role of the ocean in the decadal climate change in the north pacific 1 i have investigated features of decadal climate variability in the north pacific and clarified the role of the ocean in controlling them by analyzing historical data sets and executing experiments with a low order model detailed investigation of the variability of the wintertime aleutian low and water temperature in the subarctic frontal region implies a new scenario for the mechanism of the decadal variability the decadal variability can be interpreted as the transition process between two stable states cold and warm period in midlatitude atmosphere when the transition to a cold period occurs sea surface temperature in the subarctic frontal region begins to be lowered not only through the surface processes but by westward propagation of cold anomaly from eastern subarctic region as a baroclinic rossby wave as a result the meridional gradient of sea surface heat flux yq0 decreases its magnitude and then the forcing of the aleutian low is weakened when this weakening exceeds a threshold the transition from a cold to a warm period occurs abruptly after the transition to a warm period yq0 in turn increases its magnitude through the opposite processes to cause the reverse transition the timescale of this cycle is mainly determined by the propagation speed of a baroclinic rossby wave the el nino and southern oscillation variability both in the atmosphere and ocean can also affect the timescale by causing the thresholds for transitions to be temporarily exceeded experiments with a four variable low order model support the proposed mechanism of the decadal variability

decadal variability in the kuroshio oyashio extension simulated in an eddy resolving ogcm abstract through analysis of a hindcast integration of an eddy resolving quasi global ocean general circulation model decadal variability in the kuroshio oyashio extension region is investigated with particular emphasis on that of the subarctic oyashio and the kuroshio extension ke fronts the ke front is deep and is accompanied by a sharp sea surface height ssh gradient with modest sea surface temperature sst gradient in contrast the subarctic front is shallow and is recognized as a zone of tight gradient in sst but not ssh as a decadal scale change from a warm period around 1970 to a cool period in the mid 1980s those fronts in the model migrate southward as observed and the associated pronounced cooling is confined mainly to those frontal zones reflecting the distinctive vertical structure of the fronts the mixed layer cooling is the strongest along the subarctic front whereas the subsurface cooling and the associated salinity changes are most pronounced along the ke front concomitan

anatomy of north pacific decadal variability abstract 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 decadal variability in the model is expressed most prominently in anomalies of upper ocean streamfunction sea surface temperature sst and latent surface heat flux in the kuroshio oyashio extension koe region off japan the decadal signal off japan is initiated by changes in strength and position of the aleutian low the atmospheric perturbations excite sst anomalies in the central and eastern north pacific with opposing signs and canonical structure the atmospheric perturbations also change the ekm

global patterns of decadal scale variability observed in sea surface temperature and lower tropospheric circulation fields the global patterns associated with decadal scale variability dsv are examined by a lag correlation technique based on local anomaly indices using the fields of measured sea surface temperature sst and 850 hpa geopotential height for the last 50 years the three dominant patterns are identified and the variability is examined the first spreads over the entire pacific which is concurrent with the decadal scale modulation of the el nino southern oscillation des variability the second is confined to the local midlatitude north pacific lnp variability and the third extends over the north atlantic with the decadal north atlantic oscillation nao dna variability the global sst pattern of des variability exhibits large scale equatorial symmetry in the pacific which is similar to that of the pacific decadal oscillation but is distinguished by the signals in the subtropical frontal zones these sst anomalies are accompanied by anomalous subtropical highs that appear prior to the anomalous depression around australia the lnp variability which is related with the arctic oscillation is characterized by the sst anomalies along the north pacific subarctic frontal zone moving eastward accompanied by the anomalous aleutian low this variability develops decays without with coherent variability in the tropics it shows the 6 year quadrature phase relationship with the des variability indicative of an interdecadal variability with a period of 24 years the dna variability is featured by the atmospheric nao and by the sst anomalies in four zonal bands that spread in the north atlantic from the tropics to high latitudes this variability is independent of either the des or lnp variability

