hurricanes and climate in the caribbean during the past 3700 years bp a multiproxy analysis of lacustrine sediments cored in grand case pond at saint martin north of the lesser antilles archipelago reveals three distinct climatic periods for the last 3700 years from 3700 to 2500 yr cal bp and from 1150 yr cal bp to the present carbonate mud deposition occurred in connection with pond lowstands these periods were also punctuated by severe drought events marked by gypsum laminae and hurricane landfalls leading to marine sand inputs into the pond the intermediate time interval from 2500 to 1150 yr cal bp is typified by black organic mud deposition suggesting that hypoxic to anoxic conditions prevailed at the pond bottom these were probably linked with a perennial pond highstand and reflect more uniform and wetter climatic conditions than today the carbon isotopic composition of the ostracod perissocytheridea bisulcata shows that the lowest 13c values are recorded during the hypoxic periods as a consequence of bacterial recycling of isotopically depleted org

climate teleconnections at monthly time scales in the ligurian sea inferred from satellite data abstract the existence and spatial distribution of possible teleconnections between the south pacific and north atlantic oceans and the ligurian sea north western mediterranean are investigated in the present paper teleconnections are searched by cross correlating monthly spatio temporal time series of 1 1 km resolution sea surface temperature sst and a 22 2 km resolution sea level anomaly sla measured from satellite from march 1993 to august 1999 with two indices characterising the south pacific and the north atlantic variability the southern oscillation so and the north atlantic oscillation nao indices respectively concerning the variability induced by the north atlantic ocean it is shown that it mostly influences the sla field in the ligurian sea specifically relevant anti correlations between sla and north atlantic variability have been found in all the ligurian sub basin as expected by geographical proximity the effects of north atlantic on the sla field in the ligurian sea are instantaneous at monthly time scales instead correlations between sst and nao index are found at time lag 1 month in the southern part of the basin highlighting the memory of the ocean related to their heat capacity significant anti correlations between so index and the sst field in the ligurian sea were obtained at time lag 4 months in the coastal areas of the sub basin results also indicate that the impact of teleconnections in the area studied is not geographically uniform

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

nonlinearity of the extratropical response to tropical forcing abstract a primitive equations dry atmospheric model is used to investigate the atmospheric response to a tropical diabatic forcing pattern and explore how the atmospheric response changes as a function of the amplitude of the forcing the forcing anomaly represents a linear fit of the model forcing to a tropical sst pattern of an el nino la nina type the time averaged 500 hpa geopotential height anomaly responses of two long integrations with forcing anomalies of equal amplitudes but opposite signs show an asymmetric feature that is similar to observations and to previous modeling results related to el nino and la nina ensemble experiments with 61 different amplitudes of this forcing pattern are conducted an eof analysis of the ensemble mean of the 90 day averaged 500 hpa height for different amplitudes of forcings shows that the leading mode of the forced variability resembles the pacific north american pna pattern while the second mode is a wave train across the north atlantic to eurasia the r

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

the annular response to tropical pacific sst forcing abstract the leading pattern of northern hemisphere winter height variability exhibits an annular structure one related to tropical west pacific heating to explore whether this pattern can be excited by tropical pacific sst variations an atmospheric general circulation model coupled to a slab mixed layer ocean is employed ensemble experiments with an idealized sst anomaly centered at different longitudes on the equator are conducted the results reveal two different response patterns a hemispheric pattern projecting on the annular mode and a meridionally arched pattern confined to the pacific north american sector induced by the sst anomaly in the west and the east pacific respectively extratropical air sea coupling enhances the annular component of response to the tropical west pacific sst anomalies a diagnosis based on linear dynamical models suggests that the two responses are primarily maintained by transient eddy forcing in both cases the model transient eddy forcing response has a maximum

