Pacific Decadal Oscillation

Our analyses partition the relative influence of progressive climate change and large-scale climate drivers that can be associated with the Quasi-Biennial Oscillation (QBO), El Niño Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), solar sunspot cycle, and multi-decadal oscillations on lake ice breakup dates for thirteen Northern Hemisphere lakes. Oscillatory dynamics explain 26 % of the total variance in the time series compared with 15 % for linear trends, leaving 60 % unexplained and likely attributable, in part, to local weather. Significant oscillatory dynamics include frequencies in 2-3 year periods (9.4 % of the total variance), 3-6 year periods (8.2 %), 10-12 year periods (1.6 %) and various multidecadal periods (0.4-1.3 %). All 13 study lakes, although widely scattered in the Northern Hemisphere, had similar oscillatory dynamics and linear trends, emphasizing that global processes influence lake ice breakup locally. We illustrate that while quasi-periodic dynamics associated with large-scale climate drivers are important, they do not mask the clear evidence for progressive climate change.

SeaWiFS data provide the first systematic comparison of 10 years (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) of chlorophyll interannual variability over the California (CCS) and Humboldt (HCS) Current Systems. Dominant signals are adjacent to the coast in the wind-driven upwelling zone. Maximum anomalies in both systems are negative signals during the 1997-1998 El Niño that persist into 1999 at most latitudes. Thereafter, anomalies primarily appear to be associated with shifts in phenology, with those in the CCS stronger than those of the HSC. Prominent signals in the CCS are positive anomalies in 2001-2002 at latitudes >35°N and <30°N, and in 2005-2006 from $30 to 45°N that persist at latitudes >40°N into 2007. In the HCS, latitudinally extensive positive events occur in austral summers of [2002][2003][2003][2004]. Relationships of chlorophyll anomalies to forcing are explored through correlations to local upwelling anomalies and three indices of Pacific Ocean basin-scale variability, the Multivariate El Niño Index (MEI), the Pacific Decadal Oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO). These show that each system has strong latitudinal regionality in linkage to forcing. At higher latitudes, correlations follow expected relationships of increased (decreased) chlorophyll with positive upwelling and NPGO (MEI and PDO). At specific latitudes, notably the Southern California Bight and off Peru, where circulation and/or chlorophyll phenology differ from canonical EBUS patterns, correlations weaken or oppose those expected. Correlations excluding the El Niño period remain similar in the CCS but substantially changed in the HCS, indicating much stronger domination of El Niño conditions on HCS anomaly relationships over this 10-year period.

Studies have shown that environmental variables significantly affect variation in stock abundance of marine populations. The northern Gulf of California (NGC) is a highly productive region of interest due to its fish resources and diversity. Conservation of the marine species inhabiting the region is of public interest. Our study analysed the influence of physical environmental factors on several commercial marine species, using catch per unit effort (CPUE) as a proxy for abundance. Generalized additive models were used to test the significance of selected environmental variables on stock abundance. Deseasonalized cross-correlation analysis was used to examine time-lagged correlations between CPUE and abiotic variables to identify response timings. The results suggest that for most commercial species the sea surface temperature and the long-term climate Pacific Decadal Oscillation index are the predominant predictors for species abundance, followed by the Colorado River discharge. T...

The aim of this paper is to investigate the relationships among Interhemispheric Temperature Asymmetry (ITA) and the principal modes of natural variability: the Atlantic Multidecadal Oscillation (AMO), the Southern Oscillation Index (SOI), and the Pacific Decadal Oscillation (PDO). In particular, Granger causality tests are used to capture the linkages among these variables. Our analysis provides strong evidence that AMO causes ITA, the causal role of PDO is weak, and SOI seems to have no causal influence.

Common patterns of climatic variability across the Western Americas are modulated by tropical and extra-tropical oscillatory modes operating at different temporal scales. Interannual climatic variations in the tropics and subtropics of the Western Americas are largely regulated by El Niño-Southern Oscillation (ENSO), whereas decadal-scale variations are induced by long-term Pacific modes of climate variability such as the Pacific Decadal Oscillation (PDO). At higher latitudes, climate variations are dominated by oscillations in the Annular Modes (the Arctic and Antarctic Oscillations) which show both interannual and longer-scale temporal oscillations. Here we use a recently-developed network of tree-ring chronologies to document past climatic variations along the length of the Western Cordilleras. The local and regional characterization of the relationships between climate and tree-growth provide the basis to compare climatic variations in temperature-and precipitation-sensitive records in the Western Americas over the past 3-4 centuries. Upper-elevation records from tree-ring sites in the Gulf of Alaska and Patagonia reveal the occurrence of concurrent decade-scale oscillations in temperature during the last 400 years modulated by PDO. The most recent fluctuation from the cold-to the warm-phase of the PDO in the mid 1970s induced marked changes in R. Villalba

