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Research Article
Raju Pathak
Indian Institute of Technology Delhi
Corresponding Author
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Four generations of the NCAR Community Atmosphere Model (CAM-3, 4, 5, and 6) are evaluated for the Indian summer monsoon (ISM) simulations. Total precipitation simulated by successive versions of CAM is overestimated over the western equatorial Indian Ocean (EIO), Arabian Sea, and Western Ghats (WGs), and underestimated over the eastern EIO, Bay of Bengal (BoB), and Indo-Burmese mountains, due to overestimated convective and underestimated large-scale precipitation, respectively. Overestimation of total precipitation over the Himalayan region is increased in successive CAM variants, primarily through enhanced large-scale precipitation. Improvement in total precipitation simulation over BoB is found in successive CAM variants, with the largest improvement in CAM6. The frequency of total precipitation is overestimated for low precipitation rates and underestimated for high precipitation rates in CAM variants, except in CAM4 for high precipitation rates.
The subtropical westerly and tropical easterly jets are better simulated in CAM5-6 than CAM3-4 (highly overestimated). The easterly shear of zonal wind during the peak monsoon is highly overestimated in all CAM variants. The monsoon low-level jet over AS and peninsular India is overestimated in all CAM variants with the largest overestimation in CAM6, resulting in increased precipitation over WGs and peninsular India. We find the large underestimation in a tropical easterly jet over peninsular India and EIO in CAM3 to have improved in the successive versions. In addition, overestimation of the strength of the subtropical westerly jet and the Tibetan anticyclone seen in CAM3 has improved in successive variants of CAM. We find improvements in monsoon intra-seasonal oscillation (MISO) and associated internal dynamics and the east-west and north-south heat source in successive variants of CAM. Overall, we find many improvements in the simulation of ISM precipitation and its associated dynamics in successive variants of CAM, however, there still remain some important biases (e.g., eastward component of MISO, monsoon low-level jet, excessive precipitation over Himalayan foothills, early monsoon onset, etc.) that need to be alleviated for more realistic ISM simulations in future versions of CAM.
Keywords
Climate Modeling, NCAR CAM, Indian Summer Monsoon, MISO
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This preprint is under consideration at Theoretical and Applied Climatology. A preprint is a preliminary version of a manuscript that has not completed peer review at a journal. Research Square does not conduct peer review prior to posting preprints. The posting of a preprint on this server should not be interpreted as an endorsement of its validity or suitability for dissemination as established information or for guiding clinical practice.
Learn more about In Review
Research Article
Raju Pathak
Indian Institute of Technology Delhi
Corresponding Author
Badges
Prescreen
This manuscript passed our Prescreen assessment
Complete author information
Appropriate declaration statements
Potential risks to human health
Prescreen
Peer Review Timeline
CURRENT STATUS: Under Review
Version 1
Posted 04 May, 2021
No community comments so far
Reviewers invited
Invitations sent on 28 Apr, 2021
Editor assigned
On 13 Apr, 2021
First submitted
On 09 Apr, 2021
Metrics
Comments: 0
PDF Downloads: ...
HTML Views: ...
Subject Areas
Atmospheric Sciences
License:
This work is licensed under a CC BY 4.0 License. Read Full License
Four generations of the NCAR Community Atmosphere Model (CAM-3, 4, 5, and 6) are evaluated for the Indian summer monsoon (ISM) simulations. Total precipitation simulated by successive versions of CAM is overestimated over the western equatorial Indian Ocean (EIO), Arabian Sea, and Western Ghats (WGs), and underestimated over the eastern EIO, Bay of Bengal (BoB), and Indo-Burmese mountains, due to overestimated convective and underestimated large-scale precipitation, respectively. Overestimation of total precipitation over the Himalayan region is increased in successive CAM variants, primarily through enhanced large-scale precipitation. Improvement in total precipitation simulation over BoB is found in successive CAM variants, with the largest improvement in CAM6. The frequency of total precipitation is overestimated for low precipitation rates and underestimated for high precipitation rates in CAM variants, except in CAM4 for high precipitation rates.
The subtropical westerly and tropical easterly jets are better simulated in CAM5-6 than CAM3-4 (highly overestimated). The easterly shear of zonal wind during the peak monsoon is highly overestimated in all CAM variants. The monsoon low-level jet over AS and peninsular India is overestimated in all CAM variants with the largest overestimation in CAM6, resulting in increased precipitation over WGs and peninsular India. We find the large underestimation in a tropical easterly jet over peninsular India and EIO in CAM3 to have improved in the successive versions. In addition, overestimation of the strength of the subtropical westerly jet and the Tibetan anticyclone seen in CAM3 has improved in successive variants of CAM. We find improvements in monsoon intra-seasonal oscillation (MISO) and associated internal dynamics and the east-west and north-south heat source in successive variants of CAM. Overall, we find many improvements in the simulation of ISM precipitation and its associated dynamics in successive variants of CAM, however, there still remain some important biases (e.g., eastward component of MISO, monsoon low-level jet, excessive precipitation over Himalayan foothills, early monsoon onset, etc.) that need to be alleviated for more realistic ISM simulations in future versions of CAM.
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