Tuesday, May 7, 2013

Questions for the Day

1. Why is there a jet stream? Why does it blow from west to east?

2. Why is it so much colder on the poles than around the equator? Can more direct vs. more indirect exposure to solar radiation really explain such large temperature differences? Does stored heat transfer explain much of the rest (stored in ground/water/atmosphere)?

edit: so here's what I've read. 1 and 2 are related, so I'll start with #2 as it feeds into #1.

#2. There are several reasons for temperature differences in equator and poles, but the primary seems to be an effect of the curvature of the earth and solar energy incoming. While the amount of sun hitting the earth at the equator and poles is almost the same (we're so far away from the sun the difference in distance and slight incoming angle is negligible - like a lighthouse far away), but the amount of solar radiation at the poles is spread out over a larger surface area due to the curvature of the earth.

Here's the best link I could find that shows the difference and how the earth's curvature is the defining factor. According to the slides here it says at the equator each square meter of earth gets about 400 Watts / second of energy, while the same square meter angled at the poles gets about 180 Watts / second.

Here's another link that was good in this regard.

That said, there are considerable other factors in play. One good example is that the south pole tends to be 30-40 degrees F colder than the north pole - due in part to the south pole being on land and at higher elevation, while the north pole is ice on top of an ocean.

Now for #1. Why the jet stream and why does it blow west to east? This in part apparently is due to the rotation of the earth - but counter-intuitively the jet stream blows in the direction of the rotation of the earth. (The earth also spins west to east.). The answer here seems to tie into the fact that things at the equator are moving faster than things at the poles. (If you think about it like a record player, you could sit on the north pole/center of the record player and you'd spin, but you'd not go anywhere. As you move out from the center of the record player/toward the equator you begin picking up rotational speed).

Now where this gets counter intuitive to me the air at the equator is also moving faster right along with the earth spinning. As it gets hotter that air naturally seeks to mix with cooler air, so the only direction it can go is north or south. As it moves north or south that air also takes its faster relative speed with it - so as it moves north/south it also moves eastward through conservation of momentum. Scientists call this the Coriolis effect.

The jet stream itself seems more of a complicated interaction between different air fronts (I still don't really understand why distinct warm and cold air fronts exist in the first place as discussed in an earlier post), but the general direction is related to the spinning of the earth and the higher momentum of equatorial air as it moves away from equator.

I found this not intuitive at all, and difficult to get my head around how the wind advances in front of the spin of the earth, but here's a link

Now the most interesting post I came across was this: How would you make a planet similar to earth, but have more extreme weather? Very interesting discussion of impact of water, location of water, land masses, and length of day impacts on climate.

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