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

Aircraft measurements of aerosol sizes, intensities of direct-solar and circumsolar (aureole) radiations, and upward and downward fluxes of solar radiation were carried out over Nagoya, a typical urban area in Japan, using an optical particle counter, an aureolemeter and spectral pyranometers, respectively. Vertical profiles of optical thicknesses and volume spectra of aerosols have been successfully retrieved by inverting measured aureole intensities. The obtained values have been utilized to estimate the absorption indices of aerosols from the downward flux measurements. The results are summarized as follows: 1) The concentration and the vertical stratification of tropospheric aerosols vary considerably day by day. 2) Bimodal volume spectra of aerosols with radii smaller and larger than r*0.5 µm generally prevail in the troposphere. The former is more predominant than the latter in the haze layer, and viceversa above that layer.

Section: Vertical Profiles Of Optical Thickness and Size Distributionsupporting

confidence: 65%

Airborne Measurements of Optical Properties of Tropospheric Aerosols over an Urban Area

Tanaka

Hayasaka

Nakajima

1990

“…In the present study, size distributions of stratospheric aerosols due to the El Chichon eruption were estimated as a difference between columnar size distributions before and after the eruption. After investigating the results and referring to previous studies on El Chichon aerosols (Knollenberg and Huffman,1983;Oberbeck et al, 1983;Hofmann and Rosen, 1984;Michalsky et al, 1984;Asano et al, 1985;Spinhirne and King, 1985;Nakajima et al, 1986a), we constructed a model of stratospheric aerosols pertaining to the period after the El Chichon eruption. Size distributions of tropospheric aerosols (including the background stratospheric aerosols in the strict sense) were also derived by subtracting the modeled distribution of the El Chichon aerosols from the columnar total aerosol distributions.…”

Section: Introductionmentioning

confidence: 99%

Aerosol Monitoring Using a Scanning Spectral Radiometer in Sendai, Japan

Shiobara¹,

Hayasaka

Nakajima

et al. 1991

Measurements of direct solar irradiance and sky radiance were carried out in Sendai, Japan for the period from September 1981 to May 1985 using a scanning spectral radiometer (aureolemeter). Size distributions of columnar total aerosols were retrieved by inverting both spectral optical thickness and solar aureole radiance data.The size distribution of aerosols due to the El Chichon eruption in 1982 was estimated as the difference between columnar volume spectra before and after the eruption. The results indicate that the El Chichon aerosol had a monomodal volume spectrum with a mode radius about 0.5 ,*m; their contribution to the total aerosol volume reached the maximum in the winter of 1983, i. e. December 1982 to February 1983, then gradually decaying to the normal level prior to the eruption by the spring of 1985.A seasonal model of tropospheric aerosols over Sendai was constructed by subtracting the volume spectrum of the El Chichon aerosol model from that of the columnar total aerosols, and successfully represented by a bimodal log-normal function. The aerosols in spring and summer seasons have different features in respect of volume spectra. The coarse particle mode aerosols with radii around 3 *m are predominant in spring while the accumulation mode aerosols with radii around 0.2µm are predominant in summer.

“…Another type of optical particle counter which measures the forward scattering and has less dependence on the refractive index may be more suitable for the present purpose. On the other hand, although the retrieval of a columnar size distribution from spectral attenuation measurements is less sensitive to the refractive index, the wavelength range of the input data, **(*), can affect the inversion and, furthermore, the retrieved size distribution will include some contribution from stratospheric aerosols (Asano et al, 1985).…”

Section: Summary and Discussionmentioning

confidence: 99%

“…The optimally determined values are found to be (*l, mann and Rosen (1983) for the El Chichon aerosols during October 1982. Asano et al (1985) retrieved the size distribution for the El Chichon aerosols over Tsukuba during the 1982-83 winter. The size distribution was mono-modal with a mode radius between 0.3*m and 0.4*m in the number-size distribution.…”

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

confidence: 99%

“…The lidar backscattering-coefficient integrated over the stratosphere decreased gradually with time after the large maximum found during December 1982, and by January 1984 it was still about one fifth of the maximum value observed in the 1982-83 winter. The averaged optical thickness of 0.13 in the visible region was estimated by Asano et al (1985) for the El Chichon aerosols over Tsukuba for that winter. From these observational facts, an optical thickness of about 0.025 is attributable to stratospheric aerosols during January 1984.…”

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

confidence: 99%

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Aircraft Measurements of the Radiative Effects of Tropospheric

Asano¹

1989

Self Cite

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.