Low-Degree Coefficients

The individual degree 0 to 2 spherical harmonics 3-hourly time series for the "ATM", "OCN", "GLO" and "OBA" variability are shown (daily updated figures).

The ATM coefficients include the contribution of the atmospheric surface pressure over the continents, the static contribution of the atmospheric pressure to ocean bottom pressure elsewhere, and the much weaker contribution of upper-air density anomalies above both continents and ocean.

The OCN coefficients include the contribution of the dynamic ocean to the ocean bottom pressure. By removing the area weighted mean bottom pressure at every time-step to reduce any fluctuations in total ocean mass induced by the Boussinesq approximation employed in the ocean model, C00 should always be zero.

The GLO coefficients are obtained from the sum of ATM and OCN.

The OBA coefficients are zero over the continents and provide the simulated ocean bottom pressure that includes air and water contribution elsewhere. OBA deviates from GLO over the ocean domain only by disregarding the small contribution of upper-air density anomaly contributions to the external gravity field.

Shihora, L., Balidakis, K., Dill, R., Dahle, C., Ghobadi-Far, K., Bonin, J., Dobslaw, H. (2022). Non-tidal background modeling for satellite gravimetry based on operational ECWMF and ERA5 reanalysis data: AOD1B RL07. Journal of Geophysical Research: Solid Earth, 127, e2022JB024360. doi.org/10.1029/2022JB024360