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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 7
Atmos. Chem. Phys., 18, 4597-4615, 2018
https://doi.org/10.5194/acp-18-4597-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 18, 4597-4615, 2018
https://doi.org/10.5194/acp-18-4597-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 05 Apr 2018

Research article | 05 Apr 2018

Nonlinear response of tropical lower-stratospheric temperature and water vapor to ENSO

Chaim I. Garfinkel1, Amit Gordon1, Luke D. Oman2, Feng Li3, Sean Davis4, and Steven Pawson2 Chaim I. Garfinkel et al.
  • 1The Fredy and Nadine Herrmann Institute of Earth Sciences, Hebrew University of Jerusalem, Jerusalem, Israel
  • 2NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 3Universities Space Research Association, Columbia, MD, USA
  • 4NOAA Earth System Research Laboratory, Boulder, CO, USA

Abstract. A series of simulations using the NASA Goddard Earth Observing System Chemistry–Climate Model are analyzed in order to aid in the interpretation of observed interannual and sub-decadal variability in the tropical lower stratosphere over the past 35 years. The impact of El Niño–Southern Oscillation on temperature and water vapor in this region is nonlinear in boreal spring. While moderate El Niño events lead to cooling in this region, strong El Niño events lead to warming, even as the response of the large-scale Brewer–Dobson circulation appears to scale nearly linearly with El Niño. This nonlinearity is shown to arise from the response in the Indo-West Pacific to El Niño: strong El Niño events lead to tropospheric warming extending into the tropical tropopause layer and up to the cold point in this region, where it allows for more water vapor to enter the stratosphere. The net effect is that both strong La Niña and strong El Niño events lead to enhanced entry water vapor and stratospheric moistening in boreal spring and early summer. These results lead to the following interpretation of the contribution of sea surface temperatures to the decline in water vapor in the early 2000s: the very strong El Niño event in 1997/1998, followed by more than 2 consecutive years of La Niña, led to enhanced lower-stratospheric water vapor. As this period ended in early 2001, entry water vapor concentrations declined. This effect accounts for approximately one-quarter of the observed drop.

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The impact of El Niño in the lower stratosphere is nonlinear in spring. While moderate El Niño events lead to cooling in this region, strong El Niño events appear to lead to warming, and hence the water vapor response is nonlinear too. The net effect is that strong El Nino events, such as in 1997/1998 and 2015/2016, lead to qualitatively different water vapor impacts as compared to moderate El Nino events.
The impact of El Niño in the lower stratosphere is nonlinear in spring. While moderate El Niño...
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