Signals of El Niño Modoki in the tropical tropopause layer and stratosphere

Abstract

Abstract. The effects of El Niño Modoki events on the tropical tropopause layer (TTL) and on the stratosphere were investigated using European Center for Medium Range Weather Forecasting (ECMWF) reanalysis data, oceanic El Niño indices, and general climate model outputs. El Niño Modoki events tend to depress convective activities in the western and eastern Pacific but enhance convective activities in the central and northern Pacific. Consequently, during El Niño Modoki events, negative water vapor anomalies occur in the western and eastern Pacific upper troposphere, whereas there are positive anomalies in the central and northern Pacific upper troposphere. The spatial patterns of the outgoing longwave radiation (OLR) and upper tropospheric water vapor anomalies exhibit a tripolar form. The empirical orthogonal function (EOF) analysis of the OLR and upper tropospheric water vapor anomalies reveals that canonical El Niño events are associated with the leading mode of the EOF, while El Niño Modoki events correspond to the second mode. The composite analysis based on ERA-interim data indicate that El Niño Modoki events have a reverse effect on middle-high latitudes stratosphere, as compared with the effect of typical El Niño events, i.e., the northern polar vortex is stronger and colder but the southern polar vortex is weaker and warmer during El Niño Modoki events. According to the simulation' results, we found that the reverse effect on the middle-high latitudes stratosphere is resulted from a complicated interaction between quasi-biennial oscillation (QBO) signal of east phase and El Niño Modoki signal. This interaction is not a simply linear overlay of QBO signal and El Niño Modoki signal in the stratosphere, it is El Niño Modoki that leads to different tropospheric zonal wind anomalies with QBO forcing from that caused by typical El Niño, thus, the planetary wave propagation from troposphere to the stratosphere during El Niño Modoki events is different from that during canonical El Niño events. However, when QBO is in its west phase, El Niño Modoki events have the same effect on middle-high latitudes stratosphere as the typical El Niño events. Our simulations also suggest that canonical El Niño and El Niño Modoki activities actually have the same influence on the middle-high latitudes stratosphere when in the absence of QBO forcing.

Evaluating ENSO teleconnections using observations and CMIP5 models

“…It suggested that during EN, EP-ENSO events influence the North Pacific low in the winter and subsequently increase the planetary wave forcing and reduce the strength of the polar vortex. However, there are also controversies relating to the response of the NH to both types of ENSO, CP ENSO (Graf and Zanchettin 2012;Xie et al 2012;Hegyi and Deng 2011) and EP ENSO (Mitchell et al 2011;Manzini et al 2006) as models differ with observation. It is noteworthy that though CP ENSO and ENSO Modoki are the same in main features, they still differ in details; the same is also true for EP and Canonical ENSO.…”

“…The connection of ENSO with NH polar region through polar vortex or wave propagation is not captured well by models around Greenland area. Various studies discussed the controversies Blank in any cell means not observed or discussed in that category, while 'x' means no models match that criteria relating to connection between ENSO and NH polar region in both phases of ENSO, e.g., Modoki ENSO (Xie et al 2012;Graf and Zanchettin 2012;Hegyi and Deng 2011) and Canonical ENSO (Mitchell et al 2011;Manzini et al 2006). Identified good models are low top (EN)-inmcm4, FIO-ESM; low top (LN)-GFDL-ENM2G, ACCESS1-3, bcccsm1-1; high top (EN)-GFDL-CM3, HadGEM2-CC, MIROC-ESM; high top (LN)-no model.…”

Sensitivity of the atmospheric response to warm pool El Niño events to modeled SSTs and future climate forcings

“…Enhanced planetary wave driving, higher polar lower stratospheric temperatures, and a weaker Antarctic jet have also been identified in response to a different definition of WPEN events. Specifically, Zubiaurre and Calvo [2012] and Xie et al [2012] used the El Niño Modoki index [Ashok et al, 2007], a different metric by which to identify WPEN events, and found SH responses consistent with Hurwitz et al [2011aHurwitz et al [ , 2011b.…”

The relationship between lower-stratospheric ozone at southern high latitudes and sea surface temperature in the East Asian marginal seas in austral spring

“…Variations in tropical sea surface temperature (SST) associated with ENSO, are an important factor in the modulation of the planetary wave activity in the Northern Hemisphere that affects the interannual variability of temperature and ozone levels in the northern polar stratosphere (Sassi et al, 2004;Manzini et al, 2006;Calvo et al, 2004Calvo et al, , 2009Cagnazzo et al, 2009;Hu and Pan, 2009;Hurwitz et al, 2011a, b;Zubiaurre and Calvo, 2012;Xie et al, 2012). The long-term trend in tropical SST also has a correspondence to the trend of temperature in the southern polar stratosphere (Grassi et al, 2005(Grassi et al, , 2006Hu and Fu, 2009;Li et al, 2010;Clem et al, 2016).…”

“…It is well known that the SST changes in the eastern Pacific, the Indo-Pacific warm pool, and the Atlantic can significantly influence the northern polar stratosphere (Calvo et al, 2004Hoerling et al, 2001Hoerling et al, , 2004Cagnazzo et al, 2009;Hu and Fu, 2009;Hu and Pan, 2009;Li et al, 2010;Hurwitz et al, 2011a, b;Lin et al, 2012;Zubiaurre and Calvo, 2012;Xie et al, 2012;Li and Chen, 2014). SST variations in some regions can excite Rossby wave trains, and those waves can propagate into the northern middle-and high-latitude stratosphere (Gettelman et al, 2001;Sassi et al, 2004;Manzini et al, 2006;García-Herrera et al, 2006;Taguchi and Hartmann, 2006;Hartmann, 2007, 2008;Free and Seidel, 2009).…”