Determination of Aerosol Size Distribution from Spectral Attenuation Measurements

The aerosol optical thickness of the atmosphere was measured using a spectropyrheliometer at Tsukuba for three winter seasons from October 1980 to March 1983. The optical thickness was abnormally large in the ('82-'83) winter, because of the enhancement of the stratospheric aerosols due to the volcanic eruptions of El Chichon.Size distributions of aerosols in the vertical air column were inferred, which show characteristic features of bimodal distribution for the pre-E1 Chichon season and power law distribution for the post-E1 Chichon season.Optical properties of the El Chichon volcanic aerosols have been estimated; the stratospheric optical thickness was about 0.1 on the wavelength average in the ('82-'83) winter, and aerosol size distributions were relatively monodispersive with a mode radius around 0.3 *m. Possible effects of the enhanced stratospheric aerosols on the solar radiation budget were estimated and compared with available observations. The El Chichon induced aerosols in the ('82-'83) winter could reduce the total solar radiation on the ground by as much as 3-4% on cloudless days, and enhance the spherical albedo by about 10%.

Section: Discussionmentioning

confidence: 99%

Section: Characteristics Of Aerosol Size Distributionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Atmospheric Turbidity and Aerosol Size Distribution in Winter at Tsukuba: Effects of the Eruption of E1 Chichon

Asano¹,

Sekiguchi²,

Kobayashi³

et al. 1985

“…The sensitivity of the inversion to the refractive index has been investigated by Yamamoto and Tanaka (1969) and King et al (1978). They showed that the inverted size distributions maintain their shape for small changes in the complex refractive index.…”

Section: Estimation Of the Aerosol Size Distribution (A) Troposphericmentioning

confidence: 99%

Aircraft Measurements of the Radiative Effects of Tropospheric

Asano¹

1989

The size distribution and the complex refractive index of tropospheric aerosols have been retrieved from the simultaneous observations of solar radiation and aerosols described in Part I of this study (Asano and Shiobara, 1989). Three sets of observations over the Tsukuba area have been analyzed, for which the aerosol optical thicknesses were available from ground-based spectral attenuation measurements of direct solar radiation.The bimodal size distribution for tropospheric aerosols was approximated by a composite powerlaw distribution function. The parameters of the distribution function were determined by fitting the function to the columnar size distributions inverted from photometrically measured spectral optical thicknesses. Estimation was made of wavelength-mean effective values of the complex refractive index m*=mr-mii which optimally simulate the observed solar fluxes and heating rates for the total solar spectral region. In the simulated calculations, the observed profiles of aerosols and water vapor were considered. The single scattering properties were computed from Mie theory for the determined size distribution and for a reasonably assumed real part of the index of refraction of mr=1.52. The optimal value of mi=0.03*0.02 was estimated for the imaginary part of the index of refraction of the tropospheric aerosols.

“…Atmospheric aerosols affect on climate through radiative transfer process as well as microphysical process in cloud formation. As for the former, many researchers have reported about the absorption properties of atmospheric aerosol particles, since the atmospheric aerosols is greatly affected by the imaginary term of the refractive index (Lm(m *)) imaginary term of the refractive index (Im(m*)) (Yamamoto and Tanaka, 1972). However, the complex refractive indices of the atmospheric aerosols have not yet known well, even though various techniques have been proposed (Gerber and Hindman,1982).…”

Section: Introductionmentioning

confidence: 99%

Determination of Effective Absorption Property of Atmospheric Aerosols and Validity of that Value in Calculating the Flux Divergence. Part I Theory

Kobayashi

1986

A method of estimating the effective absorption property of atmospheric aerosols is proposed. This method is based on the dependence of reflectance of solar radiation at some altitudes on aerosol refractive index. Sensitivity studies of the monochromatic and entire solar spectrum reflectance to various radiative parameters show that this method has enough sensitivity to estimate the absorption property. This effective value may be different from the real value for an individual particle. To assess the validity of the effective value in radiative transfer calculation, modeling studies are performed, that is, some uncertainties due to complicated features, such as refractive index depending on radius and wavelength, non-Lambertian surface and wavelength dependence of the surface reflectivity are examined with a numerical model. The results indicate that these are small effects on the estimation and the effect of aerosols on earth-atmosphere radiation field can adequately be described by the effective values.