An Ecological Crisis in an Evolutionary Context: El Niño in the Eastern Pacific

¶The fields of sea-level height anomaly (SLHA) and surface zonal wind anomaly (SZWA) have been analyzed to investigate the typical evolution of spatial patterns during El Nino-Southern Oscillation (ENSO) events. Sea surface temperature (SST) changes during ENSO events are represented as an irregular interplay of two dominant modes, low-frequency mode and biennial mode. Cyclostationary principal component (PC) time series of the former variables are regressed onto the PC time series of the two dominant SSTA modes to find the spatial patterns of SLHA and SZWA consistent with the two SSTA modes. The two regressed patterns of SLHA explain a large portion of SLHA total variability. The reconstruction of SLHA using only the two components reasonably depicts major ENSO events. Although the low-frequency component of SST variability is much larger than the biennial component, the former does not induce strong Kelvin and Rossby waves. The biennial mode induces much stronger dynamical ocean response than the low-frequency mode. Further decomposition of the SLHA modes into Kelvin and Rossby components shows how these two types of equatorial waves evolve during typical ENSO events. The propagation and reflection of these waves are clearly portrayed in the regressed patterns leading to a better understanding of the wave mechanism in the tropical Pacific associated with ENSO. A close examination suggests that the delayed action oscillator hypothesis is generally consistent with the analysis results reported here. Rossby wave development in the central Pacific in the initiation stage of ENSO and the subsequent reflection of Kelvin waves at the western boundary seems to be an important mechanism for further development of ENSO. The development of Kelvin waves forced by the surface wind in the far-western Pacific cannot be ruled out as a possible mechanism for the growth of ENSO. While Kelvin waves in the far-western Pacific serve as an intiation mechanism of ENSO, they also cause the termination of existing ENSO condition in the central and eastern Pacific, thereby leading to a biennial oscillation over the tropical Pacific. The Kelvin waves from the western Pacific erode the thermocline structure in the central Pacific preventing further devlopment of ENSO and ultimately terminating it. It should be emphasized that this wave mechanism is clear and active only in the biennial mode.

More and more attention has been paid to the study of the impact of extreme climatic events on the ecological environment off the Changjiang River Estuary. In this study, the relationship between the chlorophyll concentration and ENSO (El Niño Southern Oscillation) events was studied. Several potential physical mechanisms between the ENSO and chlorophyll concentration were analyzed using observation and sensitivity experiments from a high-resolution ROMS-CoSiNE coupled model (Regional Ocean Modeling System-Carbon, Oxygen, Silicon, Nitrogen and Ecosystem) off the Changjiang River Estuary. Our results indicated that the April to August averaged chlorophyll concentration off the Changjiang River Estuary was significantly correlated with the December to February averaged ENSO indices in the previous winter. The 10 m wind speed and SST (Sea Surface Temperature) affected by an ENSO event had little effect on the chlorophyll concentration, while the discharge had a significant effect on the chlorophyll concentration off the Changjiang River Estuary, and the discharge was significantly and positively correlated with the ENSO indices. We tested the effect of interannual variations of the discharge and nutrients carried by discharge on the interannual variation in the chlorophyll concentration in the ENSO events. Two sensitivity experiments showed that when the nutrients in the freshwater discharge were kept as a constant seasonal cycle, the composite differences in the chlorophyll concentration between the positive and negative ENSO phases off the Changjiang River Estuary were reduced. When there were no nutrients in the freshwater discharge, the composite differences in the chlorophyll concentration between the positive and negative ENSO phases off the Changjiang River Estuary were reduced by one order of magnitude. The discharge can modify the stratification off the Changjiang River Estuary, and the nutrients carried by the discharge play a dominant role in determining the interannual variation of the chlorophyll concentration associated with the ENSO cycles.

