Influence of the previous North Atlantic Oscillation (NAO) on the spring dust aerosols over North China

Abstract

Abstract. The North Atlantic Oscillation (NAO) has been confirmed to be closely related to the weather-climate in many regions of the Northern Hemisphere, however, its effect and mechanism upon the formation of regional dust events (DEs) have rarely been involved in China. By using the station observation data, and multi reanalysis datasets, the influence of NAO on the dust aerosols (DAs) in China, as well as the corresponding mechanism of synoptic cause are explored in perspective of transient eddy fluxes. It is found that the DAs in the non-dust source areas show high values with a strong annual variability in north of the Yangtze River (30–40° N, 105–120° E), which is referred to as the North China hereafter. A significant negative relationship is indicated between the boreal winter NAO index and the late spring DAs in the North China with the correlation coefficient of −0.39. According to the 9 spring DEs affected significantly by negative phase of the preceding winter NAO in the North China during 1980–2020, it is shown that before the outbreak of DEs, due to the transient eddy momentum (heat) convergence (divergence) over the dust aerosol (DA) source regions, the zonal wind speed increases in upper-level troposphere, strengthening the zonal wind in the middle-lower levels through momentum downward transmission. Simultaneously, there is transient eddy momentum (heat) divergence (convergence) around the Ural Mountains, which is favorable for establishment and maintenance of the Ural ridge, as well as development of the air temperature and vorticity advections. The combined action of temperature and vorticity advections results in the Siberian Highs and Mongolian cyclone to establish, strengthen, and move southward near the surface, guiding the cold air from high latitudes southward, and is favorable to the uplift and transmission of DAs to the downstream North China. After the outbreak of DEs, change of transient eddy fluxes in the DA source regions and the Urals regions, leads to both energy and mass divergence and reduction of the zonal winds over the North China. Accompanying with the prevailing southerly airflow in south of the North China, a stable high value of DA concentration is maintained for 1–2 days. This study reveals the impact of transient eddy fluxes transport on the dusty weather anomalies modulated by the NAO negative signal in the North China, which can deepen the understanding of formation mechanism of DEs in China.

Relationship between air pollutant distribution and large-scale circulation

“…The effect of the North Atlantic Oscillation (NAO) cannot be neglected, as its large-scale climate variability model Environmental Science: Advances Paper captures the Rossby wave train propagating downstream. 63 The authors reveal that the negative phase of the preceding winter's NAO in northern China signicantly affects the dust event at around 30 °N to 40 °N and 105 °E to 120 °E. Before the dust event, owing to the transient eddy momentum convergence over the dust aerosol source regions, the zonal wind speed increases in the upper-level troposphere, and the zonal wind in the middle-lower levels strengthens through momentum downward transmission.…”