Diabatic Influence on Mesoscale Structures in Extratropical Storms (DIAMET)


This collection of articles published in Monthly Weather Review and Weather and Forecasting collects the research results from the DIAMET field and research program in the United Kingdom (UK). DIAMET is a collaboration between the Universities of East Anglia, Leeds, Manchester, and Reading, in conjunction with the UK Met Office, National Centre for Atmospheric Science, and the National Centre for Earth Observation. The overarching theme of DIAMET is the role of diabatic processes in generating mesoscale potential vorticity (PV) and moisture anomalies in cyclonic storms, and the consequences of those anomalies for the weather we experience. Such mesoscale structures come in many forms. Some, such as cold-frontal rainbands, are relatively common, whereas others such as sting jets are rare, but of great scientific interest and potentially high impact. Our focus is on two key diabatic processes: latent heat changes due to condensation/evaporation or change of phase between water and ice; and the flux of latent and sensible heat from the ocean surface, particularly under high-wind conditions. The full preface can be read here.

Collection organizers:
David M. Schultz, Centre for Atmospheric Science, School for Earth, Atmospheric, and Environmental Sciences, The University of Manchester
Geraint Vaughan, National Centre for Atmospheric Science, and Centre for Atmospheric Science, School for Earth, Atmospheric, and Environmental Sciences, The University of Manchester

Visit the DIAMET web page.

Diabatic Influence on Mesoscale Structures in Extratropical Storms (DIAMET)

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David M. Schultz
Bogdan Antonescu
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Alessandro Chiariello


According to the Norwegian cyclone model, whether a warm-type or cold-type occluded front forms depends upon which cold air mass is colder: the prewarm-frontal air mass or the postcold-frontal air mass. For example, a cold-type occlusion is said to occur when the occluded front slopes rearward with height because the prewarm-frontal air mass is warmer than the postcold-frontal air mass. This temperature difference and the resulting occluded-frontal structure in the Norwegian cyclone model is part of what is called the temperature rule. Paradoxically, no clear example of a rearward-sloping, cold-type occluded front has been found in the literature, even though the required temperature difference has been documented in several cases. This article presents the first documented, rearward-sloping, cold-type occluded front. This occluded front forms in a cyclone over the North Atlantic Ocean on 3–5 January 2003 and is documented in model output from the European Centre for Medium-Range Weather Forecasts. Cross sections through the evolving cyclone show the occluded front forms as the less statically stable warm-frontal zone ascends over the more stable cold-frontal zone. Such a stability difference between the cold- and warm-frontal zones is consistent with a previously published hypothesis that the less stable air is lifted by the more stable air to form occluded fronts, in disagreement with the temperature rule. Because warm-frontal zones and the cold air underneath tend to be more stable than cold-frontal zones and the postcold-frontal air, warm-type occluded fronts are much more common than cold-type occluded fronts, explaining why well-defined, rearward-sloping, cold-type occluded fronts are not common in the meteorological literature.

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