ENSO influence on the North Atlantic European climate: a non-linear and non-stationary approach
- 760 Downloads
El Niño Southern Oscillation (ENSO) impact on the North Atlantic European sector (NAE) is still under discussion. Recent studies have found a non stationary feature of this teleconnection, suggesting an effective modulating role of the ocean mean state. Nevertheless, physical explanations about the underlying mechanisms have been little studied in the available literature. In addition, ENSO events show different SST spatial patterns, phases, and amplitudes, which can also influence on the related remote impacts. In view of all this, in the present study a set of partially coupled experiments have been performed with a global atmospheric general circulation model in which different SST ENSO patterns are superimposed over distinct Pacific and Atlantic SST mean states. These SST background conditions are constructed according to the observational difference between periods with a distinct impact of ENSO on the leading Euro-Mediterranean rainfall mode in late winter-early spring. Our results point to two distinct mechanisms associated with ENSO that can be modulated by the SST mean state: (1) the thermally driven direct circulation (Walker and Hadley cells) connecting the Atlantic and Pacific basins, and (2) the Rossby wave propagation from the tropical Pacific to the North Atlantic. The former elucidates that the positive NAO-like pattern usually related to La Niña events could be only valid for selected decades. The latter explains a reinforced signature of Eastern Pacific Niños on the Euro-Mediterranean rainfall when the tropical Pacific is warmer than usual and the North Atlantic is colder than usual. This feature is consistent with the changing ENSO impact identified in previous studies and demonstrates how the ENSO teleconnection with the NAE climate at interannual timecales could be modulated by multidecadal changes in the SST. According to our results, the assumption of stationarity which is still common to many studies of ENSO teleconnections clearly has to be questioned.
This work was supported by the National Spanish projects: TRACS (CGL2009-10285) and MULCLIVAR (CGL2012-38923-C02-01). In particular, J.L.P. thanks the FPI Grant (BES-2010-042234) associated with TRACS project. J.L.P. also thanks the Monash Weather and Climate group of Monash University (Melbourne) for scientific discussions and incredible hospitality. The sensitivity experiments described in this paper were performed on Monash University.
- Bi D, Dix M, Marsland SJ, OFarrell S, Rashid H, Uotila P, Hirst A, Kowalczyk E, Golebiewski M, Sullivan A et al (2013) The access coupled model: description, control climate and evaluation. Aust Meteorol Oceanogr J 63(1):41–64Google Scholar
- Bulić IH, Kucharski F (2012) Delayed ENSO impact on spring precipitation over North/Atlantic European region. Clim Dyn 38(11–12):2593–2612Google Scholar
- Compo GP, Whitaker JS, Sardeshmukh PD, Matsui N, Allan RJ, Yin X, Gleason BE, Vose RS, Rutledge G, Bessemoulin P, Brönnimann S, Brunet M, Crouthamel RI, Grant AN, Groisman PY, Jones PD, Kruk MC, Kruger AC, Marshall GJ, Maugeri M, Mok HY, Nordli Ø, Ross TF, Trigo RM, Wang XL, Woodruff SD, Worley SJ (2011) The twentieth century reanalysis project. Quart J Roy Meteor Soc 137:1–28. doi: 10.1002/qj.776 CrossRefGoogle Scholar
- Livezey RE, Mo KC (1987) Tropical-extratropical teleconnections during the Northern Hemisphere winter. Part II: Relationships between monthly mean Northern Hemisphere circulation patterns and proxies for tropical convection. Mon Weather Rev 115:3115. doi: 10.1175/1520-0493(1987)115<3115:TETDTN>2.0.CO;2 CrossRefGoogle Scholar
- Sung MK, Ham YG, Kug JS, An SI (2013) An alterative effect by the tropical north atlantic SST in intraseasonally varying EL Nino teleconnection over the North Atlantic. Tellus 65. doi: 10.3402/tellusa.v65i0.19863
- Wilks DS (2011) Statistical methods in the atmospheric sciences, vol 100. Academic Press, LondonGoogle Scholar