Convective momentum transport in the tropics: What can budget studies tell us?

Reanalysis data sets provide an appealing alternative to case studies of individual storm systems as a means of establishing the role of convective momentum transport in the circulation of the tropical atmosphere. We examine reanalyses from ECMWF and NCEP over the TOGA COARE region, in order to identify contributions to the large-scale momentum budget by convective momentum transport.

Uncertainties in the reanalysis budgets are large, and above 850mb appear to mask any convective signal which may be present. Errors in the pressure gradient term are the greatest contributor to the uncertainty. Below 850mb there is evidence of mixing by shallow convection.

We then attempt to reduce the errors in the budget, first by examining a much larger region over the western Pacific, then by applying a correction to the budget residual based on constraints of cross-tropopause transport. The validity of existing parameterizations are discussed in the context of these results.