Thoughts on Changing Circulation in Warm Season

[hm2]

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:

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.

 

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/

 

[hm2]

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.

[Rainshadow]

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.

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

[hm2]

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.

[tombo82685]

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?

[hm2]

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.

[Chubbs]

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

[hm2]

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

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!

 

 

[hm2]

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

 

 

[hm2]

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?

I wanted to link this paper and forgot to when we were talking about temp trends:

https://www.pnas.org/content/pnas/115/19/4863.full.pdf

[Harbourton]

Just a quick question from a rank amateur. Why does the TUTT form in the Atlantic and what effect does it have on the tropical season.

[hm2]

On 6/8/2021 at 6:05 PM, Harbourton said:

Just a quick question from a rank amateur. Why does the TUTT form in the Atlantic and what effect does it have on the tropical season.

Hey, sorry for the late response. We had our first baby girl on 6/9 (what a ride it's been)!

The TUTT is a stationary wave that forms every year and peaks with the Northern Hemisphere's summertime monsoon season. This is when land/sea temp contrasts peak and anticyclones are the most poleward/powerful. The mid-ocean cooling/troughs are a restoring force (driven by evaporational cooling and rotating Earth) of the diabatic warming centered over the Indian and American monsoons (see the climo 300mb temp plot for JJA attached). In addition to this general relationship from land/sea contrasts and monsoons (thermodynamic relationship on rotating Earth), there is a dynamic element too. The Mid Latitude Waveguide can reinforce the TUTTs through poleward anticyclonic wavebreaking and splintering higher potential vorticity around anticyclones (e.g. downstream of Bermuda Highs). The Atlantic TUTT strength is positively correlated to tropical activity via the dry air intrusion/shear it induces. However, a proper filament or streamer can go on to produce its own tropical cyclone under the right conditions. Also, depending on the diabatic ridge strength of a TC that interacts with the TUTT, it could be strong enough to offset a TUTT since they're usually not too vertically deep. See Papin's work for more: http://www.atmos.albany.edu/student/ppapin/research_phd.php & Wang et al. https://www.pnas.org/content/117/37/22720

[Harbourton]

5 hours ago, hm2 said:

Hey, sorry for the late response. We had our first baby girl on 6/9 (what a ride it's been)!

The TUTT is a stationary wave that forms every year and peaks with the Northern Hemisphere's summertime monsoon season. This is when land/sea temp contrasts peak and anticyclones are the most poleward/powerful. The mid-ocean cooling/troughs are a restoring force (driven by evaporational cooling and rotating Earth) of the diabatic warming centered over the Indian and American monsoons (see the climo 300mb temp plot for JJA attached). In addition to this general relationship from land/sea contrasts and monsoons (thermodynamic relationship on rotating Earth), there is a dynamic element too. The Mid Latitude Waveguide can reinforce the TUTTs through poleward anticyclonic wavebreaking and splintering higher potential vorticity around anticyclones (e.g. downstream of Bermuda Highs). The Atlantic TUTT strength is positively correlated to tropical activity via the dry air intrusion/shear it induces. However, a proper filament or streamer can go on to produce its own tropical cyclone under the right conditions. Also, depending on the diabatic ridge strength of a TC that interacts with the TUTT, it could be strong enough to offset a TUTT since they're usually not too vertically deep. See Papin's work for more: http://www.atmos.albany.edu/student/ppapin/research_phd.php & Wang et al. https://www.pnas.org/content/117/37/22720

Congratulations! Enjoy the ride. Just one quick question. It would seem that the strength of the Bermuda high would have a direct impact - No?

[ACwx]

This may belong on a separate not-yet-created thread since the Quasi-Biennial Oscillation seems to only appear in discussions about winter impacts instead of summer, but I noticed this Twitter thread today and thought it was interesting that in over 50 years of records, the QBO 2-year pattern had never been disrupted, and now it has been disrupted twice since 2015.

In the thread it is noted that the '15/16 event was driven by momentum flux from the Northern Hemisphere while the '19/20 event was driven by Southern Hemisphere momentum. Potentially there may be reason to believe that climate change may lead to less predictability of the QBO.

Not sure if the QBO has as much influence as other patterns but it's fascinating that this may be something else to consider as the atmosphere continues to warm.

 

 

[rramblings]

8 hours ago, hm2 said:

Hey, sorry for the late response. We had our first baby girl on 6/9 (what a ride it's been)!

