Forcing of Precipitation over Greenland: Synoptic Climatology for 1961-1999

Schuenemann, K., J.J. Cassano, and J. Finnis

2008, Journal of Hydrometeorology , Accepted pending revisions

Analysis of the synoptic climatology and precipitation patterns over the North Atlantic region allows us to better understand the atmospheric input to the mass balance of the Greenland ice sheet. The self-organizing map (SOM) technique was applied to ERA-40 reanalysis average 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 and patterns common to each season are shown. Analysis of precipitation patterns associated with each SLP pattern revealed the details of the forcing for precipitation over Greenland. The largest precipitation events were associated with passing cyclones that created onshore flow, allowing for the air to be lifted orographically by the steep margins of the ice sheet. Greenland was divided into five sub-regions and the preferred synoptic pattern for receiving precipitation in each region is discussed. The ERA-40 reanalysis average annual precipitation over all of Greenland from 1961 to 1999 was 35.8 cm yr^-1 . Annual contributions from each SLP anomaly pattern was isolated to reveal that 50% of the precipitation over Greenland comes from only 31% of the synoptic patterns, highlighting the importance of studying Greenland precipitation on an event by event basis on a daily timescale. This synoptic climatology of the North Atlantic region can be used as a basis for understanding the synoptic forcing responsible for past and future Greenland precipitation trends, which is the focus of ongoing research.