Southern Hemisphere Summer Mesopause Responses to El Niño-Southern Oscillation

© 2016 American Meteorological Society. TL would like to thank Han-Li Liu and Chengyun Yang for helpful discussion. TL and XD are supported by the National Natural Science Foundation of China Grants 41225017 and 41421063 and the National Basic Research Program of China Grant 2012CB825605. TL's visit to ERAU is partially supported by the NSF Grants AGS-1115249 and AGS-1110199. NC acknowledges partial support from the Spanish Ministry of Economy and Competitiveness through the PALEOSTRAT project (Paleomodelización desde una perspectiva estratoférica; Ref. CGL2015-69699-R) and the European Project 603557-STRATOCLIM under program FP7-ENV.2013.6.1-2. JY is supported by the NASA AIM and TIMED satellite missions. JMR is supported under NASA SABER Grant NNX15AD22G. MGM is supported by the NASA TIMED satellite project. AZL is supported by National Science Foundation Grants AGS-1115249 and AGS-1110199. The WACCM 3.5 results were obtained from the Atmospheric Chemistry Division at the National Center for Atmospheric Research. The radiosonde dataset is downloaded from http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/index.html. We want to thank Bodil Karlsson and two other anonymous reviewers for their constructive comments on this paper.
In the Southern Hemisphere (SH) polar region, satellite observations reveal a significant upper-mesosphere cooling and a lower-thermosphere warming during warm ENSO events in December. An opposite pattern is observed in the tropical mesopause region. The observed upper-mesosphere cooling agrees with a climate model simulation. Analysis of the simulation suggests that enhanced planetary wave (PW) dissipation in the Northern Hemisphere (NH) high-latitude stratosphere during El Nino strengthens the Brewer-Dobson circulation and cools the equatorial stratosphere. This increases the magnitude of the SH stratosphere meridional temperature gradient and thus causes the anomalous stratospheric easterly zonal wind and early breakdown of the SH stratospheric polar vortex. The resulting perturbation to gravity wave (GW) filtering causes anomalous SH mesospheric eastward GW forcing and polar upwelling and cooling. In addition, constructive inference of ENSO and quasi-biennial oscillation (QBO) could lead to stronger stratospheric easterly zonal wind anomalies at the SH high latitudes in November and December and early breakdown of the SH stratospheric polar vortex during warm ENSO events in the easterly QBO phase (defined by the equatorial zonal wind at similar to 25 hPa). This would in turn cause much more SH mesospheric eastward GW forcing and much colder polar temperatures, and hence it would induce an early onset time of SH summer polar mesospheric clouds (PMCs). The opposite mechanism occurs during cold ENSO events in the westerly QBO phase. This implies that ENSO together with QBO could significantly modulate the breakdown time of SH stratospheric polar vortex and the onset time of SH PMC.
Unión Europea. FP7
National Aeronautics and Space Administration (NASA)
National Natural Science Foundation of China (NSFC)
National Basic Research Program of China
National Science Foundation (NSF)
Stratospheric and upper tropospheric processes for better climate predictions (STRATOCLIM), UE
Ministerio de Economía y Competitividad (MINECO), España
Depto. de Física de la Tierra y Astrofísica
Fac. de Ciencias Físicas
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