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A combination of careful harmonic analysis and high-resolution numerical modelling of tides in altimeter data from TOPEX/Poseidon and ERS-2 satellites allows detailed calculation of seasonal and interannual variability of sea level in coastal areas of the north-east Pacific Ocean. These calculations show large changes in sea level in marginal seas during the 1997-8 El Niño and La Niña events, as well as providing information on the origin and life cycle of large anticyclonic eddies, observed to be generated off the west coast of Canada. [ABSTRACT FROM AUTHOR]

The El Niño phenomenon – and its associated phenomena El Niño Southern Oscillation (ENSO) and La Niña – have become probably the most well-known forms of natural climatic variability. El Niño forecasts underpin regional Climate Outlook Forums in many parts of the world. The declaration of El Niño conditions can unlock development aid money and El Niño events commonly receive widespread media coverage. Yet 'El Niño' has not always meant what it does today. The name was originally applied to an annually-occurring ocean current that affected northern Peru and Ecuador, so called because it arrived at Christmas (the Christ Child). The transition in meaning to a complex global phenomenon was related as much to commercial and geopolitical priorities as to the oceanic and atmospheric observations that underpin theories of El Niño dynamics. In this paper, I argue that scientific conceptualisations of El Niño are an example of path dependency. Badging ocean-atmosphere variability as 'El Niño' is unnecessary either for the advancement of science or effective disaster risk reduction; in fact, current definitions are confusing and can create problems in preparing for El Niño-related hazards, as occurred with the 2017 'coastal' El Niño in Peru. This paper outlines the historical processes that led to the current conceptualisations of El Niño and suggests an alternative way of understanding ocean-atmosphere dynamics in the Pacific and beyond. It then considers the implications of this path-dependency on El Niño's ontological politics; that is, who gets to define El Niño, and to what end. [ABSTRACT FROM AUTHOR]

Tropical and extra-tropical storms generate extreme waves, impacting both nearby and remote regions through swell propagation. Despite their devastating effects in tropical areas, the contribution of tropical cyclones (TCs) to global wave-induced coastal risk remains unknown. Here, we enable a quantitative assessment of TC's role in extreme waves approaching global coastlines, by designing twin oceanic wave simulations with and without realistic TC wind forcing. We find that TCs substantially contribute to extreme breaking heights in tropical regions (35-50% on average), reaching 100% in high-density TC areas like the North Pacific. TCs also impact remote TC-free regions, such as the equatorial Pacific experiencing in average 30% of its extreme wave events due to TCs. Interannual variability amplifies TC-induced wave hazards, notably during El Niño in the Central Pacific, and La Niña in the South China Sea, Caribbean Arc, and South Indian Ocean coastlines. This research offers critical insights for global risk management and preparedness. This paper shows that tropical cyclones contribute between 40% and 100% of the extreme wave events approaching coastlines in basins prone to tropical cyclone activity, while they can also impact remote areas via swell propagation across the ocean. [ABSTRACT FROM AUTHOR]

Much research has raised concerns about how a warming planet will interact with natural cyclical climatic variations, and the implications for the resilience and vulnerability of coastal communities. As the anticipated effects of climate change will continue to intensify, it is necessary to understand the response and adaptive capacity of individuals and communities. Coastal communities in Ecuador have evolved in an environment of such cyclical climatic variations referred to as El Niño-Southern Oscillation (ENSO) and La Niña. These climatic events are frequently characterized by extreme variations in precipitation, violent storms, and coastal flooding during El Niño and lowered sea water temperatures and drought during La Niña. This paper draws on survey data and long-term ethnographic research in Ecuadorian coastal communities to explore how fishers understand the impacts of ENSO and implications for their livelihood decisions and resilience to climate variability. The results suggest that fishers along the coast of Ecuador understand and respond differentially to the impacts of ENSO depending on social, cultural, environmental, and geographical factors. These differential levels of response suggest that livelihood diversification may uphold social resilience, which has implications for how coastal communities may adapt to the increasingly harsh weather conditions predicted by many climate models. Our findings further suggest that the impacts of El Niño are more salient than the impacts of La Niña; these findings have significant implications for fisheries management and science communication. [ABSTRACT FROM AUTHOR]

The intricate interplay of oceanic-atmospheric variations has intensified erosive processes on sandy beaches in recent decades, with climate change expected to exacerbate these impacts in the future. Projections for the southern Atlantic and Pacific regions of continental Latin America predict increased extreme events and heightened impacts on sandy beaches, highlighting disparities in studies addressing coastal erosion and its causes. To address these risks, a systematic review is proposed to analyze historical trends and projections, aiming to inform local-level studies and management strategies for at-risk coastal communities. Reviewing 130 research papers, insights reveal the influence of climatic events like El Niño and La Niña on coastal dynamics, as well as the effects of storm intensification and extreme events such as high-intensity waves and storm surges on Latin American coasts, resulting in ecosystem, economic, and infrastructure losses. Projections indicate a rise in the population inhabiting Low Elevation Coastal Zones (LECZ) by the century's end, emphasizing the urgent need for effective management and planning. Community engagement in erosion monitoring and adaptation programs is crucial for addressing these challenges and developing robust, sustainable, long-term adaptation strategies. This study aims to enhance the understanding of coastal erosion in Latin American communities addressing future coastal risks. [ABSTRACT FROM AUTHOR]

The yellowfin tuna represents a significant fishery resource in the Pacific Ocean. Its resource endowment status and spatial variation mechanisms are intricately influenced by marine environments, particularly under varying climate events. Consequently, investigating the spatial variation patterns of dominant environmental factors under diverse climate conditions, and understanding the response of yellowfin tuna catch volume based on the spatial heterogeneity among these environmental factors, presents a formidable challenge. This paper utilizes comprehensive 5°×5° yellowfin tuna longline fishing data and environmental data, including seawater temperature and salinity, published by the Western and Central Pacific Fisheries Commission (WCPFC) and the Inter-American Tropical Tuna Commission (IATTC) for the period 2000–2021 in the Pacific Ocean. In conjunction with the Niño index, a multiscale geographically weighted regression model based on geographically weighted principal component analysis (GWPCA-MGWR) and spatial association between zones (SABZ) is employed for this study. The results indicate the following: (1) The spatial distribution of dominant environmental factors affecting the catch of Pacific yellowfin tuna is primarily divided into two types: seawater temperature dominates in the western Pacific Ocean, while salinity dominates in the eastern Pacific Ocean. When El Niño occurs, the area with seawater temperature as the dominant environmental factor in the western Pacific Ocean further extends eastward, and the water layers where the dominant environmental factors are located develop to deeper depths; when La Niña occurs, there is a clear westward expansion in the area with seawater salinity as the dominant factor in the eastern Pacific Ocean. This change in the spatial distribution pattern of dominant factors is closely related to the movement of the position of the warm pool and cold tongue under ENSO events. (2) The areas with a higher catch of Pacific yellowfin tuna are spatially associated with the dominant environmental factor of mid-deep seawater temperature (105–155 m temperature) to a greater extent than other factors, the highest correlation exceeds 70%, and remain relatively stable under different ENSO events. The formation of this spatial association pattern is related to the vertical movement of yellowfin tuna as affected by subsurface seawater temperature. (3) The GWPCA-MGWR model can fully capture the differences in environmental variability among subregions in the Pacific Ocean under different climatic backgrounds, intuitively reflect the changing areas and influencing boundaries from a macro perspective, and has a relatively accurate prediction on the trend of yellowfin tuna catch in the Pacific Ocean. [ABSTRACT FROM AUTHOR]

Mathematical algorithms relate satellite data of ocean color with the surface Chlorophyll-a concentration (Chl-a), a proxy of phytoplankton biomass. These mathematical tools work best when they are adapted to the unique bio-optical properties of a particular oceanic province. Ocean color algorithms should also consider that there are significant differences between datasets derived from different sensors. Common solutions are to provide different parameters for each sensor or use merged satellite data. In this paper, we use satellite data from the Copernicus merged product suite and in situ data from the southernmost part of the California Current System to test two widely used global algorithms, OCx and CI, and a regional algorithm, CalCOFI2. The OCx algorithm yielded the most favorable results. Consequently, we regionalized it and conducted further testing, leading to significant improvements, especially in eutrophic and oligotrophic waters. The database was then separated according to (a) dynamic boundaries in the area, (b) bio-optical properties, and (c) climatic conditions (El Niño/La Niña). Regional algorithms were obtained and tested for each partition. The Chl-a retrievals for each model were tested and compared. The best fit for the data was for the regional algorithms that considered the climatic conditions (El Niño/La Niña). These results will allow for the construction of consistent regionally adapted time series and, therefore, will demonstrate the importance of El Niño/La Niña events on the bio-optical properties of the area. [ABSTRACT FROM AUTHOR]

