Xiaochun Zhai 19 th Coherent Laser Radar Conference CLRC 2018, June 18 – 21 1 Vertical Velocity Statistics and Turbulence Characterization by Coherent Doppler Lidar during Typhoon MAWAR Xiaochun Zhai(a), Songhua Wu(a, b), Xiaoquan Song(a, b) (a)Ocean Remote Sensing Institute, College of Information Science and Engineering, Ocean University of China, Qingdao 266100, China. (b) Laboratory for Regional Oceanography and Numerical Modeling, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266100, China. *Email: [email protected]Abstract: This paper gives an analysis of CDL investigation of gravity wave and turbulence characteristics during typhoon MAWAR episode over the coastal zone in south China (CZSC). The FFT and wavelet analysis are used to subtract the organized wave-like structure. Radiosonde and ECMWF reanalysis data are used to demonstrate the existent of gravity wave and to explain its mechanism, respectively. The up/downdraft of vertical velocity in this case are analysed from different time periods. A wavelet decomposition technique is used to subtract the gravity wave from raw vertical velocity datasets, and higher-order moments and characteristic scales are also analysed base on gravity wave time series. As a result, comprehensive atmospheric dynamic characteristics and their relationship with gravity wave during MAWAR episode have been studied. Keywords: Coherent Doppler lidar, gravity wave, turbulence, typhoon 1. Introduction The coastal zone in South China (CZSC) is one of the regions with the highest level of economic development in China. It borders Nanling mountain to the north and South China Sea (SCS) to the south. Due to its special geographical location, CZSC is one of the areas that most frequently suffer from marine meteorological disasters such as typhoon, rainstorm and sea fog, and is also one of the key areas that influence the short-term climate change of China. However, due to the lack of sufficient spatial- temporal monitoring data, the understanding of the characteristics of land-ocean-atmosphere interaction and its evolution in this area is not sufficient, and the accuracy of weather prediction and forecast is not ideal as well. Therefore, there has been a pressing need for carrying out the field experiments to strengthen the knowledge of atmospheric boundary layer dynamics and thermodynamics processes and to improve the weather and short-term climate prediction. The Marine Meteorological Science Experiment Base at Bohe of Maoming (M2SE2B), located at the CZSC, is the fixed observation site for typhoon research with sophisticated and fully functional equipment. The field experiment was carried out during August - November 2017 at M2SE2B focusing on the spatial-temporal evolution of atmospheric boundary layer and air-sea interaction during typhoon landfalling. This paper presents a case study of the wind field and turbulence observations using coherent Doppler lidar (CDL) during Typhoon MAWAR episode in this experimental campaign. 2. Lidar technology and methodology Figure 1 shows the sketch map of experimental location and the outfield the experiment at M2SE2 during August-November 2017. The spatial-temporal evolution of signal-to-noise ratio (SNR) and vertical velocity are shown in figure 2. In this case study, organized wave-like structure can be seen from SNR and vertical velocity datasets. The FFT and wavelet analysis are used to subtract the large- scale coherent signal. P28
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Figure 1. (a) The experimental location (marked with red star) (b) the outfield experiment at M2SE2B.
Figure 2. Time Height Intensity of (a1)(a2) SNR (dB) and (b1)(b2)vertical velocity (m/s) at 00-08 (a1,b1) and
08-18 (a2, b2) 02 Sep 2017.
Figure 3. (a) FFT spectral power and (b)(c) wavelet analysis of vertical velocity at 02 Sep 2017: 00:00-04:00
from height 1000 m to 2000 m.
Figure 3 (a) shows that the peak frequency of FFT spectral power is about 0.0015Hz, corresponding to
the time period of about 11 min, and an apparent frequency at about 0.0016 Hz using Morlet wavelet
analysis can be seen in figure 3 (b)(c). According to the linear mountain wave theory [1], the waves that
can propagate vertically in the atmosphere can be derived by the use of Scorer parameter 2 2 2/l N U ,where N is the Brunt-Vaisala frequency, and U is the cross-mountain wind speed. Based
on the radiosonde data, a profile of the Scorer parameter is calculated shown in figure 4, a wave with
wavelength and associated wave number 2 /k can propagate in the atmosphere if 2 2k l .