Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset

Abstract

Abstract. The virtual height of the bottom side F-region (h F ) and equatorial spread-F (ESF) onsets at Chumphon (10.7 • N, 99.4 • E; 3.3 • N magnetic latitude) were compared with the behaviour of equatorial electrojet (EEJ) ground strength at Phuket (8.1 • N, 98.3 • E; 0.1 • N magnetic latitude) during the period from November 2007 to October 2008. Increase in the F-layer height and ESF onsets during the evening hours were well connected with the EEJ ground strength before sunset, namely, both the height increase and ESF onsets were suppressed when the integrated EEJ ground strength for the period from 1 to 2 h prior to sunset was negative. The finding suggests observationally that the pre-sunset E-region dynamo current and/or electric field are related to the F-region dynamics and ESF onsets around sunset.

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…The strong eastward equatorial electric field during the pre-reversal enhancement is linked to another phenomena called equatorial spread-F or plasma bubble, which is characterized by a depletion of the equatorial ionospheric plasma density (e.g., Burke et al 2004;Stolle et al 2006). Attempts have been made by several authors (e.g., Sreeja et al 2009;Uemoto et al 2010;Hajra et al 2012) to find a link between geomagnetic daily variations and the occurrence of the equatorial spread-F. For example, Uemoto et al (2010) reported that the occurrence of the equatorial spread-F is reduced when the equatorial electrojet 1-2 hours prior to the sunset is westward. Their results suggest the possibility of the detection of the equatorial spread-F using ground magnetometer data.…”

Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum

“…In addition, the daytime integrated EEJ strength values for both the hemispheres were evaluated by integrating all the hourly EEJ strengths from 07:00 to 12:00 LT. This gives the daytime integrated equatorial electrojet (IEEJ) strength values for each day (Uemoto et al, 2010;Venkatesh et al, 2015).…”

“…The transportation of plasma to higher latitudes through the EIA phenomenon is wellknown to relate with eastward electric field/EEJ and thermospheric meridional neutral wind. Older experiments from GPS measurements that unveil thermospheric meridional neutral wind effect on plasma transportation in the F region (de Paula et al, 2015) are few compared with electric field/EEJ (Venkatesh et al, 2015;Chen et al, 2008). While the electric field/EEJ is transporting the plasma across higher latitudes within low latitudes, thermospheric meridional neutral wind is modulating the transporting plasma either poleward or equatorward.…”

“…Hence, the eastward electric field plays a vital role in electron density distribution over the equatorial and low latitudes of the ionosphere. Venkatesh et al (2015) also investigated the role of EEJ in EIA using total electron content (TEC) data over the Indian and American sectors. They observed that the daily variations in EEJ strength significantly play a major role in the formation and development of EIA.…”

“…This will improve our understanding of the competitive role played by thermospheric meridional neutral winds in relation to electric field/EEJ. Chen et al (2008) and Venkatesh et al (2015) also investigated EIA morphology without considering selection of the quietest days for the estimates of solar quiet (S q ). Apart from the fact that the S q current system is crucial to the estimates of EEJ strength (Rastogi and Klobuchar, 1990;Anderson et al, 2002;Bolaji et al, 2015), the response of EIA to EEJ strength during the quietest period has not been carried out over the African-Middle Eastern sector.…”