Warm Cover – Precursory Strong Signals hidden in the Middle Troposphere for Haze Pollution

Abstract. Eastern China (EC), located on the downstream region of Tibetan Plateau (TP), is a large area that has become vulnerable to frequent haze. In addition of air pollutant emissions, meteorological conditions were a key inducement for air pollution episodes. Based on the study of the Great Smog of London in 1952 and haze pollution in EC over recent decades, it is found that the abnormal warm cover in the middle troposphere, as a precursory strong signal hidden, could connect to severe air pollution events. The convection and diffusion in the atmospheric boundary layer (ABL) were suppressed by a relatively stable structure of warm cover in the middle troposphere, leading to the ABL height decreases, which were favourable for the accumulation of air pollutants in the ambient atmosphere. The warming TP built the warm cover in the middle troposphere from the plateau to the downstream EC region and even the entire East Asian region. The frequent haze events in EC is connected with a significantly strong warm cover in the interdecadal variability. It is also revealed that a close relationship existed between interannual variations of the TP's heat source and the warm cover hidden in the middle troposphere over EC.