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Hugh A. Hutchinson, T. Stephen Dixon, Neil Adams, Kieran Jacka, Stephen F. Pendlebury, Lawrence Marsh, Lance H. Cowled, Henry R. Phillpot, Michael J. Pook, and John Turner

Abstract

An overview is presented of the analysis procedures and problems encountered in the FROST reanalysis of weather charts poleward of latitude 50°S carried out in Hobart by the Australian Bureau of Meteorology, with advice from the Institute of Antarctic and Southern Ocean Studies. A summary of findings as a result of the FROST exercise is given and some topics for research projects in the future are identified.

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John Turner, David Bromwich, Steven Colwell, Stephen Dixon, Tim Gibson, Terry Hart, Günther Heinemann, Hugh Hutchinson, Kieran Jacka, Steven Leonard, Michael Lieder, Lawrie Marsh, Stephen Pendlebury, Henry Phillpot, Mike Pook, and Ian Simmonds

An account is given of the Antarctic First Regional Observing Study of the Troposphere (FROST) project, which has been organized by the Physics and Chemistry of the Atmosphere Group of the Scientific Committee on Antarctic Research. The goals of FROST are to study the meteorology of the Antarctic, to determine the strengths and weaknesses of operational analyses and forecasts over the continent and in the surrounding ocean areas, and to assess the value of new forms of satellite data that are becoming available. FROST is based around three one-month Special Observing Periods (SOPs)—July 1994, 16 October–15 November 1994, and January 1995 for which comprehensive datasets have been established of model fields and in situ and satellite observations. High quality manual surface and upper-air analyses are being prepared for these periods to determine the extent to which non–Global Telecommunications System data can improve the interpretation of the synoptic situation. Over the ocean areas during SOP-1, incorporation of the late data resulted only in a limited improvement in the analyses, indicating that the models are correctly analyzing most of the major weather systems. Over the continent, the production of 500-hPa heights from the automatic weather station data greatly helped in the analysis process. The lack of data around west Antarctica was a major handicap in the analysis process. The rms errors in the forecasts of 500-hPa height for the Antarctic were about 20% greater than those for midlatitude areas. The forecasts from the European Centre for Medium-Range Weather Forecasts were the most accurate of those received.

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Thomas L. Delworth, Anthony Rosati, Whit Anderson, Alistair J. Adcroft, V. Balaji, Rusty Benson, Keith Dixon, Stephen M. Griffies, Hyun-Chul Lee, Ronald C. Pacanowski, Gabriel A. Vecchi, Andrew T. Wittenberg, Fanrong Zeng, and Rong Zhang

Abstract

The authors present results for simulated climate and climate change from a newly developed high-resolution global climate model [Geophysical Fluid Dynamics Laboratory Climate Model version 2.5 (GFDL CM2.5)]. The GFDL CM2.5 has an atmospheric resolution of approximately 50 km in the horizontal, with 32 vertical levels. The horizontal resolution in the ocean ranges from 28 km in the tropics to 8 km at high latitudes, with 50 vertical levels. This resolution allows the explicit simulation of some mesoscale eddies in the ocean, particularly at lower latitudes.

Analyses are presented based on the output of a 280-yr control simulation; also presented are results based on a 140-yr simulation in which atmospheric CO2 increases at 1% yr−1 until doubling after 70 yr.

Results are compared to GFDL CM2.1, which has somewhat similar physics but a coarser resolution. The simulated climate in CM2.5 shows marked improvement over many regions, especially the tropics, including a reduction in the double ITCZ and an improved simulation of ENSO. Regional precipitation features are much improved. The Indian monsoon and Amazonian rainfall are also substantially more realistic in CM2.5.

The response of CM2.5 to a doubling of atmospheric CO2 has many features in common with CM2.1, with some notable differences. For example, rainfall changes over the Mediterranean appear to be tightly linked to topography in CM2.5, in contrast to CM2.1 where the response is more spatially homogeneous. In addition, in CM2.5 the near-surface ocean warms substantially in the high latitudes of the Southern Ocean, in contrast to simulations using CM2.1.

