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In July 1929, Dr Friedrich Ritter and Dore Strauch left their spouses and the turmoil of post–World War I Germany for the remote, uninhabited, and rugged volcanic island of Floreana in the Galapagos archipelago. Their dream was to live self-sufficiently in an idyllic tropical setting unspoiled by civilization. Wealthy yachters stopping at Floreana in the early 1930s reported on the couple's pioneering enterprise to the outside world. The news created a sensation that subsequently attracted other settlers, including a mysterious Viennese faux baroness who quickly sowed discord on the island. Not all the participants in this drama survived though. A prolonged drought gripped the island from 1933 to 1935 leading to food shortages that ultimately claimed the life of Dr. Ritter, a vegetarian who unwittingly ate tainted chicken out of desperation. The bizarre intrigues and struggles to endure on Floreana were chronicled in Dore Strauch's 1936 memoir Satan Came to Eden and a 2013 Hollywood documentary based on it. A story that has not been told is how an extended period of cold La Niña conditions in 1933–35 led to the drought that caused the food shortages. We use an atmospheric reanalysis and other data sources to describe these cold conditions and how they affected the human drama that unfolded on Floreana Island. The protracted La Niña impacted other parts of the globe and in particular was a major influence on development of the 1930s Dust Bowl in the southern plains of the United States. [ABSTRACT FROM AUTHOR]

The termination of Indian Ocean Dipole (IOD) events is examined in terms of equatorial wave dynamics. In situ and satellite observations combined with an output from a linear wave model are used in this study. Our emphasis is on the 1997 IOD event but our results apply to other positive IOD events as well. We find that the termination of anomalously cold sea surface temperature (SST) in the eastern pole of the dipole is associated with a warming tendency caused by the net surface heat fluxes. However, net surface heat fluxes alone cannot explain the total change in the SST. We show that during the peak phase of an IOD event, the weakening of zonal heat advection caused by eastern boundary-generated Rossby waves combined with the reduction of vertical entrainment and diffusion creates favorable conditions for surface heat fluxes to warm the SST in the eastern basin. [ABSTRACT FROM AUTHOR]

The Pacific Decadal Oscillation (PDO), the leading mode of Pacific decadal sea surface temperature variability, arises mainly from combinations of regional air-sea interaction within the North Pacific Ocean and remote forcing, such as from the tropical Pacific and the Atlantic. Because of such a combination of mechanisms, a question remains as to how much PDO variability originates from these regions. To better understand PDO variability, the equatorial Pacific and the Atlantic impacts on the PDO are examined using several 3-dimensional partial ocean data assimilation experiments conducted with two global climate models: the CESM1.0 and MIROC3.2m. In these partial assimilation experiments, the climate models are constrained by observed temperature and salinity anomalies, one solely in the Atlantic basin and the other solely in the equatorial Pacific basin, but are allowed to evolve freely in other regions. These experiments demonstrate that, in addition to the tropical Pacific's role in driving PDO variability, the Atlantic can affect PDO variability by modulating the tropical Pacific climate through two proposed processes. One is the equatorial pathway, in which tropical Atlantic sea surface temperature (SST) variability causes an El Niño-like SST response in the equatorial Pacific through the reorganization of the global Walker circulation. The other is the north tropical pathway, where low-frequency SST variability associated with the Atlantic Multidecadal Oscillation induces a Matsuno-Gill type atmospheric response in the tropical Atlantic-Pacific sectors north of the equator. These results provide a quantitative assessment suggesting that 12–29% of PDO variance originates from the Atlantic Ocean and 40–44% from the tropical Pacific. The remaining 27–48% of the variance is inferred to arise from other processes such as regional ocean-atmosphere interactions in the North Pacific and possibly teleconnections from the Indian Ocean. [ABSTRACT FROM AUTHOR]

A major open question about El Niño-Southern Oscillation (ENSO) is what causes ENSO amplitude asymmetry, with strong El Niños generally larger than strong La Niñas. The authors examine a leading hypothesis-that the ENSO state modifies the fetch and/or wind speed of westerly wind bursts (WWBs) that create asymmetric forcing and an asymmetric ENSO response. Further, in El Niño forecasts, the number of WWBs expected increases in the month following a strong WWB when compared with the month preceding it. Using a conceptual model, a relationship is derived between the magnitude of the westerly wind burst state dependence on ENSO and ENSO asymmetry. It is found that this relationship between the magnitude of the state dependence and ENSO asymmetry holds in both the observations and 21 coupled climate models. Finally, it is found that because of state-dependent westerly wind burst forcing, extreme El Niño events tend to be of the eastern Pacific variety. [ABSTRACT FROM AUTHOR]

