Study Of The Electromagnetic Ion Cyclotron Waves Near The Cusp Latitudes

The induction magnetometer data from Antarctic Zhongshan and Davis Stations over the3th,6th,9th and12th months in2004are used, and the dynamic spectrum and cross-spectrum analysis method is adopted to statistically study the electromagnetic ion cyclotron wave (Pe1-2wave) occurrence, the center frequency and the amplitude variations with respect to the seasons and MLT, and the Pe1-2wave dependence on the solar wind condition and the geomagnetic indexes. Besides, a typical Pe1-2wave event on10:45-14:45UT March9,2004is selected for case study. With totally2932valid wave events, the results are summarized as follows:(1) The P1-2waves have a higher occurrence in March (51.4%) and September (26.1%) than in December (18.6%) and June (3.8%), and mainly occur near the magnetic local noon (59.8%over0800-1000UT). The wave center frequency is higher in postnoon than in prenoon and the wave amplitude has a maximum on0800UT. The center frequency maximizes and the amplitude minimizes in June.(2) The Pe1-2waves prefer to occur under a quiet geomagnetic conditions for Kp≤3,-40≤SYM_H≤20, Ap≤20and AE<850. The wave events occur predominantly under solar wind dynamic pressure Psw=0-8nPa, IMF Bx=-8～+9nT, By=-8～+9nT, Bz=-7～+8nT, the velocity Vp=300-650km/s and the ion densities Np=1～22cm-3. The occurrence is large when Vp=600～650km/s or Np=12-20cm-3.These results suggest that the Pe1-2wave properties near the cusp latitude are influenced significantly by the Antarctic seasonal variations and the ionospheric conductivity, and mainly generated within the inner structures in the outer magnetosphere under relatively quiet solar wind and geomagnetic conditions, and will be influenced by the solar wind activities and substorms.