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Increase In MJO Maritime Continent Phases With Climate Change

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Twofold expansion of the Indo-Pacific warm pool warps the MJO life cycle

Nature volume 575pages647651(2019)Cite this article

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The Madden–Julian Oscillation (MJO) is the most dominant mode of subseasonal variability in the tropics, characterized by an eastward-moving band of rain clouds. The MJO modulates the El Niño Southern Oscillation1, tropical cyclones2,3 and the monsoons4,5,6,7,8,9,10, and contributes to severe weather events over Asia, Australia, Africa, Europe and the Americas. MJO events travel a distance of 12,000–20,000 km across the tropical oceans, covering a region that has been warming during the twentieth and early twenty-first centuries in response to increased anthropogenic emissions of greenhouse gases11, and is projected to warm further. However, the impact of this warming on the MJO life cycle is largely unknown. Here we show that rapid warming over the tropical oceans during 1981–2018 has warped the MJO life cycle, with its residence time decreasing over the Indian Ocean by 3–4 days, and increasing over the Indo-Pacific Maritime Continent by 5–6 days. We find that these changes in the MJO life cycle are associated with a twofold expansion of the Indo-Pacific warm pool, the largest expanse of the warmest ocean temperatures on Earth. The warm pool has been expanding on average by 2.3 × 105 km2 (the size of Washington State) per year during 1900–2018 and at an accelerated average rate of 4 × 105 km2(the size of California) per year during 1981–2018. The changes in the Indo-Pacific warm pool and the MJO are related to increased rainfall over southeast Asia, northern Australia, Southwest Africa and the Amazon, and drying over the west coast of the United States and Ecuador.

  • Fig. 1: A twofold expansion of the warm pool. 41586_2019_1764_Fig1_HTML.png
  • Fig. 2: Changes in the MJO life cycle. 41586_2019_1764_Fig2_HTML.png
  • Fig. 3: Correlation between MJO phase duration and ocean–atmosphere conditions. 41586_2019_1764_Fig3_HTML.png
  • Fig. 4: Changes in global rainfall in response to the changes in MJO phase duration. 41586_2019_1764_Fig4_HTML.png
  • Extended Data Fig. 1 Typical life cycle of the MJO. 41586_2019_1764_Fig5_ESM.jpg
  • Extended Data Fig. 2 Annual average period of MJO events. 41586_2019_1764_Fig6_ESM.jpg
  • Extended Data Fig. 3 Warm pool area in multiple datasets and breakpoint analysis. 41586_2019_1764_Fig7_ESM.jpg
  • Extended Data Fig. 4 Correlation between MJO phase duration and ocean–atmosphere conditions, without removing the trends. 41586_2019_1764_Fig8_ESM.jpg
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Very nice paper, thank you for posting this.

I'm intrigued that the warm pool has been tracked since the start of the 1900s, a more than doubled warm area is massive and deserves to be highlighted more.


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8 hours ago, LibertyBell said:

Chris, do you think this might be the single largest influencer of our climate?

this ole hillbilly would surmise the SUN is the single most powerful factor.

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13 minutes ago, BillT said:

this ole hillbilly would surmise the SUN is the single most powerful factor.

well think about it this way, if the SST that far south are still in the upper 80s and low 90s, how could August SST be even warmer than that?  It's probably that the temps get that hot in August and stabilize near there until October.  Thats how you get cat 5s coming out of the GOM in October like Michael and also going into Central America or even into the Southeast.


6 of them in October, almost the equal of August (7), and significantly trailing only September (21).  The first Cat 5 in the historical records is actually an October hurricane.  Heck, there's even a November Cat 5 in that list!

Michael, Matthew, Mitch and Wilma were all famous October Cat 5s.



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This goes along with the expansion ( Globally) of the Hadley Cell into the lower Ferrel latitudes... 

Among the charming symptoms:   

shifting mean storm tracks farther N of previous century(s) observation, is recently noted; 

speeding up the tropospheric deep layer wind velocities. This may be decadally ephemeral .. lasting while the polar regions are still sufficiently differentiable relative to the subtropics in winters, such that surplus latent heat stows in the lower latitudes cause increasing slope/ geopotential gradients everywhere in the ambient means.  When/if the polar regions continue to warm, this particular effect may wane into a circumstance unknown.  

North America tending to run cooler ( though still warmer than normal at times ... ) relative to the other continental areas of the planet, due to it's unique geographical circumstance in the total Pacific-North American loading pattern - which Pac heat --> tendency for increased NE Pacific ridging ...which concomitantly supplies an enhanced tendency for western/central Canadian deep layer circulation response and NW/N conveyor(s). 

And... the MJO. It is just going to behave in concert and form, in it's own way, relative to the HC forcing/changes, just as well...   

