Transcript PatHyder - Deltares Public Wiki

Moving towards improved real-time forecast models
of the NW European shelf seas
Pat Hyder, Martin Holt, Sarah Wakelin, Jason Holt,
John Siddorn, Jeff Osborne and Enda O’Dea
JONSMOD, June 26th 2006
www.ncof.gov.uk
Outline
• Introduction to NCOF and the Met Office Ocean
Forecasting group.
• Operational shelf seas models
• Model performance evaluation
(a) Pressure gradients over steep bathymetry
(b) Turbulence
(c) Other remaining issues
• Conclusions.
www.ncof.gov.uk
What is NCOF – National Centre for Ocean
Forecasting?
It is a strategic partnership between…
• Our mission is to establish ocean forecasting as part of the
national infrastructure, based on world-class research and
development.
Improved communication
www.ncof.gov.uk
Operational Modelling at the Met Office
• The Met Office runs weather, climate and ocean
models on supercomputers divided into 2
independent halls for operational resilience.
• The operations suite comprises many (>40)
operational weather and ocean models run up to
4 times daily.
www.ncof.gov.uk
Summary of Ocean Forecasting Research group
modelling (& analyses) within Met Office
• The Ocean Forecasting Research (OFR) group at the Met Office run a number
of operational ocean models and analyses (* included today):
– Open ocean models and analyses
• FOAM/NEMO – hindcasts, analyses and forecasts of deep ocean regions
• OSTIA – new high resolution GHRSST SST analysis (*)
• FOAM-HadOCC - open ocean ecosystem, colour, CO2 fluxes
– Shelf Seas models (*)
• 2-D surge model – tide and surge forecasts (supported by POL).
• POLCOMS – 3-D forecasts of shelf seas region
• POLCOMS-ERSEM – 3-D nowcasts of ecosystem parameters (near-operational)
– Offshore wave models
• Predicts offshore ocean wave spectrum
– Near-shore wave and surf-zone models
• Overtopping
• Surf-zone predictions
MO also hosts: Oceans and
climate group
www.ncof.gov.uk
Shelf seas modelling
(POLCOMS and POLCOMS-ERSEM)
www.metoffice.com/research/ncof/shelf/
www.ncof.gov.uk
POLCOMS (developed by POL)
• 3 D baroclinic finite difference model.
• Arakawa B grid.
• Spherical polar coordinate system.
• Terrain following coordinates - s level system.
• Time splitting (different time-steps for barotropic and baroclinc
modes).
• Mellor-Yamada-Galperin 2.5 turbulence closure.
• Piecewise Parabolic Method (PPM) advection for improved
front conservation
• Linked sediment model.
• For details see: Holt and James, 2001 or
http://cobs.pol.ac.uk/modl/metfcst/POLCOMS_DOCUMENTATION/
www.ncof.gov.uk
Shelf Seas model: POLCOMS
developed by POL, applied by the Met Office
Tides
Storm surges
Seasonal
stratification
Tidal mixing
fronts
River inflows
Shelf slope
current
FOAM model
temperature,
salinity and
barotropic current.
Tidal elevation and
barotropic current,
and inverse
barometer surge
Norwegian
coastal current
(can be coupled
to sediments
and ecosystem)
1/9° by 1/6° grid
(approx. 12 km)
32 vertical levels
NWP hourly wind
and pressure
3 hourly surface
heat and
freshwater
Freshwater
inflow from
Baltic and
Rivers
www.ncof.gov.uk
Boundary Data: Operational FOAM configurations
FOAM 1º Global
FOAM 36km (1/3º) North
Atlantic and Arctic
FOAM 12km (1/9º)
North Atlantic
Boundary data to
shelf seas model
FOAM 36km (1/3º)
Indian Ocean
FOAM 27km (1/4º)
Antarctic
FOAM 12km (1/9º)
Mediterranean
All configurations have 20 levels, and are run daily (with 5 day forecasts)
www.ncof.gov.uk
Shelf seas: NW European domains
•
•
•
•
Models are run daily
Since 2000: 12km (32
level) Atlantic Margin
model nested into 1/9o
North Atlantic FOAM
model (5 day fcst)
Since 2005: 7km (18
level) Medium
Resolution Continental
Shelf (MRCS)
including sediments (2
day fcst). Ecosystem
later this year (5 day
fcst).
