Characterization of aerosols in Saga city areas in Japan with direct and diffuse solar irradiance and aureole observations K. Arai * , X. Liang Saga University, 1 Honjo, Saga 840-8502, Japan Received 28 July 2004; received in revised form 6 May 2005; accepted 15 February 2006 Abstract By using Sky Radiometer which allows measuring direct and diffuse solar irradiance as well as aureole, aerosol properties of aerosol particles in Saga, Japan is characterized. Results indicate that aerosol density, optical depth, single scattering albedo, asymmetric factor in the morning and evening are larger than those in the day time around noon, and they are also larger in summer than those in the other seasons. The changes of the aerosol density, optical depth, are the largest in summer and are the smallest in winter during the four sea- sons. It is also found that the changes of the aerosol size distribution and optical depth are larger in the morning and the evening than those in day time around noon. Ó 2006 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Aerosol parameters; Refractive index; Size distribution; Aureole; Optical depth; Single scattering albedo 1. Introduction Aerosol particles influence radiative transfer in the atmosphere and play a fundamental role in the cloud for- mation processes. They also determine to a certain extent of the radiative and heat balance in Earth-atmosphere sys- tem. In the other hand, interaction of aerosol particles with incoming and reflected solar radiation influences the qual- ity of remotely sensed images of the Earth’s surface from satellite-based and airborne platforms. Grasping the actual characterization of the aerosol has become a significant subject on the climate change, Earth environment as well as atmosphere correction. Understanding the actual char- acterization of the aerosol requires knowledge of the opti- cal properties of aerosol, such as optical depth, phase function, single scattering albedo, or their microphysical properties, such as size distribution and the refractive index. Ground-based observation of aerosol on global Earth has been carried out by NASA/AERONET. But it was per- formed in the few fields of Earth and summarily character- ized the aerosol on the global Earth. In this paper, we characterized optical depth, single scattering albedo, asym- metric factor, size distribution as well as the real and imag- inary parts of the refractive index of aerosol in Saga, Japan by observing the direct, diffuse solar irradiance as well as aureole from Sky Radiometer. We also showed their aver- age change of day and month in one year. By using an improved Arai–Ryo model (Arai and Ryo, 2003) to ana- lyze the observed data of polarization, we showed the retrieval precisions among the different scattering angle. 2. Characteristics of the instrument and observed schemes The Pom-01 Sky Radiometer can measure the direct, diffuse solar irradiance as well as aureole in solar almucan- tar and the principal plane. It consists of the seven filters which the central wavelengths are at 0.315, 0.40, 0.50, 0.675, 0.870, 0.94, and 1.02 lm. The filters of the center wavelength at 0.315 and 0.94 lm are used for deriving O 3 concentration and precipitable water, respectively. The other filters are used for aerosol remote sensing. The instru- ment is acquired with a 0.5°, half degrees angle of the field 0273-1177/$30 Ó 2006 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2006.02.036 * Corresponding author. E-mail address: arai@is.saga-u.ac.jp (K. Arai). www.elsevier.com/locate/asr Advances in Space Research 39 (2007) 23–27