ARA - Atmospheric Radiation Analysis

Analyzed RadioSoundings Archive (ARSA)

For many years, LMD has been involved in the processing and validation of level1 and level2 satellite data. Such processing or validation tasks require auxiliary datasets, a key one being radiosonde measurements. Radiosonde reports are critical for a wide range of applications as forward and inverse models validation, verification of satellite measurements, etc. In order to be fully useful for the abovementioned applications, and mainly for the one involving forward radiative transfer simulations, LMD has elaborated the ARSA database, starting from observations by worldwide distributed radiosonde stations and combining them with surface and other auxiliary observations. Several tasks are perform to answer the questions of quality and completeness of the radiosonde reports :

1. to develop and apply physically coherent quality control tests: besides the obvious elimination of gross errors, unrealistic jumps and redundant measurements (redundant reports, redundant levels), it is required that temperature measurements be available at least up to 30 hPa, that water vapor measurements be available at least up to 300 hPa, and that surface pressure be not smaller than a given value (currently: 850 hPa). Also, the TIGR dataset helps removing values that deviate by more than a certain number of standard deviation from their respective air-mass (tropical, mid-lat, polar) mean values.
2. to combine existing radiosonde measurements with other reliable data sources in order to complete the description of the atmospheric state, whenever and wherever required information is missing: most of the radiosonde reports have to be extrapolated to the upper levels of the atmosphere; also, most of them have to be completed with ozone profiles.
3. temperature, water vapour, ozone profiles profiles are interpolated to interface the 4A model: nominally 43 levels between sea level pressure and 0.0025hPa.

The resulting data set is the ARSA (Analyzed RadioSoundings Archive) database, extended on a monthly basis. Validation of ARSA data is currently performed using numerous comparisons between 4A/OP simulated and observed brightness temperatures of IASI/Metop.

You can see details on readme_ARSA_v2.7.doc.

Acknowledgements

Thanks are due to ECMWF for making available the ERA-interim outputs, the radiosonde archive and the surface station archive through their ECMWF Data Server.

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