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Cloud climatology from ATSR

Caroline Poulsen(1), Richard Siddans(1), Barry Latter(1), Roy Grainger(2), Elies Campmany(2), Gareth Thomas(2), Andy Sayer(2), Lin Wu(2), Elisa Carboni(2) and Phil Watts(3)

(1) RAL, Didcot, OX110QX, United Kingdom
(2) Oxford University, AOPP, Oxford, United Kingdom
(3) EUMETSAT, EUMETSAT, Darmstadt, Germany

Abstract

The importance of clouds to the radiation balance of the terrestrial climate is well known. The IPCC has identified clouds and their feed back processes as one of the major uncertainties in understanding climate change. The long times series of the ATSR(Along Track Scanning Radiometer) instruments provides a unique opportunity to provide not only a high quality SST climatology but also a high quality cloud climatology. In addition the information from the cloud climatology can be used in conjunction with nearby aerosol information (such as provide by Globaerosol) to infer knowledge about the interactions between aerosol and clouds. The data can also be used to improve cloud masking for other ATSR/MERIS parameter retrievals. In this paper I present a Cloud Climatology derived from ATSR-2 data called GRAPE (Global Retrieval of ATSR cloud Parameters and Evaluation). The GRAPE climatology contains information on the following cloud properties, cloud optical depth, cloud phase ,cloud particle size ,cloud top pressure ,cloud fraction and cloud water path has bee produced using all the available ATSR-2 data from 1995-2001. The algorithm uses optimal estimation in order to fully utilise all available measurements and a priori information. The algorithm uses modelled cloud characteristics combined with a fast radiative transfer and known error characteristics to find the most probable values of all cloud parameters simultaneously and with correct error estimates. Results from the entire climatology will be presented in this paper together with results from a comprehensive validation program against other satellite climatologies such as ISCCP and MODIS. The results have also been validated using ground based instrumentation such as radar. The results of the analysis are encouraging, plans and progress on extending tha analysis to AATSR will also be discussed. The Data for this project has been kindly provided by the NEODC.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry