scholarly journals Modern and sub-fossil corals suggest reduced temperature variability in the eastern pole of the Indian Ocean Dipole during the medieval climate anomaly

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Sri Yudawati Cahyarini ◽  
Miriam Pfeiffer ◽  
Lars Reuning ◽  
Volker Liebetrau ◽  
Wolf-Chr. Dullo ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
La Niña ◽  
Medieval Climate Anomaly ◽  
Climate Anomaly ◽  
Positive Indian Ocean Dipole ◽  
Sst Variability ◽  
La Nina ◽  
Fossil Corals ◽  
The Indian Ocean

AbstractWe present two 40 year records of monthly coral Sr/Ca ratios from the eastern pole of the Indian Ocean Dipole. A modern coral covers the period from 1968 to 2007. A sub-fossil coral derives from the medieval climate anomaly (MCA) and spans 1100–1140 ad. The modern coral records SST variability in the eastern pole of the Indian Ocean Dipole. A strong correlation is also found between coral Sr/Ca and the IOD index. The correlation with ENSO is asymmetric: the coral shows a moderate correlation with El Niño and a weak correlation with La Niña. The modern coral shows large interannual variability. Extreme IOD events cause cooling > 3 °C (1994, 1997) or ~ 2 °C (2006). In total, the modern coral indicates 32 warm/cool events, with 16 cool and 16 warm events. The MCA coral shows 24 warm/cool events, with 14 cool and 10 warm events. Only one cool event could be comparable to the positive Indian Ocean Dipole in 2006. The seasonal cycle of the MCA coral is reduced (< 50% of to the modern) and the skewness of the Sr/Ca data is lower. This suggests a deeper thermocline in the eastern Indian Ocean associated with a La Niña-like mean state in the Indo-Pacific during the MCA.

scholarly journals The unique mean seasonal cycle in the Indian Ocean anchors its various air-sea coupled modes across the basin

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Xinqiang Xu ◽  
Lei Wang ◽  
Weidong Yu
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Indian Ocean Dipole ◽  
El Nino ◽  
Tropical Indian Ocean ◽  
La Niña ◽  
Trade Wind ◽  
Coupled Modes ◽  
La Nina ◽  
The Indian Ocean

AbstractThe interannual variability of the sea surface temperature (SST) in the Indian Ocean is complex and characterized by various air-sea coupled modes, which occur around El Niño/La Niña's peak phase (i.e. December–January–February, DJF). Indian Ocean Dipole Mode (IODM) develops over the tropical Indian Ocean and peaks in September–October–November (SON), while Ningaloo Niño, Subtropical Indian Ocean Dipole (SIOD) and Indian Ocean Basin Mode (IOBM) occur respectively over northwest off Australia, subtropical and tropical Indian Ocean, during boreal winter to spring. The apparent contrast between their divergent regionality and convergent seasonality around DJF triggers the present study to examine the interaction between the local mean monsoonal cycle and the anomalous forcing from El Niño/La Niña. The diagnosis confirms that the Indian Ocean’s unique complexity, including the monsoonal circulation over the tropics and the trade wind over the subtropical southern Indian Ocean, plays the fundamental role in anchoring the various regional air-sea coupled modes across the basin. The SST anomalies can be readily explained by the wind-evaporation-SST (WES) mechanism, which works together with other more regional-dependent dynamic and thermodynamic mechanisms. This implies that El Niño/La Niña brings much predictability for the Indian Ocean variations.

Impact of the Indian Ocean Dipole on Evolution of the Subsequent ENSO: Relative Roles of Dynamic and Thermodynamic Processes

2021 ◽  
Vol 34 (9) ◽  
pp. 3591-3607
Author(s):  
Zhang Yue ◽  
W. Zhou ◽  
Tim Li
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Southern Oscillation ◽  
La Niña ◽  
Bjerknes Feedback ◽  
Sst Cooling ◽  
La Nina ◽  
The Indian Ocean ◽  
Thermodynamic Processes

