Assessment of the Performance of a Scanning Wind Doppler Lidar at an Urban-Mountain Site in Seoul

Winds in the planetary boundary layer (PBL) are important factors for accurate modelling of air quality, numerical weather prediction and conversion of satellite measurements to near-surface air quality information (Seibert et al., AE, 2000; Emeis et al., Meteorol. Z., 2008). In this study, we (1) evaluate wind speed (WS) and direction (WD) retrieved from Wind Doppler Lidar (WDL) measurements by two methods [so called, `sine-fitting (SF) method' and `singular value decomposition (SVD) method'] and (2) analyze the WDL data at Seoul National University (SNU), Seoul, to investigate the diurnal evolution of winds and aerosol characteristics in PBL. Evaluation of the two methods used in retrieving wind from radial velocity was done through comparison with radiosonde soundings from the same site. Winds retrieved using the SVD method from mean radial velocity of 15 minutes showed good agreement with radiosonde profiles (i.e., bias of 0.03 m s-1 and root mean square of 1.70 m s-1 in WS). However, the WDL was found to have difficulty retrieving signals under clean conditions (i.e., too small signal to noise ratio) or under the presence of near-surface optically-thick aerosol/cloud layer (i.e., strong signal attenuation). Despite this shortcoming, the WDL was able to successfully capture the diurnal variation of PBL wind. Two major wind patterns were observed at SNU; first of all, when convective boundary layer was strongly developed, thermally induced winds with large variation of vertical WS in the afternoon and a diurnal variation in WD showing characteristics of mountain and valley winds were observed. Secondly, small variation in WS and WD throughout the day was a major characteristic of cases when wind was largely influenced by the synoptic weather pattern.