Magnetospheric ULF waves with an increasing amplitude induced by solar wind dynamic pressure changes: THEMIS observations
Tuesday, 2 September 2014
Regency Ballroom (Hyatt Regency)
Xiaochen Shen1,2, Qiugang Zong2, Quanqi Shi1,3, Anmin Tian1,4, WeiJie Sun2, Yongfu Wang2 and Suiyan Fu5, (1)Shandong University at Weihai, Weihai, China, (2)Peking University, Beijing, China, (3)Shandong University at Weihai, Weihai, Shandong, China, (4)Shandong university at Weihai, Weihai, China, (5)Peking Univ, Beijing, China
Abstract:
We report the in situ observation of the magnetospheric ultra-low frequency (ULF) waves with an increasing amplitude induced by solar wind dynamic pressure changes. We check the magnetospheric responses to solar wind dynamic pressure enhancements from April 1, 2007 to December 31, 2012, and find six events of ULF wave with slow clear wave amplitude increase. The ion velocities of these waves continuously increase to 2.1 - 4.4 times during three to six wave cycles. We choose two cases for further investigating the cause of this wave amplitude increase. We find that the wave amplitude growth is mainly contributed by the toroidal mode wave. Interestingly, the wave are standing in the azimuthal direction, but propagating in the radial direction. Thus, we suspect that the wave amplitude increase may be the caused by the superposition of two wave sources. And the simple model calculation of superposing the standing wave excited by the solar wind dynamic impulse and the magnetic field perturbation in the azimuthal direction, induced by the compressional wave via passing the the magnetic field and shaking it continuously, match the observations pretty well.
