Trends in Monthly Tropopause Characteristics Observed over Taipei, Taiwan*

Abstract

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 (25801 0 N, 121827 0 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 0.038C yr 21 and statistically significant decreasing trends in CPT height at a rate of approximately 4.7 m yr 21 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.

Relationships between Tropical Cyclone Intensity and Eyewall Structure as Determined by Radial Profiles of Inner-Core Infrared Brightness Temperature

“…One of the reasons for the success of the Dvorak technique is that the IR brightness temperatures (BTs) used to assign current intensity are themselves indicators of important structural properties of the inner portion of the TC. As an example, cloud-top temperature roughly represents cloud-top height, as colder clouds are located higher in the atmosphere [this temperature-height relationship varies as a function of latitude and time of year, since tropopause heights are lower toward the poles and during the winter season; Thuburn and Craig (1997); Kossin and Velden (2004); Raman and Chen (2014)]. The temperature (height) of the clouds in the central region of a TC indicates the intensity of the updraft, which is one component of the secondary circulation (Eliassen 1951;Willoughby 1979;Shapiro and Willoughby 1982).…”