Analysis of the synoptic climatology and precipitation patterns over the North Atlantic region allows for a better understanding of the atmospheric input to the mass balance of the Greenland ice sheet. The self-organizing map (SOM) technique was applied to the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) daily sea level pressure (SLP) data from 1961 to 1999 to objectively identify synoptic SLP patterns over the North Atlantic region. A total of 35 different SLP patterns were identified. Patterns common to the winter season are characterized by deep low pressure systems that approach Greenland through an active North Atlantic storm track, whereas patterns most common to the summer months are generally weaker and approach the ice sheet from the west through Baffin Bay. The blocking, splitting, and intensification of cyclones by the high elevations of the Greenland ice sheet were identified in this analysis.Analysis of ERA-40 precipitation associated with each SLP pattern revealed that the largest precipitation events were associated with passing cyclones that created onshore flow, allowing the air to be lifted orographically by the steep margins of the ice sheet. The ERA-40 annual mean precipitation over Greenland from 1961 to 1999 was 35.8 cm yr 21 . Greenland was divided into five subregions, and the preferred synoptic patterns for receiving precipitation in each region include cyclones positioned to allow dynamic and orographic lift in each region. Annual precipitation contributions from each SLP pattern were isolated to reveal that half of the annual mean precipitation over Greenland comes from only 11 of the 35 identified synoptic patterns (31.4%), highlighting the importance of studying Greenland precipitation on an event-by-event basis on a daily time scale.

[1] 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 [2046][2047][2048][2049][2050][2051][2052][2053][2054][2055][2056][2057][2058][2059][2060][2061][2062][2063][2064][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 À1 to 45.8 cm yr À1 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.Citation: Schuenemann, K. C., and J. J. Cassano (2010), 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,

[1] Using the self-organizing map (SOM) technique, the sea level pressure synoptic climatology and precipitation of 15 Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) models are compared to that of the ERA-40 reanalysis for the North Atlantic region for the period 1961 to 1999. Three of the models, the CCCMA-CGCM3.1(T63), the MIROC3.2(hires), and the MPI-ECHAM5, best reproduce the ERA-40 synoptic climatology and are chosen for further analysis of precipitation over Greenland. The MIROC3.2(hires) is the best single performing model, in that it best matches ERA-40. Although the three-model ensemble simulates the same mean annual precipitation over Greenland as ERA-40, the ensemble simulates the mean annual precipitation differently than ERA-40. A dry bias in the CCCMA-CGCM3.1(T63) and a wet bias from the MPI-ECHAM5 cancel in the ensemble average. The mean annual precipitation difference between the model ensemble, as well as each individual model, and ERA-40 is then attributed to differences in intrapattern variability and pattern frequency components in the models that make up the ensemble. Pattern frequency differences between the model and ERA-40 indicate a difference in the occurrence of synoptic weather patterns, while intrapattern variability differences denote differences in the amount of precipitation produced when a given synoptic weather pattern occurs. Intrapattern variability differences between the models and ERA-40 are predominantly responsible for Greenland precipitation differences, but pattern frequency (circulation) differences in the models also play a small role. Part 2 of this paper uses this three-model ensemble to analyze and attribute predicted increases in precipitation over the Greenland ice sheet for the 21st century.Citation: Schuenemann, K. C., and J. J. Cassano (2009), Changes in synoptic weather patterns and Greenland precipitation in the 20th and 21st centuries: 1. Evaluation of late 20th century simulations from IPCC models,

The surface mass balance of the Greenland ice sheet has decreased in recent decades with important implications for global sea level rise. Here a climate reanalysis model is used to examine observed circulation variability and changes in precipitation across southern Greenland to gain insight into the future climate in the region. The influence on precipitation from the North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO), Icelandic Low, Azores High, regional blocking patterns, and near‐surface temperature and winds are explored. Statistically significant correlations are higher between precipitation and the Icelandic Low and near‐surface winds (0.5–0.7; p < 0.05) than correlations between precipitation and either the NAO or AMO climate indices (southwest Greenland: r = 0.12 and 0.28, respectively; and southeast Greenland: r = 0.25 and −0.07, respectively). Moreover, the recent enhanced warming in the Arctic (Arctic amplification) and the increase in the Greenland Blocking Index coincide with increased mean annual precipitation and interannual variability in southwest Greenland.