dynamical excitation of the tropical pacific ocean and enso variability by little ice age cooling tropical pacific ocean dynamics during the medieval climate anomaly mca and the little ice age lia are poorly characterized due to a lack of evidence from the eastern equatorial pacific we reconstructed sea surface temperature el nino southern oscillation enso activity and the tropical pacific zonal gradient for the past millennium from galapagos ocean sediments we document a mid millennium shift mms in ocean atmosphere circulation around 1500 1650 ce from a state with dampened enso and strong zonal gradient to one with amplified enso and weak gradient the mms coincided with the deepest lia cooling and was probably caused by a southward shift of the intertropical convergence zone the peak of the mca 900 1150 ce was a warm period in the eastern pacific contradicting the paradigm of a persistent la nina pattern

magnetotelluric observations in the western ouachita mountains southeastern oklahoma the first magnetotelluric mt analysis of the ouachita mountains region is presented magnetotelluric data acquired at 19 sites along a 60 km profile in southeastern oklahoma were used to image the western extension of the ouachita mountains and to determine the poorly known subsurface interaction between the pennsylvanian tishomingo belton uplift and the subsurface extension of the exposed western ouachita mountains drill hole data geologic mapping seismic reflection profiles and 1 d and 2 d mt derived models indicate that lying beneath the low resistivity gulf coastal plain sediments are 2 3 km of deep water lower pennsylvanian jackfork group sediments and 6 8 km of ouachita facies lithologies mainly consisting of the stanley group beneath the profile s northern section are 2 4 km of atoka formation sediments probably deposited within the arkoma basin that underlie thrusted zones of the stanley group the most unique feature is a high resistivity zone beneath stations 7 9 interpreted to be p

simulation and inversion of borehole temperature profiles in surrogate climates spatial distribution and surface coupling a heat conduction forward model driven by ground surface temperature from three 1000 year climate simulations with the state of the art echo g model has been used to simulate underground temperature perturbation profiles an inversion approach has been applied to reconstruct ground surface temperature histories from the simulated profiles and to compare them with the climate model temperatures results support the skill of borehole inversion methods to retrieve long term temperature trends and the robustness of using the present day borehole network for reconstructing sat variations

the evolution of el nino past and future abstract we review forecasts of the future of el nino and the southern oscillation enso a coupled instability of the ocean atmosphere system in the tropical pacific with global impacts enso in the modern world is briefly described and the physics of the enso cycle is discussed particular attention is given to the bjerknes feedback the instability mechanism which figures prominently in enso past and future our knowledge of enso in the paleoclimate record has expanded rapidly within the last 5 yr the enso cycle is present in all relevant records going back 130 kyr it was systematically weaker during the early and middle holocene and model studies indicate that this results from reduced amplification in the late summer and early fall a consequence of the altered mean climate in response to boreal summer perihelion data from corals shows substantial decadal and longer variations in the strength of the enso cycle within the past 1000 yr it is suggested that this may be due to solar and volcanic variations in solar insolation amplified by the bjerknes feedback there is some evidence that this feedback has operated in the 20th century and some model results indicate that it will hold sway in the greenhouse future but it is very far from conclusive the comprehensive general circulation models used for future climate projections leave us with an indeterminate picture of enso s future some predict more enso activity some less with the highly uncertain consensus forecast indicating little change

dynamics of the bingham canyon mine landslides from seismic signal analysis joint interpretation of long and short period seismic signals generated by landslides sheds light on the dynamics of slope failure providing constraints on landslide initiation and termination and on the main phases of acceleration and deceleration we carry out a combined analysis of the seismic signals generated by two massive landslides that struck the bingham canyon mine pit on 10 april 2013 inversion of the long period waveforms yields time series for the bulk landslide forces and momenta from which we deduce runout trajectories consistent with the deposit morphology comparing these time series with the short period seismic data we are able to infer when and where major changes take place in landslide momentum along the runout path this combined analysis points to a progressive fracturing of the masses during acceleration indicates that deceleration starts the moment they reach the pit floor and suggests that the bulk movement is stopped by a topographic barrier

