We examine magnetic and electric field perturbations associated with a sudden commencement (SC), caused by an interplanetary (IP) shock passing over the Earth's magnetosphere on 16 February 2013. The SC was identified in the magnetic and electric field data measured at Time History of Events and Macroscale Interactions during Substorms (THEMIS-E; THE-E: magnetic local time (MLT) = 12.4, L = 6.3), Van Allen Probe-A (VAP-A: MLT = 3.2, L = 5.1), and Van Allen Probe-B (VAP-B: MLT = 0.2. L = 4.9) in the magnetosphere. During the SC interval, THE-E observed a dawnward-then-duskward electric (E) field perturbation around noon, while VAP-B observed a duskward E field perturbation around midnight. VAP-A observed a dawnward-then-duskward E field perturbation in the postmidnight sector, but the duration and magnitude of the dawnward E perturbation are much shorter and weaker than that at THE-E. That is, the E field signature changes with local time during the SC interval. The Super Dual Auroral Radar Network radar data indicate that the ionospheric plasma motions during the SC are mainly due to the E field variations observed in space. This indicates that the SC-associated E field in space plays a significant role in determining the dynamic variations of the ionospheric convection flow. By comparing previous SC MHD simulations and our observations, we suggest that the E field variations observed at the spacecraft are produced by magnetospheric convection flows due to deformation of the magnetosphere as the IP shock sweeps the magnetopause.
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The solar wind data are available at the NASA OMNIWeb service (http://omniweb.gsfc.nasa.gov/). The THEMIS data used in this study were obtained from the THEMIS website (http://themis.ssl.berkeley.edu). The Van Allen Probe data were obtained from the coordinated data analysis web (http://cdaweb. gsfc.nasa.gov/cdaweb). The authors thank the institutes who main tain the IMAGE Magnetometer Array. IMAGE data are available at http://www.space.fmi.fi/image/. The SYM-H index is provided through WDC-C2 for Geomagnetism, Kyoto University (http://wdc.kugi. kyoto-u.ac.jp). The authors acknowl edge the use of SuperDARN data. SuperDARN is a collection of radars funded by national scientific funding agencies of Australia, Canada, China, France, Japan, South Africa, United Kingdom, and United States of America. We thank the EMFI- SIS team for providing wave data from the Van Allen Probe spacecraft which was supported by JHU/APL contract 921647 under NASA Prime contract NAS5-01072 and JHU/APL contract 131802 under NASA prime contract NNN06AA01C. 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 PE17020 of the Korea Polar Research Institute.
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- electric field
- sudden commencement