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Thoughts on Changing Circulation in Warm Season


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General observations I've noticed or found in research that I believe are prominent in warm season trends:

1. North Pacific SST gradient has shifted poleward, even if you take into account the PDO. The Tropics overall have been warming of course, but the IO / Pacific are warming more quickly than the Atlantic, which affects convection/monsoons. More on that:

2. The migration of output of divergence from the East Asian Monsoon / West Pacific Warm Pool eastward and the SST gradient shift have likely contributed to the intensified jet across the North Pacific into the North Atlantic. A few plots during the June-Oct mean: output_JwSi0W.gif.707cfad8355e7163c323110886ab773d.gifoutput_T6wrZb.gif.ce8f02e7fc36b4e77689d17b43d6eb75.gif

3. The orientation of the jet and poleward shift have created an anomalous wave train in the NH jet when comparing climo normals (this same trend was noted when comparing 1971-2000 to 1981-2010 as well, see: https://journals.ametsoc.org/view/journals/mwre/147/2/mwr-d-18-0131.1.xml). The jet has recently intensified (as you can see above) and extended across the North Atlantic. While a low level factor, the SST gradient has intensified in N. Atlantic. Part of this is the Greenland ice melt and another part is the warming western N. Atlantic basin.

wavetrains.png.e113f844620ace857ba68aea5dfbf80d.png

 

Where the arc shifts in the black line is about where the exit region of the North Atlantic jet is located. The intensification of the N. Atlantic low anomaly here, extension of jet, and wave trend, have created a strong high over the Barents' Region. This dynamic response from global circulation has sped up the sea ice loss in those areas.

https://www.ncdc.noaa.gov/snow-and-ice/regional-sea-ice/extent/Barents/

 

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300mb temperature differences between various periods are attached below for June-October time frame. The warming across the tropical and subtropical Pacific is the most noteworthy trend, but you can see it's nearly ubiquitous throughout the NH at these latitudes. This intensified gradient is the main reason the upper level jet is stronger.

More convection = more LHF. The expanding Pacific divergence, tropical forcing etc. is directly related to this regional warming trend too. It's all intensifying the extratropical jet.

300mbtemp1.png300mbtemp2.png

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On 5/21/2021 at 12:45 PM, hm2 said:

300mb temperature differences between various periods are attached below for June-October time frame. The warming across the tropical and subtropical Pacific is the most noteworthy trend, but you can see it's nearly ubiquitous throughout the NH at these latitudes. This intensified gradient is the main reason the upper level jet is stronger.

More convection = more LHF. The expanding Pacific divergence, tropical forcing etc. is directly related to this regional warming trend too. It's all intensifying the extratropical jet.

300mbtemp1.png300mbtemp2.png

Is this the reason we can’t buy a below normal summer any longer?

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On 5/23/2021 at 1:10 PM, Rainshadow6.6 said:

Is this the reason we can’t buy a below normal summer any longer?

 

Outcomes probably from the same cause (AGW). The direct moisture flux from the ocean is keeping overnight lows warmer and warmer it seems.

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23 minutes ago, hm2 said:

 

Outcomes probably from the same cause (AGW). The direct moisture flux from the ocean is keeping overnight lows warmer and warmer it seems.

Gotta imagine all the additional moisture in atmosphere will make tropical potential greater assuming conditions are favorable for development?

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13 hours ago, tombo82685 said:

Gotta imagine all the additional moisture in atmosphere will make tropical potential greater assuming conditions are favorable for development?

There's still a debate on how AGW is altering the Tropics. There is some reason to believe there has been a net latitude gain in storm tracks over time with expanded Hadley Cell trend. It also appears like when conditions aloft are favorable, hurricanes have the ability to be stronger. But there are holes in other ideas like the idea that they're slowing down with time. The Atlantic is becoming increasingly filled with exhaust basically as the Pacific output, tropical forcing-wise, continues to expand. This added exhaust has made for some very dry/storm-less times as well. This has led to the idea that we'll see more extremes in tropical output.

