Abstract
The oblique-incidence ionosonde network in North China is a very unique system for regional ionospheric observation. It contains 5 transmitters and 20 receivers, and it has 99 ionospheric observation points between 22.40° N and 33.19° N geomagnetic latitudes. The data of the ionosonde network were used to investigate the statistical characteristics of the quasi-3-h large-scale traveling ionospheric disturbances (LSTIDs). From September 2009 to August 2011, 157 cases of the quiet-time LSTIDs were recorded; 110 cases traveled southward, 46 cases traveled southwestward and only 1 case traveled southeastward. The LSTIDs mainly appeared between 10:00 and 19:00 LT in the months from September to the following May. We compared the data of the Beijing, Mohe and Yakutsk digisondes and found that the LSTIDs are most likely to come from the northern auroral region. These LSTIDs may be induced by the atmospheric gravity waves (AGWs) and presented obvious seasonal and diurnal varying features, indicating that the thermospheric wind field has played an important role.
Highlights
Large-scale traveling ionospheric disturbances (LSTIDs) are generally considered as the manifestation of the atmospheric gravity waves (AGWs) in the ionosphere and are usually observed while the geomagnetic storms and auroral substorms occur [1,2,3,4,5]
Almost all of the reported individual LSTID events occur during geomagnetic storms or auroral substorms (e.g., [7,8,9,10])
We develop four criteria to accurately recognize the LSTIDs from other ionospheric disturbances: (1) The amplitude of the enhancement or depletion exceeds the diurnal average by at least 5%. (2) At least 60% of the ionospheric observation points of the ionosonde network as well as the Beijing digisonde have recorded the same periodic disturbance
Summary
Large-scale traveling ionospheric disturbances (LSTIDs) are generally considered as the manifestation of the atmospheric gravity waves (AGWs) in the ionosphere and are usually observed while the geomagnetic storms and auroral substorms occur [1,2,3,4,5]. Joule heating and Lorentz forces caused by the enhancement of the auroral electrojet or intense precipitation of charged particles are the main excitation sources of the LSTIDs, and they have typical horizontal velocities between 300 and 1000 m/s, horizontal wavelengths of more than 1000 km and period in the range of 30 min to 5 h These periodic waves carry huge energy from the lower neutral atmosphere to the upper ionosphere and induce periodic electron density fluctuations in the ionosphere [4,6]. A vertical-incidence (VI) ionosonde operating in the high-frequency mum electron density and peak height of each ionospheric layer.
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