midlatitude atmospheric transient eddy feedbacks influenced enso associated wintertime pacific teleconnection patterns in two pdo phases the el nino southern oscillation enso associated wintertime atmospheric teleconnection patterns in two pacific decadal oscillation pdo phases are investigated using era 20c reanalysis data for 1950 2010 a strengthened enso associated pacific north american pna teleconnection pattern presents in pdo positive phase while a west pacific wp pattern over northwestern pacific and a squeezed pna pattern coexist when enso occurs in pdo negative phase the dynamical role of atmospheric transient eddy feedbacks to the teleconnection patterns are highlighted in the present study when enso occurs in pdo positive phase the uniform strengthened westerly jet anomalies downstream of the climatological main body of jet accompany with energetic transient eddy anomalies over northeastern pacific the transient eddy feedbacks largely enhance and favor the strengthened pna pattern when enso occurs in pdo negative phase the strengthened westerly jet anomalies appear to separate into two parts one locating north of the climatological main body of jet and the other at the downstream the accompanied transient eddy anomalies also split into two parts under such conditions the transient eddy feedbacks are limited over northeastern pacific and favor a weak pna pattern however the transient eddy anomalies over northwestern pacific strengthen and the feedbacks also strengthen and largely contribute to the wp pattern moreover the transient eddy anomalies over northwestern pacific seem to be anchored along the anomalously poleward strengthened oceanic subarctic frontal zone safz in pdo negative phase the enhanced atmospheric baroclinicity anomalies coupled with the strengthened safz energize atmospheric transient eddy anomalies and work as the potential maintenance in shaping the wp pattern

a general circulation model for upper ocean simulation abstract a general circulation model gcm of the ocean that emphasizes the simulation of the upper ocean has been developed this emphasis is in keeping with its future intent that of an air sea coupled model the basic model is the primitive equation model of bryan and cox with the additions of optional usage of the mellor yamada level 2 5 turbulence closure scheme and horizontal nonlinear viscosity these modifications are intended to improve the upper ocean simulations particularly sea surface temperature and heat content the horizontal grid spacing is 1 latitude 1 longitude and is global in domain the equatorial region between 10 n and 10 s is further refined in the north south direction to resolution there are 12 vertical levels with six levels in the top 70 m the model incorporates varying bottom topography prior to coupling the ocean model to an atmospheric gcm experiments have been carried out to determine the ocean gcm s performance using atmospheric forcing from observed data

midlatitude atmosphere ocean interaction during el nino part i the north pacific ocean abstract atmosphere ocean experiments are experiments are used to investigate the formation of sea surface temperature sst anomalies in the north pacific ocean during fall and winter of the el nino year experiments in which the ncar community climate model ccm surface fields am used to force a mixed layer ocean model in the north pacific no air sea feedback are compared to simulations in which the ccm and north pacific ocean model are coupled anomalies in the atmosphere and the north pacific ocean during el nino are obtained from the difference between simulations with and without prescribed warm sst anomalies in the tropical pacific in both the forced and coupled experiments the anomaly pattern resembles a composite of the actual sst anomaly field during el nino warm ssts develop along the cost of north america and cold ssts form in the central pacific in the coupled simulations air sea interaction results in a 25 to 50 reduction in the magnitude of the sst and mixed layer depth anomalies

atmospheric response to zonal variations in midlatitude sst transient and stationary eddies and their feedback midwinter storm track response to zonal variations in midlatitude sea surface temperatures ssts has been investigated using an atmospheric general circulation model under aquaplanet and perpetual january conditions zonal wavenumber 1 sst variations with a meridionally confined structure are placed at various latitudes having these sst variations centered at 308n leads to a zonally localized storm track while the storm track becomes nearly zonally uniform when the same sst forcing is moved farther north at 408 and 508n large small baroclinic energy conversion north of the warm cold sst anomaly near the axis of the storm track near 408n is responsible for the large small storm growth the equatorward transfer of eddy kinetic energy by the ageostrophic motion and the mechanical damping are important to diminish the storm track activity in the zonal direction significant stationary eddies form in the upper troposphere with a ridge trough northeast of the warm cold sst anomaly at 308n heat and vorticity budget analyses indicate that zonally localized condensational heating in the storm track is the major cause for these stationary eddies which in turn exert a positive feedback to maintain the localized storm track by strengthening the vertical shear near the surface these results indicate an active role of synoptic eddies in inducing deep tropospheric scale response to midlatitude sst variations finally the application of the model results to the real atmosphere is discussed

