A physical examination of tropopause height and stratospheric air intrusion - A case study

Temperature lapse rate, potential vorticity, Brunt-Väisälä frequency, along with VHF wind profiler observations were employed to examine the temporal variation of the tropopause height and stratospheric air intrusion during an event of tropopause folding. The present study suggests that the tropopause defined by 1.6 PVU is more adapted to analyzing stratospheric air intrusion, compared with the tropopause defined by temperature lapse rate or Brunt-Väisälä frequency. However, the latter two tropopause definitions are more relevant to localizing stratospheric air intrusions into the troposphere than the potential vorticity when the air is intruded in a slantwise direction over the observation site. The intruded air in a slantwise direction is observed as the temperature lapse rate and Brunt-Väisälä frequency anomalies, corresponding to the temperature anomaly, which is predicted as the low level tube by Bithell et al. (1999). The present study suggests that the slantwise intrusion is a type of low level tube developed during tropopause folding.