A strengthening of the Amundsen Sea low from 1979 to 2013 has been shown to largely explain the observed increase in Antarctic sea ice concentration in the eastern Ross Sea and decrease in the Bellingshausen Sea. Here it is shown that while these changes are not generally seen in freely running coupled climate model simulations, they are reproduced in simulations of two independent coupled climate models: one constrained by observed sea surface temperature anomalies in the tropical Pacific and the other by observed surface wind stress in the tropics. This analysis confirms previous results and strengthens the conclusion that the phase change in the interdecadal Pacific oscillation from positive to negative over 1979-2013 contributed to the observed strengthening of the Amundsen Sea low and the associated pattern of Antarctic sea ice change during this period. New support for this conclusion is provided by simulated trends in spatial patterns of sea ice concentrations that are similar to those observed. These results highlight the importance of accounting for teleconnections from low to high latitudes in both model simulations and observations of Antarctic sea ice variability and change.

Preseason abundance forecasts drive management of US West Coast salmon fisheries, yet little is known about how environmental variability influences forecast performance. We compared forecasts of Chinook salmon (Oncorhynchus tshawytscha) against returns for (i) key California-Oregon ocean fishery stocks and (ii) high priority prey stocks for endangered Southern Resident Killer Whales (Orcinus orca) in Puget Sound, Washington. We explored how well environmental indices (at multiple locations and time lags) explained performance of forecasts based on different methods (i.e. sibling-based, production-based, environment-based, or recent averages), testing for nonlinear threshold dynamics. For the California stocks, no index tested explained &gt;50% of the variation in forecast performance, but spring Pacific Decadal Oscillation and winter North Pacific Index during the year of return explained &gt;40% of the variation for the sibling-based Sacramento Fall Chinook forecast, with nonlinea...

The influence of present-day anthropogenic aerosols on the summer monsoon over the East Asia region was simulated using the Community Earth System Model coupled with a slab ocean model. The simulations revealed significant radiative forcing from anthropogenic aerosols and associated changes in clouds over East Asia and the northwestern Pacific; however, their spatial patterns differed from the exhibited surface temperature and precipitation responses. Two major dynamic feedback mechanisms were identified to explain such discrepancies. The wind-evaporation-sea surface temperature (WES) feedback, triggered by an initial cooling over the midlatitude sea surface, induced an equatorward expansion of ocean cooling through strengthened trade winds. The sea surface cooling excited a meridional wave pattern similar to the Pacific-Japan teleconnection pattern. Although the aerosol effect generally caused weakening in summer monsoon strength and regional precipitation over East Asia, precipitation increases were seen over the locations of the midlatitude mei-yu front and around the tropics. These precipitation increases are primarily associated with the WES feedback and teleconnection patterns. The aerosol effect also reached the upper troposphere, causing an equatorward shift of the jet stream over East Asia and the northwestern Pacific, indicating a much broader scale of teleconnection.

Global climate change has readjusted a global-scale precipitation distribution in magnitude and timing. In mountainous areas, meteorological stations and observation data are very limited, making it difficult to accurately understand the response of precipitation to global climate change. Based on ECMWF Reanalysis v5 precipitation products, Berkeley Earth global temperature, and typical atmospheric circulation indexes, we integrated a gradient descent-nonlinear regression downscaling model, cross wavelet transform, and wavelet correlation method to analyze the precipitation response in Tianshan to global climate change. This study provides a high-resolution (90 m × 90 m) precipitation dataset in Tianshan and confirms that global warming, the North Pacific Pattern (NP), the Western Hemisphere Warm Pool (WHWP), and the Atlantic Multidecadal Oscillation (AMO) are related to the humidification of Tianshan over the past 40 years. The precipitation in Tianshan and global temperature have ...

The failure to detect C3 in absorption in diffuse clouds (24), however, appears to rule out this attribution. Note added in proof: We recently received a manuscript by R. J. Glinski and J. A. Nuth (27) in which a vibrational band assignment of the 5800 A Red Rectangle emis- sion features to C3 is presented. Combining this assignment with the results described here leads to the conclusion that C3 is the carrier of the X=5797, X=5850, and nearby related diffuse interstellar absorption bands.

