Since December 2002, we have operated a portable, automated lidar (PAL) that provides data on the vertical profile of the lower atmosphere every 20 s (Fig. 1). Continuous data with such a fine temporal resolution is valuable for systematic comparison between the lidar-observed features of the atmosphere and their meteorological interpretations. The micro-pulse lidar (MPL)1 opened the way for continuously operating, automatic lidar systems. The network of MPL systems (MPLNET) is providing data on the boundary layer structure and cloud development at MPL sites. More recently, Sugimoto et al.3 have constructed a lidar network consisting of 15 sites in east Asia, giving information on Asian dust with cooperation of other lidar sites in Japan (Asian dust NET, ADNET). Instrumentally, however, the MPL system often has difficulty in long-term operations because of the failure in the detector part resulting from its configuration (a single telescope is used for both transmitting and receiving). In an attempt to cope with this problem, we have adopted the design of the PAL in which the laser is installed on the side of the telescope, thus separating the transmitter optics and the receiving telescope.

Fig. 1. Photo of PAL.

The PAL system has been operated at Chiba Prefecture Environmental Research Center (CERC), located in an industrial park, nearby an air pollution monitoring station. The aerosol concentration data measured by a beta-ray instrument at the pollution-monitoring station is compared with the (optical) extinction data from PAL, yielding the value of mass extinction efficiency (MEE) of atmospheric aerosols in the boundary layer.4'5 In this chapter, as a further extension of the PAL data analysis, we consider the relation between the PAL-observed features of aerosols/clouds and meteorological conditions that bring about such behavior of the atmosphere.

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