This study investigates the Planetary Boundary Layer (PBL) dynamics over Taiwan’s complex terrain using vehicle-based Doppler Wind Lidar. The Taichung Basin and Yulin-Chiayi Plain are selected to employ the vehicle-based aerosol and wind lidars to measure the east-to-west cross-section of aerosol and wind of the PBL. The PBL cross-section observed over the Taichung basin and Yulin-Chiayi Plain indicated the significant changes in the PBL structure, including terrain-induced vertical mixing of aerosol, wind shear, and return flow of the local circulation. The results indicate the terrain-induced eddy causes significant convection in the lower boundary layers, promoting vertical mixing.
In this study, the estimation of Convective Boundary Layer Height (CBLH) using coherent Doppler lidar with a novel deep learning approach is presented. A modified stacked hourglass network, a convolutional neural network architecture is employed to automate the retrieval of CBLH from aerosol and wind products measured by the Doppler lidar. The model is trained using a comprehensive dataset collected over one year in central Taiwan, comprising over 30,000 lidar maps. Ground truth CBLH is determined from the variance of vertical velocity, and the dataset is divided into subsets to evaluate the minimum training requirements. The results demonstrate the effectiveness of the deep learning model in accurately predicting CBLH and the possibility of deriving CBLH from the aerosol backscatter profile.
Observations of the aerosol atmosphere by means of the "LOSA-M2" aerosol Raman lidar and the "Stream Line" pulsed coherent Doppler lidar were carried out in August 2014 near village Boyarsk (Baikal Lake coast). The wind field and its impact on the stratification and dynamics of the aerosol layers in the lower troposphere were studied under various synoptic conditions. The data of simultaneous observations of wave-like motions in the boundary layer of the troposphere by two lidars are presented.
Three years (2003-2005) of aerosol optical depths (AOD) measured with CIMEL sunphotometer were compared to the surface concentrations of PM10 and PM2.5 in Northern (i.e. Taipei) and Southern (i.e. Tainan) Taiwan. The correlation between AOD and PM10 is higher in Taipei than in Tainan. Additional chemical compositions of PM10 and PM2.5 in these two sites, including ionic component, sea salt, OC/EC and crustal components, were also examined to find their relationship with the AOD. These analyses indicate that aerosols in Taipei are mainly composed of fine aerosols, whereas in Tainan more crustal material and OC exist in the coarse mode, which partially explain the higher correlation of PM10 and AOD in Taipei. Closure calculations are carried out by combining data from lidar, sunphotometer, nephelometer, aethalomter, SMPS and APS size spectrometers, as well as chemical analyses of aerosols from PM10 and PM2.5 samplers and MOUDI impactor to investigate their consistency. The observed surface single scattering albedo was also compared to that retrieved by CIMEL sunphotometer, with additional discussion on the possible explanation to the discrepancies of the comparisons. Then, lidar measurement is applied to relate aerosols at the surface to those aloft.
For the assessment of climatic impact of aerosols, the knowledge of both the temporal and spatial distributions of aerosol is essential. Laser radar, more popularly known as Lidar, has becoming one of the most powerful techniques for active detection of aerosols in the atmosphere. Lidar can provide vertically resolved of extinction and backscatter coefficients, and thereby the height of the planetary boundary layer or the nighttime residual layer. As the long-term changes in the structure and dynamics of the lower and middle troposphere is now becoming a priority, a pulsed Nd:YAG Lidar system is applied for measuring the vertical distribution of aerosol properties in the metropolitan Taipei. Two years (2004-2005) of aerosol optical depth (AOD) measured by Lidar, Cimel Sunphotometer and MODerate resolution Imaging Spectroradiometer (MODIS) were compared. The AOD shows strong seasonal variation with maximum values (AODLidar > 1, AODCimel > 1 and AODMODIS > 0.39) occurred in April. AODMODIS shows significant underestimation. AODLidar has good correlation with AODCimel, but the Lidar measurement is biased toward lower values as presented by the 0.725 slope in the linear regression. This bias is mostly caused by the Lidar blind distance at the lowest part of the atmosphere. The R-squared of AODCimel and surface PM2.5 concentration is about 0.44. This reflects the fact that the atmospheric boundary layer is often not well-mixed, so aerosols there cannot represent the total AOD value. Particles in the free troposphere also need to be concerned. Further comparison of our Lidar data with the CALIPSO measurements is intended.
Cirrus clouds are routinely observed by lidar at Chung-Li (25°N, 121°E). Their optical and microphysical properties are investigated by the height and temperature distributions, optical thickness, extinction, and depolarization ratios. Cirrus clouds with optical thickness smaller than 0.03, which are classified as subvisual cirrus clouds, have high probability of occurrence. Thin cirrus clouds have their optical thickness exponentially correlates with temperature in the region of -60 to -80C. Depolarization ratio is an important property of cirrus clouds. Although depolarization ratio for ice particle is large, vanishing depolarization ratios have been found for some clouds as high as 12 km. Depolarization ratio for all cirrus clouds distributed widely, and thin cirrus clouds near the tropopause above 16 km seem to have limited depolarization ratios. The microphysics of ice particles is discussed.
The polarization lidar measurements were carried out to investigate the optical properties of ice crystals. The cloud height, extinction-to-backscattering ratio, optical depth, and depolarization ratio for cirrus clouds in the height range of 10-17 km were analyzed. We found the cloud optical depth has a clear height dependence, with high clouds optically thin. There is an increasing trend of depolarization ratio with height between 12-16 km. There is a clear relationship between the depolarization ratio and the optical depth. For cirrus clouds at heights between 13 and 16 km region, the clouds with optical depths smaller than 0.1 have depolarization ratios about 0.3. Large depolarization ratio (0.6) was found for subvisual clouds of optical depthabout 0.02. Thick clouds with optical depth larger than 0.1 have an average depolarization ratio about 0.2.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.