Double Tropopauses and the Tropical Belt Connected to ENSO

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.

Continuous rise of the tropopause in the Northern Hemisphere over 1980–2020

“…WEGC OPSv5.6 provides global upper-air satellite data in high quality from multiple RO satellite missions (including CHAMP, GRACE, SAC-C, Formosat-3/COSMIC, and Metop) ( 25 , 52 ) and thus is widely used for climate studies ( 14 , 53 , 54 ). H was estimated from each temperature profile following the WMO lapse-rate tropopause definition ( 55 ). Monthly zonal-mean H data are extracted at 5° latitudinal intervals between 80°S and 80°N.…”

Is Hadley Cell Expanding?

“…This general tendency is also suggested in general circulation model (GCM) simulations [22], which show an equatorial shift of the STJ during El Niño. Using the high vertical resolution GPS radio occultation observations, however, Wilhelmsen et al [86] found a much lower tropopause altitude during La Niña in the east Equatorial Pacific Ocean, indicating a narrower Hadley Cell in these regions.…”

“…The subjective tropopause-metric edge with a given threshold (Z TP and ∆θ) show small broaden trends or even contraction in the Northern Hemisphere, while they generally show expansion in the Southern Hemisphere [85]. The objective tropopause-breakbased edge (TPB) experiences a poleward shifting in those using monthly zonal mean view, e.g., [32], while this edge experiences a slight equatorward displacement in those using instantaneous data allowing longitudinal variability, e.g., [54] associated with El Niño-Southern Oscillation ENSO; [86]. This discrepancy is likely caused by the large contraction of the Hadley Cell in the east Pacific [54].…”

Tropospheric Gravity Waves Increase the Likelihood of Double Tropopauses

“…Furthermore, in Wilhelmsen et al. (2020), the occurrence frequency of subtropical DTs assessed by radio occultation observations is around 55%, which is approximately 15% higher than the finding in Figure 1d.…”

“…The double tropopause (DT) event can be readily observed at midlatitudes in both hemispheres, more frequently during winter (Bischoff et al., 2007; Schmidt et al., 2006; Seidel & Randel, 2006). Particularly, DTs reveal several hotspot locations, such as near the subtropical jet stream and over high mountain ranges (Wilhelmsen et al., 2020). The DT acts to increase the STE of mass (C. Liu & Barnes, 2018; Schwartz et al., 2015).…”