Satellite derived water balance climatology for the North Atlantic: First results

Abstract

To study the local, regional, and global variability of various components of the atmospheric water balance, HOAPS (Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data) provides for the time period since 1987 global fields of evaporation and precipitation rate (among others), as averages over various time spans and spatial grid sizes. This data set has been analysed for the North Atlantic region with the ultimate goal to detect any correlation of the regional water balance with climatological quantities like the NAO (North Atlantic Oscillation) index. Both evaporation and precipitation and also their difference exhibit in the ten year average the expected spatial distribution. Strong maxima of rain and evaporation are found along the Gulf Stream region. The seasonal cycle reveals the intensified water circulation during winter time.The difference of water balance components between the very different NAO index winters 1994/95 (high) and 1995/96 (low) exhibits a marked reduction in rain in the northern North Atlantic and a corresponding increase towards the subtropical latitudes off the Spanish and north west African coast. At the same time a significant increase of the Gulf Stream rain maximum with a related decrease to the south east of the Gulf Stream region is observed. As the changes in evaporation are smaller, the fresh water balance distribution is mostly determined by the changing rain pattern. In total for the whole winter season, the fresh water flux decreases over the Gulf Stream region and off north-west Africa between high and low NAO winters by a few 100 mm and increases by the same amount elsewhere.