Tadahiro Hayasaka

Tropospheric aerosol optical properties derived from lidar, sun photometer, and optical particle counter measurements

Tropospheric aerosols have been observed for the period from November 1990 to April 1992 with a lidar, a sun photometer, and an optical particle counter. Variations of aerosol optical thickness derived from the lidar and the sun photometer data and measurements are presented. The simultaneous measurements of these instruments also allowed us to estimate the extinction-to-backscatter ratio (S(1)), which ranged from 20 to 70. Comparison of optical thicknesses derived from both instruments clearly shows the effect of Mt. Pinatubos eruption and the temporal variation of optical thickness in the stratosphere over 12 km. The possible range of the complex refractive index for the columnar mean aerosols can be deduced from the probable range of S(1) derived by the use of an S(1) diagram as a function of complex refractive index (m). The imaginary part of m can be estimated provided that the real part of m is known.

Absorption of solar radiation by stratocumulus clouds: Aircraft measurements and theoretical calculations

Abstract Aircraft observations of shortwave radiative properties of stratocumulus clouds were carried out over the western North Pacific Ocean during January 1991. Two aircraft were equipped with a pair of pyranometers and near-infrared pyranometers. Downward and upward shortwave fluxes above and below the cloud were synchronously measured by two aircraft. The cloud radiative properties, especially the absorptance obtained from measurements, were compared with those calculated. Aircraft measurements and Monte Carlo calculations showed that spatial inhomogeneities of clouds cause horizontal radiative convergence and divergence, and that vertical radiative convergence-that is, absorptance with a usual definition-apparently becomes extremely large or negative. The apparent absorptance could be corrected by a method that evaluates the true absorption from the difference between the apparent visible and near-infrared absorptions. The corrected absorptance agreed well with the theoretical absorptance calculated...

Aerosol Optical Properties in the Iranian Region Obtained by Ground-Based Solar Radiation Measurements in the Summer Of 1991

Abstract Solar radiation measurements were made using sun photometers and pyranometers during 31 May-7 June 1991 at several places in Iran and during 12 June-17 September 1991 at a fixed place, Bushehr, Iran. In the first period the aerosol optical thickness had values about 0.4 at the wavelength of 0.5 μm in the coastal area and about 0.2 in the plateau area. The Angstroms exponent, which is the slope of optical thickness spectrum, had values around 1 for large city areas and less than 0.5 for inland arid areas. Chemical analyses of sampled air indicate an effect of fossil fuel burning from local sources. Such optical and chemical characteristics of atmospheres suggest that soil-derived coarse particles contributed considerably to the atmospheric turbidity in arid areas, whereas an active generation of aerosols was dominant near large cities. Significant rises in atmospheric turbidity were observed in the earlier part of the second period at Bushehr about once a week with a duration of about one day, wh...

Airborne measurements of the optical stratification of aerosols in turbid atmospheres

A spectral scanning radiometer and corresponding algorithm of analysis were developed to evaluate optical stratification of aerosols from airborne measurements. Several flights were carried out to measure direct and circumsolar radiations simultaneously by a Swerlingen Merlin IV and a Cessna 206 aircraft. Results of the data analysis showed that our scheme can evaluate the optical depth of aerosols at any flight level from the ground to 400 mb, the highest flight level, with relative error of <10%. Vertical distribution and latitude–height cross sections of the optical thickness of aerosols and volume spectra of stratospheric aerosols were investigated.

Geometrical Thickness, Liquid Water Content, and Radiative Properties of Stratocumulus Clouds over the Western North Pacific

Abstract An algorithm was developed for retrieving cloud geometrical thickness from a measured liquid water path and equivalent width of 0.94-µm water vapor absorption band. The algorithm was applied to aircraft observations obtained by a microwave radiometer and a spectrometer in the winter of 1991 over the western North Pacific Ocean. Retrieved values of the cloud geometrical thickness are apt to be smaller than those observed by eye, especially for horizontally inhomogeneous clouds. Measured cloud albedos in the visible and near-infrared spectral region were also compared with calculated values. For homogeneous clouds there exists a single droplet size distribution that satisfies both spectral regions. However, for inhomogeneous clouds no single size distribution exists that satisfies the albedo observed in both spectral regions.

