The case of 1 April 2008 was chosen for its combination of thin and thick mixed-phase clouds and also for the overpass of CloudSat and CALIPSO satellites and the presence of in-situ measurements on the aircraft.
The opposite Figure illustrates the comparison between each IWC product. From panels a) to d) we represent the CloudSat official IWC product, the 5 km IWC product from CALIPSO, the DARDAR IWC and the RALI retrieval averaged at 1 km footprint. The black horizontal line illustrates the aircraft altitude and the vertical dashed lines split the scene in several latitude regions which will be analysed in panels e) to t). These panels show contour plots of the IWC distribution as a function of altitude, each column corresponds to the latitude region delimited by the black dashed lines and each row corresponds to one product: Panels from e) to h) show IWCCloudSat, from i) to l) IWCCALIPSO, from m) to p) IWCDARDAR and from q) to t) IWCRALI. They all include mean profiles of IWC for each product, the red line for CloudSat, the green line for CALIPSO, the magenta line for DARDAR and the blue line for RALI. From these results we can see that globally IWCCALIPSO has the lowest values and IWCCloudSat the largest values and independently on the altitude. IWCDARDAR lies mostly between the CALIPSO and CloudSat values, a result consistent with what we previously observed between stand-alone radar and lidar retrievals and synergistic retrieval. However, we observe a good agreement between the retrievals below 3 km, around 0.1gm-3, in the region starting at 70°N apart from CALIPSO since the lidar is extinguished and the information coming mainly from the radar. As expected, DARDAR and RALI retrievals show most of the time a better agreement than compared to CloudSat and CALIPSO, the retrieval techniques being identical and only the measurements changing. Fig.e and m show that DARDAR and CloudSat are in good agreement around 2 km (about ± 20%) but below, IWCCloudSat decreases while IWCDARDAR increases when altitude decreases. This behaviour has been highlighted by Stein et al. (2011), the standard version of CloudSat retrieval, ice and liquid retrievals are scaled linearly with temperature between 0°C and -20°C by adjusting the respective particle number concentrations. This leads to a smooth transition to liquid-only retrievals at temperatures above 0°C. The Varcloud retrieval assumes that the radar reflectivity is dominated by the presence of ice particles and does not account for any liquid contribution below 0°C.