The Tropopause Structure of Hurricanes Nadine (2012) and Patricia (2015)

Both observations and modeling suggest that the tropopause temperature can be an important factor in the evolution of tropical cyclones (TCs). Despite its potential importance, few observational studies have examined TC tropopause structure in detail.

Recent field campaigns collected observations of TCs with unprecedented spatial extent and resolution. Dropsondes deployed during the Office of Naval Research Tropical Cyclone Intensity Experiment (TCI) and the NASA Hurricane and Severe Storm Sentinel (HS3) have provided a wealth of new information on TC structure. This paper uses HS3 and TCI observations to analyze the tropopause structure of Hurricanes Patricia (2015) and Nadine (2012).

Hurricane Patricia is the strongest TC on record in the Western Hemisphere. TCI captured its period of extraordinary rapid intensification by deploying dropsondes every 4-8 km across the storm’s inner core. As Patricia intensified, its inner-core cold point tropopause rose dramatically. This rise was driven by strong lower-stratospheric cooling early in the intensification period combined with dramatic upper-tropospheric warming throughout the period. These temperature tendencies acted to eliminate the tropopause inversion layer over the eye, allowing the tropopause to rise by over 1 km.

Hurricane Nadine’s tropopause structure also varied dramatically across the storm. Within Nadine’s cirrus canopy, the tropopause was typically very well-defined, marked by a strong inversion layer in the lower stratosphere. Many of these soundings also included a second inversion layer in the upper troposphere, leading to two distinct upper-level stability maxima. In contrast, the cloud-free environment surrounding Nadine was characterized by a smooth, uniform transition from troposphere to stratosphere. This suggests that cirrus-related processes might have acted to alter the upper-level static stability profile.

Idealized simulations of an axisymmetric TC produced static stability structures similar to those observed in Patricia and Nadine. Potential temperature budgets and lapse rate tendencies will be computed within this framework to diagnose what led to the development of these structures in the modeled storm.