Long-Term Trends of Observed and Simulated Total Cloud Cover over the Mediterranean Region

Thursday, 18 December 2014
Josep Calbo Angrill1, Arturo Sanchez-Lorenzo1, Aaron Enriquez-Alonso1, Josep-Abel González1, Martin Wild2, Doris Folini2 and Joel R Norris3, (1)University of Girona, Girona, Spain, (2)ETH Swiss Federal Institute of Technology Zurich, Zurich, Switzerland, (3)University of California San Diego, La Jolla, CA, United States
The main limitation when studying changes in cloud forcing and their associated radiative fluxes effects is related to the difficulties in obtaining long-term and homogeneous observations of clouds. In this study, total cloud cover trends provided by different global databases have been compared among them for the Mediterranean region, and for the period 1984-2005. Specifically, databases from surface observations, several satellite projects (ISCCP, CLARA, PATMOS-x) and reanalysis products (ERA-Interim, MERRA, NCEP-DOE) have been chosen. Simulations from 44 climate models of the Coupled Model Intercomparison Project Phase 5 (CMIP5) corresponding to the historical scenario have been compared against the observations. All databases were interpolated to a 2° × 2.5° resolution grid before performing comparisons and statistical analyses. Overall, there is a relatively good agreement between the time evolution of total cloud cover provided by most of the satellite and reanalysis products, as well as from surface observations, with a mean decrease of around 1% per decade over the period 1984-2005. In addition, the historical climate model simulations also indicate a decrease of cloud cover, although with a lower magnitude as compared with observations.