Solar forcing of the semi-annual variation of length-of-day

Jean-Louis Le Mouël (1) , Elena Blanter , Mikhail Shnirman , Vincent Courtillot (1)

1 IPGP - Institut de Physique du Globe de Paris

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.

Domaines: Planète et Univers [physics]

Jean-Louis Le Mouël, Elena Blanter, Mikhail Shnirman, Vincent Courtillot. Solar forcing of the semi-annual variation of length-of-day. Geophysical Research Letters, 2010, 37, ⟨10.1029/2010GL043185⟩. ⟨insu-03605302⟩