1 rachel capon 04/2004 © crown copyright met office unified model nimrod nowcasting rachel capon...

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


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


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


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.


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)


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)


Microphysical parametrisationComplexity vs. Efficiency

Operational Unified Model Wilson and Ballard (1999)

“Cloud Resolving” Models

Enhanced Microphysics


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.


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.


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


NWP Model DomainsResearch Configuration

Horizontal Vertical (lowest km)


NWP Model Orography

12 km 4 km 1 km


Single Column Unified Model

1D column version with full physics Choice of forcing

– Observational

– Statistical

– Fixed


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

16 Rachel Capon 04/2004 © Crown copyright

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


Visibility Analysis

Visibility Analysis

Model T and Td

Satellite data

Model Aerosol concentration

Synops


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


Visibility Analysis


T+3 Forecast Analysis


10 Appendix: Figures


Temperature and Dew Point Forecasts


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


T+1 F/C Probability of Visibility < 5 km

1 rachel capon 04/2004 © crown copyright met office unified model nimrod nowcasting rachel capon...

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