An In-Situ Observational Study on the Turbulent Characteristics in the
Near-surface Layer during the Landfalling Period of Super Typhoon Maria
(2018)
Abstract
The air-sea exchanges of momentum which are often parameterized by the
variation of drag coefficient (CD) and wind speed
(un), is largely uncertain at typhoon-force
extreme values of un. This paper investigated the
relationship between CD and extreme values of
un for five different heights using the eddy
covariance method from two coastal observation towers during the
landfall of Super Typhoon Maria. In particular, our observations include
10-min average un extended to high wind speed of
42.27 m s-1. The relationship between
CD and un was parabolic
from regression analysis, and the “roll-off” of
CD and u* appeared at
about 28 m s-1. From the bottom to top heights, the
corresponding un of CD
extreme were 9.95, 12.72, 22.32, 32.57 and 38.04 m
s-1, respectively. The trend of negative tangential
turbulent flux with un was found to be the main
cause for the CD extreme drifting with heights.