This paper discusses large-scale climate variability for several marine ecosystems and suggests types of ecosystem responses to climate change. Our analysis of observations and model results for the Pacific and Atlantic Oceans concludes that most climate variability is accounted for by the combination of intermittent 1-2 year duration events, e.g. the cumulative effect of monthly weather anomalies or the more organized El Niño/La Niña, plus broad-band "red noise" intrinsic variability operating at decadal and longer timescales. While ocean processes such as heat storage and lags due to ocean circulation provide some multi-year memory to the climate system, basic understanding of the mechanisms resulting in observed large decadal variability is lacking and forces the adoption of a "stochastic or red noise" conceptual model of low frequency variability at the present time. Thus we conclude that decadal events with rapid shifts and major departures from climatic means will occur, but their timing cannot be forecast. The responses to climate by biological systems are diverse in character because intervening processes introduce a variety of amplifications, time lags, feedbacks, and non-linearities. Decadal ecosystem variability can involve a variety of climate to ecosystem transfer functions. These can be expected to convert red noise of the physical system to redder (lower frequency) noise of the biological response, but can also convert climatic red noise to more abrupt and discontinuous biological shifts, transient climatic disturbance to prolonged ecosystem recovery, and perhaps transient disturbance to sustained ecosystem regimes. All of these ecosystem response characteristics are likely to be active for at least some locations and time periods, leading to a mix of slow fluctuations, prolonged trends, and step-like changes in ecosystems and fish populations in response to climate change. Climate variables such as temperatures and winds can have strong teleconnections (large spatial covariability) within individual ocean basins, but between-basin teleconnections, and potential climate-driven biological synchrony over several decades, are usually much weaker and a highly intermittent function of the conditions prevailing at the time within the adjoining basins. As noted in the recent IPCC 4th Assessment Report, a warming trend of ocean surface layers and loss of regional sea ice is likely before 2030, due to addition of greenhouse gases. Combined with large continuing natural climate variability, this will stress ecosystems in ways that they have not encountered for at least 100s of years.

Considerable evidence has emerged of a substantial decade-long change in the north Pacific atmosphere and ocean lasting from about 1976 to 1988. Observed significant changes in the atmospheric circulation throughout the troposphere revealed a deeper and eastward shifted Aleutian low pressure system in the winter half year which advected warmer and moister air along the west coast of North America and into Alaska and colder air over the north Pacific. Consequently, there were increases in temperatures and sea surface temperatures (SSTs) along the west coast of North America and Alaska but decreases in SSTs over the central north Pacific, as well as changes in coastal rainfall and streamflow, and decreases in sea ice in the Bering Sea. Associated changes occurred in the surface wind stress, and, by inference, in the Sverdrup transport in the north Pacific Ocean. Changes in the monthly mean flow were accompanied by a southward shift in the storm tracks and associated synoptic eddy activity and in the surface ocean sensible and latent heat fluxes. In addition to the changes in the physical environment, the deeper Aleutian low increased the nutrient supply as seen through increases in total chlorophyll in the water column, phytoplankton and zooplankton. These changes, along with the altered ocean currents and temperatures, changed the migration patterns and increased the stock of many fish species. A north Pacific (NP) index is defined to measure the decadal variations, and the temporal variability of the index is explored on daily, annual, interannual and decadal time scales. The dominant atmosphere-ocean relation in the north Pacific is one where atmospheric changes lead SSTs by one to two months. However, strong ties are revealed with events in the tropical Pacific, with changes in tropical Pacific SSTs leading SSTs in the north Pacific by three months. Changes in the storm tracks in the north Pacific help to reinforce and maintain the anomalous circulation in the upper tro- The National Center for Atmospheric Research is sponsored by the National Science Foundation posphere. A hypothesis is put forward outlining the tropical and extratropical realtionships which stresses the role of tropical forcing but with important feedbacks in the extratropics that serve to emphasize the decadal relative to interannual time scales. The Pacific decadal timescale variations are linked to recent changes in the frequency and intensity of El Nifio versus La Nifia events but whether climate change associated with "global warming" is a factor is an open question.

The influence of large-scale modes of climate variability on worldwide summer and winter temperature extremes has been analyzed, namely, that of the El Niño–Southern Oscillation, the North Atlantic Oscillation, and Pacific interdecadal climate variability. Monthly indexes for temperature extremes from worldwide land areas are used describe moderate extremes, such as the number of exceedences of the 90th and 10th climatological percentiles, and more extreme events such as the annual, most extreme temperature. This study examines which extremes show a statistically significant (5%) difference between the positive and negative phases of a circulation regime. Results show that temperature extremes are substantially affected by large-scale circulation patterns, and they show distinct regional patterns of response to modes of climate variability. The effects of the El Niño–Southern Oscillation are seen throughout the world but most clearly around the Pacific Rim and throughout all of Nort...

Climate change might affect marine top predators by altering availability and nutritional quality of their prey. Climate effects vary on a regional basis, and our understanding of the relationships between fluctuations in climate and food resources in sub-arctic regions with seasonal ice cover is limited. We studied the effects of inter-annual climate variability (as reflected in the Pacific Decadal Oscillation, PDO, and the timing of the winter ice retreat) on zooplanktonplanktivorous predator linkages in one of the most productive regions of the southeastern Bering Sea, the 'Green Belt'. We examined changes in diets (species composition of chick meals and stable isotope signatures of adult blood) and relative food availability (as reflected in blood plasma concentrations of the stress hormone corticosterone) of planktivorous least auklets Aethia pusilla breeding on St. George I. (shelf-break) and St. Paul I. (shelf) during 2003 to 2005 and 2008 to 2009. We found that isotopic signatures of blood and composition of chick meals differed between the colonies. The proportion of energy-rich oceanic copepods Neocalanus spp. in the diet declined during warm years (high PDO and early ice retreat) on St. Paul but not on St. George. However, inter-annual and seasonal dynamics of corticosterone were similar between the colonies, and auklets experienced higher nutritional stress during warm compared to cold years. Our results suggest that the influx of prey-bearing water masses from the ocean basin and the retention time of oceanic copepods on the shelf are the main factors affecting composition of prey and its availability to auklets. We conclude that anticipated climate warming will negatively affect food availability of planktivorous predators in the Green Belt region of the southeastern Bering Sea.