Long-term time series of total primary production (PT) from 1969 through 2002, associated with ENSO (El Niño/Southern Oscillation) events are presented for the region off northern Baja California. PT was calculated using an empiric model in six inshore and offshore grids of the CalCOFI-IMECOCAL network in the southern California Current. In general, PT anomalies were positive from 1970 to 1975, with a period average of 0.024 GtC yr–1 for the study lines. PT changed to negative anomalies after ENSO 1976–77, with a decrease in productivity for at least 20 years, reinforced by the ENSO events of 1982–84, 1987–88, 1992–93 and 1997–98. Annual time series of PT anomalies show that during the ENSO events, values diminished by ~20% in the study area. Long-term PT changes (1976–97) originated a reduction of 0.007 GtC yr–1 (~70%), in relation to the higher production of the early 1970s (1970–75). Mean PT during 1997–98 was 0.014 GtC yr–1, increasing during 1999–2002 (0.023 GtC yr–1) toward similar values calculated for the early 1970s. Superposed Epoch Analysis proved the statistical association between the ENSO events and PT, with the probability of high production one year before (–1), diminishing during the key year (0), and recovering one year after (+1) the event off Baja California. Complete (1950–2002) PT time series showed greatest variance in the 1.43-year period. Small pelagic fish biomass estimated for inshore stations of lines 90 and 107 dropped below 200 × 103 tons after the 1976–77 period, with a recovering trend after 2000.

Southern Africa precipitation during December–March (DJFM), the height of the rainy season, is closely related with two modes of climate variability, El Niño–Southern Oscillation (ENSO) and the subtropical Indian Ocean dipole (SIOD). Recent research has found that the combined effects of ENSO and SIOD phasing are linked with changes to the regional southern Africa atmospheric circulation beyond the individual effects of either ENSO or SIOD alone. Here, the authors extend the recent research and examine the southern Africa land surface hydrology associated with the synchronous effects of ENSO and SIOD events using a macroscale hydrologic model, with particular emphasis on the evolution of the hydrologic conditions over three critical Transfrontier Conservation Areas: the Kavango–Zambezi Conservation Area, the Greater Limpopo Transfrontier Park, and the Kgalagadi Transfrontier Park. A better understanding of the climatic effects of ENSO and SIOD phase combinations is important for regional-scale transboundary conservation planning, especially for southern Africa, where both humans and wildlife are dependent on the timing and amount of precipitation. Opposing ENSO and SIOD phase combinations (e.g., El Niño and a negative SIOD or La Niña and a positive SIOD) result in strong southern Africa climate impacts during DJFM. The strong instantaneous regional precipitation and near-surface air temperature anomalies during opposing ENSO and SIOD phase combinations lead to significant soil moisture and evapotranspiration anomalies in the year following the ENSO event. By contrast, when ENSO and SIOD are in the same phase (e.g., El Niño and a positive SIOD or La Niña and a negative SIOD), the southern Africa climate impacts during DJFM are minimal.

Several previous studies have attempted to remove the effects of explosive volcanic eruptions and El Niño‐Southern Oscillation (ENSO) variability from time series of globally averaged surface and tropospheric temperatures. Such work has largely ignored the nonzero correlation between volcanic signals and ENSO. Here we account for this collinearity using an iterative procedure. We remove estimated volcano and ENSO signals from the observed global mean temperature data, and then calculate trends over 1979–1999 in the residuals. Residual trends are sensitive to the choice of index used for removing ENSO effects and to uncertainties in key volcanic parameters. Despite these sensitivities, residual surface and lower tropospheric (2LT) trends are almost always larger than trends in the raw observational data. After removal of volcano and ENSO effects, the differential warming between the surface and lower troposphere is generally reduced. These results suggest that the net effect of volcanoes and ENSO over 1979–1999 was to reduce globally averaged surface and tropospheric temperatures and cool the troposphere by more than the surface. ENSO and incomplete volcanic forcing effects can hamper reliable assessment of the true correspondence between modeled and observed trends. In the second part of our study, we remove these effects from model data and compare simulated and observed residual trends. Residual temperature trends are not significantly different at the surface. In the lower troposphere the statistical significance of trend differences depends on the experiment considered, the choice of ENSO index, and the volcanic signal decay time. The simulated difference between surface and tropospheric warming rates is significantly smaller than observed in 51 out of 54 cases considered. We also examine multiple realizations of model experiments with relatively complete estimates of natural and anthropogenic forcing. ENSO and volcanic effects are not removed from these integrations. As in the case of residual trends, model and observed raw trends are in good agreement at the surface but differ significantly in terms of the trend differential between the surface and lower troposphere. Observed and simulated lower tropospheric trends are not significantly different in 17 out of 24 cases. Our study highlights the large uncertainties inherent in removing volcano and ENSO effects from atmospheric temperature data. It shows that statistical removal of these effects improves the correspondence between modeled and observed temperature trends over the satellite era. Accounting for volcanoes and ENSO cannot fully explain the observed warming of the surface relative to the lower troposphere, or why this differential warming is not reproduced in the model simulations considered here.

Inverse methods are used to investigate changes in the precursors to El Nino Southern Oscillation (ENSO) events since the so-called 1970’s climate shift, associated with a change in the phase of the Interdecadal Pacific Oscillation (IPO). Linear Inverse Models (LIMs) constructed from tropical sea surface temperature, thermocline depth and zonal wind stress anomalies from each of the periods 1959–1978 and 1979–1998, are able to reproduce the major observed characteristics of ENSO, including its amplitude, frequency and time evolution. Each LIM possesses low-frequency and biennial ENSO modes, the former being both the least damped and the mode responsible for strongest pseudoresonance, as quantified via calculation of the resolvent norm. Because these modes are damped, ENSO variability is sustained in the stochastically forced LIMs by transiently growing perturbations, and predictability is determined by the character of the transiently growing subspace of perturbations. The optimal linear precursor over any given lead time is equivalent to the optimal perturbation of the LIM, that represents the most rapidly growing linear perturbation over that timescale. In both periods linear ENSO growth occurs through one of two trajectories associated with the 7 and 15 month optimal perturbations. The structure of these two optimal perturbations change significantly between the two periods, and their ability to predict ENSO degrades dramatically when applied to the alternate period. This suggests that ENSO precursors changed following the 1970s climate shift over both 7 and 15 month time-scales. In particular, while prior to the climate shift the heat content of the equatorial Pacific alone is a skillful ENSO predictor on 7 month lead times, afterwards Indian and south Atlantic sea surface temperature anomalies are inferred to have become important. Optimal ENSO growth over 15 months also contains a significant extra-Pacific contribution, and it is possible to skillfully hindcast some (but not all) ENSO events in both periods over 15 month lead times. Of the four considered linear precursors, only the 7 month optimal perturbation corresponding to the period 1959–1978 is able to skillfully hindcast ENSO amplitude from 1998 to the present, correctly predicting the development of El Nino conditions since February 2014. As such the optimal precursor structure appears to be related to the phase of the IPO, and we conjecture that extra-Pacific teleconnections may gain importance during a positive phase of the IPO.

A cyclostationary linear inverse model (CSLIM) is used to investigate the seasonal growth of tropical Pacific Ocean El Niño–Southern Oscillation (ENSO) events with canonical, central Pacific (CP), or eastern Pacific (EP) sea surface temperature (SST) characteristics. Analysis shows that all types of ENSO events experience maximum growth toward final states occurring in November and December. ENSO events with EP characteristics also experience growth into May and June, but CP events do not. A single dominant “ENSO mode,” growing from an equatorial heat content anomaly into a characteristic ENSO-type SST pattern in about 9 months (consistent with the delayed/recharge oscillator model of ENSO), is essential for the predictable development of all ENSO events. Notably, its seasonality is responsible for the late-calendar-year maximum in ENSO amplification. However, this ENSO mode alone does not capture the observed growth and evolution of diverse ENSO events, which additionally involve the seasonal evolution of other nonorthogonal Floquet modes. EP event growth occurs when the ENSO mode is initially “covered up” in combination with other Floquet modes. The ENSO mode’s slow seasonal evolution allows it to emerge while the other modes rapidly evolve and/or decay, leading to strongly amplifying and more predictable EP events. CP events develop when the initial state has a substantial contribution from Floquet modes with meridional mode–like SST structures. Thus, while nearly all ENSO events involve the seasonally varying ENSO-mode dynamics, the diversity and predictability of ENSO events cannot be understood without identifying contributions from the remaining Floquet modes. Significance Statement The purpose of this study is to identify structures that lead to seasonal growth of diverse types of El Niño–Southern Oscillation (ENSO) events. An important contribution from this study is that it uses an observationally constrained, empirically derived seasonal model. We find that processes affecting the evolution of diverse ENSO events are strongly seasonally dependent. ENSO events with eastern equatorial Pacific sea surface temperature (SST) characteristics are closely related to a single “ENSO mode” that resembles theoretical models of ENSO variability. ENSO events that have central equatorial Pacific SST characteristics include contributions from additional “meridional mode” structures that evolve via different physical processes. These findings are an important step in evaluating the seasonal predictability of ENSO diversity.

