The asymmetric geospace as displayed during the geomagnetic storm on 17 August 2001
Previous studies have shown that conjugate auroral features are displaced in the two hemispheres when the interplanetary magnetic field (IMF) has a transverse (Y) component. It has also been shown that a BY component is induced in the closed magnetosphere due to the asymmetric loading of magnetic fl...
| Published in: | Annales Geophysicae |
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| Main Authors: | , , , , , , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
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Published by: European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany)
2019
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| Subjects: | |
| Online Access: | https://www.ann-geophys.net/36/1577/2018/ http://hdl.handle.net/2381/43970 https://doi.org/10.5194/angeo-36-1577-2018 |
| Summary: | Previous studies have shown that conjugate auroral features are displaced in the two hemispheres when the interplanetary magnetic field (IMF) has a transverse (Y) component. It has also been shown that a BY component is induced in the closed magnetosphere due to the asymmetric loading of magnetic flux in the lobes following asymmetric dayside reconnection when the IMF has a Y component. The magnetic field lines with azimuthally displaced footpoints map into a “banana”-shaped convection cell in one hemisphere and an “orange”-shaped cell in the other. Due to the Parker spiral our system is most often exposed to a BY-dominated IMF. The dipole tilt angle, varying between ±34∘, leads to warping of the plasma sheet and oppositely directed BY components in dawn and dusk in the closed magnetosphere. As a result of the Parker spiral and dipole tilt, geospace is asymmetric most of the time. The magnetic storm on 17 August 2001 offers a unique opportunity to study the dynamics of the asymmetric geospace. IMF BY was 20–30 nT and tilt angle was 23∘. Auroral imaging revealed conjugate features displaced by 3–4 h magnetic local time. The latitudinal width of the dawnside aurora was quite different (up to 6∘) in the two hemispheres. The auroral observations together with convection patterns derived entirely from measurements indicate dayside, lobe and tail reconnection in the north, but most likely only dayside and tail reconnection in the Southern Hemisphere. Increased tail reconnection during the substorm expansion phase reduces the asymmetry. This study was supported by the Research Council of Norway under contract 223252/F50 (CoE). Stephen E. Milan was supported by the Science and Technology Facilities Council, UK, grant no ST/N000749/1. The data described in this paper are available from the authors on request (nikolai.ostgaard@uib.no). We thank Stephen B. Mende and the IMAGE FUV team at the Space Sciences Laboratory at UC Berkeley for the FUV data. The images were processed using the FUVIEW3 software (http://sprg.ssl.berkeley.edu/image/). We thank Rae Dvorsky and the Polar VIS team at the University of Iowa for the VIS Earth data. The VIS Earth images were downloaded from NASA's Space Physics Data Facility (ftp://cdaweb.gsfc.nasa.gov/pub/data/polar/vis/vis_earth-camera-full/) and processed using the XVIS 2.40 software (http://vis.physics.uiowa.edu/vis/software/). We thank Charles Smith for the ACE magnetic field data and David McComas for the ACE solar wind data. We acknowledge use of NASA/GSFC's Space Physics Data Facility's OMNIWeb service and OMNI data. The DMSP SSIES data were downloaded from http://cindispace.utdallas.edu/DMSP/. We gratefully acknowledge the Center for Space Sciences at the University of Texas at Dallas and the US Air Force for providing the DMSP thermal plasma data. The authors thank the NOAA's National Geophysical Data Center (NGDS) for providing NOAA POES data. The CHAMP mission was sponsored by the Space Agency of the German Aerospace Center (DLR) through funds of the Federal Ministry of Economics and Technology, following a decision of the German Federal Parliament (grant code 50EE0944). We thank Patricia Ritter for processing the data. For the ground magnetometer data we gratefully acknowledge the following: Intermagnet; USGS, Jeffrey J. Love; CARISMA, Ian Mann; CANMOS; the S-RAMP database, K. Yumoto and K. Shiokawa; the SPIDR database; AARI, Oleg Troshichev; the MACCS program, M. Engebretson; Geomagnetism Unit of the Geological Survey of Canada; GIMA; MEASURE, UCLA IGPP, and Florida Institute of Technology; SAMBA, Eftyhia Zesta; 210 Chain, K. Yumoto; SAMNET, Farideh Honary; the institutes that maintain the IMAGE magnetometer array, Eija Tanskanen; PENGUIN; AUTUMN, Martin Conners; DTU Space, Jürgen Matzka; South Pole and McMurdo Magnetometer, Louis J. Lanzarotti and Alan T. Weatherwax; ICESTAR; RAPIDMAG; PENGUIn; British Antarctic Survey; McMac, Peter Chi; BGS, Susan Macmillan; Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN); GFZ, Jürgen Matzka; MFGI, B. Heilig; IGFPAS, J. Reda; University of L'Aquila, M. Vellante; SuperMAG, Jesper W. Gjerloev. We acknowledge the use of SuperDARN data. SuperDARN is a collection of radars funded by national scientific funding agencies of Australia, Canada, China, France, Italy, Japan, Norway, South Africa, the United Kingdom and the United States of America. The Virginia Tech SuperDARN database (http://vt.superdarn.org, last access: 22 March 2016) is automatically accessed by the DaViTpy python toolkit. Simulation results have been provided by the Community Coordinated Modeling Center at Goddard Space Flight Center through their public “Runs on Request” system (http://ccmc.gsfc.nasa.gov, last access: 28 January 2016). The CCMC is a multiagency partnership between NASA, AFMC, AFOSR, AFRL, AFWA, NOAA, NSF and ONR (William_Longley_112213_4). Peer-reviewed Publisher Version |
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