Observation of Very Short Period Atmospheric Gravity Waves in the Lower Ionosphere Using Very Low Frequency Waves

Abstract

We present observations of very short period (<5 min) wavy fluctuations (WFs) in the lower ionosphere (75-85 km) on the night of 21 January 2016, using subionospherically propagating very low frequency signals. Four out of six transmitter signals recorded by the very low frequency/low frequency receiver at the Pisgah Astronomical Research Institute showed WFs simultaneously. However, their time of occurrence and intensities were different. Power spectral analysis indicates a period of~3-4 mins, largely associated with the two regions of strong convective and lightning activity in the lower troposphere. Background wind (at~15 and 80 km) direction shows westward propagation, suggesting important role of the convective storm located east of Pisgah Astronomical Research Institute. The GPS total electron content analysis also divulges similar WFs at upper ionospheric altitude (~300 km) on the GPS total electron content stations around the two storms. The observational analysis suggests atmospheric gravity waves from the convective regions propagate upward up into the ionospheric altitudes. Hence, the present study reinforces the strong coupling of troposphere and ionosphere through the convectively generated very short period waves.

Statistical Study of F‐Region Short Period Ionospheric Disturbances Related to Convection in the Lower Atmosphere Over Wuhan, China

“…They found that the TIDs are most likely induced by secondary gravity waves from local horizontal body forces created by the dissipation of primary gravity waves from deep convection. These findings have also been confirmed by other studies (Liu et al., 2021; Maurya et al., 2019; Miyoshi et al., 2018; Snively & Pasko, 2008; Vadas & Becker, 2018; Zhao et al., 2020). To date, the effects of convective activity on the ionosphere have various explanations.…”

“…In Figures 5 and 6, short‐period ionospheric disturbances were mainly concentrated from May to August and reached their maxima around May and June, which occurred mainly around midnight. According to previous studies that focused on gravity waves, gravity waves tend to propagate in the opposite direction to that of background winds as a result of wind‐filtering effects (Lindzen, 1981; Maurya et al., 2019; Nishioka et al., 2013). In summer, as shown in Figures 8c–8f, the zonal wind fields above the troposphere were dominated by westward winds, and the whole meridional wind fields were relatively weak.…”

Ionospheric monitoring with the Chilean GPS eyeball during the South American total solar eclipse on 2nd July 2019

“…The winds are converging from south and north of the Chile region and they strengthened with magnitudes of about 60 m/s to the east. As suggested in previous works 28 – 30 the AGWs can easily pass through the critical levels when they propagate opposite to wind direction. It means that background wind direction during eclipse time supports the AGWs propagation towards northward and opposes southward.…”

“…The wind data is used from the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis 5 product ECMWF 26 . The data are produced in 137 hybrid sigma pressure levels covering the surface to ~ 80 km altitude, with a spatial resolution of ~ 31 km 27 , which can be As suggested in previous works [28][29][30] the AGWs can easily pass through the critical levels when they propagate opposite to wind direction. It means that background wind direction during eclipse time supports the AGWs propagation towards northward and opposes southward.…”

“…Thus, AGWs propagating towards north more prominently and southward propagating waves are slowed down/attenuated. Maurya et al 30 reported thunderstorm/convection generated AGWs which are propagating opposite to the background wind direction reaching the GPS station and affecting VTEC signals. Nishioka et al 31 also discussed the important role of background wind and suggested when background wind velocity is comparable to the phase velocity of AGWs, their propagation along the wind direction are restricted/reduced.…”