Global DAily Precipitation Analysis for the validation of medium-range CLImate Predictions

Of central importance for the development process of the MiKlip system is the data and process based validation of the decadal scale prediction system during the three development stages of MiKlip. Furthermore, the generation of the decadal forecasts is based on an ensemble approach which requires the deduction of suitable probabilistic information from the different ensemble simulations. Of crucial importance is the evaluation of atmospheric water cycle components including clouds and related changes in the radiation budget. Additionally, the representation of extreme precipitation events requires the accurate simulation of precipitation variability.

Within the DAPACLIP project precipitation products for the evaluation of the MiKlip prediction system will be developed in close contact with the modelling community. These new data sets will allow to evaluate daily precipitation statistics from global and regional decadal MiKlip hindcasts. The focus will be on parameters of interest for potential users of the MiKlip predictions, such as the intensity, frequency and relative persistence of extreme precipitation and dry spells.

It is envisaged to produce data sets that are derived from a high quality global precipitation climatology (1988-2008) with daily data fields and several grid resolutions (1.0° x 1.0° and 2.5° x 2.5°; over Europe: 0.5°). The data sets will be based on an optimum combination of the in situ-based Global Precipitation Climatology Centre (GPCC) precipitation analyses for land surface areas and the satellite-derived Hamburg Ocean Atmosphere Parameters and fluxes from Satellite Data (HOAPS) precipitation analyses for ocean surface areas. An unprecedented feature in comparison to previous efforts is to allow for a traceable estimation of the uncertainty of the aspired data product.

Furthermore, the data sets and methods developed in this project will be included in the MiKlip evaluation infrastructure (project INTEGRATION ; project VECAP) for the evaluation of precipitation statistics in global and regional simulations.

Goals

• Development of baseline requirements and the technical specification of the new global daily precipitation analysis product in close contact with the modelling community within MiKlip.
• Over land daily precipitation data set:
  • Implementation of a quality control / assurance (QC/QA) scheme for the acquired in situ observed daily precipitation station data based on an adjustment of the GPCC monthly QC/QA procedures. Acquisition of additional European in situ precipitation station data from National Meteorological and Hydrological Services.
  • Climatological re-analysis of the GPCC database in order to produce a daily global gridded precipitation analysis for the time period 1988-2008 with 1.0° resolution (based on synoptic weather observation data, SYNOP) and 0.5° resolution for Europe (based on SYNOP and additionally acquired national in situ precipitation observation data).

• Over ocean daily precipitation data set:
  • Improvement of the HOAPS over ocean precipitation retrieval by implementing a 1D-Var retrieval scheme for the SSM/I that employs ECMWF reanalysis as first guess including a feasibility study for application of the scheme over land. The new retrieval system will be validated against ground based precipitation observations.
  • Development of a method to incorporate additional satellite data on cloud top temperatures, in order to improve the temporal sampling and to minimize the daily sampling error.

• Development of an objective analysis approach to merge GPCC  (land) with HOAPS (ocean) into a global daily precipitation product.
• Verification of the newly developed global daily analysis product based on regional daily precipitation analysis products and global numerical weather forecast re-analyses.
• Evaluation of precipitation statistics of global and regional decadal MiKlip hindcasts with a focus on intensity, frequency and relative persistence of extreme precipitation and dry spells. The robustness of results will be tested by applying alternative statistical approaches. Furthermore, key climate indices associated with precipitation events will be defined for model-data-comparisons and the application on decadal hindcasts and predictions.
• Implementation of automatic product access and NetCDF format via the GPCC website http://gpcc.dwd.de.
• Provision of components for the MiKlip evaluation infrastructure ( project INTEGRATION ; project VECAP) for the evaluation of precipitation statistics in global and regional simulations.