Since 2003: 1 nm (18
level) Irish Sea model
(2 day fcst)
AMM (12km)
Irish Sea
(1nm)
MRCS
(7km)
www.ncof.gov.uk
Ecosystem modelling – POLCOMS-ERSEM MRCS
• 3-D POLCOMS-ERSEM
• MRCS (7km)
• Hindcast completed for 20022006. Nowcast continues within
a week of real-time at present
but it will be operational with 5
day forecasts later this year.
John Siddorn will discuss in
more detail
Modelled Primary Production
at 10m depth
www.ncof.gov.uk
Persian Gulf Domain
• 12km grid
• 18 levels
• Shatt-al-Arab river inflow
• Hourly wind and surface
pressure and 6-hourly
averaged heat and
freshwater surface flux from
global NWP model.
• Tidal elevation and
barotropic current at open
boundary
• Climatology T&S at open
boundary
Surface to bed
temperature
difference
December
2001
www.ncof.gov.uk
Estuary scale modelling
• Under development at POL Not operational
• POLCOMS for Liverpool Bay
on 200m grid
• Includes wetting and drying
of mudflats
• River inflow
Plots show current speed
(cm/sec) and direction
www.ncof.gov.uk
Shelf Seas: Relocatable Model
• POLCOMS quasi-barotropic (constant density)
applied to any region of the worlds oceans with
tidal boundary (FES99) and wind/pressure
forcing.
• Series of nested models from large scale (12km)
nested to 4km nested to 1nm (and, if required,
nested to 200m) with several vertical levels.
• Applied for military exercises (e.g. Northern
Light 03, JV04).
www.ncof.gov.uk
Relocatable model: Yemen (JV04)
Surface currents (knots)
06Z
12z
Scale 0-1.5 knots
13z
www.ncof.gov.uk
Relocatable Model: The Solent
POLCOMS for Solent
(for Trafalgar Day
celebrations in
Portsmouth)
Barotropic (constant TS
model)
200m grid using UKHO
gridded bathymetry
Water level and
currents
Plot shows current
speed (knots – for RN)
and direction
Scale 0-2.5 knots
www.ncof.gov.uk
Model performance evaluation
www.ncof.gov.uk
POLCOMS (-ERSEM) Users and applications
Performance evaluation should be in the context of the user requirement
• MOD and NMP are major funders
• MOD: SAR, T/S structure (and sound vel.), currents visibility, TKE, AUV simulations
• MCA : Search and rescue (SAR) and Oil drift – coupling to VISAR/SARIS/OSIS.
• Offshore industry: sea-bed currents and temperature.
• EA: Operational 2-D UK surge model
Research or Developmental Users
• Provided to international projects (e.g. MARCOAST, MERSEA).
• ICES (through NORSEPP/NOOS)
• POL Coastal Observatory (Irish Sea model).
• SAMS: Eco for Marine mammal project.
• POL/NOCS – phys/eco for Ferry Box project (e.g. phosphate spill).
• PML: eco/phys for boundary conditions for regional models and comparison with satellite derived
data (RSDAS).
• Environment Agency, Fisheries Research Service (FRS) and CEFAS: Eco under evaluation for
future policy/management use.
Data available for research via ftp on request or via the ESSC LAS Server
(http://www.nerc-essc.ac.uk/godiva/ ).
www.ncof.gov.uk
Performance evaluation metrics and requirements
• As new ocean models of increasing resolution become freely available. Poor models
with low skill in their target region are likely to have few users.
• User driven accuracy requirement, i.e. feedback from customers (e.g. % error, abs.
error, r2 etc).
• Applied metrics using derived parameters (from a secondary model ), e.g. position
accuracy for SAR or accuracy of ‘weather window’ in planning offshore ops.
• Standard scientific metrics (e.g. cost functions or model efficiency parameters,
MERSEA metrics). No perfect one exists!
• Automated (and checked) daily validation to monitor performance.
• Process validation.
• Time series and spatial comparisons. More and optimised observations.
• Develop hardware, formats, tools for sharing data. Easy access to data, metadata
and documentation.
www.ncof.gov.uk
POLCOMS evaluation
• The Met Office undertake regular evaluation against SST from Met
Buoys, GHRSST OSTIA SST data, climatology data and Ferry Box
observations.
• AMM, MRCS and IS were initially developed/evaluated by POL. MRCS
physical has been evaluated statistically using a cost function.
• Irish Sea model is validated by POL through Coastal Observatory.
• POL and the Met Office are comparing AMM currents and sea levels with
the well-calibrated operational 2-D surge model, observations and the
relocatable model.
