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We propose to use observations obtained during the Fourth Convection and Moisture Experiment 4 (CAMEX-4), the Tropical Cloud Systems and Processes (TCSP) study, and the NASA African Monsoon Multidisciplinary Analysis (NAMMA) campaign, retrievals from the Tropical Rainfall Measuring Mission (TRMM) and high-resolution Weather Research and Forecasting (WRF) model simulations to study how cloud and aerosol processes in tropical cyclones (TCs) impact intensity change and rainfall. The overarching motivation is to improve hurricane intensity and precipitation forecasts that have lagged improvements in hurricane track forecasts. Although cloud/aerosol processes need to be considered in the context of flow fields, wind shear, and other dynamical factors that affect TCs, we will examine the mechanisms by which they impact the four-dimensional distribution of latent heating, distributions of updrafts and downdrafts and intensity changes through 4 specific tasks: 1) We will use in-situ observations obtained during CAMEX-4 and NAMMA to quantify how the slope, shape, and y-intercept of gamma distributions of snow, graupel and rain depend on prognostic variables used in mesoscale model parameterization schemes (water content, temperature, vertical velocity) and determine how these relationships vary in different meteorological conditions (developing and non-developing waves, mature TCs) and location (eyewall vs. inner and outer rainbands, stratiform vs. convective regions, different quadrants). 2) Simulations of Hurricane Dennis 2005 and other TCs using WRF and state-of-the-art microphysical schemes modified to account for our findings in step 1) will examine mechanisms driving updraft and downdraft evolution, addressing the roles of microphysical processes (sublimation, evaporation, melting, conversions between different hydrometeor categories) in creating and maintaining penetrative downdrafts. Sensitivity studies, statistically evaluated using TCSP and TRMM observations, will relate distributions of updrafts and downdrafts to microphysical processes and the associated latent release heat in discrete TC regions (e.g., eyewall, rainbands). 3) A comprehensive set of aircraft and space borne passive microwave and radar observations to be constructed for a wide range of TCs will be used to examine the role of varying TC morphology on the microphysical structure, precipitation production, and track and intensity changes of TCs. The links between eyewall vertical convection, or “hot towers”, and eyewall replacement cycles as indicators of processes important to changes in TC intensity will be examined. We will also examine the roles of mixed-phase, inner-core precipitation processes during structural transitions. 4) Simulations initialized with an idealized pre-TC mesoscale convective vortex in the Colorado State University Regional Atmospheric Modeling System (RAMS) will examine how dust in the Saharan Aerosol Layer (SAL) acting as cloud condensation nuclei (CCN), giant CCN (GCCN) and ice nuclei (IN) impact TC intensity in a variety of meteorological conditions (e.g., varied strength of mid-level easterly jet, shear, temperature and humidity, trade wind inversion strength). The impact of changes in convective intensity induced by the CCN in the developing rainbands on latent heat release in rainbands and in the eyewall, on the blocking of radial inflow and on the production of a cold pool will be assessed in the context of how small perturbations in input fields affect their temporal evolution.
Project PI: Greg McFarquhar/University of Illinois
University of Illinois 105 S. Gregory Street Urbana, IL 61801-3070
Email: mcfarq at illinois.edu
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