Abstract
This paper presents a technique used to empirically classify operationally defined “haze” days in South Korea from 2000 to 2007 into long-range transported (LRT) and stagnant (STG) haze cases. A total of 547 haze days were classified into these two cases by tracking consecutive 6-day synoptic weather charts and air trajectories. The meteorological features associated with long-range transport of haze were identified by contrasting the values of 35 candidate meteorological parameters corresponding to the two types of haze cases. A suitable subset of synoptic variables was then chosen to diagnose the unique meteorological features of each case. The statistical test showed that geostrophic wind speed, vorticity, vorticity advection at a geopotential height of 850 hPa, and the vertical stability index of the lower atmosphere were indicated as highly effective parameters for distinguishing between the LRT and STG cases. The classification accuracies showed 93.2%, 87.8%, 85.4%, and 84.4% for these four variables, respectively. The STG case was well characterized by negative vorticity, with stable atmospheric stability conditions and weak geostrophic wind speed, that is, ~2.8 m s−1 at a geopotential height of 850 hPa, whereas the LRT case had relatively strong geostrophic wind speed, >6 m s−1. For both cases, the location of the anticyclone played an important role in haze occurrence, directly and indirectly. A high pressure system led to stable STG haze with weak ventilation, resulting from upper-atmospheric subsidence. The LRT case was associated with a strong anticyclone that prevailed over southwestern China, maintaining the pressure gradient force that generated the westerly wind that was persistently conducive to downwind long-range transport of haze.
