Statistical Study On Particle Parameters In Earth Magnetotail Plasma Sheet

Bursty bulk flows(BBFs)are earthward high-speed plasma flows in the terrestrial plasma sheet(PS).They play a key role in the transport of mass,energy and in the magnetosphere,so the statistical features of plasma parameters in BBFs are a hotspot in magnetosphere physics.Although there are a lot of work on this topic with a low precision of plasma measurements,a more accurate particle characteristics in bursty bulk flow still need to be further studied.In this work,based on Time History of Events and Macroscale Interactions during Substorms(THEMIS)mission of NASA from January to April of the years 2008 and 2009,and the latest Magnetospheric Multiscale(MMS)mission from May to August of 2017 and 2018,we have selected 315 events of BBFs with the high precision data and studied the statistical features of plasma parameters in BBFs.Our results are as follows: the occurrence rate of BBFs increase with the AE index;compared with the quiet plasma sheet before BBFs,41% of BBF events have lower density and higher temperature,16% BBF events have higher density and lower temperature,and 44% BBF events have little change on density and temperature;the values of ion density in BBFs of the dawn side and the dusk side are similar;the ion temperature in BBFs of the dusk side is higher than that on the dawn side,and the ion temperature in the braking region is higher than that in the middle magnetotail;when T_e< 0.5 keV,the ratio of ion temperature to electron temperature is larger than 4,and when 2 keV > T_e> 0.5 keV,the ratio of ion temperature to electron temperature is 2?4.when 2 keV < T_e,the ratio of ion temperature to electron temperature is close to 1.