Regime shift in the global sea‐surface temperatures: its relation to El Niño–southern oscillation events and dominant variation modes

Abstract

Significant changes of mean state appearing widely in the global sea-surface temperature (SST) anomaly field have happened five times from the 1910s to the 1990s : 1925, 1942, 1957, 1970 and 1976. Since the regions of change spread over both hemispheres and/or multiple oceanic basins, they can be considered as 'global regime shifts'. The years of regime shifts are consistent with those of the Northern Hemisphere regime shifts reported by previous studies.It is also shown that the regime shifts have happened concurrently with El Niño-southern oscillation (ENSO) events, which seems to suggest that the ENSO event acts as a trigger of the regime shift. At the regime shift, the tropical Pacific SSTs change from La Niña (El Niño) to El Niño (La Niña) conditions within 1 year. Further, the ENSO events occur just after the regime shifts begin in the July to September (JAS) season and reach the mature phase in the January to March (JFM) season as a typical evolution of the ENSO events. After that, they continue to at least the next year.The five regime shifts detected have similar features in their seasonal evolution and persistence of signals. First, the shifts start in the JAS season: an SST change occurs in the eastern and central tropical Pacific, and a change in the mid-latitudes of the North and South Pacific appears with the opposite sign. Then the shifts in the JFM season. The spatial patterns are similar to those of the JAS season, but signals in the North Pacific become remarkable. These features resemble those corresponding to a series of evolutions of ENSO events, but the signals in the North Pacific and the North Atlantic are much stronger than those of the typical ENSO events. After the shifts have happened, the changes in spatial patterns of SST that occurred at the regime shift persist until the next shift. The persistence of signals is more prominent in the JFM season than in the JAS season.From a review of the dominant variation modes in global SSTs using empirical orthogonal function (EOF) analyses, four modes are identified: the ENSO mode, the Southern Hemisphere trend mode, the North Pacific (NP) mode, and the Arctic oscillation (AO) mode. In the years when regime shifts occur, the ENSO mode, the NP mode, and the AO mode show significant concurrent phase reversals on the global scale as previously shown in the Northern Hemisphere. These findings provide a possible reason why SST changes in the regime shift are similar but not exactly the same pattern as that of ENSO. Furthermore, it can be considered that a simultaneous phase reversal of the NP mode would suppress the growth of anticyclonic (or cyclonic) circulation in the atmosphere over the western tropical Pacific. This suggests that an ENSO event, which begins with a regime shift, would not reverse its condition and last for the following several seasons.

Determination of seasonal rainfall variability, onset and cessation in semi-arid Tharaka district, Kenya

“…Studies that have analysed rainfall variability with ENSO as the determinant include Yasunaka and Hanawa (2005), Chambers (2003), Goddard et al (2001), Nicholson et al (2000), Mamoudou et al (1995), Nicholls and Wong (1990), Hutchison (1990), Farmer (1988) and Ogallo (1988). The link between rainfall and ENSO contributed to the understanding of the interaction between the atmosphere, land and sea: this has significantly contributed to the improvement of seasonal forecasts (Phillips 2003;Hansen 2005).…”

Southern hemisphere cyclones and anticyclones: recent trends and links with decadal variability in the Pacific Ocean

“…Meinke et al, 2005;. Yasunaka and Hanawa (2005) argue that some of the important regime shifts that occurred in global SSTs during the last century have happened concurrently with ENSO events, and suggest that decadal-scale variations and the ENSO events are not independent of each other.…”

Wavelet-Based Multifractal Analysis on Climatic Regime Shifts

“…For the Niño3.4 index, the fractality changes at 1964, 1982, and 2000 do not relate to regime shifts. Not all the ENSO events are associated with regime shifts (Yasunaka and Hanawa 2005). For the NPI, the frac-tality changes around 1965 and 1991 do not relate to regime shifts.…”

“…This agrees with the results that the PNA is associated with tropical heat sources enhanced by the warming of the tropical SST, and that the PDO is associated with the strength of the PNA pattern in the troposphere. An ENSO event acts as a trigger of the regime shift (Yasunaka and Hanawa 2005), so that tropical SST excite the PNA, and teleconnections cause changes in the SST of the Northern Pacific Ocean except for the 1988/89 regime shift.…”

“…Six regime shifts were detected during the study period from the 1910s to the 1990s: the 1925/26, 1945/46, 1957/58, 1970/71, 1976/77, and 1988/89 regime shifts (Yasunaka and Hanawa 2002). The concurrent occurences of regime shifts and El Niño/ Southern Oscillation (ENSO) events suggest that the ENSO events triggered the regime shifts (Yasunaka and Hanawa 2005). The duration between each regime shift is approximately 10 years, which is identical to the Pacific Decadal Oscillation (PDO).…”