High Speed Solar Wind Streams

High-speed solar wind streams emanating from coronal holes can drive interplanetary shocks and create intense magnetic fields when interacting with streams of lower speeds (Tsurutani and Gonzales, 1997 [44]). Similarly to CME-driven disturbances, these compressed field regions can couple to the geomagnetic field and may cause geomagnetic storms. During low solar activity, coronal holes can be relatively stable, lasting for months, and reach low solar latitudes. Therefore, at solar minimum, the high-speed solar wind streams are the dominating source of geomagnetic storms, and due to solar rotation cause recurrent storms with a 27-day pattern.

At large heliospheric distances (> 1.5 AU) the shocks associated with the high-speed streams rotating with the Sun are fully developed, and form coro-tating interaction regions (CIRs). CIRs are still an other source of high-energy particles (Mason and Sanderson, 1999 [49]). However, due to low intensities and steep spectra of CIR particles, the effects are relatively insignificant.

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