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Related to diurnal variation: diurnal variation of temperature
diurnal variation[dī′ərn·əl ‚ver·ē′ā·shən]
Daily variations of the earth's magnetic field at a given point on the surface, with both solar and lunar periods having their source in the horizontal movements of air in the ionosphere.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.