Mirror Mode Waves Downstream of a Stream Interaction Region Forward Shock near 1 AU
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Mirror mode waves in the solar wind are typically observed not as quasi-periodic sinusoidal signatures, but as trains of nonperiodic structures of two types: magnetic “peaks” and magnetic “dips.” Some trains of long durations have been called mirror mode storms. In this work we report mirror mode waves downstream of a stream interaction region (SIR) forward shock observed near 1 AU on 7 May 2007 with Solar Terrestrial Relations Observatory (STEREO) and Time History of Events and Macroscale Interactions during Substorms (THEMIS) data. The high-resolution magnetic-field data (0.125-second resolution) from STEREO are scanned to search for magnetic dips and peaks (or upgoing magnetic “mesas”) in the solar wind. STEREO-A observes a mirror mode storm: the appearance of mirror mode waves (mainly magnetic peaks and upgoing mesas) is simultaneous with the entry into a high-density, high-temperature, and high plasma β accompanied by a depressed field region; the magnetic dips survive in the lower plasma-β region. STEREO-B observes mirror mode waves (mainly magnetic peaks) with different amplitudes and asymmetric forms, which can survive in a low plasma β region. THEMIS-D, which was located in the solar wind, also observes mirror mode waves (mainly magnetic peaks and upgoing mesas) as well as an enhanced ion temperature anisotropy (T ⊥≈3T ∥). The enhanced ion temperature anisotropy and high plasma β satisfy the mirror-instability criterion. These observations of STEREO and THEMIS-D show that mirror mode waves can be excited downstream of a SIR forward shock near 1 AU.
KeywordsSolar wind Shock waves Instabilities
This work was supported by the National Natural Science Foundation of China grants 41004075, 40825014, and 40890162. This work is also supported in part by the Shandong Province Natural Science Foundation, grants ZR2010DQ014, the Specialized Research Fund for State Key Laboratories by the Open Research Fund in China, and the Open Research Fund for SOA Key Laboratory for Polar Science in China (KP201105). We are grateful to M.H. Acuna and the IMPACT team for the magnetic-field data, and to A.B. Galvin and the PLASTIC team for the solar-wind data. We would like to acknowledge V. Angelopoulos for the THEMIS data. We thank B. Li, G. Li, V. Angelopoulos, and Z. Wu for their assistance in preparing this article.
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