Evaluation of water vapour in EC-Earth

For model evaluation and improvements long-term homogeneous and consistent observational data sets are needed. The EUMETSAT Satellite Application Facility on Climate Monitoring (CM-SAF) datasets have recently been made for available for the climate modelling community, including variables such as cloud and moisture and radiation variables. We have used the water vapour products for evaluation of the Rossby Centre global climate model EC-Earth.

The interaction of water vapour, clouds and radiation are crucial for the climate and its variability. Collocated measurements of these variables can help to reveal systematic biases in global and regional climate models simulations for present day and increase the confidence in climate predictions. Here we show some results from comparing the vertically integrated water vapour from EC-Earth and ERA-Interim with the CM-SAF datasets (The full report is available to the right of this page).

The EC-Earth global climate model (Hazeleger et al 2010) has been been developed from the European Centre for Medium-Range Weather Forecasts (ECWMF) model (http://ecearth.knmi.nl/). The satellite data was obtained from the EUMETSAT Climate monitoring Satellite Applications Facility database (CM-SAF http://www.cmsaf.eu) from the ATOVS sounder (1999-2011) and from the microwave imagers HOAPS SSM/I datasets over ocean (1988-2006).

Monthly mean values of EC-Earth and satellite vertically integrated water vapour (IWV) are compared to each other and to ERA-Interim reanalysis (Dee et al 2011) in Figure 1. The global distribution of July mean water vapour is well simulated by EC-Earth compared to ERA-Interim and the CM-SAF (ATOVS and SSM/I) satellite datasets, with maximum IWV values of 50-60 kg/m2 near the equator down to the very small values at the poles of less than 2kg/m2.

RC News - Ulrika Fig 1 July mean
Figure 1: July mean Water vapour for ERA-Interim and EC-Earth left column and CM- SAF ATOVS and SSM/I in the right column. Values are in kg/m2.

The differences between EC-Earth, the satellite data sets and ERA-Interim are shown in Figure 2. EC-Earth has a large dry bias over the continents compared to ERA-Interim and the ATOVS IWV data. Over the tropical ocean EC-Earth overestimates IWV compared to ERIM but also the satellite data sets have more IWV there. Over the Atlantic EC-Earth and SSM/I has less IWV than ERA-Interim.

RC News - Ulrika Figure 2 July diff
Figure 2: July mean Water vapour for ERA-Interim and the difference of EC-Earth, CM- SAF ATOVS and SSM/I compared to ERA-Interim. Values are in kg/m2.

The two satellites data sets agree fairly well with ERA-Interim as expected, since ERA-Interim data are used as input to the satellite retrievals and conversely satellite data are used as input in the ERA-Interim data assimilation. Still some significant differences were found for certain regions. ATOVS has much more IWV over tropical continents, the land/sea difference appears to be exaggerated. SSM/I has more water vapour in the tropics than ERA-Interim, while poleward from about 30° there is less IWV over mid-latitudes. Further poleward at 50°-60° the bias turns positive again. The last difference can be understood from problems detecting IWV over and near sea-ice edge.

The CM-SAF satellite data sets will help in the model evaluation and development. However, some discrepancies between the satellite data sets and ERA-Interim needs further investigation to make sure the satellite retrieval assumptions are correct.


Dee D et al 2011: The ERA-interim reanalysis: configuration and performance of the data assimilation system. ECMWF ERA Report Series 9, pp 1–71 (available online: http://www.ecmwf.int/publications/library/do/references/list/782009)

Hazeleger, W., Severijns, C., Semmler, T., Stefanescu, S., Yang, S., Wang, X., Wyser, K., Dutra, E., Baldasano, J. M., Bintanja, R., Bougeault, P., Caballero, R., Ekman, A. M. L., Christensen, J. H., van den Hurk, B., Jimenez, P., Jones, C., Kallberg, P., Koenigk, T., McGrath, R., Miranda, P., van Noije, T., Parodi, J. A., Schmith, T., Selten, F., Storelvmo, T., Sterl, A., Tapamo, H., Vancoppenolle, M., Viterbo, P., and Willén, U., 2010: EC-Earth: A Seamless Earth-System Prediction Approach in Action. Bull Amer Meteor Soc, 91, 1357-1363.

Hazeleger W, Wang X, Severijns C, Stefanescu S, Bintanja R, Sterl A, Wyser K, Semmler T, Yang S, van den Hurk B, van Noije T, van der Linden EC, van der Wiel K (2011) EC-Earth V2: description and validation of a new seamless Earth system prediction model. Clim Dyn 2011. 10.1007/s00382-011-1228-5

Trenberth, K. E., Fasullo, J., & Smith, L. (2005). Trends and variability in column-integrated atmospheric water vapor. Climate Dynamics, 24, 741-758.

Willén, U. Evaluation of EC-Earth global water vapour field simulations using CM SAF ATOVS operational products and HOAPS cliamte data sets. CDPO VS Study No 11. March 2013. http://www.cmsaf.eu