Met Office Unified Model NIMROD Nowcasting Rachel Capon

Met Office Unified Model NIMROD Nowcasting Rachel Capon Met Office JCMM 1 Rachel Capon 04/2004 © Crown copyright

Outline n Unified Model 5. +, 6. + – New Dynamics Core – Physical Parametrisations – Limited Area Configuration n n Site Specific Forecast Model n 2 Single Column Unified Model Nimrod Nowcasting System Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

New Dynamical Core Unified Model 5. x operational since Aug 2002 OLD formulation NEW formulation n n Semi-Lagrangian advection n Split-explicit time integration n Semi-implicit time integration n Horizontal B grid n Horizontal C grid n Vertical staggering – Lorenz n Vertical – Charney-Phillips n Sigma pressure coordinate n Hybrid height coordinate n 3 Eulerian 4 th order advection Quasi-hydrostatic formulation n Non-hydrostatic formulation Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

Fully-compressible deep atmosphere equns 4 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

Unified Model Dynamics What’s ‘New’ n Fully compressible, non-hydrostatic, deep atmosphere. – Universal application (Climate to microscale) n n n 5 Semi-Lagrangian, Semi Implicit solution. ud is value at departure point, found by high order interpolation. No stability limit on timestep. No additional diffusion required. Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

Unified Model Dynamics What’s ‘New’ n Terrain following height based vertical coordinate – r(i, j, k) specified n Arwakawa C Grid in horizontal (not B) – No averaging of pressure gradient – No grid decoupling u – Better geostrophic adjustment for short waves n w, , q v , (p) Charney-Philips Grid in vertical – No computational modes – More consistent with thermal wind balance – Can have complications in coupling with boundary layer parametrisation 6 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright y x

Physical Parametrisations n Edwards-Slingo Radiation – (Edwards & Slingo 1996) n Mixed phase precipitation – (Wilson & Ballard 1999) – Extending to prognostic cloud fraction (Wilson, Bushell) – Extending to prognostic cloud water, rain water, ice, snow, graupel (Forbes) n Met Office Surface Exchange Scheme (MOSES I and II) – (Cox, Essery, Betts) n Non-local Boundary Layer – (Lock et al 2000) n n New GWD scheme + GLOBE orography, smoothed (Raymond filter) Mass flux convection scheme with CAPE closure, downdraft and momentum transport, separate shallow cumulus – (Gregory and Rowntree, Kershaw, Grant) 7 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

Microphysical parametrisation Complexity vs. Efficiency Operational Unified Model Wilson and Ballard (1999) “Cloud Resolving” Models Enhanced Microphysics 8 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

MOSES II n n n Treats heterogeneous surfaces using ‘blending height’ techniques and tiles. Surface exchange from each surface type treated separately Nine surface types, – – – – – Broad Leaf Trees Needle Leaf Trees C 3 Grass C 4 Grass Shrub Urban Water Soil Ice n n 9 Each tile has fixed characteristics. 4 layer soil temperature and moisture. Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright Blending Height Surface

Tiles surface exchange n n n Each tile has a full surface energy balance. This includes a radiatively coupled ‘canopy’. In the urban case this has high thermal inertia to simulate wall effects. Work in progress (Harman, Belcher, Best) to improve urban representaion. RN H E g T g 4 s T s 4 G 10 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright s T s 4

Boundary Layer Scheme n n n 11 First order, moist Allows for non-local mixing in unstable regimes (top down/bottom up) Scheme diagnoses 6 different mixing regimes in order to represent stable, well mixed and cumulus and stratocumulus processes Scheme includes boundary layer top entrainment parametrisation. Especially well suited for stratocumulus. Improved interaction with the convection scheme New non-local stable scheme Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

NWP Model Domains Research Configuration Horizontal 12 Rachel Capon COST 722 Paris 25/06/2004 Vertical (lowest km) © Crown copyright

NWP Model Orography 12 km 13 Rachel Capon COST 722 Paris 25/06/2004 4 km © Crown copyright 1 km

Single Column Unified Model n 1 D column version with full physics n Choice of forcing – Observational – Statistical – Fixed 14 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

Site Specific Forecast Model n n n n 15 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright 1 D (semi-)automated model based on UM “physics” - full column Greatly increased resolution in BL & soil “Dynamics”=“Forcing data”: grad p, advection, etc. Simple forcing correction for orography MOSES with tile surface exchange for separate treatment of land use types Radiative canopy coupled to surface exchange Upwind satellite derived land-use determines drag & surface fluxes of heat, moisture Surface landuse weighting via a stability dependent Source Area Model

NIMROD Nowcasting System Rod Brown, Stephen Moseley n. Input – radar + satellite data – SYNOPS – Mesoscale model forecasts – Sferics n. Output includes Visibility, T, Td, total water, liquid water temp, fog probability (200 m, 1 km, 5 km), relative humidity 16 Rachel Capon 04/2004 © Crown copyright

Visibility Analysis Model T and Td Satellite data Visibility Analysis Model Aerosol concentration 17 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright Synops

Visibility Forecast n n 18 Initial analysis from satellite data and SYNOPs Trends in liquid water temperature and total mixing ratio from the Mesoscale model are applied to the analysis to produce an extrapolation forecast Forecast values are merged with the model and persistence values Visibility is diagnosed using the model aerosol concentration Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

Visibility Analysis 19 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

T+3 Forecast 20 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright Analysis

21 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

Temperature and Dew Point Forecasts 22 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright

Probabilistic Visibility Forecast n n qt qt median qt threshold 23 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright The probability of the visibility being less than 200 m, 1 km, 5 km is also forecast A triangular distribution of qt is assumed about the forecast (median) value

T+1 F/C Probability of Visibility < 5 km 24 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright