anatomy of north pacific decadal variability abstract a systematic analysis of north pacific decadal variability in a full physics coupled ocean atmosphere model is executed the model is an updated and improved version of the coupled model studied by latif and barnett evidence is sought for determining the details of the mechanism responsible for the enhanced variance of some variables at 20 30 yr timescales the possible mechanisms include a midlatitude gyre ocean atmosphere feedback loop stochastic forcing remote forcing or sampling error decadal variability in the model is expressed most prominently in anomalies of upper ocean streamfunction sea surface temperature sst and latent surface heat flux in the kuroshio oyashio extension koe region off japan the decadal signal off japan is initiated by changes in strength and position of the aleutian low the atmospheric perturbations excite sst anomalies in the central and eastern north pacific with opposing signs and canonical structure the atmospheric perturbations also change the ekm

origin of decadal el nino southern oscillation like variability in a coupled general circulation model 1 the origin of decadal el nino southern oscillation like variability hereinafter referred to as dev is analyzed in coupled general circulation model cgcm simulations the cgcm experiments test the null hypothesis for the existence of dev that is that dev is linear damped and stochastically forced by atmospheric internal dynamics in order to test this hypothesis we employ the interactive ensemble coupling strategy it is found that the spatially averaged variance of sea surface temperature anomaly ssta and heat content anomaly hca associated with the dev is linearly related to the amplitude of atmospheric internal dynamics this result suggests that the dev is primarily noise forced but that damped coupled feedbacks and or internal ocean dynamics enhance this variability the ssta variability associated with the dev appears to be of a basin type standing mode with a triangular shape however the decadal evolution of the hca associated with the dev shows a systematic westward propagation from the central north pacific and the eastern south pacific both a singular vector analysis and noise variance analysis based on the coupled simulation results support the argument that atmospheric noise in the subtropics leads to the excitation of the dev

a nonlinear theory for el nino bursting abstract a new mechanism is proposed that explains two key features of the observed el nino southern oscillation enso phenomenon its irregularity and decadal amplitude changes using a low order enso model the authors show that the nonlinearities in the tropical heat budget can lead to bursting behavior characterized by decadal occurrences of strong el nino events la nina events are not affected a feature that is also seen in enso observations one key result of this analysis is that decadal variability in the tropics can be generated without invoking extratropical processes or stochastic forcing the el nino bursting behavior simulated by the low order enso model can be understood in terms of the concept of homoclinic and heteroclinic connections it is shown that this new model for enso amplitude modulations and irregularity although difficult to prove might explain some features of enso dynamics seen in more complex climate models and the observations

regional trends in evaporation loss and water yield based on stable isotope mass balance of lakes the ontario precambrian shield surveys abstract stable isotopes of water oxygen 18 and deuterium were measured in water samples collected from a network of 300 lakes sampled in six 100 km 2 blocks centred at 49 72 n 91 46 w 48 49 n 91 58 w 50 25 n 86 62 w 49 78 n 83 98 w 48 24 n 85 49 w 47 73 84 52 w within precambrian shield drainages in the vicinity of lake superior northern ontario canada additional sampling was also conducted within the turkey lakes watershed 47 03 n 84 38 w a research basin situated in the algoma region located 50 km north of sault saint marie ontario the studies were undertaken to gain a better understanding of hydrology and geochemistry of watersheds in the region in order to better predict acid sensitivity of lakes the main objective of this paper is to describe the hydrologic variations observed based on stable isotope results evaporative isotopic enrichment of lake water was found to be systematic across the region and its deviation from the isotopic composition of precipitation was used to estimate the evaporation inflow to the lakes as well as runoff or water yield based on a simple isotope mass balance model the analysis illustrates significant variability in the water yield to lakes and reveals a pattern of positively skewed distributions in all six widely spaced blocks suggesting that a high proportion of lakes have relatively limited runoff whereas relatively few have greater runoff such basic information on the drainage structure of an area can be valuable for site specific hydrologic assessments but also has significant implications for critical loads assessment as low runoff systems tend to be less buffered and therefore are more sensitive to acidification importantly the turkey lakes sampling program also suggests that isotope based water yield is comparable in magnitude to hydrometric gauging estimates and also establishes that uncertainty related to stratification can be as high as 20 or more for individual lakes although it likely has only a minor influence on regional survey results while further analysis in gauged lake watersheds would be beneficial to constraining the accuracy of the method or calibrating it for operational use it is nevertheless a powerful tool in its present form for lake to lake and regional runoff inter comparisons

source of low frequency modulation of enso amplitude in a cgcm we study the relationship between changes in equatorial stratification and low frequency el nino southern oscillation enso amplitude modulation in a coupled general circulation model cgcm that uses an anomaly coupling strategy to prevent climate drifts in the mean state the stratification is intensified at upper levels in the western and central equatorial pacific during periods of high enso amplitude furthermore changes in equatorial stratification are connected with subsurface temperature anomalies originating from the central south tropical pacific the correlation analysis of ocean temperature anomalies against an index for the enso modulation supports the hypothesis of the existence of an oceanic tunnel that connects the south tropical pacific to the equatorial wave guide further analysis of the wind stress projection coefficient onto the oceanic baroclinic modes suggests that the low frequency modulation of enso amplitude is associated with a significant contribution of higher order modes in the western and central equatorial pacific in the light of these results we suggest that in the cgcm change in the baroclinic mode energy distribution associated with low frequency enso amplitude modulation have its source in the central south tropical pacific

tropical oceanic response to extratropical thermal forcing in a coupled climate model a comparison between the atlantic and pacific oceans abstractthe tropical oceanic response to the extratropical thermal forcing is quantitatively estimated in a coupled climate model this work focuses on comparison of the responses between the tropical atlantic and pacific under the same extratropical forcing the tropical sea surface temperature responses are comparable however the responses in the tropical subsurface in the two oceans are distinct the tropical subsurface response in the atlantic can be twice of that in the pacific the maximum subsurface temperature change in the tropical pacific occurs in the eastern lower thermocline while that in the tropical atlantic occurs in the west and well below the lower thermocline the different responses in the tropical atlantic and pacific are closely related to the different changes in the meridional overturning circulations the pacific shallow overturning circulation or the subtropical cell tends to slow down speed up in response to the extratropical warming cooling forcing the changes in the

pacific thermocline bridge revisited abstract the coupling on decadal time scales of the mid latitude and tropical pacific via an oceanic bridge in the thermocline is investigated using ocean general circulation model hindcasts and a coupled ocean atmosphere model results indicate that in the tropics decadal anomalies of isopycnal depth are forced by ekman pumping and are largely independent of the arrival of subducted anomalies in the thermocline that originate in the mid latitudes of either hemisphere in the coupled model temperature anomalies on isopycnals show little coupling from the tropics to the northern hemisphere but are lag correlated between southern hemisphere mid and low latitudes however anomaly magnitudes on the equator are small these results suggest that the oceanic bridge to the northern hemisphere explains only a small part of the observed decadal variance in the equatorial pacific coupling to the southern mid latitudes via temperature anomalies on isopycnals remains an intriguing possibility

interdecadal sea surface temperature variability in the equatorial pacific ocean part ii the role of equatorial off equatorial wind stresses in a hybrid coupled model abstract many modeling studies have been carried out to investigate the role of oceanic rossby waves linking the off equatorial and equatorial pacific ocean although the equatorial ocean response to off equatorial wind stress forcing alone tends to be relatively small it is clear that off equatorial oceanic rossby waves affect equatorial pacific ocean variability on interannual through to interdecadal time scales in the present study a hybrid coupled model hcm of the equatorial pacific between 12 5 s and 12 5 n was developed and is used to estimate the magnitude of equatorial region variability arising from off equatorial poleward of 12 5 latitude wind stress forcing the hcm utilizes a reduced gravity ocean shallow water model and a statistical atmosphere derived from monthly output from a 100 yr australian bureau of meteorology research centre now the centre for australian weather and climate research coupled general circulation model integration the equatorial region wind stress forcing i

a decadal spiciness mode in the tropics analysis of a complex climate model suggests the existence of a mode of coupled ocean atmosphere variability in the tropical pacific with the following dynamics anomalous strong pacific trade winds accelerate the north equatorial current and countercurrent at 10 to 15 n in the central pacific thermocline this causes anomalous advection across mean gradients of temperature and salinity on isopycnal surfaces and generates cool fresh spiciness anomalies of the order of 0 3 k these are advected by the mean circulation via the western boundary region to the equatorial pacific in approximately five years at the equatorial outcrops of the isopycnals the cool fresh anomalies affect the surface heat budget and are hypothesized to initiate a relaxation of the trade winds that is reinforced by positive feedbacks with the slope of the thermocline and with air sea fluxes of heat and freshwater at 5 to 10 s the decrease of the trades generates by anomalous advection cool fresh spiciness anomalies that migrate to the equator in one to two years and provide a positive feedback at 10 to 15 n the decrease of the trades decelerates north equatorial current and countercurrent and causes warm salty anomalies on isopycnals that arrive at the equator five years later and close the cycle

observational evidence for propagation of decadal spiciness anomalies in the north pacific 1 the propagation of density compensated warm salty or cool fresh spiciness anomalies in the north pacific thermocline is investigated using argo profiles for the period 2001 2008 a cool fresh spiciness anomaly on 25 25 5 kg m 3 isopycnals appears in the eastern subtropical north pacific at 120 w 150 w in 2003 2004 with a salinity anomaly of about 0 15 pss 78 this spiciness anomaly migrates southwestward and arrives in the western tropical north pacific at 145 e 175 w in 2008 with the salinity anomaly decreasing to about 0 043 pss 78 two warm salty anomalies are observed to propagate along the same path from 2003 to 2005 and after 2005 the propagation path and speed of the anomalies are in good agreement with advection by the mean geostrophic current in the course of propagation the anomalies are diffused and are subject to high frequency injection of spiciness anomalies especially in the eastern subtropical north pacific

enso prediction one year in advance using western north pacific sea surface temperatures 1 we present evidence that the de trended boreal winter sea surface temperature anomalies ssta in the western north pacific wnp are a skillful predictor for the development of the el nino southern oscillation enso by the following winter the wnp shares some similarities with the meridional mode mm located in the subtropical central and eastern north pacific both are linked to off equatorial ssta and low level wind anomalies and both appear to be strongly related to wintertime variability in the north pacific oscillation npo however in contrast with the mm the wnp is associated with an opposite signed ssta dipole located off southeastern asia and in the western tropical pacific which is accompanied by equatorial winds that may influence the level of oceanic kelvin wave activity that precedes enso events

freshening of subsurface waters in the northwest pacific subtropical gyre observations and dynamics subsurface salinity anomalies propagating between mid and low latitudes along isopycnal surfaces have been shown to play an important role in modulating ocean and climate variability in this study a sustained freshening and southwestward propagation of subsurface salinity anomalies in the northwest pacific subtropical gyre and its dynamical mechanism are investigated using observations numerical outputs and a predictive model analyses of the observations show a pronounced subsurface freshening with salinity decreasing about 0 25 psu near the 24 5 sigma surface in the northwest pacific subtropical gyre during 2003 11 this freshening is found to be related to the surface forcing of salinity anomalies in the outcrop zone 25 degrees 35 degrees n 130 degrees 160 degrees e a predictive model based on the assumption of salinity conservation along the outcrop isopycnals is derived and used to examine this surface forcing mechanism the resemblance between the spatial structures of the subsurface salinity derived from the predictive model and from observations and numerical outputs suggests that subsurface salinity anomalies are ventilated over the outcrop zone a salinity anomaly with an amplitude of about 0 25 psu generated by the surface forcing is subducted in the outcrop zone and then propagates southwestward accompanied by potential vorticity anomalies to the east of luzon strait similar to 15 degrees n in roughly one year when the anomalies reach 15 degrees n they turn and move gradually eastward toward the central pacific associated with an eastward countercurrent on the southern subtropical gyre

influence of extratropical thermal and wind forcings on equatorial thermocline in an ocean gcm the equatorial thermocline variability in the pacific in response to the extratropical thermal and wind forcings is investigated with an ocean general circulation model modular ocean model version 3 mom3 sensitivity experiments show that the extratropical wind forcing and thermal forcing contribute equally to the equatorial variability the wind induced response is attributed to the off equatorial wind within 30 8 of the equator the thermal induced response can be traced to higher latitudes the thermal forcing affects the equator mainly through the equatorward transport of the perturbation temperature by mean subduction flow the wind forcing affects the equator by changing the strength of meridional overturning circulations it is also found that the southern hemisphere contributes more to the equatorial variability than the northern hemisphere under both external forcings

decadal changes in the relationship between the tropical pacific and the north pacific 1 it has been recognized that the tropical pacific sea surface temperature sst anomaly associated with the el nino southern oscillation enso is closely tied to large scale atmospheric anomalies in the extra tropical region based on observational data this connection appears to have changed significantly since 1999 this study examines the characteristics of this connection during two sub periods 1980 1998 and 1999 2010 using cyclostationary empirical orthogonal function cseof analysis we found that the atmospheric anomalies induced by the enso alter the sst over the north pacific through surface heat flux change during the earlier period of 1980 1998 during the later period in contrast enso related atmospheric anomalies feature the north pacific oscillation npo pattern during winter which is characterized by a southward shift of the atmospheric center of action from its climatological position the npo related atmospheric anomalies extend to the subtropical pacific this extension potentially links midlatitude and tropical pacific variability through air sea interactions the physical change appears to alter the el nino characteristics into that of the central pacific el nino through the wind sst coupling mechanism this process may be related to the recent change in which the central pacific el nino occurs more frequently than the conventional eastern pacific el nino detailed descriptions of the physical changes between the tropical pacific and the north pacific are presented in this study along with the possible implications of this change

conceptualization and scale in hydrology abstract it is argued that the levels of scale at which a meaningful conceptualization of physical processes is possible are not arbitrary and their range is not continuous formulations appropriate at a given level usually are not applicable at the immediately adjoining levels this is seen as one of the important reasons for the slow progress of hydrological science on basin scale since it is dominated by different effects than those observed at the immediately lower level of channel reaches and hillslopes which represent the focus of current hydrological research the search for an appropriate level of conceptualization can proceed either upward or downward along the hierarchy of scales both possibilities are discussed and an example of the downward route is given

search for periodicity in global events in the geologic record quo vadimus periodicity hypotheses for various global events over the past approx 250 m y are reevaluated following rigorous inspection of the radiometric data base utilized therein the author suggest that these periodicities of approx 26 to approx 33 m y result from subjective use of radiometric data in the literature further search for periodicity in global events especially those involving mathematical analysis of data from the geologic time scale should be postponed until an adequate data base of high quality radiometric ages for phanerozoic time becomes available

mechanisms of tropical pacific interannual to decadal variability in the arpege orca global coupled model spatial and temporal structures of interannual to decadal variability in the tropical pacific ocean are investigated using results from a global atmosphere ocean coupled general circulation model the model produces quite realistic mean state characteristics despite a sea surface temperature cold bias and a thermocline that is shallower than observations in the western pacific the periodicity and spatial patterns of the modelled el nino southern oscillations enso compare well with those observed over the last 100 years although the quasi biennial timescale is dominant lag regression analysis between the mean zonal wind stress and the 20 c isotherm depth suggests that the recently proposed recharge oscillator paradigm is operating in the model decadal thermocline variability is characterized by enhanced variance over the western tropical south pacific 7 s the associated subsurface temperature variability is primarily due to adiabatic displacements of the thermocline as a whole arising from ekman pumping anomalies located in the central pacific south of the equator related wind anomalies appear to be caused by sst anomalies in the eastern equatorial pacific this quasi decadal variability has a timescale between 8 years and 20 years the relationship between this decadal tropical mode and the low frequency modulation of enso variance is also discussed results question the commonly accepted hypothesis that the low frequency modulation of enso is due to decadal changes of the mean state characteristics

