“Think what a place like that could do in your gravity, climate, and atmosphere. Look: winter in the part of Mesklin you know — the southern hemisphere — coincides with the world’s passage of its closest point to the sun. That’s summer in the north, and the icecap boils off — that’s why you have such terrific and continual storms at that season. We already knew that. The condensing moisture — methane — whatever you want to call it — gives up its heat and warms the air in your hemisphere, even though you don’t see the sun for three or four months. The temperature probably goes up nearly to the boiling point of methane — around minus one forty-five at your surface pressure. Isn’t that so? Don’t you get a good deal warmer in winter?”
“Yes,” admitted Barlennan.
“Very well, then. The higher temperature means that your air doesn’t get thin so rapidly with altitude — you might say the whole atmosphere expands. It expands, and pours over the edge into that bowl you’re beside like water into a sinking soup plate. Then you pass the vernal equinox, the storms the out, and Mesklin starts moving away from the sun. You cool off — right? — and the atmosphere shrinks again; but the bowl has a lot caught inside, with its surface pressure now higher than at the corresponding level outside the bowl. A lot of it spills over, of course, and tends to flow away from the cliff at the bottom — but gets deflected to the left by the planet’s spin. That’s most of the wind that helped you along. The rest is this blast you just crossed, pouring out of the bowl at the only place it can, creating a partial vacuum on either side of the cleft, so that the wind tends to rush toward it from the sides. It’s simple!”
“Did you think of all that while I was crossing the wind belt?” asked Barlennan dryly.
“Sure — came to me in a flash. That’s why I’m sure the air up there must be denser than we expected. See?”
“Frankly, no. However, if you are satisfied I’ll accept it for now. I’m gradually coming to trust the knowledge of you Flyers. However, theory or no theory, what does this mean to us practically? Climbing the slope in the teeth of that wind is not going to be any joke.”
“I’m afraid you’ll have to. It will probably die down eventually, but I imagine it will be some months before the bowl empties — perhaps a couple of Earthly years. I think, if it’s at all possible for you, Barl, it would be worth attempting the climb without waiting.”
Barlennan thought. At the Rim, of course, such a hurricane would pick up a Mesklinite bodily and drive him out of sight in seconds; but at the Rim such a wind could never form, since the air caught in the bowl would have only a tiny fraction of its present weight. That much even Barlennan now had clear.
“We’ll go now,” he said abruptly to the radio, and turned to give orders to the crew.
The Bree was guided across the stream — Barlennan had landed her on the side away from the plateau. There she was dragged well out of the river and her tie lines secured to stakes — there were no plants capable of taking the desired load growing this close to the landslide. Five sailors were selected to remain with the ship; the rest harnessed themselves, secured the draglines of their packs to the harness, and started at once for the slope.