The relationship between ENSO and East Asian Monsoon revealed by Taiwan climate variations

The ENSO associated interannual variation of Taiwan rainfall and temperature during 1951-2004 is investigated by using the data at 23 Taiwan stations and the NCEP/NCAR reanalysis data. The correlation, contingency table, and composite analyses are performed and the statistical significance of the variation in each analysis step is tested. The analysis result shows that the ENSO signal is most robust during the months from September to January. Taiwan tends to be drier (wetter) than normal during September-November of the El Niño (La Niña) developing years. On the other hand, it tends to be colder (warmer) in September-October, but warmer (colder) in November-January during the El Niño (La Niña) developing years. The temperature anomaly changes sign in November when ENSO stays mature in the same phase. We also find that temperature and rainfall signals actually do not often appear in the same ENSO event. The rainfall signal appears when the circulation anomalies over the Indian Ocean are strong, while the temperature signal appears when the anomalies are weak. Using the rainfall and temperature anomalies measured in Taiwan as a reference, we find that the associated circulation anomaly patterns are not anti-symmetric in El Niño and La Niña years. The El Niño signal in Taiwan shows stronger association with the biennial ENSO mode, with La Niña in lead, while La Niña signal does not show clear relationship with the biennial mode. The findings of this study suggest the need of classifying ENSO into different types to describe the relationship between East Asian Monsoon subsystems and different types of ENSO.