Wind Lidar Observations in the Lee of Greenland

The Greenland tip jet is a strong windstorm that forms downstream of Cape Farewell in westerly flow. This periodically developing low-level jet is an important mesoscale feature of the atmospheric flow regime in the Irminger Sea. Recently, it has been identified as an important factor in driving the deep sea circulation in this part of the Atlantic. Observations of the vertical structure of the tip jet wind field in the lee of Greenland are rare or non-existing. Here, we present airborne Doppler wind lidar and dropsonde observations of a tip jet event on 24 November 2003. The observations were performed during the Atlantic THORPEX Regional Campaign (ATReC) when the DLR research aircraft Falcon was based in Keflavik, Iceland. The two-dimensional wind cross sections of the scanning Doppler lidar have a horizontal and vertical resolution of 10 km and 100 m, respectively. Along two north-south sections the wind lidar observations show the surprisingly complex structure of the tip jet event: there are at least two different branches of low-level jets, of which the southernmost jet has greater vertical extension and is closer to the southern tip of Greenland. Synoptic-scale and mesoscale analyses place the wind lidar observations into a meteorological context. Additional idealized model simulations of a baroclinic flow past Greenland are performed to study the influence of upstream conditions on the occurrence, strength and downwind extension of the tip jet.