Abstract
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.
Highlights
2 Observations In Europe, more than 800 permanent GPS receivers have been installed as of 2009. The data from these GPS receivers are provided by several different institutes: International GNSS Service (IGS), EUREF Permanent Network (EPN), Federal Agency for Cartography and Geodesy (BKGE) in Germany, Austrian Academy of Sciences, Space Research Institute (OLG) in Austria, National Geographic Institute (IGNE) in France, Delft University of Technology (DUT) in The Netherlands, Agenzia Spatiale Italiana (ASI) in Italy, Agrarian Technological Institute of Castilla and Leon (ITACYL) in Spain, European Sea-Level Service (ESEAS), SWEPOS in Sweden, SATREF (Satellittbasert Referansesystem) in Norway, and the British Isles GPS archive Facility (BIGF) in the United Kingdom
We find that the MSTID occurrence rate strongly depends on the season and local time
Park et al (2010), who have analyzed plasma density measured by the CHAMP, KOMPSAT-1, and DMSP satellites have shown that the nighttime MSTID occurrence rate in the Asian/Oceanian region is higher during the June (December) solstice
Summary
In Europe, more than 800 permanent GPS receivers have been installed as of 2009. The data from these GPS receivers are provided by several different institutes: International GNSS Service (IGS), EUREF Permanent Network (EPN), Federal Agency for Cartography and Geodesy (BKGE) in Germany, Austrian Academy of Sciences, Space Research Institute (OLG) in Austria, National Geographic Institute (IGNE) in France, Delft University of Technology (DUT) in The Netherlands, Agenzia Spatiale Italiana (ASI) in Italy, Agrarian Technological Institute of Castilla and Leon (ITACYL) in Spain, European Sea-Level Service (ESEAS), SWEPOS (a National network of reference stations for GPS) in Sweden, SATREF (Satellittbasert Referansesystem) in Norway, and the British Isles GPS archive Facility (BIGF) in the United Kingdom. To compensate for the scarcity of the TEC data distribution, the TEC value in each pixel is smoothed temporally with a running average of 10 min, during which an ionospheric pierce point (IPP) moves approximately 50 km around the zenith of a GPS receiver. The TEC map in each epoch is smoothed spatially with the running average within a area covered by 5 pixels in latitude and 5/ cos θ pixels in longitude, where θ is latitude. TEC maps for perturbation components, covering an area of Europe between 20◦ W and 40◦ E in longitude and between 30◦ N and 75◦ N in latitude, can be obtained with a spatial resolution of approximately 80 km × 80 km at 30-s intervals (10-min smoothing). We divide the area of TEC maps almost into two regions (higher and lower latitude regions) by 55◦ N in geographic latitude to study latitudinal variations of MSTIDs
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