Statistical Study Of Cold Materials In ICMEs

Corona Mass Ejection?CME?is observed in the view field of the coronagraph,it is structural change of the corona which lasts from several minutes to hours,which appears as a new discontinuous bright feature.When CME spreads to interplanetary,it is called as Interplanetary Coronal Mass Ejection?ICME?.CME has three-part structure with bright front edge,dark cavity and bright core.The bright core is prominence.Previous research has indicated that above one-third of CMEs have a typical three-part structure.However,the corresponding prominence material characteristics are rarely detected in ICMEs.For this contradiction,we study the ionic charge states of C,O,Mg,Si and Fe to analyze the characteristics of cold material in ICME.In this paper,298 ICMEs measured by ACE and WIND satellites at Lagrange 1 point from 1998 to 2011 were used.By setting data filter conditions,219 ICME events were obtained as statistical sample.The criterion for judging the cold material in this paper is that the mean value of the C charge state is lower than the mean value in the solar wind which last for 24 hours before the ICME minus 3 times standard deviation,and the ionization temperature of the C during the time period should be less than 10^6.05 K.For the 219 events,a total of 108 Carbon Cold periods in 69 ICME events met the criteria,which account for 31%of ICMEs,it is in agreement with optical observations.The speed of these cold materials are mostly between 400-500 km/s,and cold materials mostly last 2-6 hours.Each ICME mostly contains 1-2 cold material time period.For the element charge state in cold materials,the statistical results show that there are two opposite ionization temperature characteristics:In the first type of cold materials,the average charge state of O,Mg,Si,and Fe are simultaneously lower than the mean value in the solar wind which last for 24 hours before the ICME;In the second type of cold materials,the average charge state of O,Mg,Si,and Fe are simultaneously higher than the mean value in the solar wind which last for 24 hours before the ICME plus 3 times standard deviation.In the statistical sample studied in this paper,there are six time periods containing the first type of cold materials and 15 time periods containing the second type of cold materials.Among them,the proton temperature showed increase in the 5 first type cold material time periods,and the proton temperature decreased in the 14 second type cold mass time periods.The second type of cold materials are presenting in the CME during high solar activity.The ionization temperature characteristics of this type of cold materials support the existing theoretical model of solar prominence formation,which is the formation of prominence is the result of mixture of chromospheric material and coronal material.The first type of cold materials have never been reported before.There is no corresponding prominence model.The formation mechanism of this type cold materials needs high resolution observations by SDO and Parker Solar Probe.