A5064268640- Meteorological Phenomena and Simulations
- Climate variability and models
- Wind and Air Flow Studies
- Tropical and Extratropical Cyclones Research
- Fluid Dynamics and Turbulent Flows
- Atmospheric and Environmental Gas Dynamics
- Oceanographic and Atmospheric Processes
- Atmospheric aerosols and clouds
- Air Quality and Health Impacts
- Aeolian processes and effects
- Geophysics and Sensor Technology
- Advanced Fiber Optic Sensors
- Fire effects on ecosystems
- Plant Water Relations and Carbon Dynamics
- Atmospheric chemistry and aerosols
University of Exeter
2011-2023
Met Office
2004-2008
Government of the United Kingdom
2007
University of Reading
2003
Abstract This paper revisits the mechanism for interaction of boundary layer with extratropical cyclones. Two diagnostic approaches are compared: Ekman pumping and potential vorticity. derives from stress which induces convergence ascent. vorticity contains in a single quantity both stratification. These quantities compared an idealized cyclone life cycle simulated Met Office Unified Model. A significant component thus at occlusion is forced by cold conveyor‐belt jet unstable layer. In...
Operational high‐resolution numerical weather prediction models are now able to partially resolve turbulent motions due increased computing power. The partitioning of resolved and parametrized fluxes becomes important in the representation transfer that determines state atmospheric boundary layer. In this study, successive simulations a convective layer using Met Office Large Eddy Model from large‐eddy simulation mesoscale limit compared with corresponding coarse‐grained fields examine model...
Abstract A new theoretical framework is derived for parameterization of subgrid physical processes in atmospheric models; the application to convection and boundary layer fluxes a particular focus. The derivation based on conditional filtering, which uses set quasi-Lagrangian labels pick out different regions fluid, such as convective updrafts environment, before applying spatial filter. This results coupled prognostic equations fluid components, including subfilter-scale flux terms...
Abstract Observations of the evolution atmospheric boundary layer through evening transition and early hours night are presented. Parallel simulations in a single‐column model conducted to assess performance parametrization scheme sensitivity vertical resolution. The study is set within context numerical weather‐prediction system importance synoptic situation emphasized. Comparisons also drawn with an accompanying describing large‐eddy based on these same data. These show that, when run...
Abstract As weather and climate models move towards higher resolution, there is growing excitement about potential future improvements in the understanding prediction of atmospheric convection its interaction with larger‐scale phenomena. A meeting January 2013 Dartington, Devon was convened to address best way maximise these improvements, specifically a UK context but international relevance. Specific recommendations included increased convective‐scale observations, high‐resolution virtual...
Abstract Numerical simulations of two cases morning boundary layer development are conducted to investigate the impact grid resolution on mean profiles and turbulent kinetic energy (TKE) partitioning from large eddy simulation (LES) mesoscale limit. Idealized LES, using 3‐D Smagorinsky scheme, is shown be capable reproducing evolution when compared against measurements. However, increasing spacing results in damping resolved TKE production superadiabatic temperature layer. Turbulence...
Numerical weather prediction (NWP) models are now capable of operating at horizontal resolutions in the 100-m to 1-km range, a grid spacing similar scale that turbulent eddies present atmospheric convective boundary layer (CBL). Known as 'grey zone' turbulence, this regime is characterized by significant contributions from both resolved and subgrid components represent dominant motions system. This study examines how initiation turbulence – concept commonly referred 'spin-up'– can be delayed...
Abstract Large‐eddy simulations are performed of two observed cases evening transition boundary layers over land. Although generally similar to the observations, have a poor match ageostrophic wind above layer and overestimate nocturnal 4 m speed. For one case, phase is also simulated using close observations in early evening, reproducing well morning jet. This achieved with moderate resolution (5 m) demonstrates importance good initial state. In numerical weather‐prediction context, these...
Abstract There is a range of phenomena which, if misrepresented in numerical weather prediction model, could cause localized finite‐amplitude errors the potential vorticity (PV). Examples are: convective systems, tropopause PV trough, and orographic perturbations. Motivated by this, sensitivity short‐range cyclone forecasts (up to two days) initial anomalies investigated using method termed ‘PV‐sensitivity mapping’. An PV‐anomaly perturbation applied at each grid point turn corresponding...
Nocturnal low‐level jets (LLJs) are maxima in the wind profile, which often form above stable nocturnal boundary layer. Over Sahara, world's largest source of mineral dust, this phenomenon is particular importance to emission and transport desert aerosol. We present first ever detailed large‐eddy simulations dust‐generating LLJs. Using sensitivity studies with UK Met Office model (LEM), two key controls LLJ investigated: surface roughness Coriolis force. Functional relationships derived from...
Semi-geostrophic theory has proved a powerful framework for understanding the dynamics of mid-latitude weather systems. However, one limitation is lack realistic boundary-layer representation. can be modified to include an atmospheric boundary layer by replacing geostrophic wind with ‘geotriptic’ (or Ekman-balanced) value in substantive derivative and appropriately approximating momentum diffusion term– so-called semi-geotriptic theory. until now, solutions equations using predictor–...
A single‐column model of the dry, shear‐free, convective boundary layer is presented in which non‐local transports by coherent structures such as thermals are represented partitioning fluid into two components, updraught and environment, each with a full set prognostic dynamical equations. Local eddy diffusive transport entrainment detrainment parametrizations similar to those used diffusivity mass flux schemes. The inclusion vertical diffusion velocity shown be important for suppressing an...
Abstract A new method is introduced to identify coherent structures in the convective boundary layer, based on optimizing vertical scalar flux a two-fluid representation of turbulent motions as simulated by large-eddy simulation. The approach partitions joint frequency distribution (JFD) velocity and transported into (fluid 2) their environment 1) maximizing that part resolved mean properties fluid 2 1. proposed does not rely any priori criteria for partitioning flow nor pre-assumptions...
Abstract The interaction between extratropical cyclones and the underlying boundary layer has been a topic of recent discussion in papers by Adamson et al . (2006) Beare (2007). Their results emphasize different mechanisms through which boundary‐layer dynamics may modify growth baroclinic cyclone. By using sea‐surface temperature distributions comparing low‐level winds, differences are exposed both proposed appear to be acting within single simulation. Copyright © 2007 Royal Meteorological Society
Diagnoses of circulations in the vertical plane provide valuable insights into aspects dynamics climate system. Dynamical theories based on geostrophic balance have proved useful deriving diagnostic equations for these circulations. For example, semi-geostrophic theory gives rise to Sawyer-Eliassen equation (SEE) that predicts, among other things, around mid-latitude fronts. A limitation SEE is absence a realistic boundary layer. However, coupling provided by layer between atmosphere and...
Abstract In the Tropics, positive sea surface temperature anomalies are often coupled to well‐mixed boundary layer. The layer then typically forces convergence and ascent; ascent can trigger moist convection. Established diagnostic models of boundary‐layer employ steady‐state Ekman (geotriptic) balance. Here, we extend balance include non‐stationarity. Within an idealised one‐dimensional shallow‐water framework, identify three time‐varying balanced models: planetary geotriptic (PGT)...