GREYBLS: modelling GREY-zone Boundary LayerS

Lead Research Organisation: University of Exeter
Department Name: Engineering Computer Science and Maths

Abstract

Society benefits significantly from the numerical weather forecasts provided by the Met Office. Recently, PA consulting valued the Met Office's public weather service in excess of £600 million pa. The high-resolution (small grid box) numerical weather forecasts of the Met Office provide information on, for example: surface temperature, low-level cloud and fog, and the onset of thunderstorms. This benefits the public and a wide range of industries including: agriculture, aviation, construction, wind energy, retail and transport. This project aims to deliver improvements to the high-resolution numerical weather prediction (NWP) models used to make these forecasts.

The atmospheric boundary layer is the region adjacent to the surface in which there are significant turbulent fluxes of heat, moisture and momentum. The boundary layer has a significant diurnal cycle over land forced by solar heating. It is also strongly coupled to other important processes in the atmosphere such as large-scale weather systems and convective storms. The boundary layer diurnal cycle thus plays a key role in many high-impact aspects of weather such as: surface temperature, the dispersion of pollutants and chemical species, low level cloud and fog, and the onset of thunderstorms. The diurnal cycle of the boundary layer is also important in regional climate and climate change, for example, extreme temperatures over land with increased greenhouse gas emissions. Nevertheless, there are important limitations in our understanding and ability to forecast the diurnal cycle of the boundary layer at high resolution.

The aim of this project is to develop new techniques for modelling the boundary layer at high resolution in a regime called the "grey zone". The grey zone describes the situation where the grid box of a NWP model is of comparable size to the boundary layer depth. With increasing supercomputer power, the grid boxes of NWP models are now below 5 km, so the grey zone is becoming a pressig issue. However, there is currently little understanding about how to model it. New modelling techniques will likely be required such as applying stochastic forcing. This project aims to improve our understanding by performing a systematic comparison of the possible methods for modelling the grey zone. From this understanding, we will then design a new parametrization (representation) of the boundary layer for the grey zone for use in the Met Office NWP model. Improved modelling of the grey zone will then lead to improved high resolution forecasts at the Met Office.

Planned Impact

Beneficiaries from this research

* The general public
Society benefits significantly from the numerical weather forecasts provided by the Met Office. Recently, PA consulting valued the Met Office's public weather service in excess of £600 million pa.

* The Met Office and other weather services
The high-resolution numerical weather forecasts of the Met Office and other weather services provide information on, for example: surface temperature, low-level cloud and fog, and the onset of thunderstorms. This project aims to deliver improvements to these high-resolution numerical weather prediction models.

* Industry
The forecasts of the Met Office benefits the public and a wide range of industries including: agriculture, aviation, construction, wind energy, retail and transport.

* Regional climate research
Climate change, forced by anthropogenic greenhouse gas emissions, will have major impacts on society. In order to inform policies on adaptation and mitigation in the face of climate change, the Met Office Hadley centre uses both global and regional climate simulations. Such regional climate models are similar in design to high-resolution numerical weather models. Thus, improving high-resolution numerical weather prediction models will also benefit regional climate models.

How they will benefit from this research

* The general public: through improved numerical weather forecasts provided by the Met Office. The particular weather types impacted by the expected improvements from this project include frosts and wind gusts.

* The Met Office: through an improved parametrization of the boundary layer in the high-resolution Met Office Unified model. The new parametrization will provide the best numerical representation of the atmosphere near the surface for a given grid-box size; it will therefore also make the best use of costly supercomputing resources, saving the Met Office money.

* Other weather services: through the improved understanding of high-resolution nuerical weather prediction of the boundary layer.

* Industry: through improved forecasts that depend on the boundary layer. For example, agriculture relies heavily on the surface temperature, wind-energy industry depends on the near-surface wind speed and the transport industry also relies on surface temperature forecasting when making decisions to grit the roads.

* Regional climate research: through an improved parametrization of the boundary layer in regional climate simulations. This will improve the representation of, for example, the diurnal cycle of surface temperature in a warmer climate.

Publications

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Efstathiou G (2016) Grey zone simulations of the morning convective boundary layer development in Journal of Geophysical Research: Atmospheres

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Efstathiou G (2019) A dynamic extension of the pragmatic blending scheme for scale-dependent sub-grid mixing in Quarterly Journal of the Royal Meteorological Society

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Efstathiou G (2015) Quantifying and improving sub-grid diffusion in the boundary-layer grey zone in Quarterly Journal of the Royal Meteorological Society

 
Description This project is about improving the prediction of high-impact weather using small (100 m ) grid lengths, the so called `grey zone'. We have discovered:
* Different methods of classifying turbulence in the grey zone.
* Ways of improving the representation of turbulence in the grey zone.
Exploitation Route These findings may also be extended to deep convection regimes (thunderstorms).

The Met Office plans to trial the novel sub-grid model (bounding vertical diffusion) developed in this project.
Sectors Aerospace, Defence and Marine,Environment,Government, Democracy and Justice,Transport

 
Description This project has informed the development of the Met Office high-resolution weather prediction model. The `bounded diffusion' method developed in this project is being considered as a future update to the model. Having completed this project, the Associate Research Fellow, Dr Efstathiou, has been promoted to Research Fellow on the NERC PARACON project.
Sector Aerospace, Defence and Marine,Energy,Environment,Transport
Impact Types Policy & public services

 
Description Collaboration with University of Reading Meteorology Department 
Organisation University of Reading
Department Department of Meteorology
Country United Kingdom 
Sector Academic/University 
PI Contribution We have shared Met Office LEM simulations with the University of Reading team of Drs Bopape, Coceal and Plant. We have met regularly with the Reading team, and had special one-day workshop meetings every 6 months.
Collaborator Contribution The discussion between the PDRAs Drs Bopape and Efstathiou has been beneficial in terms of support and sharing knowledge.
Impact Both the Exeter and Reading terms have submitted (or will submit in next few months) papers in the following areas: diagnosing the grey-zone (Exeter), applying the bounded-K method (Exeter), applying quadrant analysis (Reading), and higher order closures (Reading).
Start Year 2013
 
Description Met Office collaboration 
Organisation Meteorological Office UK
Department Atmospheric Processes and Parametrizations
Country United Kingdom 
Sector Private 
PI Contribution Dr George Efstathiou (PDRA on this grant) has visited the Met Office about once a month, to discuss the scientific plans of the project as well as the technical use of the Met Office LEM and UM models. George's new bounded-K parametrization, described in the paper in the publications section, has provided a potential alternative to the scheme currently operational in the boundary layer scheme of the Met Office weather and climate model.
Collaborator Contribution Drs Adrian Lock, Ian Boutle and Humphrey Lean have provided valuable advice on the numerical experiments to conduct using the Met Office LEM this last year.
Impact Original article submitted, see publications.
Start Year 2013
 
Title Improved Met Office model 
Description The findings from this project, particularly the bounded diffusion model, will contribute to future packages of improvements for the Met Office high-resolution models. This could have an improvement in high-impact weather prediction, such as for extreme precipitation. 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2016 
Impact Possible improved forecast skill for small scales.