Characteristics of winter cyclone activity in the northern North Atlantic: Insights from observations and regional modeling

摘要

Fields from the NCEP/NCAR reanalysis are used in conjunction with simulations from Polar MM5 to examine regional processes contributing to cyclone development in the sub-Arctic/Arctic sector of the North Atlantic. Strong deepening of systems (>6 hPa/6 hours) is especially common south of the tip of Greenland and in the vicinity of the mean Icelandic Low (IL). A secondary maximum is located just south of Svalbard. Composite analyses of strongly deepening systems in these areas point to the influence of pronounced preexisting low-level temperature gradients linked to ocean currents, the sea ice margin and ocean-land contrasts. The area of preferred deepening near Svalbard corresponds to the northernmost penetration of open water in the North Atlantic. Impacts of Greenland's orography are prominent in the synoptic complexity of the region. Typical synoptic situations, examined as case studies, include splitting, or “bifurcation” of cyclones at the southern tip of Greenland; orographic cyclogenesis in the lee of Greenland, at the location of the mean IL; and deepening of preexisting systems near the IL. Orographic influences are clearly captured in Polar MM5 simulations for which control runs of the three cases are compared to runs for which the orography of Greenland is removed.