Validation of the sea ice surface albedo scheme of the regional climate model HIRHAM–NAOSIM using aircraft measurements during the ACLOUD/PASCAL campaigns

Abstract. For large scale and long term Arctic climatesimulations appropriate parameterization of the surface albedoare required. Therefore, the sea ice surface (SIS) albedoparameterization of the coupled regional climate model HIRHAM–NAOSIM was examined against measurements performed during the joint ACLOUD (Arctic CLoud Observations Using airborne mea-surements during polar Day) and PASCAL (Physical feedbacks of Arctic boundary layer, Sea ice, Cloudand AerosoL) cam-paigns which were performed in May/June 2017 north of Svalbard. The SIS albedoparameterization was tested using measured quantitiesof the prognostic variablessurface temperature and snow depth to calculate the surface albedoand the individual fractions of the ice surface subtypes (snow covered ice, bare ice, and melt ponds) derived from digital camera images taken onboard of the Polar 5/6 aircraft. Based on data gained during 12 flights, it was found that the range of parameterized SIS albedofor individual days is smaller than that of the measurements. This was attributed to the biased functional dependence of the SIS albedoparameterization on temperature. Furthermore, a temporal bias was observed with higher values compared to the modeled SIS albedo(0.88 compared to 0.84 for 29 May 2017) in the beginning of the campaign, and an opposite trend towards the end of the campaign (0.67 versus 0.83 for 25 June 2017). Furthermore, the surface type fraction parameterization was tested against the camera image product which revealed an agreement within 1 %. An adjustment of the variables, defining the parameterized SIS albedo, and additionally accounting for the cloud covercould reduce the root mean squared error from 0.14 to 0.04 for cloud free/broken cloud situations and from 0.06 to 0.05 for overcastconditions.