Oct 17, 2010

Northern Hemisphere atmospheric stilling partly attributed to an increase in surface roughness

Robert Vautard, Julien Cattiaux, Pascal Yiou, Jean-Noël Thépaut & Philippe Ciais
Nature Geoscience
  • States surface winds have declined in China, the Netherlands, the Czech Republic, the United States and Australia over the past few decades
  • Analyzes the extent and potential cause of changes in surface wind speeds over the northern mid-latitudes between 1979 and 2008, using data from 822 surface weather stations
  • Shows that surface wind speeds have declined by 5–15% over almost all continental areas in the northern mid-latitudes, and that strong winds have slowed faster than weak winds
  • Finds that upper-air winds calculated from sea-level pressure gradients, and winds from weather reanalyses, exhibited no such trend
  • Finds that changes in atmospheric circulation that are captured by reanalysis data explain 10–50% of the surface wind slowdown
  • Finds that mesoscale model simulations suggest that an increase in surface roughness—the magnitude of which is estimated from increases in biomass and land-use change in Eurasia—could explain between 25 and 60% of the stilling
  • Finds regions of pronounced stilling generally coincided with regions where biomass has increased over the past 30 years, supporting the role of vegetation increases in wind slowdown