Trends in Monthly Tropopause Characteristics Observed over Taipei, Taiwan

This study presents monthly trends in the cold-point tropopause (CPT), calculated using three decades of radiosonde data from 1981 to 2010 over Taipei, Taiwan (25°01′N, 121°27′E). Multivariate regression analysis has been used to suppress the effect of natural variations, such as quasi-biennial oscillation (QBO), ENSO, solar cycle, and volcanic eruptions. From the continuous time series, statistically insignificant heating and a decrease in the height of CPT are observed. However, the trends estimated using individual monthly time series revealed new features with statistically significant increasing trends in CPT temperature at a rate of approximately 0.03°C yr−1 and statistically significant decreasing trends in CPT height at a rate of approximately 4.7 m yr−1 during summer months. An enhanced heating rate in the upper troposphere along with a suppressed cooling rate in the lower stratosphere observed over Taipei might have caused the tropopause heating trend during summer. The possible relationship between tropopause trends and lower-stratospheric ozone is also examined. The seasonal and spatial variations in trends estimated using NCEP–Climate Forecast System Reanalysis (CFSR) data reveal the spatial heterogeneity in CPT temperature trends. Initial inspection of monthly trends in tropopause characteristics suggests that the estimation of tropopause trends using the continuous time series may not exactly represent the long-term variability of individual months or seasons.