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Ann. Geophys., 23, 2487-2499, 2005
www.ann-geophys.net/23/2487/2005/
© European Geosciences Union 2005
Ionospheric foF2 anomalies during some intense geomagnetic storms
R. P. Kane
Instituto Nacional de Pesquisas Espacias, São Jose dos Campos, São Paulo, Brazil
Abstract. The global evolutions of foF2 anomalies were examined for
three very intense geomagnetic storms, namely the Halloween events of
October-November 2003 (Event X, 29–30 October 2003, Dst –401 nT; Event Y, 20–21 November
2003, Dst –472 nT), and the largest Dst storm (Event Z, 13–14 March 1989, Dst –589 nT).
For Event X, troughs (negative storms) were clearly seen
for high northern and southern latitudes. For northern midlatitudes as well
as for low latitudes, there were very strong positive effects on 29 October 2003,
followed by negative effects the next day. For Event Y, there were no troughs in
NH high latitudes for morning and evening hours but there were troughs for
night. For midlatitudes and low latitudes, some longitudes showed strong
negative effects in the early morning as expected, but some longitudes showed
strong positive effects at noon and in the evening hours. Thus, there were
many deviations from the model patterns. The deviations were erratic,
indicating considerable local effects superposed on general patterns. A
disconcerting feature was the presence of strong positive effects
during the 24 h before the storm commencement. Such a
feature appears only in the 24 h before the geomagnetic storm
commencement but not earlier. If genuine, these could imply a prediction
potential with a 24-h antecedence. For Event Z (13–14 March 1989,
equinox), all stations (all latitudes and longitudes) showed a very strong
"negative storm" in the main phase, and no positive storms anywhere.
Keywords. Ionosphere (Equatorial ionosphere – Ionospheric
disturbances – Mid-latitude Ionosphere – Polar ionosphere)
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