Search Results

You are looking at 11 - 15 of 15 items for :

  • Author or Editor: John McGregor x
  • Refine by Access: All Content x
Clear All Modify Search
Faye T. Cruz
,
Andrew J. Pitman
,
John L. McGregor
, and
Jason P. Evans

Abstract

Using a coupled atmosphere–land surface model, simulations were conducted to characterize the regional climate changes that result from the response of stomates to increases in leaf-level carbon dioxide (CO2) under differing conditions of moisture availability over Australia. Multiple realizations for multiple Januarys corresponding to dry and wet years were run, where only the leaf-level CO2 was varied at 280, 375, 500, 650, 840, and 1000 ppmv and the atmospheric CO2 was fixed at 375 ppmv. The results show the clear effect of increasing leaf-level CO2 on the transpiration via the stomatal response, particularly when sufficient moisture is available. Statistically significant reductions in transpiration generally lead to a significantly warmer land surface with decreases in rainfall. Increases in CO2 lead to increases in the magnitude and areal extent of the statistically significant mean changes in the surface climate. However, the results also show that the availability of moisture substantially affects the effect of increases in the leaf-level CO2, particularly for a moisture-limited region. The physiological feedback can indirectly lead to more rainfall via changes in the low-level moisture convergence and vertical velocity, which result in a cooling simulated over Western Australia. The significant changes in the surface climate presented in the results suggest that it is still important to incorporate these feedbacks in future climate assessments and projections for Australia. The influence of moisture availability also indicates that the capacity of the physiological feedback to affect the future climate may be affected by uncertainties in rainfall projections, particularly for water-stressed regions such as Australia.

Full access
Congbin Fu
,
Shuyu Wang
,
Zhe Xiong
,
William J. Gutowski
,
Dong-Kyou Lee
,
John L. McGregor
,
Yasuo Sato
,
Hisashi Kato
,
Jeong-Woo Kim
, and
Myoung-Seok Suh

Improving the simulation of regional climate change is one of the high-priority areas of climate study because regional information is needed for climate change impact assessments. Such information is especially important for the region covered by the East Asian monsoon where there is high variability in both space and time. To this end, the Regional Climate Model Intercomparison Project (RMIP) for Asia has been established to evaluate and improve regional climate model (RCM) simulations of the monsoon climate. RMIP operates under joint support of the Asia–Pacific Network for Global Change Research (APN), the Global Change System for Analysis, Research and Training (START), the Chinese Academy of Sciences, and several projects of participating nations. The project currently involves 10 research groups from Australia, China, Japan, South Korea, and the United States, as well as scientists from India, Italy, Mongolia, North Korea, and Russia.

RMIP has three simulation phases: March 1997–August 1998, which covers a full annual cycle and extremes in monsoon behavior; January 1989–December 1998, which examines simulated climatology; and a regional climate change scenario, involving nesting with a global model. This paper is a brief report of RMIP goals, implementation design, and some initial results from the first phase studies.

Full access
John R. Gyakum
,
Marco Carrera
,
Da-Lin Zhang
,
Steve Miller
,
James Caveen
,
Robert Benoit
,
Thomas Black
,
Andrea Buzzi
,
Cliément Chouinard
,
M. Fantini
,
C. Folloni
,
Jack J. Katzfey
,
Ying-Hwa Kuo
,
François Lalaurette
,
Simon Low-Nam
,
Jocelyn Mailhot
,
P. Malguzzi
,
John L. McGregor
,
Masaomi Nakamura
,
Greg Tripoli
, and
Clive Wilson

Abstract

The authors evaluate the performance of current regional models in an intercomparison project for a case of explosive secondary marine cyclogenesis occurring during the Canadian Atlantic Storms Project and the Genesis of Atlantic Lows Experiment of 1986. Several systematic errors are found that have been identified in the refereed literature in prior years. There is a high (low) sea level pressure bias and a cold (warm) tropospheric temperature error in the oceanic (continental) regions. Though individual model participants produce central pressures of the secondary cyclone close to the observed during the final stages of its life cycle, systematically weak systems are simulated during the critical early stages of the cyclogenesis. Additionally, the simulations produce an excessively weak (strong) continental anticyclone (cyclone); implications of these errors are discussed in terms of the secondary cyclogenesis. Little relationship between strong performance in predicting the mass field and skill in predicting a measurable amount of precipitation is found. The bias scores in the precipitation study indicate a tendency for all models to overforecast precipitation. Results for the measurable threshold (0.2 mm) indicate the largest gain in precipitation scores results from increasing the horizontal resolution from 100 to 50 km, with a negligible benefit occurring as a consequence of increasing the resolution from 50 to 25 km. The importance of a horizontal resolution increase from 100 to 50 km is also generally shown for the errors in the mass field. However, little improvement in the prediction of the cyclogenesis is found by increasing the horizontal resolution from 50 to 25 km.

Full access
Christopher J. Anderson
,
Raymond W. Arritt
,
Zaitao Pan
,
Eugene S. Takle
,
William J. Gutowski Jr.
,
Francis O. Otieno
,
Renato da Silva
,
Daniel Caya
,
Jens H. Christensen
,
Daniel Lüthi
,
Miguel A. Gaertner
,
Clemente Gallardo
,
Filippo Giorgi
,
René Laprise
,
Song-You Hong
,
Colin Jones
,
H-M. H. Juang
,
J. J. Katzfey
,
John L. McGregor
,
William M. Lapenta
,
Jay W. Larson
,
John A. Taylor
,
Glen E. Liston
,
Roger A. Pielke Sr.
, and
John O. Roads

Abstract

Thirteen regional climate model (RCM) simulations of June–July 1993 were compared with each other and observations. Water vapor conservation and precipitation characteristics in each RCM were examined for a 10° × 10° subregion of the upper Mississippi River basin, containing the region of maximum 60-day accumulated precipitation in all RCMs and station reports.

All RCMs produced positive precipitation minus evapotranspiration (PE > 0), though most RCMs produced PE below the observed range. RCM recycling ratios were within the range estimated from observations. No evidence of common errors of E was found. In contrast, common dry bias of P was found in the simulations.

Daily cycles of terms in the water vapor conservation equation were qualitatively similar in most RCMs. Nocturnal maximums of P and C (convergence) occurred in 9 of 13 RCMs, consistent with observations. Three of the four driest simulations failed to couple P and C overnight, producing afternoon maximum P. Further, dry simulations tended to produce a larger fraction of their 60-day accumulated precipitation from low 3-h totals.

In station reports, accumulation from high (low) 3-h totals had a nocturnal (early morning) maximum. This time lag occurred, in part, because many mesoscale convective systems had reached peak intensity overnight and had declined in intensity by early morning. None of the RCMs contained such a time lag. It is recommended that short-period experiments be performed to examine the ability of RCMs to simulate mesoscale convective systems prior to generating long-period simulations for hydroclimatology.

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