| Summary: | Total solar irradiance (TSI) may present the same long-term variation as the solar cycle length (SCL), corresponding to the Gleissberg cycle. It is expected that when SCL decrease, TSI increase. The analysis of stratospheric, ionospheric and solar data suggest that UV and EUV solar radiation have long-term variations that do not depend on the sunspot number Rz. The part of the UV and EUV solar flux associated to SCL, called UV(SCL) y EUV(SCL), varies in such a way that when SCL decreases, this radiation decreases. Direct indices of EUV and UV available data support this hypothesis. Through ionospheric data we estimated that EUV (SCL) is 1% and 2% of the total EUV solar flux, for a short and a long solar cycle respectively.
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