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  • Diabatic Influence on Mesoscale Structures in Extratropical Storms (DIAMET) x
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G. Vaughan, J. Methven, D. Anderson, B. Antonescu, L. Baker, T. P. Baker, S. P. Ballard, K. N. Bower, P. R. A. Brown, J. Chagnon, T. W. Choularton, J. Chylik, P. J. Connolly, P. A. Cook, R. J. Cotton, J. Crosier, C. Dearden, J. R. Dorsey, T. H. A. Frame, M. W. Gallagher, M. Goodliff, S. L. Gray, B. J. Harvey, P. Knippertz, H. W. Lean, D. Li, G. Lloyd, O. Martínez–Alvarado, J. Nicol, J. Norris, E. Öström, J. Owen, D. J. Parker, R. S. Plant, I. A. Renfrew, N. M. Roberts, P. Rosenberg, A. C. Rudd, D. M. Schultz, J. P. Taylor, T. Trzeciak, R. Tubbs, A. K. Vance, P. J. van Leeuwen, A. Wellpott, and A. Woolley

The combination of new aircraft measurements and high-resolution modeling reveal finescale wind structure in an intense extratropical windstorm. Extratropical cyclones approaching western Europe along the North Atlantic storm track are a major cause of damaging winds and heavy precipitation. 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

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David M. Schultz, Bogdan Antonescu, and Alessandro Chiariello

was discovered during the third author’s master’s thesis research ( Chiariello 2006 ). Therefore, the purpose of this article is to present this cold-type occluded front and to demonstrate its consistency with the static-stability rule. 2. Case study of a cold-type occluded front This case was found from looking at occluded fronts over the North Atlantic Ocean using model output from the European Centre for Medium-Range Weather Forecasts at 0.25° × 0.25° latitude–longitude gridded analyses. At

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Oscar Martínez-Alvarado, Suzanne L. Gray, and John Methven

1. Introduction Intense precipitation in summer over western Europe is largely associated with the passage of extratropical cyclones. Using data from the Global Precipitation Climatology Project daily precipitation dataset ( Huffman et al. 2001 ; Adler et al. 2003 ) and the ERA-Interim product ( Simmons et al. 2007 ; Dee et al. 2011 ), Hawcroft et al. (2012) determined that more than 65% of total precipitation during June–August is associated with extratropical cyclones over the United

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G. Lloyd, C. Dearden, T. W. Choularton, J. Crosier, and K. N. Bower

low pressure system developed, pushing a cold front from west to east across the United Kingdom, which eventually reached mainland Europe by 0000 UTC 30 November. This cold front was particularly active over northern England with a squall line and damage caused by a tornado reported in the greater Manchester area. Fig . 1. Met Office surface pressure charts for the (a),(b) cold front case; (c),(d) the warm front case; and (e),(f) the occluded frontal case: (left) 1200 and (right) 1800 UTC. (Source

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H. F. Dacre, P. A. Clark, O. Martinez-Alvarado, M. A. Stringer, and D. A. Lavers

generates and is enhanced by latent heating associated with cloud processes. Such feedback-driven enhancement is included in our analysis but is not isolated as a separate factor. METHOD. Cyclone tracking and dataset. Following the work of Catto et al. (2010) , we apply an objective cyclone identification and tracking algorithm ( Hodges 1995 ) to fields from the Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) for the winter periods (December–February) of

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David M. Schultz and Joseph M. Sienkiewicz

region. The term refers to Grønås's (1995) invocation of the “poisonous tail of the bent-back occlusion,” deriving from the Norwegian School's recognition of strong winds at the end of a bent-back occluded front in many cyclones that are now known as Shapiro–Keyser (1990) cyclones. Wind speed maxima resembling sting jets have been identified in other North Atlantic, North Pacific, and European cyclones (e.g., Von Ahn et al. 2005 ; Parton et al. 2010 ; Baker et al. 2013b ). Martínez

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Geraint Vaughan, Bogdan Antonescu, David M. Schultz, and Christopher Dearden

Weather Research and Forecasting Model (hereafter WRF; Skamarock et al. 2008 ) version 3.3.1, a compressible, nonhydrostatic, three-dimensional mesoscale model. The simulation used a single 356 × 266 gridpoint domain with 9-km horizontal grid spacing and 100 vertical levels. Initial and lateral boundary conditions came from the 0.25° European Centre for Medium-Range Weather Forecasts (ECMWF) analyses. The simulation was initialized at 0000 UTC 15 September 2011 and run for 42 h with output every 30

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Jeffrey M. Chagnon and Suzanne L. Gray

heat and moisture are transported from the boundary layer poleward and into the upper troposphere. These features are typical of extratropical cyclones in the North Atlantic. Fig . 1. Meteosat visible channel satellite images over the North Atlantic and western Europe, valid at (a) 1200 UTC 23 Sep 2011 (case I), (b) 1200 UTC 29 Nov 2011 (case II), and (c) 1100 UTC 24 Nov 2009 (case III). Images provided courtesy of EUMETSAT. Figure 2 presents the full PV in each of the three cases after 24 h of

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Thomas H. A. Frame, John Methven, Nigel M. Roberts, and Helen A. Titley

Titley (2010) was introduced to run on the 15-day version of the Met Office Global and Regional Ensemble Prediction System (MOGREPS-15) ( Bowler et al. 2009 ) forecasts in 2006, and has since been implemented in the European Centre for Medium-Range Weather Forecasts Integrated Forecast System. The tracking methodology is one of those being used in the Intercomparison of Mid Latitude Storm Diagnostics ( Neu et al. 2013 ). MOGREPS-15 was run as part of the THORPEX Interactive Grand Global Ensemble

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Ross N. Bannister

) programmes, and also by the European Space Agency (ESA). The author would like to thank Jonathan Flowerdew (Met Office) for useful discussions and Stefano Migliorini, Laura Baker, and Ali Rudd (University of Reading), and Simon Wilson (Met Office and National Centre for Atmospheric Science) for essential work in producing the ensemble. Use of the MONSooN computer system is acknowledged, a collaborative facility supplied under the Joint Weather and Climate Research Programme, which is a strategic

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