Abstract
In the present study, we analyze the Climate Forecast System version 2 (CFSv2) model in three resolutions, T62, T126, and T382. We evaluated the performance of all three resolutions of CFSv2 in simulating the Monsoon Intraseasonal Oscillation (MISO) of the Indian summer monsoon (ISM) by analyzing a suite of dynamic and thermodynamic parameters. Results reveal a slower northward propagation of MISO in all models with the characteristic northwest–southeast tilted rain band missing over India. The anomalous moisture convergence and vorticity were collocated with the convection center instead of being northwards. This affected the northward propagation of MISO. The easterly shear to the north of the equator was better simulated by the coarser resolution models than CFS T382. The low level specific humidity showed improvement only in CFS T382 until ~15° N. The analyses of the vertical profiles of moisture and its relation to rainfall revealed that all CFSv2 resolutions had a lower level of moisture in the lower level (< 850 hPa) and a drier level above. This eventually hampered the growth of deep convection in the model. These model shortcomings indicate a possible need of improvement in moist process parameterization in the model in tune with the increase in resolution.
Highlights
India is predominantly an agricultural country; the monsoon is of high socio-economic importance [1,2]
The distinctive findings in this study showed that, with an increase in horizontal resolution to T382, the simulated Sea Surface Temperature (SST) and tropospheric temperature is warmer than the observation; dry bias remains over the Indian landmass
In light of the performance of Climate Forecast System version 2 (CFSv2), we studied its behavior in three resolutions, T62, T126, and T382
Summary
India is predominantly an agricultural country; the monsoon is of high socio-economic importance [1,2]. [16] has explicitly shown that the CMIP5 models are able to capture the mean state of the Indian summer monsoon (ISM) broadly, but the spatial and temporal characteristics of MISO are not well represented. [23] explicitly shows that, CFSv2 (T126) captures the mean rainfall over the Indian summer monsoon region, it does so with certain systematic biases. A comprehensive comparison of performance of CFSv2 in simulating the intra-seasonal oscillations of ISM with different horizontal resolutions is required. [26] examined CFSv2 for operational extended range prediction of MISO at T126 and T382 resolution They showed that, T382 had improved climatological biases, the forecast skill of MISO from T126 was similar to T382.
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