The classical multidimensional scaling(MDS) method is introduced and applied in the study of the hour-to-hour ionospheric variability based on the ionospheric fo F2 observed at three ionosonde stations in East-Asia in 2002 and 2007. Results from the matrix eigen decompositions indicate that the annual part of the ionospheric variation is large in middle latitude and solar maximum period(2002) while low in the low latitude and solar minimum period(2007). The connectivity maps of the hour-to-hour ionospheric variability based on MDS method show some common diurnal features. The ionospheric connectivity between adjacent hours near noon hours and near midnight hours is high. The ionospheric connectivity between adjacent hours near sunrise hours and near sunset hours is poor, especially for the sunrise hours. Also there are latitudinal and solar activity dependences in this kind of connectivity. These results revealed from the ionospheric connectivity maps are useful physically and in practice for the ionospheric forecasting on the hour-to-hour scale.
Larger-scale traveling ionospheric disturbances （LSTIDs） are studied using the total electron content （TEC） data observed from 246 GPS receivers in and around China during the medium storm on 28 May 2011. It is the first attempt to get the two-dimensional TEC perturbation maps in China. Two LSTID events are detected： one is in southwestern China before mid- night propagating from low to middle latitude to the distance of about 1200 km with the phase front extending to about 500 km, and the other is in northeastern China after midnight propagating from middle to low latitudes to the distance of about 1200 km with the phase front extending to nearly 1400 km. By using the multichannel maximum-entropy method, we get the propagation parameters of these two LSTIDs. The LSTID that occurs before midnight has a higher horizontal phase velocity and a larger damping rate corresponding to the after midnight LSTID, and this may be caused by the relatively large vertical back- ground TECo and high atmospheric temperature in the southwest of China before midnight. According to the variations of magnetic H component observed in high latitudes, the source region for the after midnight LSTID is likely to be located 1400-2600 km east of 140E and north of 42N; the before midnight LSTID is propably excited by the atmospheric gravity waves （AGWs） generated by the Joule heating of the equatorial electrojet.
SONG QianDING FengWAN WeiXingNING BaiQiZHAO BiQiang
