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Numerical prediction of fog for airports : local assimilation, nowcasting and predictability

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... on other french airports. A local approach ... air traffic can be reduced half time (Paris-Cdg airport) ... useful tool for fog prediction in the airports ... – PowerPoint PPT presentation

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Title: Numerical prediction of fog for airports : local assimilation, nowcasting and predictability


1
Numerical prediction of fog for airports local
assimilation, nowcasting and predictability
  • Samuel Rémy, Stevie Roquelaure and Thierry Bergot
    (Météo-France)
  • FRAM workshop on fog, 21-22 May 2008

2
Outline
  • Description of the model
  • Operationnal use at Paris-CdG
  • Current research on COBEL-ISBA
  • Local Ensemble Prediction System (L-EPS)
  • Towards a Ensemble Kalman filter (EnKF)
  • Conclusion
  • Implementation on other french airports

3
A local approach
  • Fog is a local phenomenon, which evolves at small
    time scales
  • 3D fog modelling
  • Horizontal and vertical resolution are too coarse
  • Physical parametrization often not accurate
    enough
  • 1D fog modelling
  • Allows better vertical resolution and more
    elaborate physical parametrisations
  • Possibility of using data from a specific
    observation system
  • Allows high frequency of assimilation/simulation
    cycles (every hour for COBEL-ISBA)

4
Description of COBEL-ISBA
  • Main features of COBEL-ISBA (Météo-France,
    LA-UPS)
  • Coupling of an atmospheric model (COBEL) and of a
    surface-ground scheme (ISBA)
  • High vertical resolution (30 levels from 0.5m to
    1360m, 20 under 200m)
  • 1DVar assimilation scheme with site-specific
    observations
  • Detailed physical parametrisations for fog
    modelling

References Bergot et al. (2005), Weather and
Forecasting
5
Site-specific observation system
  • COBEL-ISBA is in currently operationnal at the
    Paris-CdG airport
  • Specific observation system consists of
  • 30 meter tower temperature and humidity
  • Soil of temperature and water content measurement
  • Shortwave and longwave radiative fluxes at 2 and
    45m
  • If fog and low clouds are detected
  • Height of the fog layer is deduced from radiative
    fluxes at 2 and 45m
  • Initial atmospheric profiles are adjusted

6
Evaluation of the forecasting system
  • For CdG Intl Airport, Low Visibility (LVP)
    conditions if
  • Ceiling is below 60m
  • And/or
  • Visibility is below 600m
  • Under LVP conditions, air traffic can be reduced
    half time (Paris-Cdg airport)
  • Evaluation with Hit Rate (HR), False Alarm Rate
    (FAR)

7
OPER score of the model (CdG)
  • COBEL-ISBA is a useful tool for forecasters at
    Paris-CdG
  • Local observations are very important

8
OPER onset and burnoff (Paris-CdG)
  • Onset time is overall too late
  • Bimodal distribution for burnoff time error
  • Possible influence of aerosols?


9
OPER reaching the forecaster
  • Intranet
  • Adequate when many airports to manage

10
Research objectives
  • Develop an ensemble
  • Probabilist forecast
  • Assess the quality of the forecast
  • Work on assimilation scheme
  • Improve the initial conditions
  • Init with fewer observations


11
Research Local Ensemble Prediction System (LEPS)
  • 54-members ensemble
  • Perturbations based on standard deviation of
    initial conditions and mesoscale forcings
  • Calibration of the ensemble by a bayesian method
    and a training dataset
  • Evaluation with Brier Score (BS)


References Roquelaure and Bergot (2008), J.
of Applied Met. And Clim.
12
LEPS comparison with operational bulletins
  • LVP forecast for 4 period of time 0-30min,
    30min-1h, 1-2h, 2-3h
  • 4 forecast classes certain, probable, unlikely,
    ruled-out
  • Night of 16-17/01/2005 low stratus


6am Bulletin
T1 T2 T3 T4
Déterministic
Probabilistic
13
Research on the assimilation scheme
  • Goal to optimize the use of local observations
  • Initial conditions for temperature and humidity
    given by
  • B is the model error variance/covariance matrix
  • Fixed 1DVAR
  • Computed with an ensemble Ensemble Kalman
    Filter (EnKF)

14
Research estimate of B
  • Computed with an ensemble
  • B matrix for temperature for different init time,
    mean over the 2004-2005 winter
  • Important diurnal cycle ground for development
    of EnKF

15
Resarch ensemble Kalman Filter
  •  On the flow  B matrixes
  • 32-members ensemble
  • Simulated observations over 15 days
  • Results more or less identical as compared with
    fixed B.

Fixed B
Forecast time
EnKF
16
Conclusion
  • COBEL-ISBA is a useful tool for fog prediction in
    the airports
  • Accurate initial conditions are very important
    for fog modelling
  • Future implementation
  • Lyon-StExupery airport
  • Paris-Orly airport
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