Manifestation of the Pacific Decadal Oscillation in the Kuroshio (original) (raw)
Related papers
2024
Recent research has revealed links between a quasi-decadal mode of climate variability over the North Pacific – the Pacific Decadal Precession (PDP) – and the North Pacific’s western boundary current’s extension – the Kuroshio Extension (KE). It is suggested that on decadal time scales the PDP both responds to and influences the KE variability. A question yet to be answered is whether it is the large-scale or the mesoscale variations of the KE region that link with the PDP evolution. Using high-resolution sea surface temperature data (1981–2018) from the global ocean Operational Sea Surface Temperature (SST) and Sea Ice Analysis, low-resolution Extended Reconstructed SST (ERSST) version 3b data (1949–2018), geopotential height reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP) we find that it is the large-scale variations in the KE region that correlate best with the PDP-like response in the overlying and downstream atmosphere as compared to the mesoscale variations. In particular, the second mode of the large-scale KE region, which is characterized by the warming (cooling) of the ocean south (north) of the KE, sets up a PDP-like north-south atmospheric pressure dipole over the North Pacific Ocean by altering the large-scale baroclinicity of the atmosphere and zonal intensification of the subtropical jet stream. In turn, there is a reduction in the zonal propagation of stationary wave energy and an enhancement of the climatological zonal wave heights over North America, which results in a downstream response over the North American continent and the formation of a subsequent east-west pressure dipole over the North Pacific and North American continent. As a result, there is a strong correlation between large-scale SST variations in the KE region and the evolution of the PDP over the next three years.
Journal of Climate, 2001
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 persisting through 1988. In the early 1980s cool SSTs emerge in the latitude of the Kuroshio-Oyashio Extension east of Japan and persist until 1989. It is shown that this region of cooling is associated with a southward displacement of the latitude of the confluence between the subpolar and subtropical gyres. This is consistent with the southward shift in the zero wind stress curl line. The timescale for the gyre adjustment is no more than 4 yr. These results compare favorably with observations that also first show the central Pacific cooling and, later, cooling east of Japan. Observations show the cooling in the Kursohio-Oyashio Extension region to be damped by surface fluxes, implying an oceanic origin. The timescale of adjustment is also supported by analyses of observations. The delayed response of the ocean to the varying winds therefore creates SST anomalies as the latitude of the gyre confluence varies. The delayed SST response is of the same sign as the locally forced SST signal suggesting that, to the extent there is a feedback, it is positive. Implications for the origins of decadal climate variability of the North Pacific are discussed.
Recent research has revealed links between a quasi decadal mode of climate variability over the North Pacific – the Pacific Decadal Precession (PDP) – and the North Pacific’s western boundary currents extension – the Kuroshio Extension (KE). It is suggested that on decadal time scales the PDP both responds to and influences the KE variability. A question yet to be answered is whether it is the large-scale or the mesoscale variations of the KE region that influence the overlying and downstream atmosphere and hence the PDP evolution. Using high-resolution sea surface temperature data (1981-2018) from the global ocean Operational Sea Surface Temperature (SST) and Sea Ice Analysis, low resolution Extended Reconstructed SST (ERSST) version 3b data (1949-2018), geopotential height data from the European Centre for MediumRange Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction we find that it is the large-scale variations in the KE region that correlate best wi...
Journal of Climate, 1999
The spatial and temporal characteristics of oceanic thermal variations in the mixed layer and main thermocline of the midlatitude North Pacific are distinctive, suggesting different physical origins. Within the main thermocline (400-m depth), the variability is dominated by a westward-intensified pattern of decadal scale, indicative of enhanced eastward geostrophic flow along the southern flank of the Kuroshio Current extension during the 1980s relative to the 1970s. The authors argue that the decadal-scale change in the strength of the Kuroshio extension was a result of the dynamical adjustment of the oceanic circulation to a decadal variation in wind stress curl according to Sverdrup theory. Four-times daily wind stress fields from the National Center for Atmospheric Research-National Centers for Environmental Prediction reanalysis project are used to compute the decadal change in Sverdrup transport associated with the 1976/77 climate transition. It is shown that the decadal changes in Sverdrup transport inferred from the wind stress curl field and in observed geostrophic flow inferred from the upper-ocean thermal field are consistent both in terms of spatial pattern and magnitude. The decadal change in depth-averaged geostrophic transport along the Kuroshio extension (referenced to 1 km) is 11.6 Sv, similar to the Sverdrup transport change (11.5-13.9 Sv). The decadal-scale thermocline variation along the western boundary between 30Њ and 40ЊN exhibits a lag of approximately 4-5 yr relative to the decadal variation in the basin-wide wind stress curl pattern. This delay may be indicative of the transient adjustment of the gyre-scale circulation to a change in wind stress curl via long baroclinic Rossby waves.
2007
The western North Pacific region is one of the centers of action of decadal time scale variations in the atmosphere and ocean, and also oceanic ecosystem can be strongly influenced by the variations. One of the key variable of the decadal variations is sea surface temperature (SST) that varies as a result of interaction between the atmosphere and ocean. To improve our understanding of the key element, SST variaions in the two frontal zones in the western North Pacific Ocean, the Kuroshio Extension and subarctic frontal zones, are investigated on the basis of an in situ observational dataset. Interannual-to-decadal variations in these two frontal zones are not highly correlated, indicating that to some extent different mechanisms induce the SST variations in the frontal zones and those two frontal zone cannot be considered as a single frontal zone as has been done in most of previous studies. Meanwhile, the results are consistent with the recent studies that suggest different mechanisms for the variations in the two frontal zones on the basis of a solution to an eddy-resolving, i.e., very high horizontal resolution, ocean general circulation model.
The meridional shifts of the Oyashio Extension (OE) and of the Kuroshio Extension (KE), as derived from high-resolution monthly sea surface temperature (SST) anomalies in 1982-2008 and historical temperature profiles in 1979-2007, respectively, are shown based on regression analysis to significantly influence the large-scale atmospheric circulation. The signals are independent from the ENSO teleconnections, which were removed by seasonally varying, asymmetric regression onto the first three principal components of the tropical Pacific SST anomalies. The response to the meridional shifts of the OE front is equivalent barotropic and broadly resembles the North Pacific Oscillation / Western Pacific pattern in a positive phase for a northward frontal displacement. The response reaches 35 m at 250 hPa for a typical OE shift, a strong sensitivity since the associated SST anomaly is 0.5 K. However, the amplitude depends on an assumed 2-month atmospheric response time. The response is stronger during winter and when the front is displaced southward. The response to the northward KE shifts primarily consists of a high centered in the northwestern North Pacific and hemispheric teleconnections. It is also equivalent barotropic, except near Kamchatka where it tilts slightly westward with height. The typical amplitude is half as large as that associated with OE shifts.
For better understanding of interactions between the Kuroshio south of Japan and the climate system in the North Pacific, variations of the satellite-derived eddyremoved volume transport of the Kuroshio through-flow (KTVT) south of Japan in 1993 -2007 and the West Pacific Pattern index (WPPI) are compared with each other. Both of KTVT and WPPI with longer periods than 8 months have dominant components with about annual period. They have a maximum in every winter while their amplitudes change year by year. By the cross correlation analysis of their around annual period components, we found that interannual variations of WPPI in May and October lead to KTVT by 41-month while those of KTVT in February and August lead to WPPI by about 4 years, suggesting that the interactions between annual period components of WPPI and KTVT are dominated by seasonal different mechanisms.
Scientific Reports, 2019
The Kuroshio Extension (KE) exhibits prominent decadal fluctuations that enhance the low-frequency variability of North Pacific climate. Using available observations, we show evidence that a preferred decadal timescale in the KE emerges from the interaction between KE and the central tropical Pacific via Meridional Modes. Specifically, we show that changes in the KE states apply a persistent downstream atmospheric response (e.g. wind stress curl, 0–12 months timescales) that projects on the atmospheric forcing of the Pacific Meridional Modes (PMM) over 9 months timescales. Subsequently, the PMM energizes the central tropical Pacific El Niño Southern Oscillation (CP-ENSO) and its atmospheric teleconnections back to the Northern Hemisphere (1–3 months timescale), which in turn excites oceanic Rossby waves in the central/eastern North Pacific that propagate westward changing the KE (~3 years timescales). Consistent with this hypothesis, the cross-correlation function between the KE and...
Anatomy of North Pacific Decadal Variability
Journal of Climate, 2002
A systematic analysis of North Pacific decadal variability in a full-physics coupled ocean-atmosphere model is executed. The model is an updated and improved version of the coupled model studied by Latif and Barnett. Evidence is sought for determining the details of the mechanism responsible for the enhanced variance of some variables at 20-30-yr timescales. The possible mechanisms include a midlatitude gyre ocean-atmosphere feedback loop, stochastic forcing, remote forcing, or sampling error.
Ocean Modelling, 2018
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights An ocean model forced by steady winds simulates the Kuroshio Extension (KE) intrinsic low-frequency variability. A new composite index specifically conceived for this phenomenon is used in the analysis. A self-sustained oscillation is characterized by four phases, each one being controlled by a specific dynamical mechanism. Analysis of the AVISO altimeter data set yields a similar oscillation in the interval 1998-2006. The conclusion is that, during that interval, the KE dynamics was controlled by an intrinsic mode of variability.