GPS observations of medium-scale traveling ionospheric disturbances over Europe

Abstract

Two-dimensional structures of medium-scale traveling ionospheric disturbances (MSTIDs) over Europe have been revealed, for the first time, by using maps of the total electron content (TEC) obtained from more than 800 GPS receivers of the European GPS receiver networks. From statistical analysis of the TEC maps obtained 2008, we have found that the observed MSTIDs can be categorized into two groups: daytime MSTID and nighttime MSTID. The daytime MSTID frequently occurs in winter. Its maximum occurrence rate in monthly and hourly bin exceeds 70% at lower latitudes over Europe, whereas it is approximately 45% at higher latitudes. Since most of the daytime MSTIDs propagate southward, we speculate that they could be caused by atmospheric gravity waves in the thermosphere. The nighttime MSTIDs also frequently occur in winter but most of them propagate southwestward, in a direction consistent with the theory that polarization electric fields play an important role in generating the nighttime MSTIDs. The nighttime MSTID occurrence rate shows distinct latitudinal difference: The maximum of the occurrence rate in monthly and hourly bin is approximately 50% at lower latitudes in Europe, whereas the nighttime MSTID was rarely observed at higher latitudes. We have performed model calculations of the plasma density perturbations caused by a gravity wave and an oscillating electric field to reproduce the daytime and nighttime MSTIDs, respectively. We find that TEC perturbations caused by gravity waves do not show dip angle dependencies, while those caused by the oscillating electric field have a larger amplitude at lower latitudes. These dip angle dependencies of the TEC perturbation amplitude could contribute to the latitudinal variation of the MSTID occurrence rate. Comparing with previous studies, we discuss the longitudinal difference of the nighttime MSTID occurrence rate, along with the E- and F-region coupling processes. The seasonal variation, of the nighttime MSTID occurrence rate in Europe, is not consistent with the theory that the longitudinal and seasonal variations of the nighttime MSTID occurrence could be attributed to those of the Es layer occurrence

Occurrence climatology of F region field‐aligned irregularities in middle latitudes as observed by a 40.8 MHz coherent scatter radar in Daejeon, South Korea

“…One might expect a higher FAI occurrence rate during a period of lower solar activity because of the fact that MSTIDs (medium-scale traveling ionospheric disturbances), which are known as an important source of middle latitude FAIs, have been detected more frequently during a solar minimum than during a solar maximum [Amorim et al, 2011;Candido et al, 2008;Duly et al, 2013;Kotake et al, 2006Kotake et al, , 2007Martinis et al, 2010;Otsuka et al, 2011Otsuka et al, , 2013. In fact, Fukao et al [1991] briefly stated that they observed the FAIs more frequently during a period of low solar activity than during a period of high solar activity.…”

Model of traveling ionospheric disturbances

“…Moreover, even a single act of AGW excitation generates TIDs observed almost for 24 h. Therefore, maxima and minima in the diurnal and seasonal dependence of the TID occurrence would be observed if the measurement accuracy is low. Tsugawa et al (2007aTsugawa et al ( , 2007b; Kotake et al (2007); Song et al (2011);Otsuka et al (2013) and Vlasov et al (2011) after almost three decades of research performed by Evans et al (1983) and Ogawa et al (1988) have also studied the diurnal and seasonal dependence of TID occurrence. However, the dependences obtained by these authors contradict each other and previous results.…”

“…5). Due to limited measurement accuracy, there exists a misconception among researchers (see, for example, Evans et al 1983;Ogawa et al 1988;Tsugawa et al 2007aTsugawa et al , 2007bKotake et al 2007;Song et al 2011;Otsuka et al 2013), concerning diurnal and seasonal occurrence of TIDs (see Sect. 5).…”

“…Energetic proton precipitation into the magnetosphere at 60°magnetic latitude can form a cusp whose length may vary from~8000 to 10 000 km, while a cusp length in a night sector is extended along L-shell up to 10-12 time zones (Halperin et al 1990). Therefore, it is no surprise that a TID front, generated by a high-latitude source, has a length that exceeds 2000 kilometers along a parallel in a zonal direction (Fedorenko et al 1997;Tsugawa et al 2007aTsugawa et al , 2007bKotake et al 2007;Song et al 2011;Otsuka et al 2013). A prior guess, asserting that relative changes of atmospheric density at distances of hundreds and thousands of kilometers from the source of local energy release, is much less than unity is quite courageous.…”

Dynamics of disturbance level of total electron content at high and middle latitudes according to GPS data

“…Зондиро-вание ионосферы радиосигналами GPS/ГЛОНАСС позволяет изучать неоднородности ионосферной плазмы. В последние годы большое внимание уде-ляется исследованию морфологии ионосферных возмущений различных масштабов в отдельных ре-гионах земного шара Kotake et al, 2006;Tsugawa et al, 2007a, b;Otsuka et al, 2011Otsuka et al, , 2013. Установлены общие характеристики переме-щающихся ионосферных возмущений (ПИВ, периоды 10-60 мин) в Европе, Японии и Северной Америке.…”