Coastal upwelling helps set the physical context for marine ecosystems, and upwelling zones are among the most productive regions of the global ocean. Unlike earlier models, two state-of-the-art climate models exhibit little change during the next century in the magnitude and seasonality of coastal upwelling, but climate models are still probably not sufficiently developed (for example, they underestimate interdecadal variability in upwelling) to provide valid projections of this key component of the coastal environment.

Climatic variability is a dominant factor affecting large wildfires in the western United States, an observation supported by palaeoecological data on charcoal in lake sediments and reconstructions from fire-scarred trees. Although current fire management focuses on fuel reductions to bring fuel loadings back to their historical ranges, at the regional scale extreme fire weather is still the dominant influence on area burned and fire severity. Current forecasting tools are limited to short-term predictions of fire weather, but increased understanding of large-scale oceanic and atmospheric patterns in the Pacific Ocean (e.g., El Niño Southern Oscillation, Pacific Decadal Oscillation) may improve our ability to predict climatic variability at seasonal to annual leads. Associations between these quasi-periodic patterns and fire occurrence, though evident in some regions, have been difficult to establish in others. Increased temperature in the future will likely extend fire seasons throughout the western United States, with more fires occurring earlier and later than is currently typical, and will increase the total area burned in some regions. If climatic change increases the amplitude and duration of extreme fire weather, we can expect significant changes in the distribution and abundance of dominant plant species in some ecosystems, which would thus affect habitat of some sensitive plant and animal species. Some species that are sensitive to fire may decline, whereas the distribution and abundance of species favored by fire may be enhanced. The effects of climatic change will partially depend on the extent to which resource management modifies vegetation structure and fuels.

Observations of snow water equivalent (SWE) in the Pacific Northwest are examined and compared with variability and trends in temperature and precipitation at nearby climate stations. At most locations, especially below about 1800 m, substantial declines in SWE coincide with significant increases in temperature, and occur in spite of increases in precipitation.

The Antarctic Circumpolar Current (ACC) plays an important role in the climate as it balances heat energy and water mass between the Pacific and Atlantic Oceans through the Drake Passage. However, because the historical measurements and observations are extremely limited, the decadal and long-term variations of the ACC around the western South Atlantic Ocean are rarely studied. By analyzing reconstructed sea surface temperatures (SSTs) in a 147-year period (1870–2016), previous studies have shown that SST anomalies (SSTAs) around the Antarctic Peninsula and South America had the same phase change as the El Niño Southern Oscillation (ENSO). This study further showed that changes in SSTAs in the regions mentioned above were enlarged when the Pacific Decadal Oscillation (PDO) and the ENSO were in the same warm or cold phase, implying that changes in the SST of higher latitude oceans could be enhanced when the influence of the ENSO is considered along with the PDO.

This paper investigates the time series properties of the temperature and precipitation anomalies in the contiguous USA by using fractional differentiation. This methodology allows to capture time trend components along with properties such as long-range dependence and the degree of persistence. For aggregated data, we find out that long memory is present in both precipitation and temperature since the integration order is significantly positive in the two cases. The time trend is also positive, being higher for the temperature. In addition, observing disaggregated data by states, for the temperature, there are only seven states where the time trend is not significant, with most of them located in Southeast areas, while for the rest of cases, the time trend is significantly positive. All cases exhibit long-range dependence, though the differencing parameter substantially changes from one state to another, ranging from 0.09 in Nebraska and Kansas to 0.18 in Florida and Michigan. For ...

