Why is N. America Colder than W. Europe - Blame the Rocky Mountains (ice, frost)

[arctic_gardener]

@ Dan in EGF,
I know you from Rob's Blog! Small world!

[Kamsack]

Originally Posted by arctic_gardener

@ Dan in EGF,
I know you from Rob's Blog! Small world!

Hi there...yes I am a more winter poster there. I have talked with Rob via phone a few times from our office. I visited the winnipeg office as part of a forecaster exchange program way back in 2000. Great stuff and always great to see other offices, esp another countries.

I dont always post in the weather forum here on C-D....depends on topic. Sometimes the climate battles get a little old.

Have you frequented Justin's FB page Manitoba Weather Centre. I follow that regularly...post some....if wanting info for someplace near the border with our forecast area (such as Cartwright to Altona-Emerson to Sprague).

[nei]

I think a bit of your confusion is thinking in terms of weather, which is extremely variable rather than climate, which is a long-term average of many different conditions.

Originally Posted by Cambium

The article kept mentioning west to east movement. Different from a 30,000 foot river of air. Much different. Again, I will ask... are you guys and this guy implying a Jet stream at 4-8 miles in the atmosphere is moved from mountains at 1-2 miles up?

Kinda... Unlike DaninEGF, I'm not a meterologist but it seems plausible to me. Imagine this oversimplified scenario:

1) A 30,000 foot "river" of air moving eastward from the west
2) Hits a north-south mountain range with an average elevation of 10,000 feet

The air suddenly has much less space than previously. What can it do?

1) The air at the lowest layer that is at or near the elevation of the mountains must rise. Perhaps it impacts the air above, forcing some of it too rise. It wouldn't stable for air at a particular elevation to be drastically denser than other, nearby air masses at the same elevation, because some of it will start to flow due to pressure differences.
2) The upper layer of the air can't move up much — it's locked by the tropopause

So some air has to along the same elevation (or really, pressure level) rather than up or down. Going north or south, will change the angular momentum of the air due to changes in the value of the coriolis force. This sets off standing Rossby waves. The mid-latiudes normally have rossby waves in the middle and upper levels atmosphere, but topography can influence them to make a particular position more likely. Here's a rather mathematically heavy article on Rossby waves:

http://www.met.wau.nl/education/MWS/...hapter%204.pdf

and one quote:

What we have described above is called a free barotropic Rossby wave. These are only weakly excited in the atmosphere (Holton, 2004). Of more importance are the forced stationary Rossby modes, which are excited by longitudinally dependent diabatic heating patterns (e.g. the ocean-continent contrasts in winter) or by flow over topography (e.g. flow over the Rocky Mountains and the Himalaya).

so mountains make Rossby waves stronger.

But wait a second.... Does that mean the jet stream was dictated by the Rockies?
Here's the jet stream setup of this morning (similar to yesterdays)... It's not even over the U.S.

The OP's article was on wintertime not summer. The summer jet stream is weaker and doesn't have the same influence on American weather. In any case, shift in air lower than the jet stream can also have an effect of the weather, perhaps we should speak of just the troposphere in general, not really sure.

Such waves are of massive scale. The southward flow takes place over all of central and eastern North America, bringing Arctic air south and dramatically cooling winters on the East Coast. The return northward flow occurs over the eastern Atlantic Ocean and western Europe, bringing mild subtropical air north and pleasantly warming winters on the far side of ocean.

Hang on... Are you saying we dont see a southward arctic airflow over the West and Northward flow in Eastern North America and that Western Europe never has a return Polar flow?? Lets start with 2012 and look at the flow in the Eastern U.S and Western U.S. We can pull up many maps proving there are times.. Were the Rocky mountains sleeping at that point?

The author never said "never". The article is about climate not weather, the author is referring to the average flow in the winter. As you know, weather is extremely variable, you can pick out many instances when the atmospheric are from average. Your example in the next post of a trough in western Europe due to a narrow high pressure and ridge setup in the Atlantic is one such example.

[quote]

Originally Posted by Cambium

What was failed to mention in the article was the peaks and bases and the "width" of the troughs and ridges.

Point is... while the trough was indeed in the East, there was a narrow high pressure and ridge setup in the Atlantic which in turn forced Polar air down to Western Europe. Temp anomalies the same day down below..

Lots more involved than just saying the Rockies cause Western Europe to have warmer averages. I hope these graphics help visualize what happens.

As to the bolded, the authors don't claim it's only the Rockies. Their claim was the Rockies are responsible for roughly half the difference (see the pdf I posted with results of what happens when a computer model "removes" mountains)

Your last map — NCEP 12/1/12 to 12/2/12 is irrevelant to the author's point. The author's point is the Rockies change the climate average, your plot is an anomaly plot where the surface temperatures are subtracted from the climate averages, so the effect is removed entirely.

[nei]

Originally Posted by Cambium

One more point... no talk about how Strong Storms affect the flow either.

http://www.ldeo.columbia.edu/res/div...GulfStream.pdf [also see page 4, for winter temperatures compared to latitude average and page 24 for results on mountains vs no mountains)

Storms (called eddies) are accounted for in the last two terms of the equation on page 16. I found the actual published associated with the article.

http://www.atmos.washington.edu/~david/Gulf.pdf

From what I could understand from the paper, the storms make the west-east temperature contrast smaller than it would be otherwise. Here's the summary about the effect of the Rockies (really, western mountains in general):

In the absence of mountains (Fig. 14(c)), the equivalent barotropic trough over the eastern North American seaboard is considerably weakened compared to the case with mountains (Fig. 14(a)). Consequently, the flow is more zonal [west-east] over North America, the North Atlantic Ocean and western Europe than when the mountains are present. The weakened northerlies over North America lead to a large warming, while the reduced southerlies over the North Atlantic Ocean and northern Europe cause cooling. The part of the Icelandic Low east of Iceland retains its full strength when the mountains are removed.

Note it talks about weakening of northerlies not disappearance, some of it would remain with or without mountains. Comparing it with ocean heat effect transport, the reason it finds the ocean effect is small compared to the Rockies is the ocean ends up warming both North America and Europe, while the Rockies cool eastern North America and warm Europe.

[das8929]

I would think Hudson Bay has a larger effect in making North America colder especially the eastern half. It is shallow so it helps moderate the summer and create cooler summers for eastern Canada explaining the very low latitude for the tree line there. And it freezes up quickly helping to reinforce Arctic air coming down.

[theunbrainwashed]

Originally Posted by das8929

I would think Hudson Bay has a larger effect in making North America colder especially the eastern half. It is shallow so it helps moderate the summer and create cooler summers for eastern Canada explaining the very low latitude for the tree line there. And it freezes up quickly helping to reinforce Arctic air coming down.

I think I had this discussion last year, either with nei in private or I posted a topic here. Let me see if I did that, because I think Hudson Bay does play a significant role in eastern North America's climate, especially considering that it when you look at temp maps of the US in winter, oftentimes Montana is warmer than the Northeast

[Mac15]

Eastern america is not cold in the summer. Now don't be daft.

[theunbrainwashed]

Originally Posted by Mac15

Eastern america is not cold in the summer. Now don't be daft.

I suggest re-reading das's post

[Mac15]

Water warms a climate.

[theunbrainwashed]

Originally Posted by Mac15

Water warms a climate.

Not necessarily. It moderates a climate, it doesn't make it warmer unless you found an economically viable way to artificially heat up the water. Moderating a climate means warming the winter temp, cooling the summer temp. Hudson Bay does nothing to warm up the winter, as most of the bay is frozen over in winter