Dominant modes of interannual variability of winter fog days over eastern China and their association with major SST variability

The present work investigates leading modes of winter fog days over eastern China and possible association with sea surface temperature (SST) variability. Based on the Empirical Orthogonal Function (EOF) analysis, two dominant interannual modes of winter fog days are identified: a monopole mode and a meridional dipole mode. The monopole mode displays a significantly positive relationship with El Niño-Southern Oscillation (ENSO). The meridional dipole mode is closely linked to North Atlantic tripole (NAT) SST anomalies. A quasi-barotropic Rossby wave train can be excited by the NAT SST anomalies and propagates eastwards to East Asia. During winters with the positive phase of the NAT SST anomalies, there appear cyclonic and anticyclonic circulation anomalies over northern and southern China, favoring less and more winter fog frequency, respectively. These observed impacts from the ENSO and NAT SST anomalies can be further reproduced by atmospheric general circulation model (AGCM) experiments. Consideration of the NAT SST anomalies can apparently improve the explained variance of winter fog days over eastern China on the basis of the common-used ENSO signal. When ENSO and NAT occur as in-phase combinations and out-of-phase combinations, winter fog days anomalies appear over southern and northern China, respectively. These results have important implications on the seasonal-to-interannual predictability of the winter fog frequency over eastern China.