The dynamical and microphysical properties of wet season convection in Darwin as a function of wet season regime

Description

A known deficiency in general circulation models (GCMs) is in their representation of convection (Arakawa, 2004), typically parameterized using given assumptions about entrainment rates and mass fluxes that depend on the dynamical and microphysical characteristics of convection and lack any sort of representation of the organization of convection. Furthermore, mechanisms that couple large-scale forcing and convective organization are poorly represented in GCMs (Del Genio, 2012). The Accelerated Climate Model for Energy (ACME) version 1 aims to run at resolutions at 25 km, too coarse for convective parameterizations used in large-eddy simulations but too fine for typical convective parameterizations used in GCMs. All of these factors prompt the need for observational data sets to validate simulations and guide model development in ACME in several regions of the globe. The Climate Model Development and Validation project aims to combine Atmospheric Radiation Measurement (ARM) measurements, with Atmospheric System Research Science and ACME modeling efforts in order to achieve this goal. The focus of this study will be at the Tropical Western Pacific (TWP) site in Darwin, Australia and the surrounding maritime continent. In Darwin, well-defined forcing regimes occur (Drosdowsky, 1996; Pope et al., 2009) during the wet season of September to April with the onset and the break of the Northern Australian Monsoon. In this study, the vertical velocities w and 3D wind fields retrieved using three-dimensional variational data retrieval (Potvin et al., 2012) from 10 years of continuous plan position indicator scans from the C-band POLarimetric (CPOL) and Berrima radars stationed at the ARM TWP site in Darwin are retrieved. Probability distribution functions of w and cross sections of 3D wind fields from the mesoscale convective system sampled during 19 to 21 January, 2006 over Darwin are shown. The median and 95th percentiles of vertical velocity w are within 1 m s-1 of the vertical velocities retrieved by Collis et al. (2013), with w up to 8 m s-1 in deep convective cores. Initial classifications of large-scale forcing and convective organization show that convection over Darwin is more aggregated in break periods compared to monsoon periods during January and February, 2006. Future plans include expanding the wind retrievals to the entire CPOL data set and comparing statistics and cross relations between forcing against Regionally Refined Mesh runs of ACME over Darwin.