Changes in synoptic weather patterns and Greenland precipitation in the 20th and 21st centuries: 2. Analysis of 21st century atmospheric changes using self-organizing maps

Using a three-model ensemble, predictions of increasing Greenland precipitation over the 21st century are analyzed using self-organizing maps (SOMs). The models that make up the three-model ensemble (CCCMA-CGCM3.1(T63), MIROC3.2(hires), and MPI-ECHAM5), which are all atmosphere-ocean global circulation models used in the Intergovernmental Panel on Climate Change Fourth Assessment Report, were chosen due to their ability to best reproduce North Atlantic surface synoptic climatology and Greenland precipitation from ERA-40. Daily sea level pressure and precipitation data from model simulations for years 1961-1999, 2046-2065, and 2081-2100 are compared, where future simulations are based on the SRES A1B emissions scenario. Results indicate that the North Atlantic storm track is predicted to shift northward through the 21st century and Greenland precipitation is predicted to increase from 35.8 cm yr(-1) to 45.8 cm yr(-1) by the end of the 21st century, a 27.8% increase. The precipitation change is attributed to changes in atmospheric circulation, which are due to changes in synoptic pattern frequency of occurrence, and changes in the amount of precipitation that occurs when a given synoptic circulation pattern occurs, termed intrapattern variability, during the future time periods. The northward shift in storm track results in less precipitation being produced dynamically over the southeast coast of Greenland, but an increase in precipitation over the remainder of the ice sheet, with largest increases over the southwest coast of Greenland and the eastern region. Intrapattern variability changes, however, dominate the future precipitation changes, accounting for 82.5% of the total change. This is due to an increase in precipitable water in the atmosphere in response to rising temperatures. Changes in sea ice and ocean temperature are also thought to contribute to this change.