Significant Atmospheric Circulation Anomalies over the North Pacific Associated with the Enhanced Pacific ITCZ during the Summer–Fall of 2014

Abstract

We describe the atmospheric features observed over the North Pacific during the summer–fall of 2014 and investigate their association with the convective activity in the intertropical convergence zone (ITCZ) and underlying oceanic conditions. During this duration, while the NINO.3 index, the area-averaged sea surface temperature anomalies (SSTAs) in the eastern equatorial Pacific, fluctuates around the threshold value for the onset of El Niño events, off-equatorial SSTAs display an equatorial antisymmetric pattern with positive (negative) anomalies north (south) of the equator. As expected from the wind–evaporation–SST feedback, the equatorial antisymmetric SSTAs accompany with anomalous southerlies, converging into a zonal belt of 5°N-10°N that induces enhanced convection in the ITCZ. Thus, the oceanic and atmospheric features in the eastern tropical Pacific are different from those in the typical El Niño events. In contrast, the observed weaker subtropical high and the shallower upper-tropospheric trough over the North Pacific are similar to the features typically found during the El Niño events. The amplitude of those anomalies, however, is much larger than that of regressed anomalies onto the NINO.3 index. A linear baroclinic model experiment indicates that the enhanced convective heating in the ITCZ contributes to sustain the anomalous atmospheric circulation.