AbstractThe complex interaction between the Indian Ocean dipole (IOD) and El Niño–Southern Oscillation (ENSO) is further investigated in this study, with a focus on the impacts of the IOD on ENSO in the subsequent year [ENSO(+1)]. The interaction between the IOD and the concurrent ENSO [ENSO(0)] can be summarized as follows: ENSO(0) can trigger and enhance the IOD, while the IOD can enhance ENSO(0) and accelerate its demise. Regarding the impacts of IOD(0) on the subsequent ENSO(+1), it is revealed that the IOD can lead to anomalous SST cooling patterns over the equatorial Pacific after the winter following the IOD, indicating the formation of a La Niña–like pattern in the subsequent year. While the SST cooling tendency associated with a positive IOD is attributable primarily to net heat flux (thermodynamic processes) from autumn to the ensuing spring, after the ensuing spring the dominant contribution comes from oceanic processes (dynamic processes) instead. From autumn to the ensuing spring, the downward shortwave flux response contributes the most to SST cooling over the central and eastern Pacific, due to the cloud–radiation–SST feedback. From the ensuing winter to the ensuing summer, changes in latent heat flux (LHF) are important for SST cooling, indicating that the release of LHF from the ocean into the atmosphere increases due to strong evaporation and leads to SST cooling through the wind–evaporation–SST feedback. The wind stress response and thermocline shoaling verify that local Bjerknes feedback is crucial for the initiation of La Niña in the later stage.

The Influence of the Indian Ocean on ENSO Stability and Flavor

2017 ◽  
Vol 30 (7) ◽  
pp. 2601-2620 ◽  
Author(s):  
Claudia E. Wieners ◽  
Henk A. Dijkstra ◽  
Will P. M. de Ruijter
Keyword(s):  
Indian Ocean ◽  
Spatial Pattern ◽  
El Niño ◽  
East Coast ◽  
El Nino ◽  
La Niña ◽  
Enso Cycle ◽  
Central Pacific ◽  
La Nina ◽  
The Indian Ocean

The effect of long-term trends and interannual, ENSO-driven variability in the Indian Ocean (IO) on the stability and spatial pattern of ENSO is investigated with an intermediate-complexity two-basin model. The Pacific basin is modeled using a fully coupled (i.e., generating its own background state) Zebiak–Cane model. IO sea surface temperature (SST) is represented by a basinwide warming pattern whose strength is constant or varies at a prescribed lag to ENSO. Both basins are coupled through an atmosphere transferring information between them. For the covarying IO SST, a warm IO during the peak of El Niño (La Niña) dampens (destabilizes) ENSO, and a warm IO during the transition from El Niño to La Niña (La Niña to El Niño) shortens (lengthens) the period. The influence of the IO on the spatial pattern of ENSO is small. For constant IO warming, the ENSO cycle is destabilized because stronger easterlies induce more background upwelling, more thermocline steepening, and a stronger Bjerknes feedback. The SST signal at the east coast weakens or reverses sign with respect to the main ENSO signal [i.e., ENSO resembles central Pacific (CP) El Niños]. This is due to a reduced sensitivity of the SST to thermocline variations in case of a shallow background thermocline, as found near the east coast for a warm IO. With these results, the recent increase in CP El Niño can possibly be explained by the substantial IO (and west Pacific) warming over the last decades.

scholarly journals The Seasonal Development of an SST Anomaly in the Indian Ocean and Its Relationship to ENSO

2007 ◽  
Vol 20 (1) ◽  
pp. 38-52 ◽  
Author(s):  
Motoki Nagura ◽  
Masanori Konda
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Surface Wind ◽  
La Niña ◽  
Seasonal Development ◽  
La Nina ◽  
The Indian Ocean ◽  
Dipole Pattern ◽  
Sst Anomaly

Abstract The seasonal development of the sea surface temperature (SST) anomaly in the Indian Ocean is investigated in relation to El Niño–Southern Oscillation (ENSO), using NOAA optimally interpolated SST and NCEP reanalysis data. The result shows that the onset season of El Niño affects the seasonal development of surface wind anomalies over the equatorial eastern Indian Ocean (EEIO); these surface wind anomalies, in turn, determine whether the SST anomaly in the EEIO evolves into the eastern pole of the dipole pattern. In years when the dipole pattern develops, surface zonal wind anomalies over the EEIO switch from westerly to easterly in spring as La Niña switches to El Niño. The seasonal zonal wind over the EEIO also switches from westerly to easterly in spring, and the anomalous wind strengthens seasonal wind from winter to summer. Stronger winds and resultant thermal forcings produce the negative SST anomaly in the EEIO in winter, and its amplitude increases in summer. The SST anomaly becomes the eastern pole of the dipole pattern in fall. In contrast, if the change from La Niña to El Niño is delayed until late summer/fall or if La Niña persists throughout the year, a westerly anomaly persists from winter to summer over the EEIO. The persistent westerly anomaly strengthens the wintertime climatological westerlies and weakens the summertime easterlies. Therefore, negative SST anomalies are produced in the EEIO in winter, but the amplitude decreases in summer, and the eastern pole is not present in fall. The above explanation also applies to onset years of La Niña if the signs of the anomalies are reversed.