• The models generally perform ‘reasonably’ well in North Sea and Irish
Sea but several performance issues remain.
www.ncof.gov.uk
POLCOMS-ERSEM evaluation
• Physical performance is pre-requisite
• Met Office regularly evaluate simulations against CEFAS SMART buoy
data and against Ferry Box data.
• POLCOMS-ERSEM MRCS evaluation is undertaken at PML using the
1988-89 data from North Sea project (extensive data set). Statistical
validation using a ‘model efficiency’ parameter (1- (cost function)2)* to
asses skill. It is a tough test as small time lags result in no skill.
• Met Office provide chlorophyll, SST and attenuation/visibility data to
PML for comparison with satellite derived parameters (RSDAS system).
www.ncof.gov.uk
Operational Sea surface Temperature
and sea Ice Analysis
Daily 1/20° global analysis using
optimal interpolation.
Using GHRSST-PP satellite
(microwave & IR) and in situ
data.
Persistence based analysis.
Analysis results available from
www.ghrsst-pp.org
www.ncof.gov.uk
Ferry Box routes and AMM, MRCS and IS domains
Very valuable data for evaluating models
More routes to come
www.ncof.gov.uk
(a) Pressure gradients over steep bathymetry
(in sigma/s coord. models)
www.ncof.gov.uk
MAWS SST Comparison: AMM & MRCS Models
Obs. – black, MRCS sfce - red, AMM sfce –
blue
(MRCS bed – yellow, AMM bed - light blue)
www.ncof.gov.uk
Atlantic Margin Model: SST underestimation
Winter - Feb
OSTIA SST
Summer - July
OSTIA SST
AMM SST
AMM SST
AMM - OST
AMM – OST
• The performance
problem is
masked at the
surface in summer
by seasonal heat
input
• Impacts on
nested models.
i.e. MRCS
www.ncof.gov.uk
AMM Portsmouth-Bilbao Ferry Box SST 2005
FB
OSTIA
3 way comparison
Model
(also planned for bio
parameters)
www.ncof.gov.uk
POLCOMS AMM revised at POL (by Sarah)
Improved representation of
slope current and heat transport
with careful smoothing of
regional bathymetry.
AMMCLIM
before
AMMCLIM
after
Operational later this year.
www.ncof.gov.uk
(b) Turbulence model performance
and its impact
www.ncof.gov.uk
Turbulence model performance
1-D model experiments (e.g Simpson/Burchard et al.) suggest:
• In general, the models get the boundary layer dissipation correct (as the
rate of production of TKE by shear is well represented in the boundary
layer).
• The models fail to correctly simulate the stratified mid water values
(because local production in this region includes sources of shear which are
not accurately represented by the models e.g. internal waves/tide).
• To include the effects of local production in this region various simple
'parameterisations' are used (e.g. minimum TKE, viscosity, diffusivity),
although none of these are physically satisfactory.
www.ncof.gov.uk
Comparing the turbulence models (from Jason Holt
(POL), The Second Warnemunde Turbulence Days (28-30
Sept 2005, IO-Warnemunde)
POLCOMS V3/V5
• Mellor-Yamada
• 1 Equation (Bakhmetev algebraic
mixing length)
• Mixing length limitation
• Stability function – Galperin
(Quasi-equilibrium)
• Minimum viscosity 10-5m2s-1 &
minimum TKE 10-6m2s-2
• Convective Adjustment
• Craig and Banner condition for
surface waves
POLCOMS V6 (GOTM)
Configuration chosen:
• k-ε
• 2 Equation (prognostic
equation for mixing length)
• Mixing length limitation
• Stability function – Canuto
(Quasi-equilibrium)
• Minimum TKE 10-6m2s-2
www.ncof.gov.uk
Direct Comparison with Scanfish data Leg 178
26 August 1998 (from Holt, TSWTD)
Too Warm
Too Shallow
Too Thick
No Surface
fronts
www.ncof.gov.uk
All roles of the vertical turbulence and heat flux model
1.8 km
Celtic Sea section 26 August 1989 (from Holt,
TSWTD)
POLCOMS
POLCOMS-GOTM
(no min visc.)