In this paper, circulation and precipitation climate patterns over the South American domain obtained from NCEP-NCAR reanalysis I, JRA-55, and ERA-40 reanalysis datasets were intercompared within the period 1970-2001 in order to verify their climatic association with the Pacific Decadal Oscillation, PDO. Although all three datasets showed similar climatic patterns during each PDO phase, they showed distinct intensities for circulation and precipitation variables. The mean low frequency flow propagation over the South Pacific during negative and positive PDO phases reached central-eastern South America with opposite signals, contributing to the modulation of the local climate. During the negative PDO phases, the northerly flow over South America is intensified, while during the positive phase it is weakened. NCEP-NCAR reanalysis I, in comparison with JRA-55 and ERA-40 values, always indicates the strongest signal for circulation and precipitation variables. NCEP-NCAR reanalysis I meridional wind at the low-level jet area was about 5 and 12% larger than the respective JRA-55 and the ERA-40 values. For the positive and negative PDO phases, only NCEP-NCAR and ERA-40 high-level zonal wind anomalies showed divergent (positive PDO) and convergent (negative PDO) patterns close to 140 • W at equatorial latitudes of the Pacific Ocean, respectively. This one indicated distinct representations of the positioning of Walker cells in the three reanalysis datasets. GPCC dataset, NCEP-NCAR, JRA-55, and ERA-40 reanalysis showed, in general, the dipole precipitation pattern over eastern South America, with signs of changes between the central-eastern and southeastern areas during PDO reversal phases. Over the central-eastern South American region, NCEP-NCAR precipitation is, on average, 57% larger than GPCC values, and 35 and 46% larger than JRA-55 and ERA-40 values, respectively. The observed patterns of anomalies for different PDO phases appeared in all reanalysis datasets, leading us to conclude that the physical meaning is independent from the datasets. Even considering the JRA-55 climate signal over South America associated with the PDO influence as the weakest one, the ability of JRA-55 to calculate monthly precipitation provided the highest linear correlation coefficient values in tropical areas, leading us to consider this dataset as the most reliable for the studied area.

The high biological production of the California Current System (CCS) results from the seasonal development of equatorward alongshore winds that drive coastal upwelling. While several climatic fluctuation patterns influence the dynamics and biological productivity of the CCS, including the El Nin ˜o-Southern Oscillation (ENSO), the Pacific Decadal Oscillation index (PDO) and the North Pacific Gyre Oscillation (NPGO), the mechanisms of interaction between climatic oscillations and the CCS upwelling dynamics have remained obscure. Here, we use Singular Spectral Analysis (SSA) to reveal, for the first time, low-frequency concordance between the time series of climatic indices and upwelling intensity along the coast of western North America. Based on energy distributions in annual, semiannual and low-frequency signals, we can divide the coast into three distinct regions. While the annual upwelling signal dominates the energy spectrum elsewhere, low-frequency variability is maximal in the regions south of 33uN. Non-structured variability associated with storms and turbulent mixing is enhanced at northerly locations. We found that the low-frequency signal is significantly correlated with different climatic indices such as PDO, NPGO and ENSO with the correlation patterns being latitude-dependent. We also analyzed the correlations between this upwelling variability and sea surface temperature (SST) and sea level pressure (SLP) throughout the North Pacific to visualize and interpret the large-scale teleconnection dynamics in the atmosphere that drive the low-frequency coastal winds. These results provide new insights into the underlying mechanisms connecting climatic patterns with upwelling dynamics, which could enhance our prediction and forecast capabilities of the effects of future oceanographic and climatic variability in the CCS.

In a water-stressed region, such as the southwestern United States, it is essential to improve current seasonal hydroclimatic predictions. Typically, seasonal hydroclimatic predictions have been conditioned by standard climate indices, for example, Niño-3 and Pacific decadal oscillation (PDO). In this work, the statistically unique relationships between sea surface temperatures (SSTs) and particular basins’ hydroclimates are explored. The regions where global SSTs are most correlated with the Little Colorado River and Gunnison River basins’ hydroclimates are located throughout the year and at varying time lags. The SSTs, from these regions of highest correlation, are subsequently used as hydroclimatic predictors for the two basins. This methodology, named basin-specific climate prediction (BSCP), is further used to perform hindcasts. The hydroclimatic hindcasts obtained using BSCP are shown to be closer to the historical record, for both basins, than using the standard climate indic...

Extremely-low discharge events of the Paranaı ´ba River basin during the austral summer season (December-February, DJF), are found to be associated with the Pacific sea surface temperature anomalies resembling the recently identified El Nin ˜o Modoki phenomenon. Extreme discharge events are identified based on their persistent flow for 7 days and more after taking retention time into consideration. Ninety percent of the extremely low discharge events during peak streamflow seasons of DJF, are found to occur during the El Nin ˜o Modoki years. A diagnostics study of atmospheric anomalies has shown a clear connection between the modified Walker circulation, associated with the El Nin ˜o Modoki, and the precipitation anomalies over the Paranaı ´ba River basin. The climate variations have direct relationship with the rainfall. Streamflow variations are considered as the surrogates to rainfalls. Thus, El Nin ˜o Modoki phase is important component to understand and predict the streamflow variations in the Paranaı ´ba River basin.

The temperature record of the last 150 years is characterized by a long-term warming trend, with strong multidecadal variability superimposed. The multidecadal variability is also seen in other (societal important) parameters such as Sahel rainfall or Atlantic hurricane activity. The existence of the multidecadal variability makes climate change detection a challenge, since Global Warming evolves on a similar timescale. The ongoing discussion about a potential anthropogenic signal in the Atlantic hurricane activity is an example. A lot of work was devoted during the last years to understand the dynamics of the multidecadal variability, and external as well as internal mechanisms were proposed. This White Paper focuses on the internal mechanisms relevant to the Atlantic Multidecadal Oscillation/Variability (AMO/V) and the Pacific Decadal Oscillation/Variability (PDO/V). Specific attention is given to the role of the Meridional Overturning Circulation (MOC) in the Atlantic. The implications for decadal predictability and prediction are discussed.

