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: A Quality Assessment Approach for their determination and evaluation
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Acronyms
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Acronym | Definition |
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ATBD | Algorithm Theoretical Basis Document | C3S | Copernicus Climate Change Service | C-ATBD | Climate ATBD | CDR | Climate Data Record | CDRP | Climate Data Record Program | CDS | Climate Data Store | CNR | Consiglio Nazionale delle Ricerche (National Research Council of Italy) | DWD | Deutscher Wetterdienst (Germany's National Meteorological Service) | ECMWF | European Centre for Medium-Range Weather Forecasts | ERA5 | ECMWF Reanalysis 5th Generation | GCOS | Global Climate Observing System | GEWEX | Global Energy and Water Exchanges | GPCC | Global Precipitation Climatology Centre | GPCP | Global Precipitation Climatology Project | GPM | Global Precipitation Measurement mission | HOAPS | Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data | ICDR | Interim Climate Data Record | IMERG | Integrated Multi-Satellite Retrievals for GPM | ISAC | Istituto di Scienze dell'Atmosfera e del Clima (Institute of Atmospheric Science and Climate) | KPI | Key Performance Indicator | NetCDF | Network Common Data Format | NIMROD | Precipitation Radar Dataset | NOAA | National Oceanic and Atmospheric Administration | OceanRAIN | Ocean Rainfall And Ice-phase precipitation measurement Network | PACRAIN | Pacific Rainfall Database | PQAD | Product Quality Assurance Document | PQAR | Product Quality Assessment Report | PUGS | Product User Guide and Specification | RMS | Root Mean Square | RV | Research Vessel | TCDR | Thematic Climate Data Record | TMPA | TRMM Multi-satellite Precipitation Analysis | TRMM | Tropical Rainfall Measurement Mission | UMD | University of Maryland | WCRP | World Climate Research Programme |
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For each GPCP time slice (daily/monthly), we compute spatial averages over the maximum area available in the respective reference datasets (i.e. between 50°S and 50°N for TMPA products, globally for ERA5, over Europe for NIMROD) for both GPCP and the respective reference datasets. Datasets with higher temporal resolution than GPCP (i.e., ERA5 hourly for comparison with GPCP daily and NIMROD) are averaged temporally to obtain daily and monthly mean values. A regridding has not been carried out at this stage because the spatial integration can be carried out regardless of the specific grids. The resulting time series for GPCP and the reference datasets are then compared. This allows us to also discuss the Key Performance Indicator (KPI) defined for the continuous monitoring of the datasets delivered to the CDS [D6].
1.3.2.2 Climatology
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The above discussion of KPI achievements is related to the TCDR only, i.e. all data until 12/2017. In compliance with a newly formulated KPI strategy [D6, section 3], we evaluate the ICDR not against a fixed target but against the performance of the TCDR in comparison to the respective TMPA products. As TMPA products were decommissioned during the lifetime of this project, we switched to ERA5 as reference for data after 12/2019 (see section KPIs for ICDR from 01/2020). We test whether the 95% confidence interval of the TCDR differences is valid as 95% confidence interval for the ICDR, too. The boundaries of the 95% confidence interval can be seen in Table 2 as:
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This check on the performance of the ICDR is verified by a binomial test at a 5% significance level, for details see [D6, Table 3]. For the GPCP monthly product, all 24 temporal instances of the ICDR (01/2018–12/2019) fall inside the boundaries, defined by the GPCP TCDR / TMPA comparison. For the GPCP daily product, 720 out of 729 temporal instances fall inside the boundaries. In both cases, we can conclude that the given boundaries are valid as a 95% or higher confidence interval of the ICDR at a significance level of 5%. Consequently, the ICDR in this time period performs sufficiently well, in line with the requirements formulated in [D6, Table 3].
KPIs for ICDR from 01/2020
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Target requirements within the present framework of brokering GPCP v2.3 monthly and v1.3 daily data to the CDS were formulated for global mean values. With TMPA products serving as reference datasets for the TCDR part of the datasets (until 12/2017) and for the ICDR part between 01/2018 and 12/2019, we adapt this requirement to the TRMM window (inside ±50° latitude). For data from 01/2020, ERA5 serves as reference dataset, so that global mean values are evaluated henceforth. The details of the analysis can be found in Section 2.2.1.1. The methodology, especially for the analysis of the accuracy of the ICDR part, is outlined in the KPI document [D6, section 3].
For the TCDR part of the datasets (until 12/2017), the accuracy, i.e., the differences between global mean values of the GPCP datasets and of a defined reference dataset, is required to remain inside ±0.3 mm/d. This requirement is met by the GPCP monthly dataset with the respective monthly TMPA product as reference. It is violated by the GPCP daily dataset with the respective daily TMPA product as reference in ~7.5% of all daily instances. However, daily and monthly data were unlikely to meet the same fixed target requirement initially designed for monthly values, due to the higher temporal variability in daily data. The minor violation is acceptable in this light.
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