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Anand Gnanadesikan, Keith W. Dixon, Stephen M. Griffies, V. Balaji, Marcelo Barreiro, J. Anthony Beesley, William F. Cooke, Thomas L. Delworth, Rudiger Gerdes, Matthew J. Harrison, Isaac M. Held, William J. Hurlin, Hyun-Chul Lee, Zhi Liang, Giang Nong, Ronald C. Pacanowski, Anthony Rosati, Joellen Russell, Bonita L. Samuels, Qian Song, Michael J. Spelman, Ronald J. Stouffer, Colm O. Sweeney, Gabriel Vecchi, Michael Winton, Andrew T. Wittenberg, Fanrong Zeng, Rong Zhang, and John P. Dunne

Abstract

The current generation of coupled climate models run at the Geophysical Fluid Dynamics Laboratory (GFDL) as part of the Climate Change Science Program contains ocean components that differ in almost every respect from those contained in previous generations of GFDL climate models. This paper summarizes the new physical features of the models and examines the simulations that they produce. Of the two new coupled climate model versions 2.1 (CM2.1) and 2.0 (CM2.0), the CM2.1 model represents a major improvement over CM2.0 in most of the major oceanic features examined, with strikingly lower drifts in hydrographic fields such as temperature and salinity, more realistic ventilation of the deep ocean, and currents that are closer to their observed values. Regional analysis of the differences between the models highlights the importance of wind stress in determining the circulation, particularly in the Southern Ocean. At present, major errors in both models are associated with Northern Hemisphere Mode Waters and outflows from overflows, particularly the Mediterranean Sea and Red Sea.

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Thomas L. Delworth, Anthony J. Broccoli, Anthony Rosati, Ronald J. Stouffer, V. Balaji, John A. Beesley, William F. Cooke, Keith W. Dixon, John Dunne, K. A. Dunne, Jeffrey W. Durachta, Kirsten L. Findell, Paul Ginoux, Anand Gnanadesikan, C. T. Gordon, Stephen M. Griffies, Rich Gudgel, Matthew J. Harrison, Isaac M. Held, Richard S. Hemler, Larry W. Horowitz, Stephen A. Klein, Thomas R. Knutson, Paul J. Kushner, Amy R. Langenhorst, Hyun-Chul Lee, Shian-Jiann Lin, Jian Lu, Sergey L. Malyshev, P. C. D. Milly, V. Ramaswamy, Joellen Russell, M. Daniel Schwarzkopf, Elena Shevliakova, Joseph J. Sirutis, Michael J. Spelman, William F. Stern, Michael Winton, Andrew T. Wittenberg, Bruce Wyman, Fanrong Zeng, and Rong Zhang

Abstract

The formulation and simulation characteristics of two new global coupled climate models developed at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL) are described. The models were designed to simulate atmospheric and oceanic climate and variability from the diurnal time scale through multicentury climate change, given our computational constraints. In particular, an important goal was to use the same model for both experimental seasonal to interannual forecasting and the study of multicentury global climate change, and this goal has been achieved.

Two versions of the coupled model are described, called CM2.0 and CM2.1. The versions differ primarily in the dynamical core used in the atmospheric component, along with the cloud tuning and some details of the land and ocean components. For both coupled models, the resolution of the land and atmospheric components is 2° latitude × 2.5° longitude; the atmospheric model has 24 vertical levels. The ocean resolution is 1° in latitude and longitude, with meridional resolution equatorward of 30° becoming progressively finer, such that the meridional resolution is 1/3° at the equator. There are 50 vertical levels in the ocean, with 22 evenly spaced levels within the top 220 m. The ocean component has poles over North America and Eurasia to avoid polar filtering. Neither coupled model employs flux adjustments.

The control simulations have stable, realistic climates when integrated over multiple centuries. Both models have simulations of ENSO that are substantially improved relative to previous GFDL coupled models. The CM2.0 model has been further evaluated as an ENSO forecast model and has good skill (CM2.1 has not been evaluated as an ENSO forecast model). Generally reduced temperature and salinity biases exist in CM2.1 relative to CM2.0. These reductions are associated with 1) improved simulations of surface wind stress in CM2.1 and associated changes in oceanic gyre circulations; 2) changes in cloud tuning and the land model, both of which act to increase the net surface shortwave radiation in CM2.1, thereby reducing an overall cold bias present in CM2.0; and 3) a reduction of ocean lateral viscosity in the extratropics in CM2.1, which reduces sea ice biases in the North Atlantic.

