Doppler lidar observations of the coherent structures in the internal boundary layer

It is important to investigate the characteristics of turbulent organized structure (TOS) developed in near surface layer because it is considered to control the vertical exchange processes of momentum, heat and other scalars between the surface and atmosphere. We conducted Coherent Doppler lidar observations over Sendai Airport on June 2007 using two lidars; Electronic Navigation Research Institute (ENRI)'s lidar (range resolution of 30 m) and National Institute of Information and Communications Technology (NICT)'s lidar (range resolution of 90 m). In this observation, we detected TOS in near surface layer and examined its physical scaling. ENRI lidar (Komatsubara and Kaku 2005) was stationed on the rooftop of ENRI's Iwanuma branch building (16.7 m above the ground) at 2.5 km west from the Pacific coast. It performed full 360 degree CAPPI (Constant-Altitude Plan Position Indicator) scans at elevation angles from 0.5 to 5.0 degree in 0.5 degree increments in the day time. In order to focus on the structure of TOS near the surface, the PPI scan data at elevation angle of 1.0 degree (from 22.0 to 48.6 m above the ground) were used. In this experiment, the atmospheric stability was slightly unstable (Iwai et al. 2008), which was estimated from vertical profiles of wind velocity and air temperature measured by heliborne sensors of Japan Aerospace Exploration Agency (JAXA). To extract the turbulent motion from the datasets of CAPPI scans, the radial velocity fluctuations are calculated by subtracting mean-radial velocity, which is estimated from the VAD (Velocity Azimuth Display) method, from the radial velocity observed by PPI scans. The horizontal distribution of the radial velocity fluctuations revealed the occurrence of the streak structures elongated along the main stream. The intervals between the streaks in the spanwise direction were estimated about 400m using a two-point correlation analysis. NICT lidar (Ishii et al. 2007), which was stationed at 4 km west from the Pacific coast, was performed the 135 degree azimuth RHI (Range Height Indicator) scan (i.e., parallel to the sea breeze flow) at almost same time as the ENRI lidar observation. According to the vertical profile of the radial wind velocity and the range-corrected SNR (signal to noise ratio) from NICT lidar, the depths of the atmospheric boundary layer and the internal boundary layer (sea breeze flow) were estimated to be about 700 m and 220 m, respectively. We compared the intervals of the streaks observed in this experiment with that in the other outdoor observation (Inagaki and Kanda 2010). The intervals of streaks are one-order different if they are scaled by mixed layer height, and it becomes a same order if they are scaled by the internal boundary layer height.