Long-term trends in foF2 over Moscow ionosonde station: Its estimate and origins |
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Authors: | HanXian Fang LiBin Weng ShengGao Yang SiCheng Wang |
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Affiliation: | [1]Institute of Meteorology, People's Liberation Army University of Science and Technology, Nanjing 211101, China [2]State Key Laboratory of Space Weather, Chinese Academy of Sciences, Beijing 100190, China |
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Abstract: | We introduce a new approach,using the International Reference Ionosphere 2007(IRI-2007)model and observations from the Moscow ionosonde station,to analyze the long-term trends of ionospheric foF2.Possible origins,whether natural or manmade, are discussed.A small but significant residual foF2 trend is found,with-0.76 MHz over the past 50 years,but-0.2 MHz after eliminating the most variations caused by solar and geomagnetic activities and the variational earth’s magnetic field.We find that this slope depends on local time and seasons.There is a pronounced diurnal negative variation in k(annual mean slope of diurnal variations),with much larger absolute values in the morning than during afternoon or evening;the largest k is about-0.0018 per year in spring,and the smallest trend of about-0.0012 per year occurs in winter.Finally,the evidence of crucial influences of geomagnetic activity and the earth’s magnetic field on the observed trends,as emphasized by the IRI-2007 empirical model,is confirmed,and the effect of CO2 contributions to the trend is also discussed,by cooling the thermospheric temperature or recombining the electron density. |
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Keywords: | ionosphere long-term trends IRI-2007 Moscow |
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