El Niño-Southern Oscillation (ENSO) in the Pacific and the analogous Atlantic Niño mode are generated by processes involving coupled ocean-atmosphere interactions known as the Bjerknes feedback. It has been argued that the Atlantic Niño mode is more strongly damped than ENSO, which is presumed to be closer to neutrally stable. In this study the stability of ENSO and the Atlantic Niño mode is compared via an analysis of the Bjerknes stability index. This index is based on recharge oscillator theory and can be interpreted as the growth rate for coupled modes of ocean-atmosphere variability. Using observational data, an ocean reanalysis product, and output from an ocean general circulation model, the individual terms of the Bjerknes index are calculated for the first time for the Atlantic and then compared to results for the Pacific. Positive thermocline feedbacks in response to wind stress forcing favor anomaly growth in both basins, but they are twice as large in the Pacific compared to the Atlantic. Thermocline feedback is related to the fetch of the zonal winds, which is much greater in the equatorial Pacific than in the equatorial Atlantic due to larger basin size. Negative feedbacks are dominated by thermal damping of sea surface temperature anomalies in both basins. Overall, it is found that both ENSO and the Atlantic Niño mode are damped oscillators, but the Atlantic is more strongly damped than the Pacific primarily because of the weaker thermocline feedback. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) is a critical control on the atmosphere, and numerical models of atmosphere-ocean circulation emphasize its accurate prediction. Yet many models demonstrate large, systematic biases in simulated SST in the equatorial 'cold tongues' (expansive regions of net heat uptake from the atmosphere) of the Atlantic and Pacific oceans, particularly with regard to a central but little-understood feature of tropical oceans: a strong seasonal cycle. The biases may be related to the inability of models to constrain turbulent mixing realistically, given that turbulent mixing, combined with seasonal variations in atmospheric heating, determines SST. In temperate oceans, the seasonal SST cycle is clearly related to varying solar heating; in the tropics, however, SSTs vary seasonally in the absence of similar variations in solar inputs. Turbulent mixing has long been a likely explanation, but firm, long-term observational evidence has been absent. Here we show the existence of a distinctive seasonal cycle of subsurface cooling via mixing in the equatorial Pacific cold tongue, using multi-year measurements of turbulence in the ocean. In boreal spring, SST rises by 2 kelvin when heating of the upper ocean by the atmosphere exceeds cooling by mixing from below. In boreal summer, SST decreases because cooling from below exceeds heating from above. When the effects of lateral advection are considered, the magnitude of summer cooling via mixing (4 kelvin per month) is equivalent to that required to counter the heating terms. These results provide quantitative assessment of how mixing varies on timescales longer than a few weeks, clearly showing its controlling influence on seasonal cooling of SST in a critical oceanic regime. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) in the southwestern tropical Indian Ocean exerts a significant influence on global climate through its influence on the Indian summer monsoon and Northern Hemisphere atmospheric circulation. In this study, measurements from a long-term moored buoy are used in conjunction with satellite, in situ, and atmospheric reanalysis datasets to analyze the seasonal mixed layer heat balance in the thermocline ridge region of the southwestern tropical Indian Ocean. This region is characterized by a shallow mean thermocline (90 m, as measured by the 20°C isotherm) and pronounced seasonal cycles of Ekman pumping and SST (seasonal ranges of -0.1 to 0.6 m day-1 and 26°–29.5°C, respectively). It is found that surface heat fluxes and horizontal heat advection contribute significantly to the seasonal cycle of mixed layer heat storage. The net surface heat flux tends to warm the mixed layer throughout the year and is strongest during boreal fall and winter, when surface shortwave radiation is highest and latent heat loss is weakest. Horizontal heat advection provides warming during boreal summer and fall, when southwestward surface currents and horizontal SST gradients are strongest, and is close to zero during the remainder of the year. Vertical turbulent mixing, estimated as a residual in the heat balance, also undergoes a significant seasonal cycle. Cooling from this term is strongest in boreal summer, when surface wind and buoyancy forcing are strongest, the thermocline ridge is shallow (<90 m), and the mixed layer is deepening. These empirical results provide a framework for addressing intraseasonal and interannual climate variations, which are dynamically linked to the seasonal cycle, in the southwestern tropical Indian Ocean. They also provide a quantitative basis for assessing the accuracy of numerical ocean model simulations in the region. [ABSTRACT FROM AUTHOR]