decadal sea level variability in the south pacific in a global eddy resolving ocean model hindcast sea level variability and related oceanic changes in the south pacific from 1970 to 2003 are investigated using a hindcast simulation of an eddy resolving ocean general circulation model ogcm for the earth simulator ofes along with sea level data from tide gauges since 1970 and a satellite altimeter since 1992 the first empirical orthogonal function mode of sea level anomalies slas of ofes exhibits broad positive slas over the central and western south pacific the corresponding principal component indicates roughly stable high low and high slas separated by a rapid sea level fall in the late 1970s and sea level rise in the late 1990s consistent with tide gauge and satellite observations these decadal changes are accompanied by circulation changes of the subtropical gyre at 1000 m depth and changes of upper ocean zonal current and eddy activity around the tasman front in general agreement with previous related studies it is found that sea level variations in the tasman sea can be explained by propagation of long baroclinic rossby waves forced by wind stress curl anomalies if the impact of new zealand is taken into account the corresponding atmospheric variations are associated with decadal variability of el nino southern oscillation enso thus decadal sea level variability in the western and central south pacific in the past three and half decades and decadal enso variability are likely to be connected the sea level rise in the 1990s which attracted much attention in relation to the global warming is likely associated with the decadal cooling in the tropical pacific

characteristic variations of sea surface temperature with multiple time scales in the north pacific abstract temporal evolution and spectral structure of sea surface temperature sst anomalies in the north pacific over the last 37 years are investigated on the three characteristic time scales shorter than 24 months hf 24 60 months es and longer than 60 months dc the leading empirical orthogonal function eof for the dc time scale is characterized by a zonally elongated monopole centered at around 40 n 180 the leading eof for the hf time scale is somewhat similar to that for the dc time scale although there are two centers of action with the same polarity at the mid and western pacific the leading eof for the es time scale however exhibits a different pattern whose center of action at the mid pacific is located farther southeastward in the time evolution of the sst anomalies associated with the leading eof of the dc time scale several anomaly periods can be identified that last five years or longer the transition from a persistent period to another with the opposite polarity is gene

seasonal variations in the southern hemisphere storm tracks and jet streams as revealed in a reanalysis dataset abstract regional characteristics of the climatological seasonal variations in southern hemisphere sh storm tracks are examined based on a reanalysis dataset when differences in vertical structure between the subpolar and subtropical jet streams spj and stj respectively are considered the regional characteristics can be interpreted reasonably well from a potential vorticity perspective of baroclinic eddy growth and downstream development of a baroclinic wave packet eddy activity in the upper and lower tropospheres is strongest in the core region of the spj over the eastern south atlantic and indian ocean throughout the year even in austral winter when the intense stj forms over the indian ocean and south pacific showing its eddy driven nature the spj accompanies the strong surface westerlies along a well defined baroclinic zone above an intense oceanic frontal zone in this core region of the storm track low level eddy activity is strongly correlated with the local near surface baroclinicity

kuroshio extension variability and forcing of the pacific decadal oscillations responses and potential feedback abstract a forcing mechanism is sought for the large scale circulation changes in the kuroshio extension region of the western north pacific ocean as inferred by topex poseidon sea surface height ssh data the low frequency signal of the kuroshio extension over the last decade was characterized by a modulation in its zonal mean flow intensity the mean kuroshio extension jet weakened progressively from 1993 to 1996 and this trend reversed after 1997 the ability to simulate the major trends in the observed ssh signals with linear vorticity dynamics leads the authors to conclude that the modulation in the zonal mean jet was remotely forced by wind stress curl anomalies in the eastern north pacific ocean related to the pacific decadal oscillations pdos to be specific the weakening strengthening trend in 1993 96 1997 2001 was caused by westward expansions of negative positive ssh anomalies south of the kuroshio extension and positive negative ssh anomalies north of the kuroshio extension emerg

