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)

You are looking at 1 - 2 of 2 items for :

  • Weather and Forecasting x
  • Refine by Access: All Content x
Clear All
Thomas H. A. Frame
John Methven
Nigel M. Roberts
, and
Helen A. Titley


The statistical properties and skill in predictions of objectively identified and tracked cyclonic features (frontal waves and cyclones) are examined in the 15-day version of the Met Office Global and Regional Ensemble Prediction System (MOGREPS-15). The number density of cyclonic features is found to decline with increasing lead time, with analysis fields containing weak features that are not sustained past the first day of the forecast. This loss of cyclonic features is associated with a decline in area-averaged enstrophy with increasing lead time. Both feature number density and area-averaged enstrophy saturate by around 7 days into the forecast. It is found that the feature number density and area-averaged enstrophy of forecasts produced using model versions that include stochastic energy backscatter saturate at higher values than forecasts produced without stochastic physics. The ability of MOGREPS-15 to predict the locations of cyclonic features of different strengths is evaluated at different spatial scales by examining the Brier skill (relative to the analysis climatology) of strike probability forecasts: the probability that a cyclonic feature center is located within a specified radius. The radius at which skill is maximized increases with lead time from 650 km at 12 h to 950 km at 7 days. The skill is greatest for the most intense features. Forecast skill remains above zero at these scales out to 14 days for the most intense cyclonic features, but only out to 8 days when all features are included irrespective of intensity.

Full access
David M. Schultz
Joseph M. Sienkiewicz


Sting jets, or surface wind maxima at the end of bent-back fronts in Shapiro–Keyser cyclones, are one cause of strong winds in extratropical cyclones. Although previous studies identified the release of conditional symmetric instability as a cause of sting jets, the mechanism to initiate its release remains unidentified. To identify this mechanism, a case study was selected of an intense cyclone over the North Atlantic Ocean during 7–8 December 2005 that possessed a sting jet detected from the NASA Quick Scatterometer (QuikSCAT). A couplet of Petterssen frontogenesis and frontolysis occurred along the bent-back front. The direct circulation associated with the frontogenesis led to ascent within the cyclonically turning portion of the warm conveyor belt, contributing to the comma-cloud head. When the bent-back front became frontolytic, an indirect circulation associated with the frontolysis, in conjunction with alongfront cold advection, led to descent within and on the warm side of the front, bringing higher-momentum air down toward the boundary layer. Sensible heat fluxes from the ocean surface and cold-air advection destabilized the boundary layer, resulting in near-neutral static stability facilitating downward mixing. Thus, descent associated with the frontolysis reaching a near-neutral boundary layer provides a physical mechanism for sting jets, is consistent with previous studies, and synthesizes existing knowledge. Specifically, this couplet of frontogenesis and frontolysis could explain why sting jets occur at the end of the bent-back front and emerge from the cloud head, why sting jets are mesoscale phenomena, and why they only occur within Shapiro–Keyser cyclones. A larger dataset of cases is necessary to test this hypothesis.

Full access