Equatorward Medium to Large-Scale Traveling: Ionospheric Disturbances of High latitude Origin During Quiet Conditions

This article presents observations of medium to large-scale traveling ionospheric disturbances (TIDs) originating from high latitudes, and propagating across the equator into the opposite hemisphere in the African-European sector during geomagnetically quiet conditions between 2010 and 2018. During the study period, four geomagnetically quiet days were selected each month. The Global Navigation Satellite Systems (GNSS) total electron content (TEC) data were used to obtain the two dimensional (2-D) TEC residuals. We have identified seven transhemispheric TIDs from the days that were analyzed with five originating in the southern and the rest in northern wintertime hemisphere. The TIDs meridional propagation velocities, periods and wavelengths are in the range of 270-322 m/s, 48-80 min and 802-1,296 km, respectively. The horizontal propagation velocities and horizontal wavelengths ranges are C-H = 120-274 m/s and lambda(H) = 379-1,104 km, respectively. Analysis of the conditions of the space weather environment rules out space weather as a source of the TIDs. While observations of the 4.3 mu m brightness temperature (BT) from the Atmospheric Infrared Sounder (AIRS) instrument on board the NASA Aqua satellite show the existence of atmospheric gravity waves (AGWs) in the troposphere-stratosphere region, it is suggested that the tertiary GWs from orographic forcing may be the likely source of the TIDs observed in this study.

Automated summary

This article presents observations of medium to large-scale traveling ionospheric disturbances (TIDs) originating from high latitudes, and propagating across the equator into the opposite hemisphere in the African-European sector during geomagnetically quiet conditions between 2010 and 2018. The study identifies the characteristics of the TIDs, including their propagation velocities, periods, and wavelengths, and suggests that tertiary gravity waves from orographic forcing may be the likely source of the observed TIDs.