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Further development of a hybrid‐isentropic GCM

Further development of a hybrid‐isentropic GCM The UK Universities' Global Atmospheric Modelling Programme hybrid‐isentropic general‐circulation model (HIGCM) uses a flexible σ‐θ;‐p vertical coordinate, where p is pressure, θ is potential temperature, and σ = p/p* where p* is surface pressure. Three major improvements to the HIGCM are presented. the first improvement is a modification to the vertical‐difference scheme so that spurious vertical motions in the isentropic domain are minimized. the second improvement is a modification to the implementation of the radiation scheme so that it is now able to damp, and does not itself create, noisy temperature profiles; this allows the model to be run without ad hoc extra vertical diffusion and so allows a cleaner comparison with σ‐p simulations. the third improvement is to extend the isentropic domain up to the top of the model thus allowing σ‐θ or σ‐θ‐p simulations to be performed. Idealized baroclinic instability life‐cycle experiments are used to investigate the impact of the new vertical scheme on the dynamical core of the HIGCM. the reduction in spurious vertical velocities is found to be substantial whilst the impact on the global conservation properties and overall evolution is found to be very small. These simulations also show that the commonly used Δ2n form of scale‐selective dissipation can seriously compromise global energy conservation when model‐layer thicknesses have significant horizontal gradients. The impact of the isentropic coordinate on the climate of the full GCM is investigated by performing perpetual January simulations using σ‐θ, σ‐θ‐p and σ‐p vertical coordinates. the most robust response to the isentropic coordinate is a warming of the southern hemisphere high‐latitude lower stratosphere. In the northern hemisphere the largest changes in zonal mean temperature are in the polar stratosphere. the possible mechanisms by which the isentropic coordinate may yield these changes are described and investigated. the results strongly suggest that many of the potential benefits of the isentropic coordinate are realized, to some extent at least, with the HIGCM. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Quarterly Journal of the Royal Meteorological Society Wiley

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References (34)

Publisher
Wiley
Copyright
Copyright © 1999 Royal Meteorological Society
ISSN
0035-9009
eISSN
1477-870X
DOI
10.1002/qj.49712555817
Publisher site
See Article on Publisher Site

Abstract

The UK Universities' Global Atmospheric Modelling Programme hybrid‐isentropic general‐circulation model (HIGCM) uses a flexible σ‐θ;‐p vertical coordinate, where p is pressure, θ is potential temperature, and σ = p/p* where p* is surface pressure. Three major improvements to the HIGCM are presented. the first improvement is a modification to the vertical‐difference scheme so that spurious vertical motions in the isentropic domain are minimized. the second improvement is a modification to the implementation of the radiation scheme so that it is now able to damp, and does not itself create, noisy temperature profiles; this allows the model to be run without ad hoc extra vertical diffusion and so allows a cleaner comparison with σ‐p simulations. the third improvement is to extend the isentropic domain up to the top of the model thus allowing σ‐θ or σ‐θ‐p simulations to be performed. Idealized baroclinic instability life‐cycle experiments are used to investigate the impact of the new vertical scheme on the dynamical core of the HIGCM. the reduction in spurious vertical velocities is found to be substantial whilst the impact on the global conservation properties and overall evolution is found to be very small. These simulations also show that the commonly used Δ2n form of scale‐selective dissipation can seriously compromise global energy conservation when model‐layer thicknesses have significant horizontal gradients. The impact of the isentropic coordinate on the climate of the full GCM is investigated by performing perpetual January simulations using σ‐θ, σ‐θ‐p and σ‐p vertical coordinates. the most robust response to the isentropic coordinate is a warming of the southern hemisphere high‐latitude lower stratosphere. In the northern hemisphere the largest changes in zonal mean temperature are in the polar stratosphere. the possible mechanisms by which the isentropic coordinate may yield these changes are described and investigated. the results strongly suggest that many of the potential benefits of the isentropic coordinate are realized, to some extent at least, with the HIGCM.

Journal

The Quarterly Journal of the Royal Meteorological SocietyWiley

Published: Jul 1, 1999

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