As the Earth moves through this evolving ballerina skirt, it is sometimes within the heliospheric current sheet, sometimes above it and sometime below it. These interaction regions consist of solar wind with very high densities and strong magnetic fieldsĪbove the current sheet, the higher speed solar wind typically has a dominant magnetic polarity in one direction and below the current sheet, the polarity is in the opposite direction. When high speed solar overtakes slow speed wind, it creates something known as a corotating interaction region. Because the Sun rotates every 27 days, the solar wind becomes a complex spiral of high and low speeds and high and low densities that looks like the skirt of a twirling ballerina (see figure). As solar activity increases, the solar surface fills with active regions, coronal holes, and other complex structures, which modify the solar wind and current sheet. This portion of the solar wind forms the equatorial current sheet.ĭuring quiet periods, the current sheet can be nearly flat. In the equatorial plane, where the Earth and the other planets orbit, the most common state of the solar wind is the slow speed wind, with speeds of about 400 kilometers per second. The north and south poles of the Sun have large, persistent coronal holes, so high latitudes are filled with fast solar wind. Coronal holes produce solar wind of high speed, ranging from 500 to 800 kilometers per second.
Solar magnetic field is embedded in the plasma and flows outward with the solar wind.ĭifferent regions on the Sun produce solar wind of different speeds and densities. We demonstrate that this solar wind forcing tool is a crucial step toward bringing heliospheric science expertise to bear on planetary exploration programs.The solar wind continuously flows outward from the Sun and consists mainly of protons and electrons in a state known as a plasma. Moreover, this modeling can help assess near-real-time magnetospheric behavior for MESSENGER or other mission analysis and/or ground-based observational campaigns. This quantity also serves as input to the global magnetohydrodynamic and kinetic magnetosphere models that are being used to explore magnetospheric and exospheric processes at Mercury. This product VBs is the electric field that drives many magnetospheric dynamical processes and can be compared with the occurrence of energetic particle bursts within the Mercury magnetosphere. We also use the relatively high-time-resolution B-field data from MESSENGER to estimate the strength of the product of the solar wind speed and southward IMF strength (Bs) at Mercury. Such parameters as solar wind dynamic pressure are key for determining the Mercury magnetopause standoff distance, for example.
We have compared upstream MESSENGER IMF and solar wind measurements to see how well the ENLIL model results compare. We have utilized the Wang-Sheeley-Arge (WSA)-ENLIL solar wind modeling tool in order to calculate the values of interplanetary magnetic field (IMF) strength (B), solar wind velocity (V) and density (n), ram pressure (~nV2), cross-magnetosphere electric field (VxB), Alfvén Mach number (MA), and other derived quantities of relevance for solar wind-magnetosphere interactions. Zurbuchen, Thomas H.Īnalysis and interpretation of observations from the MESSENGER spacecraft in orbit about Mercury require knowledge of solar wind "forcing" parameters. 2013 Articles Solar Wind Forcing at Mercury: WSA-ENLIL Model Resultsīaker, Daniel N.
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