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  • Author or Editor: Masayuki Tanaka x
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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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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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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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