Upwelling along the coasts of Java and Sumatra and its relation to ENSO
TL;DR: The upwelling along the Java-Sumatra Indian Ocean coasts is a response to regional winds associated with the monsoon climate as discussed by the authors, which migrates westward and toward the equator during the southeast monsoon (June to October).
Abstract: Upwelling along the Java-Sumatra Indian Ocean coasts is a response to regional winds associated with the monsoon climate The upwelling center with low sea surface temperature migrates westward and toward the equator during the southeast monsoon (June to October) The migration path depends on the seasonal evolution of alongshore winds and latitudinal changes in the Coriolis parameter Upwelling is eventually terminated due to the reversal of winds associated with the onset of the northwest monsoon and impingement of Indian Ocean equatorial Kelvin waves Significant interannual variability of the Java-Sumatra upwelling is linked to ENSO through the Indonesian throughflow (ITF) and by anomalous easterly wind During El Nino episodes, the Java-Sumatra upwelling extends in both time (into November) and space (closer to the equator) During El Nino (La Nina), the ITF carries colder (warmer) water shallowing (deepening) thermocline depth and enhancing (reducing) upwelling strength
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TL;DR: The Indian Ocean Dipole (IOD) events are often triggered by ENSO but can also occur independently, subject to eastern tropical preconditioning as mentioned in this paper, and the Indian Ocean has been discovered to have a much larger impact on climate variability than previously thought.
Abstract: In recent years, the Indian Ocean (IO) has been discovered to have a much larger impact on climate variability than previously thought This paper reviews climate phenomena and processes in which the IO is, or appears to be, actively involved We begin with an update of the IO mean circulation and monsoon system It is followed by reviews of ocean/atmosphere phenomenon at intraseasonal, interannual, and longer time scales Much of our review addresses the two important types of interannual variability in the IO, El Nino–Southern Oscillation (ENSO) and the recently identified Indian Ocean Dipole (IOD) IOD events are often triggered by ENSO but can also occur independently, subject to eastern tropical preconditioning Over the past decades, IO sea surface temperatures and heat content have been increasing, and model studies suggest significant roles of decadal trends in both the Walker circulation and the Southern Annular Mode Prediction of IO climate variability is still at the experimental stage, with varied success Essential requirements for better predictions are improved models and enhanced observations
1,144 citations
Cites background from "Upwelling along the coasts of Java ..."
...this upwelling season (Figure 19) [Susanto et al., 2001; Xie et al., 2002]....
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TL;DR: In this article, a method of extended singular value decomposition analysis was developed to analyze the changing characteristics of A-AM anomalies during El Nino (La Nina) from its development to decay.
Abstract: Asian–Australian monsoon (A–AM) anomalies depend strongly on phases of El Nino (La Nina). Based on this distinctive feature, a method of extended singular value decomposition analysis was developed to analyze the changing characteristics of A–AM anomalies during El Nino (La Nina) from its development to decay. Two off-equatorial surface anticyclones dominate the A–AM anomalies during an El Nino—one over the south Indian Ocean (SIO) and the other over the western North Pacific (WNP). The SIO anticyclone, which affects climate conditions over the Indian Ocean, eastern Africa, and India, originates during the summer of a growing El Nino, rapidly reaches its peak intensity in fall, and decays when El Nino matures. The WNP anticyclone, on the other hand, forms in fall, attains maximum intensity after El Nino matures, and persists through the subsequent spring and summer, providing a prolonged impact on the WNP and east Asian climate. The monsoon anomalies associated with a La Nina resemble those durin...
672 citations
Cites background from "Upwelling along the coasts of Java ..."
...iation, such as the Java‐Sumatra coastal and equatorial upwelling (Saji et al. 1999; Webster et al. 1999), Indonesian throughflow ( Susanto et al. 2001 ), change of the barrier layer due to freshwater fluxes (Saji et al. 1999; AMPXW), and fluctuations of the thermocline due to oceanic wave adjustment (Murtugudde et al. 2000; Xie et al. 2002)....
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...…08:39 PM UTC iation, such as the Java–Sumatra coastal and equatorial upwelling (Saji et al. 1999; Webster et al. 1999), Indonesian throughflow (Susanto et al. 2001), change of the barrier layer due to freshwater fluxes (Saji et al. 1999; AMPXW), and fluctuations of the thermocline due to…...
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...The Indonesian throughflow, which carries colder water, could raise the thermocline and increases the Java‐Sumatra upwelling-induced cooling ( Susanto et al. 2001 )....
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...The Indonesian throughflow, which carries colder water, could raise the thermocline and increases the Java–Sumatra upwelling-induced cooling (Susanto et al. 2001)....
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TL;DR: It is shown that the time of firing and firing rate are dissociable, and can represent two independent variables: respectively the animal's location within the place field, and its speed of movement through the field.