Variability of the North Atlantic Oscillation and the Tropical Atlantic dominate the climate of the North Atlantic sector, the underlying ocean and surrounding continents on interannual to decadal time scales. Here we review these phenomena, their climatic impacts and our present state of understanding of their underlying cause. Copyright © 2001 Royal Meteorological Society

The relationship between El Niño Southern Oscillation (ENSO) and precipitation along the Peruvian Pacific coast is investigated over 1964-2011 on the basis of a variety of indices accounting for the different types of El Niño events and atmospheric and oceanographic manifestations of the interannual variability in the tropical Pacific. We show the existence of fluctuations in the ENSO/precipitation relationship at decadal timescales that are associated with the ENSO property changes over the recent decades. Several indices are considered in order to discriminate the influence of the two types of El Niño, namely, the eastern Pacific El Niño and the central Pacific El Niño, as well as the influence of large-scale atmospheric variability associated to the Madden and Julian Oscillation, and of regional oceanic conditions. Three main periods are identified that correspond to the interleave periods between the main climatic transitions over 1964-2011, i.e. the shifts of the 1970s and the 2000s, over which ENSO experiences significant changes in its characteristics. We show that the relationship between ENSO and precipitation along the western coast of Peru has experienced significant decadal change. Whereas El Niño events before 2000 lead to increased precipitation, in the 2000s, ENSO is associated to drier conditions. This is due to the change in the main ENSO pattern after 2000 that is associated to cooler oceanic conditions off Peru during warm events (i.e. central Pacific El Niño). Our analysis also indicates that the two extreme El Niño events of 1982/1983 and 1997/1998 have overshadowed actual trends in the relationship between interannual variability in the tropical Pacific and precipitation along the coast of Peru. Overall, our study stresses on the complexity of the hydrological cycle on the western side of the Andes with regard to its relationship with the interannual to decadal variability in the tropical Pacific.

We present a new, diatom-based sea-level reconstruction for Iceland spanning the last ~500 years, and investigate the possible mechanisms driving the sea-level changes. A sea-level reconstruction from near the Icelandic low pressure system is important as it can improve understanding of ocean-atmosphere forcing on North Atlantic sea-level variability over multidecadal to centennial timescales. Our reconstruction is from Viðarhólmi salt marsh in Snaefellsnes in western Iceland, a site from where we previously obtained a 2000-yr record based upon less precise sea-level indicators (salt-marsh foraminifera). The 20 th century part of our record is corroborated by tide-gauge data from Reykjavik. Overall, the new reconstruction shows ca. 0.6 m rise of relative sea level during the last four centuries, of which ca. 0.2 m occurred during the 20 th century. Low-amplitude and high-frequency sealevel variability is super-imposed on the pre-industrial long-term rising trend of 0.65 m per 1000 years. Most of the relative sea-level rise occurred in three distinct periods: AD 1620-1650, AD 1780-1850 and AD 1950-2000, with maximum rates of ~3 ± 2 mm/yr during the latter two of these periods. Maximum rates were achieved at the end of large shifts (from negative to positive) of the winter North Atlantic Oscillation (NAO) Index as reconstructed from proxy data. Instrumental data demonstrate that a strong and sustained positive NAO (a deep Icelandic Low) generates setup on the west coast of Iceland resulting in rising sea levels. There is no strong evidence that the periods of rapid sea-level rise were caused by ocean mass changes, glacial isostatic adjustment or regional steric change. We suggest that wind forcing plays an important role in causing regional-scale coastal sea-level variability in the North Atlantic, not only on (multi-)annual timescales, but also on multi-decadal to centennial timescales.

During the positive phase of the North Pacific Oscillation, westerly wind anomalies over the subtropical North Pacific substantially increase subsurface heat content along the equator by ''trade wind charging'' (TWC). TWC provides a direct pathway between extratropical atmospheric circulation and El Niño-Southern Oscillation (ENSO) initiation. Previous model studies of this mechanism lacked the oceanatmospheric coupling needed for ENSO growth, so it is crucial to examine whether TWC-induced heat content anomalies develop into ENSO events in a coupled model. Here, coupled model experiments, forced with TWC favorable (1TWC) or unfavorable (2TWC) wind stress, are used to examine the ENSO response to TWC. The forcing is imposed on the ocean component of the model through the first winter and then the model evolves in a fully coupled configuration through the following winter. The 1TWC (2TWC) forcing consistently charges (discharges) the equatorial Pacific in spring and generates positive (negative) subsurface temperature anomalies. These subsurface temperature anomalies advect eastward and upward along the equatorial thermocline and emerge as like-signed sea surface temperature (SST) anomalies in the eastern Pacific, creating favorable conditions upon which coupled air-sea feedback can act. During the fully coupled stage, warm SST anomalies in 1TWC forced simulations are amplified by coupled feedbacks and lead to El Niño events. However, while 2TWC forcing results in cool SST anomalies, pre-existing warm SST anomalies in the far eastern equatorial Pacific persist and induce local westerly wind anomalies that prevent consistent development of La Niña conditions. While the TWC mechanism provides adequate equatorial heat content to fuel ENSO development, other factors also play a role in determining whether an ENSO event develops.

