"Your definition, please, of "cool but not cold." Please remember, some of us are from someplace south of north. My personal definition of "cool" is a temperature in the neighborhood of 50-70 degrees fahrenheit; "cold" is below 50 degrees."

Oh, okay...

It actually is mostly within the lower part of your definition of "cool", but can range up into the 60's and 70's pretty often. It must be said, however, that it is also perfectly capable of dropping below freezing at night at that time of year (and climbing to 81 two days later) - upper midwestern weather routinely defies prediction. I've done my share of boiling eggs in my undershorts (3 years in Houston Texas with regular fieldwork in the Big Thicket during the summer) - after 7 1/2 years up here I'm almost cooled off from that.

Originally posted by Electrojake
moss, your mighty clever: a Beach Climb vs. a Snow Climb.

Also...
Is the hazard your referring to in photo-1 of the Beech, nearby power lines?
Just wondering.

Electrojake
The Fair Weather Climber <grinning>

Ah, I'm not that clever but I'm glad you found the accidental pun.

You are correct the hazards are converging powerlines surrounding the tree on two sides.
-moss

I've been reading a bit about winter climate physics and got to thinking about Moss' report of the warmer temperatures as he went up the tree.

Temperature inversions (warmer air higher up) are pretty common in the winter; they're especially noticable when they trap smoke from wood stoves near the ground. Snow is very good at giving off infrared (nearly perfect blackbody radiator in physics-speak), and on a cloudless night that energy just sails off into space. The snow surface cools off a lot, and the air within a couple of meters of the snow surface cools off too. That dense, cold air just sits there on the ground - which means that you climb out of it before you're too far up the tree. The effect would be cancelled out by a moderate breeze - that would mix the air and lower the wind chill - but it could be pretty noticable (maybe several degrees) on a calm night.

I know. The southerners are thinking to themselves "Well whoopee, so it's 25 degrees up there instead of 20". We northerners will take what we can get.

Now I really wanna get up there on a clear, calm, moonlit night this winter...

Good read MarkF! I never thought about the physics behind ground temperatures. You talk about the winter cold air being heavier. Is there any physics you can tell us about the sizzling heat? Any differences in temps with altitude? Is it hotter above on a still summer day due to inversion?

Treeman wrote: "Is there any physics you can tell us about the sizzling heat? Any differences in temps with altitude? Is it hotter above on a still summer day due to inversion?"

Hmmm. A winter nighttime temperature inversion is pretty simple, but there are some other things going on in the summer.

First altitude: Other things being equal, it does get cooler with higher altitude, but given the height of a typical tree the effect is pretty small. When Steve Sillett climbs a 100 meter (about 330 feet) redwood, the temperature change from the bottom of the tree to the top due to the lapse rate is less than 2 degrees F (the rule of thumb is 1 degree C for every 100 meters, this is what meteorologists call the adiabatic lapse rate).

Summer daytime temperature inversions: From what I understand, the sort of inversions that you get in the daytime in the summer are a larger scale phenomenon having to do with air mass collisions and temperature profiles over a few thousand feet. They do a good job of, say, locking in the air pollution over the city of Houston (and making the air a lovely shade of brown), but a tree isn't tall enough to poke very far into them. On the distance scale of a tree, the air should be hotter close to the ground during the day -- but only where sunlight is getting to the ground to heat it up. In a forest, not a lot of sun gets to the ground (1-5% or thereabouts).

Summer nighttime inversions: The same physics that applies to winter nighttime inversions also works in the summer, with a caveat. The ground cools fast on a clear night, the air in contact with the ground also cools, and that cool air just sits there unless the wind blows it away. This is why clear nights are often foggy by the morning -- the air near the ground cools down below the dewpoint. The caveat is that the trees have leaves in the summer, and this blocks the ground's "view" of the sky. As far as radiating infrared, a canopy of leaves is a good bit warmer than the sky on a clear night, so the ground won't cool off so much in a forest.

None of this gets at the bigger issue with how hot or cold it feels. That has to do with energy exchange between the climber and her/his surroundings, and the air temperature differences are often a pretty small part of that. The biggest differences between the top and the bottom of the tree are sun and wind. The sun warms you up, and the wind cools you down. Tall trees often begin to stick up above the boundary _layer_ (that _layer_ close to the ground where the wind is slower due to friction with the ground), so it's almost always breezier up there. The wind cools you down less if it's hot and humid. Whether the top of the tree feels hotter or cooler in the daytime during the summer probably has a lot more to do with the arm-wrestling between the effect of sun and wind than with air temperature changes.

Sorry about all that. Asking a science prof for an explanation is like waving candy in front of a baby...

It looks like the board here has added you on as a sound scientific resource. Now if I can only memorize the "adiabatic lapse rate" term I might be able to raise some eyebrows if I could apply it with accuracy. I would have to really get high in a tree to get the full effect of that temperature change. Maybe Tengu out on the west coast could see that kind of change.

Ground friction on the wind facinates me. I often find myself comparing our air atmosphere against the thicker atmosphere of water. I can see in my minds eye the forces of a water current like a river against the bottom surfaces.