EUMETSAT GRAS SAF 2nd User Workshop June, 2003

The RoleThe Roleofof

GPS Atmosphere ProfilingGPS Atmosphere Profilinginin

Weather ForecastingWeather Forecastingand Atmosphere Researchand Atmosphere Research

Per Høeg

Atmosphere Ionosphere Research Division (AIR)Danish Meteorological Institute (DMI)

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EUMETSAT GRAS SAF 2nd User Workshop

The EPS/METOP Satellite

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EUMETSAT GRAS SAF 2nd User Workshop

The Observational Method

• The fundamental observable is the signal Doppler shift.

• Knowledge of the observational geometry results in the phase shift due to the medium along the ray path.

• The ionosphere, stratosphere and troposphere cause signal phase and amplitude changes.

Dry term Wet term Ionos. term

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101 fNCTPCPTC ew

LEO

GPS

Earth

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EUMETSAT GRAS SAF 2nd User Workshop

GRAS SAF Data Products

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EUMETSAT GRAS SAF 2nd User Workshop

Advantages of GPS Atmosphere Profiling

• Absolute measurement• The technique needs no calibration. The basics of the observation are a measurement of time.

• Global coverage• The geometry of the observation leads for one satellite to evenly distributed data on a 24-hour

interval. Observations over seas and oceans (covering 70% of the Earth) minimize the major error source in accuracy of weather forecast and climate models.

• High vertical resolution• The vertical resolution limited by the Fresnel zone of the observation leads to information of

atmosphere phenomena with scale sizes less than 0.5 km.

• Insensitive to clouds and precipitation• The wavelengths applied makes the measurement transparent to clouds and rain hampering other

space techniques.

• Data delivery• The EPS/METOP mission will deliver the operational data products with 3 hours of observation.

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EUMETSAT GRAS SAF 2nd User Workshop

Winter Frontal Zones and Jet Streams

The major frontal zones (left panel) and jet streams (upper panel) during winter.

The shaded regions (left panel) indicate major temperature contrasts mostly along mountain ranges and coasts. Arrows depict the dominant direction of the winds including the highs driving the wind patterns.

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EUMETSAT GRAS SAF 2nd User Workshop

NWP Data Assimilation

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EUMETSAT GRAS SAF 2nd User Workshop

Variational Data Assimilation

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EUMETSAT GRAS SAF 2nd User Workshop

Weather Prediction

Main indicators: Wind,Temperature, Pressure,Water Vapor

♦ Requirements for improved weather forecasting• Temperature: < 0.3 % [180 – 335 K]

• Pressure: < 0.3 % [0.5 – 1100 hPa]

• Water vapor: < 20 % [1 – 45 hPa]

• Coverage: global [data separation < 500 km]

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EUMETSAT GRAS SAF 2nd User Workshop

Weekly Coverage of Profiles

Weekly latitudinal distribution of occultations. Longitudinal variations still exist in the seven days simulation. Part of the spread in the plot is due to this effect.

For the 500 x 500 km cells the following statistics can be calculated:Average number of occultations in a cell: 22.49Standard deviation: 10.36

Average time difference (min) between profiles in each cell as function of latitude. The simulation covers a whole week of data.

Average time difference between the occultations: 482 min [8h 2min]Standard deviation: 216 min [3h 36min]

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EUMETSAT GRAS SAF 2nd User Workshop

GRAS Temperature Retrieval Accuracy

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EUMETSAT GRAS SAF 2nd User Workshop

Global Humidity Fields