Search Results

You are looking at 11 - 19 of 19 items for :

  • Author or Editor: Doug Smith x
  • Refine by Access: All Content x
Clear All Modify Search
Susanna Corti
,
Tim Palmer
,
Magdalena Balmaseda
,
Antje Weisheimer
,
Sybren Drijfhout
,
Nick Dunstone
,
Wilco Hazeleger
,
Jürgen Kröger
,
Holger Pohlmann
,
Doug Smith
,
Jin-Song von Storch
, and
Bert Wouters

Abstract

The impact of initial conditions relative to external forcings in decadal integrations from an ensemble of state-of-the-art prediction models has been assessed using specifically designed sensitivity experiments (SWAP experiments). They consist of two sets of 10-yr-long ensemble hindcasts for two initial dates in 1965 and 1995 using either the external forcings from the “correct” decades or swapping the forcings between the two decades. By comparing the two sets of integrations, the impact of external forcing versus initial conditions on the predictability over multiannual time scales was estimated as the function of lead time of the hindcast. It was found that over time scales longer than about 1 yr, the predictability of sea surface temperatures (SSTs) on a global scale arises mainly from the external forcing. However, the correct initialization has a longer impact on SST predictability over specific regions such as the North Atlantic, the northwestern Pacific, and the Southern Ocean. The impact of initialization is even longer and extends to wider regions when below-surface ocean variables are considered. For the western and eastern tropical Atlantic, the impact of initialization for the 700-m heat content (HTC700) extends to as much as 9 years for some of the models considered. In all models the impact of initial conditions on the predictability of the Atlantic meridional overturning circulation (AMOC) is dominant for the first 5 years.

Full access
Amy Solomon
,
Lisa Goddard
,
Arun Kumar
,
James Carton
,
Clara Deser
,
Ichiro Fukumori
,
Arthur M. Greene
,
Gabriele Hegerl
,
Ben Kirtman
,
Yochanan Kushnir
,
Matthew Newman
,
Doug Smith
,
Dan Vimont
,
Tom Delworth
,
Gerald A. Meehl
, and
Timothy Stockdale

Abstract

Given that over the course of the next 10–30 years the magnitude of natural decadal variations may rival that of anthropogenically forced climate change on regional scales, it is envisioned that initialized decadal predictions will provide important information for climate-related management and adaptation decisions. Such predictions are presently one of the grand challenges for the climate community. This requires identifying those physical phenomena—and their model equivalents—that may provide additional predictability on decadal time scales, including an assessment of the physical processes through which anthropogenic forcing may interact with or project upon natural variability. Such a physical framework is necessary to provide a consistent assessment (and insight into potential improvement) of the decadal prediction experiments planned to be assessed as part of the IPCC's Fifth Assessment Report.

Full access
Jeff R. Knight
,
Martin B. Andrews
,
Doug M. Smith
,
Alberto Arribas
,
Andrew W. Colman
,
Nick J. Dunstone
,
Rosie Eade
,
Leon Hermanson
,
Craig MacLachlan
,
K. Andrew Peterson
,
Adam A. Scaife
, and
Andrew Williams

Abstract

Decadal climate predictions are now established as a source of information on future climate alongside longer-term climate projections. This information has the potential to provide key evidence for decisions on climate change adaptation, especially at regional scales. Its importance implies that following the creation of an initial generation of decadal prediction systems, a process of continual development is needed to produce successive versions with better predictive skill. Here, a new version of the Met Office Hadley Centre Decadal Prediction System (DePreSys 2) is introduced, which builds upon the success of the original DePreSys. DePreSys 2 benefits from inclusion of a newer and more realistic climate model, the Hadley Centre Global Environmental Model version 3 (HadGEM3), but shares a very similar approach to initialization with its predecessor. By performing a large suite of reforecasts, it is shown that DePreSys 2 offers improved skill in predicting climate several years ahead. Differences in skill between the two systems are likely due to a multitude of differences between the underlying climate models, but it is demonstrated herein that improved simulation of tropical Pacific variability is a key source of the improved skill in DePreSys 2. While DePreSys 2 is clearly more skilful than DePreSys in a global sense, it is shown that decreases in skill in some high-latitude regions are related to errors in representing long-term trends. Detrending the results focuses on the prediction of decadal time-scale variability, and shows that the improvement in skill in DePreSys 2 is even more marked.