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10 hours ago, hm2 said:

There's still a debate on how AGW is altering the Tropics. There is some reason to believe there has been a net latitude gain in storm tracks over time with expanded Hadley Cell trend. It also appears like when conditions aloft are favorable, hurricanes have the ability to be stronger. But there are holes in other ideas like the idea that they're slowing down with time. The Atlantic is becoming increasingly filled with exhaust basically as the Pacific output, tropical forcing-wise, continues to expand. This added exhaust has made for some very dry/storm-less times as well. This has led to the idea that we'll see more extremes in tropical output.

A global signal on hurricane intensity is starting to emerge. Per article and  Kerry Emanuel, this is consistent with expectations, wouldn't have expected to detect a signal until recently due to sparse and noisy data.

https://www.pnas.org/content/117/22/11975

Screenshot_2021-05-25 Wall Street Journal article repeats multiple incorrect and misleading claims made in Steven Koonin’s [...].png

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15 hours ago, Chubbs said:

A global signal on hurricane intensity is starting to emerge. Per article and  Kerry Emanuel, this is consistent with expectations, wouldn't have expected to detect a signal until recently due to sparse and noisy data.

https://www.pnas.org/content/117/22/11975

Screenshot_2021-05-25 Wall Street Journal article repeats multiple incorrect and misleading claims made in Steven Koonin’s [...].png

A few thoughts:

1. Kossin et al. is who released the controversial "TCs are slowing down" with global warming stuff. There is a sizable opposition to that finding and legit concerns with the dataset and conclusions. However, there are equally legit defenders of the findings and points made.

2. Satellite derived methods can overestimate intensity just as easily as it can underestimate. While the data is homogeneous in 1 sense, as authors describe, the actual atmosphere is not. I have yet to see a study on how the Dvorak technique, for example, can be influenced by changing upper troposphere and lower stratosphere (UTLS) temperatures over time (it's possible it's out there and I missed it).

3. I don't need to state the obvious the the globe saw a substantial change in TC output, in general, from the 1970s/80s to the 1990s. Influences of mid-20th century aerosols possibly cooling SST then may have been the culprit to masking the AGW induced warming. For now, you can see why it would be easy to argue that "cycles" in the ocean explain the findings of the author...in particular the Atlantic. But, I don't think they can explain all findings in each basin. For example, the southern TC output is of interest, even though it's estimated from poor record.

4. There is no denying the increasing MPI of the warming SST and possible contribution to more intense TC. But complications like shifting tropical waves or developing TCs further poleward could offset maximum intensities over time. In addition, the changes in circulation I've mentioned above could complicate stability with changes in upper air.

 

As usual, this stuff is messy. Thanks for the paper!

 

 

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  • 2 weeks later...

Location of Warming & Its Effect on Summer Waveguide:

Temperature gradients determine the location of jets through the thermal wind relationship and these jets determine wave behavior. The nature of how global warmth is distributed (currently accelerated at the poles through ice/snow albedo feedback) is having an effect on the way the temp gradients and jet streams manifest. This can give rise to a structure that favors a latitude-trapping waveguide in zonal wind. In the summertime, wavenumbers 5-8 tend to get trapped under this changing structure of warming, and this can promote QRA, quasi-resonant amplification (this pattern works naturally with the NH's geography). It's possible that this weakening of the zonal wind in Mid Latitudes and acceleration at polar latitudes is responsible for the recent summertime Arctic Low (and slowdown in ice melt).

 

For the rest of the 21st century, the Mid Latitude aerosol loading is expected to drop off and possibly refocus the acceleration of the warmth here. This may temporarily reduce the QRA-temp profile and zonal wind pattern in place. However, it is not certain that will be effective and all models assume the Arctic Amplification/QRA temps will resume by end of century.

 

Papers:

https://www.nature.com/articles/srep45242?iu=&iap=false&exception=true&cust_params=

https://advances.sciencemag.org/content/advances/4/10/eaat3272.full.pdf

https://iopscience.iop.org/article/10.1088/1748-9326/abc047

 

 

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