semi distributed lumped model of a karst system under active management summary in this paper inverse modeling is used to characterize the regime of a karst aquifer subjected to extensive pumping in a conduit located upstream of its main outlet the systemic approach uses a transfer model that is based on computing the convolution integral of up to several signals e g efficient rainfall pumping to simulate flow rates and groundwater levels in both the karst conduit and the carbonate matrix at the aquifer outlet and in several parts of the catchment area the model is a semi distributed lumped model which simulates the hydrological response of a heterogeneous karst aquifer made up of different hydrologic compartments and is applied to the lez karst system france groundwater is abstracted near the system s major outlet at a higher rate than the low water spring discharge thereby mobilizing stored groundwater during low water periods active management the model s results are very satisfactory especially for the karst system outlet where the water levels are particularly well reproduced the model can also simulate the natural i e non pumping state of the karst system and thereby estimate the impact of active management on the water resource

full flow regime storage streamflow correlation patterns provide insights into hydrologic functioning over the continental us interannual changes in low median and high regimes of streamflow have important implications for flood control irrigation and ecologic and human health the gravity recovery and climate experiment grace satellites record global terrestrial water storage anomalies twsa providing an opportunity to observe interpret and potentially utilize the complex relationships between storage and full flow regime streamflow here we show that utilizable storage streamflow correlations exist throughout vastly different climates in the continental us conus across low to high flow regimes a panoramic framework the storage streamflow correlation spectrum sscs is proposed to examine macroscopic gradients in these relationships sscs helps form corroborate or reject hypotheses about basin hydrologic behaviors sscs patterns vary greatly over conus with climate land surface and geologic conditions data mining analysis suggests that for catchments with hydrologic settings that favor storage over runoff e g a large fraction of precipitation as snow thick and highly permeable permeable soil sscs values tend to be high based on our results we form the hypotheses that groundwater flow dominates streamflows in southeastern conus and great plains while thin soils in a belt along the appalachian plateau impose alimit on water storage sscs also suggests shallow water table caused by high bulk density soil and flat terrain induces rapid runoff in several regions our results highlight the importance of subsurface properties and groundwater flow in capturing flood and drought we propose that sscs can be used as a fundamental hydrologic signature to constrain models and to provide insights thatlead usto better understand hydrologic functioning

impact of the south and north pacific meridional modes on the el nino southern oscillation observational analysis and comparison abstractan interannual variability mode in the southeast pacific with a physical interpretation similar to that of the pacific meridional mode pmm in the north pacific was recently identified both modes have been shown to influence the subsequent development of el nino southern oscillation enso events this study investigates the relationship between enso and the two pmms using observational and reanalysis data the results show that the south pacific meridional mode spmm mainly favors the development of sea surface temperature anomalies sstas in the eastern equatorial pacific whereas the north pacific meridional mode npmm mainly favors the development of sstas in the central equatorial pacific both of the meridional modes are considered to be analogous in terms of their physical interpretation and can be important predictors of enso when considering different flavors of enso neither the npmm nor the spmm can be precluded as accurate indicators when forecasting particular flavors of enso

characteristics of winter precipitation variation over northern central eurasia and their connections to sea surface temperatures over the atlantic and pacific oceans abstract this study reveals spatial and temporal characteristics of precipitation variability and their teleconnections to sea surface temperatures ssts over the atlantic and pacific oceans by analyzing 68 yr of recent precipitation records over the former soviet union in addition to a general increasing trend of about 0 4 mm yr 1 or 6 decade 1 over much of the study region three major modes of precipitation variation are identified a quasi biennial variation of 2 3 yr is found over the region surrounding the caspian and aral seas an el nino timescale precipitation variation of 4 5 yr is present over southern central siberia and is associated with eastern tropical pacific ssts a quasi decadal timescale variation of about 11 12 yr is evident over central european russia this quasi decadal precipitation variation is closely linked to a major sst anomaly pattern of alternating latitudinal belts over the atlantic and sst variations over the equatorial pacific ocean these associations to ssts are str

multi year predictability in a coupled general circulation model multi year to decadal variability in a 100 year integration of a bmrc coupled atmosphere ocean general circulation model cgcm is examined the fractional contribution made by the decadal component generally increases with depth and latitude away from surface waters in the equatorial indo pacific ocean the relative importance of decadal variability is enhanced in off equatorial wings in the subtropical eastern pacific the model and observations exhibit enso like decadal patterns analytic results are derived which show that the patterns can in theory occur in the absence of any predictability beyond enso time scales in practice however modification to this stochastic view is needed to account for robust differences between enso like decadal patterns and their interannual counterparts an analysis of variability in the cgcm a wind forced shallow water model and a simple mixed layer model together with existing and new theoretical results are used to improve upon this stochastic paradigm and to provide a new theory for the origin of decadal enso like patterns like the interdecadal pacific oscillation and pacific decadal oscillation in this theory enso driven wind stress variability forces internal equatorially trapped kelvin waves that propagate towards the eastern boundary kelvin waves can excite reflected internal westward propagating equatorially trapped rossby waves rws and coastally trapped waves ctws ctws have no impact on the off equatorial sub surface ocean outside the coastal wave guide whereas the rws do if the frequency of the incident wave is too high then only ctws are excited at lower frequencies both ctws and rws can be excited the lower the frequency the greater the fraction of energy transmitted to rws this lowers the characteristic frequency reddens the spectrum of variability off the equator relative to its equatorial counterpart at low frequencies dissipation acts as an additional low pass filter that becomes more effective as latitude increases at the same time enso driven off equatorial surface heating anomalies drive mixed layer temperature responses in both hemispheres both the eastern boundary interactions and the accumulation of surface heat fluxes by the surface mixed layer act to low pass filter the enso forcing the resulting off equatorial variability is therefore more coherent with low pass filtered decadal enso indices e g nino3 sea surface temperature sst than with unfiltered enso indices consequently large correlations between variability and nino3 extend further poleward on decadal time scales than they do on interannual time scales this explains why decadal enso like patterns have a broader meridional structure than their interannual counterparts this difference in appearance can occur even if enso indices do not have any predictability beyond interannual time scales the wings around 15 20 s and sub surface variability at many other locations are predictable on interannual and multi year time scales this includes westward propagating internal rws within about 25 of the equator the slowest of these take up to 4 years to reach the western boundary this sub surface predictability has significant oceanographic interest however it is linked to only low levels of sst variability consequently extrapolation of delayed action oscillator theory to decadal time scales might not be justified

