STATISTICAL STUDY OF IPDP EVENTS OBSERVED BY THE CARISMA NETWORK OF MAGNETOMETERS

During substorms energetic ions injected from the magnetotail plasma sheet could excite electromagnetic ion cyclotron (EMIC) waves in the inner magnetosphere. As a signature of EMIC waves, ground-based magnetometers observed the Intervals of Pulsations of Diminishing Periods (IPDP). With the observations of the GOES satellite and CARISMA network of magnetometers in Canada, we analyzed the relationship between the IPDP events and substorm injection events. With the observations of magnetometers at MCMU and MSTK stations of CARISMA network between April 2005 and May 2014, we statistically analyzed the IPDP events during substorms and obtained the occurrence rate distribution in seasons and magnetic local time (MLT). A total of 128 IPDP events have been simultaneously observed by both MCMU and MSTK stations. The IPDP events have the least occurrence rate in winter (13.28%), and the highest occurrence rate in spring (32.81%). The results show that the occurrence rate of IPDP events is affected by the ionospheric conductivity and the occurrence rate of substorms. The maximum occurrence rate of the events is between 15 MLT and 18 MLT. Our result suggests that IPDP events are mainly generated by energetic anisotropic protons, which can be injected into the inner magnetosphere during substorms and drift westward and encounter the plasmaspheric plume.