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.

Reference:

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.