intraseasonal variability over tropical africa during northern summer abstract the intraseasonal variability over africa during northern summer was analyzed using 25 years of ncep ncar reanalysis and satellite data the dominant pattern of variability was one of enhanced deep convection over the whole african monsoon region it appeared to arise at least partly as a remote response to the intraseasonal madden julian oscillation over the warm pool sector twenty days prior to the maximum in convection over africa there was no signal over africa but convection was reduced over the equatorial warm pool an equatorial kelvin wave response to this change in warm pool convection propagated eastward and an equatorial rossby wave response propagated westward and between them they completed a circuit of the equator and met up 20 days later over africa where the negative midtropospheric temperature anomalies in the kelvin and rossby waves favored deep convection over west africa the kelvin wave component contained lower tropospheric westerly anomalies that acted to increase t

impacts of convectively coupled kelvin waves on environmental conditions for atlantic tropical cyclogenesis abstracthigh amplitude convectively coupled equatorial atmospheric kelvin waves cckws are explored over the tropical atlantic during the boreal summer 1989 2009 focus is given to the atmospheric environmental conditions that are important for tropical cyclogenesis cckws are characterized by deep westerly vertical wind shear to the east of its convectively active phase and easterly vertical wind shear to the west of it this dynamical signature increases vertical wind shear over the western tropical atlantic ahead of the convectively active phase and reduces vertical wind shear after its passage the opposite is true over the eastern tropical atlantic where the climatological vertical wind shear is easterly positive total column water vapor tcwv anomalies progress eastward with the convectively active phase of the cckw whereas negative tcwv anomalies progress eastward with the convectively suppressed phase during the passage of the convectively active phase of the cckw a zonally oriented strip o

lobal interactions rheologic superposition and implications for a pleistocene ice stream on the continental shelf of british columbia abstract data on structures stone striae clast pavements fabrics morphology provenance and matrix grain size of four pre late wisconsinan diamictons are presented from the lower accessible part of an 855 m long sea cliff at cape ball east coast of graham island queen charlotte archipelago british columbia the data indicate that an ice stream crossed the continental shelf from the british columbian mainland to the queen charlotte islands local queen charlotte piedmont ice coalesced with the western edge of the cordilleran ice sheet resulting in northward flow deflection along the east coast of graham island generally consistent structural and stone data indicate that diamictons were deposited as primary subglacial tills and that subglacial dynamics and rheologic conditions were complex two of the tills can be traced continuously over the cape ball section which provides a north south transect oblique to ice flow each of the two tills reveals five major changes in rheology and genesis ranging from a strong lodgement component to dominantly deformation mainly by subglacial squeeze flow true end member tills are rare and in almost all places the tills are hybrids that formed within a continuum of till forming processes commonly involving stone rotation and superposition of structures and rheologic states this could have occurred mainly in response to fluctuating till pore water content along the transect two dimensional stretches of contrasting till types probably represent a three dimensional patchwork of contrasting till rheologies and pore waters if patches of ductily deforming till were common and or widespread they could have accounted for much of the movement of cordilleran ice over glaciomarine mud on the continental shelf when sea level was much lower than present deforming probably saturated muddy till reconstituted glaciomarine would have possessed negligible shear strength resulting in a thin rapidly moving glacier most likely an ice stream that reached cape ball but failed to remove the record of previous glacial events the ice stream probably issued out of the mainland s skeena valley which is aligned with cape ball and is approximately the size of valleys in antarctica that today conduct small outlet glaciers and ice streams evidence for this and other ice streams on the northwestern continental shelf of north america imply that destabilization and rapid decay of the western edge of the cordilleran ice sheet may have been accomplished by a combination of ice streams sea level rise and extensive calving

the geomorphology and sedimentology of eskers in north central ireland abstract eskers are common glacial landforms in ireland and form regionally extensive networks that reflect stages of ice retreat of this sector of the late devensian weichselian british irish ice sheet however the sedimentary structures and composition of these eskers are poorly known despite being able to offer valuable insight into subglacial hydrological processes during deglaciation this study presents detailed morphological and sedimentary evidence from six esker systems in north central ireland where adjacent and interacting ice domes were characterized by changes in ice bed thermal and hydrological properties as well as significant ice dome centre migration morphologically esker ridges in this area vary in length size and continuity with some esker systems ascending over hills thus crossing watersheds whereas other systems are confined to basin settings esker systems commonly appear to feed terminal outwash and glaciolacustrine deltas but several systems do not show a clear terminus the internal sediments within eskers vary from concentrically bedded sands and gravels formed within enclosed tunnels to interbedded sands gravels and diamictons occasionally with water induced soft sediment deformations that are likely formed in interlobate settings in contrast with some previous glacier models that assume that esker systems are isochronous and were formed in solely subglacial settings the esker systems described here are interpreted as being of different ages formed in variously subglacial to ice marginal settings and thus cannot be used as a single snapshot of the disposition of ice domes during stages of late devensian ice retreat

