Ground-based Pc5 ULF wave power: Solar wind speed and MLT dependence |
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| Authors: | DM Pahud IJ Rae IR Mann KR Murphy V Amalraj |
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| Institution: | 1. Department of Radio Science and Engineering, School of Electrical Engineering, Aalto University, Espoo 02150, Finland;2. Center of Space and Atmospheric Research (CSAR), Physical Sciences Department, Embry-Riddle Aeronautical University, Daytona Beach, FL 32114, USA;1. Department of Physics, University of Helsinki and Helsinki Institute of Physics, P.O. Box 64, FI-00014 Helsinki, Finland;2. Finnish Meteorological Institute, P.O.Box 503, FIN-00101, Helsinki, Finland;3. University of Bergen, Department of Physics and Technology, Allgaten 55, N-5007 Bergen, Norway;1. Space & Atmospheric Physics Group, The Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, UK;2. Department of Earth, Planetary and Space Sciences, University of California, 603 Charles E. Young Drive, Los Angeles, California, CA 90095-1567, USA;1. St. Petersburg State University, Institute of Physics, St. Petersburg, Russia;2. Research Institute for Space Medicine Federal Research Clinical Center of Federal Biomedical Agency of Russia, Moscow, Russia;3. Space Climate Research Unit, University of Oulu, Finland;4. State Scientific Center of the Russian Federation Institute of Biomedical Problem of the RAS, Moscow, Russia;1. SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai 200136, China;2. CAS Key Laboratory of Basic Plasma Physics, Department of Geophysics and Planetary Science, University of Science and Technology of China, Hefei 230026, China;1. Institute of Geophysics and Planetary Physics, University of California Los Angeles, Los Angeles, CA, USA;2. Department of Earth, Planetary, and Space Sciences, University of California Los Angeles, Los Angeles, CA, USA;3. Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA |
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| Abstract: | Using over 20 years of ground-based magnetometer data from the CANOPUS/CARISMA magnetometer array, we present a statistical characterisation of Pc5 ultra-low frequency (ULF) power in the 2–10 mHz band as a function of magnetic local time (MLT), L-shell, and solar wind speed. We examine the power across L-shells between 4.2 and 7.9, using data from the PINA, ISLL, GILL and FCHU stations, and demonstrate that there is a significant MLT dependence in both the H- and D-component median 2–10 mHz power during both fast (>500 km/s) and slow (<500 km/s) solar wind speeds. The H-component power consistently dominates over D-component power at all MLTs and during both fast and slow solar wind. At the higher-L stations (L>5.4), there are strong MLT power peaks in the morning and midnight local time sectors; the morning sector dominating midnight during fast solar wind events. At lower L-shells, there is no evidence of the midnight peak and the 2–10 mHz power is more symmetric with respect to MLT except during the fastest solar wind speeds. There is little evidence in the ground-based power of a localised MLT peak in ULF power at dusk, except at the lowest L-shell station, predominantly in the H-component. The median 2–10 mHz power increases with an approximate power law dependence on solar wind speed, at all local times across the L-shell domain studied in both components. The H-component power peaks at the latitude of the GILL station, with significantly lower power at both higher and lower L-shells. Conversely, the D-component power increases monotonically. We believe that this is evidence for 2–10 mHz power accumulating at auroral latitudes in field line resonances. Finally, we discuss how such ULF wave power characterisation might be used to derive empirical radiation belt radial diffusion coefficients based on, and driven by, the solar wind speed dependence of ULF wave power. |
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