scholarly journals Representation of MJO Variability in the NCEP Climate Forecast System

2011 ◽  
Vol 24 (17) ◽  
pp. 4676-4694 ◽  
Author(s):  
Scott J. Weaver ◽  
Wanqiu Wang ◽  
Mingyue Chen ◽  
Arun Kumar
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Climate Forecast ◽  
Forecast System ◽  
Climate Forecast System ◽  
La Nina ◽  
The Indian Ocean ◽  
Ncep Climate Forecast System

The Madden–Julian oscillation (MJO) is arguably the most important intraseasonal mode of climate variability, given its significant modulation of global climate variations and attendant societal impacts. Advancing the current understanding and simulation of the MJO using state-of-the-art climate data and modeling systems is thus a necessary goal for improving MJO prediction capability. MJO variability is assessed in NOAA/NCEP reanalyses and two versions of the Climate Forecast System (CFS), CFS version 1 (CFSv1) and its update version 2 (CFSv2). The analysis leans on a variety of diagnostic procedures and includes MJO sensitivity to varying El Niño–Southern Oscillation (ENSO) phases. It is found that significant improvements have been realized in the representation of MJO variations in the new NCEP Climate Forecast System reanalysis (CFSR) as evidenced by outgoing longwave radiation (OLR) power spectral analysis and more coherent propagation characteristics of precipitation and 850-hPa zonal winds over the Eastern Hemisphere in CFSR-only depictions. Conversely, while modest improvements are realized in the CFSv2 as compared to CFSv1, in general the simulation of the MJO continues to be a challenge. Both versions produce strong eastward propagating variance of convection and wind fields in the intraseasonal frequency band. However, the simulated MJO propagates slower than the observed with difficulties traversing the Maritime Continent into the western Pacific, as noted in many previous modeling studies. The CFS shows robust intraseasonal simulations over the west Pacific during El Niño years with diminished simulation capability over the Indian Ocean during La Niña years. This is likely a manifestation of the preference for La Niña MJO activity to occur over the Indian Ocean and the simulation challenges over that domain.

The Indian Ocean Dipole: A Monopole in SST

2014 ◽  
Vol 28 (1) ◽  
pp. 3-19 ◽  
Author(s):  
Yongjing Zhao ◽  
Sumant Nigam
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
A Priori ◽  
Heat Content ◽  
Tropical Indian Ocean ◽  
Spatiotemporal Analysis ◽  
Upper Ocean Heat Content ◽  
Sst Variability ◽  
Dipole Structure ◽  
The Indian Ocean

Abstract The claim for a zonal-dipole structure in interannual variations of the tropical Indian Ocean (IO) SSTs—the Indian Ocean dipole (IOD)—is reexamined after accounting for El Niño–Southern Oscillation’s (ENSO) influence. The authors seek an a priori accounting of ENSO’s seasonally stratified influence on IO SSTs and evaluate the basis of the related dipole mode index, instead of seeking a posteriori adjustments to this index, as common. Scant observational evidence is found for zonal-dipole SST variations after removal of ENSO’s influence from IO SSTs: The IOD poles are essentially uncorrelated in the ENSO-filtered SSTs in both recent (1958–98) and century-long (1900–2007) periods, leading to the breakdown of zonal-dipole structure in surface temperature variability; this finding does not depend on the subtleties in estimation of ENSO’s influence. Deconstruction of the fall 1994 and 1997 SST anomalies led to their reclassification, with a weak IOD in 1994 and none in 1997. Regressions of the eastern IOD pole on upper-ocean heat content, however, do exhibit a zonal-dipole structure but with the western pole in the central-equatorial IO, suggesting that internally generated basin variability can have zonal-dipole structure at the subsurface. The IO SST variability was analyzed using the extended-EOF technique, after removing the influence of Pacific SSTs; the technique targets spatial and temporal recurrence and extracts modes (rather than patterns) of variability. This spatiotemporal analysis also does not support the existence of zonal-dipole variability at the surface. However, the analysis did yield a dipole-like structure in the meridional direction in boreal fall/winter, when it resembles the subtropical IOD pattern (but not the evolution time scale).