subglacial processes from drumlins in clew bay western ireland interpretation of subglacial processes and environments can be usefully informed by the stratigraphy and structures of sediments preserved within drumlins and the down ice variability of these sediments drumlins in clew bay western ireland were formed by westward late pleistocene ice flow onto the atlantic shelf but the depositional processes and environments of these sediments remain uncertain this study describes and interprets the drumlin stratigraphy and sediment properties and structures from two drumlins on the south side of clew bay drumlin sediments are dominated by massive to stratified diamicton deposited subglacially by deformation of flows of varying rheology folds shears and clastic dikes within the sediments suggest active subglacial water flow related to variations in ice flow and ice bed coupling the distal ends of the drumlins are dominated by stratified diamicton and gravel units with sandy interbeds these sediments reflect deposition in a leeside subglacial cavity formed coevally with bedform development a model is proposed that can account for sediment stratigraphic patterns and drumlin formation copyright 2015 john wiley sons ltd

seismic measurements reveal a saturated porous layer beneath an active antarctic ice stream seismic reflection studies recently conducted on ice stream b part of the marine ice sheet of west antarctica show a metres thick layer immediately beneath the ice in which both compressional p and shear s wave speeds are very low these low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure from this and from arguments presented in an accompanying paper1 to the effect that the layer would be too weak to support the shear stress exerted by the overlying ice we conclude that the layer is deforming and that the ice stream probably moves principally by such deformation

geomorphic evidence for active and inactive phases of late devensian ice in north central ireland abstract in the clogher valley north central ireland subglacial and proglacial landforms provide evidence for phases of active and inactive subglacial and ice marginal processes during the late devensian weichselian glaciation 22 13 kyr bp patterns of subglacial rogen moraines and drumlins record east to west ice flow along the valley axis during maximal ice stages eskers superimposed upon the rogen moraines and drumlins record later west to east ice flow and mark the first stages of ice retreat areas of large ice marginal non aligned ridges and mounds are separated by more extensive areas in which no deglacial landforms or sediments are present the non aligned ridges and mounds do not show a dominant directional signature have intricate basal outlines steep slopes and high relief

synoptic wave perturbations and convective systems over equatorial africa abstract spectral analysis of the outgoing longwave radiation olr time series over equatorial africa reveals large oscillations of the convection with periods of between 3 and 6 days in march and april when the intertropical convergence zone itcz migrates northward and crosses equatorial africa this periodic behavior is most pronounced with a marked peak at 5 6 days robust horizontal and vertical patterns consistent with a convectively coupled kelvin wave can be extracted by a simple composite technique based only on the phase of the convective oscillations over equatorial africa the composite reveals differences between continental and adjacent oceanic regions over the continent the stronger oscillation of the convection is associated with larger temperature and moisture anomalies near the surface suggesting an influence of diabatic processes on the amplitude of the perturbations some convective events over equatorial africa are triggered by waves propagating eastward over the equatorial a

rogen ribbed moraine identification and possible origin abstract it is emphasized that rogen moraine is a morphological term applied to a special kind of transverse moraine characteristically these ridges show transitions to drumlins it is inferred that this morphology is created in at least two steps including remoulding of pre existing landforms

