Potential remote forcing of North Atlantic SST tripole anomalies on the seesaw haze intensity between late winter months in the North China plain: A case study

Abstract

This study identified a prominent temporal seesaw haze intensity case that occurred between the late winter months of 2010 in the North China Plain (NCP), featuring considerably suppressed haze intensity in January and enhanced haze intensity in the adjacent month of February in 2011. We suggest that dramatic alternations of atmospheric and oceanic anomalies played fundamental roles in forming this seesaw haze intensity case, rather than changes in manmade emission anomalies. The suppressed haze intensity in January 2011 was tied to an equivalent barotropic cyclonic anomaly that dominated the NCP and its surroundings, which generated in situ haze-suppressed meteorology characterized by strengthened lower-level northerly anomalies with cold and dry conditions, as well as elevated boundary layer height and destabilized atmospheric stratification. In stark contrast, the enhanced haze intensity in February 2011 was connected to an equivalent barotropic anticyclonic anomaly, linking a haze-favourable meteorology opposite to that in January 2011. The pronounced North Atlantic sea surface temperature (SST) tripole anomalies, with positive anomalies in the tropical and mid-latitudinal North Atlantic and negative anomalies in the subtropical North Atlantic, made a significant contribution to the above-mentioned seesaw haze intensity case. Diagnostic analyses suggested that the January North Atlantic SST tripole anomalies were linked to a significant negative North Atlantic Oscillation (NAO)-like pattern, which acted as the source of the Rossby wave train to generate concurrent haze-suppressed meteorology over the NCP. In February, although the NAO-like pattern was drastically dampened, the enhanced barotropic cyclonic anomaly centred southeast of the Yamal Peninsula played a critical role in relaying the impact of January tripole SST anomalies, thus inducing concurrent haze-favourable meteorology. Consequently, January North Atlantic SST tripole anomalies could exert an effective modulation effect on the generation of seesaw haze intensity. The proposed mechanism was further verified using the Community Earth System Model Large Ensemble Numerical Simulation (CESM-LENS) datasets.