Listen to a conversation between a student and his geography professor.
Hi, Professor Brown.
Hi, Paul. What can I do for you?
I have a question about the final exam … I mean, will it cover everything we’ve done all term, or just what we’ve been doing since the midterm exam?
Everything we’ve done all term.
[Not very happy about that]Oh, boy. You know, I’m still not too clear about the hydrologic cycle, um … the transfer of water back and forth between the Earth and the atmosphere …
I really blew the question about it on the midterm exam. I wanna do better on the final exam, but I’m still having trouble with it.
[Sympathetic]Well—um, have you been to the tutoring center?
No, not for geography anyway. Isn’t that just for when you need help with writing … like an essay or a research paper?
Oh, no. You can get tutoring in a lot of subjects. Some graduate students from this department tutor there.
Um, that’s good to know, but I hardly go there because I have a part-time job. I never seem to be free when they’re open.
Well, they’ll be extending their hours when final exams begin—you might try then.
But um…Well since you’re here now, can I help you with something?
Well, the hydrologic cycle …
I remember we went over a diagram in class … and from what I remember … water changes back and forth from water in lakes and oceans to vapor, and then back to water again when it falls as rain or snow … as precipitation.
It’s constantly being recycled, through evaporation and condensation.
[Not sure what the problem is]That’s it, basically. Umm … so exactly what is it you don’t understand?
[Realizing he has to ask a more specific question] OK. I guess what I’m really confused about is how the topography of the land —the mountains and valleys and stuff—affect precipitation.
OK, good question … Precipitation is influenced by topography, among other things. Uhh, why don’t we talk about lake-effect snow...
It’s a phenomenon that occurs anywhere you have a large lake that doesn’t freeze, and has cold air flowing over it.
Mostly in the Northern Hemisphere.
Like the Great Lakes in the United States?
Yes. What happens is that the cold, arctic air blows across the lake from the north in winter, and as the air crosses the lake, the lower layer is warmed by the lake water, which is much warmer than the arctic air.
And as this layer is warmed and picks up moisture, it becomes lighter than the air above it …
So it starts to rise, right?
Yes. And clouds begin to form.
When the air gets close to the shore, it’s slowed down by the land, and starts to pile up.
So it rises even faster, because it has nowhere else to go.
That’s where topography comes into the picture.
[Happy he knows the answer]And then it snows because as the air rises, it cools off and loses its capacity to hold water vapor.
OK, thanks. Any chance you’ll ask this question on the final?
[Laughing] I don’t know yet … but you seem to have a handle on it.