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R. R. Burton
,
A. M. Blyth
,
Z. Cui
,
J. Groves
,
B. L. Lamptey
,
J. K. Fletcher
,
J. H. Marsham
,
D. J. Parker
, and
A. Roberts

Abstract

The ability to predict heavy rain and floods in Africa is urgently needed to reduce the socioeconomic costs of these events and increase resilience as climate changes. Numerical weather prediction in this region is challenging, and attention is being drawn to observationally based methods of providing short-term nowcasts (up to ∼6-h lead time). In this paper a freely available nowcasting package, pySTEPS, is used to assess the potential to provide nowcasts of satellite-derived convective rain rate for West Africa. By analyzing a large number of nowcasts, we demonstrate that a simple approach of “optical flow” can have useful skill at 2-h lead time on a 10-km scale and 4-h lead time at larger scales (200 km). A diurnal variation in nowcast skill is observed, with the worst-performing nowcasts being those that are initialized at 1500 UTC. Comparison with existing nowcasts is presented. Such nowcasts, if implemented operationally, would be expected to have significant benefits.

Significance Statement

A freely available, easy-to-use nowcasting package has been applied to satellite-retrieved rainfall rates for West Africa, and extrapolations have useful skill at up to 4 h of lead time.

Open access
Sonia Lasher-Trapp
,
Shailendra Kumar
,
Daniel H. Moser
,
Alan M. Blyth
,
Jeffrey R. French
,
Robert C. Jackson
,
David C. Leon
, and
David M. Plummer

ABSTRACT

The Convective Precipitation Experiment (COPE) documented the dynamical and microphysical evolution of convection in southwestern England for testing and improving quantitative precipitation forecasting. A strong warm rain process was hypothesized to produce graupel quickly, initiating ice production by rime splintering earlier to increase graupel production and, ultimately, produce heavy rainfall. Here, convection observed on two subsequent days (2 and 3 August 2013) is used to test this hypothesis and illustrate how environmental factors may alter the microphysical progression. The vertical wind shear and cloud droplet number concentrations on 2 August were 2 times those observed on 3 August. Convection on both days produced comparable maximum radar-estimated rain rates, but in situ microphysical measurements indicated much less ice in the clouds on 2 August, despite having maximum cloud tops that were nearly 2 km higher than on 3 August. Idealized 3D numerical simulations of the convection in their respective environments suggest that the relative importance of particular microphysical processes differed. Higher (lower) cloud droplet number concentrations slow (accelerate) the warm rain process as expected, which in turn slows (accelerates) graupel formation. Rime splintering can explain the abundance of ice observed on 3 August, but it was hampered by strong vertical wind shear on 2 August. In the model, the additional ice produced by rime splintering was ineffective in enhancing surface rainfall; strong updrafts on both days lofted supercooled raindrops well above the 0°C level where they froze to become graupel. The results illustrate the complexity of dynamical–microphysical interactions in producing convective rainfall and highlight unresolved issues in understanding and modeling the competing microphysical processes.

Full access

Energy and Water Cycles in a High-Latitude, North-Flowing River System

Summary of Results from the Mackenzie GEWEX Study—Phase I

W. R. Rouse
,
E. M. Blyth
,
R. W. Crawford
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J. R. Gyakum
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J. R. Janowicz
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B. Kochtubajda
,
H. G. Leighton
,
P. Marsh
,
L. Martz
,
A. Pietroniro
,
H. Ritchie
,
W. M. Schertzer
,
E. D. Soulis
,
R. E. Stewart
,
G. S. Strong
, and
M. K. Woo

The MacKenzie Global Energy and Water Cycle Experiment (GEWEX) Study, Phase 1, seeks to improve understanding of energy and water cycling in the Mackenzie River basin (MRB) and to initiate and test atmospheric, hydrologic, and coupled models that will project the sensitivity of these cycles to climate change and to human activities. Major findings from the study are outlined in this paper. Absorbed solar radiation is a primary driving force of energy and water, and shows dramatic temporal and spatial variability. Cloud amounts feature large diurnal, seasonal, and interannual fluctuations. Seasonality in moisture inputs and outputs is pronounced. Winter in the northern MRB features deep thermal inversions. Snow hydrological processes are very significant in this high-latitude environment and are being successfully modeled for various landscapes. Runoff processes are distinctive in the major terrain units, which is important to overall water cycling. Lakes and wetlands compose much of MRB and are prominent as hydrologic storage systems that must be incorporated into models. Additionally, they are very efficient and variable evaporating systems that are highly sensitive to climate variability. Mountainous high-latitude sub-basins comprise a mosaic of land surfaces with distinct hydrological attributes that act as variable source areas for runoff generation. They also promote leeward cyclonic storm generation. The hard rock terrain of the Canadian Shield exhibits a distinctive energy flux regimen and hydrologic regime. The MRB has been warming dramatically recently, and ice breakup and spring outflow into the Polar Sea has been occurring progressively earlier. This paper presents initial results from coupled atmospheric-hydrologic modeling and delineates distinctive cold region inputs needed for developments in regional and global climate modeling.

