An artists rendition of the Parker Solar Probe approaching the Sun. Astronomers have actually used data from Parker, in addition to data from other solar objectives, to study and detect Solar stream interactions. Credit: NASA/Johns Hopkins APL/Steve Gribben
When a quick solar wind stream appears from a coronal hole (a cooler area in the Suns environment) and surpasses a slower moving solar wind stream, a stream interaction region (SIR) can form. In the SIR, a density “pileup” of compressed plasma develops upstream of the interface; typically there is a peak in pressure followed by a rarefaction region in the quick solar wind component. As the SIR propagates far from the Sun, to distances of one astronomical system or beyond, the compression can form a shock that effectively accelerates charged particles. Therefore SIRs are a significant source of energetic particles in interplanetary area.
Coronal holes, the main sources of the high-speed stream, turn as the Sun turns on its axis, and the SIR structures turn with it. After a complete solar rotation, a SIR is reclassified as a corotating interaction area (CIR). SIRs and CIRs are large-scale, typically long-lived structures that, like the solar wind itself, can activate geomagnetic storms on the Earth and affect its ionosphere and thermosphere.
Additionally, these structures and their associated shocks can regulate the strength of incoming stellar cosmic rays. SIRs and CIRs vary temporally and spatially, and astronomers are working to understand how they form, progress, and continue for multiple solar rotations. Doing so needs a robust database of observations at small heliospheric ranges together with complementary measurements from other area observatories.
CfA astronomers Anthony Case, Justin Kasper, Kelly Korreck and Michael Stevens and their associates used Parker Solar Probe and its SWEAP instrument to identify CIRs and sirs; SWEAP approaches incredibly near to the Suns surface area, only about four million miles. The team combined the SWEAP results with data from the STEREO-A and Wind solar satellites orbiting farther away.
Throughout five orbits of the Parker Solar Probe, these objectives determined and classified the distances, pressures, electromagnetic fields, and speeds of eleven SIRs and CIRs, tracking their development throughout almost two years. The objective of this program is to develop a “living catalog” of SIR and CIR events with stringent identification requirements.
These results represent the very first iteration in a series of observations that will make it possible for case studies of these structures in addition to statistical analyses to comprehend their properties and development.
Recommendation: “A living brochure of stream interaction regions in the Parker Solar Probe era” by R. C. Allen, G. C. Ho, L. K. Jian, S. K. Vines, S. D. Bale A. W. Case, M. E. Hill, C. J. Joyce, J. C. Kasper, K. E. Korreck, D. M. Malaspina, D. J. McComas, R. McNutt, C. Möstl, D. Odstrcil, N. Raouafi, N. A. Schwadron and M. L. Stevens, 2 June 2021, Astronomy & & Astrophysics.DOI: 10.1051/ 0004-6361/2020 39833.
Astronomers have used information from Parker, along with information from other solar objectives, to find and study Solar stream interactions. When a quick solar wind stream appears from a coronal hole (a cooler region in the Suns atmosphere) and surpasses a slower moving solar wind stream, a stream interaction area (SIR) can form. After a complete solar rotation, a SIR is reclassified as a corotating interaction region (CIR).