In this paper, the global distribution of precipitation for 2023, in terms of global totals and regional anomaly patterns, is analyzed using information from the new Global Precipitation Climatology Project (GPCP) V3.2 Monthly product, including how the precipitation amounts and patterns from 2023 fit into the longer record from 1983–2023. The tropical pattern of anomalies for 2023 is dominated by the effect of the El Nino which began during the Northern Hemisphere spring, after three plus years of La Nina conditions. The transition from La Nina conditions through 2022 shows the rapid change in many regional features from positive to negative anomalies or the reverse. Comparison of the observed regional trend maps with climate model results indicates similarity between the observations and the model results forced by observed SSTs, while the "free-running" model ensemble shows only a broad general agreement over large regions. Global total precipitation shows about a 3% range over the span of data, with El Nino and La Nina years prominent as positive and negative features, with 2023 showing a small positive global anomaly. The ITCZ (Inter-Tropical Convergence Zone) latitude band, 0–10° N, sets a record high mean rain rate in 2023 after a steady upward trend over the decades, probably a response related to global warming. [ABSTRACT FROM AUTHOR]

In the California Current System (CCS), changes in the phenology (i.e., seasonal timing) of coastal upwelling alter the functioning of this productive marine ecosystem. Recently developed coastal upwelling indices that account for upwelling strength and nutrient flux to the surface provide a more complete understanding of bottom‐up forcing in the region. Using these indices, we describe CCS upwelling phenological variability in vertical transport and nutrient flux. Physical and biogeochemical spring transitions generally co‐occur in winter or spring, followed by increased upwelling and nutrient flux. In the latter half of the year, upwelling continues but nutrient flux wanes as declining source nutrient concentrations limit the biological efficacy of coastal upwelling. Earlier spring transitions and higher season‐integrated upwelling intensity occur during strong La Niña events at all latitudes, driven largely by stronger alongshore wind stress. Understanding phenological changes in coastal upwelling is critical, as they could have significant ecosystem consequences. Plain Language Summary: In the California Current System (CCS), coastal upwelling carries nutrient‐rich waters to the surface, supporting primary production and driving the coastal ecosystem. This upwelling varies on a seasonal and interannual basis, as reflected in recently developed indices that account for the amount of water upwelled to the surface as well as the amount of nutrients carried in that water. Generally upwelling and nutrient transport are high in the first half of the year. Upwelling persists into the second half of the year, but nutrient transport decreases as the deep‐water sources of these nutrients are depleted. Upwelling in the CCS is also affected by the El Niño Southern Oscillation. During La Niña conditions, strong trade winds enhance upwelling and nutrient transport on the California coast. This paper presents regional, seasonal and interannual patterns of upwelling and nutrient delivery in the CCS, which are important drivers of change to this coastal ecosystem. Key Points: We define new upwelling phenology indices for the California Current System that include nutrient transportWe identify spatial, seasonal, and interannual patterns of upwelling and nutrient deliveryWe relate the physical mechanisms of coastal upwelling with its biological efficacy [ABSTRACT FROM AUTHOR]

This paper scrutinizes Pakistan's acute water scarcity issues driven by population growth, diminishing supply, and recurrent droughts exacerbated by meteorological phenomena like La Nina. Regions such as Baluchistan and Sindh face severe water stress, jeopardizing livelihoods and potentially precipitating internal displacement, necessitating immediate and decisive governmental action. The absence of a coherent national water policy further complicates challenges in water storage, irrigation, and inter-provincial relations, potentially straining political dynamics. Through a comprehensive evaluation of Pakistan's water resources, this study identifies critical imperatives requiring urgent attention from policymakers. Proposed recommendations advocate for the development and implementation of a robust national water policy, strategic investments in modernized storage and irrigation infrastructure, promotion of water conservation initiatives, fostering inter-provincial collaboration, and the pursuit of cutting-edge sustainable water technologies. The successful execution of these measures would not only optimize water resource management but also underscore the government's commitment to ensuring national stability and prosperity amidst challenging environmental conditions. [ABSTRACT FROM AUTHOR]

We examine the magnitude of ENSO-correlated variations in wind-stress curl and ocean bottom pressure in the North Pacific between 1992 until 2010, using satellite observations and model output. Our analysis indicates that while there are significant fluctuations correlated with some El Niño and La Niña events, the correlation is still relatively low. Moreover, the ENSO-correlated variability explains only 50% of the non-seasonal, low-frequency variance. There are significant residual fluctuations in both wind-stress curl and ocean bottom pressure in the region with periods of 4-years and longer. One such fluctuation began in late 2002 and has been observed by the Gravity Recovery and Climate Experiment (GRACE). Even after accounting for ENSO variations, there is a significant trend in ocean bottom pressure in the region, equivalent to 0.7±0.3 cmyr-1 of sea level from January 2003 until December 2008, which is confirmed with steric-corrected altimetry. Although this low-frequency fluctuation does not appear in an ocean model, we show that the winds used to force the model have a significantly reduced trend that is inconsistent with satellite observations over the same time period. [ABSTRACT FROM AUTHOR]

During July and August of 2022, the Yangtze River Basin (YRB) experienced its most extreme high temperature (EHT) event since 1979, resulting in large numbers of human casualties and severe economic losses. This paper reveals the spatial and temporal features of the EHT over the YRB (YRB-EHT) in 2022 and disentangles its extreme nature from a historical perspective. Results showed the following: 1) The record-breaking YRB-EHT was directly caused by the adiabatic heating associated with an anomalous barotropic high pressure (or heat dome) and descending motion in the region. The intensified and westward-shifted western North Pacific subtropical high and eastward-extended South Asian high played critical roles in the formation of the heat dome and descending motion anomaly. 2) Convection anomalies over the tropical Atlantic and Pacific induced by the reintensified La Niña–like Pacific sea surface temperature anomaly pattern, along with the strong positive North Atlantic Oscillation (NAO), were the key contributing factors to the formation of the barotropic high pressure anomaly and YRB-EHT. 3) A physics-based empirical simulation model constructed using the factors of the NAO and tropical convection successfully reproduced the historical year-to-year variation of YRB temperatures, as well as the extreme in 2022, implying that the unprecedented 2022 YRB-EHT had universal dynamic origins. This study highlights the importance of the combined impacts of tropical and extratropical forcings in the record-breaking YRB-EHT in 2022, and thus may provide useful clues for seasonal predictions of summer mean or extreme temperatures in the YRB. Significance Statement: Extreme high temperatures hit the Yangtze River Basin (YRB) in summer 2022, causing large numbers of human casualties and severe economic losses. Here, from a historical perspective, we disentangle the dynamic origins of these high temperatures over the YRB. Based on evidence from both observations and model simulations, the present study highlights the importance of the combined impacts of tropical and extratropical routes of influence on these extremely high temperatures in the YRB, and thus may provide useful clues for seasonal predictions of YRB summer mean or extreme temperatures. [ABSTRACT FROM AUTHOR]

