Diabatic influences on mesoscale structures in extratropical storms

Lead Research Organisation: University of Leeds
Department Name: School of Earth and Environment

Abstract

The project is aimed at a better understanding and prediction of mesoscale structures in synoptic-scale storms. Such structures include fronts, rain bands, secondary cyclones, sting jets etc, and are important because much of the extreme weather we experience (e.g. strong winds, heavy rain) comes from such regions. Weather forecasting models are able to capture some of this activity correctly, but there is much still to learn. By a combination of measurements and modelling, mainly using the Met Office Unified Model (UM), we will work to better understand how mesoscale processes in cyclones give rise to severe weather and how they can be better represented in models and better forecast. The project is organised into three broad work packages. The first of these aims to look at real mesoscale structures in the atmosphere, using high-resolution in situ and radar measurements to derive their morphology and dynamics. The key to the latter is to calculate the production of potential vorticity by diabatic processes - especially phase changes of water (vapour/liquid/ice) and air-sea fluxes of sensible and latent heat. The associated high-resolution modelling programme will use the UM to simulate a representative number of events, diagnosing the PV tendency in the model and comparing with the measurements. Sensitivity studies and further diagnostics with the model will reveal the sensitivity of the forecasts to the correct representation of these processes and the dynamical consequences of diabatically-generated PV, both on the mesoscale and larger scales. Two student projects will investigate the role of boundary-layer processes in storm behaviour and conduct a statistical investigation of mesoscale precipitation features, based on archived radar and wind profiler data. The second WP examines particular physical processes and the way these are represented in forecast models. Convection cannot be explicitly represented in current large-scale models (it is just beginning to be resolvable by high-resolution local-area models) so it needs to be parameterised. The schemes that are used are not optimised for mid-latitude storms, where convection often initiates at altitude rather than at the Earth's surface. A combination of novel diagnostics and new (or modified) schemes aimed at improving the representation of convection will be developed in this WP. Also addressed here will be the derivation of air-sea fluxes of heat and momentum from aircraft flights, and their use (as part of a larger, ongoing international project) to derive a better parameterisation for these quantities in high wind conditions. Lastly, microphysical measurements made with the FAAM aircraft will be used to derive latent heating/cooling rates as a function of the microphysical environment and used to improve the model simulations in the first WP and to improve microphysical parameterisations in the UM The final WP addresses the problem of predictability, using a combination of ensemble and data assimilation techniques. A unique archive of forecast ensembles produced at the Met Office will be exploited to determine how well the forecast ensemble actually generates realistic mesoscale features, and the skill with which this is done (using standard measures of skill). Model errors in representing convection, air-sea fluxes and microphysics will be investigated to determine their impact on the forecasts for different flow conditions. The relationship between different model variables on the mesoscale is poorly known at present and this will be investigated using ensembles and the results of the measurement programme. Finally, novel approaches to data assimilation will be investigated through a student project.
 
Description Through a programme of airborne and ground-based measurements, we have analysed the structure of some severe weather storms over and around the UK.

We have analysed the atmospheric structure associated with the development of tornados in a cold front over the UK. We find that outbreaks of tornados follow a swath, moving with the cold front, and located in regions where there is a surge of cold air behind the system. This offers possible forecasting methods for these UK tornados.
Exploitation Route Work is currently going ahead at the Met Office, to develop automated versions of the software, to be used by forecasters.
Sectors Aerospace, Defence and Marine,Environment,Transport

 
Description Our analysis techniques for UK tornadic cold fronts have proven very powerful, and are being used by the UK Met Office to map out severe winds in other weather systems.
First Year Of Impact 2012
Sector Aerospace, Defence and Marine,Environment,Transport
Impact Types Economic

 
Description Met Office 
Organisation Meteorological Office UK
Country United Kingdom 
Sector Public 
PI Contribution Our research group analyses atmospheric processes in order to better represent them in the Met Office's forecast models. We also use those forecast models in our research, and evaluate their performance in order to identify the best strategies to improve the models.
Collaborator Contribution The Met Office brings its models and its datasets to the partnership, in addition to the considerable expertise of its staff. The Met Office also represent a conduit to the impact of our research for society, through its provision of operational weather and climate forecasts.
Impact Our research has influenced the Met Office strategy for model development, especially in regard to high-resolution models, and the convective parametrisation scheme. We have jointly influenced international strategy for atmospheric research and measurements.
 
Description Cafe Scientifique, Cockermouth 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact I presented to the Cockermouth branch of Cafe Scientifique, on the subject of prediction of the British weather, followed by extensive discussion and questions.
Year(s) Of Engagement Activity 2017
 
Description Royal Society Cafe Scientifique 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact I presented a Cafe Scientifique event at the Royal Society in London on the subject of the British Weather.
Year(s) Of Engagement Activity 2014
URL https://royalsociety.org/science-events-and-lectures/2014/12/uk-weather/