Ice clouds and Asian dust studied with lidar measurements of particle extinction-to-backscatter ratio, particle depolarization, and water-vapor mixing ratio over Tsukuba

Abstract

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.

Continuous 1064/532 nm Lidar Measurements (CORALNet-UBC) in Vancouver, British Columbia: Selected Results from a Year of Operation

“…Comparison of both panels indicates that the thin subsiding dust layer shows values of aerosol backscatter similar to the aerosol in the boundary layer (i.e., yellow and red hues in the top panel) whereas the boundary layer and dust layer are markedly different with respect to depolarization (bottom panel). Aerosol depolarization for this subsiding layers is in the range 0.18-0.35 (18-35%) and is consistent with values measured elsewhere for Asian dust (e.g., Murayama et al, 2003;Sakai et al, 2003). These high values of depolarization are indicative of nonspherical crustal particles and are easily distinguished from depolarization ratios for local anthropogenic pollution and biomass burning plumes (see example below).…”

Profiling of fine and coarse particle mass: case studies of Saharan dust and Eyjafjallajökull/Grimsvötn volcanic plumes

“…Lidar measurements close to the Saharan dust source (Freudenthaler et al, 2009) and after long-range transport towards Europe and Cape Verde show similar values from 0.3-0.35 in lofted dust-dominated aerosol layers. After long-range transport of mineral dust from desert regions in western and northern China, particle depolarization ratios in layers dominated by dust were also found in the range of 0.3-0.35 over Japan (Sakai et al, 2003a;Murayama et al, 2003;Sugimoto et al, 2003;Shimizu et al, 2004). Lidar observations at Barbados (about 4000 km west of Cape Verde, and 5000-7000 km apart from the main Saharan dust sources) indeed indicate a decrease of the particle depolarization ratio towards 0.…”

“…The polarization lidar permits the discrimination of light-depolarizing coarse-mode particles (non-spherical particles) such as volcanic dust and desert dust and nonlight-depolarizing fine-mode particles (spherical particles) such as anthropogenic haze and volcanic sulfate particles (Sakai et al, 2003a;Murayama et al, 2003;Shimizu et al, 2004;Sugimoto and Lee, 2006;Sassen, 2005;Sassen et al, 2007;Nishizawa et al, 2007;Liu et al, 2008;Freudenthaler et al, 2009;Groß et al, 2011aGroß et al, , 2012Miffre et al, 2012). The technique further allows us to determine the profiles of the coarse-mode-related and fine-mode-related backscatter coefficient (Shimizu et al, 2004;Tesche et al, 2009bTesche et al, , 2011b, and thus the estimation of the corresponding particle extinction coefficient profiles for the fine and coarse-mode fraction by means of appropriate extinction-to-backscatter ratios (lidar ratios).…”

A study on the aerosol extinction-to-backscatter ratio with combination of micro-pulse LIDAR and MODIS over Hong Kong

“…Waggoner et al (1972) retrieved an aerosol scattering-to-backscatter ratio of about 84 sr for the relative humidity smaller than 75%. A decade later, Salemink et al (1984) showed a linear increase in the LR from 25 to 70 sr for the relative humidity of 40-80% at wavelength of 532 nm near the ground. Using climatological values of aerosol size distributions, Ackermann (1998) modeled LR values for different tropospheric aerosol types at typical wavelengths (355 nm, 532 nm and 1064 nm) using Nd:YAG lasers.…”