Abstract
Abstract. The analysis of the foF2 ionosonde data acquired at mid and high latitudes reveals a general decreasing of the F2 plasma frequency over more than two solar cycles, showing steeper trends over the high latitude stations and, in particular, over Antarctica. A careful analysis of the foF2 hourly data, opportunely catalogued in different levels of magneto-ionospheric conditions, highlights the role of the geomagnetic activity in the secular change of the ionosphere and confirms the latitudinal dependence of the trends. These results suggest interesting relations with some recent findings on the rapid decrease of some important physical and statistical quantities related to the geomagnetic field over the whole globe and mainly in Antarctica. In this paper we discuss the possibility of a connection between the ionospheric trends and a possible imminent geomagnetic reversal or excursion.
Highlights
Long term changes of the middle-upper atmosphere and the role of their natural and anthropogenic causes have been recently reviewed by Lastovicka (2005) and Bremer (2005)
A careful analysis of the f oF 2 hourly data, opportunely catalogued in different levels of magneto-ionospheric conditions, highlights the role of the geomagnetic activity in the secular change of the ionosphere and confirms the latitudinal dependence of the trends. These results suggest interesting relations with some recent findings on the rapid decrease of some important physical and statistical quantities related to the geomagnetic field over the whole globe and mainly in Antarctica
The results indicate a possible increase of the geomagnetic activity during the XX century but the matter is quite debated: Clilverd and his co-authors (1998) indicate an enhancement in the number of magnetic storms; Gulyaeva (2002) find a lowering in the occurrence of the aa index quiet condition; Cliver and Ling (2002) claimed that only during the first half of the XX century the aa index shows an increasing trend
Summary
Long term changes of the middle-upper atmosphere and the role of their natural and anthropogenic causes have been recently reviewed by Lastovicka (2005) and Bremer (2005). Clilverd et al (2005) and Musula and Martini (2006) investigated again the long-term change of the aa index through the use of a new tool introduced by Svalgaard et al (2004): the IHV (Inter Hour Variability) index It is defined as an average of the six absolute differences of the successive hourly values of the H component between 19:00 and 01:00 local time (LT) and its use allows the reproduction and verification of the aa index, otherwise impossible as the original measurements do not exist in digital format. In their paper Rajaram et al (2002) found a rapid decrease in total magnetic field over a large part of Antarctica pointing out this is as a region of possible reverse magnetic flux These intriguing findings are confirmed by a recent analysis (De Santis, 2007) showing that the geomagnetic field over Antarctica is decreasing faster than on global scale
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