An algorithm for retrieving atmospheric motion from satellite measurements of tracer behavior

An algorithm is developed for determining three-dimensional atmospheric motion from global measurements of tracer behavior. The latter constitute observations of the material field, which underlies essential dynamical budgets that govern the circulation. Because it treats the material behavior as an observable, the algorithm provides a more direct means of determining atmospheric motion from space than the traditional scheme, in which material behavior must be derived from remote measurements of temperature. Incorporating observations of an ensemble of tracers (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 motion. The algorithm's direct relationship to material behavior circumvents well-known limitations of the traditional scheme for inferring atmospheric motion from space. Further, since it is based on kinematic constraints that follow directly from observables, the retrieved motion is not artificially biased towards approximate forms of the governing equations and uncertainties accompanying them, e.g., as are inherent in assimilations based on numerical models. For this reason, motion in the tropics is determined as reliably as elsewhere on the globe. Calculations under realistic conditions illustrate that the accuracy of the retrieved motion is limited chiefly by the number and quality of tracer observations. Those calculations also demonstrate that the accuracy can be improved dramatically by increasing the number of orbiting platforms from which tracer measurements are provided.