presents: forecasting for operations and design february 16 th 2011 – aberdeen
TRANSCRIPT
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PRESENTS:
FORECASTING FOR OPERATIONS AND DESIGN
February 16th 2011 – Aberdeen
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Marine Weather Forecasts
What tools do we use and how do we prepare them?
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The meteorological world has moved on a long way .....
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Nowadays marine forecasts are prepared using output from NWP – Numerical Weather Prediction
Global Atmospheric Model
Ensemble Forecasting
Spectral wave model
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Global Atmospheric Model
Solves fundamental equations describing the evolution of the atmosphere
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Fundamental to the success of a forecast is an accurate knowledge of the initial state of the atmosphere
Short-range forecast - 'first guess’
Observations of actual and derived conditions
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The model is run forward in time, typically up to a week ahead
During the run, a range of forecast information is produced at set intervals – say 1 or 3 hours
e.g. temperature, humidity, pressure, winds
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Ensemble Forecasting
Model does not fully describe processes in the atmosphere
Model resolution insufficient to capture all atmospheric features
Initial observations are not available at every point in the atmosphere
Observational data cannot be measured precisely
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Ensemble Forecasting
One method of quantifying the forecast uncertainty is by running the model a number of times
Each run has slightly different starting conditions
Each run evolves differently with time
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Ensemble Forecasting – types of output
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Spectral wave model
Solves the spectral energy density equation
Uses input from the Global Atmospheric Model, e.g. winds, sea and air temperature
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Spectral wave model
The wave model predicts the energy spectrum at each point at each time step
The energy spectrum is processed to produce significant wave height, wave period, wind wave, swell etc
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Preparing a Weather Forecast for Marine Operations
Start by examining raw forecast data of wind, waves etc
Compare starting values with actual observed data
Make allowances for model biases
Prepare the final forecast figures
Disseminate the forecast in required format – e.g. table/graph, operations checklist, 3-D plot etc.
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Providers of Marine Weather Forecasts
Most oil companies will not have their own in-house forecasting service but will contract out the provision of weather services to a specialist provider.
Forecast company – either public or private – will prepare forecasts for a number of clients using their available model data
Forecasting companies will use output from one or more global forecast centres e.g. UK Met Office, NCEP, ECMWF
Many companies have their own in-house wave model capability
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Extreme Wave Height
Gather information on wave climate from observations of wave height over as long a period as possible
Choose a distribution function to fit the ‘upper tail’ (i.e. the highest waves) of the data
Log-normalWeibullFisher Tippett
Extrapolate to a probability of exceedance of 1 in 50 years
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Extreme Wave Height (continued)
Calculate the highest likely wave corresponding to the maximum value of 50 year significant wave height
Combine with other sea-level parameters e.g. storm surge, astronomical tide
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Other Extreme Metocean Parameters
Wind
Current – Tidal, Surge, Residual
Air and Sea Temperature
Snow and Ice
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Change of Extremes in the Future
Very difficult to predict how the wave climate will respond in the future
Recent changes in North Atlantic wave height have been correlated with the phase of the North Atlantic Oscillation
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