The importance of seasonal sea-level variations from geophysical models and satellite gravimetry for excitation of length-of-day

In addition to atmospheric, oceanic, and hydrological contributions, the seasonal length-of-day variation is significantly affected by global mass redistribution between the Earth subsystems.

This study uses the new ESMGFZ barystatic sea-level product SLAM as well as estimates of the barystatic ocean bottom pressure anomalies from the GRACE Level 3 GravIS products to quantify the global mass balance.

For the annual cycle the global mass balance effect overcompensates the contributions from terrestrial hydrology. Considering the global mass balance, model based mass induced excitation on seasonal length-of-day variations

coincide well with estimates from satellite gravimetry. Moreover, the mass terms can be determined accurate enough to attribute the remaining gap in the length-of-day excitation budget between models and observation clearly

to an underestimation of atmospheric wind speeds in the global European weather forecast model by -7%.