During the positive phase of the North Pacific Oscillation, westerly wind anomalies over the subtropical North Pacific substantially increase subsurface heat content along the equator by “trade wind charging” (TWC). TWC provides a direct pathway between extratropical atmospheric circulation and El Niño–Southern Oscillation (ENSO) initiation. Previous model studies of this mechanism lacked the ocean–atmospheric coupling needed for ENSO growth, so it is crucial to examine whether TWC-induced heat content anomalies develop into ENSO events in a coupled model. Here, coupled model experiments, forced with TWC favorable (+TWC) or unfavorable (−TWC) wind stress, are used to examine the ENSO response to TWC. The forcing is imposed on the ocean component of the model through the first winter and then the model evolves in a fully coupled configuration through the following winter. The +TWC (−TWC) forcing consistently charges (discharges) the equatorial Pacific in spring and generates positive...

This paper investigates possible linear relationships between climate, hydrology, and oceanic surface variability in the Pantanal region (in South America's central area), over interannual and interdecadal time ranges. In order to verify the mentioned relations, lagged correlation analysis and linear adjustment between river discharge at the Pantanal region and sea surface temperature were used. Composite analysis for atmospheric fields, air humidity flux divergence, and atmospheric circulation at low and high levels, for the period between 1970 and 2003, was analyzed. Results suggest that the river discharge in the Pantanal region is linearly associated with interdecadal and interannual oscillations in the Pacific and Atlantic oceans, making them good predictors to continental hydrological variables. Considering oceanic areas, 51 % of the annual discharge in the Pantanal region can be linearly explained by mean sea surface temperature (SST) in the Subtropical North Pacific, Tropical North Pacific, Extratropical South Pacific, and Extratropical North Atlantic over the period.

The U.S. Climate Variability and Predictability (CLIVAR) working group on drought recently initiated a series of global climate model simulations forced with idealized SST anomaly patterns, designed to address a number of uncertainties regarding the impact of SST forcing and the role of land–atmosphere feedbacks on regional drought. The runs were carried out with five different atmospheric general circulation models (AGCMs) and one coupled atmosphere–ocean model in which the model was continuously nudged to the imposed SST forcing. This paper provides an overview of the experiments and some initial results focusing on the responses to the leading patterns of annual mean SST variability consisting of a Pacific El Niño–Southern Oscillation (ENSO)-like pattern, a pattern that resembles the Atlantic multidecadal oscillation (AMO), and a global trend pattern. One of the key findings is that all of the AGCMs produce broadly similar (though different in detail) precipitation responses to t...

El Niño Southern Oscillation (ENSO) represents the major driver of interannual climate variability at global scale. Observational and model-based studies have fostered a long-standing debate on the shape and intensity of the ENSO influence over the Euro-Mediterranean sector. Indeed, the detection of this signal is strongly affected by the large internal variability that characterizes the atmospheric circulation in the North Atlantic-European (NAE) region. This study explores if and how the low-frequency variability of North Pacific sea surface temperature (SST) may impact the El Niño-NAE teleconnection in late winter, which consists of a dipolar pattern between middle and high latitudes. A set of idealized atmosphere-only experiments, prescribing different phases of the anomalous SST linked to the Pacific Decadal Oscillation (PDO) superimposed onto an El Niño-like forcing in the tropical Pacific, has been performed in a multi-model framework, in order to assess the potential modulation of the positive ENSO signal. The modelling results suggest, in agreement with observational estimates, that the PDO negative phase (PDO -) may enhance the amplitude of the El Niño-NAE teleconnection, while the dynamics involved appear to be unaltered. On the other hand, the modulating role of the PDO positive phase (PDO + ) is not reliable across models. This finding is consistent with the atmospheric response to the PDO itself, which is robust and statistically significant only for PDO -. Its modulation seems to rely on the enhanced meridional SST gradient and the related turbulent heat-flux released along the Kuroshio-Oyashio extension. PDO -weakens the North Pacific jet, whereby favoring more poleward propagation of wave activity, strengthening the El Niño-forced Rossby wave-train. These results imply that there might be conditional predictability for the interannual Euro-Mediterranean climate variability depending on the background state.