interdecadal thermocline variability in the north pacific for 1958 97 a gcm simulation an ocean general circulation model is forced with the ncep reanalysis wind stress for 1958 97 to understand mechanisms of ocean subsurface variability with relatively high horizontal 1 83 18 and vertical 41 levels resolutions the model produces mode waters on a range of density surfaces in the western central and eastern north pacific in qualitative agreement with observations these mode waters appear as a thermostad or a region of weak stratification in the upper thermocline as they flow southward from their formation regions in the kuroshio and its extension in the model subsurface temperature variability in the central subtropical gyre reaches a maximum within the thermostad in contrast to what might be expected from the linear baroclinic rossby wave theory this variance maximum is associated with the longitudinal shift in the path of mode waters in particular deepened mixed layer and accelerated eastward currents in the kuroshio extension by wind changes in the mid 1970s act cooperatively to move the central mode waters toward the east causing large subsurface temperature anomalies besides the local maximum in the central north pacific subtropical gyre two additional maxima of the subsurface anomaly are identified in the northwestern and southern parts of the gyre respectively among these subsurface anomaly centers the one in the northwestern north pacific has a strong effect on the model sea surface temperature suggesting that the kuroshio and its extension are a key region to decadal interdecadal ocean atmosphere interaction finally possible effects of atmospheric thermal forcing are discussed

a rotated eof analysis of global sea surface temperature variability with interannual and interdecadal scales abstract spatiotemporal variability of preferred global scale sea surface temperature anomaly patterns is documented applying a varimax rotated empirical orthogonal function r eof analysis to monthly mean sst anomalies the present study focuses especially on the interdecadal variability of leading r eof modes it is first found that temporal variability of r eof1 has a quasi periodicity of 2 5 years and coincides quite well with the occurrence of the enso event hence this mode can be identified with the enso mode and distinguished from the other modes dominated by interdecadal variability the authors find that r eof2 typically shows the dominance of interdecadal variability and signals of the enso phenomenon are removed this mode is characterized by increasing indian ocean sst and decreasing central north pacific sst around 40 50 n in the recent ten or more years a further indication is that both r eof3 and r eof4 which show the dominance of interdecadal variability are fundamentally regarded a

decadal changes in the north pacific oceanic frontal zones as revealed in ship and satellite observations 1 influence of decadal climate changes upon the north pacific subarctic and subtropical oceanic frontal zones np safz and np stfz respectively is documented both satellite and ship measured sea surface temperature sst data reveal the strong confinement of wintertime decadal sst anomalies to those frontal zones the satellite data indicate that the wintertime np safz tended to be narrow and shift northward under the weakened surface westerlies during a warm event in the early 1990s the opposite was the case under the enhanced westerlies during a cool event in the mid 1980s decadal scale modulations in the frontal intensity are also evident in the satellite data a diagnosis based on a simple linearized mixed layer model suggests that the observed anomalous frontal intensity was contributed by the sign reversal of anomalous wind stress curl through the ekman processes and by an anomaly dipole of the net heat flux around the safz these decadal scale modulations in the np safz and their relationships with decadal fluctuations in the local surface westerlies are confirmed in the ship measured data over the 4 recent decades it is found that the safz happens to be a region where the decadal variability in the surface westerlies are unlikely to be masked by the higher frequency fluctuations as it almost coincides with the ridge trough line of the remote atmospheric response to the el nino southern oscillation

