altered atmospheric responses to eastern pacific and central pacific el ninos over the north atlantic region due to stratospheric interference the two types of el nino that have been identified namely the eastern pacific ep and central pacific cp el ninos are known to exert different climatic impacts on the north atlantic region during winter here we investigate the characteristics of the teleconnection of the two el nino types with a focus on the stratosphere troposphere coupling during the ep el nino polar stratospheric warming and polar vortex weakening frequently occur with a strong tendency for downward propagation near the tropopause consequently the atmospheric pattern within the troposphere over the north atlantic sector during midwinter closely resembles the negative north atlantic oscillation pattern in contrast during cp el nino events stratospheric warming events exhibit a much weaker downward propagation tendency this difference in the stratospheric circulation response arises from the different seasonal evolution of the tropospheric wave response to the two el nino types for the ep el nino the aleutian low begins growing during december and is sustained throughout the entire winter december to february which provides favorable conditions for the continuous downward propagation of the stratospheric warming we also discuss the origin of the difference in the teleconnections from the two types of el nino associated with the distinct longitudinal position of the warm sst anomaly that determines troposphere stratosphere coupling

the equatorial atlantic oscillation and its response to enso an internal equatorial atlantic oscillation has been identified by analyzing sea surface temperature sst observations the equatorial atlantic oscillation can be viewed as the atlantic analogue of the el nino southern oscillation enso phenomenon in the equatorial pacific but it is much less vigorous the equatorial atlantic oscillation is strongly influenced by the pacific enso with the equatorial atlantic sea surface temperature lagging by about six months this lag can be explained by the dynamical adjustment time of the equatorial atlantic to low frequency wind stress variations and the seasonally varying background state which favours strongest growth of perturbations in summer results of an extended range simulation with a coupled ocean atmosphere gcm support this picture

global climatic anomalies associated with extremes in the southern oscillation abstract composite temperature and precipitation anomalies during various stages of an event in the southern oscillation so have been computed for several hundred stations across the globe large regions of coherent significant signals are shown to exist for both extremes of the so with warm event signals generally opposite to those during cold events in addition during the year preceding the development of an event in the so year 1 climatic anomalies tend to be opposite to those during the following year year 0 this confirms that the biennial tendency of the so over the pacific indian ocean sectors is also present in more remote regions with climatic signals related to the so many of the signals are consistent enough from event to event to be useful for extended range forecasting purposes

structural and geochronological constraints on the tectonic evolution of the dulong song chay tectonic dome in yunnan province sw china abstract the dulong song chay tectonic dome lies on the border of china se yunnan province and northern vietnam and consists of two tectonic and lithologic units a core complex and a cover sequence separated by an extensional detachment fault these two units are overlain unconformably by late triassic strata the core complex is composed of gneiss schist and amphibolite shrimp zircon u pb dating results for the orthogneiss yield an age of 799 10 ma which is considered to be the crystallization age of its igneous protolith formed in an arc related environment a granitic intrusion within the core complex occurred with an age of 436 402 ma which probably formed during partial closure of paleotethys within the core complex metamorphic grades change sharply from upper greenschist low amphibolite facies in the core to low greenschist facies in the cover sequence there are two arrays of foliation within the core complex detachment fault and the cover sequence s 1 and s 2 the pervasive s 1 is the axial plane of intrafolial s 0 folds d 1 deformation related to this foliation is characterized by extensional structures the strata were structurally thinned or selectively removed along the detachment faults indicating exhumation of the dulong song chay tectonic dome the major extension occurred at 237 ma determined by shrimp zircon u pb and 39 ar 40 ar isotopic dating techniques regionally simultaneous tectonic extension was associated with pre indosinian collision between the south china and indochina blocks the s 2 foliation appears as the axial plane of nw striking s 1 buckling folds formed during a compressional regime of d 2 d 2 is associated with collision between the south china and indochina blocks along the jinshajiang ailao shan suture zone and represents the indosinian deformation the dulong granites intruded the dulong song chay dome at 144 2 140 2 and 116 10 ma based on 39 ar 40 ar measurement on muscovite and biotite the dome was later overprinted by a conjugate strike slip fault and related thrust fault which formed a vortex structure contemporaneously with late cenozoic sinistral movement on the ailao shan red river fault