This is not discussing how any of GW and the MJO effects say, Australia, or Indonesia or the Eurasian regions or anywhere else... Africa and Mediterranean climates ..etc. It's just mentioning that there are noteworthy and observable ongoing changes in the N/A circulation tendencies. 

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Another recent paper highlighted how unusual the initiation of the March 2015 unprecedented MJO event in phase 4 was. This helped trigger the 2015-2016 super El Niño event.


The emergence of this convection–circulation pattern signaled the onset of an MJO that later strengthened to an unprecedented amplitude (MJO real-time multivariate index24 of 4.62 on March 16, 2015 compared with the previous record of 4.02 on February 14, 1985; http://www.bom.gov.au/climate/mjo/) during its eastward propagation over the tropical Pacific in March (Fig. 2c)13.

In contrast to the canonical MJOs, which typically originate in the tropical IO, the MJO in spring 2015 initiated in the western Pacific. Our analysis revealed that only 3 out of the 75 large-amplitude MJOs (occurring in 1975, 2013, and 2015; approximately 4%) during 1974–2015 initiated in the western Pacific (i.e., phase 4 of the MJO index24, Supplementary Figure 2). Notably, only in 2015, the MJO preceded the onset of an El Niño event. No eastward-propagating tropical signals from the west but strong extratropical perturbations were observed preceding the 2015 MJO event; this lead–lag relationship implies the potential extratropical effect on triggering the MJO. Furthermore, the percentile values reported in Figs 1 and 2 show the unprecedented amplitudes of the extratropical SLP, northerly, WWB, tropical SLP anomaly crossing the central and eastern equatorial Pacific (Fig. 1c), and the MJO strength. This observation revealed the distinct characteristics associated with this MJO: the effect of extratropical forcing, atypical genesis location and timing, and the extremity of amplitudes in many aspects.

The warm ocean surface in the equatorial western Pacific might be another favorable condition conducive to MJO occurrence. A vertical cross section of the monthly ocean temperature along the equator (Supplementary Figure 3) revealed that the upper ocean in the central Pacific was approximately 1.5 K warmer in February–April 2015 than the long-term mean. This warming in the central Pacific was markedly higher than that during the onset of the 1997–98 El Niño. A previous study13 reported the effect of this warm water on MJO development in early spring 2015. An analysis of the SST evolution since early 2014 indicated that the warm SST in the central Pacific was primarily the remaining positive SST anomaly from the aborted 2014 El Niño (data not shown). The extratropical forcing in late February likely triggered the anomalous convection over this warm water and initiated the rigorous atmosphere–ocean interaction in the tropical western and central Pacific and onset of a strong MJO event.

Conclusion and Discussion

An atypical MJO initiated to the west of the dateline in early March 2015 and rapidly amplified to an unprecedented magnitude over the warm SST in the central and eastern Pacific on March 16. Following the MJO, the SST in the equatorial central–eastern Pacific encountered rapid growth and ultimately evolved to a strong El Niño comparable with the 1982–83 and 1997–98 events. Before the MJO onset, we observed a persisting high-pressure system accompanied by strong cold northerly in the extratropical western North Pacific. On the basis of data diagnostics and numerical experiments, we identified an atypical effect of extratropical perturbations in the western North Pacific on triggering the onset of the MJO in March 2015 and indirectly contributing to the onset of the 2015–16 El Niño. The main results are summarized as follows:

  1. 1

    Observational analysis indicated that the strong cold northerly, which was associated with a persisting high-pressure system in the extratropical western North Pacific, penetrated southward to the tropical western Pacific and triggered the tropical convective instability that led to the onset of the MJO at an atypical location, namely west of the dateline. The critical effect of the extratropical disturbances on the MJO onset was confirmed by numerical experiments by using an atmospheric general circulation model coupled with an ocean mixed layer model.

  2. 2

    The MJO developed rapidly to an extreme magnitude because of the favorable ocean conditions: a warm upper ocean temperature in the equatorial central and western Pacific remaining from the aborted 2014 El Niño.

  3. 3

    Both data diagnostics and numerical experiments revealed that the strong WWB associated with the MJO triggered the first pulse of downwelling Kelvin wave-like perturbations that later induced the onset of the 2015–16 El Niño.

Extratropical forcing was the unique characteristic of the reported MJO–El Niño event. The onset of El Niño by an MJO has been observed often. However, according to our review of relevant literature, the present study is the first to report the onset of an El-Niño-inducing MJO in the western Pacific triggered by extratropical perturbations. Extremity was another unique characteristic. Several aspects of perturbations, such as extratropical and tropical SLP, northerly, and the MJO reached unprecedented amplitudes. The reasons for these unique characteristics remain unknown. However, our study revealed the possible effect of extratropical forcing, which has not been considered previously, on the onset of MJO and El Niño. Such a mechanism, although it might not occur frequently, warrants further attention and may elucidate the onset of an MJO and its potential effect on El Niño.


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