the west african monsoon dynamics part ii the preonset and onset of the summer monsoon the arrival of the summer monsoon over west africa has been documented by using daily gridded rainfall data and ncep ncar reanalyses during the period 1968 90 and olr data over the period 1979 90 two steps have been characterized through a composite approach the preonset and the onset of the summer monsoon the preonset stage corresponds to the arrival in the intertropical front itf at 15 8n that is the confluence line between moist southwesterly monsoon winds and dry northeasterly harmattan bringing sufficient moisture for isolated convective systems to develop in the sudano sahelian zone while the intertropical convergence zone itcz is centered at 58n the mean date for the preonset occurrence is 14 may and its standard deviation is 9 5 days during the period 1968 90 this leads to a first clear increase of the positive rainfall slope corresponding to the beginning of the rainy season over this sudano sahelian area the onset stage of the summer monsoon over west africa is linked to an abrupt latitudinal shift of the itcz from a quasi stationary location at 58n in may june to another quasi stationary location at 108n in july august the mean date for the onset occurrence is 24 june and its standard deviation is 8 days during the period 1968 90 this leads to a second increase of the positive rainfall slope over the sudano sahelian zone signing the northernmost location of the itcz and the beginning of the monsoon season this abrupt shift occurs mostly between 108w and 58e where a meridional land sea contrast exists and it is characterized by a temporary rainfall and convection decrease over west africa preonset dates onset dates and summer rainfall amount over the sahel are uncorrelated during the period 1968 90 the atmospheric dynamics associated with the abrupt itcz shift has been investigated between the preonset and the onset stages the heat low dynamics associated with the itf controls the circulation in the low and midlevels its meridional circulation intensity is the highest at the beginning of the monsoon onset this can lead to 1 increased convective inhibition in the itcz through intrusion of dry and subsiding air from the north and 2 increased potential instability through a greater inland moisture advection and a higher monsoon depth induced by a stronger cyclonic circulation in the low levels through higher vertical wind shear due to westerly monsoon wind and midlevel african easterly jet aej increases through enhancement of the instability character of the aej and through increased shortwave radiation received at the surface during the monsoon onset once the rainfall minimum occurred due to the convective inhibition the accumulated potential instability breaks the convective inhibition the inertial instability of the monsoon circulation is released and the associated regionalscale circulation increases leading to the abrupt shift of the itcz then the itcz moves north up to 108n where thermodynamical conditions are favorable it is suggested by the authors that the abrupt shift of the itcz initiated by the amplification of the heat low dynamics could be due to an interaction with the northern orography of the atlas ahaggar mountains subsidence over and north of this orography due to both the northern branches of the heat low and of the northern hadleytype cell contributes to enhance the high geopotentials north of these mountains and the associated northeasterly winds this leads to the development of a leeward trough that reinforces the heat low dynamics maintaining an active convective itcz through enhanced moist air advection from the ocean increasing the northern hadley circulation which reinforces the high geopotentials and the interaction with the orography through a positive feedback the fact that an abrupt shift of the itcz is only observed on the western part of west africa may result from the enhancement of moisture advection which comes from the west and has a stronger impact west of the greenwich meridian the northwest southeast orientation of the atlas ahaggar crest can induce the interaction with the heat low first in the east where the mountains are nearer to the itf than in the west and second in the west another consequence of the possible orography induced interaction with the atmospheric circulation is that the induced leeward trough increasing the cyclonic vorticity in the heat low may stimulate moisture convergence in the oceanic itcz near the western coast of west africa

reconstructing the last irish ice sheet 2 a geomorphologically driven model of ice sheet growth retreat and dynamics the ice sheet that once covered ireland has a long history of investigation much prior work focussed on localised evidence based reconstructions and ice marginal dynamics and chronologies with le

glaciomarine deposition around the irish sea basin some problems and solutions reconstructing the depositional processes and setting marine or terrestrial depositional environment of late devensian age glacigenic sediments around the irish sea basin isb is critical for developing an all embracing and consistent glacial model that can account for all observed field evidence identifying episodes of marine and terrestrial glacial deposition from field data is considered the first step in achieving this goal criteria for distinguishing marine and terrestrial glacial environments in the isb include the geomorphology sedimentology and faunal content biofacies of the associated deposits exposures of glacigenic sediments around the isb are very diverse in terms of their morphosedimentary characteristics and associated biofacies and thus inferred depositional processes and setting possible reasons for the diverse geological record include the differing geometry of eastern and western isb coasts time transgressive ice retreat and differential land rebound effects as a result of forebulge collapse and neotectonics poor geochronometric control on ice sheet events has not helped the correlation of isb events with glacial and climatic events elsewhere future investigations of glacial sites around the isb should use an integrated methodological approach involving a range of geomorphological sedimentary and biofacies data and dating control where possible this will help in developing a more precise and holistic late devensian glacial model that is constrained rigorously by field geological evidence copyright 2001 john wiley sons ltd

effects of zonal flows on equatorially trapped waves abstract linear shallow water equations are employed to study the effects of basic zonal flows on equatorially trapped waves analytical solutions are obtained for constant basic zonal flows it is shown that changes in the wave structures due to the non doppler effect of the basic zonal flow are considerable for the rossby wave moderate for the westward propagating mixed rossby gravity wave but negligible for the other equatorial waves the rossby wave and the westward propagating mixed rossby gravity wave possess greater eigenfrequencies and are less trapped in westerlies than in easterlies the dependence of the rossby wave structure upon the basic zonal flow is interpreted in terms of potential vorticity conservation in basic zonal flows with meridional shears the eigenfrequencies are found to be larger in equatorial easterlies than in equatorial westerlies for the westward propagating waves but smaller for the eastward propagating waves while the meridional structures of the eastward propagating

convection over tropical africa and the atlantic ocean during northern summer part ii modulation by easterly waves abstract using meteosat data and european centre for medium range weather forecast ecmwf analyses we examine easterly waves and their relation with the cloudiness over west africa and the tropical atlantic ocean for three summers june july august and september 1983 85 spectral analysis of the low level meridional wind in the 2 8 5 1 day band reveals maximum wave amplitude near the west african coast at 20 n during august and september the wave amplitude is larger than during june and july and a secondary maximum appears around 7 5 n composites of the mean structure of the wave and the associated cloud modulation reveal consistent relationship between observed cloudiness and ecmwf analyses the phase of the wave modulation of the cloudiness is strongly dependent on the geographical location in response to changes in the mean climatological conditions this phase varies however grossly in four large land and ocean regions centered at 7 5 and 17 5 n respectively for which we derive vertical cro

