Meridionally Extending Anomalous Wave Train over Asia During Breaks in the Indian Summer Monsoon

Uppara Umakanth; Ramesh K. Vellore; R. Krishnan; Ayantika Dey Choudhury; Jagat S.H. Bisht; Giorgia Di Capua; Dim Coumou; Reik V. Donner

doi:10.1007/s41748-019-00119-8

Meridionally Extending Anomalous Wave Train over Asia During Breaks in the Indian Summer Monsoon

Uppara Umakanth, Ramesh K. Vellore, R. Krishnan^*, Ayantika Dey Choudhury, Jagat S.H. Bisht, Giorgia Di Capua, Dim Coumou, Reik V. Donner

^*Corresponding author for this work

Water and Climate Risk

Research output: Contribution to Journal › Article › Academic › peer-review

Abstract

Anomalous interactions between the Indian summer monsoon (ISM) circulation and subtropical westerlies are known to trigger breaks in the ISM on subseasonal time-scales, characterised by a pattern of suppressed rainfall over central-north India, and enhanced rainfall over the foothills of the central–eastern Himalayas (CEH). An intriguing feature during ISM breaks is the formation of a mid-tropospheric cyclonic circulation anomaly extending over the subtropical and mid-latitude areas of the Asian continent. This study investigates the mechanism of the aforesaid Asian continental mid-tropospheric cyclonic circulation (ACMCC) anomaly using observations and simplified model experiments. The results of our study indicate that the ACMCC during ISM breaks is part of a larger meridional wave train comprising of alternating anticyclonic and cyclonic anomalies that extend poleward from the monsoon region to the Arctic. A lead–lag analysis of mid-tropospheric circulation anomalies suggests that the meridional wave-train generation is linked to latent heating (LH) anomalies over the CEH foothills, Indo-China, and the Indian landmass during ISM breaks. By conducting sensitivity experiments using a simplified global atmospheric general circulation model forced with satellite-derived three-dimensional LH, it is demonstrated that the combined effects of the enhanced LH over the CEH foothills and Indo-China and decreased LH over the Indian landmass during ISM breaks are pivotal for generating the poleward extending meridional wave train and the ACMCC anomaly. At the same time, the spatial extent of the mid-latitude cyclonic anomaly over Far-East Asia is also influenced by the anomalous LH over central–eastern China. While the present findings provide interesting insights into the role of LH anomalies during ISM breaks on the poleward extending meridional wave train, the ACMCC anomaly is found to have important ramifications on the daily rainfall extremes over the Indo-China region. It is revealed from the present analysis that the frequency of extreme rainfall occurrences over Indo-China shows a twofold increase during ISM break periods as compared to active ISM conditions.

Original language	English
Pages (from-to)	353–366
Number of pages	14
Journal	Earth Systems and Environment
Volume	3
Issue number	3
DOIs	https://doi.org/10.1007/s41748-019-00119-8
Publication status	Published - Dec 2019

Funding

The authors acknowledge the Director, Indian Institute of Tropical Meteorology (IITM), Pune, India, for the encouragement and support for this work. This work is carried out under the MoES-Belmont Project Globally Observed Teleconnections and their role and representation in Hierarchies of Atmospheric Models (GOTHAM). GdC, DC, and RVD acknowledge financial support by the German Federal Ministry for Education and Research via the GOTHAM, Sacre-X and CoSy-CC2. The data providers of all used observational precipitation data sets (IMD, APHRODITE, and TRMM) and the ECMWF reanalysis (ERA-Interim) circulation products are thankfully acknowledged. The model computations were performed on the IITM high-performance computing (HPC) facility at IITM. The authors acknowledge the Director, Indian Institute of Tropical Meteorology (IITM), Pune, India, for the encouragement and support for this work. This work is carried out under the MoES-Belmont Project Globally Observed Teleconnections and their role and representation in Hierarchies of Atmospheric Models (GOTHAM). GdC, DC, and RVD acknowledge financial support by the German Federal Ministry for Education and Research via the GOTHAM, Sacre-X and CoSy-CC2. The data providers of all used observational precipitation data sets (IMD, APHRODITE, and TRMM) and the ECMWF reanalysis (ERA-Interim) circulation products are thankfully acknowledged. The model computations were performed on the IITM high-performance computing (HPC) facility at IITM.

