Abstract
Some haze-fog events in Asia have been attributed to tropical cyclone activity; however, uncertainty exists regarding the relationship between the influence of tropical cyclones and the occurrence of haze-fog events. In this study, the statistical relationship between tropical cyclones in the Northwest Pacific and the haze-fog events in northern China during summers from 2001 to 2012 were analyzed. It was found that 30.5% of regional haze-fog events were related to tropical cyclones. The influence of tropical cyclones on haze-fog events was analyzed and compared based on classification of tropical cyclones by position and path. The results showed that tropical cyclones can form advantageous conditions for regional haze-fog events through dynamic and thermal processes, such as strengthening the downdraft, and increasing relative humidity and stability. The dynamic influence was dominant when the distance between a tropical cyclone and northern China was larger than the range of tropical cyclone airflow, and the contribution of thermal influence increased as the distance decreased. Furthermore, the surrounding circulations, such as the Northwest Pacific subtropical high and the westerly trough, also contributed to the regional haze-fog events. Their position, intensity and collocation with tropical cyclones could be the determining factors for haze-fog occurrence. This study illuminates the primary mechanisms of the combined effect of tropical cyclones and the surrounding circulations on regional air quality, which could improve forecasts of summer regional haze-fog events in northern China.
Highlights
Haze and fog are two weather phenomena that can lead to low visibility, and they are deeply concerning for both the public and researchers due to their threat to human health and negative impact on transportation (Cools et al, 2010; Xu et al, 2013)
The probability distribution of the number of haze-fog stations per day during these 172 d is shown in Fig. 2, and it is similar to the distribution of all summer days, indicating that uncertainty exists regarding the relationship between the occurrence of haze-fog events and the influence of tropical cyclones, as not all tropical cyclones led to haze-fog events
Regional haze-fog events can occur on some of the tropical cyclone influencing days; uncertainties exist regarding the relationship between haze-fog formation in northern China and the influence of tropical cyclones
Summary
Haze and fog are two weather phenomena that can lead to low visibility, and they are deeply concerning for both the public and researchers due to their threat to human health and negative impact on transportation (Cools et al, 2010; Xu et al, 2013). Summer regional haze-fog occurrence in northern China under the influence of tropical cyclones was analyzed, and the conditions and detailed physical processes of how tropical cyclones lead to an increase in haze-fog events were explored.
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