foF2 long-term trends for periods including solar cycle 23

BLAS F. DE HARO BARBAS; ANA G. ELIAS; KIYOTO SHIBASAKI; JONAS R. SOUZA

Cambridge

Workshop; 8th Workshop on Long-Term Change and Trends in the Atmosphere; 2014

IAGA - ICMA - CAWSES

Solar EUV irradiance is the main ionization source of the F2 region of the Earth?s ionosphere. This makes necessary to filter out solar activity effects prior to long term trends estimation. Solar cycle 23 seems to have had a EUV emission different from that deduced from traditional solar EUV proxies. Including this solar cycle in the trend estimation then, and using traditional filtering techniques, may induce some spurious results. In the present work foF2 long-term trend is estimated using experimental values for two stations: Slough (51.5°N, 359.4°E) and Kokobunji (35.7°N, 139.5°E), and using values obtained from two models: the Sheffield University Plasmasphere Ionosphere model, SUPIM, and the International Reference Ionosphere, IRI. Then filtering is done in the usual way considering the residuals of the linear regression between foF2 and Rz and also between foF2 and F10.7, for both experimental and modeled values. foF2 trends become less negative as we include years after 2000, since foF2 systematically exceed the values predicted by a linear fit between foF2 and Rz or F10.7. foF2 trends assessed with modeled foF2 values, are less stronger than those obtained with experimental foF2 values and more stable as solar cycle 23 is included in the trend estimation. Modeled trends may be thought of as a ?zero level? trends due to all the assumptions made in the process of trend estimation, and considering that we are not dealing with ideal conditions and infinite time series. If we correct experimental trends subtracting the values of modeled trends, the values obtained approach the values expected from the greenhouse effect.