Anomalous Atmospheric Circulation Associated with the Extremely Persistent Dense Fog Events over Eastern China in the Late Autumn of 2018

Shengjie Chen,Duanyang Liu,Yan Shi,Mei Liu,Zhiming Kang

doi:10.3390/atmos12010111

Abstract

Under a declining trend of fog days in China, the duration of fog events since the 1990s reached a significant peak in the late autumn of 2018 over Eastern China. The average anomalous fog days were 4.74 d in November 2018 over Jiangsu Province in Eastern China, with a 1.73 standard deviation departure from climatology. Those fogs can thus be identified as a significantly abnormal climatic event with long duration, strong intensity, and extensive coverage. Based on the daily evolutions and correlations of atmospheric parameters, the dense fogs are revealed to be well configured by favorable metrological conditions such as weak dynamic progress, strong inversion in the lower troposphere and saturated air near the surface. If not disturbed, the intensification or duration of these conditions will further promote and maintain the development of fogs. The anomalous atmospheric background associated with those favorable meteorological conditions is revealed by composing the standardized anomalies of circulation fields during the fog days. Over the fog areas, vortex activities or cold air invasion is effectively hampered and the atmosphere inclines to be stable, due to the anomalous circulation pattern composed of the broadened jet stream, weakened jet core over Eastern China, undermined East Asian trough, declined East Asian winter monsoon, and enhanced anomalous southerly flows that transport abnormal warm and wet air to Eastern China. The vapor supplement is intensified by both sustained anomalous northward wind at the lower troposphere and anomalous westward wind in the near-surface. Overall, the numbers of standardized anomalies of 1000–200-hPa height, temperature, wind, and moisture fields during these fog days all significantly depart from climatology for that locale and time of the season, further demonstrating that the persistent dense fogs over Eastern China in the late autumn of 2018 is an unusual weather event with extreme synoptic-scale departures from normal.

Highlights

As a common meteorological phenomenon, fog is defined by horizontal atmospheric visibility of less than 1 km
We examined the atmospheric circulation anomalies related to the extremely persistent dense fog events in the late autumn of 2018 over Eastern China
The composite analysis of the original values and standard anomalies of all the daily mean circulation fields were conducted to identify the reasons for the formation of meteorological conditions advantageous to the rare persistent dense fog events over Eastern China in the late autumn of 2018

Summary

Introduction

As a common meteorological phenomenon, fog is defined by horizontal atmospheric visibility of less than 1 km. The low visibility is due to the existence of water or ice droplets with the size from 2 to 65 μm in the atmosphere near the ground [1]. On fog days with low visibility, transportation difficulties and even traffic accidents frequently occur. With stable meteorological conditions and nearly calm wind, fog can induce a congregation of aerosols, restraining the diffusion of pollutants in the air [2,3,4].

Methods

Results

Conclusion