Observed Characteristics of Precipitation Timing during the Hazes: Implication to Aerosol-Precipitation Interation

Korea has suffered from severe haze, largely domestic anthropogenic aerosols mixed with long-range transported pollutants from abroad. It is important to analyze general characteristics of different hazes in terms of time and space scales, and its relationship with precipitation. Aerosol impact on weather has not much been investigated whereas lots of studies haze characteristics and evolution of haze, and further meteorological condition to induce haze have been done. We used ground aerosol observation data at Seoul (SL) and Baengnyeongdo (BN) from 2011 to 2016 to classify severe haze episodes to Long-range transported haze (LH), Yellow sand (YS), Urban haze (UH) and Mixing haze (MH) (Lee et al., 2017). To analyze the characteristics of precipitation during the hazes with regard to timing, we checked the difference between forecast precipitation and hourly precipitation. There are 40 LH cases, 23 YS cases, 29 UH cases and 35 MH cases during 2011-2016. The ratios of the cases accompanied with precipitation are 68%, 87% and 48% for LH, YS and UH respectively. Long-term analysis of the timing of aerosol and precipitation shows that precipitation tends to precede YS while it appears to coincide with LH period. We take some statistics analysis such as Bootstrap to prove the reliability of these results. On the other hand, of total 126 episodes examined, we find out the differences between operational weather forecast and hourly precipitation in 41 cases. Interestingly light precipitation tends to last longer about within a day after enhanced aerosol loadings. Precipitation timing seems to be controlled by large scale synoptic forcing during the YS event. However, aerosols may be closely associated with precipitation through changes in cloud microphysics during the severe long-range transported haze such that enhanced aerosols can increase smaller cloud droplets and further extend light precipitation at weaker rate. This result demonstrates active interactions between aerosols and meteorology such as probable modifications of cloud microphysics and precipitation, synoptic-induced dust transport, and precipitation-scavenging in Korea, downstream of China. To understand the characteristics of aerosol’s quantitative impact on precipitation, we will further demonstrate the forecasting precipitation amount from Regional Data Assimilation and Prediction System (RDAPS).