A spectral analysis and a method using the conditional probability approach are performed on 41-year (1958-1998) monthly station pressure, temperature and precipitation data in Taiwan to identify the local climate biennial oscillation (BO) signal. Two Taiwan BO modes are identified in this study. One is the November-December (ND) temperature and the other is the January-February (JF) precipitation.
The relationship between Taiwan BO modes and certain known BO phenomena is investigated for clarifying the robustness of the modes. The ND temperature mode is found to be associated with the BO in the sea surface temperature (SST) of the South China Sea (SCS) and the BO mode of ENSO. The JF precipitation mode is also associated with the BO mode of ENSO with the enhancement of the warm anomalies of the SCS SSTs. The JF precipitation mode is observed clearly after 1982, but cannot be identified before 1982. The ND temperature mode is observed more clearly before 1982. The amplitude of fluctuation in the ND temperature is relatively small when the rhythm of the biennial fluctuation is clearer. When the biennial fluctuation is smeared by low-frequency signal after the late-1970s, the amplitude becomes larger. The effect is completely the opposite for the BO modes of JF precipitation.
The discrepancy between the BO modes of ND temperature and JF precipitation are examples showing how the local climate of Taiwan can be influenced by low-frequency variations of tropical and extratropical climate systems. The rapid warm trend of SCS SSTs and Eurasia continent since the late-1970s can enhance the BO signal of JF precipitation but weaken the signal of ND temperature.