International Mass Loading Service: Non-tidal Ocean Loading


Introduction

The Earth as a whole responses to external forces as an elastic body. As it was shown by Darwin in 1882, changes of the weight of the column of atmosphere due to variations of pressure result in crustal deformations called atmospheric pressure loading. These variations on average have the rms of 2.6 mm for the vertical component and 0.6 mm for the horizontal component, but peak to peak variations can reach 40 mm for the vertical component and 7 mm for the horizontal one. Pressure loading should be taken into account in a reduction of astronomical and space geodesy observations when the accuracy better than 2 nrad or 1 cm is required.

Variations of the atmospheric pressure changes the sea level. On large time-scales, say more than several months, the change of sea level compensates change of the atmospheric pressure so the bottom pressure remains the same. The ocean responses as an inverted barometer (IB): the higher pressure, the lower sea level. Change of the atmospheric pressure causes ocean water mass redistribution. The ocean obeys the IB model at slow motion, that corresponds to pressure changes at scales a month and longer. At smaller time scales the ocean response strongly deviates from IB model, and the full complexity of ocean dynamics (DR) should be considered. Modeling dynamic ocean (DO) response is feasible with numerical oceanic model that accounts for atmospheric forcing among other factors. Crust deformation caused by the ocean bottom pressure changes is called non-tidal ocean loading. It accounts for atmospheric pressure changes over the ocean and the DO response to that, as well as ocean repines to other forcings, excluding lunar and solar tides. We reserve the use of notion of the atmospheric pressure loading to crust deformation caused by atmospheric pressure changes over the land.

Service for the non-tidal ocean loading

On 2014.04.04 the service of non-tidal atmospheric pressure loading was established by Leonid Petrov and Jean-Paul Boy. The service is based on the spherical harmonics transform of the bottom pressure computed with the OMCT model provided by the GFZ. The service provides

References

  1. Darwin, G.H., On variations in the vertical due to elasticity of the Earth's surface, Phil. Mag., Ser. 5, col. 14, N. 90, 409--427, 1882.
  2. Farrell, W.E, Deformation of the Earth by Surface Loads, Rev. Geophys. and Spac. Phys., vol. 10(3), pp. 751--797, 1972.
  3. Dobslaw, H., Flechtner, F., Bergmann-Wolf, I., Dahle, C., Dill, R., Esselborn, S., Sasgen, I., Thomas, M.<.B> (2013). Simulating high-frequency atmosphere-ocean mass variability for dealiasing of satellite gravity observations: AOD1B RL05, J. Geophys. Res., 118(7), 3704--3711. doi:10.1002/jgrc.20271.
  4. Thomas, M., Ozeanisch induzierte Erdrotationsschwankungen Ph. D. Thesis, 2002
  5. Dobslaw, H., Thomas, M., Simulation and observation of global ocean mass anomalies, JGR, 112, C05040, 2007

Acknowledgment

This work was supported by NASA
Earth Surface & Interior program, grant NNX12AQ29G.


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Last update: 2017.01.05_08:29:04