Funders	Funder number
ERA-Interim
German Federal Ministry for Education and Research
Bundesministerium für Bildung und Forschung	CoSy-CC2
Indian Institute of Technology Madras

Keywords

Active and break periods
Extreme precipitation
Indian summer monsoon
Meridional Rossby wave
Monsoon and mid-latitude flows

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@article{da38416b7c234f058e0e805251d28986,

title = "Meridionally Extending Anomalous Wave Train over Asia During Breaks in the Indian Summer Monsoon",

abstract = "Anomalous interactions between the Indian summer monsoon (ISM) circulation and subtropical westerlies are known to trigger breaks in the ISM on subseasonal time-scales, characterised by a pattern of suppressed rainfall over central-north India, and enhanced rainfall over the foothills of the central–eastern Himalayas (CEH). An intriguing feature during ISM breaks is the formation of a mid-tropospheric cyclonic circulation anomaly extending over the subtropical and mid-latitude areas of the Asian continent. This study investigates the mechanism of the aforesaid Asian continental mid-tropospheric cyclonic circulation (ACMCC) anomaly using observations and simplified model experiments. The results of our study indicate that the ACMCC during ISM breaks is part of a larger meridional wave train comprising of alternating anticyclonic and cyclonic anomalies that extend poleward from the monsoon region to the Arctic. A lead–lag analysis of mid-tropospheric circulation anomalies suggests that the meridional wave-train generation is linked to latent heating (LH) anomalies over the CEH foothills, Indo-China, and the Indian landmass during ISM breaks. By conducting sensitivity experiments using a simplified global atmospheric general circulation model forced with satellite-derived three-dimensional LH, it is demonstrated that the combined effects of the enhanced LH over the CEH foothills and Indo-China and decreased LH over the Indian landmass during ISM breaks are pivotal for generating the poleward extending meridional wave train and the ACMCC anomaly. At the same time, the spatial extent of the mid-latitude cyclonic anomaly over Far-East Asia is also influenced by the anomalous LH over central–eastern China. While the present findings provide interesting insights into the role of LH anomalies during ISM breaks on the poleward extending meridional wave train, the ACMCC anomaly is found to have important ramifications on the daily rainfall extremes over the Indo-China region. It is revealed from the present analysis that the frequency of extreme rainfall occurrences over Indo-China shows a twofold increase during ISM break periods as compared to active ISM conditions.",

keywords = "Active and break periods, Extreme precipitation, Indian summer monsoon, Meridional Rossby wave, Monsoon and mid-latitude flows",

author = "Uppara Umakanth and Vellore, {Ramesh K.} and R. Krishnan and Choudhury, {Ayantika Dey} and Bisht, {Jagat S.H.} and {Di Capua}, Giorgia and Dim Coumou and Donner, {Reik V.}",

year = "2019",

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doi = "10.1007/s41748-019-00119-8",

language = "English",

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T1 - Meridionally Extending Anomalous Wave Train over Asia During Breaks in the Indian Summer Monsoon

AU - Umakanth, Uppara

AU - Vellore, Ramesh K.

AU - Krishnan, R.

AU - Choudhury, Ayantika Dey

AU - Bisht, Jagat S.H.

AU - Di Capua, Giorgia

AU - Coumou, Dim

AU - Donner, Reik V.

