AN ALGORITHM FOR RETRIEVING ATMOSPHERIC MOTION FROM SATELLITE MEASUREMENTS OF TRACER BEHAVIOR

An algorithm is developed for determining three-dimensional atmospheri c motion from global measurements of tracer behavior. The latter const itute observations of the material field, which underlies essential dy namical budgets that govern the circulation. Because it treats the mat erial behavior as an observable, the algorithm provides a more direct means of determining atmospheric motion from space than the traditiona l scheme, in which material behavior must be derived from remote measu rements of temperature. Incorporating observations of an ensemble of t racers (e.g., from multiple instruments or multiple orbiting platforms ) leads to a variational problem for the Lagrangian displacement field , the solution of which determines the global distribution of air moti on. The algorithm's direct relationship to material behavior circumven ts well-known Limitations of the traditional scheme for inferring atmo spheric motion from space. Further, since it is based on kinematic con straints that follow directly from observables, the retrieved motion i s not artificially biased towards approximate forms of the governing e quations and uncertainties accompanying them, e.g., as are inherent in assimilations based on numerical models. For this reason, motion in t he tropics is determined as reliably as elsewhere on the globe. Calcul ations under realistic conditions illustrate that the accuracy of the retrieved motion is limited chiefly by the number and quality of trace r observations. Those calculations also demonstrate that the accuracy can be improved dramatically by increasing the number of orbiting plat forms from which tracer measurements are provided.