Characteristics of GPS TEC variations in the polar cap ionosphere

Abstract

This paper presents statistical characteristics (occurrence rate, amplitude, and frequency) of low‐frequency (<100 mHz) variations in total electron content (TEC) observed in the polar cap ionosphere. TEC variations were primarily associated with mesoscale (tens to hundreds of kilometers) ionization structures and were observed by five Global Positioning System (GPS) receivers over a 6 year period (2009–2014). The altitude of ionization structures was estimated by using colocated ionosonde radars. High data rate receivers combined with broad spatial coverage of multisatellite TEC measurements provided high‐resolution magnetic local time/latitude maps of TEC variation characteristics, which were examined as a function of solar cycle and season. These high‐resolution maps improve upon the current observational picture of mesoscale structuring in the polar cap and provide accurate links to particular magnetospheric source regions. Occurrence of TEC variations was consistently highest in dayside regions mapping to low latitude and plasma mantle boundary layers, while largest‐amplitude TEC variations were observed in dayside regions close to the polar cusp, and lower latitudes around midnight. Occurrence and amplitude of TEC variations increased significantly during the ascending phase of the solar cycle, independent of solar wind conditions, while seasonal statistics showed highest dayside occurrence and amplitude in winter months, lowest in summer, and highest nightside occurrence and amplitude around equinox. A surprising result in the frequency distributions of TEC variations was discrete frequencies of about 2 and 4 mHz, which appeared to originate from regions corresponding to the plasma mantle, immediately poleward of the polar cusp.

GPS TEC variations in the polar cap ionosphere: Solar wind and IMF dependence

“…Average amplitudes were clearly proportional to coupling rate throughout the polar cap. For lowest rates <1000, peak average amplitudes of 3.3 TECU were observed around 13:00 MLT, 77.5° MLat, similar to the postnoon amplitude peaks observed in 2009, 2010, and summer months [ Watson et al ., ]. A nightside peak in average amplitude of 2.3 TECU was also observed around 23:45 MLT, 74.0° MLat for low coupling rates, while minimum amplitudes of 1.9 and 2.1 TECU were observed in the early morning (04:00 MLT, 74.0° MLat) and evening (19:00 MLT, 75.0° MLat) sectors, respectively.…”

“…As was discussed in Watson et al . [], a higher dayside and lower nightside occurrence is evident in the winter months, while the general rotation of the polar cap convection pattern is similar to the effect shown in Figure a. However, a seasonal dependence is evident in the IMF B Y control of the morning‐afternoon occurrence asymmetry, where a high morning (afternoon) occurrence for positive (negative) IMF B Y is observed in the winter, with a less pronounced, but opposite effect observed in the summer months.…”

“…A detailed description of the data and analysis method is available in Watson et al . []. Figure [ Watson et al ., ] is a map of the colocated GPS receivers and Canadian Advanced Digital Ionosondes (CADI) used in this study.…”

“…Map showing geomagnetic coordinates of colocated CHAIN GPS receivers and CADI ionosondes in the polar cap [ Watson et al ., ].…”

“…Mesoscale (tens to hundreds of kilometers) structures, which include polar cap patches and polar cap aurora, are of interest in this study. This study follows a previous work that examined the solar cycle and seasonal dependence of total electron content (TEC) variations due to mesoscale structuring, as well as the dominant frequencies of TEC variations [ Watson et al ., ]. The observations presented here aim to build upon the current statistical picture of TEC variations arising from mesoscale structuring in the polar cap, by investigating how the characteristics (occurrence rate and amplitude) of TEC variations depend on solar wind conditions, including the coupling rate of the solar wind and magnetosphere and the magnitude and orientation of the interplanetary magnetic field (IMF).…”