the dynamics of the west african monsoon part v the detection and role of the dominant modes of convectively coupled equatorial rossby waves abstract this study is the last in a series of papers addressing the dynamics of the west african summer monsoon at intraseasonal time scales between 10 and 90 days the signals of convectively coupled equatorial rossby er waves within the summer african monsoon have been investigated after filtering noaa outgoing longwave radiation olr data within a box delineated by the dispersion curves of the theoretical er waves two families of waves have been detected in the 10 100 day periodicity band by performing a singular spectrum analysis on a regional index of er filtered olr for each family the first eof mode has been retained to focus on the main convective variability signal within the periodicity band of 30 100 days an er wave pattern with an approximate wavelength of 13 500 km has been depicted this er wave links the mjo mode in the indian monsoon sector with the main mode of convective variability over west and central africa this confirms the investigations carried out in previous studies wi

horizontal and vertical structure of easterly waves in the pacific itcz abstract outgoing longwave radiation olr and low level wind fields in the atlantic and pacific intertropical convergence zone itcz are dominated by variability on synoptic time scales primarily associated with easterly waves during boreal summer and fall this study uses spectral filtering of observed olr data to capture the convective variability coupled to pacific easterly waves filtered olr is then used as an independent variable to isolate easterly wave structure in wind temperature and humidity fields from open ocean buoys radiosondes and gridded reanalysis products the analysis shows that while some pacific easterly waves originate in the atlantic most of the waves appear to form and strengthen within the pacific pacific easterly waves have wavelengths of 4200 5900 km westward phase speeds of 11 3 13 6 m s 1 and maximum meridional wind anomalies at about 600 hpa a warm moist boundary layer is observed ahead of the waves with moisture lofted quickly through the troposphere by deep co

sedimentology of a late pleistocene submarine moraine complex county down northern ireland the killard point moraine formed when late pleistocene ice grounded on the isostatically depressed coastal lowlands of county down northern ireland at a time of relatively high sea level the moraine consists of three major lithologic associations which prograded for about 1 km from the ice grounding zone into a glaciomarine environment at the base of the succession a diamicton association is characterized by massive and stratified diamictons that are mainly debris flows it contains a minor ice rafted debris component the overlying sand association was deposited from sediment gravity flows of low to intermediate viscosity the gravel association was deposited by high density sediment gravity flows massive mud beds or drapes occur throughout the sequence and are related to low density turbidity or contour currents sequences of this type are more common in the geological record than the literature suggests and are often explained in terms of terrestrial based deglacial models this calls for a sedimentological reappraisal of many glacigenic deposits which accumulated in areas subject to deep isostatic depression during the late pleistocene

palaeoglaciology of the last irish ice sheet reconstructed from striae evidence abstract a database comprising some 5200 individual striation measurements on bedrock surfaces across the island of ireland was used to produce maps of flowsets corresponding to individual ice flow events during the last late devensian glacial cycle these flowsets were identified on the basis of regional scale correspondence between striae orientations which when linked together spatially are able to identify consistent ice flow vectors four main chronological stages are identified on the basis of this evidence i incursion of scottish ice into ireland ii glacial maximum conditions iii ice retreat and dissolution and iv development of localised ice domes striae based reconstructions of the glaciology of the last irish ice sheet are qualitatively different from those based on bedform mainly drumlin and ribbed moraine evidence significant differences are apparent in upland areas which have fewer preserved bedforms and a higher concentration of striae combining bedform and striae datasets will enable a better understanding of the temporal evolution of the ice sheet it is likely that both datasets record a snapshot of ice flow direction and subglacial conditions and environments immediately prior to preservation of this directional evidence

impact of the madden julian oscillation on the summer west african monsoon in amip simulations at intraseasonal timescales convection over west africa is modulated by the madden julian oscillation mjo in this work we investigate the simulation of such relationship by 11 state of the art atmospheric general circulation models runs with prescribed observed sea surface temperatures in general the atmospheric model intercomparison project simulations show good skill in capturing the main characteristics of the summer mjo as well as its influence on convection and rainfall over west africa most models simulate an eastward spatiotemporal propagation of enhanced and suppressed convection similar to the observed mjo although their signal over west africa is weaker in some models in addition the ensemble average of models composites gives a better performance in reproducing the main features and timing of the mjo and its impact over west africa the influence on rainfall is well captured in both sahel and guinea regions thereby adequately producing the transition between positive and negative rainfall anomalies through the different phases as in the observations furthermore the results show that a strong active convection phase is clearly associated with a stronger african easterly jet aej but the weak convective phase is associated with a much weaker aej our analysis of the equatorial waves suggests that the main impact over west africa is established by the propagation of low frequency waves within the mjo and rossby spectral peaks results from the simulations confirm that it may be possible to predict anomalous convection over west africa with a time lead of 15 20 day

