Arctic System Reanalysis better depicts topographically-forced winds near Greenland

Abstract:

Southern Greenland is characterized by a number of low-level high wind speed weather systems that are the result of topographic flow distortion. These systems include tip jets, barrier winds and katabatic flows. Global atmospheric reanalyses have proven to be important tools in furthering our understanding of these winds and their role in the climate system. However, there is evidence that the mesoscale characteristics of these systems may be poorly resolved in these global products. Here results from the high-resolution regional Arctic System Reanalysis (ASRv1–30 km and ASRv2–15 km) are compared to the global ERA-Interim Reanalysis (ERAI), Danish Meteorological Institute surface stations and research aircraft flights from the Greenland Flow Distortion Experiment (GFDex). With respect to the observations, the ERAI reanalyses shows a bias that results in an underestimation of high wind speeds that is reduced in ASRv1 and nearly eliminated in ASRv2. In addition, there is a systematic reduction in the root mean square error between the observed and the reanalysis wind speeds as one transitions from the ERAI to the ASRv2. Case studies from GFDex reveal that mesoscale features of the winds are better captured in ASRv2 as compared to the ERAI or ASRv1. These include the development of a mesoscale low in the lee of the topography near Cape Farewell during an easterly tip jet event that results in an onshore extension of the region of high winds. The gradient in wind speed along the marginal ice zone is tighter in ASRv2 as well, with localized areas of higher wind speeds associated with katabatic flow and wind speed nadirs downstream of the fjords in the region depicted with greater detail. The decorrelation length scale for the 10m wind speeds in southeast Greenland also indicates that the ASRv2 is better able to resolve the structure in the surface wind field that is the result of complexities in the region’s topography.