Effective angular momentum functions of the Earth rotation are typically obtained from wind and pressure distributions simulated with global numerical weather prediction models.  Up-to-date angular momentum functions are currently calculated with about four days latency from operational analysis data provided by ECMWF. In addition, angular momentum functions are calculated from atmospheric reanalysis data sets, thereby allowing for a consistent interpretation and - if appropriate - correction of the decade-long record of observed Earth orientation parameters.

Here you get more information about Effective Angular Momentum (EAM).

• Dobslaw, H.; Dill, R.; Grötzsch, A.; Brzezinski, A.; Thomas, M. (2010): Seasonal polar motion excitation from numerical models of atmosphere, ocean, and continental hydrosphere. Journal of Geophysical Research, 115, B10406, DOI: 10.1029/2009JB007127.

Observations from the satellite gravity mission GRACE reveal in several regions of the Antarctic ice sheet substantial inter-annual variations in its mass balance, that are in the case of the Antarctic Peninsula and the Amundsen Sea Sector in particular distinctly anti-correlated. By incorporating atmospheric re-analysis data from ERA-40, a causal relation with the strength of the atmospheric pressure low over Amundsen Sea had been established, which itself is related to the tropical climate phenomenon ENSO by means of an atmospheric teleconnection.

• Sasgen, I.; Dobslaw, H.; Martinec, Z.; Thomas, M. (2010): Satellite gravimetry observation of Antarctic snow accumulation related to ENSO. Earth and Planetary Science Letters, 299, 3-4, 352-358, DOI: 10.1016/j.epsl.2010.09.015.

Atmospheric tides are tightly connected to daily variations in solar insolation. Absorption of solar energy by water vapor and ozone molecules leads to temperature variations in the middle atmosphere, thereby leading to horizontal and vertical wave excitation and consequently periodic variations in the wind and pressure distributions. Whereas lunisolar gravimetric tides are negligible in the atmosphere, those atmospheric tides are affected by substantial modulations of primarily seasonal character, which lead to measurable variations of the impact of atmospheric tides on the length of the day over the yearly cycle.

• Kadow, C.; Dobslaw, H.; Matthes, K.; Thomas, M. (2012): Impact of atmospheric tides simulated in a chemistry-climate model on sub-diurnal variations in UT1. Proceedings, Journées 2011 'Systèmes de référence spatio-temporels' (Vienna, Austria 2011), 144-147, DOI: 10.1016/j.epsl.2010.09.015.

Deterministic weather predictions of the ECMWF are calculated twice each day for ten days into the future. Atmospheric state variables from those prediction runs are utilized to force the global hydrological model LSDM and the ocean circulation model OMCT in order to obtain effective angular momentum functions of the Earth rotation from those three different sub-systems. Compared to currently available predictions published by the International Earth Rotation and Reference System Service (IERS) within its Bulletin A, those model-based predictions have higher skill scores in particular during the first days of the forecast period.

• Dill, R.; Dobslaw, H. (2010): Short-term Polar Motion Forecasts from Earth System Modeling Data. Journal of Geodesy, 84, 9, 529-536, DOI: 10.1007/s00190-010-0391-5.

• ECMWF