The role of updrafts in cloud evolution

Updrafts are a key element of convection, for their strength and size determine the mass flux into a cloud and influence the amount of precipitation. Consequently, understanding updraft characteristics is fundamental to obtaining a better representation of clouds in numerical weather prediction (NWP) models. Such improvements in model cloud physics lead to better rainfall forecasts and ultimately to more accurate and timely warnings of severe weather. Operational forecasters are considering NWP models that explicitly simulate updrafts without requiring a parameterization scheme. However, there is a lack of consistency in observational data to constrain the updraft and cloud features in these high-resolution models. In this project, the student will investigate updraft characteristics (size, strength, variability) in relation to storm size and evolution. Several recent field campaigns have used ground-based Doppler radars to estimate vertical velocities in many convective clouds and have proven the potential of these data to inform and constrain convection in NWP models. The student will expand this statistical evaluation to radar data from campaigns in southern England and unique 3D wind retrievals from the multi-Doppler radar setup at Darwin, Australia. The multiple sites allow for a consistent study of updraftcloud
relationships across convective regions and environments. Similarly, the student will investigate how updrafts affect cloud development and vice versa in model simulations of the observed cases; these simulations will be performed with high-resolution configurations of the Met Office Unified Model (MetUM).
This project will build on the highly successful DYMECS project (Dynamical and Microphysical Evolution of Convective Storms), a NERC-funded collaborative project between the Met Office and the University of Reading, in which we developed a statistical approach to evaluate convective storms in high-resolution NWP models. The initial objectives of the proposed project are:

1. To provide an inter-comparison of methods to retrieve vertical velocities from radar observations, checking the
consistency and differences between single-Doppler and multi-Doppler retrievals and studying the impact of these differences on updraft characteristics, specifically for model evaluation.
2. To formulate metrics for the statistical evaluation of updrafts in MetUM simulations of convective storms and to develop these metrics into a standard to be used consistently across convective regions and environments.
3. To analyse the time and length scales of updrafts in the observations and simulations and relate these to the surrounding clouds (including updraft duration and number of updrafts per cloud or storm).
Having developed a strong understanding of the simulations and observations of updrafts and its relationship with cloud evolution, the student will then investigate these cloud-updraft relationships in reference idealised simulations which are expected to be developed within the ParaCon programme (Met Office and NERC joint programme on understanding and representing convection across scales). A fully prognostic turbulence scheme and a scale-aware TKE scheme will be developed in the Circle-A project (part of ParaCon); the former will include 16 prognostics describing turbulence characteristics of the flow (stresses, scalar fluxes and variances). The student will investigate the relative importance of the various diagnostics, with the particular objective to determine which diagnostics are crucial for the physical representation of convective storms.