the link between the north pacific climate variability and the north atlantic oscillation via downstream propagation of synoptic waves abstractthe north atlantic oscillation nao response to the northeast pacific climate variability is examined using the era 40 dataset the main objective is to validate a mechanism involving downstream wave propagation processes proposed in a recent idealized companion study a low frequency planetary scale ridge trough anomaly located in the eastern pacific north american sector induces more equatorward poleward propagation of synoptic scale wave packets on its downstream side which favors the occurrence of anticyclonic cyclonic wave breakings in the atlantic sector and the positive negative nao phase the mechanism first provides an interpretation of the canonical impact of the el nino southern oscillation on the nao in late winter the wintertime relationship between the pacific north american oscillation pna and the nao is also investigated for out of phase fluctuations between the pna and nao indices i e the most recurrent situation in late winter the eastern pacific pna ridge trou

oceanic and atmospheric transport of multiyear el nino southern oscillation enso signatures to the polar regions 1 using monte carlo singular spectrum analysis mc ssa and wavelet transform wt we separate statistically significant components from time series and demonstrate significant co variance and consistent phase differences between ice conditions and the arctic oscillation and southern oscillation indices ao and soi at 2 2 3 5 5 7 and 13 9 year periods the 2 2 3 5 and 5 7 year signals detected in the arctic are generated about three months earlier in the tropical pacific ocean in contrast we show that the 13 9 year signal propagates eastward from the western pacificasequatorialcoupledwaves ecw 0 13 0 15ms 1 and then as fast boundary waves 1 3 ms 1 along the western margins of the americas with a phase difference of about 1 8 2 1 years by the time they reach the arctic our results provide evidence of dynamical connections between high latitude surface conditions tropical ocean sea surface temperatures mediated by tropical wave propagation the wintertime polar vortex and the ao index terms 1620 global change climate dynamics 3309 3309 meteorology and atmospheric dynamics climatology 1620 0312 atmospheric composition andstructure air seaconstituent fluxes 3339 4504 4504 oceanography physical air sea interactions 0312 4522 oceanography physical el nino citation jevrejeva s j c moore and a grinsted 2004 oceanic and atmospheric transport

tropical extratropical connection in the atlantic atmosphere ocean variability a question how sea surface temperature sst fluctuations in the tropical atlantic affect the north atlantic atmosphere ocean system is addressed using an atmospheric general circulation model coupled to a 50 m deep slab ocean mgcm and a linear baroclinic model a comparison of a 60 yr integration in which the tropical ssts are prescribed to observations toga ml with the control mgcm run shows that the tropical sst variations selectively enhance variance of the north atlantic oscillation nao by about 80 this is partly due to extratropical height anomalies associated with two dominant modes monopole and dipole of tropical atlantic sst variability because they both have a projection on to the nao in the toga ml run the simulated midlatitude height anomalies accompany characteristic sst anomaly patterns beneath and they are consistent with observations analyses of steady linear responses to the heating in the tropical atlantic and transient eddy feedback in midlatitude reveal that the substantial part of height anomalies is generated by the latter rather than the former the anomalous eddy forcing is however organized not only by the heating in the tropical atlantic but also by the tropical pacific sst variations through the teleconnection over north america it is suggested that the tropical atlantic sst variability does affect the north atlantic atmosphere and ocean but the dynamical connection is tenuous in comparison with the pacific

the role of synoptic waves in the formation and maintenance of the western hemisphere circulation pattern abstractprevious studies have demonstrated that the nao the leading mode of atmospheric low frequency variability over the north atlantic could be linked to northeast pacific climate variability via the downstream propagation of synoptic waves in those studies the nao and the northeast pacific climate variability are considered as two separate modes that explain the variance over the north atlantic sector and the east pacific north american sector respectively a newly identified low frequency atmospheric regime the western hemisphere wh circulation pattern provides a unique example of a mode of variability that accounts for variance over the whole north atlantic north american north pacific sector the role of synoptic waves in the formation and maintenance of the wh pattern is investigated using the ecmwf reanalysis datasets persistent wh events are characterized by the propagation of quasi stationary rossby waves across the north pacific north american north atlantic regions and by associated s

timescale dependency of spatial patterns in the variability of the northern hemisphere winter slp field 1 the arctic oscillation ao the north atlantic oscillation nao and the cold ocean warm land pattern cowl have been identified as important modes of variability in the northern hemisphere winter sea level pressure field however which one is most fundamental in describing this variability and the relationship between them are still important open questions a key uncertainty is our lack of knowledge of the linkages between the arctic north atlantic and north pacific oceans that are manifest in these modes in this study the authors investigate these linkages through a frequency dependent decomposition of the variability in the northern hemisphere sea level pressure field in particular the authors show that the spatial expression of the variability in this field has a frequency dependence that results in a nao like pattern on inter annual timescales an ao like pattern on inter decadal timescales and a cowl like pattern on multi decadal timescales

the association between enso and winter atmospheric circulation and temperature in the north atlantic region the association among enso the northern hemisphere sea level pressure slp and temperatures in europe has been analyzed during the period 1873 1995 in the first part the sst of the nino 3 region has been used to select extreme cold and warm enso events and periods that can be regarded as normal the study was carried out for winter with the constraints that the enso events were well developed during the winter of study and that they are extreme events composites of winter slp and temperatures have been made for the selected cold and warm events as well as for normal cases and compared with each other in the north atlantic area no statistically significant slp anomaly patterns were found associated with warm events while during cold events a statistically significant anomaly pattern resembling the positive phase of the north atlantic oscillation nao was found the temperature analysis shows statistically significant negative anomalies during cold events over the iberian peninsula and positive anomalies over the british isles and southern scandinavia consistent with the slp anomalies the slp and temperatures have also been analyzed for spring the patterns resemble those found for winter but the anomalies have lower amplitudes for the completion of the composite analysis the consistency among events of the relationship between enso and slp as well as between enso and temperatures was examined the results show that the significant patterns found in the composite analysis in the north atlantic area are not the result of a few major events but rather because both the slp and temperature anomalies in this area during cold enso events are stable and qualitatively similar to those found during the positive phase of the nao the possible physical basis for this association between nao and enso is discussed

rapid coastal geomorphic change in the river murray estuary of australia abstract the river murray estuary a ramsar wetland site has experienced considerable rapid coastal change during the quaternary the interplay of aeolian processes river flows tidal oscillations wave action and variations in relative sea level due to global sea level changes and land subsidence provides the energy for the ongoing dynamism often accelerated by human impacts the estuary is the terminus of the murray darling catchment which covers 1 073 million km 2 of the australian continent terminal lakes alexandrina albert and the coorong lagoon are holocene features occupying tectonically subsiding quaternary interdune areas they formed in response to eustatic sea level rise following the last glacial maximum ca 20 ka the last interglacial shoreline 125 000 yr bp parallels the modern shoreline several kilometres inland dislocation of the last interglacial shoreline demonstrates ongoing tectonic subsidence as does historical seismic activity the northern half of hindmarsh island formed during last interglacial times when it was the sink for dominant longshore transport from the southeast which pushed the river murray westward partly explaining the large bend in the river murray at goolwa the modern coastal barriers of sir richard peninsula and younghusband peninsula formed from 7000 yr ago following glacier melt and sea level rise subsequently the barriers have migrated landward sporadically exposing lagoonal sediments on the ocean beaches differential loading of the soft lagoonal sediments by advancing dunes possibly in conjunction with seismic events has deformed and elevated them to up to 10 m above present sea level apsl during the mid holocene an extensive sand flat with associated dunes formed immediately inland of the coastal barrier at least six generations of late pleistocene dune systems occur in the region for example during last glacial times the climate was drier colder and windier than at present and a system of parallel west east trending yellow red desert dunes developed around the lakes aeolian processes remain important with occasionally up to 5000 tonnes of sand being in motion along 10 km of the modern shoreline during mouth migration dunes up to 2 m high have been formed and vegetated in 12 months directly inland from the mouth and replicating the formation of older dunes on hindmarsh island elsewhere sand blown directly from the barrier system infills channels barrage construction on the beach facies of the last interglacial shoreline transformed the estuary into freshwater lakes with permanently raised water levels and reduced the tidal prism by 90 increased deposition upstream and downstream accompanied barrage construction as have accelerated lakeshore erosion and the growth and consolidation of the flood tidal delta bird island these human accelerated changes provide rapidly formed analogues of older quaternary features and aid their interpretation the shape and location of the murray mouth is constantly changing migrating over 1 6 km since the 1830s migrations of up to 6 km over the past 3000 yr have influenced sedimentation on the landward shore of the back barrier lagoonal system

the influence of atlantic sea surface temperature anomalies on the north atlantic oscillation abstract the influence of atlantic sea surface temperature sst anomalies on the atmospheric circulation over the north atlantic sector during winter is investigated by performing experiments with an atmospheric general circulation model these consist of a 30 yr run with observed sst anomalies for the period 1961 90 confined geographically to the atlantic ocean and of a control run with climatological ssts prescribed globally a third 30 yr integration with observed ssts confined to the south atlantic is made to confirm present findings the simulated interannual variance of 500 hpa wintertime geopotential heights over the north atlantic attains much more realistic values when observed atlantic ssts are prescribed circulation patterns that resemble the positive phase of the north atlantic oscillation nao become more pronounced in terms of the leading eof of winter means and a cluster analysis of daily fields the variance of an interannual nao index increases by fivefold over its control value atl

role of the gulf stream and kuroshio oyashio systems in large scale atmosphere ocean interaction a review abstract ocean atmosphere interaction over the northern hemisphere western boundary current wbc regions i e the gulf stream kuroshio oyashio and their extensions is reviewed with an emphasis on their role in basin scale climate variability sst anomalies exhibit considerable variance on interannual to decadal time scales in these regions low frequency sst variability is primarily driven by basin scale wind stress curl variability via the oceanic rossby wave adjustment of the gyre scale circulation that modulates the latitude and strength of the wbc related oceanic fronts rectification of the variability by mesoscale eddies reemergence of the anomalies from the preceding winter and tropical remote forcing also play important roles in driving and maintaining the low frequency variability in these regions in the gulf stream region interaction with the deep western boundary current also likely influences the low frequency variability surface heat fluxes damp the low frequency sst anomalies ove

atmospheric response to sea surface temperature anomalies during el nino 1997 98 as simulated by echam4 one of the strongest el nino events on record was observed in 1997 98 a time period characterized by many strong climate anomalies all over the globe to study the origin of these climate anomalies ensemble experiments have been performed with the echam4 atmospheric general circulation model at t42 resolution forced by observed sea surface temperatures ssts many of the observed climate anomalies and the well known el nino southern oscillation teleconnection patterns could be reproduced by the ensemble integrations in particular the model reproduces the observed weakening of the trade winds although it fails to simulate the early decline of the southern oscillation index in november 1997 the observed climate anomalies over the pacific the americas and the atlantic were successfully simulated the model also reproduces the observed splitting of the jet over the north atlantic which caused a very mild winter in western europe our results do not indicate that the intense 1997 summer rainfalls leading to severe flooding in eastern central europe were related to el nino with respect to the indian ocean india australia and southern africa the results were less satisfying for example the model yields reduced indian monsoon rainfall which has not been observed additional experiments with sst anomalies restricted to particular ocean basins reveal that most of the atmospheric climate anomalies in 1997 98 were related to sst anomalies in the tropical pacific in particular atlantic sst anomalies had only a marginal impact on the atmosphere

combined records from a stalagmite from barbados and from lake sediments in haiti reveal variable seasonality in the caribbean between 6 7 and 3 ka bp abstract the growth of a well dated stalagmite from barbados records high infiltration rates into the karst aquifer and hence increased rainfall intensity between 6 7 and 3 ka bp in agreement with records from lake miragoane haiti hodell et al 1991 reconstruction of the caribbean climate change over the past 10 500 years nature 352 790 793 mainly reflecting the insolation maximum of the northern hemisphere both the lake record and the stable isotope record of the stalagmite reveal additional centennial variability of recharge high oxygen isotope values in stalagmite calcite corresponding to reduced recharge are synchronous with periods of lower stable isotope values recorded in lake miragoane ostracods previously attributed to enhanced precipitation accordingly periods of increased recharge in barbados correspond to 18o enriched isotope values of ostracods which were attributed to higher evaporation precipitation ratios in the lakes we ascribe this apparent discrepancy to changes in seasonality i e winter periods of reduced temperature and relative humidity following summer months of increased precipitation at present such climate conditions occur during periods of enhanced northern atlantic oscillation nao if enhanced seasonality is a consequence of a nao situation the apparent discrepancy of high isotope values in lakes previously attributed to droughts can be reconciled with lower winter temperatures in the lakes further the correlation of solar intensity derived from 14c and 10be with the isotopic signals recorded in the lacustrine sediments suggests a solar forcing of the nao during the mid holocene

afro eurasian intermediate frequency teleconnection and modulation by enso abstractthe afro eurasian intermediate frequency atmospheric teleconnection conveys meteorological signals zonally leads to various atmospheric variations and causes extreme events along its path

