Sensitivity of climate models to seasonal variability of snow-free land surface albedo

Abstract

The seasonal variation of snow-free land surface albedo was integrated into the land surface schemes of the global climate model ECHAM5 and the regional climate model REMO to test the sensitivity of climate models to the advanced surface albedo parameterisation. This new albedo parameterisation was developed in previous studies describing the monthly varying surface albedo fields as a function of vegetation phenology derived from MODIS data products. Three model simulations were performed in order to study the sensitivity of the simulated climate to the seasonal background albedo variations: 1. control simulation with the old time-invariant surface background albedo, 2. experiment 1 with the new mean time-invariant surface background albedo field, 3. experiment 2 with the monthly varying surface background albedo as a function of the leaf area index. The analysis of the simulation results demonstrates the influence of the new albedo parameterisation on the model simulations. Strong effects occur over Europe with the regional and the global model simulations responding differently to seasonal background albedo variations. In contrast to the global simulation, where the large-scale conditions are changed by the new albedo parameterisation, in the regional simulations the circulation patterns within the model domain are not influenced. Here, the external forcing via the lateral boundaries of the regional model domain suppress changes in the large-scale circulation that might occur without the external forcing. In the regional model simulations only local effects occur mainly during the summer season, when the vertical energy exchange at the land surface is enhanced compared to the winter season. The comparison of the regional and global simulation results over Europe reveals that the global model shows higher sensitivity to the changed albedo parameterization with respect to the simulated annual temperature and precipitation cycle than the regional model. For both the regional and the global study the temperature and precipitation deviations from the observations are larger than the differences between the three model simulations.