The ionospheric storms which can make the great gradient and irregularities of electron densities are very interest phenomena for two reasons. First, they occur by the increasing solar EUV/X-ray fluxes as well as by the equatorward or poleward plasma transportations through the global changes of the neutral winds and electric fields responded to geomagnetic storms. Second, they have been the practical interests in the satellites navigations and radio communications, especially in the mid-latitudes of the dense population regions in these days. In this paper, the statistical analysis of the occurrences of the ionospheric storms in Korea are presented. The occurrences of the ionospheric storms are examined from Daejeon GPS TEC dataset between 2000 and 2010 of the full-solar cycle coverage. To discuss the physical mechanisms for ionospheric storm of positive and negative phase and their GPS signal affection in Korea, the two super geomagnetic storms cases of 29-31 October 2003 and 8-10 November 2004 are examined. The parameters to define the ionospheric storms are suggested to increase our understanding of their physical characteristics and then to apply the practical cases.

Keywords: ionospheric storms, GPS TEC, mid-latitude