Diabatic influences on mesoscale structures in extratropical storms

Lead Research Organisation: University of East Anglia
Department Name: Environmental Sciences

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.

Publications

10 25 50
 
Description We have made rare measurements of air-sea fluxes of heat, moisture and momentum during storms around the UK. We have used these observations to validate the algorithms used in numerical weather forecasting models, including that used by the UK Met office. These are broadly within the range of the observations. We have found a significant difference in observed fluxes in along and across wind directions, i.e. there is mesoscale structure in the flux fields, which is dictated by the weather system.

We have looked at the distribution of air-sea flux fields in the North Atlantic and found that the Iceland Sea is a local minima of ocean-atmosphere exchange. We've explained why this is the case.
Exploitation Route Our findings have been used by several other colleagues in their studies of weather system dynamics.
Sectors Environment

 
Description Results from the DIAMET project (Cook and Renfrew 2015) were used to evaluate several air-sea flux parameterisations, including those used at the Met Office and at ECMWF. These generally performed well, so no action was needed. This evaluation was useful in establishing quality and appropriateness of these parameterisations.
First Year Of Impact 2014
Sector Aerospace, Defence and Marine,Agriculture, Food and Drink,Energy,Environment,Leisure Activities, including Sports, Recreation and Tourism,Transport,Other
Impact Types Societal,Economic,Policy & public services

 
Description Met Office Science Advisory Committee
Geographic Reach National 
Policy Influence Type Participation in a advisory committee
Impact Advice to Met Office on continuing development of their models and services
 
Description NCAS Weather Studentship
Amount £60,000 (GBP)
Funding ID R14756 
Organisation National Centre for Atmospheric Science (NCAS) 
Sector Charity/Non Profit
Country United Kingdom
Start 11/2011 
End 11/2014
 
Title DIAMET air-sea fluxes data set 
Description Compilation of 36 flights of aircraft data - low level mainly around the UK. Mainly from DIAMET project and some from GFDEx project 
Type Of Material Database/Collection of data 
Year Produced 2013 
Provided To Others? Yes  
Impact Met Office have not changed their bulk flux parameterization, as we have shown it is within range of uncertainty GFDex data has been used to validate remote sensing algorithms. • Ricciardulli, L. and F.J.Wentz, 2011, Reprocessed QuikSCAT (V04) Wind Vectors With Ku-2011 Geophysical Model Function, technical report number 043011, Remote Sensing Systems, Santa Rosa, CA, 8pp. 
URL http://images.remss.com/papers/rsstech/2011_043011_Ricciardulli_Qscat_Ku2011.pdf
 
Description BBC One Show 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Appeared on BBC One's "The One Show" - typical audience of 7 million.
Interviewed during aircraft-based meteorology field campaign (Diamet) about use of aircraft for research

Nothing notable
Year(s) Of Engagement Activity 2012
 
Description Educational videos and material on weather forecasting and research 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact Two educational videos were made with a professional educational consultant. These are available via NCAS website. They have been publicised widely via articles on Association of Science Educators, Guardian Teachers network, Weather magazine, Royal Met Soc, and a conference

Thousands of views of the videos and downloads of the accompanying educational material
Year(s) Of Engagement Activity 2013
URL https://www.ncas.ac.uk/index.php/en/diamet-schools