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  • Author or Editor: D. G. Gray x
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G. R. Gray
,
R. J. Serafin
,
D. Atlas
,
R. E. Rinehart
, and
J. J. Boyajian

Color enhancement of images has become a powerful tool in rapid evaluation of grey-scale information. Recent advances in semiconductor technology have made possible the construction of an inexpensive digital real-time color-enhanced (or false-color) display for meteorological radar information such as reflectivity and Doppler velocities. Variable magnification allows detailed analysis of selected areas of the radar coverage.

The display was interfaced to a Doppler/reflectivity processor on the NHRE S-band radar at Grover, Colorado, during the 1974 hail season. A preliminary meteorological analysis of the Doppler color displays of the storm of 7 August 1974 demonstrates a large variety of significant features which may be observed either in real-time or subsequently. These include the regions of convergence and vorticity, major inflow and outflow regions, and turbulence. Most importantly, it is shown that the updraft cores can be identified with the easterly-momentum air which has been transported upward with the drafts from the lower levels. In view of the slow eastward motion of the storm system, the very large Doppler components found at the leading edge of the higher-level echo pattern also indicate rapid evaporation of the particles as they move out into the clear, dry environmental air. It is the resulting evaporative cooling which is responsible for the downdrafts in this vicinity. Among the many real-time applications of the color Doppler display, perhaps the most important in the artificial modification of convective storms is the location of the major inflow and updraft regions. These determine where seeding should be focused. The use of the color display also permits the ready discrimination of storm echoes from ground clutter in which they are frequently obscured. Its applicability to the detection of tornado cyclones and hurricane velocity mapping is also self-evident.

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R. T. Sutton
,
G. D. McCarthy
,
J. Robson
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B. Sinha
,
A. T. Archibald
, and
L. J. Gray

Abstract

Atlantic multidecadal variability (AMV) is the term used to describe the pattern of variability in North Atlantic sea surface temperatures (SSTs) that is characterized by decades of basinwide warm or cool anomalies, relative to the global mean. AMV has been associated with numerous climate impacts in many regions of the world including decadal variations in temperature and rainfall patterns, hurricane activity, and sea level changes. Given its importance, understanding the physical processes that drive AMV and the extent to which its evolution is predictable is a key challenge in climate science. A leading hypothesis is that natural variations in ocean circulation control changes in ocean heat content and consequently AMV phases. However, this view has been challenged recently by claims that changing natural and anthropogenic radiative forcings are critical drivers of AMV. Others have argued that changes in ocean circulation are not required. Here, we review the leading hypotheses and mechanisms for AMV and discuss the key debates. In particular, we highlight the need for a holistic understanding of AMV. This perspective is a key motivation for a major new U.K. research program: the North Atlantic Climate System Integrated Study (ACSIS), which brings together seven of the United Kingdom’s leading environmental research institutes to enable a broad spectrum approach to the challenges of AMV. ACSIS will deliver the first fully integrated assessment of recent decadal changes in the North Atlantic, will investigate the attribution of these changes to their proximal and ultimate causes, and will assess the potential to predict future changes.

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I. A. Renfrew
,
G. W. K. Moore
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J. E. Kristjánsson
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H. Ólafsson
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S. L. Gray
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G. N. Petersen
,
K. Bovis
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P. R. A. Brown
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I. Føre
,
T. Haine
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C. Hay
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E. A. Irvine
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A Lawrence
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T. Ohigashi
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S. Outten
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R. S. Pickart
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M. Shapiro
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D. Sproson
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R. Swinbank
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A. Woolley
, and
S. Zhang

Greenland has a major influence on the atmospheric circulation of the North Atlantic-western European region, dictating the location and strength of mesoscale weather systems around the coastal seas of Greenland and directly influencing synoptic-scale weather systems both locally and downstream over Europe. High winds associated with the local weather systems can induce large air-sea fluxes of heat, moisture, and momentum in a region that is critical to the overturning of the thermohaline circulation, and thus play a key role in controlling the coupled atmosphere-ocean climate system.

The Greenland Flow Distortion Experiment (GFDex) is investigating the role of Greenland in defining the structure and predictability of both local and downstream weather systems through a program of aircraft-based observation and numerical modeling. The GFDex observational program is centered upon an aircraft-based field campaign in February and March 2007, at the dawn of the International Polar Year. Twelve missions were flown with the Facility for Airborne Atmospheric Measurements' BAe-146, based out of the Keflavik, Iceland. These included the first aircraft-based observations of a reverse tip jet event, the first aircraft-based observations of barrier winds off of southeast Greenland, two polar mesoscale cyclones, a dramatic case of lee cyclogenesis, and several targeted observation missions into areas where additional observations were predicted to improve forecasts.

In this overview of GFDex the background, aims and objectives, and facilities and logistics are described. A summary of the campaign is provided, along with some of the highlights of the experiment.

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

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.

Open access
Keith A. Browning
,
Alan M. Blyth
,
Peter A. Clark
,
Ulrich Corsmeier
,
Cyril J. Morcrette
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Judith L. Agnew
,
Sue P. Ballard
,
Dave Bamber
,
Christian Barthlott
,
Lindsay J. Bennett
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Karl M. Beswick
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Mark Bitter
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Karen E. Bozier
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Barbara J. Brooks
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Chris G. Collier
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Fay Davies
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Bernhard Deny
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Mark A. Dixon
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Thomas Feuerle
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Richard M. Forbes
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Catherine Gaffard
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Malcolm D. Gray
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Rolf Hankers
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Tim J. Hewison
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Norbert Kalthoff
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Samiro Khodayar
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Martin Kohler
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Christoph Kottmeier
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Stephan Kraut
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Michael Kunz
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Darcy N. Ladd
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Humphrey W. Lean
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Jürgen Lenfant
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Zhihong Li
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John Marsham
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James McGregor
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Stephan D. Mobbs
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John Nicol
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Emily Norton
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Douglas J. Parker
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Felicity Perry
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Markus Ramatschi
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Hugo M. A. Ricketts
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Nigel M. Roberts
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Andrew Russell
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Helmut Schulz
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Elizabeth C. Slack
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Geraint Vaughan
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Joe Waight
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David P. Wareing
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Robert J. Watson
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Ann R. Webb
, and
Andreas Wieser

The Convective Storm Initiation Project (CSIP) is an international project to understand precisely where, when, and how convective clouds form and develop into showers in the mainly maritime environment of southern England. A major aim of CSIP is to compare the results of the very high resolution Met Office weather forecasting model with detailed observations of the early stages of convective clouds and to use the newly gained understanding to improve the predictions of the model.

A large array of ground-based instruments plus two instrumented aircraft, from the U.K. National Centre for Atmospheric Science (NCAS) and the German Institute for Meteorology and Climate Research (IMK), Karlsruhe, were deployed in southern England, over an area centered on the meteorological radars at Chilbolton, during the summers of 2004 and 2005. In addition to a variety of ground-based remote-sensing instruments, numerous rawinsondes were released at one- to two-hourly intervals from six closely spaced sites. The Met Office weather radar network and Meteosat satellite imagery were used to provide context for the observations made by the instruments deployed during CSIP.

This article presents an overview of the CSIP field campaign and examples from CSIP of the types of convective initiation phenomena that are typical in the United Kingdom. It shows the way in which certain kinds of observational data are able to reveal these phenomena and gives an explanation of how the analyses of data from the field campaign will be used in the development of an improved very high resolution NWP model for operational use.

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