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Using a fully coupled ocean–atmosphere model, we have investigated the response of the Indian and southeast monsoons to changes in precession, with special emphasis on the Indian Ocean. We designed our experiments in order to explore the differences between periods where the monsoon activity is strong compared to the period of reference (115 ka BP), and the seasonal timing of the insolation forcing is different. The two extreme cases are such that the maximum insolation occurs between the vernal equinox and the summer solstice in one case and between the summer solstice and the autumnal equinox in the other. Our results show that, even though the changes in the land–sea contrast that drive the monsoon flow follow quite well the differences in the insolation forcing, the regional distribution of monsoon characteristics (monsoon flow, precipitation etc.) from Africa to Southeast Asia and over the ocean substantially varies from one simulation to the other. Large differences are found in the simulated surface temperature and salinity in the Indian Ocean. They are mainly due to changes in the hydrological cycle over the basin (precipitation, evaporation and river runoff). Our results strongly emphasise that the timing of the seasonal cycle must be taken into account in analyses of past monsoons, and that it may explain some of the leads and lags reported between insolation and various monsoon proxies reported in the literature [Copyright &y& Elsevier]

The intraseasonal variability (ISV) is an intermittent phenomenon with variable perturbation patterns. To assess the robustness of the simulated ISV in climate models, it is thus interesting to consider the distribution of perturbation patterns rather than only one average pattern. To inspect this distribution, the authors first introduce a distance that measures the similarity between two patterns. The reproducibility (realism) of the simulated intraseasonal patterns is then defined as the distribution of distances between each pattern and the average simulated (observed) pattern. A good reproducibility is required to analyze the physical source of the simulated disturbances. The realism distribution is required to estimate the proportion of simulated events that have a perturbation pattern similar to observed patterns. The median value of this realism distribution is introduced as an ISV metric. The reproducibility and realism distributions are used to evaluate boreal summer ISV of precipitations over the Indian Ocean for 19 phase 3 of the Coupled Model Intercomparison Project (CMIP3) models. The 19 models are classified in increasing ISV metric order. In agreement with previous studies, the four best ISV metrics are obtained for models having a convective closure totally or partly based on the moisture convergence. Models with high metric values (poorly realistic) tend to give (i) poorly reproducible intraseasonal patterns, (ii) rainfall perturbations poorly organized at large scales, (iii) small day-to-day variability with overly red temporal spectra, and (iv) less accurate summer monsoon rainfall distribution. This confirms that the ISV is an important link in the seamless system that connects weather and climate. [ABSTRACT FROM AUTHOR]

Abstract: The Asian monsoon is comprised of the Indian and East Asian subsystems. These two components are linked to one another in varying degrees by regions of strong sensible heating (Indo-Asian landmass) and strong latent heat export (the Western Pacific Warm Pool and the southern subtropical Indian Ocean). Variability within the Indian and East Asian subsystems, interactions among them, and the extent to which they interact with other climate phenomena (e.g., ENSO) are current topics of modern and paleoclimate research. This work provides an overview of past and current paleomonsoon research on tectonic to interannual time scales with a primary focus on marine sediment records. While past and current work has contributed greatly to our understanding of paleomonsoon variability at all time scales, additional efforts are required to make further progress in two critical areas. (1) Additional efforts are needed in terms of proxy development and evaluation, requiring concerted efforts at long-term sediment trap deployments in key monsoon-influenced regions as well as development of adequate and widely available core-top databases. These are necessary to assess the impact of modern oceanographic and seafloor processes on potential monsoon proxies. (2) Additional effort is also needed in acquiring a sufficient geographic distribution of downcore records to assess linkages among the subsystems and their role in the context of extratropical climate change. These records should have high sedimentation rates (including varved sections). This requires substantial survey support to identify the most appropriate coring and drilling targets. [Copyright &y& Elsevier]