connections between the pacific ocean tropics and midlatitudes on decadal timescales abstract connections between the tropical and midlatitude pacific on decadal timescales are examined using a 137 yr run of a fully coupled ocean atmosphere general circulation model it is shown that the model does a credible job of simulating both enso scale and decadal scale variability and that there are statistically significant correlations between the midlatitudes and tropics on decadal timescales three physical mechanisms linking the regions are examined 1 oceanic advection along isopycnal surfaces from the midlatitude subduction regions to the tropics 2 coastally trapped or kelvin wave propagation between the tropics and midlatitudes and 3 near simultaneous communication between the regions affected by changes in the atmosphere it is found that communication via the atmosphere explains the strongest correlations found in the model further evidence is presented that is consistent with the idea that midlatitude sea surface temperature anomalies drive changes in the trade wind system that a

topographic and climatic influence on seasonal snow cover implications for the hydrology of ungauged himalayan basins india abstract himalayan glaciers exert considerable influence on basin hydrology and its response to climate change melt runoff generated from ungauged himalayan basins uhb requires an understanding of snow and ice cover extent along with prevailing meteorological conditions therefore an estimation of seasonal snow cover distribution topographic elevation aspect and slope and climatic variability was carried out using satellite data and meteorological observations from three automatic weather stations awss located at different elevations in an uhb chorabari glacier results suggest that the topography and the meteorological conditions of the basin influence the dynamics of snow cover and the corresponding processes responsible for the melt runoff generation the snow cover area sca has high variability in the elevation range of 3799 5000 m indicating that as glacier ablation begins sca below this elevation primarily contributes to the melt runoff likewise the eastern aspect and the slopes 0 10 and 70 80 show higher variability further the annual distribution of air temperature gradients dt dz or temperature lapse rates tlrs exhibits a bimodal pattern the mean annual tlr for the basin is 6 0 c km 1 which is lower than the traditionally used adiabatic or environmental lapse rate 6 5 c km 1 we also established the role of tlrs in the dynamics of sca which is an important parameter used for the computation of melt runoff the 0 c isotherm established indicates that the elevation zone above 5000 5500 m has persistent snow cover throughout the year and snow cover below this zone contributes to the melt runoff during the ablation season therefore validating the equilibrium line altitude ela of chorabari glacier lies within this zone since the tlr and sca vary with space and time our study in an ungauged glacierized basin of river ganga could be useful for policymakers as well as other researchers working on the regional hydrology

on the joint role of subtropical atmospheric variability and equatorial subsurface heat content anomalies in initiating the onset of enso events abstract previous research has shown that seasonal mean variations in both the subtropical extratropical sea level pressures over the central north pacific and the subsurface heat content anomalies in the western equatorial pacific are significantly related to the state of the el nino southern oscillation enso 12 18 months later here we find that positive negative subsurface temperature anomalies in the western equatorial pacific during boreal summer fall followed by negative positive anomalies in the sea level pressure fields over the subtropical central north pacific during boreal winter tend to result in positive negative mature enso events 12 15 months later i e during the following boreal winter when the intervening sea level pressure anomalies are of the same sign as the preceding heat content anomalies the correlation between the heat content anomalies and the following boreal winter enso state disappears there is still some relation between the boreal winter sea level pressure an

power law extreme flood frequency conventional flood frequency analysis ffa has been criticized both for its questionable theoretical basis and for its failure in extreme event prediction an important research issue for ffa is the exploration of models that have theoretical explanatory value as the first step towards more accurate predictive attempts self similar approaches offer one such alternative with a plausible theoretical basis in complexity theory that has demonstrable wide applicability across the geophysical sciences this paper explores a simple self similar approach to the prediction of extreme floods fifty river gauging records from the usa exhibiting an outlier event were studied fitting a simple power law pl relation to events with return period of 10 years or greater resulted in more accurate discharge and return period estimates for outlier events relative to the log pearson iii model similar success in predicting record events is reported for 12 long term rainfall records from the uk this empirical success is interpreted as evidence that self similarity may well represent the underlying physical processes generating hydrological variables these findings have important consequences for the prediction of extreme flood events the pl model produces return period estimates that are far more conservative than conventional distributions

