Effect of magnetic activity on plasma bubbles over equatorial and low-latitude regions in East Asia

The dependence of plasma bubble occurrence in the eveningside ionosphere, with magnetic activity during the period years 2001-2004, is studied here based on the TEC observations gathered by ground-based GPS receivers which are located in the equatorial and low-latitude regions in East Asia. The observed plasma bubbles consist of the plasma-bubble events in the equatorial (stations GUAM, PIMO and KAYT), and low-latitude regions (stations WUHN, DAEJ and SHAO). It is shown that most equatorial plasma-bubble events commence at 20:00 LT, and may last for >60 min. The magnetic activity appears to suppress the generation of equatorial plasma bubbles with a time delay of more than 3 h (4-9 h). While in the low-latitude regions, most plasma-bubble events commence at about 23:00 LT and last for <45 min. The best correlation between K_p and low-latitude plasma-bubble occurrence is found with an 8-9 h delay, a weak correlation exists for time delays of 6-7 h. This probably indicates that over 3 h delayed disturbance dynamo electric fields obviously inhibit the development of plasma bubbles in the pre-midnight sector.