Latitudinal variation of solar wind corotating stream interaction regions: Ulysses

Abstract

Ulysses‧ initial transit to high heliographic latitudes at a heliocentric distance of ∼5 AU has revealed systematic effects in the latitudinal evolution of corotating interaction regions (CIRs). At a latitude corresponding roughly to, but slightly less than, the inferred tilt of the coronal streamer belt and embedded heliospheric current sheet, the strong forward shocks commonly associated with CIRs at lower latitudes disappeared almost entirely; however, the reverse shocks associated with these CIRs persisted to latitudes ∼ 10° above the streamer belt. Systematic meridional flow deflections observed in association with the forward and reverse waves bounding the CIRs demonstrate that the above effect is the result of the fact that the forward waves propagate to lower latitudes and the reverse waves to higher latitudes with increasing heliocentric distance. These observational results are in excellent agreement with the predictions of a three‐dimensional model of corotating solar wind flows that originate in a tilted dipole geometry back at the Sun.