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Giichi Yamamoto and Masayuki Tanaka

Abstract

The effect of an increase of particles in the atmosphere on the global albedo and accordingly on the thermal regime of the earth is studied by solving the equation of radiative transfer in model turbid atmospheres.

Realistic model atmospheres with respect to size and vertical distributions of aerosol as well as reflectivity of the earth surface are assumed, and reflectivity at the top of the atmosphere, transniissivity at the earth surface, and absorptivity of turbid atmospheres are calculated as a function of atmospheric turbidity and the complex refractive index of the aerosol. It is shown that the thermal effect of increasing atmospheric turbidity is greatly affected by the imaginary part of the refractive index. Thus, if it takes a small value as is believed so at present, the earth-atmosphere system cools ofF with increase of turbidity, while if its value is large (ni0.05, ni being the imaginary part of the complex refractive index), heating of the earth- atmosphere system is expected due to increasing turbidity.

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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.

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Hisashi Nakamura, Masayuki Tanaka, and John M. Wallace

Abstract

The horizontal structure and dynamical properties of the teleconnection patterns in the interannual variability of the Northern Hemisphere wintertime 500 mb height field are investigated. Regression maps based on indices for the eastern Atlantic (EA), Pacific/North American (PNA), western Atlantic (WA), western Pacific (WP) and Eurasian (EU) patterns defined by Wallace and Gutzler are used to define the geographically fixed patterns. Space-spectrum analysis including a spherical harmonic decomposition is applied to these maps. Anomalous geostrophic wind fields derived from these regression maps are used to estimate the kinetic energy conversion between the climatological mean state and the wave structures associated with the teleconnection patterns.

The teleconnection patterns comprise “seesaw” and/or wavelike structures. In general, the kinetic energy of the teleconnection patterns is concentrated in total wavenumber n = 5 and 6 components with zonal wavenumbers m = 0, 1 and 2, which correspond to zonally elongated “seesaw” structures near the jetstreams. The phase tilt of the wave axes indicates that some wavecomponents of the Atlantic teleconnection patterns (EA, WA and EU) propagate wave energy equatorward, whereas the ultralong wavecomponents of the Pacific patterns (PNA and WP) exhibit poleward energy dispersion, which might possibly be related to the Southern Oscillation.

The zonal component of the extended Eliassen-Palm (E-P) flux associated with the “seesaw” structures accounts for most of the very low frequency barotropic energy conversion from the time-mean flow. The PNA and EA patterns, which have “seesaws” located in the jet exit regions, obtain kinetic energy more efficiently than the other patterns. The time scale for replenishing their kinetic energy is 3–4 days. The EU pattern, which has no “seesaw” structure, exhibits the smallest kinetic energy conversion. The fact that the WA and WP patterns straddle the storm tracks suggests that they may have a special relationship to baroclinic wave activity.

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Giichi Yamamoto, Masayuki Tanaka, and Shoji Asano

Abstract

The problem of diffuse reflection, transmission and emission of infrared radiation by water clouds is investigated in the wavelength region from 5–50 μ. The drop-size distribution of clouds is assumed to be that of altostratus measured by Diem. The phase function and other optical properties of the clouds are estimated from the value of the refractive index of water proposed by Pontier and Dechambenoy. Radiative processes due to both cloud droplets and water vapor in the cloud are taken into account, and a method of averaging the solution over a spectral interval including a number of absorption lines is developed.

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Giichi Yamamoto, Masayuki Tanaka, and Kazuo Kamitani

Abstract

The equation of radiative transfer as applied to water clouds in the window region near 10 microns is solved numerically by using values of the phase function and albedo for single scattering estimated by Deirmendjian (1964). It is found that for monochromatic radiation of 10 microns the upward intensity at the cloud top shows limb darkening and the downward intensity at the cloud base, limb brightening. For the whole window region from 8 to 12 microns, the upward flux at the cloud top and the downward flux at the cloud base, as well as the emissivity of the cloud, transmissivity at the cloud top and reflectivity at the cloud base are evaluated. When the cloud is thin, the upward flux is mostly dependent on the incident flux corresponding to the earth surface temperature, and when the cloud becomes thick, it approaches the black-body flux at the cloud temperature. The downward flux at the cloud base is very small for a thin cloud, increases with cloud thickness and approaches a constant value which is somewhat larger than the upward flux at the cloud top when the cloud becomes very thick. It is also found that the emissivity, transmissivity and reflectivity change with cloud thickness but are practically independent of both the cloud and earth surface temperatures. Therefore, by using the values of these quantities obtained in this study, one can evaluate the upward and downward fluxes for any combination of cloud and earth surface temperatures and cloud thicknesses.

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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.

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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.

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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.

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Mio Matsueda, Masayuki Kyouda, Zoltan Toth, H. L. Tanaka, and Tadashi Tsuyuki

Abstract

Atmospheric blocking occurred over the Rocky Mountains at 1200 UTC 15 December 2005. The operational medium-range ensemble forecasts of the Canadian Meteorological Center (CMC), the Japan Meteorological Agency (JMA), and the National Centers for Environmental Prediction (NCEP), as initialized at 1200 UTC 10 December 2005, showed remarkable differences regarding this event. All of the NCEP members failed to predict the correct location of the blocking, whereas almost all of the JMA members and most of the CMC members were successful in predicting the correct location. The present study investigated the factors that caused NCEP to incorrectly predict the blocking location, based on an ensemble-based sensitivity analysis and the JMA global spectral model (GSM) multianalysis ensemble forecasts with NCEP, regionally amplified NCEP, and globally amplified NCEP analyses.

A sensitive area for the blocking formation was detected over the central North Pacific. In this area, the NCEP control analysis experienced problems in the handling of a cutoff cyclone, and the NCEP initial perturbations were ineffective in reducing uncertainties in the NCEP control analysis. The JMA GSM multianalysis ensemble forecasts revealed that regional amplification of initial perturbations over the sensitive area could lead to further improvements in forecasts over the blocking region without degradation of forecasts over the Northern Hemisphere (NH), whereas the global amplification of initial perturbations could lead to improved forecasts over the blocking region and degraded forecasts over the NH. This finding may suggest that excessive amplification of initial perturbations over nonsensitive areas is undesirable, and that case-dependent rescaling of initial perturbations may be of value compared with climatology-based rescaling, which is widely used in current operational ensemble prediction systems.

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