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GLOBAL AND REGIONAL SURFACE WIND FIELD INFERENCES FROM SPACE-BORNE SCATTEROMETER DATA 56 and propagation of the leading modes of the equatorial β-plane are used. At smaller scales, once again, we invoke a wavelet decomposition constrained by the power-law behavior for wavenumber spectra in the tropics. A recent implementation of this model generates 50 realizations of the surface wind field, 4-times per day, at 50 km resolution, for the domain 20° N to 20° S, 40° E to 180° E, for the QSCAT data record for the calendar year 2000. Figure 2 depicts snapshots of five randomly selected realizations for zonal wind and divergence fields for 25 December 1999 at 0000 UTC. Differences are smallest in regions recently sampled by QSCAT. This implies that the uncertainty in the observations is smaller than the uncertainty in the approximate physics assigned in the prior model stage. Surface convergence in the tropics is a critical field in the analysis of the atmospheric deep convection process. However, single realizations of this field are rarely useful because divergence is an inherently noisy field. The production of 50 physically sensible realizations can begin to quantify the space-time properties of the signal vs. noise. The first use of this dataset will be to diagnose surface convergence patterns associated with the Madden-Julian Oscillation (MJO) in the regions where the MJO is connected to the surface by atmospheric deep convection. A Bayesian Hierarchical Air-Sea Interaction Model The Bayesian Hierarchical Model methods extend naturally to multi-platform observations and complex physical models of air-sea interactions. Berliner et al (2002) demonstrate a prototype air-sea interaction BHM for a test case that mimics polar low propagation in the Labrador Sea, given both simulated altimeter and scatterometer observations. Hierarchical thinking leads to the development of a Prior Model distribution for the surface ocean streamfunction that is the product of an ocean given atmosphere model, and a model for the atmosphere. The Prior Model stage for the atmosphere is a model similar to the Labrador Sea wind model introduced above. Figure 3 compares the evolution of the ocean kinetic energy distribution in the air-sea BHM with a case from which all altimeter data have been excluded. The BHM resolutions are 3 times coarser in space and O(1000) times coarser in temporal resolution with respect to a high-resolution âtruthâ experiment also shown in the comparison. Also, the âtruthâ fields are computed in a physical model that incorporates more sophisticated physics than those that form the basis of the Prior Model Stage in the air-sea BHM. Implications of this methodology to data assimilation issues in coupled general
