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Tomoaki Nishizawa, Shoji Asano, Akihiro Uchiyama, and Akihiro Yamazaki

Abstract

The surface direct radiative forcing and optical properties of aerosols have been analyzed from a ground-based solar radiation measurement, which was made under clear-sky conditions in Tsukuba, Japan, over two years from April 1997 to March 1999. The global and diffuse irradiances in the total and near-infrared (NIR) solar spectral regions were simultaneously measured by using two sets of the total-band and NIR-band pyranometers, respectively. The visible (VIS)-band irradiances were estimated by taking differences between the total-band and NIR-band irradiances. Spectral aerosol optical thicknesses (AOTs) in the air column were also measured, using a sun photometer. By combining the spectral AOTs and the surface diffuse irradiances, a retrieval algorithm for simultaneously estimating the effective aerosol size distribution and imaginary index of refraction (m i) was developed. Seasonal variations of the broadband surface radiative forcings and retrieved optical properties of the columnar aerosols have been studied. A close correlation was found among these parameters with similar features of seasonal variations. In winter the columnar aerosols exhibit the minimum surface radiative forcing and a minimum AOT, but the maximum m i value of 0.04. The opposite is true in summer, when the minimum m i value of 0.02 was estimated. The surface radiative forcing in the VIS band was estimated to be almost 4 times larger than in the NIR band. The total-band aerosol forcing efficiency is defined as the change in the surface radiative forcing in the total band due to a unit increase of AOT at 500 nm. This has its largest magnitude of −219 W m−2 in winter and its smallest magnitude of −150 W m−2 in summer. The results suggest that the correlated seasonal variations between the aerosol radiative forcing and the optical properties may result from seasonal changes in the dominant aerosol components.

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Takamichi Iguchi, Teruyuki Nakajima, Alexander P. Khain, Kazuo Saito, Toshihiko Takemura, Hajime Okamoto, Tomoaki Nishizawa, and Wei-Kuo Tao

Abstract

Numerical weather prediction (NWP) simulations using the Japan Meteorological Agency Nonhydrostatic Model (JMA-NHM) are conducted for three precipitation events observed by shipborne or spaceborne W-band cloud radars. Spectral bin and single-moment bulk cloud microphysics schemes are employed separately for an intercomparative study. A radar product simulator that is compatible with both microphysics schemes is developed to enable a direct comparison between simulation and observation with respect to the equivalent radar reflectivity factor Ze, Doppler velocity (DV), and path-integrated attenuation (PIA). In general, the bin model simulation shows better agreement with the observed data than the bulk model simulation. The correction of the terminal fall velocities of snowflakes using those of hail further improves the result of the bin model simulation. The results indicate that there are substantial uncertainties in the mass–size and size–terminal fall velocity relations of snowflakes or in the calculation of terminal fall velocity of snow aloft. For the bulk microphysics, the overestimation of Ze is observed as a result of a significant predominance of snow over cloud ice due to substantial deposition growth directly to snow. The DV comparison shows that a correction for the fall velocity of hydrometeors considering a change of particle size should be introduced even in single-moment bulk cloud microphysics.

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Nobuo Sugimoto, Tomoaki Nishizawa, Xingang Liu, Ichiro Matsui, Atsushi Shimizu, Yuanhang Zhang, Young J. Kim, Ruhao Li, and Jun Liu

Abstract

Continuous lidar observation was performed in Guangzhou, China, in the Pearl River Delta (PRD) observation campaign in July 2006 (PRD2006), using a two-wavelength Mie-scattering lidar (532 and 1064 nm) with a depolarization measurement channel at 532 nm. The profiles of the extinction coefficients at 532 nm were derived using the two-wavelength method. The planetary boundary layer (PBL) height and the cloud-base height were derived from the signals at 1064 nm. Two air pollution episodes occurred during the campaign, one on 10–12 July and the other on 22–24 July. Two events with a typhoon-driven flow of northern air occurred on 15 and 25 July. Elevated aerosol layers were observed at 1 km above ground level on 12 July and on 22 and 23 July. This layer was also observed by the lidar aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite (CALIPSO) at 0200 LT 23 July 2006 near Guangzhou. The distribution observed by CALIPSO and trajectory analysis revealed that the layer was probably generated within the PRD region. The time–height indication of the ground-based lidar suggested that aerosols in the elevated layer were transported to the ground by convection when the PBL height reached the elevated layer. The surface concentration of elemental carbon also exhibited a corresponding increase. The air pollution index at Guangzhou, Shaoguan, Changsha, and other cities indicated temporal variations, implying the regional transport of air pollution in the typhoon episodes. Trajectory analysis indicated that an air mass from the north arrived after 24 July in the air pollution episode of 22–25 July 2006.

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