nonlinear interdecadal changes of the el nino southern oscillation nonlinear interdecadal changes in the el nino southern oscillation enso phenomenon are investigated using several tools a nonlinear canonical correlation analysis nlcca method based on neural networks a hybrid coupled model and the delayed oscillator theory the leading nlcca mode between the tropical pacific wind stress ws and sea surface temperature sst reveals notable interdecadal changes of enso behaviour before and after the mid 1970s climate regime shift with greater nonlinearity found during 1981 99 than during 1961 75 spatial asymmetry for both sst and ws anomalies between warm el nino and cool la nina events was significantly enhanced in the later period during 1981 99 the location of the equatorial easterly anomalies was unchanged from the earlier period but in the opposite enso phase the westerly anomalies were shifted eastward by up to 25 according to the delayed oscillator theory such an eastward shift would lengthen the duration of the warm events by up to 45 but leave the duration of the cool events unchanged supporting evidence was found from a hybrid coupled model built with the lamont dynamical ocean model coupled to a statistical atmospheric model consisting of either the leading nlcca or cca mode

a fiji multi coral δ18o composite approach to obtaining a more accurate reconstruction of the last two centuries of the ocean climate variability in the south pacific convergence zone region the limited availability of oceanographic data in the tropical pacific ocean prior to the satellite era makes coral based climate reconstructions a key tool for extending the instrumental record back in time thereby providing a much needed test for climate models and projections we have generated a unique regional network consisting of five porites coral 18o time series from different locations in the fijian archipelago our results indicate that using a minimum of three porites coral 18o records from fiji is statistically sufficient to obtain a reliable signal for climate reconstruction and that application of an approach used in tree ring studies is a suitable tool to determine this number the coral 18o composite indicates that while sea surface temperature sst variability is the primary driver of seasonal 18o variability in these fiji corals annual average coral 18o is more closely correlated to sea surface salinity sss as previously reported our results highlight the importance of water mass advection in controlling fiji coral 18o and salinity variability at interannual and decadal time scales despite being located in the heavy rainfall region of the south pacific convergence zone spcz the fiji 18o composite presents a secular freshening and warming trend since the 1850s coupled with changes in both interannual ia and decadal interdecadal d i variance the changes in ia and d i variance suggest a re organization of climatic variability in the spcz region beginning in the late 1800s to period of a more dominant interannual variability which could correspond to a southeast expansion of the spcz

observational evidence of winter spice injection abstract temperature and salinity t s profiles from the global array of argo floats support the existence of spice formation regions in the subtropics of each ocean basin where large destabilizing vertical salinity gradients coincide with weak stratification in winter in these characteristic regions convective boundary layer mixing generates a strongly density compensated sdc layer at the base of the well mixed layer the degree of density compensation of the t s gradients of an upper ocean water column is quantified using a bulk vertical turner angle tub between the surface and upper pycnocline the winter generation of the sdc layer in spice formation zones is clearly seen in argo data as a large amplitude seasonal cycle of tub in regions of the subtropical oceans characterized by high mean tub in formation regions argo floats provide ample evidence of large abrupt spice injection t s increase on subducted isopycnals due to vertical mixing associated with the winter increase in tub a simp

major episodes of geologic change correlations time structure and possible causes abstract published data sets of major geologic events of the past 250myr extinction events sea level lows continental flood basalt eruptions mountain building events abrupt changes in sea floor spreading ocean anoxic and blackshale events and the largest evaporite deposits have been synthesized with estimated errors these events show evidence for a statistically significant periodic component with an underlying periodicity formally equal to 26 6 myr and a recent maximum close to the present time the cycle may not be strictly periodic but a periodicity of 30myr is robust to probable errors in dating of the geologic events the intervals of geologic change seem to involve jumps in sea floor spreading associated with episodic continental rifting volcanism enhanced orogeny global sea level changes and fluctuations in climate the period may represent a purely internal earth pulsation but evidence of planetesimal impacts at several extinction boundaries and a possible underlying cycle of 28 36 myr in crater ages suggests that highly energetic impacts may be affecting global tectonics a cyclic increase in the flux of planetesimals might result from the passage of the solar system through the central plane of the milky way galaxy an event with a periodicity and mean phasing similar to that detected in the geologic changes

tropical pacific sea surface temperatures and preceding sea level pressure anomalies in the subtropical north pacific 1 the correspondence of sea surface temperature sst anomalies to changes in antecedent large scale sea level pressure anomalies is investigated using reanalysis data by statistically examining linearly coupled precursor sea level pressure fields and subsequent sst fields for different lag periods it is possible to isolate a precursor mode of sea level pressure slp variability in the central subtropical north pacific that precedes variations in the january march el nino southern oscillation enso by approximately 12 15 months a sea level pressure index which captures the important characteristics of this precursor mode of variability is developed and evaluated it is shown that both analyzed and observed versions of the index are significantly correlated with the january march enso one year later the slp index is then used to examine the evolution of the surface circulation and temperature structures leading up to mature enso events initially the january march subtropical north pacific slp anomalies are associated with changes in the intensity of the subtropical trade wind regime over the north pacific as well as with sst anomalies over the eastern equatorial pacific and subtropical central pacific in agreement with the correlation statistics associated with the slp and lagged nino3 4 indices both the sea level pressure field and the sst field subsequently develop enso like structures over the course of the following year significant discussion of these results and pertinent areas of future research are provided within the broader context of the enso system