evaluating controls on ice dynamics in the north east atlantic using an event stratigraphy approach abstract an event stratigraphy approach is used to examine controls on late devensian age glacial events in ireland the event stratigraphy based on onshore geological evidence is constructed from relative age relationships of cross cutting bedforms found behind ice margins and radiometric dates from ice marginal landforms the event stratigraphy can be compared with the greenland grip ice core 18o proxy climate record and high resolution marine records in the north east atlantic these records reflect different aspects of the coupled ice ocean atmosphere system on different scales prior to heinrich event 1 at 14 5 14c kyr bp cal 17 kyr bp the glacial event stratigraphy in ireland more closely matches events recorded in north atlantic marine cores after heinrich event 1 the ireland glacial event stratigraphy better fits with the greenland 18o record this shift in phasing relations in the north east atlantic following heinrich event 1 reflects a range of variables including onshore ice retreat changes in sea ice cover and strengthened thermohaline circulation the grip event stratigraphy may therefore not always be the most appropriate standard against which to compare all glacial climate records in the north east atlantic region late devensian glacial events in ireland match better to shifts observed in the marine record suggesting an ocean driver of glacial events in north west europe

radiocarbon constraints on the history of the western irish ice sheet prior to the last glacial maximum accelerator mass spectrometer c 14 dating of in situ monospecific marine microfaunas and reworked shells records high relative sea level on the western coast of ireland between ca 40 and 19 call calibrated ka requiring substantial isostatic loading by the irish ice sheet iis during that interval glacial and marine deposits also record a rapid fluctuation of the us margin onto the continental shelf ca 28 cal ka evidence that the coast was not subsequently overridden by the iis indicates that at least for this sector of the ice sheet the ice margin during the last glacial maximum lgm was less extensive than the 28 cal ka event our data from western ireland support c 14 and cl 36 chronologies from the irish sea basin in identifying an us that was as extensive and thick as the lgm iis for much of the 20 k y interval prior to the lgm

subglacial bedform geomorphology of the irish ice sheet reveals major configuration changes during growth and decay the belated realisation that ribbed rogen moraines form such an integral part of irish geomorphology and the piecemeal approach to previous drumlin mapping is probably responsible for the highly contrasting views of palaeoflow patterns of the irish ice sheet using a high resolution 25 m digital elevation model we present morphological maps of a large part 100 100 km of the so called drumlin belt of north central ireland the landforms comprise mostly ribbed moraine much larger than found elsewhere up to 16 km in length which in places are superimposed on each other contrary to most prior assessments we find the bedform record to contain numerous and overlapping episodes of bed formation ribbed moraine drumlins and crag and tails that provide a palimpsest record of changing flow geometries these demonstrate an ice sheet with a centre of mass and flow geometry that changed during growth and decay using distinctive flow patterns and relative age relationships between them we reconstruct ice sheet evolution into four phases during a single glacial cycle in phase 1 early in the glacial cycle scottish and local ice coalesced to form a northeast centred irish ice sheet as it grew its centre of mass migrated southwards culminating in a major n s divide positioned down the east of ireland phase 2 ca last glacial maximum during retreat the centre of mass migrated at least 120 km northwards and became established in northwest ireland and at this point a dramatic bedforming event produced one of the world s largest and most contiguous ribbed moraine fields phase 3 final deglaciation is thought to be by fragmentation into many topographically controlled minor ice caps phase 4 rather than any dramatic or unexpected behaviour the reconstructed phases indicate a relatively predictable pattern of ice sheet growth and decay with changes in centres of mass and does not require major readvances or ice stream events copyright 2001 john wiley sons ltd

palaeo ice streams abstract the location and behaviour of ice streams is one of the most important controls on ice sheet configuration and stability in order to reconstruct former ice sheets we need to know ice stream location and timing once identified the beds of palaeo ice streams provide an unprecedented opportunity to glean information about their basal environment something that remains very difficult under contemporary ice streams this paper represents the first synthesis and discussion of palaeo ice stream research from a variety of former ice sheets and includes new insights relating their configuration and activity to the evidence they leave behind the ambiguous use of the term ice stream is addressed and four possible configurations for ice streams are presented diagnostic landforms and landform assemblages that we would expect an ice stream to produce are discussed and the temporal context of bedform generation is described as either a rubber stamped or smudged bedform imprint resulting from isochronous or time transgressive landform generation in particular we focus on the configuration of terrestrially terminating ice streams for which there are no modern analogues technological advances in marine geophysics are helping to generate a convergence of interest between antarctic glaciology and palaeo glaciology it is suggested that investigations around the fringes of contemporary ice sheets i e west antarctica can provide evidence that directly links the geomorphological record of palaeo ice streams with their contemporary counterparts in addition computational advances and modelling adaptations have permitted the incorporation of ice streams within ice sheet models we argue that data from palaeo ice stream beds are invaluable to ice sheet stream modelling experiments and will help us understand ice stream operation and the linkages between climate perturbations and both palaeo and contemporary ice sheets

