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Delancey · 21-12-2013, 05:09

Quote:

Originally Posted by hpeer

Delancey,

Great image, helps put words around this discussion.

Going back to your post of the 10kPa polar views....
The Borth polar cell is strong, the South non exsistant.

I can see why they would change summer to winter, but to go away? That is new to me.

I'm really just guessing a bit on that one so, can't back it up, been wrong before. Trying to make sense of it all. Been waiting most of my life to see the winds in 3D. Also, where I was in the Arctic was mostly inland, so would have to add my experiences were likely specific to my location not typical FWIW.

Delancey · 21-12-2013, 05:22

Another thing I am trying to understand is how barometric pressure relates to altitude and the thickness of the troposphere. If the troposphere thickness varies, do the upper and lower pressure limits remain somewhat constant regardless of location?

Is barometric pressure always within a certain range on the ground and is it always with a certain range at the tropopause? Meaning does any section of the atmosphere contain the same mass of air as a section anywhere else? Does a thin layer of cold dense air at the pole equal a thicker but hotter and less dense air at the equator? Therefore 500 hPa at the equator is say 5,000 feet altitude but only 2,500 ft? (Just throwing numbers out)

Or, is the atmosphere thicker and also more dense at the equator? Then seems to me the atmospheric pressure at sea level would be greater at the equator than the poles, but it isn't, is it?

**hpeer** · 22-12-2013, 13:40

I think I can answer a bit of this, but hope others more knowledgable than I chime in

Quote:

Originally Posted by Delancey

Another thing I am trying to understand is how barometric pressure relates to altitude and the thickness of the troposphere. If the troposphere thickness varies, do the upper and lower pressure limits remain somewhat constant regardless of location?

Is barometric pressure always within a certain range on the ground
( yes, the range is on your barometer, roughly)

and is it always with a certain range at the tropopause? Meaning does any section of the atmosphere contain the same mass of air as a section anywhere else? Does a thin layer of cold dense air at the pole equal a thicker but hotter and less dense air at the equator? Therefore 500 hPa at the equator is say 5,000 feet altitude but only 2,500 ft? (Just throwing numbers out)
(I believe that is correct)

Or, is the atmosphere thicker and also more dense
(No, less dense)
at the equator? Then seems to me the atmospheric pressure at sea level would be greater at the equator than the poles, but it isn't, is it?

Atmospheric pressure is about equal, roughly. That image you posted of the circulation and Hadley cells shows the simplified version of the circulation.

Air warms near the equator, gets less dense and rises. As it rises is kinda "spills over the colder, heavier air towards the poles. It then cools, because it is now very high up, and returns to the surface. In the meantime Earth is spinning and that imparts E-W or W-E motion creating the prevailing winds.

So it is the convention currents circulating in the atmosphere that equalize the pressure while the spinning creates winds. Sort of anyway.

http://en.wikipedia.org/wiki/Hadley_cell

DeepFrz · 22-12-2013, 20:45

Google this "earth air circulation patterns" and you will get much information. It is a very complicated subject and as you probably realize the weather is very difficult to predict. The huge super computers dedicated to this job barely do an adequate job, although the weather forecasting does seem to be getting better.

Delancey · 23-12-2013, 04:44

Polar Easterlies, Prevailing Westerlies, Trade Winds, Equatorial Doldrums, convection, radiation, etc. I understand all that.

If the atmospheric pressure is roughly the same all over it's because gravity is pulling an equivalent mass of air down roughly the same all over the earth, right?

But problem, the earth is not a perfect sphere, it's squished in the middle which mean the air at the equator is further away from the center mass (of the earth) and not as affected by its gravity? Also, the air is a fluid medium and is being flung away at the equator by centrifugal force?

So what gives? Is there a relatively greater mass of air at the equator being acted on by relatively less gravity to produce roughly the same pressure at the poles as at the equator?

I mean, the troposphere is more than twice as thick at the equator than the poles. That seems like a lot to me.

S/V Alchemy · 23-12-2013, 07:48

Warmer air rises, and colder air sinks. The spin of the earth (Coriolis effect) imparts a shear on these vertically moving bodies of air. Gravity, while slightly variable around the Earth, is not nearly as great a factor as the fact that rising and falling air masses are tugged by the earth's spin and are sheared by very strong upper atmospheric streams or "jets".

While in the broad sense, this makes the earth's weather patterns predictable (which is why wind pilots are helpful), in the narrow, specific sense, the daily weather is nearly infinitely complex and therefore less predictable. "Snow in July" or "late winter hurricane" are rare, but can't be excluded. The more the sailor knows about the broad strokes of climate (time of year, effect of land masses, latitudes), the less surprising individual incidents of bad or favourable weather will seem.

Delancey · 23-12-2013, 10:13

Here's a neat one-

https://www.youtube.com/watch?v=oRsY_UviBPE

S/V Alchemy · 23-12-2013, 12:27

What strikes me about that is how regular the Southern Ocean "parade of gales" is when compared to the irregular nature of weather systems over the more "heavily dirted" Northern Hemisphere.

DeepFrz · 24-12-2013, 18:07

I find these things absolutely fascinating.

DeepFrz · 31-12-2013, 13:01

There is just a huge weather system over the North Atlantic and the North Sea. Winds from the Canadian Continent

and Europe mixing in a huge low pressure system.

goboatingnow · 31-12-2013, 19:54

Quote:

Originally Posted by DeepFrz

There is just a huge weather system over the North Atlantic and the North Sea. Winds from the Canadian Continent

and Europe mixing in a huge low pressure system.

You mean the current wind map as of today. Nothing unusual it that , at this time of years, occurs every 2-3 days , what's unusual this year is the complete lack of the Scandinavian high pressure area that blocks the Atlantic lows , we getting daytime temps in the 10-15 degrees c range , which is better then Summer in some cases!

Dave