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No. 53: Sep-Oct 1987

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Are the soviet plumes only orographic clouds?

F.C. Parmenter-Holt, a NOAA scientist, has reacted to the recent discussions of Soviet plume events as follows:

"I believe that these clouds are naturally occurring, orographically-induced formations. When winds blow perpendicular to the 2,500-plus foot glacial ridge, along the northern portion of the island, a long gravitywave pattern is established downwind, on the lee side. The cases collected by Matson show sharp boundaries conforming to the contour of this glacial barrier."

The Matson reference is Science News, March 28, 1987, p. 204. (Parmenter-Holt, Frances C.; "Plumes and Peaks," Science News, 131:403, 1987.)

Comment. Parmenter-Holt could well be correct in some cases, for wave-like orographic clouds often form in the lee of mountain ranges, such as the Rockies. Some of the plumes, however, extend for 175 kilometers, as described above. This is pretty long for a glacial ridge. Then, too, one should inquire whether such plumes occur near similar ridges in northern climes and not just over Soviet territory.

From Science Frontiers #53, SEP-OCT 1987. � 1987-2000 William R. Corliss