Large variations in the thermosphere and ionosphere during minor geomagnetic disturbances in April 2002 and their association with IMF By

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Read Full Article (file size: 4460594 bytes) Cited by JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, A03303, doi:10.1029/2004JA010683, 2006 Large variations in the thermosphere and ionosphere during minor geomagnetic disturbances in April 2002 and their association with IMF B_y L. Goncharenko Haystack Observatory, Massachusetts Institute of Technology, Westford, Massachusetts, USA J. Salah Haystack Observatory, Massachusetts Institute of Technology, Westford, Massachusetts, USA G. Crowley Southwest Research Institute, San Antonio, Texas, USA L. J. Paxton John Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA Y. Zhang John Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA A. Coster Haystack Observatory, Massachusetts Institute of Technology, Westford, Massachusetts, USA W. Rideout Haystack Observatory, Massachusetts Institute of Technology, Westford, Massachusetts, USA C. Huang Haystack Observatory, Massachusetts Institute of Technology, Westford, Massachusetts, USA S. Zhang Haystack Observatory, Massachusetts Institute of Technology, Westford, Massachusetts, USA B. Reinisch Center for Atmospheric Research, University of Massachusetts Lowell, Lowell, Massachusetts, USA V. Taran Institute for Ionosphere, Kharkiv, Ukraine Abstract We investigate the variations in the thermosphere and ionosphere using multi-instrument observations during the April 2002 period, with a particular focus on periods during small geomagnetic disturbances. Large and long-lasting reductions in the daytime electron density were observed at midlatitudes by incoherent scatter radars, ionosondes, and GPS receivers. These reductions reached 30–50% and were observed over an extended longitudinal area. They propagated to middle latitudes (35–40°N) in the case of a weak geomagnetic disturbance (K _p = 3−) and to low latitudes (0–10°N) in the case of a stronger disturbance (K _p = 5−). Data from the GUVI instrument aboard the TIMED satellite reveal a reduction in the daytime O/N₂ ratio in the coincident area. Similar decreases are also predicted by the TIMEGCM/ASPEN model in both O/N₂ ratio and electron density, though the magnitude of the decrease from the model is smaller than observed. We suggest that these ionospheric and thermospheric disturbances result from high-latitude energy input and efficient transport of regions with reduced O/N₂ to lower latitudes. We discuss the possible role of a strong positive B _y component of the interplanetary magnetic field in the transport of regions with reduced O/N₂. Received 14 July 2004; accepted 9 December 2005; published 15 March 2006. Keywords: electron density; thermospheric composition; thermospheric wind. Index Terms: 0355 Atmospheric Composition and Structure: Thermosphere: composition and chemistry; 2435 Ionosphere: Ionospheric disturbances; 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions (2431); 2788 Magnetospheric Physics: Magnetic storms and substorms (7954); 3369 Atmospheric Processes: Thermospheric dynamics (0358). Read Full Article (file size: 4460594 bytes) Cited by Citation: Goncharenko, L., et al. (2006), Large variations in the thermosphere and ionosphere during minor geomagnetic disturbances in April 2002 and their association with IMF B_y, J. Geophys. Res., 111, A03303, doi:10.1029/2004JA010683. Copyright 2006 by the American Geophysical Union.

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