Low-wind climatology (1979–2018) over Europe from ERA5 reanalysis

Abstract

Research on wind speed characteristics is of interest for many disciplines from renewable energy to ecology. Whereas mean values and trends are commonly studied, less attentions is paid to the evaluation of other features such as low-wind conditions. However, there is no clear definition of “low-wind” on the literature. Here we propose the Beaufort scale to characterize low-wind values over Europe through a fixed threshold of 3.3 m/s (“light breeze" category). Climatological (1979–2018) assessment is performed using ERA5 reanalysis hourly data. The limited amount of observational stations indicate a 40-year averaged amount of around 3500 low-wind hours/year, comparable to the corresponding ERA5 reanalysis cells, which shows severe limitations over mountainous areas. The European domain features a strong north–south low-wind hours gradient. Remarkable patterns are obtained over coasts and complex orography regions. Seasonal low-wind variability range around 20–25% for most of the regions, and interannual coefficient of variability from 0.05 to 0.17. Oceanic regions present smaller low-wind values than land areas, with Atlantic and Mediterranean regions behaving differently. The largest annual spells (consecutive) hourly low-wind episodes are within the range from 5 to 10 days, (from 120 to 240 h) over many land areas. Annual mean hourly wind spells typically extend from 15 to 25 h, with more than 200 episodes.