twentieth century tropical sea surface temperature trends revisited 1 this study compares the global distribution of 20th century sst and marine air temperature trends from a wide variety of data sets including un interpolated archives as well as globally complete reconstructions apart from the eastern equatorial pacific all datasets show consistency in their statistically significant trends with warming everywhere except the far northwestern atlantic the largest warming trends are found in the middle latitudes of both hemispheres two of the sst reconstructions exhibit statistically significant cooling trends over the eastern equatorial pacific in disagreement with the un interpolated sst and marine air temperature datasets which show statistically significant warming in this region twentieth century trends in tropical marine cloudiness precipitation and slp from independent data sets provide physically consistent evidence for a reduction in the strength of the atmospheric walker circulation accompanied by an eastward shift of deep convection from the western to the central equatorial pacific

tropical river flow and rainfall reconstructions from coral luminescence great barrier reef australia 1 rainfall and river flow in northeast queensland australia are highly seasonal and show high interannual and decadal variability that is modulated by el nino southern oscillation enso events and the pacific decadal oscillation pdo reconstructions of october september freshwater input to the great barrier reef lagoon and october september queensland rainfall are developed from visual assessment of the occurrence and intensity of luminescent lines in massive porites from up to 25 coral cores from 15 nearshore reefs regularly influenced by river flood plumes separate reconstructions are developed for four rivers herbert burdekin pioneer and fitzroy and these are used to reconstruct total annual freshwater flow into the great barrier reef 69 74 variance calibrated and an index of queensland rainfall 53 57 variance calibrated the reconstructions extend back to 1631 but are most reliable from 1661 and capture significant decadal variability the reconstructions provide insights into long term tropical rainfall and river flow variability and the behavior of enso and the pdo over several centuries significant though weak relationships are found between these reconstructions and an independent reconstruction of enso the reconstructions highlight that observations from the instrumental records of high interannual and decadal rainfall and river flow variability in northeast australia also characterize the past few centuries although there appears to be no overall trend toward wetter or drier conditions the reconstructions suggest that the variability of rainfall and river flow has increased during the twentieth century with more very wet and very dry extremes than in earlier centuries as projected for the region as a consequence of global warming

asymmetry in the duration of el nino and la nina abstract el nino and la nina are not a simple mirror image but exhibit significant differences in their spatial structure and seasonal evolution in particular sea surface temperature sst anomalies over the equatorial pacific cold tongue are larger in magnitude during el nino compared to la nina resulting in positive skewness of interannual sst variations the associated atmospheric deep convection anomalies are displaced eastward during el nino compared to la nina because of the nonlinear atmospheric response to sst in addition to these well known features an analysis of observational data for the past century shows that there is a robust asymmetry in the duration of el nino and la nina most el ninos and la ninas develop in late boreal spring summer when the climatological cold tongue is intensifying and they peak near the end of the calendar year after the mature phase el ninos tend to decay rapidly by next summer but many la ninas persist through the following year and often reintensify in

the impact of convection on enso from a delayed oscillator to a series of events abstract the ncar community climate system model version 3 ccsm3 exhibits persistent errors in its simulation of the el nino southern oscillation enso mode of coupled variability the amplitude of the oscillation is too strong the dominant 2 yr period too regular and the width of the sea surface temperature response in the pacific too narrow with positive anomalies extending too far into the western pacific two changes in the parameterization of deep convection result in a significant improvement to many aspects of the enso simulation the inclusion of convective momentum transport cmt and a dilution approximation for the calculation of convective available potential energy cape are used in development integrations and a striking improvement in enso characteristics is seen an increase in the periodicity of enso is achieved by a reduction in the strength of the existing short circuited delayed oscillator mode the off equatorial response is weaker and less tropically confined largely as a

