Computing Atmospheric Excitation Functions for Earth Rotation/Polar Motion

Author: David Salstein
February 2, 2005
Journal Article
Cahiers du Centre Europeen de Geodynamique et de Seismologie

Salstein, D.A., 2005: Computing Atmospheric Excitation Functions for Earth Rotation/Polar Motion, Cahiers du Centre Europeen de Geodynamique et de Seismologie, 24, 83-88.

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The weather forecasting and data assimilation systems resident at the world’s large meteorological centers are used to produce analyses of meteorological parameters from which excitations of earth rotation/polar motion are calculated. The meteorological systems involve up to three procedures generally known as the model, assimilation, and initialization steps. The weather data that are assimilated into the systems are taken by a heterogeneous group of instruments, which are ground-, air- and space-based. Earth rotation excitation functions are in fact calculations of the angular momentum of the atmosphere, and as such are derived from the surface pressure and wind fields; winds are more related to the axial, length of day, component and pressures to the polar motion component. The pressure-based angular momentum may be modified by the actions of the ocean, the degree to which it acts as an inverted barometer. The world’s major meteorological centers produce the fields necessary to produce these quantities, both in an operational and in a retrospective way, known as reanalysis. Measures of wind-based polar motion are especially investigated for their strong subdiurnal variability. The atmospheric community investigates as well models that are only driven by boundary conditions to see how well they may simulate the atmosphere; we use the diagnostics of atmospheric excitations of Earth rotation/polar motion to check if such models are successful. Other lengthy simulations of atmospheric models provide an indication of changes in angular momentum in the past and possible increases in the future related to climate variability and potential greenhouse gas increases.