Effects of Moisture Budget Changes on Pacific Evaporation Associated with Pacific Decadal Oscillation and ENSO in Boreal Winter

This study assesses the influence of El Niño-Southern Oscillation (ENSO) and Pacific decadal oscillation (PDO) on the distribution of the Pacific evaporation anomaly in boreal winter during 1958-2015 by using Objectively Analyzed air-sea Fluxes (OAFlux) data. Furthermore, we also examine contributions of individual water budget terms in the moisture balance equation to the evaporation anomaly. The results show that the winter evaporation over the eastern tropical Pacific, the subtropical northwestern Pacific, and central northern Pacific are significantly influenced by ENSO. The water vapor is anomalously divergent (convergent) over the central northern Pacific during El Niño (La Niña), which increases (decreases) the atmospheric water vapor content and enhances (reduces) evaporation. However, the anomalous water vapor convergence (divergence) leads to evaporation decrease (increase) over the subtropical northwestern Pacific. Besides, the increase (decrease) in rainfall results in evaporation increase (decrease) over the eastern tropical Pacific. Meanwhile, this relationship between ENSO and evaporation anomaly is not stationary over those areas and can be modulated by PDO. When El Niño (La Niña) is accompanied with warm (cold) PDO phase, the increase (decrease) in evaporation obvious intensifies over the central northern Pacific mainly due to the increased (decreased) atmospheric water vapor content caused by the increase (decrease) in rainfall, and the storm track is abnormally stronger (weaker). When El Niño (La Niña) is accompanied with cold (warm) PDO phase, the decrease (increase) in obviously intensifies over the subtropical northwestern Pacific and tropical eastern Pacific, which is related to the enhancement of anomalous moisture advection caused by humidity changes.