surface temperature patterns associated with the southern oscillation abstract the typical global and large scale regional temperature patterns associated with the low warm and high cold phases of the southern oscillation so are investigated a total of 12 separate regions were found to have consistent temperature patterns associated with low phase of the so while 11 areas were found to have temperature patterns associated with the high phase of these areas 9 have expected temperature patterns during both phases of the so in the tropics temperature anomalies are of the same sign as the so related sea surface temperature sst anomaly in all land regions except for one area in the west pacific three extratropical responses to the low phase of the so are found over north america and one is found in japan high so temperature patterns were found in the extratropies for japan western europe and northwestern north america the identified temperature responses are more consistent in tropical regions than in the extratropies the so can influence the estimation of

land sea linkage of holocene paleoclimate on the southern bering continental shelf detailed diatom records within surface and core sediments from the southern bering continental shelf sbcs reveal that the holocene evolution of sea ice distribution is associated with low pressure patterns holocene sea ice distribution over the sbcs was mainly controlled by the location of the aleutian low the corresponding paleoceanographic and paleoclimate conditions can be divided into three stages 1 the early holocene before 7000 cal yr bp was characterized by extensive sea ice distribution under two low pressure cells which covered the western bering sea and the gulf of alaska respectively 2 between 3000 and 7000 cal yr bp the low pressure system over the gulf of alaska became weak causing total sea ice mass over the sbcs to retreat 3 in the past 3000 years prevailing southwesterly winds over the sbcs due to the developing aleutian low have reduced further sea ice cover on the sbcs these paleoclimatic changes were probably a response to enso variation the timings of water mass exchanges on the sbcs coincided with sea level change along the alaskan peninsula as a result subsequent morphologic alterations have also influenced the paleoceanographic condition of the sbcs the effect of the surface coastal water and bottom marine water on the sbcs intensified about 6000 cal yr bp when sea level increased

the spring relationship between the pacific north american pattern and the north atlantic oscillation the pacific north american pattern pna and north atlantic oscillation nao are two dominant modes of low frequency variability in the northern hemisphere winter generally these two patterns are separable and uncorrelated in both space and time however dating back to the 1970s there have been studies which have linked the aleutian and icelandic low intensities and shown that a significant temporal correlation does on occasion occur each of these semi permanent low pressure systems is a part of the pna and nao patterns respectively and therefore given a link between the two semi permanent low pressure systems we explore whether a link between the pna and nao also appears recently studies have found such a link during the winters of certain decades the present study documents an observed relationship between the pna and nao which is consistently present during the spring and early summer this relationship is shown to be due to the fact that the pna and nao are spatially overlapping projections of the same pattern of variability given by the first eof of 500 hpa geopotential height both the pna and nao patterns correlate more strongly to the first eof s spatial pattern resembling the aleutian low icelandic low seesaw pattern than the rotated eof reof loading patterns used to compute their respective indices furthermore when the two patterns are correlated the effect of el nino on the northern hemisphere is separate from the pattern associated with the pna finally we examine a 21 year period in the winter for which the pna and nao are significantly correlated and find that the conclusions drawn from the spring hold true the results presented herein demonstrate that defining the pna and nao based upon typical loading patterns may not be the ideal approach especially given that the patterns are spatially similar and covary in time

observed decadal midlatitude and tropical atlantic climate variability two common indicators of atlantic climate variability viz the north atlantic oscillation nao and the cross intertropical convergence zone itcz sea surface temperature sst gradient are examined for their frequency characteristics and midlatitude tropical links sst anomalies north and south of the itcz are found to be uncorrelated on all time scales while the sea level pressure slp fluctuations associated with the nao display a coherent seesaw between iceland and the azores this out of phase relationship spans a broad range of time scales but is particularly strong in the 5 10 year period band strong broadband coherence between the nao and the tropical atlantic cross itcz sst difference is found in the 8 20 year period band suggesting a significant midlatitude tropical interaction moreover tropical atlantic ssts on both sides of the itcz separately exhibit significant coherence with the nao index and slp variability over iceland and the azores based on these findings we hypothesize that the tropical atlantic ta ocean atmosphere interaction is affecting north atlantic climate variability

