Short‐term relationship of total electron content with geomagnetic activity in equatorial regions

Abstract

The short‐term relationship between equatorial ionosphere and geomagnetic activity is examined. Hourly averages of the total electron content (TEC) and critical frequency of the F2 layer (foF2) are compared with the Dst index, a proxy for equatorial geomagnetic activity, at three local times (0700–0800, 1200–1300, and 1600–1700 LT) from March 1998 to August 1999. Owing to the geomagnetic latitude and local times used, positive storms, almost exclusively, are observed (cf. Prölss, 1995). While foF2 measurements over an extended period (∼10 years) have been studied (Matsushita, 1959) and TEC and foF2 are coupled, TEC measurements can provide a significantly better signal‐to‐noise ratio. At timescales of 2–3, 3–5, 5–9, and 9–11 days, there are significant correlations (∼0.4 at local noon, when all the data are included) between TEC and Dst. These correlations increase from morning to afternoon. By comparison, correlations between foF2 and Dst are significantly smaller, ∼0.2 (near the noise level) at local noon. Even during geomagnetically quiet times (Dst > −20), a clear correlation (0.21, which exceeds the 95% confidence level by 0.05) is seen between TEC and Dst at the shortest timescale examined. As geomagnetic activity increases, the correlations increase rapidly. For example, when moderate levels of geomagnetic activity (Dst > −50) are included for observations at local noon, distinct correlations (∼0.3) are seen and persist for all but the longest timescale; with higher levels of geomagnetic activity included, there are distinct correlations at all the timescales examined. The presence of a significant correlation at quiet conditions and persistence of the correlation at moderate levels of activity are both unexpected.

Investigation into potential TEC changes due to 9 seismic tremors of 2021–2022

“…Anomalies following the earthquake were seen in this instance as well. Wang et al (2008) demonstrated comparable findings of brief TEC enhancements in the equatorial zone, with correlations between TE and Dst displaying a rising trend from morning to afternoon, even amidst periods of low geomagnetic activity.…”

Global empirical model of TEC response to geomagnetic activity

“…[25] The basic idea of each global empirical TEC model which describes the response to the geomagnetic activity is to define a set of analytical expressions which describe the most probable TEC values at given geomagnetic activity index, day of the year, geographic location, and LT. The investigations on the f o F 2 response to the geomagnetic activity [Muhtarov et al, 2002;Wang et al, 2008] indicated that this is a delayed response which can be satisfactorily modeled by assuming that the geomagnetic influence is imposed on the inertial system described by an inhomogeneous differential equation from a first order [Kutiev and Muhtarov, 2003]. In the present study, the cross-correlation analysis, however, indicated that the rTEC response to the geomagnetic activity has to be presented by a sum of two responses with different time delay constants and with different signs of the cross-correlation function.…”

Removal of solar radiation effect based on nonlinear data processing technique for Seismo-Ionospheric Anomaly before few earthquakes

“…In ionospheric research, Krankowski et al (2005) performed wavelet analysis to understand better the temporal variability of the main periodicities present in TEC time series, observed in the European region. Wang et al (2008) used wavelet filters through wavelet transform for three data series, TEC, foF2, and Dst observations, and represented them using scaling and wavelet filters to average and decompose consecutive points. Details of multiband wavelets and filter banks can be found in the work of Vaidyanathan (1993), Strang and Nguyen (1996), and Sun et al (2001).…”