Length of day changes associated with the Madden-Julian oscillation

Abstract

The previously reported spectral peak near 50 days in time series of length of day (LOD) is shown to occur in conjunction with episodes of tropical convective activity associated with the Madden-Julian oscillation (MJO). When the convective signal of the MJO is absent, LOD exhibits a red spectrum at intraseasonal timescales. LOD is shown to be in phase with the convective anomaly due to the MJO over the date line and out of phase with the convective anomaly over the Indian Ocean. A composite angular momentum budget, made relative to the convective signal of the MJO, reveals that the zonal surface stress only partially accounts for the observed tendency of LOD. In order to balance the angular momentum budget, an additional mountain torque is postulated to occur. -from Author