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Utilisation of satellite data
in the verification of HIRLAM cloud
forecasts
Christoph Zingerle and Pertti Nurmi
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● verification, the task
● the forecasting system HIRLAM
● observations = satellite data
● making forecast and observation comparable
● an example
● summary
● future
Contents
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Task
● Verification of the HIRLAM cloud forecast
- detection of deficiencies in the cloud forecast scheme
- feasibility of different approaches to verification using satellite data
- methodology of verifying cloud forecasts and its operational implementation
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HIRLAM at FMI
- FMI is running the reference HIRLAM (RCR) operationally
- resolution 0.2 deg horizontal (438x336 grid points, ~ 22 km)
40 levels vertical (up to 10 hPa)
- semi-lagrangian advection
- 3D–Var analysis (no satellite data)
- lateral boundary conditions from ECMWF
- Denmark, Finland, Iceland, Ireland, Netherlands, Norway,
Spain and Sweden (France)
● HIgh Resolution Limited Area Model
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HIRLAM RCR domain
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Satellite Observations
● satellite data at FMI from:
- METEOSAT 7/8:
high resolution (temporal and spatial)
coarse resolution at the edges - like Finland - with limb darkening
- NOAA polar orbiting satellites
high spatial resolution
coarse temporal resolution
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Observation – Forecast
● Model to Satellite: ● Satellite to Model:
- transferring the parameters
forecasted by the model to
observations
- Radiative Transfer Model
uses model data to simulate
observed radiances and Tb’s
- transferring the observations
to parameters forecasted by
the model
- Cloud classification scheme
generally thresholding methods
based on typical cloud properties
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Model to Satellite
● Radiative Transfer Model (RTM)- RTTOV 7
- a fast RTM for the assimilation of satellite data
calculates radiances (and Tb's) as seen by a satellite instrument
uses profiles of temperature
humidity
cloud fraction
cloud liquid water
cloud ice water
ozone
surface properties
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Model to Satellite
● 'synthetic' NOAA AVHRR image (10.8µ)
- 24 h forecast from HIRLAM
- AVHRR because of the
high resolution provided
even at the poles
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Observation Re-sampling
● NOAA AVHRR satellite image
- re-sampling needed
- preprocessed (AAPP) AVHRR image (calibrated and navigated) pixel center in the grid-box corresponding to the HIRLAM grid pixel assigned to this grid-box
- Assumptions:
HIRLAM grid value represents average over all the values in box
neighbouring pixels don't differ much from each other
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full resolution, 30.4.2004 (10.8µ) after re-sampling, 30.4.2004 (10.8µ)
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simulated, 30.4.2004 (10.8µ) observed, 30.4.2004 (10.8µ)
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Difference:observed - simulated
Difference > 40 K:Model error?
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observed / simulated Tbrelative frequency of Tb
observedsimulated
Summary distributions
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Summary
● RTTOV - a tool to simulate satellite measurements as close as possible- surface parameters and transmission (clouds) dependent
● observations - simple re-sampling of NOAA AVHRR data is sufficient- re-sampling will be more sophisticated for other instruments
● verification of HIRLAM- cloud forecast scheme not yet verified extensively- approach to verification looks promising
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Future
● examine approaches to verification- satellite to observation approach (SAFNWC software)- pattern recognition methods
● expand to other satellite data (instruments)
- Meteosat data over Europe- polar orbiting satellites over Scandinavia and Nordic Countries
● operational verification- refine methodology to verify cloud forecasts- improve the operational verification package of FMI