Joel Finnis

Synoptic Forcing of Precipitation over Greenland: Climatology for 1961–99

Abstract 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 p...

Simulated Arctic Ocean Freshwater Budgets in the Twentieth and Twenty-First Centuries

The Arctic Ocean freshwater budgets in climate model integrations of the twentieth and twenty-first century are examined. An ensemble of six members of the Community Climate System Model version 3 (CCSM3) is used for the analysis, allowing the anthropogenically forced trends over the integration length to be assessed. Mechanisms driving trends in the budgets are diagnosed, and the implications of changes in the Arctic–North Atlantic exchange on the Labrador Sea and Greenland–Iceland–Norwegian (GIN) Seas properties are discussed. Over the twentieth and the twenty-first centuries, the Arctic freshens as a result of increased river runoff, net precipitation, and decreased ice growth. For many of the budget terms, the maximum 50-yr trends in the time series occur from approximately 1975 to 2025, suggesting that we are currently in the midst of large Arctic change. The total freshwater exchange between the Arctic and North Atlantic increases over the twentieth and twenty-first centuries with decreases in ice export more than compensated for by an increase in the liquid freshwater export. Changes in both the liquid and solid (ice) Fram Strait freshwater fluxes are transported southward by the East Greenland Current and partially removed from the GIN Seas. Nevertheless, reductions in GIN sea ice melt do result from the reduced Fram Strait transport and account for the largest term in the changing ocean surface freshwater fluxes in this region. This counteracts the increased ocean stability due to the warming climate and helps to maintain GIN sea deep-water formation.