Formation and Evolution of Corotating Interaction Regions and their Three Dimensional Structure |
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Authors: | JT Gosling VJ Pizzo |
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Institution: | (1) Los Alamos National Laboratory, Los Alamos, New Mexico, USA;(2) Space Environment Center, NOAA, Boulder, Colorado, USA |
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Abstract: | Corotating interaction regions are a consequence of spatial variability in the coronal expansion and solar rotation, which
cause solar wind flows of different speeds to become radially aligned. Compressive interaction regions are produced where
high-speed wind runs into slower plasma ahead. When the flow pattern emanating from the Sun is roughly time-stationary these
compression regions form spirals in the solar equatorial plane that corotate with the Sun, hence the name corotating interaction
regions, or CIRs. The leading edge of a CIR is a forward pressure wave that propagates into the slower plasma ahead, while
the trailing edge is a reverse pressure wave that propagates back into the trailing high-speed flow. At large heliocentric
distances the pressure waves bounding a CIR commonly steepen into forward and reverse shocks. Spatial variation in the solar
wind outflow from the Sun is a consequence of the solar magnetic field, which modulates the coronal expansion. Because the
magnetic equator of the Sun is commonly both warped and tilted with respect to the heliographic equator, CIRs commonly have
substantial north-south tilts that are opposed in the northern and southern hemispheres. Thus, with increasing heliocentric
distance the forward waves in both hemispheres propagate toward and eventually across the solar equatorial plane, while the
reverse shocks propagate poleward to higher latitudes. This paper provides an overview of observations and numerical models
that describe the physical origin and radial evolution of these complex three-dimensional (3-D) heliospheric structures.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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