easterly wave regimes and associated convection over west africa and tropical atlantic results from the ncep ncar and ecmwf reanalyses ncep ncar and ecmwf daily reanalyses are used to investigate the synoptic variability of easterly waves over west africa and tropical atlantic at 700 hpa in northern summer between 1979 1995 1979 1993 for ecmwf spectral analysis of the meridional wind component at 700 hpa highlighted two main periodicity bands between 3 and 5 days and 6 and 9 days the 3 5 day easterly wave regime has already been widely investigated but only on shorter datasets these waves grow both north and south of the african easterly jet aej the two main tracks noted over west africa at 5 n and 15 n converge over the atlantic on latitude 17 5 n these waves are more active in august september than in june july their average wavelength phase speed varies from about 3000 km 8 m s 1 north of the jet to 5000 km 12 m s 1 south of the jet rainfall convection and monsoon flux are significantly modulated by these waves convection in the inter tropical convergence zone itcz being enhanced in the trough and ahead of it with a wide meridional extension compared to the 3 5 day waves the 6 9 day regime is intermittent and the corresponding wind field pattern has both similar and contrasting characteristics the only main track is located north of the aej along 17 5 n both over west africa and the atlantic the mean wavelength is higher about 5000 km long and the average phase speed is about 7 m s 1 then the wind field perturbation is mostly evident at the aej latitude and north of it the perturbation structure is similar to that of 3 5 days in the north except that the more developed circulation centers moving more to the north lead to a large modulation of the jet zonal wind component south of the aej the wind field perturbation is weaker and quite different the zonal wind core of the jet appears to be an almost symmetric axis in the 6 9 day wind field pattern a clockwise circulation north of the aej being associated with a counter clockwise circulation south of the jet and vice versa these 6 9 day easterly waves also affect significantly rainfall convection and monsoon flux but in a different way inducing large zonal convective bands in the itcz mostly in the trough and behind it as opposed to the 3 5 day wave regime these rainfall anomalies are associated with anomalies of opposite sign over the guinea coast and the sahelian regions over the continent these waves are more active in june july and in august september over the ocean gate phase i gave an example of such an active 6 9 day wave pattern considered as a sequence of weak easterly wave activity this phase was also a sequence of high 6 9 day easterly wave activity we suggest that the 6 9 day regime results from an interaction between the 3 5 day easterly wave regime maintained by the barotropic baroclinic instability of the aej and the development of strong anticyclonic circulations north of the jet over west africa and both north and south of the jet over the atlantic significantly affecting the jet zonal wind component the permanent subtropical anticyclones azores libya st helena could help initiation and maintenance of such regime over west africa and tropical atlantic based on an a priori period band criterion our synoptic classification has enabled us to point out two statistical and meteorological easterly wave regimes over west africa and tropical atlantic ncep ncar and ecmwf reanalyses are in good agreement the main difference being a more developed easterly wave activity in the ncep ncar reanalyses especially for the 3 5 day regime over the atlantic

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

observations of a convectively coupled kelvin wave in the eastern pacific itcz abstract a case study of a convectively coupled kelvin wave in the eastern pacific intertropical convergence zone itcz is presented as observed during the 1997 pan american climate studies pacs tropical eastern pacific process study tepps the large scale convective envelope associated with this disturbance with a zonal scale of approximately 1000 2000 km propagates eastward at 15 m s 1 along the mean convective axis of the itcz this envelope consists of many smaller scale westward moving convective elements with zonal scales on the order of 100 500 km as the convectively coupled kelvin wave disturbance propagates eastward it exerts a strong control on local convection radar and vertical profiler data collected aboard the noaa r v ronald h brown during the wave passage show that convection deepens rapidly as the kelvin wave approaches from the west progressing from isolated shallow cumuli to organized deep convective features within just 12 h initially rainfall in the vicinity of the s

ice flow stages and glacial bedforms in north central ireland a record of rapid environmental change during the last glacial termination satellite imagery is a useful tool to assess large scale 10 3 km 2 geological patterns satellite imagery of north central ireland shows cross cut and overprinted subglacial bedform patterns bedform lineations supported by sedimentary evidence are used to reconstruct four ice flow stages named a d during the termination of the last devensian glaciation 22 000 13 000 radiocarbon 14 c years bp flow stage a relates to southwesterly flow of scottish ice across eastern ireland flow stage b during the last glacial maximum c 25 000 22 000 14 c years bp records southeasterly ice flow from dispersal centres in northern parts of ireland transverse subglacial ridges rogen moraines formed during stage b are the largest area of this ridge type in western europe flow stage c records erosional headcutting in the rogen moraine field and sediment streamlining drumlinization by ice streams drawn into the irish sea basin this flow stage is constrained by ams radiocarbon dates from marine microfaunas to around 14 500 14 c years bp flow stage d records drumlinization from an inland centre in the lough neagh basin overall bedform patterns can be used to reconstruct ice mass history and evaluate controls on ice activity including millennial scale changes in amphi north atlantic climate field evidence of bedform relationships also casts doubt on current concepts of drumlinization and the role of pervasive sediment deformation in glacial systems

