Subtropics-Related Interannual Sea Surface Temperature Variability in the Central Equatorial Pacific

Abstract

Interannual sea surface temperature (SST) variability in the central equatorial Pacific consists of a component related to eastern Pacific SST variations (called Type-1 SST variability) and a component not related to them (called Type-2 SST variability). Lead–lagged regression and ocean surface-layer temperature balance analyses were performed to contrast their control mechanisms. Type-1 variability is part of the canonical, which is characterized by SST anomalies extending from the South American coast to the central Pacific, is coupled with the Southern Oscillation, and is associated with basinwide subsurface ocean variations. This type of variability is dominated by a major 4–5-yr periodicity and a minor biennial (2–2.5 yr) periodicity. In contrast, Type-2 variability is dominated by a biennial periodicity, is associated with local air–sea interactions, and lacks a basinwide anomaly structure. In addition, Type-2 SST variability exhibits a strong connection to the subtropics of both hemispheres, particularly the Northern Hemisphere. Type-2 SST anomalies appear first in the northeastern subtropical Pacific and later spread toward the central equatorial Pacific, being generated in both regions by anomalous surface heat flux forcing associated with wind anomalies. The SST anomalies undergo rapid intensification in the central equatorial Pacific through ocean advection processes, and eventually decay as a result of surface heat flux damping and zonal advection. The southward spreading of trade wind anomalies within the northeastern subtropics-to-central tropics pathway of Type-2 variability is associated with intensity variations of the subtropical high. Type-2 variability is found to become stronger after 1990, associated with a concurrent increase in the subtropical variability. It is concluded that Type-2 interannual variability represents a subtropical-excited phenomenon that is different from the conventional ENSO Type-1 variability.

The influence of El Niño–Southern Oscillation regimes on eastern African vegetation and its future implications under the RCP8.5 warming scenario

“…In our methodology the coupling of tropical Pacific sea surface temperature-eastern African rainfall variability emerges from the data, and this shift in the influence region agrees well with previous studies that identify an increase in the intensity of central Pacific (CP) ENSO in the future from GCM outputs (Kim and Yu, 2012). While CP ENSO is thought to be forced by changes in the atmospheric circulation, the mechanism for eastern Pacific ENSO is rather associated with thermocline variations in the oceanic circulation (Yu et al, 2010), and the seasonal impacts produced by these two types of ENSO could differ. For example, wetter patterns of EP El Niño events in eastern Africa might not occur under CP El Niño events, and CP La Niña events could induce drier conditions in the southern parts of the region than EP La Niña events (Wiedermann et al, 2017), which could result in prolongated drought events for the eastern African region.…”

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

“…1b). Yu and Kao (2007) also noticed there are two different types of ENSO, moreover, Kao and Yu (2009) and Yu et al (2010) explain the different mechanisms which lead to the different two kinds of El Niño events. Ashok et al (2007) found that the evolution of El Niño Modoki events is related to a tripolar pattern of sea level pressure anomalies, and noted the presence of two anomalous Walker circulation cells associated with El Niño Modoki events, versus the single cell that is associated with canonical El Niño events.…”

Linkage between the dominant modes in Pacific subsurface ocean temperature and the two type ENSO events

“…Yu et al [14] and Yu and Kim [15] found that the EP-ENSO is possibly produced by the delayed oscillator or the recharged oscillator after they have examined the structure of subsurface ocean temperature (SOT), but the possible linkage between the CP-ENSO and the SOT variations is still unclear. In this regard, the aim of this study is to identify the possible linkage between the two types ENSO events and the variations in the SOT anomalies, particularly on the interdecadal time scale.…”