Brazil is increasingly affected by extreme weather events due to climate change, with pronounced regional differences in temperature and precipitation patterns. The southeast region is particularly vulnerable, frequently experiencing severe droughts and extreme heatwaves linked to atmospheric blocking events and intense rainfall episodes driven by the South Atlantic Convergence Zone (SACZ). These phenomena contribute to recurring climate-related disasters. The country's heavy reliance on hydropower heightens its susceptibility to droughts, while growing evidence points to intensifying dry spells and wildfires across multiple regions, threatening agricultural output and food security. Urban areas, particularly, are experiencing more frequent and severe heatwaves, posing serious health risks to vulnerable populations. This study investigates the links between global teleconnection indices and synoptic-scale systems, specifically blocking events and SACZ activity, and their influence on Brazil's extreme heat, drought conditions, and river flow variability over the past 30 to 40 years. By clarifying these interactions, the research aims to enhance understanding of how large-scale atmospheric dynamics shape climate extremes and to assess their broader implications for water resource management, energy production, and regional climate variability.

Because of the need for information related to the variability and predictability of sea level on season-to-longer time scales, the Pacific ENSO Applications Climate (PEAC) Center runs the El Niño-Southern Oscillation (ENSO)-based canonical correlation analysis (CCA) statistical model to generate sea level forecasts for the U.S.-affiliated Pacific Islands (USAPI) region with lead times of 3–6 months in advance. However, in order to meet the increasing demand for longer lead-time (e.g., 6–12 months) forecasts, the PEAC Center, as part of the advances in operational sea level forecasts, recently incorporated both SST and zonal wind components of trade winds (U) for modulating sea level variability on longer time scales. The combined SST and U-based forecasts are found to be more skillful on longer time scales. This improvement has enabled the capability of our clients in the USAPI region to develop a more efficient long-term response plan for hazard management. In a recent “Regional I...

For the first time, trends of five climate change indices related to extreme precipitation events in the Hawaiian Islands are investigated using daily observational records from the 1950s to 2007. Four indices [simple daily intensity index (SDII), total number of day with precipitation ≥25.4 mm (R25), annual maximum consecutive 5-day precipitation amount (R5d), and the fraction of annual total precipitation from events exceeding the 1961–90 95th percentile (R95p)] describe the intensity (SDII), frequency (R25), and magnitude (R5d and R95p) of precipitation extremes, and the fifth index [consecutive dry days (CDD)] describes drought conditions. The annual probability density functions (PDFs) of precipitation indices for two epochs (i.e., 1950–79 and 1980–2007) are analyzed. Since the 1980s, there has been a change in the types of precipitation intensity, resulting in more frequent light precipitation and less frequent moderate and heavy precipitation intensity. The other three precip...

The objective of this study is to develop an operational canonical correlation analysis (CCA) statistical model for sea‐level forecasts in the U. S.‐affiliated Pacific Islands (USAPI) with lead times of several months or longer. The El Niño‐Southern Oscillation (ENSO) climate cycle and the sea‐surface temperatures (SSTs) in the tropical Pacific Ocean are taken as the primary factors in modulating sea‐level variability on the seasonal time scales.Observations revealed that the sea‐level variations in the USAPI are sensitive to ENSO cycle with low sea level during El Niño and high sea level during La Niña events. The correlation between the sea‐level variability and the fluctuations of tropical Pacific SSTs has been found to be strong. The cross‐validated results indicated that the SST‐based CCA model is potentially useful in predicting seasonal sea‐level variations in the USAPI. For all target seasons at 1‐ and 2‐season lead times, the average correlation skill has been found to be 0...

Southern Africa (SA) and eastern Africa (EA) experienced a sequence of severe droughts in December–February (SA DJF) 2015–2016, October–December (EA OND) 2016 and March–April–May 2017 (EA MAM). This sequence contributed to severe food insecurity. While climate variability in these regions is very complex, the goal of this study is to analyse the role played by unusually warm Indo–Pacific SSTs, where unusual is defined as a 1‐in‐6 year event. We use observed sea‐surface temperatures (SST) and satellite–gauge rainfall observations, a 20‐member ensemble of Community Atmospheric Model version 5.1 simulations (CAM5), and a 40‐member ensemble of climate change simulations from the Community Earth Systems Model version 1 (CESM1) Large Ensemble Community Project (LENS) to explore climate conditions associated with warm events identified based on eastern and western Pacific SSTs. Our analysis suggests that strong El Niño&#39;s may be followed by warm western Pacific SST conditions, which can...

A primitive equation ocean general circulation model is used to investigate climate impacts in the North Pacific Ocean in the 1996 to 2003 period. The objective is to assess the model ability to reproduce observed modes of variability and study their impact in the northeast Pacific. This work is done within the framework of the U.S. Global Ecosystem (GLOBEC) Northeast Pacific Program studying the links between climate variability and ecosystem dynamics. Three large‐scale events are considered: The 1997/1998 El Niño, the 1999 “regime shift,” and the 2002 cold/fresh subsurface anomalous water mass that was observed in the Gulf of Alaska and off the coast of Oregon. The circulation model is shown to generate the correct seasonal to interannual large‐scale variability and is able to represent the climatic signals of interest in the eastern Pacific. We show that the influence of the 1997/1998 El Niño reached the coastal Gulf of Alaska and induced an increase in the upper ocean heat conte...