estimating rates of debris flow entrainment from ground vibrations debris flows generate seismic waves as they travel downslope and can become more dangerous as they entrain sediment along their path we present field observations that show a systematic relation between the magnitude of seismic waves and the amount of erodible sediment beneath the flow specifically we observe that a debris flow traveling along a channel filled initially with sediment 0 34 m thick generates about 2 orders of magnitude less spectral power than a similar sized flow over the same channel without sediment fill we adapt a model from fluvial seismology to explain this observation and then invert it to estimate the level of bed sediment and rate of entrainment beneath a passing series of surges our estimates compare favorably with previous direct measurements of entrainment rates at the site suggesting the approach may be a new indirect way to obtain rare field constraints needed to test models of debris flow entrainment

deep soil temperature as proxy for surface air temperature in a coupled model simulation of the last thousand years 1 the relationship between terrestrial deep soil temperature tdst and surface temperature sat at interannual and centennial timescales has been investigated in a simulation of the last millennium with a three dimensional climate model driven by estimations of historical external forcing tdst is loosely related to borehole temperature profiles which have been recently used to reconstruct long term temperature trends in the last centuries recently questions about the validity of boreholes based reconstructions have been raised in the simulation at interannual time scales the connection between tdst and sat is stable being stronger in the summer half year than in the winter half year at long timescales annual tdsl is a good proxy for annual sat and their variations are almost indistinguishable from each other both tdsl and terrestrial sat overestimate the variations of global mean sat this may be a source for the disagreement between statistical reconstructions of global sat and terrestrial borehole measurements

el nino southern oscillation enso and decadal scale climate variability at 10 n in the eastern pacific from 1893 to 1994 a coral based reconstruction from clipperton atoll we have developed a 101 year 1893 1994 subseasonal oxygen 18o and carbon 13c isotopic time series from clipperton atoll in the eastern pacific using the coral porites lobata in agreement with linsley et al 1999 we find that seasonal and interannual coral 18o variability at clipperton results from variability in both water temperature and salinity three new coral time series demonstrate the reproducibility of a secular coral 18o trend of 0 35 since 1910 but show varying 13c trends strong decadal scale variability in the 18o record appears related to the pacific decadal oscillation pdo through postulated changes in the strengths of the equatorial counter current and north equatorial current interannual variability in this coral 18o record is directly related to the el nino southern oscillation enso and isolation of this frequency band indicates reduced enso variability in the eastern equatorial pacific in the period 1925 to 1940 in agreement with instrumental and other pacific coral records

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

unprecedented recent warming of surface temperatures in the eastern tropical pacific ocean climate variability in the tropical pacific ocean influences climate across much of the planet a diatom based record of sea surface temperatures from el junco lake galapagos reveals that the most recent half century is the warmest 50 year period in the past 1 200 years through its intimate connection with the el nino southern oscillation system climate variability in the tropical pacific ocean influences climate across much of the planet but the history of temperature change in the tropical pacific ocean during recent millennia is poorly known the available annually resolved records1 2 are discontinuous and rarely span more than a few centuries longer records at coarser temporal resolution suggest that significant oceanographic changes observed at multi year to multi century resolution have had important effects on global climate3 4 5 here we use a diatom record from el junco lake galapagos to produce a calibrated continuous record of sea surface temperature in the eastern tropical pacific ocean at subdecadal resolution spanning the past 1 200 years our reconstruction reveals that the most recent 50 years are the warmest 50 year period within the record because our diatom based sea surface temperature index resembles northern hemisphere temperature reconstructions we suggest that with continued anthropogenic warming the eastern tropical pacific ocean may continue to warm

