Analysis of observed rapid increases in surface wind speed

Abstract

A database of 21 million hourly observations from 200 weather stations in Iceland within the period from January 1993 until March 2017 is explored to assess rapid increases of wind speed. In the summer, strong winds are more frequent in the afternoon than at night, while rapid increases in wind speed are slightly more frequent at night. Westerly winds have a relatively high frequency of rapid increases in wind speed, while easterly winds have a relatively low frequency of rapid increases in wind speed. This can be explained by the form and tracks of cyclones. Rapid increases in wind speed are particularly frequent in northern Iceland. They occur in winds blowing from the central highlands and typically in stably stratified air masses. Analysis of winds at individual stations reveals a large impact of topography and that the wind direction distribution for strong wind events may be quite different from the wind direction distribution for rapid increases in wind speed. However, a simple and general connection between the height and distance to nearby mountains and the frequency of rapid increases in wind speed has not been found. At stations with a high frequency of rapid increases in wind speed, downslope flow is a very important contributor, while gap and corner winds are not.