7 km
www.ncof.gov.uk
POLCOMS-GOTM Tests at CS in 3D (from
Holt, TSWTD)
CS
Sharper pycnocline
POLCOMS-GOTM
POLCOMS
www.ncof.gov.uk
Diffusivity at CS (from Holt, TSWTD)
POLCOMS-GOTM
POLCOMS
min visc. 10-5
25 hr means
www.ncof.gov.uk
Typical profile (SW Approaches, 400m)
ρ
T
q2
S
Minimum TKE value appears
to over-ride closure for
significant sections of the
water column
www.ncof.gov.uk
Impact of turbulence errors
PHYSICS
Pycnocline is (1) too shallow (and therefore warm) and (2) too diffuse.
Can be sharpened by changing closure scheme and in particular background diffusivity
but remains too shallow – candidates for additional surface turbulent sources are
langmuir circulation, convective mixing and poorly represented wind/wave mixing.
SEDIMENTS
Re-suspension is a balance between turbulence and settling velocity – impact of errors
needs investigation.
BIOLOGY
1) Many complex interactions associated with turbulence.
2) Turbulence is a control on production (Huisman, 1999).
The timing of spring bloom can be shifted by several weeks by changing the background
diffusivity and closure scheme (see John’s talk).
www.ncof.gov.uk
Initial evaluation
Simpson et al, 1996
compared TKE
observations at mixed and
stratified sites in Irish Sea
with simulated TKE from
Mellor-Yamada (level 2.5) 1
equation closure in a 1-D
turbulence model. Model
was OK at M1 but there
was an error of in ε by
factor ~ 104 at S1 in
thermocline. We try to
replicate this with IS model
www.ncof.gov.uk
Mixed Site (~53.9oN 4.48oW), M1 - ε
IS model is broadly similar to
obs/mod. result presented by
Simpson but
1)High surface ε due to C&B
condition
Not: not colocated in time
Obs: 27 Mar 93 (LP, 7.5m, 1.0m/s)
Mod: 10 Feb 04 (LP, 8.1m, 1.0m/s)
www.ncof.gov.uk
Stratified Site, S1 (~53.9oN 5.57oW) - ε
IS model is broadly similar to
mod/obs. presented by
Simpson but:
1) High surface ε due to C&B
condition
2) Underestimation of ε in
thermocline is not evident
perhaps due to minimum
TKE density.
Not colocated in time:
S obs: 7 Jul 93 (LP, 8.0m, 0.45m/s)
Mod: 10 Jul 04 (LP, 5.6m, 0.35m/s)
www.ncof.gov.uk
Planned future work
• More evaluation with co-located observations is required to
estimate uncertainty/error. This is relevant to both to model
performance and direct TKE applications.
• Provision of model TKE data to DSTL for comparison with
observations (some undertaken and more planned).
• Comparison with AUTOSUB TKE observations in the Irish Sea to
be undertaken in July ’06.
• A project to compare historical TKE observations/simulations and
estimate the direct errors and impact on error in
diffusion/viscosity/sediment re-suspension and cross-pycnocline
fluxes (collaboration with POL/UWB/MO – J Holt, T Rippeth, J
Sharples).
www.ncof.gov.uk
(c) Other remaining model performance
issues
www.ncof.gov.uk
Other remaining model performance issues
1) River inputs - real-time/forecast river flow estimates are required
(persistence/routing models?). Also sediment and nutrient loads.
2) Observations to understand initial/boundary/forcing conditions - particularly
sub-surface, in remote regions and for ecosystem parameters (e.g. atmos.
nutrient sources) and sediments (bed load, types, size, settling vel., cohesion,
coastal erosion sources, etc.)
4) Optics – improved optical model (and underlying sediments) or forcing by
satellite derived attenuation.
4) Larger domains - Advection into/out of domain is problem for sed/eco
models (e.g. nutrient from Gironde/Loire river into MRCS or sediment loss from
MRSC domain).
5) Improved model formulations (difficult to determine requirement without
better initial conditions & forcing).
www.ncof.gov.uk
Conclusions
www.ncof.gov.uk
Conclusions
1) Hydrodynamic models are of sufficient skill to meet some but by no means
all user requirements.
2) Care is needed with representation of bathymetry to ensure slope currents
and resulting heat and water mass transports are well represented.
3) Other key areas where improvement is needed are turbulence, river inputs,
more observations (particularly sediment/biogeochemical parameters).
4) Ecosystem models are still developmental. Key areas were is improvement
is needed are: underlying physical/sediment/optical models, river forcing
and more observations.
5) You can never do enough evaluation and more observations are required!
Better communication (obs-mod-user) and improved data availability should
help.
www.ncof.gov.uk
Questions?
www.ncof.gov.uk