The LMDZ4 general circulation model: climate performance and sensitivity to parametrized physics with emphasis on tropical convection

Abstract

The LMDZ4 general circulation model is the atmospheric component of the IPSL-CM4 coupled model which has been used to perform climate change simulations for the 4th IPCC assessment report. The main aspects of the model climatology (forced by observed sea surface temperature) are documented here, as well as the major improvements with respect to the previous versions, which mainly come form the parametrization of tropical convection. A methodology is proposed to help analyse the sensitivity of the tropical Hadley- Walker circulation to the parametrization of cumulus convection and clouds. The tropical circulation is characterized using scalar potentials associated with the horizontal wind and horizontal transport of geopotential (the Laplacian of which is proportional to the total vertical momentum in the atmospheric column). The effect of parametrized physics is analysed in a regime sorted framework using the vertical velocity at 500 hPa as a proxy for large scale vertical motion. Compared to Tiedtke s convection scheme, used in previous versions, the Emanuel s scheme improves the representation of the Hadley-Walker circulation, with a relatively stronger and deeper large scale vertical ascent over tropical continents, and suppresses the marked patterns of concentrated rainfall over oceans. Thanks to the regime sorted analyses, this differences are attributed to intrinsic differences in the vertical distribution of convective heating, and to the lack of self-inhibition by precipitating downdraughts in Tiedtke s parametrization. Both the convection and cloud schemes are shown to control the relative importance of large scale convection over land and ocean, an important point for the behaviour of the coupled model

Relative contributions of climate change, stomatal closure, and leaf area index changes to 20th and 21st century runoff change: A modelling approach using the Organizing Carbon and Hydrology in Dynamic Ecosystems (ORCHIDEE) land surface model

“…The forcing that we have used for our experiments in terms of climate results from two coupled ocean atmosphere climate experiments using the IPSL_CM4 model [Marti et al, 2010]. The atmosphere component of this coupled model is LMDZ.3.3 [Hourdin et al, 2006], with a resolution of 96 × 72 × 19 points in longitude × latitude × altitude. This atmospheric module includes the ORCHIDEE land surface scheme.…”

Future discharge drought across climate regions around the world modelled with a synthetic hydrological modelling approach forced by three general circulation models

“…Through the EU-WATCH project, simulation outcome from three GCMs was available on a global scale. The GCMs included are ECHAM5 (Roeckner et al, 2003;Jungclaus et al, 2006), CNRM3 (Royer et al, 2002;Salas-Mélia, 2002) and IPSL (Hourdin et al, 2006;Madec et al, 1998;Fichefet and Maqueda, 1997;Goosse and Fichefet, 1999). Each GCM provides meteorological forcing for the period 1960-2100.…”

Skill assessment of three earth system models with common marine biogeochemistry

“…The atmospheric component is LMDZ-4 developed at LMD (Laboratoire de Météorologie Dynamique) with a horizontal resolution of 3.75°9 2.5°and 19 vertical levels (Hourdin et al 2006). The land component is the global land-vegetation model ORCHIDEE (Organizing Carbon and Hydrology in Dynamic EcosystEms, Krinner et al 2005), which simulates interactions between land and atmosphere.…”

“…As before, IPSLCM5 combines the four major components of the climate system, but it now also includes a module for tropospheric chemistry, aerosols, and online interactions with land vegetation. The atmosphere and land models of IPSLCM5 are updated versions of those used in IPSLCM4, namely, the atmospheric general circulation model LMDZ (Hourdin et al 2006) and the ORCHIDEE land-surface model (Krinner et al 2005). The atmospheric and land components use the same regular horizontal grid with 96 9 96 points, representing a resolution of 3.6°9 1.8°, while the atmosphere has 39 vertical levels.…”