We have statistically studied sudden commencement (SC) by using the data acquired from Van Allen Probes (VAP) in the inner magnetosphere (L = 3.0–6.5) and GOES spacecraft at geosynchronous orbit (L =∼ 6.7) from October 2012 to September 2017. During the time period, we identified 85 SCs in the inner magnetosphere and 90 SCs at geosynchronous orbit. Statistical results of the SC events reveal the following characteristics. (1) There is strong seasonal dependence of the geosynchronous SC amplitude in the radial BV component at all local times. However, BV shows weak seasonal variation on the dayside in the inner magnetosphere. (2) The local time dependence of the SC amplitude in the compressional BH component at geosynchronous orbit is similar to that in the inner magnetosphere. (3) In a nightside region of L = 5.0–6.5, ∼19% of BH events are negative, while ∼58% of BH events are negative at geosynchronous orbit. (4) The amplitude of the SC-associated Ey perturbations varies systematically with local time with a morning-afternoon asymmetry near noon. These observations can be explained by spatial and/or temporal changes in the magnetopause and cross-tail currents, which are caused by changes in the solar wind dynamic pressure, with respect to spacecraft positions.
Bibliographical noteFunding Information:
The solar wind and IMF data are provided by Coordinated Data Analysis Web (CDAWeb) (http://cdaweb.gsfc. nasa.gov). The Van Allen Probe data were obtained from the coordinated data analysis web (http://cdaweb.gsfc.nasa.gov/cdaweb). GOES magnetic field data were obtained from the National Oceanic and Atmospheric Administration (NOAA), http://ngdc.noaa.gov/. The SYM-H index is provided through WDC-C2 for Geomagnetism, Kyoto University (http://wdc.kugi. kyoto-u.ac.jp). This work was supported by BK21+ through the National Research Foundation (NRF) funded by the Ministry of Education of Korea. The work of K. -H. Kim was supported by the Basic Science Research Program through NRF funded by NRF-2016R1A2B4011553 and also supported by project PE18020 of the Korea Polar Research Institute.
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