scholarly journals Preconditions for El Niño and La Niña onsets and their relation to the Indian Ocean

2005 ◽  
Vol 32 (5) ◽  
Author(s):  
Jong-Seong Kug
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
La Nina ◽  
The Indian Ocean

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.

scholarly journals Interactive Feedback between ENSO and the Indian Ocean

2006 ◽  
Vol 19 (9) ◽  
pp. 1784-1801 ◽  
Author(s):  
Jong-Seong Kug ◽  
In-Sik Kang
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Western Pacific ◽  
Easterly Wind ◽  
Mature Phase ◽  
La Nina ◽  
The Indian Ocean ◽  
The Western Pacific

Abstract A feedback process of the Indian Ocean SST on ENSO is investigated by using observed data and atmospheric GCM. It is suggested that warming in the Indian Ocean produces an easterly wind stress anomaly over Indonesia and the western edge of the Pacific during the mature phase of El Niño. The anomalous easterly wind in the western Pacific during El Niño helps a rapid termination of El Niño and a fast transition to La Niña by generating upwelling Kelvin waves. Thus, warming in the Indian Ocean, which is a part of the El Niño signal, operates as a negative feedback mechanism to ENSO. This Indian Ocean feedback appears to operate mostly for relatively strong El Niños and results in a La Niña one year after the mature phase of the El Niño. This 1-yr period of phase transition implies a possible role of Indian Ocean–ENSO coupling in the biennial tendency of the ENSO. Atmospheric GCM experiments show that Indian Ocean SST forcing is mostly responsible for the easterly wind anomalies in the western Pacific.

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.

scholarly journals Wind-Driven Response of the Northern Indian Ocean to Climate Extremes*

2007 ◽  
Vol 20 (13) ◽  
pp. 2978-2993 ◽  
Author(s):  
Tommy G. Jensen
Keyword(s):  
Indian Ocean ◽  
Ocean Circulation ◽  
Bay Of Bengal ◽  
El Niño ◽  
Arabian Sea ◽  
El Nino ◽  
Ocean Model ◽  
La Niña ◽  
Northern Indian Ocean ◽  
La Nina

Abstract Composites of Florida State University winds (1970–99) for four different climate scenarios are used to force an Indian Ocean model. In addition to the mean climatology, the cases include La Niña, El Niño, and the Indian Ocean dipole (IOD). The differences in upper-ocean water mass exchanges between the Arabian Sea and the Bay of Bengal are investigated and show that, during El Niño and IOD years, the average clockwise Indian Ocean circulation is intensified, while it is weakened during La Niña years. As a consequence, high-salinity water export from the Arabian Sea into the Bay of Bengal is enhanced during El Niño and IOD years, while transport of low-salinity waters from the Bay of Bengal into the Arabian Sea is enhanced during La Niña years. This provides a venue for interannual salinity variations in the northern Indian Ocean.

scholarly journals The Years of El Niño, La Niña, and Interactions with the Tropical Indian Ocean

2007 ◽  
Vol 20 (13) ◽  
pp. 2872-2880 ◽  
Author(s):  
Gary Meyers ◽  
Peter McIntosh ◽  
Lidia Pigot ◽  
Mike Pook
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Sea Surface ◽  
El Nino Southern Oscillation ◽  
La Nina ◽  
The Indian Ocean

Abstract The Indian Ocean zonal dipole is a mode of variability in sea surface temperature that seriously affects the climate of many nations around the Indian Ocean rim, as well as the global climate system. It has been the subject of increasing research, and sometimes of scientific debate concerning its existence/nonexistence and dependence/independence on/from the El Niño–Southern Oscillation, since it was first clearly identified in Nature in 1999. Much of the debate occurred because people did not agree on what years are the El Niño or La Niña years, not to mention the newly defined years of the positive or negative dipole. A method that identifies when the positive or negative extrema of the El Niño–Southern Oscillation and Indian Ocean dipole occur is proposed, and this method is used to classify each year from 1876 to 1999. The method is statistical in nature, but has a strong basis on the oceanic physical mechanisms that control the variability of the near-equatorial Indo-Pacific basin. Early in the study it was found that some years could not be clearly classified due to strong decadal variation; these years also must be recognized, along with the reason for their ambiguity. The sensitivity of the classification of years is tested by calculating composite maps of the Indo-Pacific sea surface temperature anomaly and the probability of below median Australian rainfall for different categories of the El Niño–Indian Ocean relationship.

scholarly journals Spatial and seasonal responses of precipitation in the Ganges and Brahmaputra river basins to ENSO and Indian Ocean dipole modes: implications for flooding and drought

2015 ◽  
Vol 15 (1) ◽  
pp. 147-162 ◽  
Author(s):  
M. S. Pervez ◽  
G. M. Henebry
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Indian Ocean Dipole ◽  
El Nino ◽  
La Niña ◽  
Ganges Basin ◽  
La Nina ◽  
Brahmaputra Basin ◽  
The Ganges ◽  
Seasonal Responses

Abstract. We evaluated the spatial and seasonal responses of precipitation in the Ganges and Brahmaputra basins as modulated by the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) modes using Global Precipitation Climatology Centre (GPCC) full data reanalysis of monthly global land-surface precipitation data from 1901 to 2010 with a spatial resolution of 0.5° × 0.5°. The GPCC monthly total precipitation climatology targeting the period 1951–2000 was used to compute gridded monthly anomalies for the entire time period. The gridded monthly anomalies were averaged for the years influenced by combinations of climate modes. Occurrences of El Niño alone significantly reduce (88% of the long-term average (LTA)) precipitation during the monsoon months in the western and southeastern Ganges Basin. In contrast, occurrences of La Niña and co-occurrences of La Niña and negative IOD events significantly enhance (110 and 109% of LTA in the Ganges and Brahmaputra Basin, respectively) precipitation across both basins. When El Niño co-occurs with positive IOD events, the impacts of El Niño on the basins' precipitation diminishes. When there is no active ENSO or IOD events (occurring in 41 out of 110 years), precipitation remains below average (95% of LTA) in the agriculturally intensive areas of Haryana, Uttar Pradesh, Rajasthan, Madhya Pradesh, and Western Nepal in the Ganges Basin, whereas precipitation remains average to above average (104% of LTA) across the Brahmaputra Basin. This pattern implies that a regular water deficit is likely, especially in the Ganges Basin, with implications for the agriculture sector due to its reliance on consistent rainfall for successful production. Historically, major droughts occurred during El Niño and co-occurrences of El Niño and positive IOD events, while major flooding occurred during La Niña and co-occurrences of La Niña and negative IOD events in the basins. This observational analysis will facilitate well-informed decision making in minimizing natural hazard risks and climate impacts on agriculture, and supports development of strategies ensuring optimized use of water resources in best management practice under a changing climate.

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