ESA / ECSAT CCIWV.REP.022 Water Vapour Climate Change Initiative (WV_cci) - CCI+ Phase 2 D2.2 between 100 hPa and 300 hPa, the bias-corrected VRWV monthly mean data of all instruments are used to calculate the average; below 300 hPa (troposphere), only original VRWV monthly mean data from IMS before bias-correction are used to calculate the average. In the lower stratosphere, the amount of BBH observations is not enough for a reliable bias- correction to the limb satellite observations and the original limb WV has a relatively high accuracy, thus the bias-corrected data are not included in the merged product.
In the troposphere, the original nadir VRWV profiles retrieved from IMS also show very high accuracy and only the original month mean data are used in the merged product. An example of the merged VRWV CDR-4 product is shown in Figure 3-5. Figure 3-5: Merged VRWV monthly product at 250 hPa for July 2010. All data are included in one NetCDF4 file, which includes the merged data and the corresponding uncertainty for each grid point. 3.4 Assumptions and limitations The main assumption in the algorithm to construct the VRWV CDR-4 product in the UTLS region is that VRWV profiles from BBH observations are representative for the bias-correction applied to the VRWV data from satellite instruments.
Due to the limited spatial and temporal coverage of the BBH observations, a bias-correction of the VRWV profile data based on a validation with coincident BBH observations is not feasible. Instead, the tropopause height, a 20