1 rachel capon 04/2004 © crown copyright met office unified model nimrod nowcasting rachel capon...
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1 Rachel Capon 04/2004 © Crown copyright
Met Office Unified Model NIMROD
Nowcasting
Rachel Capon
Met Office JCMM
2 Rachel Capon COST 722 Paris 25/06/2004 © Crown copyright
Outline
Unified Model 5.+, 6.+ – New Dynamics Core
– Physical Parametrisations
– Limited Area Configuration
Single Column Unified Model Site Specific Forecast Model Nimrod Nowcasting System
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New Dynamical Core Unified Model 5.x
operational since Aug 2002
OLD formulation Eulerian 4th order advection Split-explicit time integration Horizontal B grid Vertical staggering – Lorenz Sigma pressure coordinate Quasi-hydrostatic formulation
NEW formulation Semi-Lagrangian advection Semi-implicit time
integration Horizontal C grid Vertical – Charney-Phillips Hybrid height coordinate Non-hydrostatic
formulation
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Fully-compressible deep atmosphere equns
tan 12 sin
cos2 cosr
u
D u uv p uwwv F
Dt r r r
2 tan 12 sin v
r vwD v u pu
r r rF
Dt
2 21
2 cosrw
p
r rg
u vu F
r
D w
Dt
0rr
D
Dt
u rD FDt
p RT
2
2
cos1 1,
cos cosr
r
wvD u v uw
D
r
r r rt t r rr
u
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Unified Model Dynamics What’s ‘New’
Fully compressible, non-hydrostatic, deep atmosphere.– Universal application (Climate to microscale)
Semi-Lagrangian, Semi Implicit solution.
(1 )t dt t t dt td d
DuForcing u u Forcing Forcing
Dt
ud is value at departure point, found by high order
interpolation.
No stability limit on timestep. No additional diffusion required.
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Unified Model Dynamics What’s ‘New’
Terrain following height based vertical coordinate– r(i,j,k) specified
Arwakawa C Grid in horizontal (not B)– No averaging of pressure gradient
– No grid decoupling
– Better geostrophic adjustment for short waves
Charney-Philips Grid in vertical– No computational modes
– More consistent with thermal wind balance
– Can have complications in coupling with boundary layer parametrisation
w,,q
u v
x
y
,(p)
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Physical Parametrisations Edwards-Slingo Radiation
– (Edwards & Slingo 1996)
Mixed phase precipitation – (Wilson & Ballard 1999)– Extending to prognostic cloud fraction (Wilson, Bushell)– Extending to prognostic cloud water, rain water, ice, snow, graupel
(Forbes)
Met Office Surface Exchange Scheme (MOSES I and II)– (Cox, Essery, Betts)
Non-local Boundary Layer – (Lock et al 2000)
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)
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Microphysical parametrisationComplexity vs. Efficiency
Operational Unified Model Wilson and Ballard (1999)
“Cloud Resolving” Models
Enhanced Microphysics
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Blending Height
Surface
MOSES II 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– C3 Grass– C4 Grass– Shrub– Urban– Water– Soil– Ice
Each tile has fixed characteristics.
4 layer soil temperature and moisture.
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s Ts4g Tg
4
H E s Ts4
G
RN
Tiles surface exchange 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.
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Boundary Layer Scheme 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 strato-cumulus.
Improved interaction with the convection scheme
New non-local stable scheme
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NWP Model DomainsResearch Configuration
Horizontal Vertical (lowest km)
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NWP Model Orography
12 km 4 km 1 km
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Single Column Unified Model
1D column version with full physics Choice of forcing
– Observational
– Statistical
– Fixed
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Site Specific Forecast Model 1D (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
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NIMROD Nowcasting SystemRod Brown, Stephen Moseley
Input
– radar + satellite data
– SYNOPS
– Mesoscale model forecasts
– SfericsOutput includes
Visibility, T, Td, total water, liquid water temp, fog probability (200m, 1km, 5km), relative humidity
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Visibility Analysis
Visibility Analysis
Model T and Td
Satellite data
Model Aerosol concentration
Synops
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Visibility Forecast
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
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Visibility Analysis
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T+3 Forecast Analysis
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10 Appendix: Figures
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Temperature and Dew Point Forecasts
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Probabilistic Visibility Forecast
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
qt
qt threshold
qt median
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T+1 F/C Probability of Visibility < 5 km