Research Article| February 01, 2000 Influence of El Niño–Southern Oscillation (ENSO) events on the evolution of central California's shoreline Curt D. Storlazzi; Curt D. Storlazzi 1Department of Earth Sciences and Institute of Marine Sciences, University of California, Santa Cruz, California 95064-1077 Search for other works by this author on: GSW Google Scholar Gary B. Griggs Gary B. Griggs 1Department of Earth Sciences and Institute of Marine Sciences, University of California, Santa Cruz, California 95064-1077 Search for other works by this author on: GSW Google Scholar Author and Article Information Curt D. Storlazzi 1Department of Earth Sciences and Institute of Marine Sciences, University of California, Santa Cruz, California 95064-1077 Gary B. Griggs 1Department of Earth Sciences and Institute of Marine Sciences, University of California, Santa Cruz, California 95064-1077 Publisher: Geological Society of America Received: 23 Apr 1998 Revision Received: 07 Apr 1999 Accepted: 19 May 1999 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2000) 112 (2): 236–249. https://doi.org/10.1130/0016-7606(2000)112<236:IOENOE>2.0.CO;2 Article history Received: 23 Apr 1998 Revision Received: 07 Apr 1999 Accepted: 19 May 1999 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Curt D. Storlazzi, Gary B. Griggs; Influence of El Niño–Southern Oscillation (ENSO) events on the evolution of central California's shoreline. GSA Bulletin 2000;; 112 (2): 236–249. doi: https://doi.org/10.1130/0016-7606(2000)112<236:IOENOE>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Significant sea-cliff erosion and storm damage occurred along the central coast of California during the 1982–1983 and 1997–1998 El Niño winters. This generated interest among scientists and land-use planners in how historic El Niño–Southern Oscillation (ENSO) winters have affected the coastal climate of central California. A relative ENSO intensity index based on oceanographic and meteorologic data defines the timing and magnitude of ENSO events over the past century. The index suggests that five higher intensity (relative values 4–6) and 17 lower intensity (relative values 1–3) ENSO events took place between 1910 and 1995. The ENSO intensity index correlates with fluctuations in the time series of cyclone activity, precipitation, detrended sea level, wave height, sea-surface temperature, and sea-level barometric pressure. Wave height, sea level, and precipitation, which are the primary external forcing parameters in sea-cliff erosion, increase nonlinearly with increasing relative ENSO event intensity. The number of storms that caused coastal erosion or storm damage and the historic occurrence of large-scale sea-cliff erosion along the central coast also increase nonlinearly with increasing relative event intensity. These correlations and the frequency distribution of relative ENSO event intensities indicate that moderate- to high-intensity ENSO events cause the most sea-cliff erosion and shoreline recession over the course of a century. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

This study is based on 27 series of daily water level (DWL) records in the downstream reaches of the Sinnamary River during the November to June rainy season: 22 series prior to dam closure, two series during filling and three series during dam operation. Five of these series (4 before and 1 during dam operation) corresponded with El Nino events, six (all prior to dam closure) with La Nina events. Before dam closure, monthly DWL were significantly higher during La Nina events from November to June, and significantly lower during El Nino events in January, February, May and June, than during years with no particular El Nino-Southern Oscillation (ENSO) event. Maximum monthly DWL were significantly higher during La Nina events than during years with no particular ENSO event in February, March and May only. The date of occurrence of the seasonal maximum DWL did not vary significantly with ENSO events. A greater number of days with high DWL were recorded during rainy seasons corresponding with La Nina events than during years with no particular ENSO event but El Nino events reduced the occurrence of high DWL in June only. Dam operation significantly increased monthly DWL in the downstream reaches of the Sinnamary River from November to January whatever the ENSO event considered. During the 1997-98 rainy season, which corresponded with an El Nino event, the dam amplified the impact of lower rainfall by completely removing high DWL. It is concluded that in the future, dam operators will have to restore periods of high DWL during rainy seasons characterised by El Nino events, or present nurseries will no longer play their role for sustaining fish diversity in the downstream reaches of the Sinnamary River.