Both models have been used to conduct a suite of climate change simulations for the 2007 Intergovernmental Panel on Climate Change (IPCC) assessment report and are able to simulate the main features of the observed warming of the twentieth century. The climate sensitivities of the CM2.0 and CM2.1 models are 2.9 and 3.4 K, respectively. These sensitivities are defined by coupling the atmospheric components of CM2.0 and CM2.1 to a slab ocean model and allowing the model to come into equilibrium with a doubling of atmospheric CO2. The output from a suite of integrations conducted with these models is freely available online (see http://nomads.gfdl.noaa.gov/).

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Ian M. Brooks, Margaret J. Yelland, Robert C. Upstill-Goddard, Philip D. Nightingale, Steve Archer, Eric d'Asaro, Rachael Beale, Cory Beatty, Byron Blomquist, A. Anthony Bloom, Barbara J. Brooks, John Cluderay, David Coles, John Dacey, Michael Degrandpre, Jo Dixon, William M. Drennan, Joseph Gabriele, Laura Goldson, Nick Hardman-Mountford, Martin K. Hill, Matt Horn, Ping-Chang Hsueh, Barry Huebert, Gerrit De Leeuw, Timothy G. Leighton, Malcolm Liddicoat, Justin J. N. Lingard, Craig Mcneil, James B. Mcquaid, Ben I. Moat, Gerald Moore, Craig Neill, Sarah J. Norris, Simon O'Doherty, Robin W. Pascal, John Prytherch, Mike Rebozo, Erik Sahlee, Matt Salter, Ute Schuster, Ingunn Skjelvan, Hans Slagter, Michael H. Smith, Paul D. Smith, Meric Srokosz, John A. Stephens, Peter K. Taylor, Maciej Telszewski, Roisin Walsh, Brian Ward, David K. Woolf, Dickon Young, and Henk Zemmelink

Abstract

No Abstract available.

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Ian M. Brooks, Margaret J. Yelland, Robert C. Upstill-Goddard, Philip D. Nightingale, Steve Archer, Eric d'Asaro, Rachael Beale, Cory Beatty, Byron Blomquist, A. Anthony Bloom, Barbara J. Brooks, John Cluderay, David Coles, John Dacey, Michael DeGrandpre, Jo Dixon, William M. Drennan, Joseph Gabriele, Laura Goldson, Nick Hardman-Mountford, Martin K. Hill, Matt Horn, Ping-Chang Hsueh, Barry Huebert, Gerrit de Leeuw, Timothy G. Leighton, Malcolm Liddicoat, Justin J. N. Lingard, Craig McNeil, James B. McQuaid, Ben I. Moat, Gerald Moore, Craig Neill, Sarah J. Norris, Simon O'Doherty, Robin W. Pascal, John Prytherch, Mike Rebozo, Erik Sahlee, Matt Salter, Ute Schuster, Ingunn Skjelvan, Hans Slagter, Michael H. Smith, Paul D. Smith, Meric Srokosz, John A. Stephens, Peter K. Taylor, Maciej Telszewski, Roisin Walsh, Brian Ward, David K. Woolf, Dickon Young, and Henk Zemmelink

As part of the U.K. contribution to the international Surface Ocean-Lower Atmosphere Study, a series of three related projects—DOGEE, SEASAW, and HiWASE—undertook experimental studies of the processes controlling the physical exchange of gases and sea spray aerosol at the sea surface. The studies share a common goal: to reduce the high degree of uncertainty in current parameterization schemes. The wide variety of measurements made during the studies, which incorporated tracer and surfactant release experiments, included direct eddy correlation fluxes, detailed wave spectra, wind history, photographic retrievals of whitecap fraction, aerosolsize spectra and composition, surfactant concentration, and bubble populations in the ocean mixed layer. Measurements were made during three cruises in the northeast Atlantic on the RRS Discovery during 2006 and 2007; a fourth campaign has been making continuous measurements on the Norwegian weather ship Polarfront since September 2006. This paper provides an overview of the three projects and some of the highlights of the measurement campaigns.

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