Statistical study of medium-scale traveling ionospheric disturbances in low-latitude ionosphere using an automatic algorithm

Pin-Hsuan Cheng,Jia-Ting Lin,Panthalingal Krishanunni Rajesh,Chia-Hung Chen,Hanli Liu,M T Chang,Charles Lin,Yuichi Otsuka

doi:10.1186/s40623-021-01432-1

Abstract

This study investigates the medium-scale traveling ionospheric disturbances (MSTIDs) statistically at the low-latitude equatorial ionization anomaly (EIA) region in the northern hemisphere. We apply the automatic detection algorithm including the three-dimensional fast Fourier transform (3-D FFT) and support vector machine (SVM) on total electron content (TEC) observations, derived from a network of ground-based global navigation satellite system (GNSS) receivers in Taiwan (14.5° N geomagnetic latitude; 32.5° inclination), to identify MSTID from other waves or irregularity features. The obtained results are analyzed statistically to examine the behavior of low-latitude MSTIDs. Statistical results indicate the following characteristics. First, the southward (equatorward) MSTIDs are observed almost every day during 0800–2100 LT in Spring and Winter. At midnight, southward MSTIDs are more discernible in Summer and majority of them are propagating from Japan to Taiwan. Second, northward (poleward) MSTIDs are more frequently detected during 1200–2100 LT in Spring and Summer with the secondary peak of occurrence between day of year (DOY) 100–140 during 0000–0300 LT. The characteristics of the MSTIDs are interpreted with additional observations from radio occultation (RO) soundings of FORMOSAT-3/COSMIC as well as modeled atmospheric waves from the high-resolution Whole Atmosphere Community Climate Model (WACCM) suggesting that the nighttime MSTIDs in Summer is likely connected to the atmospheric gravity waves (AGWs).

Highlights

Traveling ionospheric disturbances (TIDs) are known as the manifestation of atmospheric gravity waves (AGWs) of lower atmospheric origins (Hines 1960) in the ionosphere
The occurrence rate of northward medium-scale TIDs (MSTIDs) (Fig. 3d–f ) demonstrates that they are more frequently observed around 1200–2100 local time (LT) from Spring to Fall with a secondary peak occurring around 0000–0300 LT between day of year (DOY) 100–140
It is noteworthy that the LT dependence of the southwestward MSTIDs takes place much later after sunset than those reported in the previous literature (Behnke 1979; Saito et al 1998; Garcia et al 2000; Shiokawa et al 2003a; Kotake et al 2006; Tsugawa et al 2007a; Kubota et al 2011; Hernández-Pajares et al 2012; Otsuka et al 2013), suggesting an alternative driving mechanism should be proposed

Summary

Introduction

Traveling ionospheric disturbances (TIDs) are known as the manifestation of atmospheric gravity waves (AGWs) of lower atmospheric origins (Hines 1960) in the ionosphere. MSTIDs were previously categorized into daytime and nighttime types according to their wave characteristics. Cheng et al Earth, Planets and Space (2021) 73:105 in northwest–southeast (NW–SE) direction (HernandezPajares et al 2012; Kotake et al 2006; Otsuka et al 2011). The nighttime MSTID has a unique frontal alignment in the northwest–southeast (NW–SE) direction with propagation direction in equator westward direction (Behnke 1979; Saito et al 1998; Garcia et al 2000; Shiokawa et al 2003a; Kotake et al 2006; Tsugawa et al 2007a; Kubota et al 2011; Hernández‐Pajares et al 2012; Rajesh et al 2016). It is due to such a special frontal alignment, the phenomenon was originally explained by Perkins instability (c.f. Perkins 1973; Behnke 1979; Garcia et al 2000)

Methods

Results

Conclusion