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Spiral clouds on Mars: A new atmospheric phenomenon
Author(s) -
Gierasch P.,
Thomas P.,
French R.,
Veverka J.
Publication year - 1979
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl006i005p00405
Subject(s) - orbiter , northern hemisphere , mars exploration program , atmospheric circulation , climatology , geology , atmospheric sciences , sublimation (psychology) , atmosphere of mars , clockwise , environmental science , physics , martian , astronomy , amplitude , psychology , quantum mechanics , psychotherapist
Viking Orbiter images obtained during the 1978 northern summer on Mars show unusual spiral cloud patterns at high northern latitudes. Well‐developed spirals occurred only during early summer at a time when the sublimation of the annual CO 2 frost cap in the north had ceased. The systems ranged in size from 200 to 500 km and all spirals were wound in a counterclockwise sense. An explanation is proposed, based on the radiatively driven instability described by Gierasch, Ingersoll, and Williams. The model predicts disturbances with the correct scale and lifetime. However, the successful development of the spirals depends on the existence of weak mean winds, suggesting that these instabilities can only develop at special null points in the general circulation. We argue that such special circumstances are most likely to occur during early northern summer and are less likely to obtain at a comparable season in the southern hemisphere.