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

how are large western hemisphere warm pools formed during the boreal summer the western hemisphere warm pool whwp stretches from the eastern north pacific to the tropical north atlantic and is a key feature of the climate of the americas and africa in the summers following nine el nino events during 1950 2000 there have been five instances of extraordinarily large warm pools averaging about twice the climatological annual size these large warm pools have induced a strengthened divergent circulation aloft and have been associated with rainfall anomalies throughout the western hemisphere tropics and subtropics and with more frequent hurricanes however following four other el nino events large warm pools did not develop such that the mere existence of el nino during the boreal winter does not provide the basis for predicting an anomalously large warm pool the follow ing summer in this paper we find consistency with the hypothesis that large warm pools result from an anomalous divergent cir culation forced by sea surface temperature sst anomalies in the pacific the so called atmospheric bridge we also find significant explanations for why large warm pools do not always develop if the el nino event ends early in the eastern pacific the pacific warm anomaly lacks the persistence needed to force the atmospheric bridge and the atlantic portion of the warm pool remains normal if sst anomalies in the eastern pacific do not last much beyond february of the fol lowing year then the eastern north pacific portion of the warm pool remains normal the overall strength of the pacific el nino does not appear to be a critical factor we also find that when conditions favor a developing atmospheric bridge and the winter atmosphere over the north atlantic conforms to a negative north atlantic oscillation nao pattern as in 1957 58 and 1968 69 the forcing is reinforced and the warm pool is stronger on the other hand if a positive nao pat tern develops the warm pool may remain normal even if other circumstances favor the atmospheric bridge as in 1991 92 finally we could find little evidence that interactions internal to the tropical atlantic are likely to mitigate for or against the formation of the largest warm pools although they may affect smaller warm pool fluctuations or the warm pool persistence

the nonlinear northern hemisphere winter atmospheric response to enso 1 a nonlinear projection of the tropical pacific sea surface temperature anomalies ssta onto the northern hemisphere winter 500 mbar geopotential height z500 by a neural network reveals asymmetric atmospheric patterns associated with el nino and la nina while the linear response of z500 to tropical pacific ssta is largely confined over north pacific and north america the nonlinear response mainly a quadratic response to the ssta reveals that regardless of the sign of the ssta positive z500 anomalies are found over the central eastern north america north atlantic and western europe and negative z500 anomalies over the west coast of north america scandinavia and eastern europe consistent with the positive pacific north america pna teleconnection pattern and the positive north atlantic oscillation nao pattern being excited

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 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

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

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

teleconnections between enso and north atlantic in an echo g simulation of the 1000 1990 period 1 the north atlantic sea level pressure anomalies slpa associated with el nino southern oscillation enso have been analyzed in a quasi millennial 1000 1990 simulation with the echo g model in november december the enso related slpa over the north atlantic area are weak while a realistic pattern already appears over the north pacific and north america in january march the slpa over north atlantic are stronger and realistic from the north pacific to europe the aleutian low is strengthened weakened slpa are positive negative over the north central and north eastern parts of north america and slpa display a negative positive nao like pattern over north atlantic during warm cold enso events as in observations the results also confirm the existence of a strong inter event slpa associated with warm and cold enso events especially over the north atlantic while the relationship is stationary at multidecadal timescales it seems that neither the intensity nor geographical longitude of the equatorial pacific sea surface temperature anomaly ssta and intensity of tropical atlantic ssta nor the volcanic forcing simply introduced here as a decrease of the solar constant significantly induce an inter event variability which seems in this run mostly of atmospheric origin

the dominance of dispersion in the evolution of bed material waves in gravel bed rivers bed material waves are temporary zones of sediment accumulation created by large sediment inputs recent theoretical experimental and field studies examine factors influencing dispersion and translation of bed material waves in quasi uniform gravel bed channels exchanges of sediment between a channel and its floodplain are neglected within these constraints two factors influence relative rates of dispersion and translation 1 interactions between wave topography flow and bed load transport and 2 particle size differences between wave material and original bed material our results indicate that dispersion dominates the evolution of bed material waves in gravel bed channels significant translation requires a low froude number which is uncharacteristic of gravel bed channels and low wave amplitude which for a large wave can be achieved only after substantial dispersion wave material of small particle size can promote translation but it primarily increases bed load transport rate and thereby accelerates wave evolution copyright 2001 john wiley sons ltd

