Medium Scale Traveling Ionospheric Disturbances Observed by the SuperDARN Radars Located in the Asian Mid-Latitude

Abstract

Medium-scale traveling ionospheric disturbances (MSTIDs) manifest as quasi-periodic enhancements and depletions in ionospheric electron density, primarily caused by ion-neutral collisions, plasma instabilities, and electromagnetic forcing. Super Dual Auroral Radar Network (SuperDARN) radars are powerful instruments that can be used to study the ionospheric irregularities, MSTIDs, and many other phenomena. Newly built SuperDARN radars were deployed in the Chinese mid-latitude region (CN-DARN) to provide us with the opportunity to study the propagation and evolution of MSTIDs on a larger scale in the Asian region. In this paper, a southwestward propagation of MSTIDs in Asia was observed by two Japanese SuperDARN radars: the Hokkaido East Radar (HOK), Hokkaido West Radar (HKW), and two Chinese SuperDARN radars: Siziwang East Radar (SZE), and Siziwang West Radar (SZW), in combination with 630-nm all-sky airglow imager (ASAI) and Global Navigation Satellite System - Total Electron Content (GNSS-TEC) measurements. The dominant direction of the MSTIDs was toward the southwest at −117 $\pm$ 8 to −145 $\pm$ 6°. Horizontal wavelengths ranged from 321 $\pm$ 37 to 462 $\pm$ 36 $km$, periods were between 24 $\pm$ 2 and 30 $\pm$ 2 min, and horizontal phase velocities varied from 182 $\pm$ 36 to 257 $\pm$ 37 $m{s}^{-1}$. Specifically, the equal periods are as observed by SuperDARN radars in E- and F-regions, and the period of the Es layer observed by a nearby digisonde is in accordance with the radar observations. This provides strong evidence that a coupling existed between the E- and F-regions when MSTIDs were passing over the Asian sector. Moreover, the E- and F-regions quasi-periodic echoes also indicate that there were small-scale ionospheric irregularities possibly modulated by the observed MSTIDs or vice-versa.