A dark October in Beijing 2016

In recent years, haze pollution events in Beijing have increased sharply, and the haze pollution of Beijing in October 2016 reached a new high. Meteorological conditions are thought to have influences on the haze occurrence, yet the associated atmospheric circulation of haze in October and why the most severe haze pollution occurred in 2016 is still unclear. Here, the authors show through daily observation and reanalysis data that key regions of North Atlantic and North Pacific sea surface temperature （SST） anomalies may be the main factors for this most severe haze event. Since 2013, the SSTs of these two key regions have increased dramatically and reached a peak, which could have induced the severe haze pollution by affecting the Eurasia teleconnection （EU） and the North Pacific Oscillation, with these factors then providing favorable dynamic and thermodynamic conditions for haze development.

Interdecadal variability of summer precipitation in the Three River Source Region: Influences of SST and zonal shifts of the East Asian subtropical westerly jet

Summer precipitation in the Three Rivers Source Region(TRSR)of China is vital for the headwaters of the Yellow,Yangtze,and Lancang rivers and exhibits significant interdecadal variability.This study investigates the influence of the East Asian westerly jet(EAWJ)on TRSR rainfall.A strong correlation is found between TRSR summer precipitation and the Jet Zonal Position Index(JZPI)of the EAWJ from 1961 to 2019(R=0.619,p<0.01).During periods when a positive JZPI indicates a westward shift in the EAWJ,enhanced water vapor anomalies,warmer air,and low-level convergence anomalies contribute to increased TRSR summer precipitation.Using empirical orthogonal function and regression analyses,this research identifies the influence of large-scale circulation anomalies associated with the Atlantic–Eurasian teleconnection(AEA)from the North Atlantic(NA).The interdecadal variability between the NA and central tropical Pacific(CTP)significantly affects TRSR precipitation.This influence is mediated through the AEA via a Rossby wave train extending eastward along the EAWJ,and another south of 45°N.Moreover,the NA–CTP Opposite Phase Index(OPI),which quantifies the difference between the summer mean sea surface temperatures of the NA and the CTP,is identified as a critical factor in modulating the strength of this teleconnection and influencing the zonal position of the EAWJ.