multi model assessment of the late winter extra tropical response to el nino and la nina el nino southern oscillation enso is known to affect the northern hemisphere tropospheric circulation in late winter january march but whether el nino and la nina lead to symmetric impacts and with the same underlying dynamics remains unclear particularly in the north atlantic three state of the art atmospheric models forced by symmetric anomalous sea surface temperature sst patterns mimicking strong enso events are used to robustly diagnose symmetries and asymmetries in the extra tropical enso response asymmetries arise in the sea level pressure slp response over the north pacific and north atlantic as the response to la nina tends to be weaker and shifted westward with respect to that of el nino the difference in amplitude can be traced back to the distinct energy available for the two enso phases associated with the non linear diabatic heating response to the total sst field the longitudinal shift is embedded into the large scale rossby wave train triggered from the tropical pacific as its anomalies in the upper troposphere show a similar westward displacement in la nina compared to el nino to fully explain this shift the response in tropical convection and the related anomalous upper level divergence have to be considered together with the climatological vorticity gradient of the subtropical jet i e diagnosing the tropical rossby wave source in the north atlantic the enso forced slp signal is a well known dipole between middle and high latitudes different from the north atlantic oscillation whose asymmetry is not indicative of distinct mechanisms driving the teleconnection for el nino and la nina

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

equal mobility of gravel in streams the remains of the day 1 the concept of equal mobility of gravel transport is 2 decades old the weak form of the hypothesis states that in order to transport the coarse half of the mean annual gravel load through a river reach at a rate equal to the fine half the coarser material must be overrepresented on the bed surface giving rise to a mobile bed armor the degree of mobile bed armoring necessary to accomplish this diminishes with increasing bed shear stress the strong form of the hypothesis states that the grain size distribution of the gravel portion of the bed load should be similar to that of the substrate and finer than that of the surface layer here the hypothesis is subjected to a rigorous test in the laboratory under controlled conditions which are nevertheless chosen to be as representative as possible of actual field conditions the grain size distributions used in the experiment included both model gravel and model sand at the end of the experiment the entire surface layer and a significant depth of substrate were removed from an entire reach of the channel and sieved the results of the experiment confirmed the weak form of equal mobility the surface layer was significantly coarsened compared with the bed load even when the sand was excluded from the size distributions the strong form of equal mobility was also supported by the experiment in that the size distribution of the gravel substrate was nearly identical to the size distribution of the gravel portion of the load the gravel substrate was however slightly but measurably coarser than the gravel load a tendency that has been observed in the field in cases for which the strong form is not satisfied

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

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

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

influence of the arctic oscillation and el nino southern oscillation enso on ice conditions in the baltic sea the wavelet approach 1 variability in time series of ice conditions in the baltic sea is examined within the context of atmospheric circulation represented by the north atlantic oscillation nao and arctic oscillation ao winter indices using the wavelet approach we develop methods of assessing statistical significance and confidence intervals of cross wavelet phase and wavelet coherence cross wavelet power for the time series indicates that the times of largest variance in ice conditions are in excellent agreement with significant power in the ao at 2 2 3 5 5 7 7 8 and 12 20 year periods similar patterns are also seen with the southern oscillation index soi and nino3 sea surface temperature nino3 series wavelet coherence shows in phase linkages between the 2 2 7 8 and 12 20 year period signals in both tropical and arctic atmospheric circulation and also with ice conditions in the baltic sea these results are consistent with gcm simulations showing dynamical connections between high latitude surface conditions tropical sea surface temperatures mediated by tropical wave propagation the wintertime polar vortex and the ao and with models of sea ice and oceanic feedbacks at decadal periods

