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- PublicationOpen AccessAssessment of the tropical Indo-Pacific climate in the SINTEX CGCM(2003)
; ; ; ; ;Gualdi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Guilyardi, E.; Laboratoire d Océanographie Dynamique et de Climatologie, Unité Mixte de Recherche CNRS-IRD-UPMC,Université Pierre et Marie Curie, Paris,France ;Delecluse, P.; Laboratoire d Océanographie Dynamique et de Climatologie, Unité Mixte de Recherche CNRS-IRD-UPMC,Université Pierre et Marie Curie, Paris,France; ; ; A new coupled GCM (SINTEX) has been developed. The model is formed by the atmosphere model ECHAM-4 and the ocean model ORCA. The atmospheric and oceanic components are coupled through OASIS. The domain is global and no flux correction is applied. In this study, we describe the ability of the coupled model to simulate the main features of the observed climate and its dominant modes of variability in the tropical Indo-Pacific. Three long experiments have been performed with different horizontal resolution of the atmospheric component in order to assess a possible impact of the atmosphere model resolution onto the simulated climate. Overall, the mean state is captured reasonably well, though the simulated SST tends to be too warm in the tropical Eastern Pacific and there is a model tendency to produce a double ITCZ. The model gives also a realistic representation of the temperature structure at the equator in the Pacific and Indian Ocean. The slope and the structure of the equatorial thermocline are well reproduced. Compared to the observations, the simulated annual cycle appears to be underestimated in the eastern equatorial Pacific, whereas a too pronounced seasonal variation is found in the Central Pacific. The main basic features of the interannual variability in the tropical Indo-Pacific region are reasonably well reproduced by the model. In the Indian Ocean, the characteristics of the simulated interannual variability are very similar to the results found from the observations. In the Pacific, the modelled ENSO variability appears to be slightly weaker and the simulated period a bit shorter than in the observations. Our results suggest that, both the simulated mean state and interannual variability are generally improved when the horizontal resolution of the atmospheric mode component is increased.212 244 - PublicationRestrictedAtmospheric horizontal resolution affects tropical climate variability in coupled models(2008-04)
; ; ; ; ; ; ; ; ; ;Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Gualdi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Behera, S.; Frontier Research System FRCGC, Yokohama, Japan ;Luo, J.-J.; Frontier Research System FRCGC, Yokohama, Japan ;Masson, S.; Frontier Research System FRCGC, Yokohama, Japan ;Guilyardi, E.; IPSL/LSCE, Gif-sur-Yvette, France ;Delecluse, P.; IPSL/LSCE, Gif-sur-Yvette, France ;Yamagata, T.; Frontier Research System FRCGC, Yokohama, Japan; ; ; ; ; ; ; ; The effect of horizontal resolution on tropical variability is investigated within the modified SINTEX model, SINTEX-F, developed jointly at INGV, IPSL and at the Frontier Research System. The horizontal resolutions T30 and T106 are investigated in terms of the coupling characteristics, frequency and variability of the tropical ocean-atmosphere interactions. It appears that the T106 resolution is generally beneficial even if it does not eliminate all the major systematic errors of the coupled model. There is an excessive shift west of the cold tongue and ENSO variability, and high resolution has also a somewhat negative impact to the variability in the East Indian Ocean. A dominant two-year peak for the NINO3 variabilty in the T30 model is moderated in the T106 as it shifts to longer time scale. At high resolution new processes come into play, as the coupling of tropical instability waves, the resolution of coastal flows at the Pacific Mexican coasts and improved coastal forcing along the coast of South America. The delayed oscillator seems the main mechanism that generates the interannual variability in both models, but the models realize it in different ways. In the T30 model it is confined close to the equator, involving relatively fast equatorial and near-equatorial modes, in the high resolution, it involves a wider latitudinal region and slower waves. It is speculated that the extent of the region that is involved in the interannual variability may be linked to the time scale of the variability itself.213 20 - PublicationRestrictedThe interannual variability in the tropical Indian Ocean as simulated by a CGCM(2003-01-11)
; ; ; ; ; ;Gualdi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Guilyardi, E.; CGAM, Reading, UK ;Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Delecluse, P.; LODYC, Paris, France; ; ; ; The interannual variability in the tropical Indian Ocean, and in particular the Indian Ocean di- pole mode (IODM), is investigated using both obser- vations and a multi-decadal simulations performed by the coupled atmosphere–ocean general circulation model SINTEX. Overall, the characteristics of the simulated IODM are close to the features of the ob- served mode. Evidence of significant correlations be- tween sea level pressure anomalies in the southeastern Indian Ocean and sea surface temperature anomalies in the tropical Indian and Pacific Oceans have been found both in observations and a multi-decadal simulation. In particular, a positive SLP anomaly in the southeastern part of the basin seems to produce favorable conditions for the development of an IODM event. The role played by the ocean dynamics both in the developing and closing phases of the IODM events is also inves- tigated. Our results suggest that, during the developing phase, the heat content and SST variability associated with the IODM are influenced by a local response of the ocean to the winds, and a remote response with the excitation of Kelvin and Rossby waves. Ocean wave dynamics appear to be important also during the dying phase of the IODM, when equatorial downwelling Kelvin waves transport positive heat content anomalies from the western to the eastern part of the basin, suppressing the zonal heat content anomaly gradient. The results obtained from the model suggest a mechanism for the IODM. This mechanism is generally consistent with the characteristics of the observed IODM. Furthermore, it might give some clue in understanding the correlation between IODM and ENSOactivity found both in the model and in the observations.343 101 - PublicationRestrictedThe role of mean ocean salinity in climate(2010)
; ; ; ; ; ;Williams, P. D.; NationalCentreforAtmosphericScience, DepartmentofMeteorology, UniversityofReading, UK ;Guilyardi, E.; NationalCentreforAtmosphericScience, DepartmentofMeteorology, UniversityofReading, UK ;Madec, G.; Laboratoired’OcéanographieetdeClimat:ExpérimentationetApprocheNumérique(LOCEAN/IPSL),CNRS/UniversitéParisVI,France ;Gualdi, S.; Centro Euro-Mediterraneo per i Cambiamenti Climatici CMCC/INGV ;Scoccimarro, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; ; We describe numerical simulations designed to help elucidate the role of ocean salinity in climate. Using a general circulation model, we study a 100-year sensitivity experiment in which the global-mean salinity is doubled from its present observed value, by adding 35 psu everywhere. The salinity increase produces a rapid global-mean sea-surface warming of 0.8◦ within a few years, caused by reduced vertical mixing associated with changes in cabbeling. The warming is followed by a gradual global mean sea-surface cooling of 0.4 ◦C over the next few decades, caused by an increase in the vertical (downward) component of the isopycnal diffusive heat flux. We find no evidence of impacts on the variability of either the Atlantic thermohaline circulation or the El Ni ̃no/Southern Oscillation. The mean strength of the Atlantic meridional overturning is slightly reduced and the North Atlantic Deep Water penetrates less deeply. Nevertheless, our results dispute claims that higher salinities for the world ocean have profound consequences for the thermohaline circulation. In additional experiments with doubled atmospheric carbon dioxide, we find that the amplitude and spatial pattern of the global warming signal are modified in the hypersaline ocean. In particular, the ocean’s contribution to the climate sensitivity is significantly reduced. We infer the existence of a non-linear interaction between the climate responses to modified carbon dioxide and modified salinity.129 25