Comparison of the Synoptic Environments Conducive to Eastward versus Southeastward Transport of Asian Dust Events

Fujung Tsai,Wei-Nai Chen

doi:10.1155/2014/467659

Abstract

Asian dust events that travel eastward and southeastward in the lower troposphere affect different areas near the coastal East Asia. To understand the synoptic differences between the two types of dust events, four dust events from 2006 to 2009 are selected for each type and the synoptic environment is compared. Surface measurements, trajectory analyses, and a regional dust model are also applied to further analyze each type. Results show that the strength of the low-level trough and the surface anticyclonic system are important in determining the transport route of dust event. A deep 700–850 hPa trough extending far south beyond 30°N associated with an intense surface anticyclone with maximum pressure greater than 1020 hPa over coastal East Asia favors southeastward movement of dust event. The prevailing northwesterlies or northerlies behind the deep trough and ahead of the intense surface anticyclone promote the southeastward movement of dust event. Since intense surface anticyclones often associated with strong dust events, severe dust activities tend to move southeastward. In contrast, a shallow trough accompanied by a weak surface high locating north of 30°N over the coastal East Asia favors an eastward transport route.

Highlights

Asian dust is mainly generated from China during springtime, when cyclonic activity and the induced strong surface wind favor the generation of dust from the dry surface
On the other hand, during southeastward transport, concentrations of particulate matter less than 10 μm in diameter (PM10) can be enhanced over 400, 600, and 1000 μg m−3 in cities over or near Southeast China, such as Hong Kong, Xiamen, and Taiwan, respectively [12,13,14]
The results show that the dust parcels of the southeastward events all locate south of the strong surface anticyclone near Southeast China while the parcels of the eastward events all remain between the surface cyclone and anticyclone over Japan, a result consistent with the study of the first event of the two types

Summary

Introduction

Asian dust is mainly generated from China during springtime, when cyclonic activity and the induced strong surface wind favor the generation of dust from the dry surface. Previous studies show that both eastward and southeastward transport increase aerosol concentration over the coastal areas of East and Southeast China [6,7,8,9]. When the surface anticyclone moves southeastward, dust can be carried to the subtropics In these previous studies, the synoptic environment favoring the eastward and southeastward movement of dust events is discussed, the difference between lower level transport of the two types is unclear. The synoptic environment favoring the eastward and southeastward movement of dust events is discussed, the difference between lower level transport of the two types is unclear It is still unknown why some dust events moving near the surface layer are allowed to be transported far southeastward into the South China Sea, whereas others are transported shallower and eastward and mainly affect the East Asian midlatitudes. A depolarization ratio greater than 0.06 is suggested for distinguishing dust particles from other type aerosol particles [25]

Data and Model

Synoptic Characteristic of the Two Types

Case Study

Conclusions