the nonlinear association between enso and the euro atlantic winter sea level pressure a nonlinear projection of the tropical pacific sea surface temperature anomalies ssta onto the northern hemisphere winter sea level pressure slp anomalies by neural networks nn was performed to investigate the nonlinear association between el nino southern oscillation enso and the euro atlantic winter climate while the linear impact of enso on the euro atlantic winter slp is weak the nn projection reveals statistically significant slp anomalies over the euro atlantic sector during both extreme cold and warm enso episodes suggesting that the euro atlantic climate mainly responds to enso nonlinearly the nonlinear response mainly a quadratic response to the ssta reveals that regardless of the sign of the ssta positive slp anomalies are found over the north atlantic stretching from eastern canada to europe with anomaly center located just northwestward of portugal and negative anomalies centered over scandinavia and norwegian sea consistent with the excitation of the positive north atlantic oscillation pattern

el nino southern oscillation drives north atlantic oscillation as revealed with nonlinear techniques from climatic indices 1 based on the nonlinear techniques for estimation of coupling between oscillatory systems we investigate the dynamics of climatic modes characterizing global and the northern hemisphere nh processes in particular indices of the north atlantic oscillation nao and el nino southern oscillation enso for 1950 2004 are analyzed the methods based on phase dynamics modeling and nonlinear granger causality are used we infer that enso affects nao during the last half a century with confidence probability higher than 0 95 the influence is characterized with time delay in the range from a couple of months up to three years and increases during the last decade

contributions of downstream eddy development to the teleconnection between enso and the atmospheric circulation over the north atlantic abstractthe spatiotemporal evolution of various meteorological phenomena associated with el nino southern oscillation enso in the north pacific north american north atlantic sector is examined using both ncep ncar reanalyses and output from a 2000 yr integration of a global coupled climate model particular attention is devoted to the implications of downstream eddy developments on the relationship between enso and the atmospheric circulation over the north atlantic the el nino related persistent events are characterized by a strengthened pacific subtropical jet stream and an equatorward shifted storm track over the north pacific the wave packets that populate the storm tracks travel eastward through downstream development the barotropic forcing of the embedded synoptic scale eddies is conducive to the formation of a flow that resembles the negative phase of the north atlantic oscillation nao the more frequent and higher persistence of those episodes during el nino winters contribute to the prevale

the influence of sea surface temperature anomalies on low frequency variability of the north atlantic oscillation the influence of sea surface temperature anomalies ssta on multi year persistence of the north atlantic oscillation nao during the second half of the twentieth century is investigated using the center for ocean land atmosphere studies cola atmospheric gcm agcm with an emphasis on isolating the geographic location of the ssta that produce this influence the present study focuses on calculating the atmospheric response to the ssta averaged over 1988 1995 1961 1968 corresponding to the observed period of strong persistence of the positive negative phase of the decadal nao the model response to the global 1988 1995 average ssta shows a statistically significant large scale pattern characteristic of the positive phase of the nao forcing with the global 1961 1968 average ssta generates a nao of the opposite polarity compared to observations however all large scale features both in the model and observations during this period are weaker in magnitude and less significant compared to 1988 1995 additional idealized experiments show that over the northern center of the nao the non linear component of the forced response appears to be quite important and acts to enhance the positive nao signal on the other hand over the southern center where the model response is the strongest it is also essentially linear the 1988 1995 average ssta restricted to the western tropical pacific region produce a positive nao remarkably similar in structure but stronger in magnitude than the model response to the global and tropical indo pacific 1988 1995 forcing a 200 hpa geopotential height response in these experiments shows a positive anomaly over the southern center of the nao embedded in the rossby wave trains propagating from the western tropical pacific indian ocean ssta lead to much weaker positive nao primarily through the effect on its northern center sst forcing confined to the north atlantic north of equator does not produce a response statistically different from the control simulation suggesting that it is not strong enough to significantly affect the phase of the decadal nao inclusion of the south atlantic north of 45 south does not change this result