Measurements from three long-term moored buoys are used to investigate the impact of barrier layer thickness (BLT) on the seasonal cycle of sea surface temperature (SST) in the central tropical North Atlantic Ocean. It is found that seasonal variations of the BLT exert a considerable influence on SST through their modulation of the vertical heat flux at the base of the mixed layer, estimated as the residual in the mixed layer heat balance. Cooling associated with this term is strongest when the barrier layer is thin and the vertical temperature gradient at the base of the mixed layer is strong. Conversely, thick barrier layers are associated with a significant reduction in the vertical temperature gradient at the base of the mixed layer, which suppresses the upward transfer of cooler water into the mixed layer. Forced ocean and coupled ocean–atmosphere models that do not properly simulate the barrier layer may have difficulty reproducing the observed seasonal cycle of SST in the tropical North Atlantic. [ABSTRACT FROM AUTHOR]

The article discusses the field experiment MISMO conducted in the central equatorial Indian Ocean from October to December 2006 with the key platforms of the research vessel (R/V) Mirai, a moored buoy array, and land-based sites in the Maldive Islands. The intensive observation period focused on the mature and decaying phases of Indian Ocean Dipole (IOD) event. The in situ atmospheric and oceanic measurements show the complexity of physical processes during convection's initiation linked with intraseasonal variability of the area. It stresses that further studies are needed to verify speculations concerning the relationship between the Madden-Julian oscillation (MJO) and IOD. However, MISMO is considered a challenging experiment to understand MJO from in situ observations.

The El Niño-Southern Oscillation (ENSO) cycle of alternating warm El Niño and cold La Niña events is the dominant year-to-year climate signal on earth. ENSO originates in the tropical Pacific through interactions between the ocean and the atmosphere, but its environmental and socioeconomic impacts are flet worldwide. Spurred on the powerful 1997-1998 El Niño, efforts to understand the causes and consequences of ENSO have greatly expanded in the past few years. These efforts reveal the breadth of ENSO's influence on the Earth system and the potential to exploit its predictability for societal benefit. However, many intertwined issues regarding ENSO dynamics, impacts, forecasting, and applications remain unresolved. Research to address these issues will not only lead to progress across a broad range of scientific disciplines but alos provide an opportunity to educate the public and policy makers about the importance of climate variability and change in the modern world. [ABSTRACT FROM AUTHOR]

The role of horizontal oceanic heat advection in the generation of tropical North and South Atlantic sea surface temperature (SST) anomalies is investigated through an analysis of the oceanic mixed layer heat balance. It is found that SST anomalies poleward of 10° are driven primarily by a combination of wind-induced latent heat loss and shortwave radiation. Away from the eastern boundary, horizontal advection damps surface flux–forced SST anomalies due to a combination of mean meridional Ekman currents acting on anomalous meridional SST gradients, and anomalous meridional currents acting on the mean meridional SST gradient. Horizontal advection is likely to have the most significant effect on the interhemispheric SST gradient mode through its impact in the 10°–20° latitude bands of each hemisphere, where the variability in advection is strongest and its negative correlation with the surface heat flux is highest. In addition to the damping effect of horizontal advection in these latitude bands, evidence for coupled wind–SST feedbacks is found, with anomalous equatorward (poleward) SST gradients contributing to enhanced (reduced) westward surface winds and an equatorward propagation of SST anomalies. [ABSTRACT FROM AUTHOR]

