Trajectory model

Isentropic trajectories are computed using both NCEP balanced winds, and STRATAN winds. The trajectories are checked by examining the conservation of Ertel's potential vorticity (Epv) [Newman et al., 1988]. Validation includes the simulation of the volcanic SO2 debris clouds from Cerro Hudson and Mt. Spurr [Schoeberl et al., 1993]. Trajectories appear to be accurate up to a week, depending on flow conditions and analysis accuracy. At polar latitudes during winter, large zonal winds rapidly cause degradation of zonal position numerical accuracy as a result of wind errors. In general, isentropic trajectory integrations longer than about two weeks are not accurate for determining position [Austin and Tuck, 1985]. However, latitudinal trajectory positions still retain some skill, since zonal average meridional velocities are much smaller than zonal velocities. Thus, meridional position errors are smaller due to the smaller absolute wind error. The latitudinal position (within 5 to 10 degrees) can be accurately predicted but the longitudinal position will be uncertain for 7--10 day integrations. The trajectory model can also perform non-isentropic integrations using heating rates provided by an external radiative transfer computation.

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Last Updated: 1997-01-14
Web Curator: Leslie R. Lait (Hughes STX) (lrlait@ertel.gsfc.nasa.gov)
Responsible NASA organization/official: Dr. P. K. Bhartia, Atmospheric Chemistry and Dynamics Branch/Head