scaling and physiographic controls on streamflow behaviour on the precambrian shield south central ontario summary relationships explaining streamflow behaviour in terms of drainage basin physiography greatly assist efforts to extrapolate streamflow metrics from gauged to ungauged basins in the same landscape the dorset environmental science centre desc has monitored streamflow from 22 small basins 3 4 190 5 ha on the precambrian shield in south central ontario in some cases since 1976 the basins exhibit regional coherence in their interannual response to precipitation however there is often a poor correlation between streamflow metrics from basins separated by as little as 1 km this study assesses whether inter basin variations in such metrics can be explained in terms of basin scale and physiography several characteristics annual maximum minimum and average flow exhibited simple scaling with basin area while magnitude range and timing of annual maximum daily runoff showed scaling behaviour consistent with the representative elementary area rea concept this rea behaviour is partly attributed to convergence of fractional coverage of the two dominant and hydrologically contrasting land cover types in the desc region with increasing basin size three principal components pcs explained 82 4 of the variation among basin physiographic properties and several runoff metrics magnitude and timing of annual minimum daily runoff mean number of days per year with 0 streamflow exhibited significant relationships with one or more pc significant relationships were obtained between basin quickflow qf production and the pcs on a seasonal and annual basis almost all of which were superior to simple area based relationships basin physiography influenced qf generation via its control on slope runoff water storage and hydrologic connectivity however this role was minimized during spring when qf production in response to large rain on snow events was relatively uniform across the desc basins the pc based relationships and inter seasonal changes in their form were consistent with previous research conducted at point slope and basin scales in the desc region and perceptions of key hydrological processes in these small basins may not have been as readily obtained from scaling studies using streamflow from larger basins this process understanding provides insights into scaling behaviour beyond those derived from simple scaling and rea analyses the physiography of the study area is representative of large portions of the precambrian shield such that basin streamflow behaviour could potentially be extended across much of south central ontario this would assist predictions of streamflow conditions at ungauged locations development and testing of hydrological models for this landscape and interpretation of inter basin and intra annual differences in hydrochemical behaviour on the southern precambrian shield

flood basalts and large igneous provinces from deep mantle plumes fact fiction and fallacy abstract flood basalts large igneous provinces and all intraplate magmatism are almost unanimously ascribed to features called mantle plumes in current geodynamics literature in the starting plume model flood basalts and any associated hotspot tracks have been ascribed to the melting of a large plume head and a narrow tail respectively and the deccan flood basalt province of india and the laccadives maldives chagos reunion island volcanic chain in the indian ocean are widely thought to be an excellent example supporting this model however the existing geodynamic thermal petrological geochemical and geochronological constraints on deccan volcanism do not require or support a mantle plume origin a new interpretation made here rules out any role for the reunion plume in deccan volcanism and even questions the notion that the reunion hotspot is the manifestation of an underlying reunion plume the laccadives reunion hotspot track is viewed here as caused by a southward propagating fracture based on the published radiometric age data and the ultimate cause of deccan volcanism is argued to be mega scale lithospheric rifting the appreciation of the great original areal extent of the deccan nearly as far as the southern tip of peninsular india solves the hitherto unsolved problem of the cause of the uplift of the 1500 km long western ghats escarpment this cause being combined surface erosion and magmatic underplating hypothesized mantle plumes do not appear responsible for most large igneous provinces instead their very existence is questionable no geological evidence of any kind geochemical petrological thermal topographic requires mantle plumes the self contradictions and special pleading that proliferate in plume explanations are unjustified and unnecessary if one accepts based on various grounds that a globe encircling enriched mantle layer the perisphere may overlie a deeper depleted mantle which is the source of morb the systematic geochemical variations along the laccadive reunion chain can be explained by this model and are not consistent with a plume tail experiencing entrainment from surrounding morb mantle as in the current plume model hotspot tracks may not reflect plate motion above stationary deep mantle upwellings but the stress state of the lithosphere as originally proposed decades ago the locations of large igneous provinces hotspots and hotspot tracks are strongly controlled by lithospheric architecture and history they are not placed randomly on the globe indifferent to the surface geology neither are large igneous provinces sudden chance events within the vastness of geological time which plume theories typically allege

using glacier area ratio to quantify effects of melt water on runoff summary twenty four headwater catchments with varying glacier area ratios gars in the eastern and central tian shan mountains were simulated by the glacier enhanced soil and water assessment tool swat model from 1961 to 2007 the mean catchment gar ranges between 0 7 and 44 8 with a mean of 8 6 through synthetic analysis of the glacio hydrological processes simulation results of the catchments it was found that the gar is an effective index that can be used to interpret quantitatively the varying influences of glaciers on runoff across catchments among the twenty four catchments the ratio of glacier melt contribution rgmc to runoff varies between 3 5 and 67 5 with a mean of 24 0 the ratio of ice melt contribution rimc between 1 4 and 35 8 with a mean of 10 5 the ratio of ice melt in glacier melt between 33 4 and 59 1 with a mean of 43 4 the runoff coefficient rc between 0 24 and 0 90 with a mean of 0 52 and the coefficient of variation cv of runoff between 0 10 and 0 29 with a mean of 0 18 based on synthetic analysis it was found that 1 power functions fit the relations between rgmc rimc rc and cv and gar with high certainty 2 the cv decreases with increasing gar while others increase and 3 these power functions change sensitively with gar when gar is less than 10 implicating that a small change in gar may cause remarkable changes in rgmc rimc rc and cv in the less glacierized catchments