Abstract: In the brain, hippocampal pyramidal cells use temporal as well as rate coding to signal spatial aspects of the animal's environment or behaviour. The temporal code takes the form of a phase relationship to the concurrent cycle of the hippocampal electroencephalogram theta rhythm. These two codes could each represent a different variable. However, this requires the rate and phase to vary independently, in contrast to recent suggestions that they are tightly coupled, both reflecting the amplitude of the cell's input. Here we show that the time of firing and firing rate are dissociable, and can represent two independent variables: respectively the animal's location within the place field, and its speed of movement through the field. Independent encoding of location together with actions and stimuli occurring there may help to explain the dual roles of the hippocampus in spatial and episodic memory, or may indicate a more general role of the hippocampus in relational/declarative memory.
594 citations
TL;DR: In this article, the authors analyzed ocean current and stratification data along with satellite-derived wind measurements, and found that during the boreal winter monsoon, the wind drives buoyant, low-salinity Java Sea surface water into the southern Makassar Strait, creating a northward pressure gradient in the surface layer of the strait.
Abstract: Approximately 10 million m3 x s(-1) of water flow from the Pacific Ocean into the Indian Ocean through the Indonesian seas. Within the Makassar Strait, the primary pathway of the flow, the Indonesian throughflow is far cooler than estimated earlier, as pointed out recently on the basis of ocean current and temperature measurements. Here we analyse ocean current and stratification data along with satellite-derived wind measurements, and find that during the boreal winter monsoon, the wind drives buoyant, low-salinity Java Sea surface water into the southern Makassar Strait, creating a northward pressure gradient in the surface layer of the strait. This surface layer 'freshwater plug' inhibits the warm surface water from the Pacific Ocean from flowing southward into the Indian Ocean, leading to a cooler Indian Ocean sea surface, which in turn may weaken the Asian monsoon. The summer wind reversal eliminates the obstructing pressure gradient, by transferring more-saline Banda Sea surface water into the southern Makassar Strait. The coupling of the southeast Asian freshwater budget to the Pacific and Indian Ocean surface temperatures by the proposed mechanism may represent an important negative feedback within the climate system.
299 citations
TL;DR: In this article, the authors investigated the thermocline flows related to the shallow overturning circulations and estimates of subduction and upwelling in the Indian Ocean and concluded that the roll is mostly confined to the surface-mixed layer and is of little consequence for the meridional heat transport.
218 citations
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TL;DR: An analysis of observational data over the past 40 years shows a dipole mode in the Indian Ocean: a pattern of internal variability with anomalously low sea surface temperatures off Sumatra and high seasurface temperatures in the western Indian Ocean, with accompanying wind and precipitation anomalies.
Abstract: For the tropical Pacific and Atlantic oceans, internal modes of variability that lead to climatic oscillations have been recognized1,2, but in the Indian Ocean region a similar ocean–atmosphere interaction causing interannual climate variability has not yet been found3. Here we report an analysis of observational data over the past 40 years, showing a dipole mode in the Indian Ocean: a pattern of internal variability with anomalously low sea surface temperatures off Sumatra and high sea surface temperatures in the western Indian Ocean, with accompanying wind and precipitation anomalies. The spatio-temporal links between sea surface temperatures and winds reveal a strong coupling through the precipitation field and ocean dynamics. This air–sea interaction process is unique and inherent in the Indian Ocean, and is shown to be independent of the El Nino/Southern Oscillation. The discovery of this dipole mode that accounts for about 12% of the sea surface temperature variability in the Indian Ocean—and, in its active years, also causes severe rainfall in eastern Africa and droughts in Indonesia—brightens the prospects for a long-term forecast of rainfall anomalies in the affected countries.
4,385 citations
TL;DR: The new NOAA operational global sea surface temperature (SST) analysis is described in this paper, which uses 7 days of in situ (ship and buoy) and satellite SST.
Abstract: The new NOAA operational global sea surface temperature (SST) analysis is described. The analyses use 7 days of in situ (ship and buoy) and satellite SST. These analyses are produced weekly and daily using optimum interpolation (OI) on a 1° grid. The OI technique requires the specification of data and analysis error statistics. These statistics are derived and show that the SST rms data errors from ships are almost twice as large as the data errors from buoys or satellites. In addition, the average e-folding spatial error scales have been found to be 850 km in the zonal direction and 615 km in the meridional direction. The analysis also includes a preliminary step that corrects any satellite biases relative to the in situ data using Poisson's equation. The importance of this correction is demonstrated using recent data following the 1991 eruptions of Mt. Pinatubo. The OI analysis has been computed using the in situ and bias-corrected satellite data for the period 1985 to present.
2,766 citations
TL;DR: It is concluded that the 1997–98 anomalies—in spite of the coincidence with the strong El Niño/Southern Oscillation event—may primarily be an expression of internal dynamics, rather than a direct response to external influences.
