Impact of the LMDZ atmospheric grid configuration on the climate and sensitivity of the IPSL-CM5A coupled model

Abstract

The IPSL-CM5A climate model was used to perform a large number of control, historical and climate change simulations in the frame of CMIP5. The refined horizontal and vertical grid of the atmospheric component, LMDZ, constitutes a major difference compared to the previous IPSL-CM4 version used for CMIP3. From imposed-SST (Sea Surface Temperature) and coupled numerical experiments, we systematically analyze the impact of the horizontal and vertical grid resolution on the simulated climate. The refinement of the horizontal grid results in a systematic reduction of major biases in the mean tropospheric structures and SST. The mid-latitude jets, located too close to the equator with the coarsest grids, move poleward. This robust feature, is accompanied by a drying at mid-latitudes and a reduction of cold biases in mid-latitudes relative to the equator. The model was also extended to the stratosphere by increasing the number of layers on the vertical from 19 to 39 (15 in the stratosphere) and adding relevant parameterizations. The 39-layer version captures the dominant modes of the stratospheric variability and exhibits stratospheric sudden warmings. Changing either the vertical or horizontal resolution modifies the global energy balance in imposed-SST simulations by typically several W/m 2 which translates in the coupled atmosphere-ocean simulations into a different global-mean SST. The sensitivity is of about 1.2 K per 1 W/m 2 when varying the horizontal grid. A re-tuning of model parameters was thus required to restore this energy balance in the imposed-SST simulations and reduce the biases in the simulated mean surface temperature and, to some extent, latitudinal SST variations in the coupled experiments for the modern climate. The tuning hardly compensates, however, for robust biases of the coupled model. Despite the wide range of grid configurations explored and their significant impact on the present-day climate, the climate sensitivity remains essentially unchanged.

Mechanisms Determining the Winter Atmospheric Response to the Atlantic Overturning Circulation

“…However, a large cold bias is simulated at about 408 in both hemispheres in the atmosphere and the sea surface (see Dufresne et al 2013, their Fig. 7), which is linked to the atmospheric jet stream being too equatorward (Hourdin et al 2013), as found in many other climate models (Barnes and Polvani 2013).…”

“…The IPSL-CM5A-LR climate model, where LR stands for low resolution, was developed at IPSL for the CMIP5 experiments (Dufresne et al 2013). Its atmospheric component is LMDZ version 5A (LMDZ5A; Hourdin et al 2013), where A indicates standard physical parameterizations. It has a low horizontal resolution of 2.58 in latitude and 3.758 in longitude, but it is a high-top model with 39 vertical levels up to 4 Pa.…”

Sensitivity of the radiative forcing by stratospheric sulfur geoengineering to the amount and strategy of the SO<sub>2</sub> injection studied with the LMDZ-S3A model

“…In this study we use the atmospheric general circulation model LMDZ (Hourdin et al, 2006(Hourdin et al, , 2013 with the new sectional stratospheric sulfate aerosol module S3A described in detail in Kleinschmitt et al (2017). 20 In the present configuration, LMDZ is run with 96×96 grid-points on the horizontal -i.e., a resolution of 1.89…”

“…• in longitude which is the same as for LMDZ5A (Hourdin et al, 2006(Hourdin et al, , 2013 -and 79 layers on the vertical in order to improve the vertical resolution in the stratosphere. Although it is possible to couple LMDZ interactively to an ocean model to form the IPSL coupled atmosphere-ocean model, we decided here to only perform simulations with fixed sea surface temperatures (SST).…”

Comparative Spectral Analysis and Correlation Properties of Observed and Simulated Total Column Ozone Records

“…The performance of the model was tested against observations and other CCM models [6,[8][9][10][11]. The most extended comparison project was the CCM Validation Activity in two runs (CCMVal-1, CCMVal-2), where 18 leading global CCMs are investigated by several observationally-based performance metrics in order to quantify the ability of models in reproducing the dynamics of stratospheric ozone [12].…”