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

northern hemisphere winter atmospheric transient eddy heat fluxes and the gulf stream and kuroshio oyashio extension variability abstractspatial and temporal covariability between the atmospheric transient eddy heat fluxes i e t and q in the northern hemisphere winter january march and the paths of the gulf stream gs kuroshio extension ke and oyashio extension oe are examined based on an atmospheric reanalyses and ocean observations for 1979 2009 for the climatological winter mean the northward heat fluxes by the synoptic 2 8 days transient eddies exhibit canonical storm tracks with their maxima collocated with the gs and ke oe the intraseasonal 8 days 3 months counterpart while having overall similar amplitude shows a spatial pattern with more localized maxima near the major orography and blocking regions lateral heat flux divergence by transient eddies as the sum of the two frequency bands exhibits very close coupling with the exact locations of the ocean fronts linear regression is used to examine the lead lag relationship between interannual changes in the northward heat fluxes by the transient

the reemergence of sst anomalies in the north pacific ocean abstract sea surface temperature sst data and two different upper ocean temperature analyses are used to study the winter to winter recurrence of sst anomalies in the north pacific ocean the ssts recur when temperature anomalies that form in the deep ocean mixed layer in late winter early spring are isolated from the atmosphere in the summer seasonal thermocline and then reemerge at the surface when the mixed layer deepens during the following fall winter this reemergence mechanism is evaluated over the basin by correlating the time series of the leading pattern of ocean temperature anomalies in the summer seasonal thermocline 60 85 m in august september with sst anomalies over the course of the year the results indicate that the dominant large scale sst anomaly pattern that forms in the north pacific during late winter with anomalies of one sign in the central pacific and the opposite sign along the coast of north america is sequestered in the seasonal thermocline in summer and returns to the

distribution and modification of north pacific intermediate water in the kuroshio oyashio interfrontal zone abstract a multiship ctd survey was conducted in the kuroshio oyash interfrontal zone in the area of 30 41 n 140 e 180 from may to june 1992 to examine the distribution modification process and formation site of north pacific intermediate water npiw low salinity oyashio water and high salinity kuroshio water merge along the kuroshio extension just off the east coast of japan and together flow eastward eastward geostrophic transport and salinity across the kuroshio strong current indicate that the mixture of the kuroshio and oyashia waters along the kuroshio extension can produce new npiw transport estimate suggests that the new npiw bifurcates into the interfrontal zone and into the recirculation of the subtropical gyre a salinity minimum structure can he also created due to the isopycnal mixing along the kuroshio extension between the oyashio and kuroshio waters which have different salinity and vertical velocity structures the low salinity oyashio water seen along the oyashio branches and t

the subarctic frontal zone in the north pacific characteristics of frontal structure from climatological data and synoptic surveys the subarctic front is a thermohaline structure across the north pacific separating colder fresher water to the north from warmer saltier water to the south levitus s 1982 data and 72 conductivity temperature depth salinity temperature depth sections are used to show the spatial and seasonal variations of the climatological frontal zone and the characteristics of the frontal structure in synoptic surveys the temperature gradient in the mean frontal zone is stronger in the western pacific and decreases eastward while the salinity gradient has less variation across the pacific the temperature gradient also has larger seasonal variation with a maximum in spring than the salinity gradient the synoptic surveys show that the frontal zone is narrower and individual fronts tend to be stronger in the western pacific than in the eastern pacific density gradients tend to be more compensated at the strongest salinity fronts than at the strongest temperature fronts a horizontal minimum of vertical stability is found south of the subarctic halocline outcrop the northern boundary of the north pacific intermediate water merges with the frontal zone west of 175 w and is north of the northern boundary of the subarctic frontal zone in the eastern pacific the shallow salinity minima start within the subarctic frontal zone in the eastern pacific