Abstract: Climate variability in the Indian Ocean region seems to be, in some aspects, independent of forcing by external phenomena such as the El Nino/Southern Oscillation1,2,3,4 But the extent to which, and how, internal coupled ocean–atmosphere dynamics determine the state of the Indian Ocean system have not been resolved Here we present a detailed analysis of the strong seasonal anomalies in sea surface temperatures, sea surface heights, precipitation and winds that occurred in the Indian Ocean region in 1997–98, and compare the results with the record of Indian Ocean climate variability over the past 40 years We conclude that the 1997–98 anomalies—in spite of the coincidence with the strong El Nino/Southern Oscillation event—may primarily be an expression of internal dynamics, rather than a direct response to external influences We propose a mechanism of ocean–atmosphere interaction governing the 1997–98 event that may represent a characteristic internal mode of the Indian Ocean climate system In the Pacific Ocean, the identification of such a mode has led to successful predictions of El Nino5; if the proposed Indian Ocean internal mode proves to be robust, there may be a similar potential for predictability of climate in the Indian Ocean region
1,913 citations
TL;DR: In this article, an ocean general circulation model is employed to investigate the dynamic and thermodynamic processes that caused the SSTAs associated with this and other similar Indian Ocean (IO) events.
Abstract: An anomalous climatic event occurred in the Indian Ocean (IO) region during 1997–1998, which coincided with a severe drought in Indonesia and floods in parts of eastern Africa. Cool sea surface temperature anomalies (SSTAs) were present in the eastern IO along and south of the equator. Beginning in July 1997, warm SSTAs appeared in the western IO, and they peaked in February 1998. An ocean general circulation model is employed to investigate the dynamic and thermodynamic processes that caused the SSTAs associated with this and other similar IO events. The eastern cooling resulted from unusually strong upwelling along the equator and Sumatra. The Sumatran upwelling was forced both locally by the stronger alongshore winds and remotely by equatorial and coastal Kelvin waves. By the end of 1997, weakening of the winds and the associated reduction in latent heat loss led to the elimination of the cold SST anomalies in the east. The western warming was initiated by weaker Southwest Monsoon winds and maintained by enhanced precipitation forcing, which resulted in a barrier layer structure. Analysis of the mixed layer temperature equation indicates that a downwelling Rossby wave contribution was crucial for sustaining the warming into February 1998. It is tempting to suppose that the 1997 event was related to the El Nino-Southern Oscillation (ENSO) event that took place in the Pacific at the same time. Indeed, weaker IO events occur quite regularly in the control run that evolve similarly to the 1997 event, and they are often but not always related to ENSO. We speculate that these events represent a natural mode of oscillation in the IO, which is externally forced by ENSO but also excited by ocean-atmosphere interactions internal to the IO.
556 citations
TL;DR: In this article, an empirical orthogonal function (EOF) analysis of anomalies of sea surface temperature (SST), dynamic height, and depth of the 20°C isotherm D 20 identifies two distinctive signals.
Abstract: The expendable bathythermograph (XBT) line Fremantle-Sunda Strait transects the eastern Indian Ocean between northwestern Australia and Java. It was established in 1983 with low-density sampling and upgraded to a frequently repeated line (>18 times per year) in 1987 to monitor currents. The observations during 1983 to 1994 are described and related to the field of wind stress. Variation of thermal structure shows a rich mixture of annual, semiannual, and interannual timescales. Empirical orthogonal function (EOF) analysis of anomalies of sea surface temperature (SST), dynamic height, and depth of the 20°C isotherm D 20 identifies two distinctive signals. The El Nino - Southern Oscillation (ENSO) signal (EOF 1) appears throughout the region and is strongest off the coast of Australia. A modulation of the annual signal (EOF 2) appears off the coast of Java. EOF 2 has a shorter timescale than the ENSO signal, and its temporal coefficients are correlated to zonal winds over the equatorial Indian Ocean. For both EOFs, anomalously low SST and dynamic height occur at the same time as anomalously shallow D 20 and vice versa for opposite anomalies. The XBT data are used with a climatological temperature-salinity relationship to calculate net, relative (0/400 dbar) geostrophic transports T through the section. For long timescales, T is representative of Indonesian throughflow. The variations associated with ENSO show a maximum during the La Nina of 1988-1989 and minima during the El Ninos of 1986-1987 and 1991-1994. The peak-to-trough amplitude of the ENSO signal is 5 Sv. The ENSO signal in throughflow is discussed in terms of earlier studies. For the shorter timescales, T is representative of currents from the Indian Ocean flowing in and out of the region between northwestern Australia and Indonesia, changing the volume of upper layer water stored there. Associated with EOF 2, a sharp peak in westward transport developed during May to October 1994.
436 citations