the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Feb 2025
The Complex Teleconnections and Feedback Mechanisms between Mainland Indochina's Southwest Monsoon and Arctic Ocean Climate Variability
Abstract. In recent decades, the Arctic climate has changed significantly, especially with a rapid decrease in Arctic Sea ice (ASI) extent in September. This study explores how natural climate variations, specifically linked to the Mainland Indochina Southwest Monsoon (MSWM), affect ASI in September using 40 years of data (1981–2020). The study found that strong MSWM years are associated with less ASI drifting to the Atlantic basin during September, leading to increased sea ice particularly in the Beaufort Sea area. Conversely, weak MSWM years tend to correspond with decreased ASI in certain locations. The MSWM influences the North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO), altering their typical patterns during strong and weak MSWM years due to interactions between monsoonal heating and the atmosphere-ocean system. During strong MSWM years, a positive NAO and negative NPO weaken the Beaufort Sea High Pressure (BSHP), whereas, during weak MSWM years, the reverse occurs, strengthening the BSHP. And the intensity of the BSHP influences Arctic air-sea interaction, influencing the movement of cold airmass and the track of the transpolar drift stream. This leads to increased sea ice formation during strong MSWM years and decreased formation during weak MSWM years in the Beaufort-Chukchi Sea region.
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RC1: 'Comment on egusphere-2025-521', Anonymous Referee #1, 08 Mar 2025
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The review of “The Complex Teleconnections and Feedback Mechanisms between Mainland Indochina's Southwest Monsoon and Arctic Ocean Climate Variability” manuscript by Kyaw Than Oo and colleagues.
The reviewed manuscript deals with the interesting teleconections between Mainland Indochina Southwest Monsoon and Arctic extratropical climate variability of the Northern Hemisphere (actually not only Arctic as the title claims because NAO is definitely not an Arctic index). Despite the subject being interesting, I recommend rejecting the manuscript basing on it having (1) not enough novelty and (2) not being convincing on the causality and even its direction.
That said, the manuscript is generally well written. The methodology used is correct, the language and general layout of the text are very good. So why do I propose to reject it?
(1) Practically everything the manuscript does is showing correlation between the monsoon in the studied area and some phenomena in the Arctic and generally extratropical Northern Hemisphere. The correlations are well known which the (generally) correct literature review shows, especially the teleconnections with Arctic Ocean sea ice variability, NAO, high pressure system over Siberia etc. They have been shown in multiple papers. I agree that the difference in using a slightly different study area and a new monsoon index could be a reason for a new paper (a weak reason because the paper would still repeat the findings of many previous ones) but there is an even greater problem.
(2) The manuscripts tries to state that it is the Mainland Indochina Southwest Monsoon which influences Arctic sea ice, NAO and surface air pressure over Siberia (rather than the other way) without any evidence for that except for rather vague statements about Rossby waves. The problem is that the literature generally agrees on the inverse direction of causality so what the authors do here is an extraordinary claim which should require extraordinary evidence and no such evidence is provided. For example the cited Chatterjee et al. (2021) states that the mechanism of this teleconnection is "propagation of Rossby wave trains from northwest Europe towards East Asia", while Krishnamurti et al., (2015), which the authors wrongly classify as agreeing with their direction of causality, claims that "The warm phase of [Atlantic Multidecadal Oscillation] may influence the monsoon through the summer North Atlantic Oscillation (SNAO)". As for the Arctic sea ice, Guo et al, (2014), also cited, show how "spring Arctic sea ice impacts the East Asian summer monsoon" (the very title of the paper). The temporal difference strongly implies the direction of influence and I find it a fault of the manuscript that it did not try looking at correlations with time lags, the simplest way to establish what is influenced by what. There is only one paper agreeing with the direction the authors try to push, Grunseich & Wang, (2016). Even as I disagree with it, I have to admit it makes a better case than the reviewed manuscript.
The direction of the influence NAO -> temperature of Siberia and hence also the local high pressure system is pretty obvious because NAO is the index of zonal circulation of the Atlantic sector and Siberia is downwind of this very circulation. The Arctic sea ice <-> NAO relation is more interesting with NAO causing the ice movement variability the manuscript attributes to the monsoon, while the extent of summer sea ice influencing the wintertime NAO through Siberian snow amount, then Siberian high pressure system, then Rossby waves to and from the stratosphere (there is a lot of literature on this, some it that cited in the manuscript). The same zonal circulation makes the strength of the monsoon dependable on both the temperature of the North Atlantic (AMO) and the mid-latitude western circulation (NAO) because both influence the temperature of inner Eurasia. The reason for a possible inverse influence is not so obvious and considering the statistically significant correlation of NAO and Arctic Circulation (AO), the index of mid-latitude Northern Hemisphere zonal circulation, this would also require an explanation of how the monsoon on south-eastern Asia is able to influence the circulation of almost the whole Northern Hemisphere. The problem I see here is that one could take any parameter anywhere which correlates with NAO or AO and make a similar paper claiming that the parameter somehow controls the zonal circulation of the Northern Hemisphere. If proven (for example thanks to its predictive nature), such relationship would be a discovery but without such evidence, it would be very dubious. We know of such influences which do exist, especially for wintertime NAO (not the season studied in the paper) but so far not for other seasons.
I concentrated my critique on the NAO and Arctic sea ice teleconnection as those topics are closest to me, but the same is probably true about the Pacific indexes the manuscript writes about.
I also have some minor comments, mostly of language nature.
- In lines 152-152 the authors say they “conducted substantial examination tests to check the dependability structures”. This requires improving.
- The sentence in lines 341-342 has no verb and is generally impossible to understand: “Homogeneous sea level pressure (SLP) anomalies, there are significant positive and negative correlations between rainfall over specific regions.”.
Citation: https://doi.org/10.5194/egusphere-2025-521-RC1
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