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Seasonal Cycle of Indian Monsoon & Understanding teleconnections using Energetics approach

Dominant Seasonal Modes of Indian Rainfall

Physical mechanisms behind the monthly evolution of Indian Rainfall particularly during the summer monsoon season are not well known. Our objective is to find out the existence of physical modes that can explain these monthly evolutions every year. We found out the dominant modes using standard PC analysis and considered the first two modes for our study which explains 51% of the total variance. Physical mechanisms behind these patterns are found in this study.

Key Observations:

The Second mode peaks in June. The rest of the season shows a damping pattern.
The first mode is insignificant in June and becomes active during the rest of the season.

What we looked for:

Physical mechanisms of these seasonal modes and their inter-annual variabilities are found.

Results:

Inter-annual variability of June rainfall is associated with Madden-Julian Oscillation activities along with a strong mean background precipitable water state.
First seasonal mode variations show a good resemblance with evolving ENSO-related moisture flux variability.

Future attempts:

Why does evolving ENSO/first seasonal mode not impact June rainfall but impact post-June rainfall?

Onset Phase Rainfall governed by MJO phase transition

Second mode peaks in June, and we have shown that this mode is related to the Fast and Slow progress of the onset of rainfall. This fast and slow progress of monsoon onset is mainly governed by the Normal and slow phase transition of MJO. Click the MJO-Pwat button to watch the animation of how MJO-driven precipitable water vapor changes over the Indian land during the years with fast monsoon progress.

MJO-Pwat

Tropical Precipitation Variations:

Click on this

Energy Flux Framework:

In the seasonal time scale, the region of intense rainfall/convection over the tropical belt coincides the region where the blue line (Energy flux equator i.e. from where the meridional energy flux diverges out) and the cyan line (Energy flux prime meridian where the zonal energy flux diverges out) crosses each other.

Here, we have found out that, the minimum Energy Flux Potential (EFP intersection point of EFE and EFPM) which essentially represent the source region of energy from where divergence of energy fluxes will take place. These EFP min zones are the region of intense convection/precipitation. This Zones stays for 7 months October-April over the Western-Central Pacific region and then suddenly jumps to the Bay of Bengal region and stays there for May-September. Here, I am asking, why is the intense convection zone stays over 7 months on one region and 5 months over other and why is there a sudden jump from April-May and September-October?

This can explain the onset and retreat of South Asian and East Asian Summer Monsoon.

Energetic constraints on the South Asian Monsoon

EFE, one or two months prior to the Onset, has a predictive value. Early Kerala Onset is related to more northward shift of EFE during April & May, and vice versa.
EFPM is related to the interannual variability of the South Asian Monsoon precipitation, whereas EFE is uncorrelated with seasonal monsoon rainfall.
EFE is related to the mean Monsoon condition, wheras EFPM is related to interannual variability of South Asian Summer Monsoon.
We show that EFPM position variations are related to the ENSO, dominant interannual variability of SASM precipitation, paricularly toward the end of the season.

EFPM-ENSO

Toward the end of the season, a significant change in the EFPM position is evident. This leads to longer SASM in La Niña years compared to El Niño years.

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