detection of landslides and submarine slumps using broadband seismic networks 1 we detected 52 seismic events associated with landslides and submarine slumps on 8 august 2009 when typhoon morakot hit taiwan these events were neither felt nor reported because their seismic energy was primarily in the long period band 20 50 s most of these events were located in mountain areas where the accumulated rainfall was extremely high though some were found offshore southern taiwan among all events the fatal landslide earthquake was located at hsiaolin village where 474 people were buried inversion modelling of the seismic waveforms generated by the hsiaolin landslide shows that the seismic source was represented by single force consistent with downhill sliding some offshore seismic events indicate that submarine slumps probably occurred along submarine canyons and steep slopes our study shows that broadband seismic monitoring can be used to issue early warnings for mitigating disasters generated by inland and offshore landslides

hydrologic changes in colorado during the mid holocene and younger dryas abstract the stratigraphy of upper big creek lake ubc an overflowing lake in northern colorado indicates that the lake responded to a series of hydroclimatic changes over the past 13 000 years modern sediments in eight comparator lakes from across wyoming and colorado facilitate the stratigraphic interpretation by showing that littoral sediments have exponentially higher sand content lower loss on ignition loi and lower net accumulation rates than off shore sediments sand layers in two near shore cores from ubc share the characteristics of the modern littoral sediments 80 sand 1 9 m below its outlet from 12 500 to 11 300 and from 7500 to 2100 cal yr bp ground penetrating radar gpr profiles consistent with the low water episodes show correlative sand layers and submerged wave cut scarps around the lake margin the stratigraphic features correlate with those formed in the comparator lakes during extensive droughts at 11 300 6900 6000 and 4800 3400 cal yr bp as well as a series of north south anti phased droughts between 5800 and 1200 cal yr bp lake closure at ubc amplified the local changes and demonstrates that climate changes can increase the extent of intermittent streamflow in the rocky mountains relative to today

assessing millennial scale variability during the holocene a perspective from the western tropical pacific we investigate the relationship between tropical pacific and southern ocean variability during the holocene using the stable oxygen isotope and magnesium calcium records of cooccurring planktonic and benthic foraminifera from a marine sediment core collected in the western equatorial pacific the planktonic record exhibits millennial scale sea surface temperature sst oscillations over the holocene of 0 5 c while the benthic 18oc document 0 10 millennial scale changes of upper circumpolar deep water ucdw a water mass which outcrops in the southern ocean solar forcing as an explanation for millennial scale sst variability requires 1 a large climate sensitivity and 2 a long 400 year delayed response suggesting that if solar forcing is the cause of the variability it would need to be considerably amplified by processes within the climate system at least at the core location we also explore the possibility that sst variability arose from volcanic forcing using a simple red noise model our best estimates of volcanic forcing falls short of reproducing the amplitude of observed sst variations although it produces power at low frequency similar to that observed in the md81 record although we cannot totally discount the volcanic and solar forcing hypotheses we are left to consider that the most plausible source for holocene millennial scale variability lies within the climate system itself in particular ucdw variability coincided with deep north atlantic changes indicating a role for the deep ocean in holocene millennial scale variability

mechanisms of enso forcing of hemispherically symmetric precipitation variability summary the patterns of precipitation anomalies forced by the el nino southern oscillation during northern hemisphere winter and spring are remarkably hemispherically symmetric and in the mid latitudes have a prominent zonally symmetric component observations of global precipitation variability and the moisture budget within atmospheric reanalyses are examined to argue that the zonally symmetric component is caused by interactions between transient eddies and tropically forced changes in the subtropical jets during el nino events the jets strengthen in each hemisphere and shift equatorward changes in the subtropical jet influence the transient eddy momentum fluxes and the eddy driven mean meridional circulation during el nino events eddy driven ascent in the mid latitudes of each hemisphere is accompanied by low level convergence and brings increased precipitation this changes in the transient eddy and stationary eddy moisture fluxes almost exactly cancel each other and in sum do not contribute to the zonal mean precipitation anomalies propagation of anomalous stationary waves disrupts the zonal symmetry flow around the deeper aleutian low and the eastward extension of the pacific jet stream supply the moisture for increased precipitation over the eastern north pacific and the western seaboard of the united states while transient eddy moisture convergence supplies the moisture for increased precipitation over the southern united states in each case increased precipitation is fundamentally caused by anomalous ascent forced by anomalous heat and vorticity fluxes

