Superposed epoch analysis of corotating interaction regions at 0.3 and 1.0 AU: A comparative study

Abstract

Applying the superposed epoch analysis technique to 16 and to 31 well-defined, nonshock-associated stream-stream interaction regions observed by the Helios spacecraft in the distance ranges 0.3 to 0.4 AU and 0.9 to 1.0 AU, respectively, we obtain the average azimuthal variation in the solar wind density, velocity and temperature, in the magnetic field strength, and in the total proton plasma plus magnetic field pressure across CIRs at these two radial distances separately. For the radial evolution of these interaction regions we find by comparison: (1) due to compressional and rarefactional effects the amplitudes of all parameterg.•p question taken along the leading as well as along the trailing part of the CIR are steadily increasing'•ith the most pronounced increase in the pressure; (2) at the same time even the leading portion of the velocity profile steepens; (3) simultaneously, the positions in azimuth of the overall maximum values of the solar wind density and temperature, of the magnetic field strength and of the plasma plus magnetic field pressure are getting steadily lined up in longitude; (4) at the same time the leading portions of all profiles are steepening into discontinuous, shocklike structures. Thus, this analysis provides observational evidence for the following results obtained earlier from numerical simulation studies: Stream steepening does occur within 1 AU, and the probability of corotating shocks to form is, on average, much higher beyond than at or within 1 AU.

The proton and electron radiation belts at geosynchronous orbit: Statistics and behavior during high‐speed stream‐driven storms

“…Prior to the storm the superposed average of the density of the streamer belt plasma is slightly higher than the density of the coronal hole plasma during the storm; this is caused by the presence of noncompressive density enhancements in the solar wind [ Gosling et al , ; Borrini et al , ] likely to be sector‐reversal‐region plasma [ Xu and Borovsky , ]. Near the time of storm onset the number density is particularly high owing to the compression of the solar wind in the corotating interaction region [ Gosling et al , ; Richter and Luttrell , ; Borovsky and Denton , ].…”

Relativistic‐electron dropouts and recovery: A superposed epoch study of the magnetosphere and the solar wind

“…In Figure 3c, the superposed average of the solar wind number density is plotted. The solar wind is compressed in the CIR by the dynamic‐pressure difference of the fast wind overtaking the slow wind and so the density is increased [ Hundhausen , 1973; Richter and Luttrell , 1986]. Prior to the passage of the stream interface the high density is compressed slow wind and any high density after the interface is compressed fast wind.…”

The trailing edges of high‐speed streams at 1 AU

“…Corotating interaction regions have been well studied [ Hundhausen , ; Richter and Luttrell , ; Pizzo , , ; Crooker and Gosling , ; Jian et al ., ; Tessein et al ., ], in part because CIRs drive geomagnetic storms [ Denton et al ., ; Tsurutani et al ., ; Borovsky and Denton , , ; Richardson et al ., ; Lavraud et al ., ; Solomon et al ., ]. The trailing edges of high‐speed streams are less studied [ Carovillano and Siscoe , ; Tu and Marsch , ; Gosling and Pizzo , ; Pagel et al ., ; Ko et al ., ]: the trailing edges of high‐speed streams drive the latter portions of high‐speed‐stream‐driven geomagnetic storms wherein geomagnetic activity is subsiding, but the Earth's electron radiation belt is still being energized [ Tsurutani et al ., ; McPherron et al ., ; Borovsky and Denton , , ].…”