Abstract
The boundary layer structure is crucial to the formation and intensification of typhoons, but there is still a lack of high-precision turbulence observations in the typhoon boundary layer due to limitations of the observing instruments under typhoon conditions. Using joint observations from multiple ground-based Doppler wind lidars (DWL) collected by the Shanghai Typhoon Institute of China Meteorological Administration (CMA) during the transit of Typhoon Lekima (8–11 August 2019), the characteristics of the wind field and physical quantities (including turbulent kinetic energy (TKE) and typhoon boundary layer height (TBLH)) of the boundary layer of typhoon Lekima were analyzed. The magnitude of TKE was shown to be related not only to the horizontal wind speed but also to the presence of a strong downdraft, which leads to a rapid increase of TKE. The magnitudes of TKE in different quadrants of Typhoon Lekima were also found to differ. The TKE in the front right quadrant of the typhoon was 2.5–6.0 times that in the rear left quadrant and ~1.7 times that in the rear right quadrant. The TKE over the island was larger than that over the urban area. Before Typhoon Lekima made landfall, the TKE increased with decreasing distance to the typhoon center. After typhoon landfall, the TKE changes were different on the left and right sides of the typhoon center, with the TKE on the left decreasing rapidly, while that on the right changed little. The typhoon boundary layer height calculated by five methods was compared and was found to decrease gradually before typhoon landfall and increased gradually afterward. The trends of the TBLH calculated using helicity and TKE were consistent, and both determine the TBLH well, while the maximum tangential wind speed height (humax) was larger than the height calculated by other methods. This study confirms that DWL has a strong detecting capability for the finescale structure of the typhoon boundary layer and provides a powerful tool for the validation of numerical simulations of typhoon structure.
Highlights
A critical element in many boundary layer parameterization schemes used in typhoon numerical models is the determination of the boundary layer height (BLH), as BLH is a key variable that regulates the vertical distribution of turbulent fluxes and helps to determine
In numerical models where turbulent fluxes are parameterized by a first-order K-profile method, the BLH is usually defined as the height at which the bulk Richardson number (Ri) reaches a threshold value, where Ri is defined as the ratio of buoyancy to shear forcing [14]
Indicates the height where 10% of Vmax is located; Umax is the maximum value of the tangential wind, and humax is the height where the maximum tangential wind speed is located; HZ is the vertical helicity; Zi is the height at a vertical level; SNR is signal to noise ratio; and TKE refers to the turbulent kinetic energy. hH represents the height corresponding to the maximum value of the absolute value of the first-order vertical derivative of the helicity with height; hSNR and hTKE are calculated by the same method as hH
Summary
We use these joint observation data to study the evolution of TKE in the boundary layer during the intensity change of Typhoon Lekima as well as to evaluate the TBLH calculated by different methods. This helps to understand the characteristics of the physical processes in the boundary layer during the intensity change of the landfalling typhoon. We discuss the capability of ground-based DWL for observing the finescale structure of typhoons, which can be used to evaluate model ability to simulate the finescale structure of the TBL
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