the nonlinear transient atmospheric response to tropical forcing abstract ensemble integrations using a primitive equation dry atmospheric model were performed to investigate the atmospheric transient response to tropical thermal forcings that resemble el nino and la nina the response develops in the north pacific within 1 week after the integration the signal in the north atlantic and europe is established by the end of the second week significant asymmetry was found between the responses in el nino and la nina that is similar to the observations that is one feature is that the 550 hpa positive height response in the north pacific of the la nina run is located about 30 west of the negative response of the el nino run another feature is that the responses in the north atlantic and europe for the la nina and el nino cases have similar patterns with the same polarity the first feature is established within 2 weeks of the integration while the second feature develops starting from the end of the second week several factors contribute to this nonlinearity of the

shift in enso teleconnections recorded by a northern red sea coral abstract el nino southern oscillation enso teleconnections over europe and the middle east are evaluated using an oxygen isotope coral time series from the northern red sea and various instrumental datasets a shift in the correlation between the nino 3 index and the red sea coral record in the 1970s is detected and it is shown that this shift can be attributed to nonstationary circulation regimes and related enso teleconnections it is found that positive anomalies of oxygen isotope in the red sea coral record from the middle 1930s to the late 1960s are associated with a strong pacific north atlantic teleconnection accompanied by a weak aleutian low a more zonal flow at midlatitudes and la nina conditions in tropical pacific in contrast positive anomalies of oxygen isotopes in the red sea coral after the 1970s are related to el nino conditions and weaker pan pacific atlantic circulation regimes using the window correlation of the northern red sea coral record with two coral records from the tropi

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

rotational atmospheric circulation during north atlantic european winter the influence of enso the dominant variability modes of the north atlantic european rotational flow are examined by applying a principal component analysis pca eof to the 200 hpa streamfunction mid winter anomalies jan feb monthly means the results reveal that when this norm is used the leading mode eof1 does not correspond to the traditional north atlantic oscillation nao which appears in our analysis as the second leading mode eof2 but is the local manifestation of the leading hemispheric streamfunction eof the regression of this regional mode onto the global sst field exhibits a clear el nino signature with no signal over the atlantic while the associated upper height anomalies resemble the tropical northern hemisphere tnh pattern east of north america this tnh like wavetrain produces a meridional dipole like pattern at lower levels although in some ways this pattern resembles the nao eof2 the dynamics of these two modes are very different in that only eof2 is associated with a latitudinal shift of the north atlantic stormtrack thus the choice of the streamfunction norm in the eof analysis allows the separation of two different phenomena that can produce similar dipolar surface pressure anomalies over the north atlantic but that have different impact on european climate these two modes also differ on their contribution to variability at lower levels while nao eof2 is mostly confined to the north atlantic tnh eof1 has a more annular global character at upper levels nao eof2 also produces a global pattern but with no annular structure reminiscent of the circumglobal teleconnection

impact of enso on the atmospheric variability over the north atlantic in late winter role of transient eddies abstractthe dynamical mechanism for the late winter teleconnection between el nino southern oscillation enso and the north atlantic oscillation nao is examined using the output from a 2000 yr integration of a coupled general circulation model gcm the coupled model captures many salient features of the observed behavior of both enso and nao as well as their impact on the surface climate in late winter both the observational and model data indicate more occurrences of negative phase of nao in late winter during el nino events and positive nao in la nina episodes the potential role of high frequency transient eddies in the above teleconnection is diagnosed during el nino winters the intensified transient disturbances along the equatorward shifted north pacific storm track extend their influences farther downstream the eddy induced negative height tendencies are found to be more coherent and stronger over north atlantic than that over north pacific these negative height tendencies over the north

