ESA / ECSAT CCIWV.REP.022 Water Vapour Climate Change Initiative (WV_cci) - CCI+ Phase 2 D2.2 for each month in 2010–2014 with a horizontal resolution of 5 degrees by 5 degrees in latitude and longitude. In the vertical dimension, the L2 VRWV profiles are interpolated to 26 pressure levels from 1000 hPa up to 10 hPa (1000, 950, 900, 850, 800, 750, 700, 650, 600, 550, 500, 450, 400, 350, 300, 250, 225, 200, 175, 150, 125, 100, 70, 50, 30, 10 hPa), as also specified in the PSD [RD-9]. For all sensors, the monthly average is computed as the mean of VRWV profiles - & ( ., /, 0) : -(., /, 0) = - & ( ., /, 0) , (Equation 5) where 1 is the number of measurements.
Note that for IMS, the average VRWV is calculated based on the logarithm of mixing ratio, same as the original VRWV profiles. The uncertainty of the monthly mean 2 3 can be estimated as the standard error of the mean: 2 3 ( ., /, 0) = 45 ( ., /, 0)/1 , (Equation 6) where 5 ( ., /, 0) is the variance of the WV measurements calculated as: 5 ( ., /, 0) = # - & ( ., /, 0) −-(., /, 0)] . (Equation 7) Figure 3-3 shows an example of bias-correction of the MLS observations and comparison against reanalyses (ERA5 and MERRA2) for the period of 2010 to 2014. The bias-correction method can increase the water vapour in the upper troposphere, which is known to be too dry in the original observations. 17