NWP in the Met Office
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Transcript of NWP in the Met Office
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NWP in the Met Office
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Topics to be covered...
1. Describing the atmosphere2. Using observations 3. Model mathematics4. Operational models purposes5. Model outputs
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OBSERVATIONS
HUMAN FORECASTER
CUSTOMERS
NUMERICAL FORECASTS
The Weather Prediction Process
R&D
ARCHIVES
VE
RIF
ICA
TIO
N
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Unified Model
• Met. Office has several requirements:
• local forecasting
• global forecasting
• climate modelling
• ocean and wave modelling
• a common model:
• shares code and operating structure
• is modular where differences are necessary
• gives considerable savings in maintenance cost
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Unified Model configurations
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Met Office models
Based on Unified Model
• Global
• North Atlantic and European model
• 4km and 12km Mesoscales
• Crisis Area Mesoscale Models
• Stratospheric
• FOAM ocean forecasting models
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Met Office models
Other models including
• Wave (Global, European, UK Waters)
• Surge
• NAME
• SSFM
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Fundamentals of NWP
1. Specify atmospheric initial conditions in a numerical form
2. Use equations describing atmospheric physical processes to predict how the initial state will evolve
3. Output the forecast in a useful form for the user
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1. Describing the atmosphere
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Specify the properties in the grid box
from observational data (temp, pressurehumidity, wind etc.)
Grid length
Grid point
Unified Model is a gridpoint model
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GM Vertical resolution – 50 levels
In boundary layer levels are terrain-following
In free atmosphere levels are height coordinates
In between levels are a combination of the 2
Lowest model levels present/new 70Lat 10m/2.5m for windat 20m/5m for temp
65 km
17.5 km
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Global, North Atlantic & European, mesoscale models
Global Model (GM)
Horizontal Resolution: Mid-latitude 40km
Timestep: 20mins
Vertical levels: 50, then 70
Grid:Standard lat/long type, with filtering near the poles
Global Model (GM)
Horizontal Resolution: Mid-latitude 40km
Timestep: 20mins
Vertical levels: 50, then 70
Grid:Standard lat/long type, with filtering near the poles
Mesoscale Model (MES)
Horizontal Resolution: 12km/4km Timestep: 5/ 1.7 mins
Vertical levels: 38, eventually 70
Grid:Rotated lat/long (‘Equatorial Lat-long Fine-mesh’ - ELF)
Mesoscale Model (MES)
Horizontal Resolution: 12km/4km Timestep: 5/ 1.7 mins
Vertical levels: 38, eventually 70
Grid:Rotated lat/long (‘Equatorial Lat-long Fine-mesh’ - ELF)
North Atlantic & European Model (NAE)
Horizontal Resolution: 12km Timestep: ~5 mins
Vertical levels: 38, eventually 70
Grid:Rotated lat/long (‘Equatorial Lat-long Fine-mesh’ - ELF)
North Atlantic & European Model (NAE)
Horizontal Resolution: 12km Timestep: ~5 mins
Vertical levels: 38, eventually 70
Grid:Rotated lat/long (‘Equatorial Lat-long Fine-mesh’ - ELF)
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2. Using observations
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Data assimilation
• GM uses 4-D VAR; 12km MES and NAE 3-D VAR
• 4km MES has no data assimilation yet• Model is run for an assimilation period
prior to the forecast
• 6 hrs for GM model
• 3 hrs for the MES and NAE
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Data assimilation
• Observations firstly quality controlled against
• climate data
• model background field
• nearby obs.
• Then inserted into the run at or near their validity time to nudge the model towards reality
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Using observations
Models try to make the best possible use of observations
GP
GPGP
GP GP
GPGP
GP
GP
ship
ship
airep
synopsynop
synop
synop
synop
sonde sonde
Observations arechecked for qualityand interpolated ontothe model grid points
Different types of datahave different areas ofinfluence
SEA
LAND
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Moisture Observation Pre-processing System (MOPS)
Used only in 12km MES/NAE
Latent heating and cooling important in driving mesoscale systems
MOPS is an analysis of humidity, cloud and precipitation for 12km MES and NAE
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Soil moisture in the GM
No longer reset weekly to climatology New soil moisture nudging scheme Not as complex as MOPS Produced verifiable improvement, especially surface
temperatures
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3. Model Mathematics
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Model variables
• PRIMARY PROGNOSTIC variables are explicitly calculated using the primitive equations
• ANCILLARY FIELDS are fixed lower boundary conditions
• SECONDARY PROGNOSTIC variables are calculated at each timestep from the prognostic variables.
