Northern Hemisphere winter blocking

The figure shows blocking frequency, for blocking events that persist at least five days, during Northern Hemisphere winter (December-January-February) in two subsets of CMIP5 coupled ocean-atmosphere general circulation models. The model-mean blocking frequency shown in panel (a) is for models with high vertical resolution in the 5-15 km atmospheric layer, while that in panel (b) is for models with coarse vertical resolution in this layer. The 5-15 km layer encompasses the upper troposphere and lowermost extratropical stratosphere. The substantial improvement in blocking frequency for models with higher vertical resolution - particularly over Europe and Greenland - suggests that dynamical processes important to blocking require good vertical resolution at the interface between the troposphere and stratosphere.


Anstey, J.A., Davini, P., Gray, L.J., Woollings, T.J., Butchart, N., Cagnazzo, C., Christiansen, B., Hardiman, S.C., Osprey, S.M., Yang, S. Multi-model analysis of Northern Hemisphere winter blocking, Part I: Model biases and the role of resolution. JGR, accepted.