Abstract
The ERA5 reanalysis product has been compared with hourly near-surface wind speed and gust observations across Sweden for 2013–2017. ERA5 shows closer agreement than the previous ERA-Interim reanalysis with regard to both mean wind speed and gust measurements, although significant discrepancies are still found for inland and mountainous regions. Therefore, attempts have been made to improve formulations of the gust parametrization used in ERA5 by adding an elevation-dependency and by adjusting the convective gust contribution. Major improvements, especially over mountain regions, are achieved when the elevation differences among the stations are considered. Closer agreement between the observed and parametrized gusts is reached when the convective gust contribution is also tuned. The newly designed gust parametrization was also tested for Norway, which is characterized by more complex topography. Wind gusts from the selected Norwegian stations are more realistically simulated when both the elevation-dependency and the tuned convective contribution are implemented, although the parametrized gusts are still negatively biased. Such biases are not explained by the different in gust duration in recorded wind gusts between Sweden and Norway.
Highlights
Storms with heavy rainfall and strong winds have been identified as by far the costliest among various types of climate-related and geophysical disasters, with twice the reported losses for either flooding or earthquakes (Wallemacq et al 2018)
This study examines the gust parametrization adopted in ERA5 to understand if the estimated gusts with the current formulation match the measured gust
ERAINT and ERA5 wind outputs are compared with observed WS and WG series to evaluate the skills of these reanalysis products in simulating wind across Sweden
Summary
Storms with heavy rainfall and strong winds have been identified as by far the costliest among various types of climate-related and geophysical disasters, with twice the reported losses for either flooding or earthquakes (Wallemacq et al 2018). Across Scandinavia, the occurrence of extreme winds can affect aviation security, as well as damage buildings and forests, representing severe hazards to people, properties and transport (Achberger et al 2006; Suomi et al 2014). To define the occurrence of extreme wind events, just looking at the near-surface (~ 10 m height) mean wind speed (hereafter, WS), i.e. the mean wind over the last 10 min (WMO 1987), is not sufficient. To capture the abrupt increase in wind and its turbulent signature, the World Meteorological Organization (WMO 1987) suggests recording the so-called near-surface (~ 10 m height) peak or wind gust (hereafter, WG), defined as the maximum 3 s wind speed.
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