Atmospheric torques on land and ocean and implications for Earth's angular momentum budget

Abstract

The exchange of angular momentum between the atmosphere and the oceans and solid Earth is examined using 40 years of atmospheric angular momentum (AAM) and ocean and land torque data from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis. Land torques are the dominant driving mechanism for AAM at submonthly periods. Ocean torques are as important as land torques at periods of 3 months and longer, however. With the exception of the annual and semiannual bands the ocean torque seems to mainly damp the AAM signals. The importance of the ocean torque implies a three‐way interaction among atmosphere, oceans, and solid Earth. For an ocean that simply transmits to the solid Earth the angular momentum exchanged with the atmosphere, with a delay of a few days at most, the analyzed torques imply that AAM should lead the length of day (LOD), which is contrary to the observations at monthly and longer periods. Sources of missing angular momentum variability, either from atmospheric or other origins, that can potentially explain the observed AAM and LOD phase relationship are discussed.