A statistical analysis of the global distribution of inner magnetospheric upper-band chorus waves based on Van Allen Probes EMFISIS observations

作者：Gu Xu-Dong; Yin Qian; Zhou Ruo-Xian; Yi Juan; Ni Bin-Bin^*; Xiang Zheng; Cao Xing; Zou Zheng-Yang; Fu Song; Zhou Chen; Shi Run; Zhao Zheng-Yu; He Feng-Ming; Tan Jia-Qiang; Zheng Cheng-Yao; Wang Hao

来源：Acta Geophysica Sinica, 2017, 60(4): 1259-1267.

DOI：10.6038/cjg20170402

• Upper-band chorus
• Inner magnetosphere
• Statistical analysis
• Averaged wave amplitude
• Occurrence rate

Based on the nearly three-year wave data from the EMFISIS instrument onboard the Van Allen Probes, a statistical analysis of the global distribution of inner magnetospheric upper band chorus is performed in detail with respect to the level of geomagnetic activity. The emphasis is placed upon the quantitative variations of average upper-band chorus wave amplitude with L shell (L), magnetic local time (MLT) and magnetic latitude (MLAT) and the occurrence pattern of upper-band chorus waves at different amplitude levels. The results indicate that there exists a strong positive correlation between the average wave amplitude and the geomagnetic activity level, and the averaged wave amplitude can be larger than 40 pT during geomagnetically active periods. While wave amplitude reaches the maximum in the central region (L = 4 similar to 6) of outer radiation belt, upper-band chorus cannot be observed at L<similar to 3. Averaged wave amplitude is found to be strongest during the interval from nightside to dawnside and is weakest during the interval from afternoonside to duskside. Dayside upper-band chorus can be observed at different geomagnetical conditions with relatively small wave amplitude. It is found that upper-band chorus is mainly distributed at vertical bar MLAT vertical bar <10 degrees. Averaged wave amplitude is strongest in the region of 21-09 MLT and vertical bar MLAT vertical bar <5 degrees, and can be about 100 pT during geomagnetically active periods. In addition, the occurrence rate of moderate amplitude (10-30 pT) upper-band chorus is statistically found to be highest (similar to 15%) near the equatorial region in the MLT sector from nightside to dawnside (23-09 MLT). Upper-band chorus with strong wave amplitude has the lowest occurrence rate and is generally observed at the nightside (01-05 MLT). Combined with the global distribution and occurrence pattern of lower-band chorus we have already established, the global distribution and occurrence pattern of upper-band chorus established in this study will improve the understanding of the quantitative contributions of this important magnetospheric wave to the dynamic behaviors of the Earth's plasma sheet, radiation belts and ring current.

• 出版日期2017-4
• 单位武汉大学