Simultaneous observations of large-scale traveling ionospheric disturbances on the nightside and dayside middle latitude

H T Cai,F Yin,S Y Ma,Y W Liu,J S Xu

doi:10.5194/angeo-30-1709-2012

Abstract

Abstract. In this paper, we present further observational evidence for the transpolar propagation of large-scale traveling ionospheric disturbances (LSTIDs) from their nightside source region to the dayside reported by Cai et al. (2011). Slant total electron content (STEC) observed by longitudinally aligned GPS receiver chains in North American and European sectors was analyzed to demonstrate presences of LSTIDs at both nightside and dayside mid-latitude. Signatures of TID were inferred from phase difference in time series of STEC perturbations (TECP) derived from measurements of ground-based GPS receivers, which are separated by hundreds of kilometers longitudinally. Periods of the daytime and nighttime ionospheric disturbances were estimated to be around 128 min, being in good agreement with that of the transpolar AGW (atmospheric gravity wave) recorded by EISCAT (European Incoherent Scatter Scientific Association)/ESR (EISCAT Svalbard Radar) radars. On the dayside, the LSTID moved equatorward with an average phase speed of ~440 m s−1. In North American sector, however, southward speed of the nighttime LSTID was much slower, being around 160 m s−1. We suggest that the observed daytime and nighttime mid-latitude LSTIDs are likely to have the same source region, being located somewhere at nighttime auroral latitude. Having been launched on the nightside, the waves propagate simultaneously equatorward and poleward. The equatorward-moving waves are recorded by GPS receiver chain in North American sector. The poleward-moving waves, however, cross the polar cap from nightside to dayside and then are detected consecutively at high and mid-latitudes by EISCAT/ESR radars and GPS receiver chains, respectively.

Highlights

Properties of the traveling ionospheric disturbances (TIDs) have been investigated extensively recently by means of observations and numerical simulation
We have presented observations of large-scale TIDs (LSTIDs) on both the dayside and nightside, which are likely to originate from the same source region
The daytime mid-latitude LSTID seems to be a consequence of the transpolar atmospheric gravity waves (AGW)/TID reported by Cai et al (2011), which must have been launched on the nightside during substorm activity and have propagated poleward from the source region

Summary

Introduction

Properties of the traveling ionospheric disturbances (TIDs) have been investigated extensively recently by means of observations and numerical simulation (as reviewed by Hocke and Schlegel, 1996, and references therein). The simultaneous presence of TIDs at high, mid- and low latitudes, and in both Northern and Southern Hemispheres, propagating from both auroral regions toward the geographic Equator, was detected during magnetically disturbed periods (Valladares et al, 2009). The authors suggested that the disturbance had propagated across the northern polar cap from the nighttime auroral source during substorm conditions. They did not provide any observational evidence to support their hypothesis. This paper contributes further support for the hypothesis of Cai et al (2011), focusing on propagations of the induced LSTID from the same source on both nightside and dayside mid-latitude.

Data and method

Geomagnetic activity

Observations of LSTID on the dayside

Observations of LSTID on the nightside

Discussion

Summary