Physics
Scientific paper
Oct 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008jgra..11300a09m&link_type=abstract
Journal of Geophysical Research, Volume 113, Issue 5, CiteID A00A09
Physics
2
Magnetospheric Physics: Magnetic Storms And Substorms (7954), Magnetospheric Physics: Auroral Phenomena (2407), Magnetospheric Physics: Plasma Waves And Instabilities (2471), Magnetospheric Physics: Magnetosphere/Ionosphere Interactions (2431)
Scientific paper
Strong geomagnetic storms are of great scientific interest because they drive the magnetosphere to an extreme state and result in nontypical magnetosphere-ionosphere coupling. The present study examines the ground-based signatures of the magnetosphere-ionosphere disturbances during the recovery phase of the very intense storm on 7-8 November 2004. The recovery phase took place under steady and slightly negative (~-5 nT) values of the IMF Bz. We compare this event with previously documented storm recovery phases occurring under positive IMF Bz and accompanied by morning Pc5 geomagnetic pulsations. During the period studied in this article the strongest pulsation activity was recorded in the evening and midnight sectors of the Earth. We analyze observations from the Scandinavian multipoint ground-based instrumentation: (1) geomagnetic variations and pulsations, (2) auroras in visual wavelengths, and (3) energetic particle precipitation (riometer data). We show that several enhancements in electrojet, auroral, and energetic precipitation activity were recorded at auroral latitudes. The activations lasted 0.5-2 hours, and the associated negative magnetic field deviations were often more than 1000 nT. Only one of these activations shows typical substorm behavior (poleward expansion and geostationary particle injection). We demonstrate remarkably good correlation between the magnetic variations and cosmic noise absorption variations (in pulsations and slower variations) as well as between the optical auroras and cosmic noise absorption (Imaging Riometer for Ionospheric Studies riometer system) both in time and in space. Thus the auroral precipitation revealed a very coherent behavior over a wide energy range (~1-40 keV) during the analyzed period. The images acquired by the network of MIRACLE all-sky cameras show that the auroral distribution exhibited double oval configuration during our event. Double oval is often observed during so-called Steady Magnetospheric Convection (SMC) episodes. Furthermore, multiple auroral streamers were recorded, implying probable occurrence of bursty bulk flows (BBFs) in the magnetotail. The absence of recurrent geostationary injections, the wide oval configuration, and BBF signatures lead us to suggest that the intermediate period between the two November 2004 superstorms can be attributed to a SMC period. Mapping the motion of ionospheric signatures to the magnetotail with the Tsyganenko 96 models suggests BBF earthward speeds of ~600-800 km/s. We suppose that the main drivers for the above described recurrent and intensive ionospheric phenomena are energy input from the solar wind due to slightly negative values of IMF Bz as well as huge energy storage in the magnetotail due to the previous storm main phase.
Kauristie Kirsti
Kleimenova N. G.
Kornilova T. A.
Kozyreva O. V.
Mäkinen S.
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