On the signatures of equatorial and extratropical wave forcing in tropical tropopause layer temperatures

Temperatures in the tropical tropopause layer (TTL) play an important role in stratosphere–troposphere exchange and in the formation and maintenance of thin cirrus clouds. Many previous studies have examined the contributions of extratropical and equatorial waves to the TTL using coarse-vertical-resolution satellite and reanalysis data. In this study, the authors provide new insight into the role of extratropical and equatorial waves in the TTL using high-vertical-resolution GPS radio occultation data.

The results examine the influence of four different wave forcings on the TTL: extratropical waves that propagate vertically into the stratosphere, extratropical waves that propagate meridionally into the subtropical stratosphere, extratropical waves that propagate meridionally into the subtropical troposphere, and the equatorial planetary waves. The vertically and meridionally propagating extratropical stratospheric waves are associated with deep, zonally symmetric temperature anomalies that extend and amplify with height throughout the lower-to-middle tropical stratosphere. In contrast, the extratropical tropospheric waves and the equatorial planetary waves are associated with tropical temperature anomalies that are confined below 20-km altitude. The equatorial planetary waves dominate the zonally asymmetric component of the TTL temperature field, and both the equatorial planetary waves and the extratropical tropospheric waves are linked to large temperature variability in a 1–2-km-deep layer near the tropical tropopause. The fine vertical scale of the TTL temperature features associated with the equatorial planetary waves and the extratropical tropospheric waves is only readily apparent in high-vertical-resolution data.