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Systematic Errors in the IPCC AR4 Model Simulations of Atmospheric and Terrestrial Components of the Arctic Ocean Freshwater Budget

Systematic Errors in the IPCC AR4 Model Simulations of Atmospheric and Terrestrial Components of the Arctic Ocean Freshwater Budget

Tatyana Pavlova, Vladimir Kattsov, Valentin Meleshko

Voeikov Main Geophysical Observatory, St.Petersburg, Russia

IPCC AR4 ensemble simulations of atmospheric and terrestrial components of the Arctic Ocean freshwater budget are considered. Precipitation and its difference with evapotranspiration over the Arctic Ocean and its terrestrial watersheds, including the basins of the four major rivers draining into the Arctic Ocean: the Ob, the Yenisey, the Lena, and the Mackenzie, are main foci of the analysis. Compared to the previous (IPCC TAR) generation of AOGCMs, there are some indications that the models as a class have improved in simulations of the arctic precipitation. In spite of observational uncertainties, the models still appear to oversimulate area-averaged precipitation over the major river basins. The model-mean precipitation biases in the Arctic and sub-Arctic have retained their major geographical patterns, which are at least partly attributable to the insufficiently resolved local orography, as well as to biases in large scale atmospheric circulation and sea-ice distribution. The river discharge into the Arctic Ocean is also slightly oversimulated. The simulated annual cycle of precipitation over the Arctic Ocean is in qualitative agreement between the models as well as with observational and reanalysis data. This is also generally the case for the seasonality of precipitation over the Arctic Ocean's terrestrial watersheds, with a few exceptions. Some agreement is demonstrated by the models in reproducing positive 20th century trends of precipitation in the Arctic, as well as positive area-averaged P-E late-20th century trends over the entire terrestrial watershed of the Arctic Ocean.