Ocean Currents Explain Why Northern Hemisphere Is Soggier

vinces99 writes "A quick glance at a world precipitation map shows that most tropical rain falls in the Northern Hemisphere. The Palmyra Atoll, at 6 degrees north, gets 175 inches of rain a year, while an equal distance on the opposite side of the equator gets only 45 inches. Scientists long believed that this was a quirk of the Earth's geometry – that the ocean basins tilting diagonally while the planet spins pushed tropical rain bands north of the equator. But a new University of Washington study shows that the pattern arises from ocean currents originating from the poles, thousands of miles away. The findings, published (paywalled) Oct. 20 in Nature Geoscience, explain a fundamental feature of the planet's climate, and show that icy waters affect seasonal rains that are crucial for growing crops in such places as Africa's Sahel region and southern India."

Re:Junk Science

[i kan reed]

Yes, very nice straw-man, but the real concern here is that if the sub-surface ocean currents cause rainfall in the northern hemisphere, climate change is bad news for northern-hemisphere populations. We've seen noticeable drop-offs and changes in those currents correlated quite strongly(and explained quite thoroughly by thermodynamic principals) with increasing ocean temperatures.

What about elevation?

[justthinkit]

Isn't most of the land in the Northern Hemisphere? When clouds are forced to go upward to pass over a land mass, they are more inclined to drop their rain load. Isn't that basically how it all works?

Land mass, altitude, etc...

[Anonymous Coward]

From what I remember of my climatology course, rainfall is tightly tied to the oceanic currents. In the northern hemisphere there are a lot of things going on. We have more land mass, resulting in more "circles" of currents [wikipedia.org]. The axis of the earth impacts insolation [wikipedia.org] and global wind patterns [wikipedia.org], which create areas of evaporation and condensation at particular lattitudes on the earth. These currents change with the elevation of land mass, but by and large hard rock doesn't hold heat nearly as well as water, so you get a (sometimes drastic) temperature difference and condensation above land, which of course results in various wind patterns and rainfall. What is also interesting is look at the deserts of the northern hemisphere, notice how they are all at the same latitude?
  This stuff has been known for years, I'm not sure how this is really "news".