Vertical advection of temperature is the primary mechanism by which El Niño–Southern Oscillation (ENSO) time-scale sea surface temperature (SST) anomalies are generated in the eastern equatorial Pacific. Variations in vertical advection are mediated primarily by remote wind-forced thermocline displacements, which control the temperature of water upwelled to the surface. However, during some ENSO events, large wind stress variations occur in the eastern Pacific that in principle should affect local upwelling rates, the depth of the thermocline, and SST. In this study, the impact of these wind stress variations on the eastern equatorial Pacific is addressed using multiple linear regression analysis and a linear equatorial wave model. The regression analysis indicates that a zonal wind stress anomaly of 0.01 N m-2 leads to approximately a 1°C SST anomaly over the Niño-3 region (5°N–5°S, 90°–150°W) due to changes in local upwelling rates. Wind stress variations of this magnitude occurred in the eastern Pacific during the 1982/83 and 1997/98 El Niños, accounting for about 1/3 of the maximum SST anomaly during these events. The linear equatorial wave model also indicates that depending on the period in question, zonal wind stress variations in the eastern Pacific can work either with or against remote wind stress forcing from the central and western Pacific to determine the thermocline depth in the eastern Pacific. Thus, zonal wind stress variations in the eastern Pacific contribute to the generation of interannual SST anomalies through both changes in local upwelling rates and changes in thermocline depth. Positive feedbacks between the ocean and atmosphere in the eastern Pacific are shown to influence the evolution of the surface wind field, especially during strong El Niño events, emphasizing the coupled nature of variability in the region. Implications of these results for understanding the character of event-to-event differences in El Niño and La Niña are discussed. [ABSTRACT FROM AUTHOR]

The output from an ocean general circulation model driven by observed surface forcing (1958–97) is used to examine the evolution and relative timing of the different branches of the Pacific Subtropical–Tropical Cells (STCs) at both interannual and decadal time scales, with emphasis on the 1976–77 climate shift. The STCs consist of equatorward pycnocline transports in the ocean interior and in the western boundary current, equatorial upwelling, and poleward flow in the surface Ekman layer. The interior pycnocline transports exhibit a decreasing trend after the mid-1970s, in agreement with observational transport estimates, and are largely anticorrelated with both the Ekman transports and the boundary current transports at the same latitudes. The boundary current changes tend to compensate for the interior changes at both interannual and decadal time scales. The meridional transport convergence across 9°S and 9°N as well as the equatorial upwelling are strongly correlated with the changes in sea surface temperature (SST) in the central and eastern equatorial Pacific. However, meridional transport variations do not occur simultaneously at each longitude, so that to understand the phase relationship between transport and SST variations it is important to consider the baroclinic ocean adjustment through westward-propagating Rossby waves. The anticorrelation between boundary current changes and interior transport changes can also be understood in terms of the baroclinic adjustment process. In this simulation, the pycnocline transport variations appear to be primarily confined within the Tropics, with maxima around 10°S and 13°N, and related to the local wind forcing; a somewhat different perspective from previous studies that have emphasized the role of wind variations in the subtropics. [ABSTRACT FROM AUTHOR]

Abstract: An unprecedented compilation of Sea Surface Salinity (SSS) data collected in the three tropical oceans (30°N–30°S) is examined for the period 1970–2003. The SSS data are derived mainly from 13 trans-oceanic Voluntary Observing Ship tracks and from 35 TAO/TRITON and 13 PIRATA mooring sites. Owing to the climatic importance of SSS, the data are used to present an overview of SSS variability, to evaluate the SSS time and space scales, and to assess the ability of the present in situ (and future satellite) observing system to adequately resolve the variability of interest. After quality control procedures, SSS is analyzed both as gridded fields (2° longitude, 1° latitude, 1 month) and as high-resolution records (0.02° latitude/longitude and one day). The gridded fields are used to describe the mean, standard deviation, and seasonal SSS cycle, as well as to estimate the characteristic scales for SSS. Results show that the monthly standard deviation of SSS mostly ranges within 0.1–0.3, except in regions with strong seasonal cycles (e.g., in the Atlantic and Pacific Inter-Tropical Convergence Zones and south of India) or prominent ENSO (El Niño Southern Oscillation) signals (e.g., in the western Pacific warm pool and in the South Pacific Convergence Zone) where standard deviations can range from 0.4 up to 1.4. The time scale for SSS is generally less than 3 months, while it reaches 4–8 months in regions where the variability is controlled mostly by ENSO. The meridional scale for SSS is generally 2–3° latitude, increasing to 4–7° latitude in the western Pacific warm pool and poleward of 10–20° latitude. The zonal scale for SSS is 15–20° longitude in the equatorial Pacific and in the South Pacific Convergence Zone (SPCZ), and 4–7° longitude along 8–10°N in the Indian Ocean. Decorrelation scales in the western Pacific warm pool tend to be smaller during La Niña time periods, with values approaching those found for the central Pacific. The signal to noise ratios are on average of the order of 1–1.5, meaning that part of the variability is not resolved from gridded fields. High-resolution records are thus used to assess the short time/space SSS variability on time and space scales shorter than the above-noted grid sizes. It is shown that the mean expected variability of SSS over a period of 10 days in a 1° latitude and 2° longitude box (i.e., the resolution requirement for the Global Ocean Data Assimilation Experiment (GODAE)) is about 0.2, with, however, notable regional differences in this value. The implications of this short time/space variability are discussed in the context of the 0.1 SSS GODAE accuracy requirement. [Copyright &y& Elsevier]