Full access
Gerald A. Meehl
,
Lisa Goddard
,
George Boer
,
Robert Burgman
,
Grant Branstator
,
Christophe Cassou
,
Susanna Corti
,
Gokhan Danabasoglu
,
Francisco Doblas-Reyes
,
Ed Hawkins
,
Alicia Karspeck
,
Masahide Kimoto
,
Arun Kumar
,
Daniela Matei
,
Juliette Mignot
,
Rym Msadek
,
Antonio Navarra
,
Holger Pohlmann
,
Michele Rienecker
,
Tony Rosati
,
Edwin Schneider
,
Doug Smith
,
Rowan Sutton
,
Haiyan Teng
,
Geert Jan van Oldenborgh
,
Gabriel Vecchi
, and
Stephen Yeager

This paper provides an update on research in the relatively new and fast-moving field of decadal climate prediction, and addresses the use of decadal climate predictions not only for potential users of such information but also for improving our understanding of processes in the climate system. External forcing influences the predictions throughout, but their contributions to predictive skill become dominant after most of the improved skill from initialization with observations vanishes after about 6–9 years. Recent multimodel results suggest that there is relatively more decadal predictive skill in the North Atlantic, western Pacific, and Indian Oceans than in other regions of the world oceans. Aspects of decadal variability of SSTs, like the mid-1970s shift in the Pacific, the mid-1990s shift in the northern North Atlantic and western Pacific, and the early-2000s hiatus, are better represented in initialized hindcasts compared to uninitialized simulations. There is evidence of higher skill in initialized multimodel ensemble decadal hindcasts than in single model results, with multimodel initialized predictions for near-term climate showing somewhat less global warming than uninitialized simulations. Some decadal hindcasts have shown statistically reliable predictions of surface temperature over various land and ocean regions for lead times of up to 6–9 years, but this needs to be investigated in a wider set of models. As in the early days of El Niño–Southern Oscillation (ENSO) prediction, improvements to models will reduce the need for bias adjustment, and increase the reliability, and thus usefulness, of decadal climate predictions in the future.

Full access
Paolo Ruggieri
,
Alessio Bellucci
,
Dario Nicolí
,
Panos J. Athanasiadis
,
Silvio Gualdi
,
Christophe Cassou
,
Fred Castruccio
,
Gokhan Danabasoglu
,
Paolo Davini
,
Nick Dunstone
,
Rosemary Eade
,
Guillaume Gastineau
,
Ben Harvey
,
Leon Hermanson
,
Saïd Qasmi
,
Yohan Ruprich-Robert
,
Emilia Sanchez-Gomez
,
Doug Smith
,
Simon Wild
, and
Matteo Zampieri

Abstract

The influence of the Atlantic multidecadal variability (AMV) on the North Atlantic storm track and eddy-driven jet in the winter season is assessed via a coordinated analysis of idealized simulations with state-of-the-art coupled models. Data used are obtained from a multimodel ensemble of AMV± experiments conducted in the framework of the Decadal Climate Prediction Project component C. These experiments are performed by nudging the surface of the Atlantic Ocean to states defined by the superimposition of observed AMV± anomalies onto the model climatology. A robust extratropical response is found in the form of a wave train extending from the Pacific to the Nordic seas. In the warm phase of the AMV compared to the cold phase, the Atlantic storm track is typically contracted and less extended poleward and the low-level jet is shifted toward the equator in the eastern Atlantic. Despite some robust features, the picture of an uncertain and model-dependent response of the Atlantic jet emerges and we demonstrate a link between model bias and the character of the jet response.

Open access
Kevin J. Noone
,
Doug W. Johnson
,
Jonathan P. Taylor
,
Ronald J. Ferek
,
Tim Garrett
,
Peter V. Hobbs
,
Philip A. Durkee
,
Kurt Nielsen
,
Elisabeth Öström
,
Colin O’Dowd
,
Michael H. Smith
,
Lynn M. Russell
,
Richard C. Flagan
,
John H. Seinfeld
,
Lieve De Bock
,
René E. Van Grieken
,
James G. Hudson
,
Ian Brooks
,
Richard F. Gasparovic
, and
Robert A. Pockalny

Abstract

A case study of the effects of ship emissions on the microphysical, radiative, and chemical properties of polluted marine boundary layer clouds is presented. Two ship tracks are discussed in detail. In situ measurements of cloud drop size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside-cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to remotely sensed measurements of cloud radiative properties.

The authors examine the processes behind ship track formation in a polluted marine boundary layer as an example of the effects of anthropogenic particulate pollution on the albedo of marine stratiform clouds.

Full access
Kevin J. Noone
,
Elisabeth Öström
,
Ronald J. Ferek
,
Tim Garrett
,
Peter V. Hobbs
,
Doug W. Johnson
,
Jonathan P. Taylor
,
Lynn M. Russell
,
Richard C. Flagan
,
John H. Seinfeld
,
Colin D. O’Dowd
,
Michael H. Smith
,
Philip A. Durkee
,
Kurt Nielsen
,
James G. Hudson
,
Robert A. Pockalny
,
Lieve De Bock
,
René E. Van Grieken
,
Richard F. Gasparovic
, and
Ian Brooks

Abstract

The effects of anthropogenic particulate emissions from ships on the radiative, microphysical, and chemical properties of moderately polluted marine stratiform clouds are examined. A case study of two ships in the same air mass is presented where one of the vessels caused a discernible ship track while the other did not. In situ measurements of cloud droplet size distributions, liquid water content, and cloud radiative properties, as well as aerosol size distributions (outside cloud, interstitial, and cloud droplet residual particles) and aerosol chemistry, are presented. These are related to measurements of cloud radiative properties. The differences between the aerosol in the two ship plumes are discussed;these indicate that combustion-derived particles in the size range of about 0.03–0.3-μm radius were those that caused the microphysical changes in the clouds that were responsible for the ship track.

