ice ages/atmospheric circulation

[granpa]

 

http://en.wikipedia.org/wiki/Atmospheric_circulation#Latitudinal_circulation_features

 

The wind belts and the girdling the planet are steered by three cells: the Hadley cell, the Ferrel cell, and the Polar cell (the interpretation of the latter two is complex).

 

 

it is my understanding that during most of earths history that air rose at the equator and sank at the pole in one continuous cell and that it was very much warmer. there was no ice at the poles.. further I can see no reason why one couldnt have just 2 cells.

 

so it seems to me that the earth could have 3 different climates. one with 3 cells like today. one with 2 cells. and one with only one cell. now the one with 1 cell is certainly very warm. could it be that ice ages occur when the earths climate goes into a phase with only 2 cells?

 

would there be any way to test this?

[insane_alien]

but that wouldn't work, it simply wouldn't be stable and would require some impressive surface winds near the poles(a few hundred miles an hour). it would also result in the poles being colder as the air decending on them would be very cold from being in the upper atmosphere for so long.

[granpa]

but that wouldn't work, it simply wouldn't be stable and would require some impressive surface winds near the poles(a few hundred miles an hour). it would also result in the poles being colder as the air decending on them would be very cold from being in the upper atmosphere for so long.

I cant really comment on that since it seems to be beyond me but I would like to hear more about how you arrive at these conclusions. do you have any links I could follow?

[insane_alien]

i don't have any links but its a simple conservation of mass and energy problem,

 

if i have a flow of gas from the equator at even a few miles per hour which goes all the way to the pole and then sinks it will have to be moving very fast as the area over which it has to flow will be decreasing rapidly. even accounting for compression as it sinks the velocity will be very large.

 

as for the poles being colder in this case, you can actually see it with the hadley cell, the decending cold air cools areas such as the sahara, they would get hotter if it wasn't for the cooling effect of this cell. the reason it has a cooling effect is because the warm air radiates its energy out into space while in the upper atmosphere and doesn't get more until it gets close to the ground.

 

corriolis forces also place upper limits on cell size, if they extended to the poles there would be permanent hurricanes at both poles. the shear forces involved tend to granulate convection cells.

[granpa]

seems more likely to me that the air would simply descend over a larger area. and I'm pretty sure the upper air already spends enough time in the upper atmosphere to reach an equilibrium temp. spending longer shouldnt make any difference.

[insane_alien]

actually it would, because the heat input into the upper atmosphere would primarily be at the equator therefore the air above the poles would get much colder.

 

as to your point about the air decending over a larger area, exactly, just so happens that this area is large enough for two more cells to form.

 

i don't know if you have ever had it properly explained to you just why there are three cells, have you?

 

there are two driving cells, the hadley cell which is driven by hot air rising at the equator and the polar cell which is driven by cold air sinking. the ferrel cell operates in the reverse of what you would expect from a heat driven process as the air is sinking in the warmer latitudes and rising in the colder latitudes, this is because it is driven primarily by airs viscosity and the currents of the hadley and polar cells. hope this makes it a bit clearer.

[granpa]

the polar front probably has something to do with it too.

 

also different cells have different depths. not sure how that factors in.

[insane_alien]

well the polar front is the boundary between polar and ferrel cells. (hot air from the ferrel cell gets lifted by colder denser air from the polar cell)

 

the different depths are due to temperature and to a lesser extent the rotation of earth causing gravity to have less of an effect at the equator.

[granpa]

it gets lifted a little bit by the cold polar air then the heat released as water vapour condenses into rain causes it to rise much more. the energy released is no doubt what drives the ferrel cell in reverse.

 

I dont disbelieve you but I'm not sure what you mean about temp. all I know is that air rises until it reaches the stratisphere. yet the base of the stratisphere is for some strange reason at different heights at different latitudes. the diagram below shows it varying continuously from pole to equator but other diagrams I've seen show it changing suddenly as one goes from one cell to another. it probably does both.

 

now certainly on a large enough planet the atmospheric circulation must indeed break up into smaller cells. but just because the earth today has 3 cells doesnt seem to me to prove that it cant have 2 ar even 1 cell.

 

however you raise a lot of good points so its far from obvious what the case really is.

 

edit:ok. that makes sense now. air at the equator is warmer so it carries more water vapour so it rises to a greater height so the base of the stratisphere is higher.

Edited December 22, 2008 by granpa
multiple post merged

[czimborbryan]

My crazy idea is that there is much more radiation exiting the planet through the poles which creates a refridgeration effect (besides the already accepted idea about the sun's rays...).

[Sayonara]

I don't think you have put a lot of thought into that.