Full access
Robert M. Rauber
,
Bjorn Stevens
,
Harry T. Ochs III
,
Charles Knight
,
B. A. Albrecht
,
A. M. Blyth
,
C. W. Fairall
,
J. B. Jensen
,
S. G. Lasher-Trapp
,
O. L. Mayol-Bracero
,
G. Vali
,
J. R. Anderson
,
B. A. Baker
,
A. R. Bandy
,
E. Burnet
,
J.-L. Brenguier
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W. A. Brewer
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P. R. A. Brown
,
R Chuang
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W. R. Cotton
,
L. Di Girolamo
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B. Geerts
,
H. Gerber
,
S. Göke
,
L. Gomes
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B. G. Heikes
,
J. G. Hudson
,
P. Kollias
,
R. R Lawson
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S. K. Krueger
,
D. H. Lenschow
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L. Nuijens
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D. W. O'Sullivan
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R. A. Rilling
,
D. C. Rogers
,
A. P. Siebesma
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E. Snodgrass
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J. L. Stith
,
D. C. Thornton
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S. Tucker
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C. H. Twohy
, and
P. Zuidema

Shallow, maritime cumuli are ubiquitous over much of the tropical oceans, and characterizing their properties is important to understanding weather and climate. The Rain in Cumulus over the Ocean (RICO) field campaign, which took place during November 2004–January 2005 in the trades over the western Atlantic, emphasized measurements of processes related to the formation of rain in shallow cumuli, and how rain subsequently modifies the structure and ensemble statistics of trade wind clouds. Eight weeks of nearly continuous S-band polarimetric radar sampling, 57 flights from three heavily instrumented research aircraft, and a suite of ground- and ship-based instrumentation provided data on trade wind clouds with unprecedented resolution. Observational strategies employed during RICO capitalized on the advances in remote sensing and other instrumentation to provide insight into processes that span a range of scales and that lie at the heart of questions relating to the cause and effects of rain from shallow maritime cumuli.

Full access
Robert M. Rauber
,
Harry T. Ochs III
,
L. Di Girolamo
,
S. Göke
,
E. Snodgrass
,
Bjorn Stevens
,
Charles Knight
,
J. B. Jensen
,
D. H. Lenschow
,
R. A. Rilling
,
D. C. Rogers
,
J. L. Stith
,
B. A. Albrecht
,
P. Zuidema
,
A. M. Blyth
,
C. W. Fairall
,
W. A. Brewer
,
S. Tucker
,
S. G. Lasher-Trapp
,
O. L. Mayol-Bracero
,
G. Vali
,
B. Geerts
,
J. R. Anderson
,
B. A. Baker
,
R. P. Lawson
,
A. R. Bandy
,
D. C. Thornton
,
E. Burnet
,
J-L. Brenguier
,
L. Gomes
,
P. R. A. Brown
,
P. Chuang
,
W. R. Cotton
,
H. Gerber
,
B. G. Heikes
,
J. G. Hudson
,
P. Kollias
,
S. K. Krueger
,
L. Nuijens
,
D. W. O'Sullivan
,
A. P. Siebesma
, and
C. H. Twohy
Full 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
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Dave Bamber
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Christian Barthlott
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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.

Full access
Douglas J. Parker
,
Alan M. Blyth
,
Steven J. Woolnough
,
Andrew J. Dougill
,
Caroline L. Bain
,
Estelle de Coning
,
Mariane Diop-Kane
,
Andre Kamga Foamouhoue
,
Benjamin Lamptey
,
Ousmane Ndiaye
,
Paolo Ruti
,
Elijah A. Adefisan
,
Leonard K. Amekudzi
,
Philip Antwi-Agyei
,
Cathryn E. Birch
,
Carlo Cafaro
,
Hamish Carr
,
Benard Chanzu
,
Samantha J. Clarke
,
Helen Coskeran
,
Sylvester K. Danuor
,
Felipe M. de Andrade
,
Kone Diakaria
,
Cheikh Dione
,
Cheikh Abdoulahat Diop
,
Jennifer K. Fletcher
,
Amadou T. Gaye
,
James L. Groves
,
Masilin Gudoshava
,
Andrew J. Hartley
,
Linda C. Hirons
,
Ishiyaku Ibrahim
,
Tamora D. James
,
Kamoru A. Lawal
,
John H. Marsham
,
J. N. Mutemi
,
Emmanuel Chilekwu Okogbue
,
Eniola Olaniyan
,
J. B. Omotosho
,
Joseph Portuphy
,
Alexander J. Roberts
,
Juliane Schwendike
,
Zewdu T. Segele
,
Thorwald H. M. Stein
,
Andrea L. Taylor
,
Christopher M. Taylor
,
Tanya A. Warnaars
,
Stuart Webster
,
Beth J. Woodhams
, and
Lorraine Youds

Abstract

Africa is poised for a revolution in the quality and relevance of weather predictions, with potential for great benefits in terms of human and economic security. This revolution will be driven by recent international progress in nowcasting, numerical weather prediction, theoretical tropical dynamics, and forecast communication, but will depend on suitable scientific investment being made. The commercial sector has recognized this opportunity and new forecast products are being made available to African stakeholders. At this time, it is vital that robust scientific methods are used to develop and evaluate the new generation of forecasts. The Global Challenges Research Fund (GCRF) African Science for Weather Information and Forecasting Techniques (SWIFT) project represents an international effort to advance scientific solutions across the fields of nowcasting, synoptic and short-range severe weather prediction, subseasonal-to-seasonal (S2S) prediction, user engagement, and forecast evaluation. This paper describes the opportunities facing African meteorology and the ways in which SWIFT is meeting those opportunities and identifying priority next steps. Delivery and maintenance of weather forecasting systems exploiting these new solutions requires a trained body of scientists with skills in research and training, modeling and operational prediction, and communications and leadership. By supporting partnerships between academia and operational agencies in four African partner countries, the SWIFT project is helping to build capacity and capability in African forecasting science. A highlight of SWIFT is the coordination of three weather forecasting “Testbeds”—the first of their kind in Africa—which have been used to bring new evaluation tools, research insights, user perspectives, and communications pathways into a semioperational forecasting environment.

Open access