The surface currents in coastal areas are closely related to the ecological environment and human activities, and are influenced by both local and remote factors of different timescales, resulting in complex genesis and multi-timescale characteristics. In this research, 9-year-long, hourly high-frequency radar (HFR) surface current observations are utilized together with satellite remote sensing reanalysis products and mooring data, and based on the Empirical Orthogonal Function (EOF) and correlation analysis, we revealed the multi-timescale characteristics of the surface currents in Fremantle Sea (32°S), Southwestern Australia, and explored the corresponding driving factors as well as the impact of El Niño-Southern Oscillation (ENSO) on the nearshore currents. Results show that the currents on the slope are dominated by the southward Leeuwin Current (LC), and the currents within the shelf are dominated by winds, which are subject to obvious diurnal and seasonal variations. The strong bathymetry variation there, from a wide shelf in the north to a narrow shelf in this study region, also plays an important role, resulting in the frequent occurrence of nearshore eddies. In addition, the near-zonal winds south of 30°S in winter contribute to the interannual variability of the Leeuwin Current at Fremantle, especially in 2011, when the onshore shelf circulation is particularly strong because of the climatic factors, together with the wind-driven offshore circulation, which results in significant and long-lasting eddies. The southward Leeuwin Current along Southwestern Australia shows a strong response to interannual climatic variability. During La Niña years, the equatorial thermal anomalies generate the westward anomalies in winds and equatorial currents, which in turn strengthen the Leeuwin Current and trigger the cross-shelf current as well as downwelling within the shelf at Fremantle, whereas during El Niño years, the climate anomalies and the response of coastal currents are opposite. This paper provides insights into the multi-timescale nature of coastal surface currents and the relative importance of different driving mechanisms. It also demonstrates the potential of HFR to reveal the response of nearshore currents to climate anomalies when combined with other multivariate data. Meanwhile, the methodology adopted in this research is applicable to other coastal regions with long-term available HFR observations. [ABSTRACT FROM AUTHOR]

Prediction of El Niño–Southern Oscillation (ENSO) is hindered by a spring predictability barrier (SPB). In this paper, we investigate the effects of the Indian Ocean (IO) on the SPB. Using a seasonally varying extended IO–ENSO recharge oscillator model, we find that the SPB is much weakened when IO is coupled with ENSO. To gauge the relative role of the Indian Ocean dipole (IOD) and the Indian Ocean Basin (IOB) modes in weakening ENSO SPB, we develop an empirical dynamical model, the linear inverse model (LIM). By coupling/decoupling the IOB or IOD mode with ENSO, we show that the IOB significantly weakens eastern Pacific and central Pacific ENSO SPBs, while the IOD plays a weaker role. The evolution of the optimum initial structures also illustrates the importance of the IOB in ENSO SPB. Moreover, the IOB strongly influences the forecast skill of La Niña SPB rather than El Niño SPB. This point is also identified through six coupled models from the North American multimodel ensemble. It may be related to the role of the IO in the asymmetry in the duration of El Niño and La Niña. The IOB-induced easterly wind anomalies are conducive to the development of La Niña and thus the prediction of La Niña events, whereas these anomalous easterlies are less important during the development of El Niño and the related forecast of El Niño events. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of advancing deforestation in the southwestern Amazon on local hydroclimate. For this purpose, a high-resolution mesoscale model, coupled with a land surface model and a hydrologic routing model, is integrated for five years in two experiments, one control without changes in land use and another changing land use annually. During the rainy season, simulated higher precipitation volumes are reduced with the expansion of pasture lands. In the dry periods, mainly in August, there is an increase in precipitation over some deforested areas, which can be associated with mesoscale circulations induced by the heterogeneous surface. In general, land-use changes reduce evapotranspiration and the net radiation at the surface and increase the sensible heat flux during the dry season. In the rainy period, there is an increase in evapotranspiration with the intensification of deforestation, which modifies the other components of energy balance. Results suggest that the impact of LUCC on the local climate is more affected by conditions that generate precipitation extremes (El Niño/La Niña events) than by the abrupt increase in the annual deforestation rate. Land-use changes reduce the streamflow in all sub-basins of Ji-Parana during the dry season. In the rainy season, LUCC increases the streamflow during periods with normal precipitation conditions and La Niña in almost all sub-basins, except in the sub-basin with more than 20% deforestation. [ABSTRACT FROM AUTHOR]

The Pacific Equatorial Undercurrent (EUC) flows eastward across the Pacific at the equator in the thermocline. Its variability is related to El Niño. Moored acoustic Doppler current profiler (ADCP) measurements recorded at four widely separated sites along the equator in the EUC were compared to currents generated by version 4 release 4 of the Estimating the Circulation and Climate of the Ocean (ECCOv4r4) global model–data synthesis product. We are interested to learn how well ECCOv4r4 currents could complement sparse in situ current measurements. ADCP measurements were not assimilated in ECCOv4r4. Comparisons occurred at 5-m depth intervals at 165°E, 170°W, 140°W, and 110°W over time intervals of 10–14 years from 1995 to 2010. Hourly values of ECCOv4r4 and ADCP EUC core speeds were strongly correlated, similar for the EUC transport per unit width (TPUW). Correlations were substantially weaker at 110°W. Although we expected means and standard deviations of ECCOv4r4 currents to be smaller than ADCP values because of ECCOv4r4's grid representation error, the large differences were unforeseen. The appearance of ECCOv4r4 diurnal-period current oscillations was surprising. As the EUC moved eastward from 170° to 140°W, the ECCOv4r4 TPUW exhibited a much smaller increase compared to the ADCP TPUW. A consequence of smaller ECCOv4r4 EUC core speeds was significantly fewer instances of gradient Richardson number (Ri) less than 1/4 above and below the depth of the core speed compared to Ri computed with ADCP observations. We present linear regression analyses to use monthly-mean ECCOv4r4 EUC core speeds and TPUWs as proxies for ADCP measurements. Significance Statement: Hundreds of scientific papers have used ECCO data products generated with a continually evolving state-of-the-art ocean-model–data synthesis system. We ask, How representative is the latest version of ECCO equatorial ocean currents? We use independent in situ current measurements as the reference dataset to establish the accuracy of ECCO currents in the tropical Pacific. Attention is focused on the Pacific Equatorial Undercurrent (EUC) because it contributes to the formation of El Niño and La Niña events. ECCO EUC core speeds were smaller in magnitude and less variable in time compared to observations. As a consequence, ECCO currents generated smaller vertical mixing in the EUC compared to that inferred from current measurements. We developed a linear regression model to improve representation of monthly-mean ECCO currents. [ABSTRACT FROM AUTHOR]

Nepal experienced record-breaking summer monsoon precipitation in 2020, becoming the wettest year of the last four decades (1980–2020). This paper explores the role of large-scale atmospheric circulation and sea surface temperature patterns in tipping an otherwise typical wet summer into an extreme one in 2020. The unusually high precipitation was fuelled by the Western North Pacific Anticyclone (WNPAC), concomitant with the strong presence of moist static energy and enhanced vertical velocity in and near Nepal. Sea surface temperature anomalies showed an intense Indian Ocean warming and features of a La Niña, succeeding a weak El Niño event that had sustained the WNPAC. The southwesterly winds on the northern flank of then WNPAC contributed excess moisture transport and convergence to Nepal, consequently resulting in elevated precipitation. This feature is consistent with previous wet summer years, but the presence of WNPAC in those years followed the El Niño event. Therefore, it appears that the Indo-western Pacific Ocean Capacitor (IPOC) effect exerts the above-normal precipitation for the summer of 2020 without involving the El Niño event, while anthropogenic warming may have further tipped the balance. [ABSTRACT FROM AUTHOR]

The investigation of the propagation of swells throughout the ocean has long been a subject of significant interest in physical oceanography. This paper investigates the interannual variability of the Pacific swell pools and examines the factors contributing to their formation using the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 re-analysis dataset. Our results show that the interaction between swell propagation and wind fields influences the formation and development of Pacific swell pools. The eastern and southern Pacific swell pools are mainly caused by the northward propagation of swells from the South Pacific; the western and northern swell pools are primarily influenced by the southward propagation of swells from the North Pacific; and the central part of the swell pools is the result of the combined impact of both swell propagation from the north and south Pacific. The size of the swell pools in the Pacific Ocean is at its maximum in the northern hemisphere during the winter (December, January, and February) and at its minimum during the summer (June, July, and August). Due to the impact of the low-pressure systems, the swell pools in the winter hemisphere are relatively small, while the swell pools in the summer hemisphere are significantly larger. There is a relationship between the swell pools and ENSO events. When an El Niño event (La Niña event) occurs, the swells propagating to the low latitudes of the Pacific Ocean from high latitudes will strengthen (weaken), resulting in an increase (decrease) in the size of the swell pools. Analyzing the spatial and temporal distribution of the swell pools is important for understanding the large-scale effect of waves. [ABSTRACT FROM AUTHOR]

