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Nocturnal wind‐directional shear in complex terrain
Author(s) -
Mahrt L.,
Richardson Scott,
Stauffer David,
Seaman Nelson
Publication year - 2014
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.2369
Subject(s) - geology , terrain , shear (geology) , wind shear , wind direction , nocturnal , wind speed , geodesy , geomorphology , meteorology , geography , physics , petrology , oceanography , cartography , astronomy
In the weak‐wind nocturnal boundary layer, the wind direction near the surface may vary substantially with height. The directional shear is caused by transient modes and shallow, terrain‐induced motions. This study examines the large directional shear for nocturnal data collected in the lowest 10 m from three field programs. The directional shear in two broad valleys with high sidewalls is dominated by transient motions within the valley cold pool. In contrast, the directional shear within a shallow narrow valley is dominated by terrain‐induced down‐valley drainage flows, in spite of the fact that the magnitude and height of the valley sidewalls are much smaller than the other two valleys. The relative contribution of the directional shear to the total vector shear is examined as a function of wind speed and stability.