late winter generation of spiciness on subducted isopycnals the origins of density compensating anomalies of temperature and salinity spice are investigated using a model forced with the most realistic surface products available over the 40 years 1958 97 in this hindcast the largest interannual spiciness anomalies are found in the pacific ocean near the isopycnal s 0 5 25 5 where deviations as great as 1 28c and 0 6 psu are generated equatorward of winter outcropping in the eastern subtropics in both hemispheres these source regions are characterized by very unstable salinity gradients and low mean density stratification in winter two related signatures of winter mixing in the southeast pacific sep are density that is well mixed deeper than either temperature or salinity and subsurface density ratios that approach 1 all ocean basins in the model are shown to have regions with these characteristics and signatures however the resultant spiciness signals are focused on different isopycnals ranging from s 0 5 25 0 in the northeast pacific to s 0 5 26 5 in the south indian ocean a detailed examination of the sep finds that large positive anomalies are generated by diapycnal mixing across subducted isopycnals e g s 0 5 25 5 whereas negative anomalies are the result of a steady isopycnal advection moderated by vertical advection and heave there is considerable interannual variability in the strength of anomalies and in the density on which they occur historical observations are consistent with the model results but are insufficient to verify all aspects of the hindcast including the processes of anomaly generation in the sep it was not possible to relate isopycnal anomaly genesis to local surface forcing of any kind a complex scenario involving basinwide circulation of both the ocean and atmosphere especially of surface water through the subtropical evaporation zones is put forward to explain the decadal time scale evident in sep salinity anomalies on s 0 5 25 5 pacific anomalies generated on s 0 5 25 5 can be traced along mean geostrophic streamlines to the western boundary where decadal salinity variations at 78s are about 2 times as large order 60 1 psu as at 128n although there may be more variance on shallower isopycnals in the north at least portions of the s 0 5 25 5 signals appear to continue along the boundary to a convergence at the equator suggesting that the most robust sources of pacific spiciness variance coincide with equatorial exchange pathways

wind driven interdecadal variability in the eastern tropical and south pacific 1 simulated interface elevation anomalies with a reduced gravity model forced by observed wind stress are used to investigate the origin of thermocline depth fluctuations in the eastern tropical and south pacific at interdecadal timescales it is found that interdecadal thermocline depth fluctuations in the eastern equatorial pacific and along the western coast of the americas are fundamentally driven by zonal wind fluctuations in the western equatorial pacific thus positive negative interface elevation anomalies which correspond to shallower deeper thermocline depths in the eastern tropical pacific and along the west coast of central and south america are related to easterly westerly anomalies in the western sector of the equatorial pacific however off equatorial wind fluctuations maintain and reinforce the interdecadal variability observed along the eastern equatorial pacific and along the west coast of south america in the latter region equatorial off equatorial wind forcing is relatively more important equatorward poleward of 30 s in the eastern equatorial pacific interface elevation anomalies are negatively correlated with sea surface temperature sst at interdecadal timescales according to our results the sst interdecadal anomalies are in part 50 60 driven by wind fluctuations likely through the modulation of vertical advection of cold waters which depends primarily on the thermocline depth forced remotely or locally by winds this relationship was especially strong during the 1970s and 1980s a period characterized by the larger zonal wind stress interdecadal fluctuations observed in the western equatorial pacific

the south pacific meridional mode a mechanism for enso like variability in this study the authors investigate the connection between the south pacific atmospheric variability and the tropical pacific climate in models of different degrees of coupling between the atmosphere and ocean a robust mode of variability defined as the south pacific meridional mode spmm is identified in a multimodel ensemble of climate model experiments where the atmosphere is only thermodynamically coupled to a slab ocean mixed layer the physical interpretation of the spmm is nearly identical to the north pacific meridionalmode npmm withtheoff equatorialsoutheasttradewindvariabilityalteringthelatentheatflux and sea surface temperature sst and initiating a wind evaporation sst feedback that propagates signals into the tropics the authors also show that a positive cloud feedback plays a role in the development of this mode butthiseffectismodeldependent whilephysicallyanalogoustothenpmm thespmmhasastronger expression in the equatorial pacific and directly perturbs the zonal gradients of sst and sea level pressure slp on the equator thus leading to enso like variability despite the lack of ocean atmosphere dynamical coupling further analysis suggests that the spmm is also active in fully coupled climate models and observations this study highlights the important role of the southern hemisphere in tropical climate variability and suggests that including observations from the data poor south pacific could improve the enso predictability

megadroughts in the indian monsoon region and southwest north america and a mechanism for associated multidecadal pacific sea surface temperature anomalies abstract a 1360 yr control run from a global coupled climate model the parallel climate model is analyzed it simulates megadroughts in the southwestern united states and indian monsoon regions the megadroughts represent extreme events of naturally occurring multidecadal precipitation variations linked to the dominant pattern of multidecadal sst variability in the indian and pacific oceans gaining insight into the occurrence of megadroughts thus requires an understanding of the mechanism that is producing this multidecadal sst variability analysis of the model variability shows that the mechanism involves atmosphere ocean and tropical midlatitude interactions with a crucial element being wind forced ocean rossby waves near 20 n and 25 s in the pacific whose transit times set the decadal time scale at the western boundary the rossby waves reflect into the equatorial pacific to affect thermocline depth the resulting feedbacks involving surface temperature winds and the strength of the subtropi