Aug 1, 2004

Factors contributing to the summer 2003 European heatwave

Black, Emily, Blackburn, Mike, Harrison, Giles, Hoskins, Brian, Methven, John
  • States the extreme temperatures and lack of precipitation in Europe from May to August 2003 were related to persistent anticyclonic conditions throughout the period
  • States that over the east Atlantic, during May the Azores anticyclone and west African ITCZ were both displaced to the north, while the extratropical storm track was concentrated further south than normal, resulting in a pattern with five zonal bands in cloud and radiative forcing anomalies both at the surface and at TOA
  • Finds that the anomalously clear skies and downward net radiative fluxes led to high SSTs in a strip extending to the west-south-west of Portugal (with flanking low SST anomalies to the north and south)
  • Finds that the clear skies and downward net radiative fluxes also contributed to a strong loss of moisture from the European land surface
  • Finds that during June, the storm track shifted even further south and the anomalous high was much weaker over the Atlantic; however, the high persisted over Europe, resulting in extremely strong radiative anomalies, heating of the land surface, and enhanced latent and sensible heat fluxes into the atmosphere which together almost balanced the radiative anomalies
  • Finds the strong ground heat flux contributed to exceptionally warm nights, sustaining the thermal stress which led to the increased human mortality across Europe
  • Summarizes that in summer 2003 the large-scale atmospheric circulation enabled a dominance of the local heat balance over Europe under clear skies and with an increasingly dry land surface – the result was the exceptionally high temperatures. It is not known at this time why the large-scale circulation had the character it did