This paper discussed the use of stable isotope compositions of precipitation (δ2H and δ18O) to understand its characteristics and the parameters controlling meteorological conditions in Malaysia. The meteoric water line for Malaysia, or MMWL established in this study are δ2H = (7.43 ± 0.05)δ18O + (7.33 ± 0.11) (n = 595, r2 = 0.97) for individual values, and δ2H = (7.07 ± 0.20)δ18O + (4.90 ± 0.75) (n = 51, r2 = 0.96) for annual precipitation weighted means. No major variations in local meteoric water lines established between the stations, except for one (i.e., Cameron Highlands), which was found to be significantly different due to its high deuterium excess, or d value, attributed to moisture recycling (re–evapotranspiration) from the surrounding dense rainforest area. The precipitation moisture came from the two monsoon systems; the Northeast monsoon (NEM) and Southwest monsoon (SWM). They differ only slightly in their isotope signatures, where the NEM (winter monsoon) is 0.38‰ more negative than the SWM (summer monsoon), and the rainfall amount and temperature have a relatively weak influence on the stable isotopes in precipitation. Rainfall δ18O is poorly correlated with the monthly rainfall amount and temperature, with very low r2 values (–0.4‰/100 mm; 0.09 and 0.7‰/°C; 0.06, respectively). The seasonal variability of isotopic compositions of precipitation in this region is controlled by the insubstantial but conspicuous inverse correlation amount effect. The seasonal patterns of δ2H and δ18O are evident, with higher values observed during the NEM and lower values observed during SWM. However, the temporal variations of rainfall δ2H and δ18O during NEM and SWM are almost indistinguishable due to local climatic conditions, prevailing atmospheric circulations, and sources of precipitation. The apparent sign of El Niño and La Niña events (2015 and 2017, respectively) of the El Niño–Southern Oscillation (ENSO) cycle were successfully identified from this study, indicated by the heavier δ18O from the peaks in the annual precipitation amount versus δ18O annual precipitation weighted mean plot, while La Niña corresponds to the lighter values of the rainfall isotopes. [ABSTRACT FROM AUTHOR]

Based on satellite-observed and reanalysis data, this study investigates a thermal front east of the Gulf of Thailand (TFEGT) during the winter from 1982 to 2021. TFEGT exhibits distinct seasonal and interannual variation, emerging in December, peaking in February, gradually diminishing in March, and completely dissipating in April. Notably, the occurrence probability, area, and intensity of the thermal front are significantly higher in January and February compared with December and March. Through the application of a mixed temperature equation, we identify that geostrophic advection, driven by windinduced western boundary current in the South China Sea (SCS), plays a crucial role in the formation of the TFEGT. In winter, the prevailing northeast monsoon propels the western boundary current through wind stress curl, causing the southward transport of cold water from north to south. This cold water encountered warm water within the Gulf of Thailand (GoT), leading to the formation of TFEGT. Furthermore, the interannual variation of TFEGT is closely associated with the El Niño-Southern Oscillation (ENSO). In El Niño (La Niña) years, the northeast monsoon weakens (enhances), resulting in a weaker (stronger) western boundary current, ultimately influencing the weakening (enhancement) of TFEGT. [ABSTRACT FROM AUTHOR]

Simple Summary: Spring in Europe has been trending earlier for almost half a century. Long-distance migrant birds, such as the Willow Warbler and Pied Flycatcher, which breed in Europe, have arrived earlier too. It is broadly accepted that warming springs in temperate regions explain the earlier arrival of migrants. However, migration started weeks earlier and thousands of kilometres away. There must be additional cues elsewhere triggering migration. Meteorologists have developed measures of atmospheric circulation which are related to climate variability in wide regions. One of them is the Southern Oscillation Index, which reflects El Niño/La Niña that cause droughts and floods in the southern hemisphere. Other atmospheric circulation patterns, measured by the North Atlantic Oscillation Index and Indian Ocean Dipole, help predict total rainfall for a whole season in various parts of Africa and Europe. Good rains are associated with plant growth and with insect abundance. Insects provide food for most of these migrants. Therefore, this paper asks the question: "Is the timing of arrival of long-distance migrants in spring related to the climates they experience in the places where they are over the year prior to arrival in Europe?" This paper says the answer is "Yes". Earlier springs in temperate regions since the 1980s, attributed to climate change, are thought to influence the earlier arrival of long-distance migrant passerines. However, this migration was initiated weeks earlier in Africa, where the Southern Oscillation, Indian Ocean Dipole, North Atlantic Oscillation drive climatic variability, and may additionally influence the migrants. Multiple regressions investigated whether 15 indices of climate in Africa and Europe explained the variability in timing of arrival for seven trans-Saharan migrants. Our response variable was Annual Anomaly (AA), derived from standardized mistnetting from 1982–2021 at Bukowo, Polish Baltic Sea. For each species, the best models explained a considerable part of the annual variation in the timing of spring's arrival by two to seven climate variables. For five species, the models included variables related to temperature or precipitation in the Sahel. Similarly, the models included variables related to the North Atlantic Oscillation (for four species), Indian Ocean Dipole (three), and Southern Oscillation (three). All included the Scandinavian Pattern in the previous summer. Our conclusion is that climate variables operating on long-distance migrants in the areas where they are present in the preceding year drive the phenological variation of spring migration. These results have implications for our understanding of carry-over effects. [ABSTRACT FROM AUTHOR]

El Niño-Southern Oscillation (ENSO) asymmetry in predictability on springtime initial condition remains unclear. From the perspective of the spring predictability barrier (SPB), this paper investigates the ENSO asymmetry in SPB and explores the potential factors that may lead to this asymmetry. Both the observation and 29 Coupled Model Intercomparison Project Phase 6 (CMIP6) models show that the spring sea surface temperature (SST) persistence is significantly higher in El Niño years than that in La Niña years, and the SPB intensity is stronger in La Niña years than that in El Niño years. Through the recharge oscillator model, observation and CMIP6 models, we demonstrate that the nonlinear wind stress response to SST anomalies in spring is the main cause of the asymmetric SPB intensity. By the mixed-layer heat budget of the tropical Pacific in the spring, we further identify that a stronger response of zonal wind stress in El Niño events can cause a stronger zonal advection feedback, which finally leads to a weaker SPB and enhances the predictability of El Niño. In contrast, the cooling SST in the spring only leads to weak easterly anomalies, the zonal advection feedback is relatively weaker, thus SPB is stronger and the predictability of La Niña is lower. From the perspective of SPB, we suggest that El Niño is more predictable than La Niña. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of ENSO on water quality by looking at COD, SS, and Escherichia coli along the Crocodile River. Water samples were collected between 2016 and 2021 at three strategic sites on the river and were tested in an accredited laboratory. Python (version 3.8), Spyder and Microsoft Excel 2019 were used to analyze the data. The highest COD concentration (800 mg/L) was recorded at the White River site during El Niño, followed by 600 mg/L during the normal period, and 240 mg/L during the La Niña period. In 2019 during La Niña and the normal period, the E. coli levels were centered in one place at 60 cfu/100 mL, while in 2021 no E. coli levels were detected from the La Niña, El Niño, and normal periods. The suspended solids in this study were more prevalent in the White River (upstream) during the El Niño period. These analyses demonstrate that it is possible to evaluate the local effects associated with large-scale climate variability. [ABSTRACT FROM AUTHOR]

