Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsa41a1837o&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SA41A-1837
Physics
[2427] Ionosphere / Ionosphere/Atmosphere Interactions, [2435] Ionosphere / Ionospheric Disturbances, [2443] Ionosphere / Midlatitude Ionosphere, [6929] Radio Science / Ionospheric Physics
Scientific paper
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, we have found that the observed MSTIDs can be categorized into two groups. One group is daytime MSTIDs, which frequently occur in winter. Since most of the daytime MSTIDs propagate southward, we speculate that the daytime MSTIDs could be caused by atmospheric gravity waves in the thermosphere. Second group is nighttime MSTIDs, which also frequently occur in winter but propagate southwestward. This propagation direction is consistent with the idea that polarization electric fields play an important role in generating nighttime MSTIDs. 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 does not show dip angle dependences and that TEC perturbations caused by the oscillating electric field have larger amplitude at lower latitude than higher latitude. These dip angle dependence in the amplitude of TEC perturbations could contribute to the latitudinal dependences of the MSTID occurrence rate. By comparing with previous studies, we discuss longitudinal dependence of the nighttime MSTID occurrence rate, along with the E and F region coupling processes. Seasonal variation of the nighttime MSTID occurrence rate in Europe is not consistent with the idea that the longitudinal and seasonal dependences of the nighttime MSTID occurrence could be attributed to those of the Es layer occurrence. Acknowledgements: GPS data were provided by IGS, EPN, BKGE, OLG, IGNE, DUT, ASI, ITACYL, ESEAS, SWEPOS, SATREF, and BIGF.
Nakagawa Shota
Nishioka Masaya
Otsuka Yoichi
Shiokawa Kazuhiko
Tsugawa Takuya
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