From AMS Glossary
Revision as of 20:10, 25 April 2012 by Perlwikibot
(Also called upper-level low, upper cyclone, upper low, high-level cyclone, low aloft.) A cyclonic circulation existing in the upper air; specifically as seen on an upper-level constant-pressure chart.
This term is often restricted to such cyclones associated with relatively little cyclonic circulation in the lower atmosphere.