role of tropical pacific ssts in global medieval hydroclimate a modeling study 1 the role of tropical pacific ssts in driving global medieval hydroclimate is assessed using fossil coral records from palmyra atoll tropical pacific sea surface temperature sst boundary conditions are derived for the period 1320 1462 a d these boundary conditions consist of la nina like mean state conditions in the tropical pacific with inter annual and decadal variability about that altered state the reconstructed ssts in the tropical pacific are used to force a 16 member ensemble of atmospheric general circulation model agcm simulations coupled to a one layer ocean model outside of the tropical pacific the agcm simulations of medieval climate are compared with modern climate simulations for the period 1856 2005 a d and are shown to reproduce many aspects of medieval hydroclimate found in paleo proxy records for much of the western hemisphere northern eurasia and the northern tropics these results suggest that many features of global medieval hydroclimate changes can be explained by changes in tropical pacific ssts though the potential role for other oceans is also discussed

a pacific centennial oscillation predicted by coupled gcms internal climate variability at the centennial time scale is investigated using long control integrations from three state of the art global coupled general circulation models in the absence of external forcing all three models produce centennial variability in the mean zonal sea surface temperature sst and sea level pressure slp gradients in the equatorial pacific with counterparts in the extratropics the centennial pattern in the tropical pacific is dissimilar to that of the interannual el nino southern oscillation enso in that the most prominent expression in temperature is found beneath the surface of the western pacific warm pool some global repercussions nevertheless are analogous such as a hemispherically symmetric atmospheric wave pattern of alternating highs and lows centennial variability in western equatorial pacific sst is a result of the strong asymmetry of interannual ocean heat content anomalies while the eastern equatorial pacific exhibits a lagged bjerknes like response to temperature and convection in the west the extratropical counterpart is shown to be a flux driven response to the hemispherically symmetric circulation anomalies emanating from the tropical pacific significant centennial length trends in the zonal sst and slp gradients rivaling those estimated from observations and model simulations forced with increasing co 2 appear to be inherent features of the internal climate dynamics simulated by all three models unforced variability and trends on the centennial time scale therefore need to be addressed in estimated uncertainties beyond more traditional signal to noise estimates that do not account for natural variability on the centennial time scale

el nino southern oscillation extrema in the holocene and last glacial maximum 1 the el nino southern oscillation enso is the largest engine of interannual climate variability on the planet yet its past behavior and potential for future change are poorly understood and vigorously contested reconstructions of past enso are indispensable for testing climate models tasked with predicting future enso activity in a warming world but suitable geologic archives are scarce especially for the last glacial period here we reconstruct mean climate and enso variability in the holocene and last glacial maximum lgm from oxygen isotopic ratios 18o of individual foraminifera retrieved from deep sea sediments our results document coordinated adjustments of the tropical pacific enso system between two diametrically opposite states an amplified enso state in the lgm associated with a reduced zonal temperature gradient and a damped enso state in the mid holocene with enhanced gradient orbital precession provided the switch between these states and acted as the dominant external driver of the tropical pacific enso system in the past 25 000 years the linked response of the mean state and variability to orbital forcing provides an integrated framework for testing enso theory and models

analyzing high frequency seismic signals generated during a landslide using source discrepancies between two landslides abstract high frequency seismic signals are generated during landslides and can be analyzed to obtain detailed information regarding landslide dynamics however a better understanding of the physical process that produces such high frequency signals is required the two massive landslides that occurred on april 11 2013 in the bingham canyon mine pit utah usa generated low and high frequency seismic signals using the low frequency signals we inverted the force time functions of the two events and estimated their dynamics we used the signals generated by the two events and filtered in three frequency bands to obtain the source discrepancies between the two events by analyzing these source discrepancies we found that the low and medium frequency signals were generated due to the bulk movement of sliding material furthermore the medium frequency signals contained information regarding small particle impacts along the sliding path the high frequency 1 3 hz signals are controlled by small scale process of sliding materials and are sum of stochastic phenomena this clarification of the source of the high frequency signals is expected to improve the analyses of seismic signals generated during landslides

