Multi-scale processes driving tropical convection and influence of the aerosol

Abstract

The long-term goal of our project is to develop constrains model parameterizations for tropical rain forest and to assess how these constrains are perturbed by pollution. The present proposal addresses the fundamental subject of atmospheric variability in Amazonia and aerosol effects on this variability. A two-pronged approach is planned with a focus on the region of the GOAmazon campaign: (1) Statistical analysis of data from the GOAmazon sites in view of properties relevant to convection and its interaction with the aerosol, and 2) Aerosol effects on convective clouds and precipitation, including the roles of aerosols in changing regional climate and atmospheric circulation for clean and polluted situations. In situ data collected by the GOAmazon campaign and output from a hierarchy of numerical models ranging from general circulation models of the coupled atmosphere-ocean system to cloud resolving models will be extensively used. In reference to approach (1), we will concentrate on three aspects. The first aspect refers to the effect of free propospheric humidity on deep convective onset. We have developed a set of statistics to quantify convection onset based on data and instrumentation from other tropical DOE ARM sites (e.g. Nauru). The second aspect in approach (1) refers to the variability of vertical shear and relative humidity in the lower troposphere. Studies with numerical models have demonstrated that these properties of the atmosphere can play a role in whether aerosols suppress or enhance convective strength. The third aspect refers to the intraseasonal regimes of lower tropospheric winds in central Amazonia.Studies with observational data have shown that vertically integrated moisture convergence in the GOAmazon sites can have significant differences. In reference to approach (2), we will stratify the data from the GOAmazon sites according to aerosol information (e.g., mass loading, size distribution and chemical composition). Then we will assess the regulating effects of aerosols on selected individual deep convective clouds by running simulations using a cloud resolving model (CRM) coupled with detailed spectral bin microphysics for cases of pristine and polluted conditions. The international collaboration US-Brazil will allow the exchange of expertise in different numerical models of the atmosphere and their use in research of aerosol effects. Short-time exchanges of senior personnel and longer stays of other project. (AU)