Abstract
A detailed analysis of double tropopause (DT) occurrences requires vertically well resolved, accurate, and globally distributed information on the troposphere‐stratosphere transition zone. Here, we use radio occultation observations from 2001 to 2018 with such properties. We establish a connection between El Niño‐Southern Oscillation (ENSO) phases and the distribution of DTs by analyzing the global and seasonal DT characteristics. The seasonal distribution of DTs reveals several hotspot locations, such as near the subtropical jet stream and over high mountain ranges, where DTs occur particularly often. In this study, we detect a higher number of DTs during the cold La Niña state while warmer El Niño events result in lower DT rates, affecting the structure of the tropopause region. Close to the Niño 3 region, this relates to a much lower first lapse rate tropopause altitude during La Niña and corresponds to an apparent narrowing of the tropical belt there.
Highlights
The tropopause, the transition zone between the troposphere and the stratosphere, is of substantial importance to the exchange between these two atmospheric regimes (Holton et al, 1995)
We detect a higher number of double tropopause (DT) during the cold La Niña state while warmer El Niño events result in lower DT rates, affecting the structure of the tropopause region
We exploited these characteristics to investigate for the first time the relation of El Niño‐Southern Oscillation (ENSO) and the occurrence of DTs in global multiyear radio occultation (RO) observations
Summary
The tropopause, the transition zone between the troposphere and the stratosphere, is of substantial importance to the exchange between these two atmospheric regimes (Holton et al, 1995). Depending on season and latitude, the tropopause is typically found at around 16 km in the tropics and at around 9 km at high latitudes (e.g., Schmidt et al, 2005; Seidel & Randel, 2006). The more complex structure and variability of the upper troposphere and lower stratosphere (UTLS) region at midlatitudes, related to this overlap and the existence of DTs there, is key to understand the stratosphere‐troposphere exchange (e.g., Boothe & Homeyer, 2017). The STJ is of special interest, because it marks a region where midlatitudinal and tropical air meet, but the STJs are linked to Rossby wave breaking events, which again are associated to DTs and stratosphere‐troposphere exchange
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