scholarly journals Interannual to Decadal Variability of Tropical Indian Ocean Sea Surface Temperature: Pacific Influence versus Local Internal Variability

2020 ◽  
pp. 1-50
Author(s):  
Lei Zhang ◽  
Gang Wang ◽  
Matthew Newman ◽  
Weiqing Han
Keyword(s):  
Indian Ocean ◽  
Indian Ocean Dipole ◽  
Tropical Indian Ocean ◽  
Tropical Pacific ◽  
Sea Surface ◽  
External Influence ◽  
Sst Variability ◽  
The Pacific ◽  
The Indian Ocean ◽  
The Tropical Pacific

AbstractThe Indian Ocean has received increasing attention for its large impacts on regional and global climate. However, sea surface temperature (SST) variability arising from Indian Ocean internal processes has not been well understood particularly on decadal and longer timescales, and the external influence from the Tropical Pacific has not been quantified. This paper analyzes the interannual-to-decadal SST variability in the Tropical Indian Ocean in observations and explores the external influence from the Pacific versus internal processes within the Indian Ocean using a Linear Inverse Model (LIM). Coupling between Indian Ocean and tropical Pacific SST anomalies (SSTAs) is assessed both within the LIM dynamical operator and the unpredictable stochastic noise that forces the system. Results show that the observed Indian Ocean Basin (IOB)-wide SSTA pattern is largely a response to the Pacific ENSO forcing, although it in turn has a damping effect on ENSO especially on annual and decadal timescales. On the other hand, the Indian Ocean Dipole (IOD) is an Indian Ocean internal mode that can actively affect ENSO; ENSO also has a returning effect on the IOD, which is rather weak on decadal timescale. The third mode is partly associated with the Subtropical Indian Ocean Dipole (SIOD), and it is primarily generated by Indian Ocean internal processes, although a small component of it is coupled with ENSO. Overall, the amplitude of Indian Ocean internally generated SST variability is comparable to that forced by ENSO, and the Indian Ocean tends to actively influence the tropical Pacific. These results suggest that the Indian-Pacific Ocean interaction is a two-way process.

A Subtropical Cyclonic Gyre Associated with Interactions of the MJO and the Midlatitude Jet

2012 ◽  
Vol 140 (2) ◽  
pp. 343-357 ◽  
Author(s):  
John Molinari ◽  
David Vollaro
Keyword(s):  
Indian Ocean ◽  
Wave Breaking ◽  
Active Phase ◽  
La Niña ◽  
Boreal Summer ◽  
Northwest Pacific ◽  
Cyclonic Gyre ◽  
Exit Region ◽  
La Nina ◽  
The Indian Ocean

This paper describes a large cyclonic gyre that lasted several days in the northwest Pacific during July 1988. Cyclonic winds at 850 hPa extended beyond the 2000-km radius with a radius of maximum winds of 700–800 km. The gyre exhibited clear skies within and north of its center. Active convection extended 4000 km in longitude to its south. The Madden–Julian oscillation (MJO) was in its active phase in the Indian Ocean prior to gyre formation. Consistent with earlier studies, diabatic heating in the MJO was associated with an anomalous upper-tropospheric westerly jet over the northeast Asian coast and a jet exit region over the northwest Pacific. Repeated equatorward wave-breaking events developed downwind of the jet exit region. One such event left behind a region of lower-tropospheric cyclonic vorticity and convection in the subtropics that played a key role in the gyre formation. A second wave-breaking event produced strong subsidence north of the mature gyre that contributed to its convective asymmetry. Gyres from 1985 and 1989 were compared to the 1988 case. All three gyres developed during an active MJO in the Indian Ocean. Each gyre displayed the same strong convective asymmetry. Each developed in July or August during the climatological peak in breaking Rossby waves in the northwest Pacific. Finally, all of the gyres developed during La Niña at nearly the same location. This location and the convective structure of the gyres closely matched composite La Niña anomalies during boreal summer.

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