Mean flow-transient perturbation interaction in the Southern Hemisphere: A simulation using a variable-resolution GCM

The ability of an atmospheric general circulation model to reproduce fundamental features of the wintertime extratropical Southern Hemisphere (SH) circulation is evaluated with emphasis on the daily variability of the SH mean flow and the mean flow-transient perturbations interaction. Two 10-year si...

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Detalles Bibliográficos
Publicado: 2002
Materias:
atmospheric circulation
extratropical environment
general circulation model
Southern Hemisphere
winter
Acceso en línea:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_09307575_v18_n8_p661_Carril
http://hdl.handle.net/20.500.12110/paper_09307575_v18_n8_p661_Carril
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
id paper:paper_09307575_v18_n8_p661_Carril
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spelling paper:paper_09307575_v18_n8_p661_Carril2023-06-08T15:52:35Z Mean flow-transient perturbation interaction in the Southern Hemisphere: A simulation using a variable-resolution GCM atmospheric circulation extratropical environment general circulation model Southern Hemisphere winter The ability of an atmospheric general circulation model to reproduce fundamental features of the wintertime extratropical Southern Hemisphere (SH) circulation is evaluated with emphasis on the daily variability of the SH mean flow and the mean flow-transient perturbations interaction. Two 10-year simulations using a new version of the LMDZ GCM with a stretched grid scheme centered at 45 °S and forced by climatological SST are performed: a high (144× 73) and low (64× 33) horizontal resolution runs. The performance of both simulations was determined by comparing several simulated fields (zonal wind, temperature, kinetic energy, transient eddy momentum and heat fluxes, Eliassen-Palm fluxes, Eady growth rate and baroclinic conversion term) against the European Centre for Medium Range Weather Forecast reanalyses (ERA). High and low-resolution simulations are similar in many respects; in particular, both experiments reproduce the main patterns of the southern extratropical large-scale circulation satisfactorily. Increasing resolution does not improve universally some spurious aspects of the low resolution simulation (e.g. the cold bias in the high polar troposphere, the debilitated subtropical jet, the low baroclinic conversion rate). Those aspects present little sensitivity to the model resolution. The interaction between transient eddies and zonal mean flow are examined. The low-resolution experiment is able to qualitatively represent the acceleration/deceleration of the mean flow by transient perturbations, south/north of 30 °S with an accuracy similar to that of the high-resolution experiment. Although both experiments represent the baroclinic structure of the mean flow satisfactorily, the model underestimates some transient properties due to the underestimation of the baroclinic conversion term in middle latitudes. Such misrepresentation does not improve with increasing resolution and is related to the relatively weak meridional temperature gradient and the inadequate geographical distribution of the eddy heat fluxes. In particular, the eddy kinetic energy is always underestimated. Eddy kinetic energy does not improve convincingly with increasing resolution, suggesting that the adequate representation of the storm tracks is highly influenced by the physical parametrizations. 2002 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_09307575_v18_n8_p661_Carril http://hdl.handle.net/20.500.12110/paper_09307575_v18_n8_p661_Carril
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic atmospheric circulation
extratropical environment
general circulation model
Southern Hemisphere
winter
spellingShingle atmospheric circulation
extratropical environment
general circulation model
Southern Hemisphere
winter
Mean flow-transient perturbation interaction in the Southern Hemisphere: A simulation using a variable-resolution GCM
topic_facet atmospheric circulation
extratropical environment
general circulation model
Southern Hemisphere
winter
description The ability of an atmospheric general circulation model to reproduce fundamental features of the wintertime extratropical Southern Hemisphere (SH) circulation is evaluated with emphasis on the daily variability of the SH mean flow and the mean flow-transient perturbations interaction. Two 10-year simulations using a new version of the LMDZ GCM with a stretched grid scheme centered at 45 °S and forced by climatological SST are performed: a high (144× 73) and low (64× 33) horizontal resolution runs. The performance of both simulations was determined by comparing several simulated fields (zonal wind, temperature, kinetic energy, transient eddy momentum and heat fluxes, Eliassen-Palm fluxes, Eady growth rate and baroclinic conversion term) against the European Centre for Medium Range Weather Forecast reanalyses (ERA). High and low-resolution simulations are similar in many respects; in particular, both experiments reproduce the main patterns of the southern extratropical large-scale circulation satisfactorily. Increasing resolution does not improve universally some spurious aspects of the low resolution simulation (e.g. the cold bias in the high polar troposphere, the debilitated subtropical jet, the low baroclinic conversion rate). Those aspects present little sensitivity to the model resolution. The interaction between transient eddies and zonal mean flow are examined. The low-resolution experiment is able to qualitatively represent the acceleration/deceleration of the mean flow by transient perturbations, south/north of 30 °S with an accuracy similar to that of the high-resolution experiment. Although both experiments represent the baroclinic structure of the mean flow satisfactorily, the model underestimates some transient properties due to the underestimation of the baroclinic conversion term in middle latitudes. Such misrepresentation does not improve with increasing resolution and is related to the relatively weak meridional temperature gradient and the inadequate geographical distribution of the eddy heat fluxes. In particular, the eddy kinetic energy is always underestimated. Eddy kinetic energy does not improve convincingly with increasing resolution, suggesting that the adequate representation of the storm tracks is highly influenced by the physical parametrizations.
title Mean flow-transient perturbation interaction in the Southern Hemisphere: A simulation using a variable-resolution GCM
title_short Mean flow-transient perturbation interaction in the Southern Hemisphere: A simulation using a variable-resolution GCM
title_full Mean flow-transient perturbation interaction in the Southern Hemisphere: A simulation using a variable-resolution GCM
title_fullStr Mean flow-transient perturbation interaction in the Southern Hemisphere: A simulation using a variable-resolution GCM
title_full_unstemmed Mean flow-transient perturbation interaction in the Southern Hemisphere: A simulation using a variable-resolution GCM
title_sort mean flow-transient perturbation interaction in the southern hemisphere: a simulation using a variable-resolution gcm
publishDate 2002
url https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_09307575_v18_n8_p661_Carril
http://hdl.handle.net/20.500.12110/paper_09307575_v18_n8_p661_Carril
_version_ 1768543332461445120

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