Atmospheric angular momentum and length of day
Benedict, William L.
Haney, Robert Lee
Shaw, William J.
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Changes in the globally integrated absolute angular momentum of the atmosphere were computed from the Fleet Numerical Oceanography Center NOGAPS wind analyses and compared to astronomically measured changes in length of day [LOD) obtained from the U.S. \aval Observatory, Washington D.C. The two time series were subjected to both time and frequency domain analysis. In the time domain, digital filters were used to isolate seasonal and subseasonal components. In the frequency domain, energy density, coherence and phase were computed over periods from 2 days to 1000 days. Over 90°o of the total variance in astronomically determined LOD can be explained by meteorological phenomena. Fluctuations in LOD are coherent and in phase with lluctuations in the globally integrated angular momentum of the Earth's shell (crust, mantle and oceans; liquid core is excluded) at almost all periods less than 365 days. Annual fluctuations in LOD appear to originate in the midlatitudes and propagate equatorward. Subseasonal fluctuations (30 to 100 day periods) appear to be a tropical phenomena.
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