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This paper describes the use of a web application system, called 4-Dimensional Visual Delivery (4DVD), to visualize and deliver climate data. The focus of this paper is on the monthly data from the NOAA-CIRES-DOE Twentieth Century Reanalysis (20CR) project Version 2c. The 20CR is a global model at a spatial resolution about 2° latitude-longitude. The temporal coverage is from January 1851 to December 2014. The monthly data include numerous climate variables, such as temperature, pressure, precipitation rate, zonal wind, meridional wind, albedo, and longwave radiation flux. We show how to use the 4DVD system to conveniently visualize, deliver, and analyze the 20CR data of these parameters on a globe or on a 2D latitude-longitude map. We analyze the temporal and spatial patterns of zonal wind and precipitation over Niño 4 region (5° N-5° S, 160° E-150° W). The monthly NASA Global Precipitation Climatology Project (GPCP) data are used to compare the results from 20CR. GPCP data used in this 4DVD application are defined on 2.5° latitude-longitude grid boxes from January 1979 to January 2019. The 4DVD figures successfully show the reverse of zonal wind direction from the east-to-west wind to the west-to-east wind on the grid box (2° S, 176° W) in the Niño 4 region during an El Niño event. The spectral analysis shows the annual and semi-annual cycles in the zonal wind data on this grid box. The GPCP data are used to support the analysis results of 20CR zonal data. The precipitation data over the grid box (1.25° S, 176.25° W) in the Niño 4 region show clear El Niño signals (persistent extreme precipitation more than 6 mm/day) and clear La Niña signals (persistent "dry" with near-zero precipitation). The spectral analysis of the precipitation data time series over this grid box shows no annual cycle. [ABSTRACT FROM AUTHOR]

This paper utilizes a fine scale parameterization scheme based on strain spectra and characterizes the temporal and spatial distributions of diapycnal turbulent mixing in the West Pacific Warm Pool. We use Array for Real‐Time Geostrophic Oceanography (Argo) profiles from 2011 to 2022 to generate the turbulent dissipation rate (ε) as a representative of internal‐wave‐induced mixing. We then discuss the influence of El Niño‐Southern Oscillation (ENSO) on turbulent mixing by considering seafloor topography, thermocline depth, and ENSO phases. Results indicate that ENSO can influence the vertical stratification in the ocean by changing the depth of the thermocline, causing the change of interaction between internal tides and seafloor topography, thereby affecting the intensity and vertical distribution of diapycnal turbulent mixing. During La Niña years, the value of ε is larger compared to that of El Niño years. Compared to rough regions, the thermocline variations induced by ENSO have a more pronounced impact in the smooth regions. The variability in turbulent mixing influenced by ENSO is crucial for heat and substance exchange in the equatorial Pacific. [ABSTRACT FROM AUTHOR]

Prediction of summer precipitation in north China (NCP) has long been a challenge partly because its low correlation with previous sea surface temperature (SST) anomalies (SSTA) limits the application of SST in NCP prediction. This study aims to extract optimal predictors of NCP from the SST field using an objective method—empirically optimal screening (EOS). It finds that the optimal precursory signal of NCP lies in the change of SSTA from winter to spring rather than the SSTA itself. This study identifies two optimal precursory signs predicting a positive (negative) NCP anomaly: the anomalous SST cooling (warming) from winter to spring in the coastal area of Somalia and Peru. Interestingly, these two presummer conditions have considerable independence, but they lead to a similar summer development of La Niña (El Niño). In summer, the tropical precipitation anomaly pattern associated with La Niña (El Niño) development excites a meridional wave train over the western Pacific and the circumglobal teleconnection in the Northern Hemisphere. Both of the anomalous wave trains show abnormal high (low) pressure over northeast Asia, which induces the south (north) wind anomalies over north China and produces abundant (deficient) precipitation there. These results highlight the importance of the SST evolution from winter to spring, break through the limitation of SST application in NCP prediction, and thus bring a prospect of improving NCP forecast skills. Significance Statement: Sea surface temperature (SST) anomalies are most used as predictors in climate prediction. However, the forecast of summer precipitation in north China is limited by its low correlation with prior SST anomalies. In this paper, we find that the optimal precursory signal of north China precipitation (NCP) is not the SST anomaly itself, but the changes of SST anomalies from winter to spring in the coastal area of Somalia and Peru. These two precursory signals are almost independent yet indicate similar summer situations leading to NCP anomaly. These results highlight the importance of the dynamic evolution of sea surface temperature in improving the forecast skill of NCP. [ABSTRACT FROM AUTHOR]

The Eastern African region is witnessing changes in climate conditions and rising sea levels due to the influences of global warming interacting with weather phenomena such as El Nino and La Nina. These trends, as well as more intense extreme weather events, highlight the urgent need for appropriate adaptation responses at both the national and local level. This is especially the case for the numerous small islands of the region that are particularly vulnerable to climate change. This paper reports on a study that examined coping and adaptation responses to climate and non-climate stressors among coastal communities on two Zanzibar islands (Pemba and Unguja) in Tanzania. The study focused on three of the primary livelihood activities on the islands, namely, seaweed growing, fishing, and crop and livestock farming. Using mainly survey data, we explored the responses of farmers, fishermen, and seaweed growers to multiple shocks and stressors. We further investigated responses that were discontinued for various reasons, as well as any barriers to adaptation encountered by these communities. We found that coastal communities in both Kiuyu Mbuyuni, Pemba and Matemwe, Unguja face a range of interrelated shocks and stressors linked to their livelihood activities, some of which they were able to respond to primarily through coping strategies. However, their attempts to adapt in the longer term as well as to venture outside their traditional activities were constrained by several barriers. Some of these barriers operate beyond the individual and community capability to overcome, while others—like social and cultural barriers—can be addressed at the local level but need a concerted effort and political will. We draw the findings together into a conceptual framework to help unpack the implications these hold for coastal communities on the two islands. We then suggest ways to build resilience in local livelihoods and overcome barriers to climate change adaptation in the future. [ABSTRACT FROM AUTHOR]

The climate variability associated with the ENSO phenomenon has a significant impact on wetlands, affecting the total precipitation input and hydrological flows of these ecosystems. The objective of this paper is to study the trophic status variation of an urban tropical wetland under ENSO conditions, through dynamic modeling. The results suggest an increase in precipitation, by 3.32 times, during the La Niña phase compared to the El Niño phase. Wetland input total phosphorus (TP) concentrations are 1.85 times lower during La Niña. This is probably due to a dilution effect exerted by the increase in surface runoff volumes from the basin. The findings suggest a reduction in wetland hydraulic retention time (HRT) during La Niña (1.33 times) compared to El Niño. This trend causes the TP concentration inside the wetland to decrease, possibly due to an increase in the water volume stored (dilution), and by the exit of this nutrient due to a shorter hydraulic renewal (HRT/La Niña < HRT/El Niño). The occurrence of a high input of TP concentration to the wetland does not necessarily indicate a high trophic status index (TSI). This is because the trophic status of the wetland is possibly more associated with HRT rather than input TP concentration. The trophic status of the wetland during the La Niña tends to be eutrophic. Lastly, under ENSO scenarios, the use of Aizaki's method is suggested, because it considers HRT as a decisive factor for the calculation of wetland trophic status. [ABSTRACT FROM AUTHOR]

Previous studies have revealed that extratropical forcing can lead to changes in the intertropical convergence zone (ITCZ). Based on reanalysis data from 1979 to 2019, this paper discusses the influence of the South Pacific Ocean Dipole (SPOD, a dominant mode between the subtropics and extratropics in the South Pacific) and its coordination with ENSO in the ITCZ. Results show that SPOD has an effect on the position and intensity of the ITCZ, especially in the region around Niño4. From the latitudes of ITCZ axes and precipitation averaged over 160°E–160°W, positive (negative) SPOD events force a northward (southward) shift in the ITCZ in boreal winter (DJF), while the position moves in the opposite direction in boreal summer (JJA). In addition, ENSO can obviously enhance the influence of SPOD on the ITCZ. It is evident that there is a wider range of northward (southward) shift in the ITCZ under both positive SPOD and El Niño (negative SPOD and La Niña) conditions during DJF. Similar to DJF, both positive SPOD and El Niño (negative SPOD and La Niña) events still cause the ITCZ to move toward (away from) the equator during JJA, except that the magnitude of the movement in JJA is less than that in DJF. Precipitation averaged over 160°E–160°W is at a maximum under both positive SPOD and El Niño events, which have the greatest influence on ITCZ intensity, followed by both negative SPOD and La Niña in DJF, while in JJA, ITCZ intensity is most sensitive to negative SPOD events. [ABSTRACT FROM AUTHOR]

