ESC seminar No. 29
Mass and wind Atmospheric Angular Momentum variations at intraseasonal and diurnal periodicities
- Date
- Friday, November 09, 2007, 11:00-12:00
- Place
- Conference Room, 1F Earth Simulator Research Building, YES
- Speaker
- Dr. Francois Lott (Laboratoire de Meteorologie Dynamique, Paris)
- Language
- English
Abstract
The partition between the mass term and the wind term in the variations of the axial Atmospheric Angular Momentum (AAM) depends on the time scales at which the surface torques act. At periodicities around and below 1 month but above few days, the mass AAM variations compare with the wind AAM variations because i) the mountain torque is dominant, ii) some major mountain ranges are in the Northern and mid-latitudes, iii) the response to the mountain torque at these latitude is in geostrophic balance. At these frequencies, the mountain torque is found to affect the Arctic Oscillationi (AO) because the AO variations are associated with substantial mass AAM variations.
At diurnal and sub-diurnal periodicities the response to the torques is no longer balanced and contains axisymmetric tidal modes of motion. For these modes of motion, the variations in mass and wind AAM can be very large compared to the torque that produced them. These large and almost compensating variations can induce errors in some evaluations of the Earth Orientation Parameters.
Tee dataset used are the ECMWF reanalysis ERA40, the NCEP reanalisys, and climatic integrations done with the GCM LMDz.
Contact
Keiko TakahashiMultiscale Simulation Research Group,
Earth Simulator Center
Tel: 045-778-5834
e-mail:
