North Pacific Sea Surface Temperature Research Articles

Multi-time scale stream flow predictions: The support vector machines approach

Effective lead-time stream flow forecast is one of the key aspects of successful water resources management in arid regions. In this research, we present new data-driven models based on Statistical Learning Theory that were used to forecast flows at two time scales: seasonal flow volumes and hourly stream flows. The models, known as Support Vector Machines, are learning systems that use a hypothesis space of linear functions in a Kernel induced higher dimensional feature space, and are trained with a learning algorithm from optimization theory. They are based on a principle that aims at minimizing the generalized model error (risk), rather than just the mean square error over a training set. Due to Mercer's condition on the kernels the corresponding optimization problems are convex and hence have no local minima. Empirical results from these models showed a promising performance in solving site-specific, real-time water resources management problems. Stream flow was forecasted using local-climatological data and requiring far less input than physical models. In addition, seasonal flow volume predictions were improved by incorporating atmospheric circulation indicators. Specifically, use of the North-Pacific Sea Surface Temperature Anomalies (SSTA) improved flow volume predictions.

Climate precursors of multidecadal drought variability in the western United States

Low‐frequency (periodicities lower than 20 years) hydrologic variability in the western United States over the past 500 years is studied using available tree‐ring reconstructions of Palmer Drought Severity Index (PDSI), streamflow, and climate indices. Leading rotated principal component (RPC) scores of a gridded tree‐ring reconstruction of the PDSI from 1525 to 1975 are significantly correlated with indices representing large‐scale climate variations from the Pacific and Atlantic Oceans. RPC1 (31%) is related to the influence of North Pacific sea surface temperature (SST) variations, indexed by the Pacific Decadal Oscillation (PDO). RPC2 (24%) is apparently related to North Atlantic SST variations, indexed by the Atlantic Multidecadal Oscillation (AMO). RPC3 (19%) is moderately correlated with a smoothed version of the Southern Oscillation Index. Consistent with recent studies of instrumental data, RPC1 (PDO) and RPC2 (AMO) explain a large part of the multidecadal hydrologic variability of the interior western United States. Western U.S. PDSI variability exhibits significant pentadecadal (and longer) oscillations in the epochs from circa 1525 to 1650 and 1850 to 1975, while bidecadal oscillations are prevalent in the middle epoch from circa 1650 to 1850. The changes in spectral characteristics of western U.S. PDSI were related to similar changes in the PDO (and therefore in RPC1). In contrast, RPC2 had a regular periodicity of 51 years for the past ∼500 years. This regularity is intriguing, and although RPC2 was primarily related to the AMO in this study, the influence from Pacific climate cannot be discarded.

Decadal North Pacific sea surface temperature variability and the associated global climate anomalies in a coupled general circulation model

We explore the characteristics of decadal North Pacific sea surface temperature (SST) variability along with its relationship to global climate variations based on the analysis of a long‐term coupled model simulation (300 years). Two key regions of North Pacific decadal variability, i.e., the western North Pacific (WNP) and central North Pacific (CNP) SST variability, are defined. While the global atmospheric patterns associated with decadal WNP variability are localized around east Asia and the western North Pacific, those of decadal CNP variability have both a local and a remote manifestation. The midlatitude response to decadal CNP variability is examined on the basis of El Nino and Southern Oscillation (ENSO) variability on interannual and decadal timescales. Decadal CNP variability can destructively or constructively interfere with the midlatitude response to interannual ENSO variability.

Mid Holocene origin of the sea-surface salinity low in the subarctic North Pacific

IMAGES core MD01-2416 (51°N, 168°E) provides the first centennial-scale multiproxy record of Holocene variation in North Pacific sea-surface temperature (SST), salinity, and biogenic productivity. Our results reveal a gradual decrease in subarctic SST by 3–5 °C from 11.1 to 4.2 ka and a stepwise long-term decrease in sea surface salinity (SSS) by 2–3 p.s.u. Early Holocene SSS were as high as in the modern subtropical Pacific. The steep halocline and stratification that is characteristic of the present-day subarctic North Pacific surface ocean is a fairly recent feature, developed as a product of mid-Holocene environmental change. High SSS matched a salient productivity maximum of biogenic opal during Bølling-to-Early Holocene times, reaching levels similar to those observed during preglacial times in the warm mid-Pliocene prior to 2.73 Ma. Similar productivity spikes marked every preceding glacial termination of the last 800 ka, indicating recurrent short-term events of mid-Pliocene-style intense upwelling of nutrient-rich Pacific Deepwater in the Pleistocene. Such events led to a repeated exposure of CO 2-rich deepwater at the ocean surface facilitating a transient CO 2 release to the atmosphere, but the timing and duration of these events repudiate a long-term influence of the subarctic North Pacific on global atmospheric CO 2 concentration.

The impact of internal atmospheric variability on the North Pacific SST variability

The impact of internal atmospheric variability on North Pacific sea surface temperature (SST) variability is examined based on three coupled general circulation model simulations. The three simulations differ only in the level of atmospheric noise occuring over the ocean at the air-sea interface. The amplitude of atmospheric noise is controlled by use of the interactive ensemble technique. This technique simultaneously couples multiple realizations of a single atmospheric model to a single realization of an ocean model. The atmospheric component models all experience the same SST, but the ocean component is forced by the ensemble averaged fluxes thereby reducing the impact of internal atmospheric dynamics at the air-sea interface. The ensemble averaging is only applied at the air-sea interface so that the internal atmospheric dynamics (i.e., transients) of each atmospheric ensemble member is unaffected. This interactive ensemble technique significantly reduces the SST variance throughout the North Pacific. The reduction in SST variance is proportional to the number of ensemble members indicating that most of the variability can simply be explained as the response to atmospheric stochastic forcing. In addition, the impact of the internal atmospheric dynamics at the air-sea interface masks out much of the tropical-midlatitude SST teleconnections on interannual time scales. Once this interference is reduced (i.e., applying the interactive ensemble technique), tropical-midlatitude SST teleconnections are easily detected.

ENSO-Forced Variability of the Pacific Decadal Oscillation

Variability of the Pacific decadal oscillation (PDO), on both interannual and decadal timescales, is well modeled as the sum of direct forcing by El Nino-Southern Oscillation (ENSO), the ''reemergence'' of North Pacific sea surface temperature anomalies in subsequent winters, and white noise atmospheric forcing. This simple model may be taken as a null hypothesis for the PDO, and may also be relevant for other climate integrators that have been previously related to the PDO.

Atmospheric anomalies related to interdecadal variability of SST in the North Pacific

Anomalous patterns of the atmospheric circulation and climate are studied corresponding to the two basic interdecadal variation modes of sea surface temperature (SST) in the North Pacific, namely, the 25–35-year mode and the 7–10-year mode. Results clearly indicate that corresponding to the positive and negative phases of the interdecadal modes of SST anomaly (SSTA) in the North Pacific, the anomalous patterns of the atmospheric circulation and climate are approximately out of phase, fully illustrating the important role of the interdecadal modes of SST. Since the two interdecadal modes of SSTA in the North Pacific have similar horizontal structures, their impacts on the atmospheric circulation and climate are also analogous. The impact of the interdecadal modes of the North Pacific SST on the atmospheric circulation is barotropic at middle latitudes and baroclinic in tropical regions.

Red noise and regime shifts

The analysis of interdecadal physical and biological variability is made challenging by the relative shortness of available time series. It has been suggested that rapid temporal changes of the most energetic empirical orthogonal function of North Pacific sea surface temperature (sometimes called the Pacific Decadal Oscillation or PDO) represents a “regime shift” between states with otherwise stable statistics. Using random independent time series generated to have the same frequency content as the PDO, we show that a composite analysis of climatic records recently used to identify regime shifts is likely to find them in Gaussian, red noise with stationary statistics. Detection of a shift by this procedure is not evidence of nonlinear processes leading to bi-stable behavior or any other meaningful regime shift.

Interannual Covariance between Japan Summer Precipitation and Western North Pacific SST

A statistical analysis is conducted of the covariance between summer precipitation in Japan and concurrent variations of sea surface temperature (SST) in the Western North Pacific (WNP; 120‐160 � E, 0‐60 � N). To this end, a singular value decomposition (SVD) is applied to observed monthly anomalies of the two fields for the period 1961‐1998 (38 summer seasons). The first coupled mode of the SVD explains as much as 71% of the total cross-covariance between WNP SST and Baiu precipitation. It is characterized by a zonally elongated dipole in the SST anomaly with opposite loadings on either side of about 30 � N and a precipitation anomaly with its maximum in southern Japan. The patterns indicate a negative correlation between Japan’s summer precipitation and the sea surface temperature in the East China Sea, Japan Sea and Kuroshio-Oyashio extension. Simpler composite analyses confirm the robustness of the coupling. In a linear regression analysis, the score of the WNP SST explains 30% of the domain mean summer precipitation variance, which is larger than the variance accounted for by lagged and concurrent ENSO-indices. Composites related to the mode’s precipitation score were found to support both directions of the atmosphere‐ocean interaction. On the one hand, the anomalies in radiation and evaporation at the sea surface would be sufficiently large to induce the observed temperature variations in the northern pole of the SST pattern. On the other hand, the possibility for an atmospheric response to the SST is supported by the consistency of anomalies in lower‐tropospheric baroclinicity and moisture flux divergence with the underlying SST distribution.

NEW ENGLAND DROUGHT AND RELATIONS WITH LARGE SCALE ATMOSPHERIC CIRCULATION PATTERNS1

ABSTRACT: To provide a basis for regional hydroclimatic forecasting, New England (NE) precipitation and streamflow are compared with indices for the El Niño/Southern Oscillation, the Pacific North American (PNA) pattern, and the North Atlantic Oscillation (NAO). Significant positive correlations are found between the NAO index and monthly streamflow at western inland locations, with the strongest seasonal correlations occurring in winter. Smoothed records for the winter NAO and winter streamflow are highly correlated at some sites, suggesting that interrelationships are most significant in the low frequency spectrum. However, correlations between the NAO and precipitation are not significant, so further examination of other factors is needed to explain the relationship between the NAO and streamflow. NAO related regional air temperature, sea surface temperature (SST), storm tracking, and snowfall variability are possible mechanisms for the observed teleconnection. Exceptionally cool regional air temperatures, and SSTs, and unique regional storm track patterns characterized NE's climate during the famous 1960s drought, suggesting that concurrent (persistent) negative NAO conditions may have contributed to the severity of that event. Monthly and winter averaged regional streamflow variability are also significantly correlated with the PNA index. This, along with results from previous studies, suggests that tropospheric wave character and associated North Pacific SST anomalies are also related to NE regional drought conditions.

Decadal variability of the Danube river flow in the lower basin and its relation with the North Atlantic Oscillation

AbstractThe decadal variability (>5 years) of the Danube river flow in the lower basin and its connection with the North Atlantic Oscillation (NAO) is analysed for the period 1931–95. Associated linkages with precipitation (PP) in the European sector, global sea surface temperature (SST) and atmospheric circulation for the period 1931–81, and the 500 hPa geopotential heights (G500) over the Northern Hemisphere for the period 1948–95 are also investigated.The results show that there is an out‐of‐phase relationship between the time series of the Danube river flow anomalies and the NAO index. The time series of a PP index, defined as the average of normalized precipitation anomalies over a large area including the Danube basin, presents a time evolution similar to that of the river flow anomalies.The correlation maps between the river flow anomalies and global SST show coherent large‐scale patterns. High values of the Danube river flow are associated with a tripole‐like SST structure in the North Atlantic similar to that appearing during the negative phase of the NAO, and with negative SST anomalies in the central North Pacific and positive SST anomalies in the eastern and central tropical Pacific. Physically consistent sea level pressure and 500 hPa geopotential height are obtained. Copyright © 2002 Royal Meteorological Society.

The Atmospheric Bridge: The Influence of ENSO Teleconnections on Air–Sea Interaction over the Global Oceans

During El Nino-Southern Oscillation (ENSO) events, the atmospheric response to sea surface temperature (SST) anomalies in the equatorial Pacific influences ocean conditions over the remainder of the globe. This connection between ocean basins via the ''atmospheric bridge'' is reviewed through an examination of previous work augmented by analyses of 50 years of data from the National Centers for Environmental Prediction- National Center for Atmospheric Research (NCEP-NCAR) reanalysis project and coupled atmospheric general circulation (AGCM)-mixed layer ocean model experiments. Observational and modeling studies have now established a clear link between SST anomalies in the equatorial Pacific with those in the North Pacific, north tropical Atlantic, and Indian Oceans in boreal winter and spring. ENSO-related SST anomalies also appear to be robust in the western North Pacific during summer and in the Indian Ocean during fall. While surface heat fluxes are the key component of the atmospheric bridge driving SST anomalies, Ekman transport also creates SST anomalies in the central North Pacific although the full extent of its impact requires further study. The atmospheric bridge not only influences SSTs on interannual timescales but also affects mixed layer depth (MLD), salinity, the seasonal evolution of upper-ocean temperatures, and North Pacific SST variability at lower fre- quencies. The model results indicate that a significant fraction of the dominant pattern of low-frequency (.10 yr) SST variability in the North Pacific is associated with tropical forcing. AGCM experiments suggest that the oceanic feedback on the extratropical response to ENSO is complex, but of modest amplitude. Atmosphere- ocean coupling outside of the tropical Pacific slightly modifies the atmospheric circulation anomalies in the Pacific-North America (PNA) region but these modifications appear to depend on the seasonal cycle and air- sea interactions both within and beyond the North Pacific Ocean.

The Role of Sea Surface Temperatures in Interactions between ENSO and the North Pacific Oscillation

The North Pacific Oscillation (NPO) is a decadal to interdecadal fluctuation of sea surface temperatures (SSTs) in the North Pacific. Previous works have shown that during individual El Nino and La Nina winters, atmospheric circulation anomalies over North America are characteristically different for different phases of the NPO. Two physical mechanisms could account for this observed link between North Pacific SSTs and ENSO's effects over North America: 1) NPO SSTs could force changes in the overlying atmosphere that modulate ENSO's effects, and 2) the atmosphere could undergo internal variability that both modulates ENSO's effects and imprints a characteristic pattern of North Pacific SSTs. The first mechanism suggests methods for increasing the skill of seasonal climate predictions by incorporating the state of the North Pacific, using simple persistence of SSTs if nothing else. The second mechanism implies that North Pacific SSTs add no information that could be used to improve seasonal climate predictions of ENSO's effects. Analysis of a 300-yr run of a coupled ocean-atmosphere model shows that it exhibits links between NPO and ENSO similar to those observed. It is found that specifying NPO SSTs does not force these links. This suggests that the association found between NPO SSTs and ENSO's effects is primarily due to the fact that both are responding to the same internal atmospheric variability. In such a case, incorporating accurate predictions of NPO SSTs into ENSO prediction schemes would have little ability to improve forecasts of ENSO's effects.

The Characteristic Variability of Boreal Wintertime Atmospheric Circulation in El Niño Events

Abstract The influence of the Pacific sea surface temperature (SST) on the characteristic variability of boreal wintertime atmospheric circulation among El Nino events is investigated by carrying out singular value decomposition (SVD) analysis and general circulation model (GCM) experiments. From the SVD analysis of SST and 300-hPa streamfunction in the El Nino winter, the first mode associated with the strength of the El Nino mode itself has a positive trend in its time series and the second mode associated with the North Pacific SST variation includes substantial event-to-event variability. The second mode is thus important for explaining the inter–El Nino variability in atmospheric circulation. Four El Ninos among 15 El Nino events from 1950 to 1998 have a mainly positively contribution from the first SVD mode, and the other four events are influenced by the second mode as well as the first mode. The atmospheric responses related to the latter four events show the weakening of the Aleutian low and an e...

Variations of the East Asian Jet Stream and Asian–Pacific–American Winter Climate Anomalies

In this study, the authors apply the NCEP-NCAR reanalysis and other observations to depict the association of the Asian-Pacific-American climate with the East Asian jet stream (EAJS). With an emphasis on boreal winter seasons and on interannual timescales, they analyze the variations of the EAJS and their relationships with El Nino-Southern Oscillation (ENSO) and extratropical North Pacific sea surface temperature (SST), and assess the relative connections of the EAJS and ENSO to the anomalies of atmospheric circulation, surface temperature, and precipitation in the Asian-Pacific-American region. It is found that the EAJS is coupled to a teleconnection pattern spanning the entire Asian-Pacific-American region with the strongest signals over east Asia and the western Pacific. This pattern differs significantly from that associated with ENSO, which influences the earth's climate extensively with a strongest impact on the climate over the central Pacific and east. A strong EAJS is associated with an intensification of the weather and climate systems in Asia and over the Pacific such as deepening of the east Asian trough and the Aleutian low and strengthening of the east Asian winter monsoon. It is linked to colder and drier conditions in east Asia and stronger convection over the tropical Asia-Australia sector. Compared with ENSO, the EAJS seems to link to the climate signals of Asia and the Pacific more strongly. An intensified EAJS is also associated with anomalies of temperature and precipitation in North America due to the related changes in stationary wave patterns. While the EAJS does not strongly link to the tropical central-eastern Pacific SST, it is significantly associated with the extratropical North Pacific SST, more specifically the second most dominant mode of the empirical orthogonal function analysis of the SST. In addition, a strong (weak) EAJS seems to follow a large (small) meridional gradient of the western Pacific SST associated with warming (cooling) in the Tropics-subtropics and cooling (warming) in the extratropics.

The Pacific Decadal Oscillation

The Pacific Decadal Oscillation (PDO) has been described by some as a long-lived El Nino-like pattern of Pacific climate variability, and by others as a blend of two sometimes independent modes having distinct spatial and temporal characteristics of North Pacific sea surface temperature (SST) variability. A growing body of evidence highlights a strong tendency for PDO impacts in the Southern Hemisphere, with important surface climate anomalies over the mid-latitude South Pacific Ocean, Australia and South America. Several independent studies find evidence for just two full PDO cycles in the past century: “cool” PDO regimes prevailed from 1890–1924 and again from 1947–1976, while “warm” PDO regimes dominated from 1925–1946 and from 1977 through (at least) the mid-1990's. Interdecadal changes in Pacific climate have widespread impacts on natural systems, including water resources in the Americas and many marine fisheries in the North Pacific. Tree-ring and Pacific coral based climate reconstructions suggest that PDO variations—at a range of varying time scales—can be traced back to at least 1600, although there are important differences between different proxy reconstructions. While 20th Century PDO fluctuations were most energetic in two general periodicities—one from 15-to-25 years, and the other from 50-to-70 years—the mechanisms causing PDO variability remain unclear. To date, there is little in the way of observational evidence to support a mid-latitude coupled air-sea interaction for PDO, though there are several well-understood mechanisms that promote multi-year persistence in North Pacific upper ocean temperature anomalies.

Streamflow Variability (1965 to 1998) in Five Northwest Territories and Nunavut Rivers

In Canada, the Northwest Territories and Nunavut have been characterized as two regions prone to anthropogenically-forced climate change. This study focuses on identifying trends in streamflow on selected rivers in the two territories. Streamflow data from five Water Survey of Canada hydrometric stations were analyzed, with the assumption that there are trend, cyclic and stochastic components in the 1965–1998 time series. Only two statistically significant linear trends in mean annual streamflow, spring freshet timing or magnitude were identified. Warmer early spring temperatures were found to bring earlier spring freshets in mainland Nunavut. Neither exhibited linear trends from 1965 to 1998. Increasing summer temperatures in the Northwest Territories have not resulted in increases in evapotranspiration and a decrease in water available for runoff, perhaps because of feedbacks which stabilize the hydrologic regime. The cyclic trends in many of the time series are related to the Pacific Decadal Oscillation (PDO) index, which is a measure of north Pacific sea surface temperatures and sea level pressure. There was a six year lag between a mid-1970s shift to a warm PDO phase and wetter conditions in arctic rivers. This lag was extended to ten years at the subarctic rivers because of higher storage demands after the 1965–1975 dry period. The lack of a linear trend in the PDO index between 1965 and 1998 corroborates the lack of linear trends in the mean annual streamflow time series. In light of the findings, further research is recommended on the nature of possible hydrologic feedbacks that control northern runoff regimes and the processes which link north Pacific temperature and northern Canadian streamflow regimes.

The Relationship of the North American Monsoon to Tropical and North Pacific Sea Surface Temperatures as Revealed by Observational Analyses

The North American monsoon is a seasonal shift of upper- and low-level pressure and wind patterns that brings summertime moisture into the southwest United States and ends the late spring wet period in the Great Plains. The interannual variability of the North American monsoon is examined using the NCEP-NCAR reanalysis (1948-98). The diurnal and seasonal evolution of 500-mb geopotential height, integrated moisture flux, and integrated moisture flux convergence are constructed using a 5-day running mean for the months May through September. All of the years are used to calculate an average daily Z score that removes the diurnal, seasonal, and intraseasonal variability. The 30-day average Z score centered about the date is correlated with Pacific sea surface temperature anomaly (SSTA) indices associated with the El Nino-Southern Oscillation (ENSO) and the North Pacific oscillation (NPO). These indices are Nino-3, a North Pacific index, and a Pacific index that combines the previous two. Regional time-evolving precipitation indices for the Southwest and Great Plains, which consider the total number of wet or dry stations in a region, are also correlated with the SSTA indices. The use of nonnormally distributed point source precipitation data is avoided. Teleconnections are computed relative to the climatological evolution of the North American monsoon, rather than to calendar months, thus more accurately accounting for the climatological changes in the large-scale circulation. Tropical and North Pacific SSTs are related to the occurrence of the Pacific Transition and East Pacific teleconnection patterns, respectively, in June and July. A high (low) NPO phase and El Nino (La Nina) conditions favor a weaker (stronger) and southward (northward) displaced monsoon ridge. These teleconnection patterns affect the timing and large-scale distribution of monsoon moisture. In the Great Plains, the spring wet season is lengthened (shortened) and early summer rainfall and integrated moisture flux convergence are above (below) average. In the Southwest, monsoon onset is late (early) and early summer rainfall and integrated moisture flux convergence are below (above) average. Relationships with Pacific SSTA indices decay in the later part of the monsoon coincident with weakening of the jet stream across the Pacific and strengthening of the monsoon ridge over North America. The most coherent summer climate patterns occur over the entire western United States when the Pacific index is substantially high or low, such as during the Midwest flood of 1993 and drought of 1988. The Pacific index in spring is a good predictor of early summer height anomalies over the western United States when the time evolution of the North Pacific SST dipole is considered.

Wind-Driven Shifts in the Latitude of the Kuroshio–Oyashio Extension and Generation of SST Anomalies on Decadal Timescales*

Abstract The causes of decadal variations of North Pacific sea surface temperatures (SSTs) are examined using a hindcast performed with an ocean general circulation model thermodynamically coupled to an atmospheric mixed layer model (OGCM–AML model) and forced by the time history of observed surface winds. The “shift” in North Pacific Ocean climate that occurred around 1976/77 is focused on since this is the best observed example available. After the 1976/77 shift the Aleutian low deepened and moved to the southeast of its previous position. This placed anomalous cyclonic flow over the North Pacific. The SST response, as simulated by the ocean model, consisted of two components: a fast and local part and a delayed and remote part. In the central Pacific stronger westerlies cool the ocean by increased equatorward Ekman drift. Here the dynamical cooling is sufficiently large that the surface fluxes damp the SST anomaly. This Ekman response is fast and local and cools the SSTs beginning in 1977 and persistin...

The role of eastern North Pacific tropical storms in the rainfall climatology of western Mexico

AbstractThis paper explores the role that tropical storms (TS) of the eastern North Pacific play in the rainfall climatology of western Mexico. It uses an 18‐station rainfall grid, along with a data base of storm tracks (1949–1997). TS rainfall is defined by a distance threshold, so that for each station in the grid, daily rainfall recorded when a TS is located within 550 km of the station is considered as TS‐derived; rainfall recorded in the absence of a TS or when a storm is beyond 550 km from a station is by default ‘non‐TS’ rainfall. A variety of statistics are presented to demonstrate the static associations that exist between TS activity and regional rainfall patterns. In sum, they clearly suggest that improved seasonal forecasts of TS activity in the eastern North Pacific will be critical to advancing seasonal climate prediction for Mexico. This study also addresses the interannual variability in TS and non‐TS rainfall. Principal component analysis is used to define the region's primary modes of rainfall variation. Considering the temporal behaviour of the rainfall modes, analyses reveal no statistically significant trends in TS rainfall. In contrast, non‐TS rainfall modes exhibit significant trends. This study provides support for the idea that these trends are partly tied to long‐period fluctuations in the ocean–atmosphere system. The results also indicate that while TS rainfall is not subject to trend behaviour, its year‐to‐year fluctuations, apparently, are linked to large‐scale processes like El Niño–Southern Oscillation (ENSO) and the state of North Pacific sea‐surface temperatures (SSTs). Copyright © 2001 Royal Meteorological Society