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Solar forcing of the semi‐annual variation of length‐of‐day
Author(s) -
Le Mouël JeanLouis,
Blanter Elena,
Shnirman Mikhail,
Courtillot Vincent
Publication year - 2010
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2010gl043185
Subject(s) - variation (astronomy) , atmospheric sciences , forcing (mathematics) , cosmic ray , amplitude , sunspot , sunspot number , environmental science , solar minimum , solar cycle , solar variation , irradiance , physics , climatology , annual cycle , day length , intensity (physics) , cosmic cancer database , solar wind , astrophysics , geology , plasma , optics , biology , photoperiodism , quantum mechanics , magnetic field , horticulture
We study the evolution of the amplitude A of the semi‐annual variation of the length‐of‐day (lod) from 1962 to 2009. We show that A is strongly modulated (up to 30%) by the 11‐yr cycle monitored by the sunspot number WN . A and WN are anticorrelated, WN leading A by 1‐yr. A is therefore directly correlated with galactic cosmic ray intensity. The main part of the semi‐annual variation in lod is due to the variation in mean zonal winds. We conclude that variations in mean zonal winds are modulated by the solar activity cycle through variations in irradiance, solar wind or cosmic ray intensity.