Reply on RC1

Abstract

The canonical view of the northeast Asian anomalous anticyclone (NAAA) is a crucial factor for determining poor air quality in the North China Plain (NCP) on the interannual timescale. However, there is considerable intraseasonal variability in the NAAA in early winter (November to January), and the corresponding mechanism of its impacts on air pollution in the NCP is not well understood. Here, we find that the intraseasonal NAAA usually establishes quickly on day −3 with a life span of eight days, and its evolution is closely tied to the Rossby wave from upstream (i.e., the North Atlantic). Moreover, we find that the NAAA with a westward tilt might be mainly related to the wavenumbers 3−4. Further results reveal that under this background, the probability of regional air pollution for at least three days in the NCP is as high as 69 % (80 % at least two days) in NDJ period 2000−2021. In particular, air quality in the NCP tends to deteriorate on day 2 prior to the peak day of the NAAA and reaches a peak on day −1 with a life cycle of four days. In the course of air pollution, a shallower atmospheric boundary layer and stronger surface southerly wind anomaly associated with the NAAA in the NCP appear 1 day earlier than poor air quality, which provides dynamic and thermal conditions for the accumulation of pollutants and finally occurrence of the air pollution on the following day. Furthermore, we show that the stagnant air leading to poor air quality is determined by the special structure of temperature in the vertical direction of the NAAA, while weak ventilation conditions might be related to a rapid buildup of the NAAA. The present results quantify the impact of the NAAA on air pollution in the NCP on the intraseasonal timescale.