Effects Of Solar Wind Conditions On The Occurrence Rate Of Flux Transfer Events

Investigating Flux transfer events?FTEs?is important for understanding the magnetic reconnection.It has been forty years since the event had been identified from the observation.Many works showed that the condition of solar wind could play a role in this event.So far,however,no one has studied the effect of solar wind parameters on the occurrence rate of FTEs in a comprehensive way by simulations,and the relation between Mach number and FTEs occurrence is still unclear.Therefore,using global MHD simulations,the occurrence rate of FTEs on the dayside magnetopause was investigated.There are three cases,the inputted parameters are as follows:?1?V_X=300 km/s,_YV=_ZV=0,n_SW=48.4cm^-3,_ZB=-33 nT,_YB=33nT,B_X=0,T=91000K;?2?V_X=750km/s,_YV=_ZV=0,n_SW=7.744cm^-3,_ZB=-13.2n T,_YB=13.2nT,B_X=0,T=91000K;?3?V_X=1200km/s,_YV=_ZV=0,n_SW=3.025cm^-3,_ZB=-8.3nT,_YB=8.3nT,B_X=0,T=91000K.In this way,these cases can not only have different Mach number,2,5,8,respectively,but also have same solar wind ram pressure and electric field,which can nearly keep the same location and shape of magnetopause as well as total reconnection rate.Using a recently developed diagnose method,FTEs can be identified throughout the dayside magnetopause?local time is approximately 8-16?in 3740 s.The signals from our simulations are consistent with those from former works of observations as well as simulations.Under a higher threshold,10 nT,the number of identified FTEs is 78 when the Mach number is 2.It decreases to 38 when the Mach number increases to 5,and then declines to 25 as the Mach number increases to 8.And it shows that the case under lower Mach number condition has higher FTEs' occurrence rate,while higher Mach number has less FTEs.Even we used a lower threshold,5nT,it also shows that the number of FTEs decreases with increasing Mach numbers.Under lower Mach number condition,the value of??the ratio of plasma to magnetic field pressure?in the magnetosheath is relatively low.However,the higher Mach number condition leads to a higher value of?in the magnetosheath.The difference of magnetosheath?and magnetopause?might play a role in the process of reconnection which indirectly affects the FTEs occurrence.Meanwhile,the other different magnetosheath conditions caused by disparate intensities of bow shock could also work on the occurrence rate.Furthermore,since planets with different heliocentric distance have different solar wind Mach numbers,this study might propose that planet with a larger heliocentric distance may have less FTEs because of the increasing Mach number,which could provide a new insight for the studies of FTEs on the other planets.