tracking the extent of the south pacific convergence zone since the early 1600s 1 the south pacific convergence zone spcz is the largest and most persistent spur of the intertropical convergence zone at the southeastern edge of the spcz near 170 w and 15 20 s a surface ocean salinity frontal zone exists that separates fresher western pacific warm pool water from saltier and cooler waters in the east this salinity front is known to shift east and west with the phase of the el nino southern oscillation we have generated subannually resolved and replicated coral oxygen isotopic time series from fiji 17 s 179 e and rarotonga 21 5 s 160 w that have recorded interannual displacements of the salinity front over the last 380 years and also indicate that at lower frequencies the decadal mean position of the salinity front and eastern extent of the spcz has shifted east west through 10 to 20 of longitude three times during this interval the most recent and largest shift began in the mid 1800s as the salinity front progressively moved eastward and salinity decreased at both sites our results suggest that sea surface salinity at these sites is now at the lowest levels recorded and is evidence for an unprecedented expansion of the spcz since the mid 1800s the expansion of the spcz implies a gradual change in the south pacific to more la nina like long term mean conditions this observation is consistent with the ocean thermostat mechanism for the pacific coupled ocean atmosphere system whereby exogenous heating of the atmosphere would result in greater warming in the western pacific and a greater east west surface temperature gradient components 8034 words 7 figures 2 tables

megadroughts in southwestern north america in echo g millennial simulations and their comparison to proxy drought reconstructions abstractsimulated hydroclimate variability in millennium length forced transient and control simulations from the echam and the global hamburg ocean primitive equation echo g coupled atmosphere ocean general circulation model aogcm is analyzed and compared to 1000 years of reconstructed palmer drought severity index pdsi variability from the north american drought atlas nada the ability of the model to simulate megadroughts in the north american southwest is evaluated nasw 25 42 5 n 125 105 w megadroughts in the echo g aogcm are found to be similar in duration and magnitude to those estimated from the nada the droughts in the forced simulation are not however temporally synchronous with those in the paleoclimate record nor are there significant differences between the drought features simulated in the forced and control runs these results indicate that model simulated megadroughts can result from internal variability of the modeled climate system rather than as a response to changes

coral oxygen isotope records of interdecadal climate variations in the south pacific convergence zone region 1 the south pacific convergence zone spcz a region of high rainfall is a major feature of subtropical southern hemisphere climate and contributes to and interacts with circulation features across the pacific yet its past temporal variability and forcing remain only partially understood here we compare coral oxygen isotopic 18o series spanning a d 1997 1780 and a d 2001 1776 from two genera of hermatypic corals in fiji located within the spcz to examine the fidelity of these corals in recording climate change and spcz interdecadal dynamics one of these coral records is a new 225 year subannually resolved 18o series from the massive coral diploastreaheliopora diploastrea s use in climate reconstructions is still relatively new but this coral has shown encouragingly similar interannual variability to porites the coral genus most commonly used in pacific paleoclimate studies in fiji we observe that interdecadal 18o variance is also similar in these two coral genera and diploastrea contains a larger amplitude interdecadal signal that more closely tracks instrumental based indices of pacific interdecadal climate change and the spcz than porites both coral 18o series record greater interdecadal variability from 1880 to 1950 which is consistent with the observations of folland et al 2002 who reported higher variability in spcz position before 1945 these observations indicate that diploastrea will likely provide a significant new source of long term climate information from the spcz region

