83rd Annual

Tuesday, 11 February 2003
Atmospheric mass and momentum signals in climate and Earth studies
David A. Salstein, AER, Lexington, MA
Poster PDF (839.0 kB)
The mass and the angular momentum of the atmosphere are properties whose variability relates to both climate and geodetic signals. Total atmospheric dry mass is very nearly conserved, but water substance is exchanged with the oceans and Earth below. The horizontal distribution of atmospheric mass changes on a number of time scales, possessing signals of climate modes, with meridional and zonal variations. Such variability is being measured by the new “Gravity Recovery and Climate Experiment” satellite system, an important priority of which is to monitor changes in hydrological signals on areas the size of moderate-sized river basins. The angular momentum of the atmosphere is a signal that changes on many climatic time scales due to internal redistribution in the atmosphere and exchange across its lower boundary. It responds to certain climate patterns like the El Nino and the North Atlantic Oscillation, which are observed in geodetic properties of the Earth such as its rotation rate, reckoned by the small changes in the length of day, and the motions of the pole. Atmospheric pressure, moreover, loads the crust, leading to small vertical deformations and thus impacts the geodetic reference frame. Global analyses, like the NCEP-NCAR reanalysis system, capture both mass and angular momentum signals with considerable success; general circulation models have been used to simulate past variability and forecast future changes in these quantities. Relevant diagnostics are collected, calculated, analyzed and archived by the “Special Bureau for the Atmosphere” of the International Earth Rotation Service, and include: atmospheric angular momentum in the axial and equatorial directions, torque interactions that exchange angular momentum across the lower interface, and harmonics of surface pressure, including the global mean surface pressure.

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