An El Niño of moderate intensity developed in the tropical Pacific in 2002/03. This event, though not as strong as the 1997/98 El Niño, had significant impacts on patterns of weather variability worldwide. The evolution of the 2002/03 El Niño is documented through comprehensive satellite and in situ observations from the El Niño–Southern Oscillation (ENSO) Observing System. These observations underscore the importance of both episodic atmospheric forcing and large-scale low-frequency ocean–atmosphere interactions in the development of the event. * Pacific Marine Environmental Laboratory Contribution 2584 and Joint Institute for the Study of the Atmosphere and Ocean Contribution 990 [ABSTRACT FROM AUTHOR]

The atmospheric response to the oceanic forcing in the eastern Pacific along the northern equatorial sea surface temperature (SST) front is investigated in terms of sensible and latent heat flux during the 6-month period from 28 July 1999 to 27 January 2000 and the 7-month period from 28 June 2000 to 27 January 2001. Of particular interest is the atmospheric boundary layer (ABL) response to oceanic tropical instability waves (TIWs) that distort the SST front during May-January in normal years. In previous studies, time series of surface heat fluxes clearly show the influence of TIWs, but the relationship to spatial patterns of SST and wind speed has been inferred only from sparse in situ data. In this study, satellite observations are used as a basis for compositing in situ data from moorings to compensate for the lack of a spatially dense mooring array. The variability in the position of the SST front caused by westward-propagating TIWs enables fixed mooring locations to measure the ABL response from a large range of locations relative to the front. The satellite data enable determination of the precise location of the mooring relative to the front. The advantage of this strategy is the recurring measurement of the ABL response to the SST front over the 13-month period considered here. The results indicate that the TIW-induced perturbations of sensible heat flux are spatially shifted in phase toward the east relative to the perturbations of SST The maximum fluxes of sensible heat are not centered directly over the warmest water, but are shifted toward the portion of the frontal region where a disequilibrium boundary layer is expected due to the advection of colder air from the equatorial region. The latent heat flux pattern is approximately in phase with the SST, with only a slight shift to the east. The changes of sensible and latent heat fluxes across the SST front have typical magnitudes of about 12 and 125 W m[sup -2], respectively. The sensible and latent... [ABSTRACT FROM AUTHOR]

This paper describes observed changes in surface winds, sea surface temperature (SST), and the volume of water warmer than 208C (WWV) in the equatorial Pacific Ocean for the period 1980--99. The purpose is to test recent hypotheses about the relationship between variations in WWV and the El Nino--Southern Oscillation (ENSO) cycle. The results confirm inferences based on theory, models, and previous empirical analyses using proxy data (namely sea level) that ENSO involves a recharge and discharge of WWV along the equator and that the cyclic nature of ENSO results from a disequilibrium between zonal winds and zonal mean thermocline depth. The authors also find that the magnitude of ENSO SST anomalies is directly related to the magnitude of zonal mean WWV anomalies. Furthermore, for a given change in equatorial WWV, the corresponding warm El Nino SST anomalies are larger than the corresponding cold La Nina anomalies. This asymmetry between the warm and cold phases of the ENSO cycle implies differences in the relative importance of physical processes controlling SST during El Nino and La Nina events. [ABSTRACT FROM AUTHOR]

Discusses factors which contributed to the strength of the 1997-98 El Nino. The physical mechanisms responsible; Role of the El Nino/Southern Oscillation (ENSO); Large-scale ocean-atmosphere interactions and equatorial ocean dynamics; The Madden-Julian Oscillation (MJO) and the Pacific Decadal Oscillation (PDO); Global warming trends and the ENSO cycle; Ideas from computer models; Complexity of the problem.

A summary is presented of an article published online at http://dx.doi.org/10.1126/science.aav4236 concerning pantropical climate interactions such as the El Niño-Southern Oscillation (ENSO) climate system. It comments on the influence that tropical ocean-atmosphere interactions can have on climate systems and the impact that Indian and Atlantic Oceans can have on ENSO. It speculates on how correcting systematic model errors in the Atlantic could have on future climate change projections.