PY - 2019/12

Y1 - 2019/12

N2 - Anomalous interactions between the Indian summer monsoon (ISM) circulation and subtropical westerlies are known to trigger breaks in the ISM on subseasonal time-scales, characterised by a pattern of suppressed rainfall over central-north India, and enhanced rainfall over the foothills of the central–eastern Himalayas (CEH). An intriguing feature during ISM breaks is the formation of a mid-tropospheric cyclonic circulation anomaly extending over the subtropical and mid-latitude areas of the Asian continent. This study investigates the mechanism of the aforesaid Asian continental mid-tropospheric cyclonic circulation (ACMCC) anomaly using observations and simplified model experiments. The results of our study indicate that the ACMCC during ISM breaks is part of a larger meridional wave train comprising of alternating anticyclonic and cyclonic anomalies that extend poleward from the monsoon region to the Arctic. A lead–lag analysis of mid-tropospheric circulation anomalies suggests that the meridional wave-train generation is linked to latent heating (LH) anomalies over the CEH foothills, Indo-China, and the Indian landmass during ISM breaks. By conducting sensitivity experiments using a simplified global atmospheric general circulation model forced with satellite-derived three-dimensional LH, it is demonstrated that the combined effects of the enhanced LH over the CEH foothills and Indo-China and decreased LH over the Indian landmass during ISM breaks are pivotal for generating the poleward extending meridional wave train and the ACMCC anomaly. At the same time, the spatial extent of the mid-latitude cyclonic anomaly over Far-East Asia is also influenced by the anomalous LH over central–eastern China. While the present findings provide interesting insights into the role of LH anomalies during ISM breaks on the poleward extending meridional wave train, the ACMCC anomaly is found to have important ramifications on the daily rainfall extremes over the Indo-China region. It is revealed from the present analysis that the frequency of extreme rainfall occurrences over Indo-China shows a twofold increase during ISM break periods as compared to active ISM conditions.

AB - Anomalous interactions between the Indian summer monsoon (ISM) circulation and subtropical westerlies are known to trigger breaks in the ISM on subseasonal time-scales, characterised by a pattern of suppressed rainfall over central-north India, and enhanced rainfall over the foothills of the central–eastern Himalayas (CEH). An intriguing feature during ISM breaks is the formation of a mid-tropospheric cyclonic circulation anomaly extending over the subtropical and mid-latitude areas of the Asian continent. This study investigates the mechanism of the aforesaid Asian continental mid-tropospheric cyclonic circulation (ACMCC) anomaly using observations and simplified model experiments. The results of our study indicate that the ACMCC during ISM breaks is part of a larger meridional wave train comprising of alternating anticyclonic and cyclonic anomalies that extend poleward from the monsoon region to the Arctic. A lead–lag analysis of mid-tropospheric circulation anomalies suggests that the meridional wave-train generation is linked to latent heating (LH) anomalies over the CEH foothills, Indo-China, and the Indian landmass during ISM breaks. By conducting sensitivity experiments using a simplified global atmospheric general circulation model forced with satellite-derived three-dimensional LH, it is demonstrated that the combined effects of the enhanced LH over the CEH foothills and Indo-China and decreased LH over the Indian landmass during ISM breaks are pivotal for generating the poleward extending meridional wave train and the ACMCC anomaly. At the same time, the spatial extent of the mid-latitude cyclonic anomaly over Far-East Asia is also influenced by the anomalous LH over central–eastern China. While the present findings provide interesting insights into the role of LH anomalies during ISM breaks on the poleward extending meridional wave train, the ACMCC anomaly is found to have important ramifications on the daily rainfall extremes over the Indo-China region. It is revealed from the present analysis that the frequency of extreme rainfall occurrences over Indo-China shows a twofold increase during ISM break periods as compared to active ISM conditions.

KW - Active and break periods

KW - Extreme precipitation

KW - Indian summer monsoon

KW - Meridional Rossby wave

KW - Monsoon and mid-latitude flows

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JO - Earth Systems and Environment

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ER -

Meridionally Extending Anomalous Wave Train over Asia During Breaks in the Indian Summer Monsoon

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