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

Abstract

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 −1 , to a jet filling almost the whole of the Denmark Strait with maximum wind speed exceeding 40 m s −1 . 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 −1 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 precisely controlled by synoptic-scale systems.

Forecast Impact of Targeted Observations: Sensitivity to Observation Error and Proximity to Steep Orography

“…The second hypothesis tested is that it is the spreading of observational data from the Greenland sondes that causes the forecast degradation. The first hypothesis is motivated by the effect of Greenland's orography on the local airflow, blocking and distorting it, creating southerly barrier winds, creating tip jets in the lee of Greenland, and altering the temperature profiles by introducing strongly stratified elevated layers (Petersen et al 2009). Sondes placed close to any such steep orography may measure these local effects, which would then make the sonde data unrepresentative of the larger area around it.…”

Multidecadal Mobility of the North Atlantic Oscillation

“…For example, the EA pattern modulates precipitation over southwest England and the Iberian Peninsula (Rodriguez-Puebla et al 1998) and influences the position of the primary North Atlantic storm track and jet streams (Seierstad et al 2007;Woollings et al 2010a). Moore et al (2011) showed that EA pattern played a role in anomalous NAO positive conditions that occurred during the winter of 2007, forcing more frequent barrier winds along the southeast coast of Greenland (Renfrew et al 2008;Petersen et al 2009). In addition, it has been proposed that the EA pattern, in conjunction with the NAO, was responsible for the extremely cold temperatures over Europe during December 2010 (Moore and Renfrew 2012).…”

A climatology of low‐level jets in the mid‐latitudes and polar regions of the Northern Hemisphere

“…Parish, 1982) and Greenland (e.g. Petersen et al, 2009). Katabatic flows, which are very common over continental ice sheets, can also lead to the formation of LLJs (Renfrew and Anderson, 2006).…”