The objective of the proposed research is to identify and understand trends and long-term changes in tropical rainfall characteristics in relation to large scale circulation variations, climate variability and change. The proposed research will address one of the key priority science questions in the NASA earth science strategic plan: Is the atmospheric water cycle accelerating? Research will focus on the specific science issues regarding the trends or long-term shift of rainfall characteristics; frequency of occurrence seasonality and preferred geographic locations of extreme events; relationship of trends to distributions and microphysical properties of suspended particles in the atmosphere (aerosol, clouds and precipitation), as well as large scale circulation and water cycle balance. The research will be based on a synergistic observational and modeling approach, using primarily GPCP and TRMM rainfall products, in conjunction with cloud and aerosol data from MODIS and surface wind from Quikscat, as well as ancillary data from NCAR NCEP reanalysis. The trend analysis will be carried out over the global tropics, and details of physical processes and validation will be conducted over target regions of the western and eastern tropical Atlantic, including the Caribbean. Data from field campaigns such as from CRYSTAL-FACE, TCSP and NASA AMMA will be used, as deemed appropriate. The data analysis will provide validation and forcing functions or constraints for modeling studies using the Goddard cloud ensemble model (GCE), GEOS-5, and embedded GCE-GEOS Multi-Model Framework. Five research tasks will be proposed, i) Detection of long-term trend in rainfall characteristics, and analysis of extremes using GPCP (~25 years), and TRMM (~ 8 years), ii) Determination of changes in rainfall characteristics to rain and cloud structures using TRMM rainfall products, iii) Correlative studies to unravel the role of rainfall efficiency and their relationship to convective cycles and possible regulation by aerosols, iv) cloud scale modeling of cloud nucleation processes on rainfall efficiency, v) GCM modeling of effects of cloud microphysics associated with activation of cloud condensation nuclei on rain distribution, and interaction with large scale dynamics. Expected outcome and benefits of the proposed research include: a) Better understanding of physical processes that determine the long-term changes of rainfall and rainfall characteristics, b) Reduce the uncertainty in climate model simulation and prediction of atmospheric water cycle processes, c) Provide assessment of potential of extreme precipitation events, possible mitigation measures that will benefit society.