The El Niño–Southern Oscillation (ENSO) is the dominant interannual variability affecting global weather and climate. However, limited observational records hinder our understanding of the evolution of natural ENSO variability and its driving mechanisms. In this study, ENSO variations from 665 to 749 CE (Common Era) were investigated using monthly sea surface temperature (SST) records of the northern South China Sea derived from coral strontium to calcium ratios of sub‐fossil Porites obtained at the Xisha Islands. The results suggested the existence of cold conditions in this period relative to the twentieth century. No change in SST seasonality for the CE was found that is in agreement with the orbitally controlled insolation seasonality at that time. ENSO variability during 665–749 CE was enhanced by 39% than that during 1980–2014 CE and exhibited fluctuations. A persistent dampened ENSO variability with frequent El Niño events from 665 to 700 CE was followed by a rapid increase in variability to a level double that of the present. The frequency of La Niña events increased during this time. The abrupt transformation of ENSO activity at 700 CE was attributed to the increased natural radiative forcing induced by intense solar irradiance and weak volcanism. This paper demonstrates that ENSO variability can be influenced by external forcings, such as changes in solar and volcanic activity, and not only by the internal dynamics of the climate system. Plain Language Summary: Reconstructing the amplitude and frequency of historical El Niño and La Niña events will allow us to better understand the driving mechanisms of their evolution and improve predictions of ENSO under anthropogenic climate change. This study reconstructed monthly sea surface temperature (SST) from 665 to 749 CE using a continuous sub‐fossil coral Sr/Ca record from Xisha Islands. We demonstrated that the northern South China Sea and its adjacent area experienced cold conditions during this period, with no change in SST seasonality relative to the present. Our results also revealed that ENSO variability during 665–749 CE exhibited significant fluctuations from a state with dampened ENSO to one with amplified ENSO, accompanied by a transition from frequent El Niño to La Niña anomalies. The abrupt increase in ENSO variability after 700 CE was triggered by the increased solar irradiance and weak volcanic eruptions. This suggests that in addition to the internal dynamics of the climate system, ENSO variability is also influenced by external forcings. Key Points: Cooler conditions and similar sea surface temperature seasonality compared to the present characterized 665–749 CEEl Niño–Southern Oscillation (ENSO) variability during 665–749 CE was 39% higher than that during 1980–2014 CEEnhanced solar activity triggered an abrupt increase in ENSO variability at 700 CE [ABSTRACT FROM AUTHOR]

The effects of ENSO have been considered as the major variables in weather changes in the Middle East. This issue has been shown by regression indexes in a number of papers. Weather forecasts could be influenced by some variables that have uncertainty, so the deterministic approaches may lead to incorrect predictions. The proposed algorithm can be used when some variables have uncertainty. In this study, a fuzzy-based probabilistic approach has been chosen to show the effect of El Niño and La Niña on the monthly total precipitation in northern coasts of the Oman Gulf. [ABSTRACT FROM AUTHOR]

The paper uses reanalysis data and model outputs to quantify relative contributions of the El Niño‐Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) to the vertical structure variability of the Indonesian Throughflow (ITF) using multiple regression analysis. In comparing ENSO to IOD events, it becomes evident that ENSO plays a more significant role in ITF upper layer (0–300 m) transport, while the IOD has a greater impact on ITF lower layer (300–760 m) transport. Given the larger anomaly in ITF upper layer transport, ENSO dominates the interannual variability of ITF transport. Moreover, ITF transport is influenced by different physical processes associated with varying phases of ENSO and the IOD. The month‐by‐month contributions reveal that the IOD primarily controls ITF transport during El Niño development years, while ENSO has more influence during El Niño decaying years. Plain Language Summary: The Indonesian Throughflow (ITF) transports warm water from the tropical western Pacific Ocean to the tropical eastern Indian Ocean, altering the vertical stratification and heat content of the Indian Ocean. Thus, its transport variability is influenced by two large‐scale climatic phenomena, El Niño (or La Niña) in the Pacific Ocean and the Indian Ocean Dipole (IOD). However, the responses of upper layer and lower layer transports to these two climatic phenomena are different. Upper layer transport is mainly controlled by El Niño, while lower layer transport is mainly controlled by the IOD. The whole transport was primarily controlled by the IOD during El Niño development year and by the ENSO during El Niño decay year. The results are important for studying the influence of the vertical structure of the ITF on the interannual variability in the upper Indian Ocean circulation. Key Points: Indonesian Throughflow (ITF) transport is primarily controlled by the Indian Ocean Dipole (IOD) during the El Niño developing year and by El Niño‐Southern Oscillation (ENSO) during the El Niño decaying yearENSO has a greater impact on the ITF compared to the IOD because of differences in their amplitude, peak time, and durationWind anomalies drive ITF upper layer transport, while ITF lower layer transport is primarily controlled by IOD/ENSO‐induced wave dynamics [ABSTRACT FROM AUTHOR]

El Niño Southern Oscillation (ENSO) events yield precipitation deficits and ensuing droughts, often damaging regional forests, in many parts of the world. The relative roles of ENSO, other natural climate changes, and anthropogenic factors on the forest clearing of Easter Island over the last millennium are still debated. Here, we analyze Easter Island precipitation changes using in situ, satellite‐derived and reanalysis products spanning the last 4–7 decades, and 46 monthly 156‐year‐long (1850–2014) simulations derived from 25 CMIP5 and 21 CMIP6 (Coupled Model Intercomparison Project phases 5 and 6) General Circulation Models. Our analysis shows that La Niña events, the cold phases of ENSO, cause precipitation deficits of −0.2 to −0.3 standard deviation (relative to long‐term mean) in all analyzed data types. ENSO‐like events are further examined over the last millennium (850–1981). A new multiproxy reconstruction of the NINO3.4 index based on proxy records from the Past Global Changes 2k database and Random Forest method is produced. Our reconstruction reveals unusual high recurrences of La Niña‐like situations during the fifteenth to seventeenth centuries, which likely induced significant precipitation deficits on the island. These situations are compared to published vegetation reconstructions based on pollen analyses derived from sedimentary cores collected in three island sites. We conclude the environmental consequences of cumulative precipitation deficits over long‐lasting La Niña‐like situations reconstructed here over the fifteenth to seventeenth centuries were likely favoring drought and forest flammability. La Niña events should be better accounted for among the causes of forest clearing on Easter Island. Plain Language Summary: Easter Island is a small remote island located in the south‐eastern Pacific Ocean. It is home of several scientific enigmas: the origin of early settlements, the construction of the giant moai statues, and causes of the forest clearing. Was the forest clearing abrupt, gradual, homogenous in time and space, human‐induced (in line with the ecocide hypothesis), or related to natural climate variability? The question we address in this paper is related to the natural climate variability hypothesis, focusing on the El Niño Southern Oscillation (ENSO) phenomenon. We analyze ENSO effects on Easter Island precipitation from three instrumental (1950–2021) and 42‐simulation data sets (1850–2014). Our analysis shows the cold phases of ENSO, also known as La Niña, cause significant precipitation deficits over the island in all analyzed data types. Then, we provide a new up‐to‐date reconstruction of ENSO over 850–1981. We found a large number of La Niña‐like situations during the fifteenth‐seventeenth centuries. These situations are compared to vegetation reconstructions derived from sedimentary cores collected in three island sites. We conclude that the environmental consequences of cumulative precipitation deficits during long‐lasting La Niña‐like situations could be an additional cause of the forest clearing of Easter Island. Key Points: Analysis of independent data sets shows precipitation deficits over Eastern Island during La Niña events over the period 1850–2021A new reconstruction of El Niño Southern Oscillation episodes reveals a large number of La Niña‐like situations during the fifteenth to seventeenth centuriesHigh repetitions of La Niña events, favoring drought, likely played a role in the forest clearing of the island, on top of other stressors [ABSTRACT FROM AUTHOR]

