Multilevel Tower Observations of Vertical Eddy Diffusivity and Mixing Length in the Tropical Cyclone Boundary Layer during Landfalls

Tang, Jie; Zhang, Jun A.; Aberson, Sim D.; Marks, Frank D.; Lei, Xiaotu

doi:10.1175/JAS-D-17-0353.1

i

Multilevel Tower Observations of Vertical Eddy Diffusivity and Mixing Length in the Tropical Cyclone Boundary Layer during Landfalls

2018
By Tang, Jie ; Zhang, Jun A. ; Aberson, Sim D. ; ...

Details

Journal Title:

Journal of the Atmospheric Sciences
Personal Author:

Tang, Jie ; Zhang, Jun A. ; Aberson, Sim D. ; Marks, Frank D. ; Lei, Xiaotu
NOAA Program & Office:

OAR (Oceanic and Atmospheric Research) ; NWS (National Weather Service) ; AOML (Atlantic Oceanographic and Meteorological Laboratory)
Description:

This study analyzes the fast-response (20 Hz) wind data collected by a multilevel tower during the landfalls of Tropical Storm Lionrock (1006), Typhoon Fanapi (1011), and Typhoon Megi (1015) in 2010. Turbulent momentum fluxes are calculated using the standard eddy-correlation method. Vertical eddy diffusivity K-m and mixing length are estimated using the directly measured momentum fluxes and mean-wind profiles. It is found that the momentum flux increases with wind speed at all four levels. The eddy diffusivity calculated using the direct-flux method is compared to that using a theoretical method in which the vertical eddy diffusivity is formulated as a linear function of the friction velocity and height. It is found that below similar to 60 m, K-m can be approximately parameterized using this theoretical method, though this method overestimates K-m for higher altitude, indicating that the surface-layer depth is close to 60 m in the tropical cyclones studied here. It is also found that K-m at each level varies with wind direction during landfalls: K-m estimated based on observations with landward fetch is significantly larger than that estimated using data with seaward fetch. This result suggests that different parameterizations of K-m should be used in the boundary layer schemes of numerical models forecasting tropical cyclones over land versus over the ocean.
Source:

Journal of the Atmospheric Sciences, 75(9), 3159-3168.
DOI:

https://doi.org/10.1175/JAS-D-17-0353.1
Format:

PDF
Document Type:

Journal Article
Funding:

Grant no. NA12NWS4680004
Rights Information:

Other
Compliance:

Submitted
Main Document Checksum:

urn:sha-512:0e6c75cc42d9cb28fedf49239c80c5dcfcdb79afae90ffae94cd467e8ead96784e0e26824655901134a2a820703c31c7bda51a86a5204e3e867dc337f27521f8
Download URL:

https://repository.library.noaa.gov/view/noaa/19516/noaa_19516_DS1.pdf
File Type:

[PDF - 2.01 MB ]

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