The tropospheric particle extinction-to-backscatter ratio, the depolarization ratio, and the water-vapor mixing ratio were measured by use of a Raman lidar and a polarization lidar during the Asian dust seasons in 2001 and 2002 in Tsukuba, Japan. The apparent (not corrected for multiple-scattering effects) extinction-to-backscatter ratios (Sp) showed a dependence on the relative humidity with respect to ice (RHice) obtained from the lidar-derived water-vapor mixing ratio and radiosonde-derived temperature; they were mostly higher than 30 sr in dry air (RHice < 50%), whereas they were mostly lower than 30 sr in ice-supersaturated air (RHice > or = 100%), where the apparent extinction coefficients were larger than 0.036 km(-1). Both regions showed mean particle depolarization ratios of 20%-22%. Comparisons with theoretical calculations and the previous experiments suggest that the observed dependence of Sp on RHice is attributed to the difference in the predominant particles: nonspherical aerosols (mainly the Asian dust) in dry air and cloud particles in ice-supersaturated air.

No abstract

No abstract

In April 2002, a severe dust storm occurred in the Taklimakan Desert. A large amount of the dust was lifted up by the dust storm and gradually removed in the following few days. The whole event of the dust storm was observed by the Mie-scattering depolarization lidar at Aksu, Xinjiang, China (40.62°N, 80.83°E , 1028 m above mean sea level). This paper describes the dust event and the removal process that was observed by the lidar.During the dust storm (April 13-16), a dense dust layer developed from the ground up to 5.5 km. The backscattering ratio was 20 or more, and the depolarization ratio was 15-25％. Due to the absorption of the laser beam by the heavy dust, a normal lidar observation was impossible for several hours. In this study, we estimated the backscattering ratio at the lowest height during the dust storm by solving the lidar equation directly.After the dust storm (April 17-20), a clear diurnal variation of the top of the dust layer was found by the lidar. An investigation of the lidar signals at different heights shows that there were two types of the removal process of the dust. The lidar signals at lower heights (less than the 2 km) gradually decreased during the post-dust storm period. This result indicates that the gravitational settling of the relatively large

The vertical distribution profiles of the water vapor mixing ratio (w) were measured by Raman lidar at the Meteorological Research Institute, Japan, during the period from 2000 to 2004. The measured values were compared with those obtained with radiosondes, hygrometers on a meteorological observation tower, and global positioning system (GPS) antennas near the lidar site. The values of w obtained with the lidar were lower than those obtained with the corrected Meisei RS2-91 radiosonde by 1.2% on average and higher than those obtained with the corrected Vaisala RS80-A radiosonde by 17% for w ≥ 0.5 g kg−1. The lidar data were higher than those radiosondes’ data by 19% or 33% for w &lt; 0.5 g kg−1. The vertical variations of w obtained with the lidar differed from those obtained with the Meisei RS-01G radiosonde and Meteolabor Snow White radiosonde by 5% on average for w ≥ 0.5 g kg−1. The lidar data were lower than those radiosondes’ data by 37% or 39% for w &lt; 0.5 g kg−1. The temporal variations of w obtained with the lidar and the hygrometers on the meteorological tower agreed to within 0.4% at a height of 213 m, although the absolute values differed systematically by 9%–14% due to the incomplete overlap of the laser beam and the receiver’s field of view at heights between 50 and 150 m. The precipitable water vapor obtained with the lidar indicated a mean positive bias of 2 mm (9%–11%) relative to those obtained with GPS. The lidar water vapor calibration coefficient that was calculated using RS2-91 radiosonde data varied by 11% during an 18-month period. Therefore, it is necessary to develop an accurate, yet convenient, method for determining the calibration coefficient for the use of the lidar.