Yuzo Mano

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

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.

Backscattering linear depolarization ratio measurements of mineral, sea-salt, and ammonium sulfate particles simulated in a laboratory chamber

The backscattering linear depolarization ratios of major types of tropospheric aerosol particles (Asian and Saharan mineral dust, sea salt, and ammonium sulfate) were measured using a laboratory chamber for interpreting the polarization lidar measurement of tropospheric aerosols. The values obtained from Asian and Saharan mineral particles were 0.39 +/- 0.04 to 0.05 (mean +/- standard deviation) for a high number of concentrations in the supermicrometer range and 0.17 +/- 0.03 to 0.14 +/- 0.03 in the submicrometer range. The values were 0.08 +/- 0.01 for sea-salt crystals, 0.04 +/- 0.003 for ammonium sulfate crystals, and 0.01 +/- < or = 0.001 for both liquid droplets in the submicrometer range. These values can serve as a reference for estimating aerosol type using lidar measurement.

Assessment of the nonsphericity of mineral dust from geostationary satellite measurements

Optical thickness of Asian dust aerosols over the Yellow Sea and the Sea of Japan were retrieved from the visible data of the Geostationary Meteorological Satellite (GMS-5) observed on April 7 and 8, 2000, through look-up tables generated by the doubling and adding method. The retrieved optical thickness, by using conventional spherical particle models, showed unnatural decrease in the middle of day time. The decrease disappeared by the use of the semiempirical theory for nonspherical particles by Pollack and Cuzzi [J. Atmos. Sci. 37 (1980) 868.]. These results are explained by the difference of the phase functions between spherical and nonspherical particles and also the variation of the scattering angle for the target dust area during the satellite measurements. Our results confirm that the use of nonspherical particle model improves the retrieval of dust optical thickness from space.

No evidence for solar absorption anomaly by marine water clouds through collocated aircraft radiation measurements

No observational evidence was found for the so-called anomalous solar absorption by maritime water clouds through collocated aircraft measurements taken during the Japanese Cloud-Climate Study (JACCS) program. The aircraft experiment has been carried out by using two aircraft equipped with various instruments for wintertime stratocumulus clouds over an area centered at (29°N, 129°E) in the East China Sea. Here we have carefully analyzed solar absorption by the water stratocumulus clouds observed on February 2, 1998. The visible-band net fluxes measured above and below the cloud layer were almost the same within measurement accuracy; this means no substantial absorption in the visible spectral region. On the other hand, there were significant differences as much as 50–80 W m−2 between the near-infrared-band net fluxes measured above and below the cloud layer; this difference corresponds to absorptance of 6–10% of the total-band solar irradiance above the cloud layer. Without cloud particles, water vapor absorption was estimated to be about 4% of the total-band irradiance for the layer. Distributions along the flight legs of the measured visible-band and near-infrared-band absorptance were in phase in their positions with zero mean visible-band absorptance. The measured radiation budget averaged over long distances along the flight legs for the inhomogeneous cloud layers agreed well with theoretical counterparts calculated for plane-parallel, homogeneous cloud models based on the observed microphysical parameters.

Fast radiative-transfer model based on the correlated k-distribution method for a high-resolution satellite sounder

A fast radiative-transfer model for the Atmospheric Infrared Sounder (AIRS) was developed by use of a correlated k-distribution method. Transmittances produced by the correlated k-distribution method are systematically displaced from those produced by a line-by-line method, and empirical correction is possible. A fast radiative model that includes this empirical correction has exhibited practical performance in tests of transmittance and brightness temperature that used an independent set of atmospheric profiles.

Liquid Water Cloud Measurements Using the Raman Lidar Technique: Current Understanding and Future Research Needs

AbstractThis paper describes recent work in the Raman lidar liquid water cloud measurement technique. The range-resolved spectral measurements at the National Aeronautics and Space Administration Goddard Space Flight Center indicate that the Raman backscattering spectra measured in and below low clouds agree well with theoretical spectra for vapor and liquid water. The calibration coefficients of the liquid water measurement for the Raman lidar at the Atmospheric Radiation Measurement Program Southern Great Plains site of the U.S. Department of Energy were determined by comparison with the liquid water path (LWP) obtained with Atmospheric Emitted Radiance Interferometer (AERI) and the liquid water content (LWC) obtained with the millimeter wavelength cloud radar and water vapor radiometer (MMCR–WVR) together. These comparisons were used to estimate the Raman liquid water cross-sectional value. The results indicate a bias consistent with an effective liquid water Raman cross-sectional value that is 28%–46%...

Comparisons of the mineral dust optical thickness retrieved from Geostationary Meteorological Satellite with ground-based radiometer measurements

Abstract Optical thickness of the Asian dust aerosols over the ocean near Japan was retrieved from the visible data of the Geostationary Meteorological Satellite (GMS-5) from April 7 to 22, 2002 using the method by Masuda et al. [Remote Sens. Environ. 82 (2002) 238] in which the nonsphericity of dust particles was taken into account. The retrieved optical thicknesses were then compared with those derived from the sunphotometer and the skyradiometer measurements. The mean and the standard deviation of the optical thickness difference, GMS minus radiometers, were −0.03 and 0.17, respectively, for 85 samples where the optical thickness ranges from 0.25 to 1.07.

Optical modeling of irregularly shaped ice particles in convective cirrus

A model of convectively generated cirrus particles consistent with the shape properties of measured cirrus particles is proposed. A database of single scattering properties of modeled ice particles at visible to infrared wavelengths was constructed using the finite-difference time-domain and geometric-optics-integral-equation methods for advanced analysis of satellite/ground-based remote sensing data.