Vertical Profiles of Aeolian Dust in a Desert Atmosphere Observed using Lidar in Shapotou, China

Abstract

We analyzed the time series data of dust vertical profiles, observed using polarization elastic lidar, from April 8 th -21 st , 2002, during the first intensive observation period of the Aeolian Dust Experiment on Climate impact (ADEC), in Shapotou, Ninxia Province in China. We conducted the analysis with consideration to the upper atmospheric soundings and surface weather data. The results are summarized as follows. 1) A well-mixed dust layer dominated in the boundary layer sampled from around 11 a.m. until around 1 or 2 a.m. local time (Beijing time). Under well-mixed conditions, the mixed layers grew well with dry convections in the boundary layer, especially during the day and in the early evening. 2) Dry convections developed deeper during synoptic low-pressure conditions because of the systematic upward motions prevalent in the low-pressure systems. Vertical wind shear affected growth of the mixed layer as well, that is, weak vertical wind shear condition was favorable for the growth of the mixed layer. The deepest mixed layer was observed on April 13 th at a thickness of about 6-km above ground, when the pressure was the lowest, the vertical wind shear was very weak, and the atmosphere was dry. The aspect ratios (horizontal/vertical scale ratios) of the convections decreased under low-pressure and weak-shear conditions. On the other hand, the aspect ratios of the convections increased dramatically under highpressure and strong-shear conditions, because convection growth was suppressed by systematic downdrafts of the high-pressure system and by strong vertical wind shears.

Retrieval of Asian Dust Amount over Land using ADEOS-II/GLI near UV Data

“…The result is a little bit larger than the retrieved mode radius for the coarse mode (1 to 6 µm) with the skyradiometer observation (Uchiyama et al 2005), but it is reasonable for Kosa particles in the same order of magnitude. The GLI retrieved optical thickness 0.34 at 500nm is larger than the value of 0.30 with a LIDAR measurement at 532 nm (Yasui et al 2005), and, on the other hand, smaller than the value of 0.59 at 500nm with a skyradiometer measurement. Here, we use the LIDAR data only at lower than 4 km height, since the signals above 4 km height suffered from severe noises.…”

Modeling Study of Diurnally Varying Convective Boundary Layer and Dust Transport over Desert Regions

“…The horizontal grid size is 500 m, which may be sufficient to resolve boundary-layer coherent convective motion, since Yasui et al (2005) estimated its horizontal size as 4.3 7.3 km. The vertical grid size is 20 810 m (stretched).…”

“…Following the analyses by Yasui et al (2005), we use the sounding at 00Z 13 April 2002 to represent a deep mixed-layer structure in fine weather ( Fig. 1).…”

“…Diurnal variability of dust mobilization and concentration is responsible for 20 50% of the total temporal variability in East Asia (Luo et al 2004). Yasui et al (2005) clearly demonstrated the diurnal variability of dust concentration in the planetary boundary layer in fairweather conditions through the lidar observations conducted at a desert site of Shapotou (at 37.46°N and 104.95°E, 1250 m above the sea level) in the south of the Tenger Desert, and pointed out that boundary-layer thermal convection plays a role in determining the vertical distribution of dust in those conditions.…”

Strong Updraft at a Sea-Breeze Front and Associated Vertical Transport of Near-Surface Dense Aerosol Observed by Doppler Lidar and Ceilometer

“…It was assumed that the wavelength dependence of the backscatter coefficient was nearly negligible since the backscattering was in the geometric optical region where the wavelengths of the Mie lidar and ceilometer were much smaller than the particle diameter at dense clouds. The Mie lidar was placed about 6 m north-east of the ceilometer and its backscatter coefficient was calibrated by a method described in Yasui et al (2005). For the ceilometer, the wavelength of the transmitted beam is on the same order as the scattering particle matter (e.g., aerosol, fog, mist, cloud, and precipitation).…”