Large-scale divergent circulations are part of the atmospheric dynamic response to diabatic heating from condensation, radiative processes, and surface heat fluxes. Vertical motion and the associated divergent wind is thus intimately tied to the hydrologic cycle and the global heat balance. Despite its importance, the divergent circulation is too small in comparison to the rotational flow to measure directly with any accuracy. Vertical motions are recovered diagnostically from reanalyses and, as such, are subject to shortcomings in model physics, numerics, and data availability.
We use several GEWEX pre-EOS data sets derived from satellite data to assess interannual divergent flow anomalies in the NCEP, GSFC, and GSFC DAO analyses. Among the data sets are monthly, 2.5 degree gridded precipitation (MSU and SSM/I-based), TOA radiative fluxes from ERBS, surface radiative fluxes from the SRB project, and surface latent and sensible flux estimates from SSM/I. Most of these data sets can be considered as independent of the reanalysis fields. In this study we use simple integral constraints in the form of heat, moisture, and mass continuity enforced through the satellite-derived data sets to derive corrections to the divergent circulation produced from the reanalyses.
We examine the ability of the integral constraints to recover mean horizontal and vertical components of tropical divergent flow. In particular, we examine seasonal variations of these features over the Americas. Anomalies associated with a warm / cool ENSO couplet are also considered.