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Role of land-surface vegetation in the march of Indian monsoon onset isochrones in a coupled model

Chakraborty, A and Samuel, JB and Paleri, A (2022) Role of land-surface vegetation in the march of Indian monsoon onset isochrones in a coupled model. In: Quarterly Journal of the Royal Meteorological Society .

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Official URL: https://doi.org/10.1002/qj.4398


Although the Climate Forecast System version-2 model simulates an overall dry bias in boreal summer mean rainfall over Indian land, the deficiency is particularly prominent over northwest India. The prevailing dryness limits the interannual prediction skill of the Indian summer monsoon rainfall and its subseasonal variability because of poor representation of latent heating due to weak moist convection and the resulting circulation. Here, we show that land-surface vegetation plays a crucial role in determining the dry bias in the Climate Forecast System version-2 model. We replaced the land-surface model's existing vegetation type over India with that derived from recent satellite-based observations. The modifications helped improve the seasonal mean rainfall over northwest India by 6. The improvements are especially noticeable during the monsoon season's onset (14) and withdrawal (10) phases. Simulations with modified vegetation advanced the onset dates over Kerala, central India, and northwest India closer to that observed. This improvement in the mean onset dates is most prominent over northwest India. Such an improvement was possible owing to a substantial reduction of long rainfall hiatus after onset over Kerala in the simulation with modified vegetation. The modification makes the spatial orientation of monsoon onset isochrones more realistic. We found that although the vertically integrated moisture flux is eastward over most of the Indian monsoon region during its onset phase, its intraseasonal components are westward. In other words, at the intraseasonal time-scale, moisture propagates against the prevailing low-level westerlies. This intraseasonal eddy moisture transport advances onset from the Bay of Bengal toward the far northwest parts of the Indian land. The representation of such intraseasonal moisture seepage in the model updated with satellite-derived vegetation types was improved. Our study indicates the necessity of greater attention to land-surface representations for improved predictions of onset dates. © 2022 Royal Meteorological Society.

Item Type: Journal Article
Publication: Quarterly Journal of the Royal Meteorological Society
Publisher: John Wiley and Sons Ltd
Additional Information: The copyright for this article belongs to John Wiley and Sons
Keywords: Atmospheric thermodynamics; Climate models; Forecasting; Moisture; Seepage; Surface measurement; Vegetation, moisture; CFSv2; Indian monsoon; Intra-seasonal; Intraseasonal eddy moisture seepage; Land surface; Land-surface vegetation; Monsoon onset; Onset; Surface vegetation, Rain
Department/Centre: Division of Mechanical Sciences > Divecha Centre for Climate Change
Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited: 25 Jan 2023 09:17
Last Modified: 25 Jan 2023 09:17
URI: https://eprints.iisc.ac.in/id/eprint/79506

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