The authors examine the processes behind ship track formation in a moderately polluted marine boundary layer as an example of the effects that anthropogenic particulate pollution can have in the albedo of marine stratiform clouds.

Full access

Decadal Prediction

Can It Be Skillful?

Gerald A. Meehl
,
Lisa Goddard
,
James Murphy
,
Ronald J. Stouffer
,
George Boer
,
Gokhan Danabasoglu
,
Keith Dixon
,
Marco A. Giorgetta
,
Arthur M. Greene
,
Ed Hawkins
,
Gabriele Hegerl
,
David Karoly
,
Noel Keenlyside
,
Masahide Kimoto
,
Ben Kirtman
,
Antonio Navarra
,
Roger Pulwarty
,
Doug Smith
,
Detlef Stammer
, and
Timothy Stockdale

A new field of study, “decadal prediction,” is emerging in climate science. Decadal prediction lies between seasonal/interannual forecasting and longer-term climate change projections, and focuses on time-evolving regional climate conditions over the next 10–30 yr. Numerous assessments of climate information user needs have identified this time scale as being important to infrastructure planners, water resource managers, and many others. It is central to the information portfolio required to adapt effectively to and through climatic changes. At least three factors influence time-evolving regional climate at the decadal time scale: 1) climate change commitment (further warming as the coupled climate system comes into adjustment with increases of greenhouse gases that have already occurred), 2) external forcing, particularly from future increases of greenhouse gases and recovery of the ozone hole, and 3) internally generated variability. Some decadal prediction skill has been demonstrated to arise from the first two of these factors, and there is evidence that initialized coupled climate models can capture mechanisms of internally generated decadal climate variations, thus increasing predictive skill globally and particularly regionally. Several methods have been proposed for initializing global coupled climate models for decadal predictions, all of which involve global time-evolving three-dimensional ocean data, including temperature and salinity. An experimental framework to address decadal predictability/prediction is described in this paper and has been incorporated into the coordinated Coupled Model Intercomparison Model, phase 5 (CMIP5) experiments, some of which will be assessed for the IPCC Fifth Assessment Report (AR5). These experiments will likely guide work in this emerging field over the next 5 yr.

Full access
William J. Merryfield
,
Johanna Baehr
,
Lauriane Batté
,
Emily J. Becker
,
Amy H. Butler
,
Caio A. S. Coelho
,
Gokhan Danabasoglu
,
Paul A. Dirmeyer
,
Francisco J. Doblas-Reyes
,
Daniela I. V. Domeisen
,
Laura Ferranti
,
Tatiana Ilynia
,
Arun Kumar
,
Wolfgang A. Müller
,
Michel Rixen
,
Andrew W. Robertson
,
Doug M. Smith
,
Yuhei Takaya
,
Matthias Tuma
,
Frederic Vitart
,
Christopher J. White
,
Mariano S. Alvarez
,
Constantin Ardilouze
,
Hannah Attard
,
Cory Baggett
,
Magdalena A. Balmaseda
,
Asmerom F. Beraki
,
Partha S. Bhattacharjee
,
Roberto Bilbao
,
Felipe M. de Andrade
,
Michael J. DeFlorio
,
Leandro B. Díaz
,
Muhammad Azhar Ehsan
,
Georgios Fragkoulidis
,
Sam Grainger
,
Benjamin W. Green
,
Momme C. Hell
,
Johnna M. Infanti
,
Katharina Isensee
,
Takahito Kataoka
,
Ben P. Kirtman
,
Nicholas P. Klingaman
,
June-Yi Lee
,
Kirsten Mayer
,
Roseanna McKay
,
Jennifer V. Mecking
,
Douglas E. Miller
,
Nele Neddermann
,
Ching Ho Justin Ng
,
Albert Ossó
,
Klaus Pankatz
,
Simon Peatman
,
Kathy Pegion
,
Judith Perlwitz
,
G. Cristina Recalde-Coronel
,
Annika Reintges
,
Christoph Renkl
,
Balakrishnan Solaraju-Murali
,
Aaron Spring
,
Cristiana Stan
,
Y. Qiang Sun
,
Carly R. Tozer
,
Nicolas Vigaud
,
Steven Woolnough
, and
Stephen Yeager
Full access