• Tanmoy Goswami

      Articles written in Journal of Earth System Science

    • Performance of a very high-resolution global forecast system model (GFS T1534) at 12.5 km over the Indian region during the 2016–2017 monsoon seasons

      Mukhopadhyay P Prasad V S Phani Murali Krishna R Medha Deshpande Malay Ganai Snehlata Tirkey Sahadat Sarkar Tanmoy Goswami Johny C J Kumar Roy Mahakur M Durai V R Rajeevan M

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      A global forecast system model at a horizontal resolution of T1534 ($\sim$12.5 km) has been evaluated for the monsoon seasons of 2016 and 2017 over the Indian region. It is for the first time that such a high-resolution global model is being run operationally for monsoon weather forecast. A detailed validation of the model therefore is essential. The validation of mean monsoon rainfall for the season and individual months indicates a tendency for wet bias over the land region in all the forecast lead time. The probability distribution of forecast rainfall shows an overestimation (underestimation) of rainfall for the lighter (heavy) categories. However, the probability distribution functions of moderate rainfall categories are found to be reasonable. The model shows fidelity in capturing the extremely heavy rainfall categories with shorter lead times. The model reasonably predicts the large-scale parameters associated with the Indian summer monsoon, particularly, the vertical profile of the moisture. The diurnal rainfall variability forecasts in all lead times show certain biases over different land and oceanic regions and, particularly, over the north–west Indian region. Although the model has a reasonable fidelity in capturing the spatio-temporal variability of the monsoon rain, further development is needed to enhance the skill of forecast of a higher rain rate with a longer lead time.

    • 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.

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