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Ann. Geophys., 23, 163-181, 2005
www.ann-geophys.net/23/163/2005/
© European Geosciences Union 2005
Observations of the April 2002 geomagnetic storm by the global network of incoherent scatter radars
L. P. Goncharenko1, J. E. Salah1, A. van Eyken2, V. Howells3, J. P. Thayer4, V. I. Taran5, B. Shpynev6, Q. Zhou7, and J. Chau8
1Massachusetts Institute of Technology, Haystack Observatory, Westford, MA, USA
2EISCAT Scientific Association, PO Box 432, Longyearbyen, Norway
3Space Physics Division, Rutherford Appleton Laboratory, Didcot, Oxon, UK
4University of Colorado, Aerospace Engineering Sciences Boulder, CO, USA
5Institute for Ionosphere, Kharkov, Ukraine
6Institute for Solar-Terrestrial Physics, Irkutsk, Russia
7Electrical and Computer Eng. Dept., Miami University, Oxford, OH, USA
8Radio Observatorio de Jicamarca, Instituto Geofisico del Peru, Lima 33, Peru
Abstract. This paper describes the ionospheric response to a geomagnetic storm beginning on
17 April 2002. We present the measurements of ionospheric parameters in the
F-region obtained by the network of eight incoherent scatter radars. The main
effects of this storm include a deep decrease in the electron density observed at
high and middle latitudes in the pre-noon sector, and a minor enhancement in the
density observed in the daytime sector at middle latitudes. Extreme plasma heating
(>1000-3000 K) is observed at high latitudes, subsiding to 200-300K at subauroral
latitudes. The western hemisphere radar chain observed the prompt penetration of
the electric field from auroral to equatorial latitudes, as well as the daytime
enhancement of plasma drift parallel to the magnetic field line, which is related
to the enhancement in the equatorward winds. We suggest that in the first several
hours after the storm onset, a negative phase above Millstone Hill (pre-noon
sector) results from counteracting processes - penetration electric field,
meridional wind, and electrodynamic heating, with electrodynamic heating being the
dominant mechanism. At the lower latitude in the pre-noon sector (Arecibo and
Jicamarca), the penetration electric field becomes more important, leading to a
negative storm phase over Arecibo. In contrast, in the afternoon sector at
mid-latitudes (Kharkov, Irkutsk), effects of penetration electric field and
meridional wind do not counteract, but add up, leading to a small (~15%), positive
storm phase over these locations. As the storm develops, Millstone Hill and
Irkutsk mid-latitude radars observe further depletion of electron density due to
the changes in the neutral composition.
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