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In this paper, we report on the frequency of false onsets of wet season rainfall in the case of the Northern Australian wet season and investigate the role of large‐scale tropical climate processes such as the El Niño–Southern Oscillation, Indian Ocean Dipole (IOD) and Madden–Julian Oscillation. A false onset occurs when a wet season rainfall onset criterion is met, but follow‐up rainfall is not received for weeks or months later. Our analysis of wet season rainfall data from 1950 through 2020 shows a false onset occurs, on average, between 20 and 30% of wet seasons across all of northern Australia. This increases at a regional and local level such as at Darwin, the Northern Territory (NT), and parts of Queensland's north coast to over 50%. Seasonal climate influences, such as a La Niña pattern and a negative IOD that typically expedite the wet season rainfall onset, also increase the likelihood of a false onset over northern Australia. Our analysis also finds that periods of false onsets can sometimes, but not always, coincide with periods of rapid soil moisture depletion. The false rainfall onsets that develop into flash drought can be potentially disruptive and costly and are of potential significance for agriculture and fire management in northern Australia, and in other monsoonal climates that also typically experience a slow build‐up to the seasonal monsoon. In conclusion, effective rainfall indicates that many seasons experience 'false onsets' with dry conditions after early rainfall. We propose that false onsets are a physical characteristic of the climate of northern Australia which occurs with relatively high frequency. In addition, these false onsets may sometimes co‐occur with a flash drought. [ABSTRACT FROM AUTHOR]

This paper investigates the causes for the interdecadal change in the relationships between early and late summer precipitation over South China (SC). It is found that the correlations of the precipitation over SC between June and August shift from weak positive in 1979–1995 to significantly negative in 1996–2019. Further analysis demonstrates that the distinct evolution of sea surface temperature (SST) pattern between the two periods accounts for the interdecadal variations of their relationships. Although the warming of the tropical western Indian Ocean (WIO) in June favors increasing precipitation over the SC via enhancing the Northwest Pacific Subtropical High (NWPSH) during the whole period, the associated SST anomalies in August are rather different between the two periods. Specifically, the WIO warming in June corresponds to slightly positive anomalies over the tropical central-eastern Pacific in August during the 1979–1995, which has weak impact on the NWPSH and results in a weak precipitation correlation between June and August. However, the WIO warming in June corresponds to La Niña's rapid development in August during the 1996–2019, which favors the enhancement of the NWPSH via increasing the regional Hadley circulation. Due to the climatologically northward movement of NWPSH from June to August, the enhanced NWPSH in August acts to decrease the precipitation over SC, causing a significantly negative correlation between precipitation in June and August. Overall, the distinct evolution of tropical SST pattern is the key factor inducing the change of the relationships between June and August precipitation in the two periods. [ABSTRACT FROM AUTHOR]

This paper investigates the impacts of extratropical Pacific on El Niño‐Southern Oscillation (ENSO) spring predictability barrier (SPB). Using an empirical dynamical model – Linear Inverse Model (LIM), we find that the dynamics of the northern and southern extratropical Pacific can significantly and equally weaken the Eastern Pacific (EP)‐ENSO SPB, while the North Pacific is more important for weakening the Central Pacific (CP)‐ENSO SPB. The evolution of the extratropical optimum initial structures illustrates the different roles of the northern and southern extratropical Pacific in crossing EP and CP ENSO SPBs and demonstrates the decisive role that the South Pacific initial condition plays in ENSO diversity. Additionally, the extratropical Pacific greatly influences the forecast skill of El Niño during SPB, while tropical dynamics may be more important for crossing the SPB of La Niña. Plain Language Summary: The spring predictability barrier (SPB) is a sudden reduction of the prediction skill of the El Niño‐Southern Oscillation (ENSO) in the boreal spring. Using a linear dynamical model, we find the correlation forecast skill of Central Pacific ENSO in boreal spring and summer is significantly enhanced by including the dynamics of northern extratropical Pacific, therefore weakening the SPB. For the Eastern Pacific ENSO, both the northern and southern extratropical dynamics are equally important for weakening the SPB. Our results also show that the initial state of southern extratropical Pacific may determine the type of ENSO. Additionally, including the extratropical dynamics helps to improve the forecast skill of El Niño events in boreal spring and summer while the extratropical dynamics may not be essential for the prediction of La Niña. Key Points: A linear dynamical model suggests that including the dynamics of extratropical Pacific can significantly weaken the ENSO SPBNorth Pacific plays a role both in the central and eastern Pacific, while South Pacific may be essential in determing ENSO diversityExtratropical Pacific greatly influences the forecast skill of El Niño during SPB, while the impact on La Niña is limited [ABSTRACT FROM AUTHOR]

Ocean waves are crucial for driving various oceanic processes. In this study, the spatial and temporal distribution of significant wave height (SWH) in the North Pacific (NP) is analyzed using the 42-year ERA5 reanalysis dataset from European Centre for Medium-Range Weather Forecasts (ECMWF). The presence of an ENSO signal is confirmed in wave fields of the North Pacific. Furthermore, the spatial distributions of swells and wind waves are analyzed using the Empirical Orthogonal Function (EOF) method, revealing that waves can transport large-scale signals from the NP to lower latitudes through swells. In addition, our research reveals a relationship between ENSO and Stokes drift in the NP. Stokes drift contributes positively to the maintenance of stable sea surface temperatures (SSTs) by transporting more (less) water towards the equatorial Pacific during El Niño (La Niña year) years. It is further noted that during strong ENSO events, the strength of the Stokes drift anomaly intensifies accordingly, which implies a strong link between wave-induced transport and ENSO. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to determine the impact of rare disaster risks, captured by the El Niño-Southern Oscillation (ENSO) cycle, on the volatility of Treasury securities of the United States (US) involving 1- to 360-month maturities. We use a random coefficient panel-data-based heterogeneous autoregressive-realized variance (HAR-RV) model over the monthly period of 1961:06 to 2019:12, with the monthly RV derived from the sum of squared daily changes in yield within a month. Our results show a positive and statistically significant (at the 1% level) impact of the ENSO cycle on RV, with the results being robust to alternative metrics of the ENSO, consideration of lagged values, and decomposition of the ENSO cycle into El Niño and La Niña phases, with the former having a relatively stronger effect. Based on the panel estimation method using heterogeneous slope coefficients, we find that the impact on the entire term-structure is positive yet stronger at the two-ends and the middle-part of the term-structure. Our findings have important implications for investors in US Treasury securities. [ABSTRACT FROM AUTHOR]

Southeastern South America is subject to considerable precipitation variability on seasonal to decadal timescales and has undergone very heavy land‐cover changes (LCCs) since the middle of the past century. The influence of local LCC and precipitation as drivers of regional evapotranspiration (ET) long‐term trends and variability remains largely unknown in the region. Here, ensembles of stand‐alone dynamic global vegetation models (DGVMs) with different atmospheric forcings are used to disentangle the influence of those two drivers on austral summer ET from 1950 to 2010. This paper examines the influence of both the El Niño‐Southern Oscillation (ENSO) and the dipole‐like first‐mode of southeastern South American precipitation variability (EOF1) on regional ET. We found that in the lower La Plata Basin, ET was driven by precipitation variability and showed a positive summer trend. Moreover, the region showed marked seasonal anomalies during El Niño and La Niña summers but mainly during EOF1 phases. On the contrary, in the upper La Plata Basin, LCCs forced the negative summer ET trend and particularly reduced the summer anomalies of the late 1990s, a period of ENSO and EOF1‐positive phases. In the South Atlantic Convergence Zone region, the high ET uncertainty across ensemble members impeded finding robust results, which highlights the importance of using multiple DGVMs and atmospheric forcings instead of relying on single model/forcing results. [ABSTRACT FROM AUTHOR]