The TUTT is a stationary wave that forms every year and peaks with the Northern Hemisphere's summertime monsoon season. This is when land/sea temp contrasts peak and anticyclones are the most poleward/powerful. The mid-ocean cooling/troughs are a restoring force (driven by evaporational cooling and rotating Earth) of the diabatic warming centered over the Indian and American monsoons (see the climo 300mb temp plot for JJA attached). In addition to this general relationship from land/sea contrasts and monsoons (thermodynamic relationship on rotating Earth), there is a dynamic element too. The Mid Latitude Waveguide can reinforce the TUTTs through poleward anticyclonic wavebreaking and splintering higher potential vorticity around anticyclones (e.g. downstream of Bermuda Highs). The Atlantic TUTT strength is positively correlated to tropical activity via the dry air intrusion/shear it induces. However, a proper filament or streamer can go on to produce its own tropical cyclone under the right conditions. Also, depending on the diabatic ridge strength of a TC that interacts with the TUTT, it could be strong enough to offset a TUTT since they're usually not too vertically deep. See Papin's work for more: http://www.atmos.albany.edu/student/ppapin/research_phd.php & Wang et al. https://www.pnas.org/content/117/37/22720

 Congrats on your baby girl

[hm2]

19 hours ago, Harbourton said:

Congratulations! Enjoy the ride. Just one quick question. It would seem that the strength of the Bermuda high would have a direct impact - No?

It might be one of those things where the Bermuda/Azores Ridge and, say, TUTT or PVS activity are both stronger than normal (and therefore correlated) but not necessarily causal. The Pacific and Americas will take turns pulsating monsoonal fluxes...we plot these pulses on time longitude maps and think they're MJO waves. But more often than not in the summertime, it's just pulsing monsoons with high frequency kelvin waves embedded within. These dictate which monsoonal ridge perks up and how the wave trains may behave. In the case of the Bermuda High, it's not necessarily its strength as much as how prolific is the Rossby Wave Breaking (RWB) in the Mid Latitude waveguide. Strong anticyclonic wave breaking from North America into the N. Atlantic will likely promote equatorward displacements of higher PV and reinforce the TUTT.

[hm2]

18 hours ago, ACwx said:

This may belong on a separate not-yet-created thread since the Quasi-Biennial Oscillation seems to only appear in discussions about winter impacts instead of summer, but I noticed this Twitter thread today and thought it was interesting that in over 50 years of records, the QBO 2-year pattern had never been disrupted, and now it has been disrupted twice since 2015.

In the thread it is noted that the '15/16 event was driven by momentum flux from the Northern Hemisphere while the '19/20 event was driven by Southern Hemisphere momentum. Potentially there may be reason to believe that climate change may lead to less predictability of the QBO.

Not sure if the QBO has as much influence as other patterns but it's fascinating that this may be something else to consider as the atmosphere continues to warm.

 

 

A warmer planet means more convection, more westerly flows and rossby wave sources and potential new-comers to the wave-driven momentum process over the Tropics. The westerly QBO promotes an expanded Tropical Heating with more off-equator sources. I don't think it's a coincidence that its those shear stresses that have done that lately.

[greg ralls]

On 6/28/2021 at 12:18 PM, hm2 said:

Hey, sorry for the late response. We had our first baby girl on 6/9 (what a ride it's been)!

 

 

Congratulations!

[Rainshadow]

On 6/28/2021 at 12:18 PM, hm2 said:

Hey, sorry for the late response. We had our first baby girl on 6/9 (what a ride it's been)!

The TUTT is a stationary wave that forms every year and peaks with the Northern Hemisphere's summertime monsoon season. This is when land/sea temp contrasts peak and anticyclones are the most poleward/powerful. The mid-ocean cooling/troughs are a restoring force (driven by evaporational cooling and rotating Earth) of the diabatic warming centered over the Indian and American monsoons (see the climo 300mb temp plot for JJA attached). In addition to this general relationship from land/sea contrasts and monsoons (thermodynamic relationship on rotating Earth), there is a dynamic element too. The Mid Latitude Waveguide can reinforce the TUTTs through poleward anticyclonic wavebreaking and splintering higher potential vorticity around anticyclones (e.g. downstream of Bermuda Highs). The Atlantic TUTT strength is positively correlated to tropical activity via the dry air intrusion/shear it induces. However, a proper filament or streamer can go on to produce its own tropical cyclone under the right conditions. Also, depending on the diabatic ridge strength of a TC that interacts with the TUTT, it could be strong enough to offset a TUTT since they're usually not too vertically deep. See Papin's work for more: http://www.atmos.albany.edu/student/ppapin/research_phd.php & Wang et al. https://www.pnas.org/content/117/37/22720

Congratulations!