Abstract
Abstract The Diabatic Influences on Mesoscale Structures in Extratropical Storms (DIAMET) project aims to improve forecasts of high-impact weather in extratropical cyclones through field measurements, high-resolution numerical modeling, and improved design of ensemble forecasting and data assimilation systems. This article introduces DIAMET and presents some of the first results. Four field campaigns were conducted by the project, one of which, in late 2011, coincided with an exceptionally stormy period marked by an unusually strong, zonal North Atlantic jet stream and a succession of severe windstorms in northwest Europe. As a result, December 2011 had the highest monthly North Atlantic Oscillation index (2.52) of any December in the last 60 years. Detailed observations of several of these storms were gathered using the U.K.’s BAe 146 research aircraft and extensive ground-based measurements. As an example of the results obtained during the campaign, observations are presented of Extratropical Cyclone Friedhelm on 8 December 2011, when surface winds with gusts exceeding 30 m s–1 crossed central Scotland, leading to widespread disruption to transportation and electricity supply. Friedhelm deepened 44 hPa in 24 h and developed a pronounced bent-back front wrapping around the storm center. The strongest winds at 850 hPa and the surface occurred in the southern quadrant of the storm, and detailed measurements showed these to be most intense in clear air between bands of showers. High-resolution ensemble forecasts from the Met Office showed similar features, with the strongest winds aligned in linear swaths between the bands, suggesting that there is potential for improved skill in forecasts of damaging winds.
Highlights
We report on initial results from the Diabatic Influences on Mesoscale Structures in Extratropical Storms (DIAMET) project, which aims to improve our understanding and predictions of mesoscale structures within extratropical cyclones by means of field measurements, high-resolution modeling, and improved design of ensemble forecasting and data assimilation systems
A research project on storms presents an excellent opportunity for outreach activities, and in DIAMET we collaborated with an award-winning educational consultant, Heather Reid, to develop a package of educational resources for school children related to our key science aims
intensive observation period (IOP) 8 took the investigators into the extreme winds of Extratropical Cyclone
Summary
Results from the DIAMET Project by G. A particular problem in forecasting these cyclones is that the highest-impact weather within them arises from mesoscale structures such as fronts and bands of strong winds. These structures are influenced by diabatic processes (those that add or remove heat from the air) such as latent heating and cooling associated with phase changes of water, fluxes of heat and moisture from the Earth’s surface, and radiative flux convergence. Key elements in diabatic processes are turbulence, convection, and cloud physics—small-scale phenomena that cannot be represented explicitly in numerical weather prediction models. We report on initial results from the Diabatic Influences on Mesoscale Structures in Extratropical Storms (DIAMET) project, which aims to improve our understanding and predictions of mesoscale structures within extratropical cyclones by means of field measurements, high-resolution modeling, and improved design of ensemble forecasting and data assimilation systems.
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