Pacific and Atlantic Decadal Variability Reflected by the Winter Temperature in Taiwan During the Period 1911-2010

The sea surface temperature (SST) of the marginal seas off the east coast of China is known for its large warming trend during the twentieth century. The more than one hundred years of high quality temperature observation in Taiwan is extremely valuable as an additional reliable measurement independent from the observations of SST. The temperature data at six long-history meteorological stations is analyzed using a data adaptive method Ensemble Empirical Mode Decomposition (EEMD). The 100-year (1911-2010) time series of the temperatures are decomposed into five intrinsic mode functions (IMFs) and a centennial secular trend (ST). The statistically significant multi-decadal modes (period > 40 years) tend to appear in the temperature data of winter months. With reference to the multi-decadal modes, a warm regime with the length of near two decades (1930s and 1940s) and a cold regime (1970s and 1980s) are identified. The decades from early 1950s to mid-1970s appeared as a transition phase with a sharp cooling trend. The strong cooling makes the warming rate of the background climate become less impressive before 1980. In the past one or two decades, Taiwan climate saw a transition from cold to warm. The warming rate represented by the ST, which is the trend derived using EEMD after filtering out all low-frequency cyclic variations, is much larger than the linearly regressed trend particularly during the decades after 1990. The warm and cold regimes of Taiwan climate are in-phase with the Atlantic multidecadal oscillation (AMO). The termination of the warm (cold) regime is found to be associated with the weakening (strengthening) of the North Pacific subtropical gyre. The rapid warming after 1990s can be resulted from the combined effect of negative PDO and positive NPGO, although the possibility of anthropogenic influence cannot be completely ruled out.