An overview of barrier winds off southeastern Greenland during the Greenland Flow Distortion experiment

During the Greenland Flow Distortion experiment, barrier flow was observed by an instrumented aircraft on 1, 2, 5 and 6 March 2007 off southeastern Greenland. During this time period the barrier flow increased from a narrow jet, ∼15 m/s, to a jet filling almost the whole of the Denmark Strait with maximum wind speed exceeding 40 m/s. Dropsonde observations show that the barrier flow was capped by a sharp temperature inversion below mountain height. Below the inversion was a cold and dry jet, with a larger northerly wind component than that of the flow above, which was also warmer and more moist. Thus, the observations indicate two air masses below mountain height: a cold and dry barrier jet of northern origin and, above this, a warmer and moister air mass that was of cyclonic origin. Numerical simulations emphasize the non-stationarity of the Greenland barrier flow and its dependence on the synoptic situation in the Greenland–Iceland region. They show that the barrier jet originated north of the Denmark Strait and was drawn southward by a synoptic-scale cyclone, with the strength and location of the maximum winds highly dependent on the location of the cyclone relative to the orography of Greenland. Experiments without Greenland's orography suggest a 20 m/s enhancement of the low-level peak wind speeds due to the presence of the barrier. Thus, the Greenland barrier flows are not classic geostrophically balanced barrier flows but have a significant ageostrophic component and are preciselycontrolled by synoptic-scale systems.