Model Representation of Mesoscale Convective Systems

A Mesoscale Convective System (MCS) is an organisation of many convective thunderstorms, each a few km in scale, into a coherent entity on scales of hundreds of km. We use the term to encompass a range of organised convective phenomena, including squall lines, supercells, and mesoscale convective complexes. Global numerical weather prediction models, with grids of 15-20 km, and climate models, with grids of 50-100 km, cannot fully resolve MCS. At the same time, MCS cannot be parametrised using conventional approaches. Biases in the representation of the MJO, Asian Monsoons and ITCZ, as well as too few strong precipitation events, have been linked to deficiencies in the representation of MCS in models.

This project aims to develop a new parametrisation of the dynamical coupling between MCS and the larger scales, primarily for use within global ensemble systems. We will couple our approach to the new CoMorph convection scheme. While CoMorph shows substantial improvements in initiating organisation, coupling of MCS to the large scales remains a problem. The representation we develop will be stochastic: i.e., we will represent the probability of different MCS tendencies conditioned on the resolved scale flow. Stochastic schemes are well suited to the grey zone, where parametrised motions are poorly constrained by the grid-scale variables, and so are very uncertain.

Some links for this work:

Talks:

1. A discussion of progress on the stochastic parameterization, presented at the AOGS2023 conference.
2. A discussion of progress on the stochastic parameterization, presented (by Hannah Christensen) at the IUGG conference.
3. An introduction to the project, presented at a plenary meeting of the ParaCon programme.

Posters:

1. A poster on environmental precursors of MCS, (presented by Mark Muetzelfeldt), at the AMS 20th Mesoscale Processes conference.
2. A poster on initial experiments with an MCS scheme in the UM, (presented by Zhixiao Zhang), at the AMS 20th Mesoscale Processes conference.