Multi-model analysis of Northern Hemisphere winter blocking: Model biases and the role of resolution
Journal of Geophysical Research Atmospheres 118:10 (2013) 3956-3971
Abstract:
Blocking of the tropospheric jet stream during Northern Hemisphere winter (December-January-February) is examined in a multi-model ensemble of coupled atmosphere-ocean general circulation models (GCMs) obtained from the Coupled Model Intercomparison Project Phase 5 (CMIP5). The CMIP5 models exhibit large biases in blocking frequency and related biases in tropospheric jet latitude, similar to earlier generations of GCMs. Underestimated blocking at high latitudes, especially over Europe, is common. In general, model biases decrease as model resolution increases. Increased blocking frequency at high latitudes in both the Atlantic and Pacific basins, as well as more realistic variability of Atlantic jet latitude, are associated with increased vertical resolution in the mid-troposphere to lowermost stratosphere. Finer horizontal resolution is associated with higher blocking frequency at all latitudes in the Atlantic basin but appears to have no systematic impact on blocking near Greenland or in the Pacific basin. Results from the CMIP5 analysis are corroborated by additional controlled experiments using selected GCMs. Key PointsCMIP5 models have large blocking biases and associated jet biasesIncreased spatial resolution is associated with reduced blocking and jet biasesVertical and horizontal resolution give blocking changes in different regions ©2013. American Geophysical Union. All Rights Reserved.Atmospheric blocking in a high resolution climate model: Influences of mean state, orography and eddy forcing
Atmospheric Science Letters 14:1 (2013) 34-40
Abstract:
An underestimate of atmospheric blocking occurrence is a well-known limitation of many climate models. This article presents an analysis of Northern Hemisphere winter blocking in an atmospheric model with increased horizontal resolution. European blocking frequency increases with model resolution, and this results from an improvement in the atmospheric patterns of variability as well as a simple improvement in the mean state. There is some evidence that the transient eddy momentum forcing of European blocks is increased at high resolution, which could account for this. However, it is also shown that the increase in resolution of the orography is needed to realise the improvement in blocking, consistent with the increase in height of the Rocky Mountains acting to increase the tilt of the Atlantic jet stream and giving higher mean geopotential heights over northern Europe. Blocking frequencies in the Pacific sector are also increased with atmospheric resolution, but in this case the improvement in orography actually leads to a decrease in blocking © 2013 Royal Meteorological Society and British Crown.EXPLAINING EXTREME EVENTS OF 2012 FROM A CLIMATE PERSPECTIVE
BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY 94:9 (2013) S1-S74
Influence of the Southern Annular Mode on Projected Weakening of the Atlantic Meridional Overturning Circulation
JOURNAL OF CLIMATE 26:20 (2013) 8017-8036
Variability of the North Atlantic summer storm track: mechanisms and impacts on European climate
ENVIRONMENTAL RESEARCH LETTERS 8:3 (2013) ARTN 034037