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

interdecadal variability of the enso north atlantic oscillation connection in boreal summer understanding the combined effect of el nino southern oscillation enso and the north atlantic oscillation nao is of great importance for climate seasonal prediction extreme climate events in particular results in this study show that during the last hundred years 1900 to present the enso nao connection experiences a notable interdecadal change in summer june august according to a 21 year sliding correlation between them namely from no significant correlation uncoupling before the mid 1970s to a significant correlation coupling after the mid 1970s comparison analysis between the coupling epoch 1977 1997 and the uncoupling epoch 1958 1976 shows that the most pronounced circulation anomalies take place over the extratropical north pacific further analysis and numerical experiments suggest that a poleward propagating rossby wave train possibly enhanced by sea surface temperature anomalies in the extratropical north pacific associated with the developing phases of enso during the later epoch is responsible for connecting the enso signal with the nao 2012 crown in the right of canada published by johnwiley sons ltd

enso influence on the north atlantic european climate a non linear and non stationary approach el nino southern oscillation enso impact on the north atlantic european sector nae is still under discussion recent studies have found a non stationary feature of this teleconnection suggesting an effective modulating role of the ocean mean state nevertheless physical explanations about the underlying mechanisms have been little studied in the available literature in addition enso events show different sst spatial patterns phases and amplitudes which can also influence on the related remote impacts in view of all this in the present study a set of partially coupled experiments have been performed with a global atmospheric general circulation model in which different sst enso patterns are superimposed over distinct pacific and atlantic sst mean states these sst background conditions are constructed according to the observational difference between periods with a distinct impact of enso on the leading euro mediterranean rainfall mode in late winter early spring our results point to two distinct mechanisms associated with enso that can be modulated by the sst mean state 1 the thermally driven direct circulation walker and hadley cells connecting the atlantic and pacific basins and 2 the rossby wave propagation from the tropical pacific to the north atlantic the former elucidates that the positive nao like pattern usually related to la nina events could be only valid for selected decades the latter explains a reinforced signature of eastern pacific ninos on the euro mediterranean rainfall when the tropical pacific is warmer than usual and the north atlantic is colder than usual this feature is consistent with the changing enso impact identified in previous studies and demonstrates how the enso teleconnection with the nae climate at interannual timecales could be modulated by multidecadal changes in the sst according to our results the assumption of stationarity which is still common to many studies of enso teleconnections clearly has to be questioned

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

sediment pulses in mountain rivers 1 experiments 1 sediment often enters rivers in discrete pulses associated with landslides and debris flows this is particularly so in the case of mountain streams the topographic disturbance created on the bed of a stream by a single pulse must be gradually eliminated if the river is to maintain its morphological integrity two mechanisms for elimination have been identified translation and dispersion according to the first of these the topographic high translates downstream according to the second of these it gradually diffuses away in any given river both mechanisms may operate this paper is devoted to a description of three controlled experiments on sediment pulses designed to model conditions in mountain streams each of the experiments began from the same mobile bed equilibrium with a set rate and grain size distribution of sediment feed in one experiment the median size of the pulse material was nearly identical to that of the feed sediment in the other two the pulse material differed in grain size distribution from the feed sediment being coarser in one case and finer in the other case in all cases the mode of pulse deformation was found to be predominantly dispersive a result that constitutes the main conclusion of this paper the pulses resulted in a notable but transient elevation of sediment transport rate immediately downstream when the pulse was coarser than the ambient sediment the bed downstream remained armored and a migrating delta formed in the backwater upstream when the pulse was finer than the ambient sediment translation was observed in addition to dispersion the presence of the finer material notably elevated the transport of ambient coarse material on the bed downstream in part 2 cui et al 2003 the experimental results are used to test a numerical model

north atlantic oscillation sensitivity to the el nino southern oscillation polarity in a large ensemble simulation a large ensemble modeling experiment with the melbourne university general circulation model is presented thirty 17 year long independent simulations were performed all integrations were forced by the same observed sea surface temperatures obtained from the atmospheric model intercomparison project ii the simulations were analyzed to assess the sensitivity of the north atlantic oscillation nao to the el nino southern oscillation enso polarity the results show signals of the enso phases both in the mean strength of the nao as well as in its internal variability during the cold enso phase the probability density function of the nao index presents a small but positive mean value whereas it is negative during the warm enso phase also the nao variability associated with each enso phase shows a different behavior during the warm phase the probability density function of the nao index presents a larger variance and suggests a bimodality whereas no bimodality is suggested in the cold phase

