Assessing the planetary angular momentum budget with atmospheric upper air and ocean model data

Author: Rui M. Ponte, David Salstein, R.D. Rosen and D. Stammer
Date: 
July 21, 1999
Type: 
Presentation
Venue: 
XXII IUGG General Assembly, Birmingham, England
Citation: 

Salstein, D.A., R.M. Ponte, R.D. Rosen, and D. Stammer, 1999. Assessing the planetary angular momentum budget with atmospheric upper air and ocean model data. XXII IUGG General Assembly, Birmingham, England, July 1999, invited.

Atmospheric and oceanic information are used in combination with Earth rotation parameters to assess the angular momentum budget of the planet about the axis of rotation, on a variety of timescales. For the atmospheric data the 50-year long NCEP/NCAR reanalysis products capture variability at levels as high as 10 hPa. In addition, separate data sets of the stratosphere include comprehensive calculations on levels as high as 0.3 - 1 hPa. Because stratospheric winds vary strongly at semiannual, annual, and quasi-biennial timescales, incorporating these data is particularly important. We assess the regions within the atmosphere that have the strongest variations on intraseasonal, seasonal, and interannual timescales. In the last case, El Niño events are clearly related to the strength of the zonal circulation in the atmosphere. Available estimates of oceanic axial angular momentum, calculated from model-derived zonal current and mass fields, are also used to assess the role of the ocean in explaining some of the discrepancies still present in the solid Earth and atmosphere's combined angular momentum budget. In considering excitations for polar motion in the equatorial plane, atmospheric and oceanic effects can approach similar magnitudes on a number of timescales. Within the atmosphere, the mass field, related to surface pressure, is the agent that most excites polar motion on subseasonal scales. We discuss the extent to which a closed budget is achieved within the estimated uncertainties in all momentum quantities, as a function of timescale.