ENSO and climatic signals across the Indian Ocean Basin in the global context: part I, interannual composite patterns

Abstract

This study focuses on the interplay between mean sea level pressure (MSLP), sea surface temperature (SST), and wind and cloudiness anomalies over the Indian Ocean in seasonal composite sequences prior to, during, and after strong, near-global El Niñ o and La Niñ a episodes. It then examines MSLP and SST anomalies in the 2-2.5-year quasi-biennial (QB) and 2.5-7-year low-frequency (LF) bands that carry the bulk of the raw ENSO signal. Finally, these fields were examined in conjunction with patterns of correlations between rainfall and joint spatiotemporal empirical orthogonal function (EOF) time series band pass filtered in the QB and LF bands. The seasonal composites indicate that the El Niñ o-1 (La Niñ a-1) pattern tends to display a more robust and coherent (weaker and less organized) structure during the evolution towards the mature stage of the event. The reverse tends to be apparent in the cessation period after the peak phase of an event, when El Niñ o events tend to collapse quite quickly. Climatic variables over the Indian Ocean Basin linked to El Niñ o and La Niñ a events show responses varying from simultaneous, to about one season's lag. In general, SSTs tend to evolve in response to changes in cloud cover and wind strength over both the north and south Indian Ocean. There are also strong indications that the ascending (descending) branch of the Walker circulation is found over the African continent (central Indian Ocean) during La Niñ a phases, and that the opposite configuration occurs in El Niñ o events. These alternations are linked to distinct warm-cool (cool-warm) patterns in the north-south SST dipole over the western Indian Ocean region during the El Niñ o (La Niñ a) events. An examination of MSLP and SST anomaly patterns in the QB and LF bands shows that signals are more consistent during El Niñ o-1 and El Niñ o sequences than they are during La Niñ a-1 and La Niñ a sequences. The QB band has a tendency to display the opposite anomaly patterns to that seen on the LF band during the early stages of event onset, and later stage of event cessation, during both El Niñ o-Southern Oscillation (ENSO) phases. El Niño events tend to be reinforced by signals on both bands up to their mature phase, but are then seen to erode rapidly, as a result of the presence of distinct La Niñ a anomalies on the QB band after their peak phase. During La Niña events, the opposite is observed during their cessation phase. Both QB and LF bands often display SST dipole anomalies that are not clearly evident in the raw composites alone. An eastern Indian Ocean SST dipole shows a tendency to occur during the onset phase of particular El Niño or La Niñ a episodes, especially during the austral autumn-winter (boreal spring-summer) and, when linked to tropical-temperate cloud bands, can influence Australian rainfall patterns. Analyses of seasonal correlations between rainfall and joint MSLP and SST EOF time series on QB and LF bands and their dynamical relationship with MSLP and SST anomalies during El Niñ o and La Niñ a events...

Rainfall reliability, a neglected factor in explaining convergence and divergence of plant traits in fire‐prone mediterranean‐climate ecosystems

“…Nevertheless, we suspect that, apart from global climatic phenomena -such as the North Atlantic Oscillation (NAO) and the El Niño-Southern Oscillations (ENSO) -as main explanatory variables (e.g. Reason et al ., 2000;Rodrigo et al ., 2001;Haylock & Goodess, 2004), the influence of topography may account for differences among regions. Deacon et al .…”

Interannual variability of the South Indian Countercurrent

“…However, it is not clear whether ENSO, IOD, TBO, and SIOD are completely independent of each other, as extensively discussed in several papers [e.g., Reason et al, 2000;Xie et al, 2002;Meehl and Arblaster, 2002;Ashok et al, 2003;Shinoda et al, 2004;Bracco et al, 2005;Schott et al, 2009;Morioka et al, 2013]. For example, the TBO is defined as the tendency for a relatively strong monsoon year to be followed by a weak one, and vice versa [Meehl and Arblaster, 2002].…”

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.…”