Changed relation between sunspot numbers, solar UV/EUV radiation and TSI during the declining phase of solar cycle 23

Details Changed relation between sunspot numbers, solar UV/EUV radiation and TSI during the declining phase of solar cycle 23 Changed relation between sunspot numbers, solar UV/EUV radiation and TSI during the declining phase of solar cycle 23

Feb 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jastp..73..235l&link_type=abstract

Journal of Atmospheric and Solar-Terrestrial Physics, Volume 73, Issue 2-3, p. 235-240.

Physics

6

Scientific paper

We study the mutual relation of sunspot numbers and several proxies of solar UV/EUV radiation, such as the F10.7 radio flux, the HeI 1083 nm equivalent width and the solar MgII core-to-wing ratio. It has been noted earlier that the relation between these solar activity parameters changed in 2001/2002, during a large enhancement of solar activity in the early declining phase of solar cycle 23. This enhancement (the secondary peak after the Gnevyshev gap) forms the maximum of solar UV/EUV parameters during solar cycle 23. We note that the changed mutual relation between sunspot numbers and UV/EUV proxies continues systematically during the whole declining phase of solar cycle 23, with the UV/EUV proxies attaining relatively larger values for the same sunspot number than during the several decennia prior to this time. We have also verified this evolution using the indirect solar UV/EUV proxy given by a globally averaged f0(F2) frequency of the ionospheric F2 layer. We also note of a simultaneous, systematic change in the relation between the sunspot numbers and the total solar irradiance, which follow an exceptionally steep relation leading to a new minimum. Our results suggest that the reduction of sunspot magnetic fields (probably photospheric fields in general), started quite abruptly in 2001/2002. While these changes do not similarly affect the chromospheric UV/EUV emissions, the TSI suffers an even more dramatic reduction, which cannot be understood in terms of the photospheric field reduction only. However, the changes in TSI are seen to be simultaneous to those in sunspots, so most likely being due to the same ultimate cause.

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