Coupling CALIOP observations and regional simulations at 20km resolution: is that a good candidate to study cloud variability at the regional scale?

International audienceThis work aims to study the clouds' role on regional climate variability. At first order, European climate is driven by large scale circulations. However, clouds are known to have two major radiative effects impacting the surface temperature: the greenhouse effect and the albedo effect. These effects are strongly dependent on macrophysical and microphysical properties of clouds. It is then necessary to consider the vertical distribution of clouds to better understand their impact on regional climate. Since June 2006, A-train observations are available and allow the description of this vertical distribution and of other microphysical properties. However, the sampling is limited when considering small scale variability. To complete these observations, we use a regional climate model which may allow to extend the period of study and to better understand the link between clouds and surface temperature. In this study we address the ability of our tools to study impact of clouds on European climate at a resolution suitable to take into account the complex terrain of this area. Seasonal and inter annual clouds variability is presented for observations and simulations. We also evaluate the amplitude of clouds variability in the simulations and the uncertainties linked to the satellite sampling. B. Effect of satellite under sampling GCM Oriented Calipso Cloud Product-GOCCP (Chepfer et al., 2010) Using the microphysical properties of the simulated clouds, we compute the SR that would be observed by the CALIOP lidar. We can then use the same cloud diagnostics for both observations and simulations WRF-MedCordex simulations Adaptation of COSP Lidar Simulator 2 GOCCP products have been used for this study: o Scattering Ratio: SR = í µí°´í µí±í µí°µ í µí±¡í µí±í µí±¡ í µí°´í µí±í µí°µ í µí±í µí±í µí± o Cloud fraction (z) : % of SR>5 on 20km grid (tab. 1) Altitude (km) altitude latitude Fig3: Instant SR 19/01/2009 night: (a) Observations, (b) WRF simulations and (c) WRF+lidar simulator simulations We use a WRF simulation performed in the framework of MED-CORDEX (downscaling of ERA-interim reanalyses) at 20 km resolution that covers the Mediterranean domain, over the period 1989-2011 (details in Stefanon et al., 2014).-horizontal resolution: 20km-28 vertical levels, outputs every 3 hours o Very similar profiles of cloud fraction (CF) o High clouds (10 km): in average, differences need to compute CF from mixing ratio