|
|
 |
|
|
Ann. Geophys., 26, 1189-1197, 2008
www.ann-geophys.net/26/1189/2008/
© European Geosciences Union 2008
Long-term trends in the ionospheric E and F1 regions
J. Bremer
Leibniz-Institute of Atmospheric Physics, 18225 Kühlungsborn, Schloss-Str. 6, Germany
Abstract. Ground based ionosonde measurements are the most
essential source of information about long-term variations in the
ionospheric E and F1 regions. Data of such observations have been derived at
many different ionospheric stations all over the world some for more than 50
years. The standard parameters foE, h'E, and foF1 are used for trend
analyses in this paper. Two main problems have to be considered in these
analyses. Firstly, the data series have to be homogeneous, i.e. the
observations should not be disturbed by artificial steps due to technical
reasons or changes in the evaluation algorithm. Secondly, the strong solar
and geomagnetic influences upon the ionospheric data have carefully to be
removed by an appropriate regression analysis. Otherwise the small trends in
the different ionospheric parameters cannot be detected.
The trends derived at individual stations differ markedly, however their
dependence on geographic or geomagnetic latitude is only small.
Nevertheless, the mean global trends estimated from the trends at the
different stations show some general behaviour (positive trends in foE and
foF1, negative trend in h'E) which can at least qualitatively be explained
by an increasing atmospheric greenhouse effect (increase of CO2 content
and other greenhouse gases) and decreasing ozone values. The positive foE
trend is also in qualitative agreement with rocket mass spectrometer
observations of ion densities in the E region. First indications could be
found that the changing ozone trend at mid-latitudes (before about 1979,
between 1979 until 1995, and after about 1995) modifies the estimated mean
foE trend.
Full Article in PDF (1081 KB) |
|
|
