Articles written in Journal of Earth System Science

    • Evaluation of SP-CAM and SP-CCSM in capturing the extremes of summer monsoon rainfall over Indian region


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      The simulation of the Asian monsoon rainfall and its extreme events with high fidelity remains a challenge even for the present day state-of-the-art models with conventional treatment of convection. A multi-scale approach vis-a-vis the super-parameterization appears to overcome the uncertainty of convective parameterization and thereby improve models ability to simulate rainfall. In this study, performance of super-parameterized community climate system model’s atmospheric only (SPCAM) forced with observed SST and coupled (SPCCSM) versions have been evaluated to capture Indian summer monsoon rainfall characteristics. Analyses show that, simulation of rainfall and its extremes are better represented in the atmospheric model (SPCAM) over the Indian landmass. This is largely because of better representation of convection in the uncoupled version. It is also observed that 2–10 day synoptic mode of the summer monsoon has a large variance over Indian region which may be broadly responsible for extreme events, and SPCAM captures this synoptic variability reasonably well. Our study also indicates that models may have poor moisture holding capacity. This problem is more prominent in SPCCSM.

    • Evaluation of the convective mass flux profiles associated with cumulus parameterization schemes of CMIP5 models


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      While the numerical models are being run with increasing resolutions, the parameterization of cumulus convection used in the general circulation models, irrespective of closure assumption and trigger mechanism, continue to use the mass flux framework. To address one of the most important components of convective parameterization, vertical profile of mass flux is examined. We have compared the convective mass flux of the Coupled Model Intercomparison Project Phase 5 (CMIP5) models during Boreal summer over the Eastern Pacific, Western Pacific and Indian Ocean with that of ERA – Year of Tropical Convection (YOTC) reanalysis dataset. The analyses suggest that most of the models overestimate the mass flux by an order over all the oceanic basins and interestingly the vertical structure also appears similar for all the CMIP5 models irrespective of ocean basins. In view of this, we state that the improper mass flux distribution in the cumulus parameterization schemes of global models need to be improved to reduce some of the uncertainties arising from the cumulus schemes of climate models which in turn impact the precipitation bias of the models.

    • Correction to: Evaluation of the convective mass flux profiles associated with cumulus parameterization schemes of CMIP5 models


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    • Evaluation of convective parameterization schemes in simulation of tropical cyclones by Climate Forecast System model: Version 2


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      Recently, a high resolution atmospheric general circulation model, i.e., Global Forecast System has been operationalized for 10 days weather forecast over Indian region. However, for extreme weather systems such as cyclones, different physical processes and their interactions with atmosphere and ocean play an important role in cyclone intensity, track, etc. Keeping this in view, Coupled Forecast System model version 2 has been used to evaluate the simulation for three severe cyclones (Phailin, Viyaru and Lehar) of 2013. In the present study, along with already existing mass-flux cumulus parameterization, i.e., Simplified Arakawa–Schubert (SAS) and revised SAS (RSAS) parameterization schemes, an additional convective adjustment scheme, i.e., Betts–Miller–Janjic (BMJ) is implemented and its performance is evaluated for the Indian Ocean cyclones. The experiments are conducted with three cumulus schemes at three different resolutions (T126, T382, and T574). Both SAS and RSAS overestimate convective rain, whereas BMJ scheme produces convective rain comparable with the observation due to the fact that BMJ produces deeper convection and does not trigger the convection too often. BMJ sustains the instability and deep convection longer thereby impacting the cyclone intensity and heavy rainfall associated with it. It is also noted that BMJ is efficient in producing rain than the SAS and RSAS. From the analyses of OLR and rain rate, BMJ is found to simulate a much realistic relation of cloud and precipitation. The paper argues that compared to available SAS and RSAS, BMJ scheme realistically produces heavy precipitation associated with the tropical cyclone over Indian region in a coupled model.

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