Optical and chemical properties of urban aerosols in Sendai and Sapporo, Japan

Abstract Simultaneous measurements of size distribution, complex refractive index and chemical components of urban aerosols were intermittently carried out in Sendai and Sapporo, Japan, for the period from February 1986 to June 1987. Applying an inversion-library method to the phase functions measured by a polar nephelometer, size distribution and complex refractive index were retrieved. On the other hand, chemical components were analysed for the aerosol samples on a quartz fiber filter and a Teflon filter collected by two high-volume samplers. Among various components, elemental carbon as well as water content is most effective for the optical properties and its effect is found to be qualitatively different between winter and the other seasons. This difference seems to depend on the contribution of coarse particles.

Short-cut transport path for Asian dust directly to the Arctic: a case study

Asian dust can be transported long distances from the Taklimakan or Gobi desert to North America across the Pacific Ocean, and it has been found to have a significant impact on ecosystems, climate, and human health. Although it is well known that Asian dust is transported all over the globe, there are limited observations reporting Asian dust transported to the Arctic. We report a case study of a large-scale heavy dust storm over East Asia on 19 March 2010, as shown by ground-based and space-borne multi-sensor observations, as well as NCEP/NCAR reanalysis data and HYSPLIT trajectories. Our analysis suggests that Asian dust aerosols were transported from northwest China to the Arctic within 5 days, crossing eastern China, Japan and Siberia before reaching the Arctic. The results indicate that Asian dust can be transported for long distances along a previously unreported transport path. Evidence from other dust events over the past decade (2001-2010) also supports our results, indicating that dust from 25.2% of Asian dust events has potentially been transported directly to the Arctic. The transport of Asian dust to the Arctic is due to cyclones and the enhanced East Asia Trough (EAT), which are very common synoptic systems over East Asia. This suggests that many other large dust events would have generated long-range transport of dust to the Arctic along this path in the past. Thus, Asian dust potentially affects the Arctic climate and ecosystem, making climate change in the Arctic much more complex to be fully understood.

Comparison of Global and Seasonal Characteristics of Cloud Phase and Horizontal Ice Plates Derived from CALIPSO with MODIS and ECMWF

AbstractThis study analyzed the global and seasonal characteristics of cloud phase and ice crystal orientation (CTYPE-lidar) by using the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). A dataset from September 2006 to August 2007 was used to derive the seasonal characteristics. The discrimination scheme was originally developed by Yoshida et al., who classified clouds mainly into warm water, supercooled water, and randomly oriented ice crystals or horizontally oriented ice plates. This study used the following products for the comparison with CTYPE-lidar: (i) the vertical feature mask (VFM) of the National Aeronautics and Space Administration (NASA), (ii) the Moderate Resolution Imaging Spectroradiometer (MODIS), and (iii) European Centre for Medium-Range Weather Forecasts (ECMWF). Overall, the results showed that the CTYPE-lidar discrimination scheme was consistent with the outputs from VFM, MODIS, and E...

Air truth validation of cloud albedo estimated from NOAA advanced very high resolution radiometer data

A comparison was carried out between cloud albedos observed in situ by aircraft and cloud albedos calculated with visible optical thickness retrieved from the NOAA advanced very high resolution radiometer channel 1 radiance data. The results show that the observed and calculated cloud albedos in the visible region are coincident with each other in a few percent for both homogeneous stratus and rather inhomogeneous stratocumulus clouds as long as the cloud amount is large. In the near-infrared region, on the other hand, the observed albedo is lower than that evaluated from the satellite data for stratocumulus clouds, while the observed and calculated albedos are consistent for stratus clouds. From the aircraft observation of solar radiative flux this discrepancy is not ascribed to the uncertainty in the near-infrared absorption processes as discussed in previous studies.

Changes in stratospheric aerosols and solar insolation due to Mt. Pinatubo eruption as observed over the western Pacific

The authors present the results of sunphotometer and pyranometer readings taken from ships in the western Pacific in the latitude range 30{degrees}N to 30{degrees}S, following the Mt. Pinatubo eruption. The sunphotometer data shows a definite columnar rise in aerosol content via optical thickness following the eruption. The pyranometer showed a drop in solar insolation, which was actually larger than what would have been expected from models based on the aerosol increase.