Interdecadal Variations in ENSO Teleconnection to the Indo–Western Pacific for 1870–2007

Abstract

Slow modulation of interannual variability and its relationship to El Niñ o-Southern Oscillation (ENSO) isinvestigated for the period of 1870-2007 using shipboard surface meteorological observations along a frequently traveled track across the north Indian Ocean (NIO; from the Gulf of Aden through Malacca Strait) and the South China Sea (to Luzon Strait). During the decades in the late nineteenth-early twentieth century and in the late twentieth century, the El Niñ o-induced NIO warming persists longer than during the 1910s-mid-1970s, well into the summer following the peak of El Niñ o. During the epochs of the prolonged NIO warming, rainfall drops and sea level pressure rises over the tropical northwest Pacific in summer following El Niñ o. Conversely, during the period when the NIO warming dissipates earlier, these atmospheric anomalies are not well developed. This supports the Indian Ocean capacitor concept as a mechanism prolonging El Niñ o influence into summer through the persistent Indian Ocean warming after El Niñ o itself has dissipated.The above centennial modulation of ENSO teleconnection to the Indo-northwest Pacific region is reproduced in an atmospheric general circulation model forced by observed SST. The modulation is correlated not with the Pacific decadal oscillation but rather with the ENSO variance itself. When ENSO is strong, its effect in the Indo-northwest Pacific strengthens and vice versa. The fact that enhanced ENSO teleconnections occurred 100 years ago during the late nineteenth-early twentieth century indicates that the recent strengthening of the ENSO correlation over the Indo-western Pacific may not entirely be due to global warming but reflect natural variability.

Asymmetry of the winter extra-tropical teleconnections in the Northern Hemisphere associated with two types of ENSO

“…In this case, the distinct effects of the different background state on the equatorward wave rays are responsible for this asymmetry. Under the CP El Niño-type background state, the equatorward wave rays tend to be reflected at the latitudes where the zonal wind equals zero (U = 0), and then successfully captured 1 3 regression, are usually employed by most of the studies (e.g., Chowdary et al 2012;Wang et al 2008a;Wu et al 2003;among others). Actually, climate responses to ENSO are not simply opposite, but show an apparent nonlinearity between the warm and cold phases (Zhang et al 2014a(Zhang et al , 2015.…”

Future change of the Indian Ocean basin-wide and dipole modes in the CMIP5

“…Recent studies have found significant warming and changes in the Indian Ocean SST during recent few decades based on observation (Abram et al 2008;Alory et al 2007;Chowdary et al 2012;Ihara et al 2008). Ihara et al (2008) showed that the western equatorial Indian Ocean warms more than the eastern counterpart during recent decades; the mean SST gradient across the equatorial Indian Ocean is anomalously positive to the west reduced.…”

Attribution of the summer warming since 1970s in Indian Ocean Basin to the inter‐decadal change in the seasonal timing of El Niño decay phase

“…The long-term IOB SST warming has commonly been attributed to the anthropogenic effect associated with global warming [Barnett et al, 2005;Pierce et al, 2006]. Nevertheless, decadal changes over the Indian Ocean have been found closely related to ENSO [Cole et al, 2000;Allan et al, 1995;Reason et al, 2000;Xie et al, 2010;Chowdary et al, 2012]. For example, Allan et al [1995] suggested that the epochal changes in the mean condition over the south Indian Ocean are in-phase with ENSO-related correlation patterns.…”

“…For example, Allan et al [1995] suggested that the epochal changes in the mean condition over the south Indian Ocean are in-phase with ENSO-related correlation patterns. Chowdary et al [2012] showed the epochal change in the persistency of the El Niño-induced warmer SST anomalies over the north Indian Ocean. This study will examine the interdecadal variation of the basinwide SST in the Indian Ocean and provide evidence to show that, during the past 140 years, the most significant interdecadal IOB warming exists around 1970s, and it is intimately related to decadal changes of ENSO since 1970s.…”