The Arctic stratospheric response to El Niño (EN) and La Niña (LN) is evaluated in a 41 member ensemble of the period 1980 to 2009 in the Goddard Earth Observing System Chemistry-Climate Model. We consider whether the responses to EN and LN are equal in magnitude and opposite in sign, whether the responses to moderate and extreme events are proportionate, and if the response depends on whether sea surface temperature anomalies (SSTs) peak in the Eastern Pacific (EP) or Central Pacific (CP). There is no indication of any nonlinearities between EN and LN, though in ~ 15% of the ensemble members the stratospheric sudden warming (SSW) frequencies for EN and LN are similar, suggesting that a similar SSW frequency for EN and LN, as has occurred over the past ~ 60 years, can occur by chance. The response to extreme EN events is not proportionate to the amplitude of the underlying SST anomalies in spring. EP EN events preferentially increase zonal wavenumber 1 and decrease zonal wavenumber 2 as compared to CP EN events, however the zonal-mean Arctic stratospheric and subpolar surface response is generally little different between EP EN and CP EN once one accounts for the relative weakness of CP events. These differences between EP and CP events and between moderate and extreme EN events only emerge if at least 25 events are composited, however, due to the small signal-to-noise ratio, and hence these differences may be of little practical benefit.
Bibliographical noteFunding Information:
This study was supported by the Israel Science Foundation (Grant Number 1558/14) and by a European Research Council starting grant under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 677756). We thank those involved in model development at GSFC-GMAO, and support by the NASA MAP program. High-performance computing resources were provided by the NASA Center for Climate Simulation (NCCS). We thank Valentina Aquila from American University, Washington DC, USA. for making available some of the GEOSCCM integrations used here, and our anonymous reviewers for their constructive comments. El Niño indices based on the ERSSTv5 data were downloaded from http://www.cpc.ncep.noaa.gov/data/indices/ersst5.nino.mth.81-10.ascii.
© 2019, The Author(s).