sedimentation in a subglacial lake enniskerry eastern ireland abstract field relationships between a subglacial lake fill from the enniskerry basin eastern ireland provide evidence for dynamic links between the sedimentary fill regional subglacial meltwater flow and regional ice dynamics the basin fill 6 7 km2 forms an integral part of an extensive 30 km subglacial meltwater system which developed parallel to north south ice flow along the western marginal sector of the late pleistocene irish sea glacier high magnitude sediment fluxes were directed into the subglacial lake southwards across the northern basin rim from two nye type channels and westwards by a rothlisberger type channel the resulting subaqueous fans typically consist of cones of coarse boulder gravels deposited by jet effluxes overlain by cross bedded sands and foreset gravels in places these are eroded and overlain by multistorey dish shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head a variety of gravelly and sandy bedforms indicate that sediment migrated over efflux cores towards deeper parts of the basin facies variability within the ice proximal fans and spreads record deposition from a wide range of high and low density turbulent flows traction currents density underflows suspension and sediment gravity flows a surficial drape of winnowed diamict is related to areal resedimentation as jet effluxes closed down at one site the gravelly sequence shows a largely conformable transition upwards into glaciotectonised gravel and basal till in the lee of the basin rim elsewhere the upper part of the sediment pile is occasionally deformed by the drag of the ice roof a series of sequential events is postulated for the evolution of the subglacial drainage system and subglacial lake development initially a rock ridge transverse to ice flow resulted in the development of a relatively low pressure lee zone along the northern margin of the basin ice sheet decoupling within the basin was enhanced by water migration into this low pressure lee zone which also melted an ice roof cavity closure and maintenance of the ice roof was prevented by a fast ice flux generated by intense marine downdraw in the main ice lobe centred in the irish sea basin regional ice directed meltwater pressure gradients and erosion enhanced subglacial lake development in the lowest topographic point of the system major inlet and outlet nye type channels incised transverse to the rims of the basin testify to the intensity of ice directed drainage along the marginal sector of the irish sea glacier in a wider context the concepts of high magnitude subglacial meltwater flow coupled with high rates of debris flux invoked for the subglacial basin fill are also necessary to explain the thick tidewater sequences present in adjacent sectors of the irish sea basin

evidence of two independent modes of convection at intraseasonal timescale in the west african summer monsoon 1 two main independent modes of convection at intraseasonal timescale in the west african summer monsoon are highlighted one depicts a meridional dipole of convection over west africa linked to a modulation of the latitude of the inter tropical convergence zone itcz it is associated with a westward propagative signal of the convection over the sahel and to a modulation of cyclonic vorticity at these latitudes the other one is characterized by a stationary uniform modulation of convection in the itcz without any significant modulation of its latitudinal location it is associated with a modulation of the zonal wind component over the eastern equatorial atlantic the dominant periodicity of these two modes is around 15 days it is necessary to take into account the relative parts of these two modes in order to accurately analyze the mechanisms involved in intraseasonal variability of the african monsoon

the west african monsoon dynamics part i documentation of intraseasonal variability intraseasonal variability in the west african monsoon is documented by using daily gridded datasets of rainfall and convection and reanalyzed atmospheric fields over the period 1968 90 rainfall and convection over west africa are significantly modulated at two intraseasonal timescales 10 25 and 25 60 day leading to variations of more than 30 of the seasonal signal a composite analysis based on the dates of the maximum minimum of a regional rainfall index in wet dry sequences shows that these sequences last on average 9 days and belong to a main quasiperiodic signal of about 15 days a secondary periodicity of 38 days is present but leads to a weaker modulation during a wet dry sequence convection in the itcz is enhanced weakened and its northern boundary moves to the north south while the speed of the african easterly jet decreases increases the speed of the tropical easterly jet increases decreases and the monsoon flow becomes stronger weaker all these features being similar to the ones associated with interannual variability characterizing wet and dry years this modulation of convection at intraseasonal timescales is not limited to west africa but corresponds to a westward propagating signal from eastern africa to the western tropical atlantic an enhanced monsoon phase is associated with stronger cyclonic activity in the low levels over the sahel associated with stronger moisture advection over west africa five days before the full development of the wet phase a stronger cyclonic circulation at 20 e induces enhanced southerly winds along 25 e where convection enhances while another westwardpropagating cyclonic circulation is located at 0 this atmospheric pattern is linked to the enhancement of the subsiding branch of the northern hadley cell at 35 n northerly advection of drier air over west africa and to increased dry convection in the heat low at 20 n it propagates westward leading to a zonally extended area of enhanced monsoon winds over west africa consistent with the occurrence of the wet phase