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Primary prognostic variables
• Horizontal and vertical wind components• potential temperature• specific humidity• cloud water and ice• surface pressure• surface temperature• soil temperature• canopy water content• snow depth
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Ancillary fields
• land/sea mask• soil type• vegetation type• grid-box mean and variance of
orography• sea surface temperature• proportion of sea-ice cover• sea-ice thickness• sea surface currents
Prognostic Prognostic variables in variables in coupled coupled atmosphere/atmosphere/ocean ocean modelsmodels
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Global model orography
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NAE Model orography
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12km / 4km MES Model orography
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Model variables
• PRIMARY PROGNOSTIC variables are explicitly calculated using the primitive equations
• SECONDARY PROGNOSTIC variables are calculated by the parameterisation schemes
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Model variables
• primary prognostic variables
•horizontal and vertical wind components
•potential temperature
•specific humidity
•cloud water and ice
•surface pressure
•surface temperature
•soil temperature
•canopy water content
•snow depth
• secondary prognostic variables
•boundary layer depth
•sea surface roughness
•convective cloud amount
•convective cloud base
•convective cloud top
•layer cloud amount
•ozone mixing ratio
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Parametrised processes
1. Layer cloud and precipitation2. Convective cloud and precipitation3. Radiative processes4. Surface and sub-surface processes5. Gravity wave drag
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*
1. Layer cloud and precipitation
**
**
*** *
*
**
*
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Convective cloud model
Terminal outflow of mass, heat,water vapour and cloud water/ice
Mixing at cloudedge
Subsidence outside cloudsto compensate for upward
motion within clouds 0 C°
2. Convective cloud and precipitation
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3. Radiative processes
LongwaveradiationShortwave
radiation
Diffuseshortwave
Layer cloud
Cumulus.cloud
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4. Surface and sub-surface processes
Heat, moistureand momentum
transport byturbulent eddies
SeaLand
Sublimation
Heat fluxthrough soil
Netradiation
Evaporationfrom
vegetation
Heat fluxfrom sea
Heat fluxfrom sea
Heat fluxfrom ice
Sublimationfrom ice
Evaporationfrom soil
Evaporationfrom sea
Drainageinto soil
Interception ofppn by canopy
Snow
Sea ice
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5. Gravity wave drag
14 km
12 km
10 km
8 km
6 km
4 km
2 km
= Const
Tropopause
Wavebreaking
Wavebreaking
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Boundary conditions
• Lower and upper boundaries
• Lateral boundaries
• Land & sea: ancillary fields
• Stratosphere: ‘lid’ to model
• required in MES and NAE models
• primary prognostic variables required at each grid point
• NAE and 12km MES supplied from global model
• 4km MES supplied from NAE
• possible source of error
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4. Purposes of Operational Models
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Global model
• 4 times daily• Run times … 00Z, 06Z,12Z, 18Z • Data accepted up to T+1 hour 45 min• Out to T+144 (6 days) at 00Z and 12Z, T+48
at 06Z and 18Z• Takes 2hr 15 mins to run out to T+144, 1hr
15min for T+48
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Global model
• Used for:-
• regional synoptic guidance
• medium range guidance
• civil aviation products
• mesoscale model boundary conditions
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North Atlantic & European model
• Run times … 00, 06, 12 and 18Z • Takes boundary conditions from Global Model (previous GM run)
• Run partly overlaps with the GM• Out to T+48
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North Atlantic & European model
• Used for:-
• wider range of products to international customers
• Improved Synoptic development guidance
• Better for rapid developments and extremes
• Boundary conditions for 4km MES
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Advantages of NAE Model
• Large domain
• Captures developing systems over North Atlantic
• Covers all of Europe and European Nimrod area
• includes some other model areas
• Higher resolution than GM (12km-v-40km)
• Better for rapid developments and extremes
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12km Mesoscale model
• Run times … 00Z, 06Z, 12Z and 18Z • Takes boundary conditions from Global Model
• Runs in parallel with the GM (starts 10 mins later)
• Out to T+48 (2 days)
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12km Mesoscale model
• Used for:-
• UK local detail (ppn, cloud,temp,wind)
• Input to other systems (SSFM, and Nowcasting systems etc.)
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4km MES model
• Run times … 03Z, 09Z, 15Z, 21Z• Takes boundary conditions from NAE Model • Out to T+36• No data assimilation
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Model Dependencies (simplified!)
GLOBALGLOBAL
12KM MES12KM MES
GLOBAL WAVEGLOBAL WAVE
FOAMFOAM
UK WATERS WAVEUK WATERS WAVE
EUROPEAN WAVEEUROPEAN WAVE
SURGESURGE
SHELF SEASSHELF SEAS
NAMENAME
Scheduling must account for all dependencies and timeliness requirements of each model run
SSFMSSFM
NAE MODELNAE MODEL
4KM MES4KM MES
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Any questions?GM, NAE and MES output.http://www-nwp/~meso/current_mesglob_charts.html
NWP Gazettehttp://www.metoffice.gov.uk/research/nwp/publications/nwp_gazette/index.html
NWP technical reportshttp://www.metoffice.gov.uk/research/nwp/publications/papers/technical_reports/index.html4km mesoscale runs:http://www-nwp/~meso/current_uk4mesglob_charts.html