Trends in the F2 ionospheric layer due to long-term variations in the Earth?s magnetic field

ANA G. ELIAS

Saint Petersburg

Workshop; 5th Workshop on Long-Term Changes and Trends in the Atmosphere; 2008

IAGA - ICMA - CAWSES, Antarctic Research Institute (AARI)

The Earth?s magnetic field presents long-term variations with changes in the dip angle (I) and, consequently, in the sin(I)cos(I) factor, which affects the thermospheric neutral winds that move the conducting plasma of the ionosphere. The horizontal thermospheric wind (U) drives ions and electrons along the geomagnetic field lines at speed U cos(I) from equator to pole during day, and from pole to equator during night. Thus, the vertical component, U sin(I)cos(I), lowers the F2-peak (hmF2) during daytime and raises it during nighttime, decreasing or increasing the peak electron density (measured through foF2). An increase in the sin(I)cos(I) factor would induce, during daytime, an additional lowering of the F-region with a decrease in foF2, while during nighttime, it would result in an additional raise of the layer with an increase in foF2. A decrease in the sin(I)cos(I) factor would produce the opposite effect. A theoretical approximation is developed in order to assess trends in foF2 and hmF2 due to variations in I. Ionospheric trends which depend on location (latitude and longitude), time and season are obtained. Under this theoretical framework, a comparison between Northern and Southern latitudes is made. Compared to the expected effects of greenhouse gases increasing trend over the F2 region, the Earth?s magnetic field may be able to produce stronger trends and also to explain some seasonal and daily variation patterns. Long-term variations in geomagnetic activity is another possible mechanism which may induce trends in the F2 region with seasonal and daily variation patterns. In order to elucidate the origin of the F2-region trends and to explain the experimental trend values observed, a theoretical assessment should be done taking into account long-term variations in the three possible mechanisms altogether: greenhouse gases, geomagnetic activity, and Earth?s magnetic field.