Trends in noon and midnight foF2 related to greenhouse gases and Earth's magnetic field secular variation

JAVIER ZAMORA; NICOLAR BACHI; ANA G. ELIAS; BLAS F. DE HARO BARBAS

Praga

Congreso; 26th IUGG General Assembly (International Union of Geodesy and Geophysics); 2015

IUGG - IAGA - IAMAS

Long term trends in the ionosphere are linked mainly to the increase in greenhouse gases concentration, but also to natural causes such as geomagnetic activity long-term changes and secular variations in the Earth?s main magnetic field. The expected effects from variations in the Earth?s magnetic field, mainly the dip angle (I), are analyzed in the present work. In theory, these effects during day should be opposite to those during night. foF2 data of Huancayo (12.0°S, 75.3°W) and Ottawa (45.4°N, 75.9°W) are analyzed at 12 LT and 0 LT. Noon trends agree qualitatively with the trends expected from I variation at the corresponding locations. Trends at midnight, which are expected to be opposite to those observed at noon, agrees only in the case of Huancayo. In the case of Ottawa the midnight trend is statistically not different from cero. This is possible to explain by the decreasing trend expected from greenhouse gases effect which would offset the increasing trend expected.. In the case of Huancayo this does not happen since there is an additional effect. Huancayo is an equatorial ionospheric station located north of the dip-equator, under the influence of the equatorial ionization anomaly (EIA). The dip equator is moving away from the station, so an increase in foF2 should be expected from the displacement of the EIA trough, which follows the dip equator secular movement. The quantification of natural effects on trends is an important contribution to one of the present focus of climate science that is the determination of the extent to which human activities are altering the planetary energy balance.