The Role of Elevated Mixed Layers in Severe Weather

[ThompNickSon]

Calm Days,

I would hate to see you change the thread as long as this line of thought has anything to do with the prevalence of EML's in the US and their relevance to severe weather here. Let me try and restate, for your correction, what I take that relevance is. In my original post that accompanied the opening of this thread, I wondered at the persistance of EML's. You seem to have identified pockets of dry air, that come off the high deserts of Asia and persist indefinitely, out over the Pacific. Tracking these packets across the Pacific led you to wonder about the "seams" between the satellites and how they are filled in with pictures of different characteristics, because these fill-ins were making it hard for you to track these dry pockets all the way from ASIA to the US. Do I have all of this right. Please correct me firmly if I do not, so that I don't confuse subsequent readers.

Thanks for your help,

N

[ThompNickSon]

Dear Calm_Days,

While I have your attention, I am wondering if you or anybody else had had any thoughts about my query concerning elevated COLD pools. We have one of those bearing down on us in Massachusetts right now, and the prediction is for cold clear nights and showery cool days. As usual, I wondering, if they are colder (we are talking POTENTIAL temperature, here, remember) than the layers below them, why do they stay up. I assume that the answer is that they are condition unstable; i.e., only with the heating of the atmosphere during the day do they become more dense than the layers below.

If you (or anybody else) feels that this question is answered above, and I have forgotten, please point me to the answer.

N

PS: I am NOT in NM at the moment.

[ThompNickSon]

So, here is another example of a forecast of showery weather due to an elevated COLD pool.

BY THURSDAY THE

COLD CORE IS DIRECTLY OVERHEAD. SO WEDNESDAY IS A TRANSITION FROM

STRATIFORM TO CONVECTIVE...THURSDAY MAINLY CONVECTIVE. SUFFICIENT

INSTABILITY BOTH DAYS TO INDICATE A CHANCE OF THUNDER.

I will try to remember to post a skewT on Thursday, if this thing verifies. The synoptic situation is an upper low to the west of NE which will spawn a coastal low for Wednesday and move over NE bringing with it said "cold pool". The result is chilly showery weather.

Like elevated mixed layers (which are warm, but very dry) an elevated cold pool seems anomolous because relatively cold air is relatively dense. I assume, therefore, the air in a cold pool is conditionally cold ... i.e., it's cold relative to what the air below it will be when heated by the sun on thursday. (Cold here, always refers to "potential temperature".) Hence the prediction of convective showers.

N

[calm_days]

In my original post that accompanied the opening of this thread, I wondered at the persistance of EML's. You seem to have identified pockets of dry air, that come off the high deserts of Asia and persist indefinitely, out over the Pacific. Tracking these packets across the Pacific led you to wonder about the "seams" between the satellites and how they are filled in with pictures of different characteristics, because these fill-ins were making it hard for you to track these dry pockets all the way from ASIA to the US.

 

Yes, there seemed to be persistent very dry pockets that did finally dislodge.  I used to notice a similar phenomenon in the tropics in the winter, and began to notice something like this was happening this time in spring and summer.  It is like a block, but not a pressure block that moves and shifts, something that seemed more structural.

 

I have continued to try and understand what is being shown in these images; it doesn't seem to be a meteorological feature as it only appears at 2100 UT still, but there have been two of them and they move gradually to the west apparently until moving out of frame of this specific satellite.  The second one seems like it will be present for a while longer.   

 

[calm_days]

University of Toronto - Heat engine model of atmosphere mini article

A press article about the research release

"Constrained work output of the moist atmospheric heat engine in a warming climate"

 

 

Some very pertinent excerpts

 

"By viewing the atmospheric circulation as a heat engine, we were able to rely on the laws of thermodynamics to analyze how the circulation would change in a simulation of global warming," said Laliberte. "We used these laws to quantify how the increase in water vapour that would result from global warming would influence the strength of the atmospheric circulation."

 

The scientists concluded that the increase in water vapour was making the process less efficient by evaporating water into air that is not already saturated with water vapour. They showed that this inefficiency limited the strengthening of atmospheric circulation, though not in a uniform manner. Air masses that are able to reach the top of the atmosphere are strengthened, while those that can not are weakened.

 

~

 

This article and definitely the research as well seems very close to the exact subject matter you have been extrapolating over these past few years.  While it is not everyone's area of interest, I have found it among one of the best forward-thinking topics here on the forum, though there are many, this one really has been addressing the direct connection between the changing atmosphere and storm system dynamics from the start. 

 

Thank you for creating and maintaining this topic, I am glad for you to be able to return some time and see these articles!  Also, I have found the published research:

(http://www.sciencemag.org/content/347/6221/540)