meridional shift of the kuroshio extension induced by response of recirculation gyre to decadal wind variations abstract the meridional shift of the kuroshio extension to decadal wind variations is examined by analyzing the hindcast simulation of a high resolution 1 12 1 12 north pacific ocean general circulation model ogcm and by conducting a series of idealized ogcm experiments the meridional shift of the kuroshio extension in the hindcast is consistent with observations and former studies using a series of sensitivity experiments in idealized settings the following possible mechanism for this shift is proposed the baroclinic rossby waves that arise in the northern half of the subtropical gyre cannot directly enter the kuroshio oyashio extension region due to the strong kuroshio extension jet when the rossby waves accompanying the negative positive sea surface height anomalies propagate westward and reach the region to the east of the recirculation gyre the difference in thermocline depth between the recirculation gyre and the region to its east becomes larger smaller resulting in stronger weaker baroclinic instabilities these stronger weaker instabilities cause a shallower deeper thermocline in the recirculation gyre to compensate for this shrinking stretching the recirculation gyre migrates southward northward leading to the southward northward shift of the kuroshio extension

influence of the meridional shifts of the kuroshio and the oyashio extensions on the atmospheric circulation abstract 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 lagged 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 may reach 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 but not the pattern or statistical significance strongly depends on the lag and an

upper ocean thermal variations in the north pacific during 1970 1991 abstract a newly available extensive compilation of upper ocean temperature profiles was used to study the vertical structure of thermal anomalies between the surface and 400 m depth in the north pacific during 1970 1991 a prominent decade long perturbation in climate occurred during this time period surface waters cooled by 1 c in the central and western north pacific and warmed by about the same amount along the west coast of north america from late 1976 to 1988 comparison with data from coads suggests that the relatively sparse sampling of the subsurface data is adequate for describing the climate anomaly the vertical structure of seasonal thermal anomalies in the central north pacific shows a series of cold pulses beginning in the fall of 1976 and continuing until late 1988 that appear to originate at the surface and descend with time into the main thermocline to at least 400 m depth individual cold events descend rapidly 100 m yr 1 superimposed upon a slower cooling 15 m yr 1 the inter

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

late holocene palaeolimnology of bal lake northern nigeria a multidisciplinary study abstract a multidisciplinary study of lake sediments from bal lake a small saline lake in the sahel zone of northeastern nigeria provides evidence for changing precipitation evaporation ratios over the last 1000 cal years climatic and environmental changes over this period have been reconstructed using evidence from ostracod faunal assemblages and shell chemistry sediment properties and palynology and the sequences dated by a combination of 137 cs 210 pb and ams radiocarbon methods the results testify to major hydrological changes in the sahel over the last millennium the end of a major drought phase that is seen in other records from the manga grasslands is dated to around 950 ad this was followed by a prolonged freshwater phase of the lake from the 12th to the 16th century ad which points to wetter conditions a period of higher salinity and hence drier and more variable conditions from the 1700s to the mid 1900s was followed by a pronounced drying trend into the 20th century

the forcing of the pacific decadal oscillation the pacific decadal oscillation pdo defined as the leading empirical orthogonal function of north pacific sea surface temperature anomalies is a widely used index for decadal variability it is shown that the pdo can be recovered from a reconstruction of north pacific sea surface temperature anomalies based on a first order autoregressive model and forcing by variability of the aleutian low el nino southern oscillation enso and oceanic zonal advection anomalies in the kuroshio oyashio extension the latter results from oceanic rossby waves that are forced by north pacific ekman pumping the sst response patterns to these processes are not orthogonal and they determine the spatial characteristics of the pdo the importance of the different forcing processes is frequency dependent at interannual time scales forcing from enso and the aleutian low determines the response in equal parts at decadal time scales zonal advection in the kuroshio oyashio extension enso and anomalies of the aleutian low each account for similar amounts of the pdo variance these results support the hypothesis that the pdo is not a dynamical mode but arises from the superposition of sea surface temperature fluctuations with different dynamical origins

evidence for a wind driven intensification of the kuroshio current extension from the 1970s to the 1980s 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 308 and 408n 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

