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

摘要

Using a three-model ensemble, predictions of increasing Greenland precipitation overthe 21st century are analyzed using self-organizing maps (SOMs). The models that makeup the three-model ensemble (CCCMA-CGCM3.1(T63), MIROC3.2(hires), and MPI-ECHAM5), which are all atmosphere-ocean global circulation models used in theIntergovernmental Panel on Climate Change Fourth Assessment Report, were chosen dueto their ability to best reproduce North Atlantic surface synoptic climatology andGreenland precipitation from ERA-40. Daily sea level pressure and precipitation data frommodel simulations for years 1961-1999, 2046-2065, and 2081-2100 are compared,where future simulations are based on the SRES A 1 B emissions scenario. Results indicatethat the North Atlantic storm track is predicted to shift northward through the 21st centuryand Greenland precipitation is predicted to increase from 35.8 cm yr~(-1)to 45.8 cm yr~(-1)bythe end of the 21st century, a 27.8% increase. The precipitation change is attributed tochanges in atmospheric circulation, which are due to changes in synoptic patternfrequency of occurrence, and changes in the amount of precipitation that occurs when agiven synoptic circulation pattern occurs, termed intrapattern variability, during the futuretime periods. The northward shift in storm track results in less precipitation beingproduced dynamically over the southeast coast of Greenland, but an increase inprecipitation over the remainder of the ice sheet, with largest increases over the southwestcoast of Greenland and the eastern region. Intrapattern variability changes, however,dominate the future precipitation changes, accounting for 82.5% of the total change. Thisis due to an increase in precipitable water in the atmosphere in response to risingtemperatures. Changes in sea ice and ocean temperature are also thought to contribute tothis change.