Statistical Analysis Of Multi-spacecraft Observations On CIR Evolution Jingjing Wang (Space Physics)

STEREO-BEHIND(STB) and STEREO-AHEAD(STA) drifted behind and ahead of ACEaround the Sun, with longitudinal separation increasing day by day. CIR driven by high speedsolar wind from coronal holes swept STB, ACE, and STA sequentially. Currently, solar windobservations on ACE are the direct basis for Earth space environment forecasting.Based on interplanetary magnetic field and solar wind observations on STB,ACE and STA,statistical characteristics of CIR parameters and similarity of solar wind velocity observationswas discussed. It was found that: (1)Linear correlation coefficient of wind velocity observationsin each 27-day on STB, ACE and STA decreased with longitudinal separation. Average of linearcorrelation coefficient of wind velocity observations on STB and ACE in 2007, 2008 and 2009was 0.93, 0.85 and 0.74, respectively. (2)Linear correlation coefficient of maximum CIR speed onSTB and ACE was 0.84. (3)These results showed that, there was a strong similarity between CIRobservations on STB and ACE.Assuming high speed stream transmitted uniformly and radially from coronal holes,characteristics of CIR travel time from STB to ACE with their longitudinal separation increasedfrom 0°to 70°was discussed. Statistical variation characteristics of high speed stream parameterswas analysed. It was found that: (1)CIR arrival time on ACE could be predicted by CIRobservations on STB. The average and maximum errors of travel time was 0.217 day and 0.952day, respectively. The maximum errors of travel time increased with longitudinal separation. Theaverage and maximum errors of travel time reduced to 0.194 day and 0.489 day respectively aftercorrected by speed variances. (2)Characteristic parameters of the same CIR on STB and ACEsuch as speed and proton temperature showed the least difference, while proton density and totalpressure showed relatively large difference. The average and maximum range of difference onCIR characteristic parameters observed by STB and ACE, such as maximum speed, maximumproton temperature, maximum total pressure, maximum magnetic field and maximum magnetic southward components, increased with longitudinal separation, while they decreased onmaximum proton density. (3)These results showed that, CIR observations on STB could be usedas reference of CIR characteristics on ACE, and provided basis for forecasting of Earth spaceenvironment disturbance.Characteristics of parameters in two samples of recurrent CIRs which lasted for 25 CR and27 CR and came from the same coronal hole respectivelywas discussed. Characteristics ofsources of these samples, coronal holes, was discussed in Backmapped Carrington Longitude.Statistical characteristics of CIR parameters evolution around SI in these samples was analysed. Itwas found that: (1)Sources of these samples, coronal holes, moved at 4.5°per CR toward thedirection of longitude increasingly in Backmapped Carrington Longitude. (2)There wassignificant characters of CIR parameters and range of differences in CIR parameters observed bymulti-spacecraft between growth phase, maturation phase and decay phase in these samples.(3)These results showed that, the significant characters of range of differences in CIR parametersbetween growth phase, maturation phase and decay phase in recurrent CIRs from the samecoronal holes could be used as reference of CIR characteristics on ACE.