It is usually thought that a year consists of four seasons: spring, summer, autumn and winter. Taiwan basically follows the rule. Taiwan climate is mainly governed by monsoons. Therefore, the beginning of summer (winter) can be interpreted as the inward movement of summer (winter) monsoons. Considering the important role of mei-yu period, Chen (2000) pointed out that mei-yu should be added as a season between spring and summer.The overall object of this work is to increase our knowledge of Taiwan seasonal change, especially winter season. Monsoons will be applied to identify the characteristics of winter. International data sets of observations in pentad resolution will be employed. These observed data sets include global and regional data which are NCEP reanalysis, CMAP precipitation, ECMWF reanalysis and CWB data.Our analyses show that the Taiwan winter monsoons can be divided into two parts. It implies that the first half of winter is dominated by the continental high and the last half of winter is controlled by climate systems over the western North Pacific. Taiwan rainfall associated with the latter time period exhibits positive relationship with the eastern equatorial Pacific sea surface temperature, a feature of El Nino/Southern Oscillation (ENSO).
