Properties of Stream Interactions at One AU During 1995 – 2004 |
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| Authors: | L Jian C T Russell J G Luhmann R M Skoug |
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| Institution: | (1) Institute of Geophysics and Planetary Physics, University of California, Los Angeles, 595 Charles E. Young Dr. East, 6862 Slichter, Los Angeles, CA, 90095, U.S.A.;(2) Institute of Geophysics and Planetary Physics, University of California, Los Angeles, 595 Charles E. Young Dr. East, 6869 Slichter, Los Angeles, CA, 90095, U.S.A.;(3) Space Sciences Laboratory, University of California, Berkeley, CA, 94720, U.S.A.;(4) Los Alamos National Laboratory, Los Alamos, NM, 87545, U.S.A. |
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| Abstract: | A stream interaction region (SIR) forms when a fast solar stream overtakes a slow stream, leading to structure that evolves
as an SIR moves away from the Sun. Based on Wind (1995 – 2004) and ACE (1998 – 2004) in situ observations, we have conducted a comprehensive survey of SIRs at one AU, including a separate assessment of the longer-lasting
corotating interaction regions (CIRs) that recur on more than one solar rotation. In all there are 196 CIRs, accounting for
about 54% of the 365 SIRs. The largest proportion of CIRs to SIRs (64%) appears in 1999, and the smallest proportion (49%)
is in 2002. Over the ten years, the annual number of SIR events varies little, from 32 up to 45. On average, the occurrence
rate of shocks at SIRs at one AU is about 24%. Seventy percent of the SIRs with shocks have only forward shocks, more than
twice the percentage of SIRs with only reverse shocks. This preponderance of forward shocks is consistent with the deflections
of forward and reverse shocks relative to the ecliptic plane. In order to help address the effect of SIRs and CIRs on geomagnetic
activity, we determine the solar-cycle variation of the event duration, scale size, the change in velocity from slow stream
to fast stream, and the solar-cycle variation of the maximum magnetic field, peak total perpendicular pressure, and other
properties. These statistics also provide a baseline for future studies at other heliocentric distances and for validating
heliospheric models.
Electronic Supplementary Material Supplementary material is available for this article at |
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