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Solar wind speed and coronal flux-tube expansion
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1990
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Solar wind speed at 1 AU is linked to coronal flux‑tube expansion, with high‑speed stream boundaries arising from steep expansion gradients at coronal hole edges. The study aims to predict daily Earth wind speeds using a current‑free extrapolation of the observed photospheric magnetic field into the corona. This prediction is based on extrapolating the photospheric field into the corona without currents to estimate flux‑tube expansion. Observations over 22 years confirm an inverse correlation between 1‑AU wind speed and coronal flux‑tube expansion, and modeling with a heliospheric current sheet shows that flux tubes near hole axes expand most at 1‑AU, matching low‑density high‑speed streams. Published in The Astrophysical Journal, June 1990 (DOI 10.1086/168805).
view Abstract Citations (705) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Solar Wind Speed and Coronal Flux-Tube Expansion Wang, Y. -M. ; Sheeley, N. R., Jr. Abstract The hypothesis that the solar wind speed at 1 AU and the rate of magnetic flux-tube expansion in the corona are inversely correlated is shown to be consistent with observations extending over the last 22 years. This empirical relationship allows the daily wind speeds at earth to be predicted from a current-free extrapolation of the observed photospheric field into the corona. The narrow boundaries of high-speed wind streams are attributed to steep gradients in the flux-tube expansion rates at the edges of coronal holes. When a heliospheric current sheet is included in the model, it is found that the flux tubes near the hole axis, although diverging more slowly than those near the hole boundary in the corona, have undergone the greatest net expansion at 1 AU, an effect consistent with the low densities within high-speed streams. Publication: The Astrophysical Journal Pub Date: June 1990 DOI: 10.1086/168805 Bibcode: 1990ApJ...355..726W Keywords: Magnetic Flux; Solar Corona; Solar Wind Velocity; Current Sheets; Magnetohydrodynamics; Photosphere; Solar Magnetic Field; Solar Physics; SUN: CORONA; SUN: SOLAR WIND full text sources ADS |