within a narrow belt of latitudes (±3°) over the dip equator (Egedal 1947), is caused by an eastward current in the E-region of the ionosphere, called the equatorial electrojet (EEJ) (Chapman 1951). The strength of the electrojet current in a particular longitude zone is determined by deducting the diurnal range of H or X component at a Longitudinal dependence of the EEJ Day-to-day variability of the EEJ, at a site or between longitudinally separated sites, is amply documented between different longitudinal sectors (Rastogi 1962b) as well as from satellite observations (Langel et al 1993). Statistical correlations for day-to-day variation of EEJ strength and solar wind parameters from ground and satellite data indicate good correlation between the two (Rastogi and Chandra, 1974). Jadhav et al (2002) derived the day-to-day EEJ strength using the satellite and simultaneous ground magnetic observatory data for the Indian and American sectors, corroborating the results of analysis made by Rastogi (1962b). The recent work by Adimula et al (2011) again discussed the longitudinal variability in EEJ showing strongest electrojet strength in the South American sector (approximately 59° W) with an average peak more than 100 nT and weakest in Malaysian sector (approximately 101° E) with 70 nT
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