Anomalous surface O changes in North China Plain during the northwestward movement of a landing typhoon.

As high impact weather in a large scale, typhoon movement from the northwest Pacific into inland regions influencing ambient O changes is unclear, especially in North China Plain (NCP). A landing Typhoon Ampil during July 17-24, 2018 was studied herein to characterize the surface O anomalies during its movement over NCP. Landing typhoons present large negative O anomalies at the center of the typhoon and positive O anomalies 600-1700 km away from the center. During the northwest movement of Typhoon Ampil to the NCP, the area and magnitude of both positive and negative O anomalies shrank, particularly in the western and northern periphery, where the typical diurnal change of O dissipated with nocturnal O enhancement in the NCP. The spatiotemporal patterns of surface O anomalies in the NCP were induced significantly during various stages of typhoon movement with a stable structure in the atmospheric boundary layer, strong solar radiation on sunny days, and stratosphere-to-troposphere transport (STT) in the typhoon periphery, depending on the changing intensity, distance, and orientation of the typhoon center. Among them, the STT played a considerable role and contributed 32% to the positive anomalies of surface O in the NCP. Under the influence of westerly jets and high pressure at mid-latitudes on the typhoon movement, strong wind convergences in the upper troposphere were formed intensifying the downdraft of O-rich stratospheric air to the boundary layer in the NCP with an asymmetrical distribution of surface positive O anomalies over the periphery of typhoon. This study could improve our understanding of regional ozone changes with meteorological influences.