Influence of Surface-Based Stable Layer Development on Asian Dust Behaviour Over Tokyo |
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Authors: | Nobumitsu Tsunematsu Hironori Iwai Shoken Ishii Motoaki Yasui Yasuhiro Murayama Kohei Mizutani |
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Institution: | (1) Environmental Sensing and Network Group, Applied Electromagnetic Research Centre, National Institute of Information and Communications Technology, Tokyo, Japan;(2) Centre for Environmental Remote Sensing, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba-shi, Japan |
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Abstract: | The relationship between local meteorological fields and the behaviour of airborne Asian dust that arrived in the Tokyo metropolitan
area on 1 April 2007 with the passage of a synoptic-scale cold front has been investigated through Doppler lidar observations,
experiments using a regional atmospheric numerical model, and analyses of surface and upper-air meteorological observations.
Results of the Doppler lidar observations showed that the Asian dust passed above the metropolitan area with strong south-westerly
winds with speeds of 15–26 m s−1. Meteorological fields reproduced by the numerical experiments showed the development of a surface-based stable layer in
the metropolitan area caused by nocturnal radiational cooling near the ground surface and south-westerly warm air advection
at upper levels. The blocking effect of the mountainous region located to the west of the metropolitan area induced an area
of stagnant air inside the metropolitan area and promoted the stable layer development. Although strong downdrafts prevailed
in the upper air, the airborne Asian dust did not spread to the ground when the stable layer was formed. These results strongly
indicate that the developed stable layer prevented strong downdrafts from spreading to the ground, acting as an obstacle to
the transport of the Asian dust particles from the upper air towards the ground. This is considered to be one of the main
causes of the low appearance frequency of Asian dust phenomena near the ground in the Tokyo metropolitan area and eastern
Japan. |
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Keywords: | Asian dust Doppler lidar observations Numerical experiments Surface-based stable layer Tokyo metropolitan area |
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