predicting western north pacific ocean climate abstract it is shown that wintertime sea surface temperature anomalies in the confluence region of the kuroshio oyashio currents in the western north pacific can be skillfully predicted at lead times of up to 3 yr the predictions are based on the history of the wind stress over the north pacific and oceanic rossby wave dynamics the predictions may be exploitable in fisheries research and other ecological applications

decadal shifts of the kuroshio extension jet application of thin jet theory abstractmeridional shifts of the kuroshio extension ke jet on decadal time scales are examined using a 1960 2004 hindcast simulation of an eddy resolving ocean general circulation model for the earth simulator ofes the leading mode of the simulated ke represents the meridional shifts of the jet on decadal time scales with the largest southward shift in the early 1980s associated with the climate regime shift in 1976 77 a result confirmed with subsurface temperature observations the meridional shifts originate east of the date line and propagate westward along the mean jet axis a trajectory inconsistent with the traditionally used linear long rossby waves linearized in cartesian coordinates although the phase speed is comparable to that in the traditional framework the zonal scale of these westward propagation signals is about 4000 km and much larger than their meridional scale to understand the mechanism for the westward propagation of the ke jet shifts the authors consider the limit of a thin

late pliensbachian early toarcian early jurassic environmental changes in an epicontinental basin of nw europe causses area central france a micropaleontological and geochemical approach abstract we present an integrated work based on calcareous nannofossil and benthic foraminiferal assemblages and geochemical analyses of two upper pliensbachian lower toarcian sections located in the central south france the studied sections tournadous and saint paul des fonts represent the proximal and the distal part respectively of the jurassic causses basin one of the small partly enclosed basins belonging to the epicontinental shelf of the nw tethys at the transition from late pliensbachian to early toarcian the causses basin recorded an emersion in response to the global sea level fall our data indicate severe environmental conditions of marine waters including salinity decrease and anoxia development occurring in the early toarcian the acme of this deterioration coincides with the early toarcian anoxic event t oae but due to the restricted nature of the basin anoxia persisted until the end of the early toarcian mainly in the deeper parts of the basin the micronutrients and organic organic matter fluxes were probably high during the entire studied time interval as shown by nannofossil and foraminiferal assemblages however nannoplankton production drastically decreased during the t oae as demonstrated by very low nannofossil fluxes and only taxa tolerant to low saline surface waters could thrive at the same time benthic foraminifers temporarily disappeared in response to sea bottom anoxia our study demonstrates that environmental changes related to the t oae are well recorded even in small partly enclosed basins of nw europe like the causses basin within this area the effects of global changes like sea sea level and temperature fluctuations are modulated by local conditions mainly controlled by the morphology of the basin

annual and interannual variability in the kuroshio current system abstract individual seasonal 300 m temperature maps were constructed over the kuroshio current system from 130 e to 170 w for a 4 year period from summer 1976 through spring 1980 using transpac xbt data and jodc temperature depth data quasi stationary meanders in the kuroshic current system occurred at 137 c i e kuroshio meander at 144 e and 150 e i e lee wave meanders and near 160 e i e meander over the shatsky rise a composite of the paths of the kuroshio i e the 12 c isotherm from the individual seasonal maps and the total variance map finds nodes i e minima and anti nodes i e maxima of variability to have existed along the mean kuroshio path the anti nodes coincided with the location of the quasi stationary meanders the nodes in between zonal propagation of temperature anomalies accounted for 20 30 of the total interannual variance these temperature anomalies propagated eastward at 0 5 1 5 cm s 1 in the region 140 155 e and westward at 1 to 2 cm s 1 in the re

a modeling study of the relative roles of tropical and extratropical sst anomalies in the variability of the global atmosphere ocean system abstract in three parallel experiments an atmospheric general circulation model has been subjected to observed monthly varying sea surface temperature ssi conditions in each of the following domains near global ocean goga run tropical pacific toga run and midlatitude north pacific moga run four independent realizations were obtained for the model response to the sequence of sst anomalies during the 1946 88 period in each of the above regions the principal modes of coupling between the imposed sst forcing and the simulated northern hemisphere wintertime 5 1 5 mb height field in various experiments have been identified using a singular value decomposition svd procedure the leading svd mode for the goga experiment is qualitatively similar to that based on observational data although the amplitudes of the simulated height anomalies are notably lower than the observed value the sst pattern of this mode resembles that associated with el nino events the accompanying 5 1 5 mb height anomaly i