reduced enso variability at the lgm revealed by an isotope enabled earth system model studying the el nino southern oscillation enso in the past can help us better understand its dynamics and improve its future projections however both paleoclimate reconstructions and model simulations of enso strength at the last glacial maximum lgm 21 ka bp have led to contradicting results here we perform model simulations using the recently developed water isotope enabled community earth system model icesm for the first time model simulated oxygen isotopes are directly compared with those from enso reconstructions using the individual foraminifera analysis ifa we find that the lgm enso is most likely weaker comparing with the preindustrial the icesm suggests that total variance of the ifa records may only reflect changes in the annual cycle instead of enso variability as previously assumed furthermore the interpretation of subsurface ifa records can be substantially complicated by the habitat depth of thermocline dwelling foraminifera and their vertical migration with a temporally varying thermocline

numerical modeling of landquakes the thurwieser landslide that occurred in italy in 2004 and the seismic waves it generated have been simulated and compared to the seismic signal recorded a few tens of kilometers from the landslide source i e landquake the main features of the low frequency seismic signal are reproduced by the simulation topography effects on the flowing mass have a major impact on the generated seismic signal whereas they weakly affect low frequency wave propagation simulation of the seismic signal makes it possible to discriminate between possible alternative scenarios for flow dynamics and to provide first estimates of the rheological parameters during the flow as landquakes are continuously recorded by seismic networks our results provide a new way to collect data on the dynamics and rheology of natural flows

mechanisms of hemispherically symmetric climate variability inspired by paleoclimate evidence that much past climate change has been symmetric about the equator the causes of hemispherically symmetric variability in the recent observational record are examined using the national centers for environmental prediction national center for atmospheric research reanalysis dataset and numerical models it was found that the dominant cause of hemispherically symmetric variability is the el nino southern oscillation during an el nino event the tropics warm at all longitudes and the subtropical jets in both hemi spheres strengthen on their equatorward flanks poleward of the tropical warming there are latitude belts of marked cooling extending from the surface to the tropopause in both hemispheres at all longitudes and in all seasons the midlatitude cooling is caused by changes in the eddy driven mean meridional circulation changes in the transient eddy momentum fluxes during an el nino event force upper tropospheric ascent in midlatitudes through a balance between the eddy fluxes and the coriolis torque the eddy driven ascent causes anomalous adiabatic cooling which is primarily balanced by anomalous diabatic heating using a quasigeostrophic spherical model forced by an imposed surface eddy disturbance of chosen wave number and frequency it is shown that the anomalous eddy momentum fluxes are caused by the impact that the changes in the tropically forced subtropical jets have on the propagation in the latitude height plane of transient eddies changes in zonal winds and associated changes in the meridional gradient of potential vorticity create an anomalous region of low meridional wavenumber in the midlatitudes that refracts waves away both poleward and equatorward tropical forcing of variability in the eddy driven mean meridional circulation is another way in addition to rossby wave teleconnections whereby the tropics can influence extratropical climate unlike teleconnections this mechanism causes climate variability that has strong zonally and hemispherically symmetric components and operates throughout the seasonal cycle

el nino events and their relation to the southern oscillation 1925 1986 relationships among sea surface temperatures ssts at the coast of peru and offshore river discharge in northern peru and sea level pressure at darwin australia during the period 1925 1986 are investigated using time series plots frequency distributions and a simple statistical analysis it is shown that ssts undergo a larger seasonal cycle offshore than at the coast exhibit more interannual variability during the warm than the cool season are positively skewed during much of the year and exhibit greatest month to month persistence during the cool season many but not all episodes of above normal coastal ssts are accompanied by enhanced river discharge in northern peru comparison of the darwin pressure and coastal sst records during the past 60 years shows that el nino events episodes of above normal ssts along the coast of peru have occurred both in advance of and subsequent to major negative swings of the southern oscillation and associated climatic changes in the central equatorial pacific in addition el nino events and negative swings of the southern oscillation have occurred separately hence el nino and the southern oscillation are more loosely coupled than other studies would imply