Year: 2019
Type: article
Abstract: The interplanetary evolution of 11 magnetic clouds (MCs) recorded by at least two radially aligned spacecraft is studied. The in situ magnetic field measurements are fitted to a cylindrically symmetric Gold–Hoyle force-free uniform-twist flux-rope configuration. The analysis reveals that in a statistical sense, the expansion of the studied MCs is compatible with self-similar behavior. However, individual events expose a large scatter of expansion rates, ranging from very weak to very strong expansion. Individually, only four events show an expansion rate compatible with isotropic self-similar expansion. The results indicate that the expansion has to be much stronger when the MCs are still close to the Sun than in the studied 0.47–4.8 au distance range. The evolution of the magnetic field strength shows a large deviation from the behavior expected for the case of isotropic self-similar expansion. In the statistical sense, as well as in most of the individual events, the inferred magnetic field decreases much slower than expected. Only three events show behavior compatible with self-similar expansion. There is also a discrepancy between the magnetic field decrease and the increase of the MC size, indicating that magnetic reconnection and geometrical deformations play a significant role in the MC evolution. About half of the events show a decay of the electric current as expected for self-similar expansion. Statistically, the inferred axial magnetic flux is broadly consistent with remaining constant. However, events characterized by a large magnetic flux show a clear tendency toward decreasing flux.
Source: The Astrophysical Journal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Awards: Predicting solar storm arrivals at Earth, Forbush decrease model for expanding CMEs affecting Earth and Mars, G495187929, IN THE PROPOSED WORK WE CONTINUE AND EXTEND OUR EFFORTS OF THE PREVIOUS THREE YEARS (26WIND PUBLICATIONS IN 2013-2016; AND 3 IN THE REVIEW PROCESS) IN VARIOUS AREAS OF HELIOSPHERIC AND MAGNETOSPHERIC PHYSICS. THE MAGNETOSPHERIC ASPECT INVOLVES WIND AS L1 MONITOR OF INTERPLANETARY CONDITIONS WHEN INVESTIGATING HOW MAGNETOSPHERIC-IONOSPHERIC COUPLING PROCESSES AND THE STRUCTURE OF RECONNECTION LAYERS ARE CONTROLLED BY INTERPLANETARY PARAMETERS. TOPICS INCLUDE (I) TRADITIONAL AND NON-TRADITIONAL ASPECTS OF SUBSTORM EVOLUTION; (II) THE EFFECT OF A LARGE GUIDE FIELD ON THE STRUCTURE OF THE DISSIPATION REGION IN COLLISIONLESS RECONNECTION AND (III) GEOEFFECTS ELICITED BY SMALL SOLAR WIND TRANSIENTS (STS) PARTICULARLY THOSE WHICH DEPEND ON FACT THAT STS ARE MAGNETICALLY-DOMINATED STRUCTURES (LOW ALFV EN MACH NUMBER). WORK ON THE GEOMAGNETIC TAIL IS ALSO PROPOSED USING DATA ACQUIRED BY WIND DURING PASSAGES THROUGH AND NEAR THE GEOMAGNETIC TAIL. SPECIFICALLY WE INVESTIGATE: (I) A FLUX ROPE STRUCTURE SEEN BY WIND IN THE DISTANT TAIL AND PRECEDING AN INTERVAL OF TAIL FLAPPING IN THE CONTEXT OF SIGNATURES OF TRAVELING CONVECTION VORTICES SEEN BY VARIOUS MAGNETOSPHERIC PROBES AT THE SAME TIME. (II) EFFECT OF THE ANGLE BETWEEN THE SOLAR WIND VELOCITY AND THE IMF ON THE STRENGTH OF DRAPING-RELATED MAGNETOSHEATH ACCELERATION IN THE DISTANT TAIL. IN THE INTERPLANETARY AREA WE PROPOSE WORK ON CERTAIN ASPECTS OF SMALL SOLAR WIND TRANSIENTS AT 1 AU: A COMPREHENSIVE SURVEY OVER 2 SOLAR CYCLES USING WIND AND STEREO DATA; DEPENDENCE OF THEIR OCCURRENCE FREQUENCY ON BOTH SOLAR CYCLE PHASE AND SOLAR WIND SPEED; AND THEIR ANALYTICAL MODELING AND HOW THE MODELS CHOSEN (FORCE FREE VERSUS NON-FORCE FREE) DEPEND ON SOLAR CYCLE PHASE. WE WILL TAKE ALL OPPORTUNITIES TO USE WIND OBSERVATIONS IN THE CONTEXT OF MAGNETOSPHERE MULTISCALE (MMS) MISSION STUDIES OF THE RECONNECTION REGION ON THE DAYSIDE AND IN THE TAIL. THE STRUCTURE OF THE DISSIPATION REGION IS KNOWN BE DISTORTED BY ASYMMETRIES IN THE DENSITY AND MAGNETIC FIELDS AND THE PRESENCE OF A GUIDE FIELD. ON THESE WIND CAN PROVIDE IMPORTANT INFORMATION. THE PROPOSED WORK WILL ENHANCE THE SCIENTIFIC RETURNS OF THE WIND MISSION. PROVISION IS ALSO MADE TO MAINTAIN THE SWE/ELECTRON INSTRUMENT WHICH PROVIDES VALUABLE DATA TO THIS EFFORT., Initiation of solar flares: reconnection, heating and particle acceleration
OpenAlex ID: W2937643147