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

deformation within an exposed salt wall recumbent folding and extrusion of evaporites in the dead sea basin abstract despite the enormous global interest in salt tectonics which is largely driven by its importance to hydrocarbon exploration direct field based studies of salt exposed at the earth s surface are rare however mount sedom located at the western side of the dead sea basin presents one such opportunity for detailed analysis of salt and the associated sedimentary and structural record of its movement the sedom salt wall is a 10 km 1 5 km n s trending ridge comprising a range of late miocene pliocene evaporites and clastics which have penetrated the overlying pleistocene clastic sequence the salt wall displays a moderate steep west dipping western margin and an overturned west dipping eastern flank the sedimentary record of passive wall growth includes sedimentary breccia horizons that locally truncate underlying beds and are interpreted to reflect sediments having been shed off the crest of the growing salt wall structurally the overturned eastern flank is marked by upturn within the overburden extending for 300 m from the salt wall deformation within the evaporites is characterised by ductile folding and boudinage while a 200 m thick clastic unit within the salt wall forms a tight recumbent fold traceable for 5 km along strike and associated with a 500 m wide inverted limb this overturned gently dipping limb is marked by ne directed folding and thrusting sedimentary injections and a remarkable attenuation of the underlying salt from 380 m to

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

a nonlinear expression of the north atlantic oscillation in the north pacific 1 the north atlantic oscillation nao has been identified as an important mode of variability in the climate system our knowledge of its impacts is based largely on linear analysis techniques as a result nonlinearities associated with it are largely unknown in this study we use recently proposed nonlinear compositing and one sided regression techniques as well as a new rectified regression technique to show that the nonlinear expression of the nao is fundamentally different from its linear expression in particular we show that its nonlinear expression is amplitude but not sign dependent and has a center of action in the north pacific sector that is associated with the east asia jet stream eajs and the aleutian low

holocene climate variability as derived from alkenone sea surface temperature and coupled ocean atmosphere model experiments holocene climate modes are identified by the statistical analysis of reconstructed sea surface temperatures ssts from the tropical and north atlantic regions the leading mode of holocene sst variability in the tropical region indicates a rapid warming from the early to mid holocene followed by a relatively weak warming during the late holocene the dominant mode of the north atlantic region sst captures the transition from relatively warm cold conditions in the eastern north atlantic and the western mediterranean sea the northern red sea to relatively cold warm conditions in these regions from the early to late holocene this pattern of holocene sst variability resembles the signature of the arctic oscillation north atlantic oscillation ao nao the second mode of both tropical and north atlantic regions captures a warming towards the mid holocene and a subsequent cooling the dominant modes of holocene sst variability emphasize enhanced variability around 2300 and 1000 years the leading mode of the coupled tropical north atlantic holocene sst variability shows that an increase of tropical sst is accompanied by a decrease of sst in the eastern north atlantic an analogy with the instrumental period as well as the analysis of a long term integration of a coupled ocean atmosphere general circulation model suggest that the ao nao is one dominant mode of climate variability at millennial time scales

stochastic forcing of sediment routing and storage in channel networks the stochastic field of sediment supply to the channel network of a drainage basin depends on the large scale interactions among climatically driven processes such as forest fire and rainstorms topography channel network topology and basin scale during infrequent periods of intense erosion large volumes of colluvium are concentrated in parts of a channel network particularly near tributary junctions the rivers carry bed material and wash load downstream from these storage sites at different rates the bed material travels slowly creating transient patterns of sediment transport sediment storage and channel morphology along the channel network as the concentrations of bed material migrate along the network their waveforms can undergo changes by diffusion interference at tributary junctions and loss of mass through temporary sediment storage in fans and terraces and through particle abrasion which converts bed material to wash load we investigated how these processes might influence the sediment mass balance in channels of third and higher order in a 215 km 2 drainage basin within the oregon coast range over a simulated 3000 year period with a climate typical of the late holocene we used field measurements and a simulation model to illustrate interactions between the major controls on large scale processes functioning over long periods of time in complex drainage basins

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

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