The effects of typhoon Matsa on the ionosphere are studied by using GPS-TEC data observed at about 50 GPS stations. It is shown that the ionosphere has been already influenced and TEC tends to increase before the landing of Matsa, and the difference of TEC from its monthly median over the typhoon area is about 5 TECU. With the landing of Matsa, both the magnitude and the area of increased TEC decrease. One day after the landing of Matsa, TEC reaches its minimum and is lower than the monthly median. In comparison of TEC along the typhoon's path with that along three reference paths far from the typhoon, it is found that typhoon's impact on TEC can be fully distinguished. The evolution of TEC variation has the same tendency as reported typhoon-induced foF2.typhoon Matsa, ionosphere, GPS, coupling, TEC map Citation:

. With a new factor, effective sunspot number R eff , the results show that there were giant positive disturbances of foF2 around the epicentral zone on 9 May, 3 days prior to the earthquake. Our results indicate that the observed positive ionospheric disturbances were most possibly associated with the imminent earthquake and the new analytic method has good prospects in practice.

[1] Spread F is a widely studied subject, and the occurrence of spread F is affected by many factors. One of these factors is acoustic gravity waves (AGWs) which are very important in seeding spread F. Since most of the AGWs in the ionosphere originate from the lower atmosphere, there should be some regional features of spread F due to the different meteorological or ground conditions immediately beneath the local ionosphere. In this paper, a data set with a time coverage of one solar cycle from two Chinese stations located at exactly the same latitude and a 38 degrees separation in longitude, and having sharp contrasts of ground meteorological conditions, are used to make comparisons of spread F occurrence rates. The results showed that the total number of occurrence or occurrence percentage at Changchun station (very near the coast) is always much higher than that at Urumqi station (in the very center of the Europe-Asia continent). The annual maxima of spread F occurrence are in summer and winter. Other features of spread F occurrence at these two stations are in agreement with known properties of spread F. However, the great difference of occurrence frequency between the two stations is striking and worth further studying.

On 12 May 2008 at 14:28 BJT, a great earthquake (M=8.0) occurred in Wenchuan (31.00°N, 103.40°E), China. The hourly foF2 from 5 to 12 May have been analyzed over four ionospheric observatories: Kunming (25.00°N, 102.70°E), Chongqing (29.50°N, 106.40°E), Lhasa (29.63°N, 91.17°E), and Lanzhou (36.07°N, 103.87°E). The results show that foF2 were notably abnormal from upper bound (the maximum abnormality up to 65% at 17:00 BJT) and lasted about 3 h on 9 May over Chongqing station. Moreover, there were obvious perturbations of foF2 on the same day over other stations except Lhasa. Taking into account that the solar activity and geomagnetic activity were very quiet during this period, we can conclude that the observed positive ionospheric perturbations were likely associated with the imminent earthquake.ionospheric perturbations, earthquake precursors, seismo-ionospheric coupling Citation:Since the phenomenon related to ionospheric perturbation caused by the earthquake at Kurile Islands in August 1969 was reportedP [1],P many researchers have devoted themselves to seismo-ionospheric study and there have been numerous observational studies of ionopshereic anomalies prior to strong earthquakes P [2-8]P . An excellent review of ionospheric precursors has been presented recently by Pulinets et al. P [9]P .However, the existence of the ionospheric precursors of earthquake is still an open issue because on one hand, the physical mechanism of seismo-ionospheric coupling is not well understood and on the other hand, there is a lack of appropriate ionospheric data that one could obtain more reliable evidence of the ionospheric precursors of earthquake. For these reasons, further observations to search ionospheric perturbations related to pre-earthquake seismic activity are urgently needed to shed light on the problem.In this paper, we report observations of the giant perturbations in the ionosphere F2 layer foF2 prior to the Wenchuan earthquake with M=8.0, which occurred at 14:28 BJT, 12 May 2008. Data obtained at four ground-based ionospheric stations located at different distances from the earthquake epicenter are analyzed. The possible mechanism that could be responsible for the observed pre-earthquake ionospheric anomalies is discussed.

1] Using the global positioning system (GPS) cycle slip (CS) data detected from the observation of six GPS stations in 2001 over the China low-latitude region, the temporal dependence of CS occurrence during solar active year and its cause are analyzed. It is found that the variations of CS occurrence with local time and seasons are obvious. First, the diurnal dependence of CS occurrence detected from six GPS stations is obvious and the distribution of CS occurrence with local time is very similar. On the whole, from 0100 to 1900 LT the CS seldom occurs, and the CS occurrence increases at about 1900 LT, reaches its maximum at about 2200 LT, and then decreases gradually. This temporal distribution of CS occurrence is related with the diurnal variation of ionospheric irregularities above a certain intensity level over the low-latitude region. Second, the seasonal dependence of CS occurrence is also obvious, and the CS occurs more frequently in the equinox months than in other months, which is coincided with the seasonal occurrence of ionospheric scintillation over the Asia-Pacific longitude sector. Besides the synoptic seasonal distribution of CS occurrence, the CS occurrence at some special period exhibits an obvious consistency in these six stations. Finally, the CS occurrence shows some connections with the geomagnetic activity. The cases of inhibiting and generating effect of the geomagnetic activity on CS occurrence are found during the active solar years. It is considered that these dependences of the CS occurrence are related with the variations of the ionospheric irregularities or scintillation in the China low-latitude region. (2010), Temporal dependence of GPS cycle slip related to ionospheric irregularities over China low-latitude region, Space Weather, 8, S04D08,