Search Results

You are looking at 1 - 4 of 4 items for :

  • Author or Editor: Masayuki Tanaka x
  • Journal of Applied Meteorology and Climatology x
  • Refine by Access: All Content x
Clear All Modify Search
Tadahiro Hayasaka, Nobuyuki Kikuchi, and Masayuki Tanaka

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 with plane-parallel cloud models. It is also inferred that the anomalous absorption pointed out by aircraft observations in previous studies does not exist.

Full access
Masayuki Tanaka, Tamio Takamura, and Teruyuki Nakajima

Abstract

Angular distributions of the intensity of light scattered by airborne particles were measured for both parallel and perpendicularly polarized components. A precision polar nephelometer was constructed for use of this study. The data were analyzed using a newly developed inversion library method to give a simultaneous estimate of the complex index of refraction m = mrmii of aerosols and their size distribution, where mr is the real part and mi the imaginary part of the refractive index. Results of 302 measurements show that the monthly mean values of mr and mi vary within the range 1.47–1.57 and 0.009–0.037, respectively, depending upon the relative humidity.

The size distribution of aerosols can be approximated by the log-normal distribution function; the mean radius and the standard deviation are found to be rg = 0.138 μm and σg = 2.56, respectively, as geometrical mean values for the whole data.

Full access
Makoto Kuji, Tadahiro Hayasaka, Nobuyuki Kikuchi, Teruyuki Nakajima, and Masayuki Tanaka

Abstract

An algorithm was developed to retrieve both the optical thickness and the effective particle radius of low-level marine clouds simultaneously from National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (AVHRR) data. The algorithm uses the combination of the visible (channel 1) and the middle-infrared (channel 3) reflected radiation. The thermal component in the middle infrared was corrected with the thermal-infrared (channel 4) radiance by a statistical technique using a regressive formula. The liquid water path (i.e., vertically integrated liquid water content) was also estimated as a by-product. The algorithm was applied to AVHRR datasets for which almost-synchronized airborne observations were conducted around the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) and the Western North Pacific Experiment (WENPEX) regions. The two regions are different in the characteristics of cloud fields:summer stratus and stratiform clouds that result from outbreaks of cold air mass over the warm sea in winter seasons, respectively.

In the FIRE region, the retrieved parameters are almost consistent with those of in situ airborne observations, even when using a more practical approach than the algorithms adopted in previous studies, but there is still a discrepancy between the satellite-derived results and those of in situ airborne observations around the drizzle-dominated portion. In the WENPEX region, it is suggested that cloud fractional coverage in a pixel may cause error in the retrieval, particularly for horizontally inhomogeneous cloud field analyses with an assumption of a plane-parallel atmospheric model. It is found also that the thermal-infrared information has a potential to estimate the inhomogeneity of cloud fields as a result of the comparison between stratus and broken cloud cases.

Full access
Tadahiro Hayasaka, Teruyuki Nakajima, Yasushi Fujiyoshi, Yutaka Ishizaka, Takao Takeda, and Masayuki Tanaka

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.

Full access