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Vertical Eddy Diffusivity in the Tropical Cyclone Boundary Layer during Landfall
oleh: Chen Chen
Format: | Article |
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Diterbitkan: | MDPI AG 2022-06-01 |
Deskripsi
This study investigated surface layer turbulence characteristics and parameters using 20 Hz eddy covariance data collected from five heights with winds up to 42.27 m s<sup>−1</sup> when Super Typhoon Maria (2018) made landfall. The dependence of these parameters including eddy diffusivities for momentum (<i>K</i><sub>m</sub>) and heat (<i>K</i><sub>t</sub>), vertical mixing length (<i>L</i><sub>m</sub>), and strain rate (<i>S</i>) on wind speed (<i>u</i><sub>n</sub>), height, and radii was examined. The results show that momentum fluxes (τ), turbulent kinetic energy (TKE), and <i>K</i><sub>m</sub> had a parabolic dependence on <i>u</i><sub>n</sub> at all five heights outside three times the RMW, the maximum of <i>K</i><sub>m</sub> and <i>S</i> increased from the surface to a maximum value at a height of 50 m, and then decreased with greater heights. However, <i>K</i><sub>m</sub> and <i>S</i> were nearly constant with wind and height within two to three times the RMW from the TC center before landfall. Our results also found the |τ|, TKE, and <i>K</i><sub>m</sub> were larger than over oceanic areas at any given wind, and <i>K</i><sub>m</sub> was about one to two orders of magnitude bigger than <i>K</i><sub>t</sub>. The turbulence characteristic and parameters’ change with height and radii from the TC center should be accounted for in sub-grid scale physical processes of momentum fluxes in numerical TC models.