Western US streamflow and atmospheric circulation patterns during El Niño-Southern Oscillation

This paper contributes to the climate-economy literature by analysing the role of weather patterns in influencing the transmission of global climate cycles to economic growth. More specifically, we focus on El Nino Southern Oscillation (ENSO) events and their interactions with local weather conditions, taking into account the heterogeneous and cumulative effects of weather patterns on economic growth and the asymmetry and nonlinearity in the global influence of ENSO on economic activity. Using data on 75 countries over the period 1975-2014, we provide evidence for the negative growth effects of ENSO events and show that there are substantial differences between its warm (El Nino) and cold (La Nina) phases and between climate zones. These differences are due to the heterogeneity in weather responses to ENSO events, known as teleconnections, which has so far not been taken into account by economists, and which will become more important in the climate-economy relationship given that climate change may substantially strengthen long-distance relationships between weather patterns around the world. We also show that the negative growth effects associated with these teleconnections are robust to the definition of ENSO events and more important over shorter meteorological onsets.

This paper analyzed the effects of various stages of El Nino southern oscillation (ENSO) events on the variability of temporal and spatial summer rainfall over northeast Ethiopia, where multiple hazards occurred. For this paper, precipitation and ENSO index data were used from 1983 to 2015. To investigate the relationship between summer rainfall and ENSO stages over the region, correlation and composite analysis was used. The composite analysis aimed to determine the link between sea surface temperature (SST) and rainfall in the study area. The findings show that there is a strong and positive connection between southern India, the Atlantic, and most of the western Pacific Ocean and rainfall in northeastern Ethiopia. The results also showed that La Nina’s development stage favors increased rainfall with extended spatial distribution over the region and that El Nino’s development stage favors less rainfall with the restricted spatial distribution. Future progress in the ENSO forecast is therefore important for future increases in summer rainfall in northeast Ethiopia.

An index capturing the anomalies of the zonal wind at 925 hPa from 1950 to 2010 was defined to explore the relationship between the fluctuations of the Caribbean low-level jet (CLLJ) and the main climate variability modes affecting the Intra-Americas Sea Region. El Niño Southern Oscillation (ENSO) events, here defined using the Niño 3.4 index, are found to be the most important variability modes for the jet anomalies, in agreement with previous studies. However, the Pacific Decadal Oscillation (PDO) and the Pacific/North American (PNA) teleconnection pattern also show significant correlations with the CLLJ anomaly index during February. The North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) reveal a possible interaction with the jet anomalies that could be connected with the cold fronts and cold air surges arriving to the Caribbean basin from the Northern Hemisphere during winter. A composite technique is used to explain the correlations with the Pacific indexes. We found that ENSO events are connected to CLLJ anomalies by modulating the sea-level pressure (SLP) near the east coast of the United States and the Aleutian Low. The pattern displayed by the SLP anomalies (SLPa) is also associated with the PNA. During warm (cold) ENSO phases, negative (positive) anomalies in the SLP field over the east coast of North America produce cyclonic (anticyclonic) circulations at low levels. However, the ENSO signal in the SLPa and the PNA pattern are modulated by the phases of the PDO. Results indicate that when the ENSO and PDO are in phase (out of phase), the SLPa signal is enhanced (weakened or cancelled), affecting the CLLJ anomalies in both direction and intensity, also changing the spatial distribution of precipitation.

Combined influence of ENSO and North Atlantic Oscillation (NAO) on Eurasian Steppe during 1982–2018

This study evaluates the relationships between El Nino-Southern Oscillation (ENSO) indices and South Florida hydrology and proposes applications to water management decision making. ENSO relations to the Upper Kissimmee Basin rainfall, watershed for Lake Okeechobee, and cumulative sea surface temperature (SST) anomalies at Nino 3.4 were evaluated. Additionally, relationship between ENSO and Lake Okeechobee inflows, Arbuckle Creek and Josephine Creek flows were analyzed. Hydrology of the northern watersheds of the South Florida water management system is linked to ENSO events. Dry season (November-May) rainfall and flows are higher than average during El Nino years and lower during La Nina years, at the 90% confidence level or higher. The relationship is strongest when the ENSO event is strong as shown with analysis of correlation. ENSO prediction has more certainty than hydrologic prediction for a region. Identifying ENSO and hydrologic relationships can aid water management decision making by providing a lead-time of months to mitigate drought or flood impacts. The ENSO tracking method, which was published in a previous study, is presented to track ENSO strength and event type to provide supplemental outlook on dry season rainfall for Lake Okeechobee operations. Lake Okeechobee, which is the main storage in the South Florida water management system, is regulated by a schedule with a limited band of stage fluctuation because of susceptibility of the Herbert Hoover Dike to wave erosion and seepage at high stages. An early decision making approach to storage management with respect to ENSO related hydrology, is presented based on tracking the strength of ENSO events.