dynamical role of mode water ventilation in decadal variability in the central subtropical gyre of the north pacific abstract decadal variability in the interior subtropical north pacific is examined in the geophysical fluid dynamics laboratory coupled model cm2 1 superimposed on a broad classical subtropical gyre is a narrow jet called the subtropical countercurrent stcc that flows northeastward against the northeast trade winds consistent with observations the stcc is anchored by mode water characterized by its low potential vorticity pv mode water forms in the deep winter mixed layer of the kuroshio oyashio extension koe east of japan and flows southward riding on the subtropical gyre and preserving its low pv characteristic as a thick layer of uniform properties the mode water forces the upper pycnocline to shoal and the associated eastward shear results in the surface intensified stcc on decadal time scales in the central subtropical gyre 15 35 n 170 e 130 w the dominant mode of sea surface height variability is characterized by the strengthening and weakening of the stcc because of variations

covariations of sea surface temperature and wind over the kuroshio and its extension evidence for ocean to atmosphere feedback abstract satellite microwave measurements are analyzed revealing robust covariability in sea surface temperature sst and wind speed over the kuroshio extension ke east of japan ocean hydrodynamic instabilities cause the ke to meander and result in large sst variations increased reduced wind speeds are found to be associated with warm cold sst anomalies this positive sst wind correlation in ke is confirmed by in situ buoy measurements and is consistent with a vertical shear adjustment mechanism namely an increase in sst reduces the static stability of the near surface atmosphere intensifying the vertical turbulence mixing and bringing fast moving air from aloft to the sea surface south of japan the kuroshio is known to vary between nearshore and offshore paths these paths are very persistent and can last for months to years as the kuroshio shifts its path coherent wind changes are detected from satellite data in particular winds are high south of tokyo when the kuroshio takes the near

interannual variability of the kuroshio extension system and its impact on the wintertime sst field altimetry data from the first 7 yr topex poseidon t p mission october 1992 september 1999 are analyzed to investigate the interannual variability in regions of the kuroshio extension and its southern recirculation gyre large scale interannual changes of the kuroshio extension system are characterized by the oscillation between an elongated state and a contracted state in the elongated state the kuroshio extension has a larger eastward surface transport a greater zonal penetration and a more northerly zonal mean path all these characteristics are closely connected to the presence of an intense zonally elongated southern recirculation gyre in its contracted state the kuroshio extension has a smaller eastward surface transport a more southerly mean path and is accompanied by a weaker southern recirculation gyre during the t p period the kuroshio extension changed from the elongated state in 1992 93 to the contracted state in 1996 97 and back to the elongated state since late 1997 in addition to these large scale changes the mesoscale eddy field also exhibited prominent interannual changes in the kuroshio extension region in the upstream region between the izu ridge and the shatsky rise the eddy kinetic energy level was generally low while the kuroshio extension was in its elongated state and high while in the contracted state downstream of the shatsky rise on the other hand the eke level was high low when the kuroshio extension was in the elongated contracted state the large scale interannual changes in the kuroshio extension system have a significant impact on the regional wintertime sst anomaly field the warm cold wintertime sst anomalies tend to persist in years when the kuroshio extension is in its elongated contracted state a diagnostic analysis of the surface ocean heat balance indicates that the nonseasonal geostrophic advection by the ocean circulation works to reduce increase the wintertime sst anomalies when the kuroshio extension changes from an elongated contracted state to a contracted elongated state the sst anomalies associated with the large scale changes of the kuroshio extension have an area averaged peak topeak amplitude of 18c and appear independent of the interannual sst changes in the tropical pacific ocean