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OBSERVATION ON COUNTER-GRADIENT TRANSPORT OF MOMENTUM FLUX IN LOW ATMOSPHERE BOUNDARY LAYER DURING TYPHOON MEGI
Author(s): 
Pages: 1263-1269
Year: Issue:  6
Journal: Oceanologia et Limnologia Sinica

Keyword:  typhoonboundary layercounter-gradient flux of momentumcoherent structure;
Abstract: To explain the observational data of counter-gradient transport of momentum flux in lower atmospheric boundary layer, we studied very-high-frequency data measured by ultrasonic wind instruments that installed on a multilayer tower(N24°2′9.6″, E117°54′; 100 m tall on 29 m base above sea level) near sea shore by diagnostic method. A case of landfall typhoon Megi in 2010 was selected. Result show that the counter-gradient transport of momentum occurred in a small proportion(<16%) in lower boundary layer of the typhoon, although it moved along the gradient direction on longer time scale, e.g., one hour. The phenomenon in higher layers was more obvious than that in lower ones, stronger in the area of typhoon core and weakened away from it, and less in early and outskirt of typhoon. The vertical counter-gradient flux of momentum is closely related to the coherent structure of low-frequency disturbance. When wind disturbance in horizontal and vertical directions was in-phase, the counter-gradient flux of momentum would occur easier due to loose coherence structure between the disturbances in the two directions. The averaged spatial scales were 258 m and 35 m and the temporal scales were 123 s and 13 s in horizontal and vertical directions respectively, both are smaller than those of common ones of low-frequency disturbances in low layer boundary atmosphere of typhoon.
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