On the Evolution and Structure of a Radiation Fog Event in Nanjing |
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Authors: | LIU Duanyang YANG Jun NIU Shengjie and LI Zihua |
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Institution: | Key Laboratory for Atmospheric Physics and Atmospheric Environment, Nanjing University of Information Science & Technology, Nanjing 210044,Key Laboratory for Atmospheric Physics and Atmospheric Environment, Nanjing University of Information Science & Technology, Nanjing 210044,Key Laboratory for Atmospheric Physics and Atmospheric Environment, Nanjing University of Information Science & Technology, Nanjing 210044,Key Laboratory for Atmospheric Physics and Atmospheric Environment, Nanjing University of Information Science & Technology, Nanjing 210044 |
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Abstract: | An extremely dense radiation fog event during 10--11 December 2007
was studied to understand its macro-/micro-physics in relation to dynamic and
thermodynamic structures of the boundary layer, as well as its structural
evolution in conjunction with the air-surface exchange of heat and water vapor.
The findings are as follows. The extreme radiation fog process was divisible
into formation, development, mature, and dissipation phases, depending on
microstructure and visibility. This fog event was marked by rapid evolution
that occurred after sunrise, when enhanced surface evaporation and cold air
intrusion led to a three order of magnitude increase in liquid water content
(LWC) in just 20 minutes. The maximum droplet diameter (MDD) increased
four-fold during the same period. The fog structure was two-layered, with the
top of both the surface-layer and upper-layer components characterized by
strong temperature and humidity inversions, and low-level jets existed in the
boundary layer above each fog layer. Turbulence intensity, turbulent kinetic
energy, and friction velocity differed remarkably from phase to phase: these
features increased gradually before the fog formation and decreased during the
development phase; during the mature and dissipation phases these
characteristics increased and then decreased again. In the development and
mature stages, the mean kinetic energy of the lower-level winds decreased
pronouncedly, both in the horizontal and vertical directions. |
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Keywords: | Nanjing dense fog dynamic and thermodynamic structures intrusion turbulence |
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