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

linear and nonlinear winter atmospheric responses to extreme phases of low frequency pacific sea surface temperature variability this study examines northern hemisphere winter djfm atmospheric responses to opposite strong phases of interdecadal low frequency lf pacific sea surface temperature sst forcing which resembles el nino southern oscillation enso on a longer time scale in observations and gfdl and cam4 model simulations over the pacific north america pna sector linear observed responses of 500 hpa height z500 anomalies resemble the pna teleconnection pattern but show a pna like nonlinear response because of a westward z500 shift in the negative lf relative to the positive lf lf phase significant extratropical linear responses include a north atlantic oscillation nao like z500 anomaly a dipole like z500 anomaly over northern eurasia associated with warming over mid high latitude eurasia and a southern annular anomaly pattern associated with warming in southern land areas significant nonlinear z500 responses also include a nao like anomaly pattern models forced by lf and lf sst anomalies reproduce many aspects of observed linear and nonlinear responses over the pacific north america sector and linear responses over southern land but not in the north atlantic european sector and eurasia both models simulate pna like linear responses in the north pacific north america region similar to observed but show larger pna like lf responses resulting in a pna nonlinear response the nonlinear pna responses result from both nonlinear western tropical pacific rainfall changes and extratropical transient eddy feedbacks with lf tropical pacific forcing only lftp and lftp climatological sst elsewhere cam4 simulates a significant nao response to lftp including a linear negative and nonlinear positive nao response

high and low latitude types of the downstream influences of the north atlantic oscillation using reanalysis data we find that the downstream propagating quasi stationary rossby wave train associated with the north atlantic oscillation nao generally propagates along a high low latitude pathway during warm cold el nino southern oscillation enso boreal winters consistent with the different propagation directions of the nao related downstream wave train during the warm cold enso winters the nao is associated with significant 300 hpa geopotential height anomalies over eastern siberia the arabian sea the east coast of asia at around 40 n and the north pacific and the near surface air temperature perturbations associated with the nao over the high latitudes of asia are relatively strong weak based on these differences we argue that the nao has two distinct types of downstream influence a high latitude type and a low latitude type furthermore we argue that the two types of nao s downstream influence are modulated by the intensity of the subtropical potential vorticity pv meridional gradient over africa when this gradient is weak strong as in the warm cold enso winters the nao s downstream influence tends to be of the high low latitude type these results are further supported by analysis of intraseasonal nao events we separate nao events into two categories in terms of the intensity of the subtropical pv gradient over africa composites of the nao events accompanied by a weak strong subtropical pv gradient show that the nao related downstream wave train tends to propagate along a high low latitude pathway

the southern oscillation part i global associations with pressure and temperature in northern winter abstract we describe the global correlations between a measure of the southern oscillation and sea level pressure and surface air temperature in the northern winter the stability of these correlations were tested on the northern hemisphere for an 80 year period and it turned out that most stable correlation coefficients were found over india the north pacific ocean the rocky mountains and the central and western north atlantic ocean on the southern hemisphere most records are too short for a similar test but the following may tentatively be said about the southern oscillation in middle and high southern latitudes when pressure is low in lower latitudes over the south pacific ocean it tends to be high at higher latitudes of that ocean high over east antarctica and low in the belt of westerlies in the indian and south atlantic oceans in the zonal average on both hemispheres the pressure gradients in this extreme of the oscillation tend to be steeper at lower latitudes and flatter at higher latitud

the early twentieth century arctic high fact or fiction reconstructions of monthly mean sea level grid point pressure from station pressure data over the arctic region using an objective technique have revealed two serious errors in the gridded data first all gridded data from the u s historical weather map series for the arctic ocean area away from the north atlantic sector appears to be between 4 and 6 mb too high before about 1931 the semi permanent arctic high produced in the early historical map series was the result of a lack of basic station data and the belief amongst many north american meteorologists of the 1920s and 1930s of the existence of a polar or glacial anticyclone the second error affects only north western north america for the years 1899 1909 here pressure is again too high compared with reconstructed data the cause of this error is not immediately apparent but is probably the result of an erroneous correction to sea level for stations in the region both errors seriously affect the homogeneity of the gridded arctic series the objective scheme used to reveal the errors can also be used to derive correction factors for the gridded data prior to 1931

the relationship between the north atlantic oscillation and el nino southern oscillation we have applied a multiresolution cross spectral analysis technique to resolve the temporal relationship between the nao and enso the study shows significant coherence between nao and nino3 sst in about 70 of the warm enso events from 1900 to 1995 of which 33 and 37 are associated with a 5 to 6 year period e1 and a 2 to 4 year period e2 oscillation terms in the spectral decomposition respectively the dominant teleconnection pattern associated with changes in the mean atmospheric circulation during the initial winter of a typical e1 and e2 events is the positive phase of the pacific north american pna pattern non coherence between the nao and enso occurs during relatively weak nino3 sst anomaly with a teleconnection pattern which shows a strong negative phase of the nao and a pattern which resembles a weak eastward shifted negative phase of the pna pattern