In this paper, we investigate whether the relationship between the El Niño‐Southern Oscillation and tropical cyclone (TC) rain rate over the western North Pacific (WNP) changes between the global warming slowdown (2001–2012) and resumption (2013–2020) periods. Using high‐resolution satellite rainfall data, we show that the average TC rain rate increases by 9% but decreases by 14% during the recent El Niño and La Niña years (since 2013), respectively. During the El Niño years, the increase is related to higher TC track density at lower latitudes, where more water vapor and stronger convergence are present. On the other hand, the decrease in TC rain rate during the recent La Niña years is mainly related to an increase in track density at higher latitudes and a decrease in TC intensity. These changes in TC track density and intensity are both associated with the strengthening of the subtropical high since 2013. Plain Language Summary: The impacts on various weather phenomena associated with the global surface warming slowdown (or "hiatus": 1998–2012) and its subsequent resumption since 2013 have been extensively investigated. An unresolved issue is whether the tropical cyclone (TC) rain rate over the western North Pacific (WNP) basin has also changed, especially during the El Niño (or La Niña) years. Considering the availability of high‐resolution satellite rainfall data, we mainly focus on the period of 2001–2020 (slowdown period: 2001–2012; resumption period: 2013–2020). Our results show that, consistent with the increase in atmospheric water vapor after the global warming resumption, the average TC rain rate has increased by ∼2%. However, TC rain rate increases in El Niño years but decreases in La Niña years during the resumption period. This opposite change in TC rain rate is mainly influenced by the strengthened WNP subtropical high. Our findings suggest that it is necessary to properly consider the influence of the subtropical high on the projections in TC migration, intensity, and rain rate under global warming. Key Points: Compared with El Niño‐Southern Oscillation (ENSO) years in the global warming slowdown period, tropical cyclone (TC) rain rate increases and decreases in recent El Niño and La Niña yearsThis opposite change in TC rain rate in recent ENSO years is mainly affected by the changes in TC track density and TC intensityChanges in TC track density and intensity are both influenced by the extremely strengthened subtropical high since 2013 [ABSTRACT FROM AUTHOR]

This paper shows more evidence for the existing spatial–temporal synchronization of the air surface temperature and pressure within the lower stratospheric ozone, which is unevenly distributed over the globe. The focus of this study is put on the region of formation and manifestation of El Niño Southern Oscillation (ENSO). Statistical analysis of data (covering the period 1900–2019) displays a well pronounced covariance of ozone at 70 hPa with (i) Nino3.4 index, (ii) air surface temperature, and (iii) sea level pressure, in each grid-point with spatial resolution of 5° in latitude and longitude. The ozone impact could be found at different time scales—from interannual (altering the ENSO phase transition) to interdecadal. Moreover, the centers of action of ozone on the sea level temperature and pressure are positioned at different places, depending on the temporal scale of variability—from the tropical Central Pacific—at interannual and interdecadal, to extratropics—at subdecadal time scales. We show also that positive ozone anomalies at 70 hPa trigger a cooling of the sea surface, with a delay of 9 record's time intervals. The ozone depletion, on the other side, is followed by a sea level warming with a delay of 1–2 record's time intervals. [ABSTRACT FROM AUTHOR]

Understanding past changes in the characteristics of climate extremes forms an essential part of viable countermeasures to cope with climate-induced risks in a rapidly warming world. Thus, this paper endeavored to explore possible non-monotonic trend components in heavy rainfall events over the Central Highlands (Vietnam) by employing Şen's innovative trend analysis method in conjunction with the well-defined extreme rainfall indices. The outcomes show less spatially coherent trends in the intensity, frequency, and duration of extreme rainfall events across the study area, and most analyzed indices exhibited non-monotonic trend forms. The overall trends in the intensity and frequency, represented by maximum 1-day, 5-day precipitation amount (Rx1day, Rx5day), very and extremely wet days (R95p and R99p), and the number of very and extremely heavy precipitation days (R20mm and R50mm), were characterized by significant increases at three or four sites. Concerning dry and wet extremes, observed increases in consecutive dry days (CDD) and decreases in consecutive wet days (CWD) were identified significantly simultaneously at three sites. There is high domination of significant increases in high-value subgroups of these indices. Several sites also exposed significantly increasing trend behaviors in these indices within all low-, medium-, and high-value subgroups, thereby implying the intensity and frequency have intensified over recent decades. This study also indicated potential linkages between annual peaks of several extreme rainfall indices, characterizing intensity, frequency, and wet duration, usually coincided with negative Indian Ocean Dipole and La Niña events, while dry extremes were usually found during El Niño events based on correlation analysis. [ABSTRACT FROM AUTHOR]

In this paper, the different effects of the eastern equatorial Pacific (EP) and central equatorial Pacific (CP) Ocean El Niño–Southern Oscillation (ENSO) events on interannual variation in the diurnal sea surface temperature (SST) are explored in both the Niño-3 and Niño-4 regions. In the Niño-3 region, the diurnal SST anomaly (DSSTA) is negative during both EP and CP El Niño events and becomes positive during both EP and CP La Niña events. However, the DSSTA in the Niño-4 region is positive in El Niño years and negative in La Niña years, which is opposite to that in the Niño-3 region. Further analysis indicates that the incident shortwave radiation (SWR), wind stress (WS), and upward latent heat flux (LHF) are the main factors causing the different interannual variations in the DSST. In the Niño-3 region, decreased SWR and increased LHF lead to a negative DSSTA in EP El Niño years, and enhanced WS and increased LHF cause a negative DSSTA in CP El Niño years. Conversely, in that same region, increased SWR and decreased LHF lead to a positive DSSTA in EP La Niña years, and reduced WS and decreased LHF cause a positive DSSTA in CP La Niña years. In the Niño-4 region, the reduced trade wind plays a key role in producing the positive DSSTA, whereas the decreased SWR has an opposite effect that reduces the range of the DSSTA during both EP and CP El Niño events, and conversely the enhanced trade wind plays a key role in producing the negative DSSTA, whereas the increased SWR has an opposite effect that increases the range of the DSSTA during both EP and CP La Niña events. [ABSTRACT FROM AUTHOR]

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In 1976, a pilot experiment, called first Equatorial Mooring (EQUA-1), tested an innovative technique for anchoring a taut-line surface mooring at 0°, 150°W where the water depth is 4.5 km. The 36-day deployment contained a wind recorder and fixed-level current meters at 50 and 100 m in the Equatorial Undercurrent (EUC). The following year, in a second pilot experiment, named EQUA-2, a similar mooring was deployed at 0°, 125°W for 99 days. EQUA-2, with current meters at 10, 50, 100, 150, and 200 m, recorded a surge in EUC transport during April 1977 when 3-day-averaged eastward current speeds at 50-m depth reached 2 m s−1. The associated eastward transport per unit meridional width over the 50–200-m layer was 190 m2 s−1. Based on observations recorded in April 1980, the EQUA-2 pulse would correspond to a total EUC transport surge of about 38 Sv (1 Sv ≡ 106 m3 s−1) and would represent an equatorially trapped first-mode baroclinic Kelvin wave. This paper describes EQUA Project observations and why and how I created the high-risk-of-failure opportunity to record pioneering time series measurements at the equator. The enduring legacy of the EQUA Project is the sustained maintenance of in situ surface wind and upper-ocean current and temperature measurements at numerous sites in the equatorial oceans, starting in the Pacific to improve forecasts of the El Niño and La Niña phenomenon. For example, the 40-yr records of surface wind and upper-ocean current and temperature measurements at 0°, 110°W and 0°, 140°W are some of oceanography's longest time series recorded far from land. [ABSTRACT FROM AUTHOR]

Previous studies have recognized the societal relevance of climatic extremes on the seasonal time scale and examined physical processes leading to individual high-impact extreme seasons (e.g., extremely wet orwarm seasons). However, these findings have not yet been generalized beyond case studies since at any specific location only very few seasonal events of such rarity occurred in the observational record. In this concept paper, a pragmatic approach to pool seasonal extremes across space is developed and applied to investigate hot summers and cold winters in ERA-Interim and the Community Earth System Model Large Ensemble (CESM-LENS). We identify spatial extreme season objects as contiguous regions of extreme seasonal mean temperatures based on statistical modeling. Regional pooling of extreme season objects in CESM-LENS then yields considerable samples of analogs to even themost extreme ERA-Interimevents. This approach offers numerous opportunities for systematically analyzing large samples of extreme seasons, and several such analyses are illustrated. We reveal a striking co-occurrence of ElNiño to La Niña transitions and the largest ERA-Interim midlatitude extreme summer events. Moreover, we perform a climate model evaluation with regard to extreme season size and intensitymeasures and estimate how often an extreme winter like the coldNorth American 2013/14 winter is expected anywhere inmidlatitude regions. Furthermore, we present a large set of simulated analogs to this event, whichmakes it possible to studycommonalities and differences of their underlying physical processes. Finally, substantial but spatially varying climatological differences in the size of extreme summer and extreme winter objects are identified. [ABSTRACT FROM AUTHOR]