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Energetic Constraints on the South Asian Summer Monsoon Interannual Variability

Sujatra Bhattacharyya¹

Ori Adam²

Arindam Chakraborty¹^,³

¹Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bengaluru, India

²Hebrew University of Jerusalem, Jerusalem, Israel

³Divecha Centre for Climate Change, Indian Institute of Science, Bengaluru, India

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Monthly variations in the Tropical Precipitation

Seasonal Meridional migration of the tropical zonal band of Precipitation.

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Energy Flux Framework:

Atmospheric Energy Balance:

At the Monthly timescale, neglecting the tendency term

Helmholtz Decomposition:

Zonal & Meridional energy fluxes:

Schneider et al., 2014; Adam et al., 2016; Boos & Korty, 2016

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Meridional & Zonal NEI contrast

Monsoon-Energy-Breeze

Monsoon-ITCZ

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Energetic Constraints over the South Asian Monsoon

Both seasonal Zonal and Meridional Shifts in Precipitation are responsible for Monsoons over South Asia.

EFE and EFPM (Rising branch of Meridional and Zonal Overturning Circulations, respectively) shifts over South Asia (Shown by Boos & Korty, 2016 & Tuckman et al., 2024) and are independent.

Correlation Coefficient b/w seasonal mean EFE & EFPM during SASM: -0.16 (Insignificant)

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Monsoon Precipitation vs EFE & EFPM variations

EFE exhibits a strong correlation with monsoon onset variations at a lead time of 1-2 months. However, it shows very little correlation with precipitation throughout the peak monsoon season.

EFPM shows a stronger correlation with precipitation throughout the monsoon season.

EFE doesn’t contribute to the interannual variations of the monsoon. The interannual variations are mainly related to the EFPM.

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EFE can be used to predict Monsoon Onset in Kerala

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Energetic Constraints on the Interannual Monsoon Variability

Towards the end of the season, a significant change in the EFPM location can be observed

Bhattacharyya & Chakraborty 2025 have shown that ENSO impacts the Indian Monsoon strongly at the end of the Season.

Q. Does ENSO show its largest impact on SASM at the end of the season?

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ENSO-SASM relationship

EFPM stays longer over the South Asian monsoon domain during La Niña years compared to El Niño years.

Anomalous positive zonal NEI can be observed over the Asian domain compared to the Pacific during Niña-Niño conditions.

Thus, EFPM stays longer over the South Asian domain during La Niña years.

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Conclusions

This study merges the ITCZ and Energy Breeze interpretations of Regional Monsoons.
Hemispheric meridional NEI contrasts result in ITCZ/EFE shifts
Land-Ocean zonal NEI contrasts drive EFPM shifts.
EFE establishes a mean monsoon condition over South Asia.
EFPM is related to the interannual variations of the Monsoon.
EFPM stays for a longer period over South Asia during La Niña years compared to El Niño years.

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Thank You

Mail ID: sujatrab@iisc.ac.in ; sujatra1bht@gmail.com