rogen moraine an example of glacial reshaping of pre existing landforms abstract rogen moraine is widely distributed in the core areas of the former scandinavian and laurentide ice sheets it is generally agreed upon that these gently arched ice flow transverse ridges can be used in reconstructions of paleo ice flow patterns and that they indicate a melted bed or poly thermal basal ice regime however the processes of ridge generation have been contentious this study proposes a two stage formation of rogen moraine based on detailed sedimentological and structural investigations in excavated trenches in a rogen moraine landscape in the province of dalarna central sweden field data suggest that rogen moraine ridges are the reshaped remains of pre existing transverse moraine ridges originally deposited from ice cored moraines in an ice marginal zone due to back and down wasting of ice cores inter ridge troughs were filled with debris flow and fluvial deposits which after landscape inversion were transformed to areas of transverse and hummocky moraines it is proposed that this primary landscape formation occurred during an early weichselian deglaciation this relict landscape was later preserved beneath cold based mid to late weichselian ice sheet s which turned wet based during the preboreal deglaciation phase and re moulded the precursor landforms into rogen moraine

landform modification by palaeo ice streams in east central ireland in eastern ireland subglacial bedforms including drumlins and rogen moraines were modified by headward erosion along two ice streams which had over lapping flow tracks the ice streams which hadtidewater termini are dated by geochrono metric and morphostratigraphic methods to 5 15 0 14 ckyr bp castleblaney ice stream and 13 8 14 ckyr bp armagh ice stream bedforms along ice stream tracks show a morphological continuum which reflects a down ice increase in the degree of modification by ice stream activity i e resulting in unmodified remoulded overprinted cross cut streamlined bedforms the down ice changes inbedform types are inferred to relate to changes in subglacial drainage and sediment transport mechanisms bedform and sedi mentary evidence suggest that discrete subglacial meltwater channels which developed up ice changed in a down ice direction to unchannelized flows which deepened towards the ice margin meltwater release from subglacial cavities and produced by strain heating at sheared ice stream margins probably helped support ice stream flow which ended as the volume of subglacial meltwater discharge decreased dated millennial scale cycles of ice activity may be related to instability at tidewater margins followed by complex thermal and hydraulic responses within the ice mass

three dimensional structure and dynamics of african easterly waves part i observations the mean structure of african easterly waves aews over west africa and the adjacent atlantic is isolated by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered satellite derived outgoing longwave radiation these results are compared with previous studies and an idealized modeling study in a companion paper which provides evidence that the waves bear a close structural resemblance to the fastest growing linear normal mode of the summertime basic state flow over africa there is a significant evolution in the three dimensional structure of aews as they propagate along 10 n across west africa at this latitude convection occurs in northerly flow to the east of the greenwich meridian then shifts into the wave trough and finally into southerly flow as the waves propagate offshore into the atlantic itcz in contrast to the north of the african easterly jet along 15 n convection remains in southerly flow throughout the waves trajectory along 10 n over west africa the location of convection is consistent with the adiabatic dynamical forcing implied by the advection of perturbation vorticity by the mean thermal wind in the zonal direction as in the companion paper offshore and along 15 n the relationship between the convection and dynamics is more complex and not as easily explained in terms of dynamical forcing alone

origin of convectively coupled kelvin waves over south america convectively coupled kelvin waves over the south american continent are examined through the use of temporal and spatial filtering of reanalysis satellite and gridded rainfall data they are most prominent from november to april the season analyzed herein the following two types of events are isolated those that result from preexisting kelvin waves over the eastern pacific ocean propagating into the continent and those that apparently originate over amazonia forced by disturbances propagating equatorward from central and southern south america the events with precursors in the pacific are mainly upper level disturbances with almost no signal at the surface those events with precursors over south america on the other hand originate as upper level synoptic wave trains that pass over the continent and resemble the cold surges documented by garreaud and wallace as the wave train propagates over the andes it induces a southerly low level wind that advects cold air to the north precipitation associated with a cold front reaches the equator a few days later and subsequently propagates eastward with the characteristics of a kelvin wave the structures of those waves originating over the pacific are quite similar to those originating over south america as they propagate to eastern south america and into the atlantic south america kelvin waves that originate over neither the pacific nor the midlatitudes of south america can also be identified in a composite sense these form over the eastern slope of the andes mountains close to the equator there are also cases of cold surges that reach the equator yet do not form kelvin waves the interannual variability of the pacific originating events is related to sea surface temperatures in the central eastern pacific ocean when equatorial oceanic conditions are warm there tends to be an increase in the number of disturbances that reach south america from the pacific

convectively coupled kelvin waves in cmip5 coupled climate models this study provided a quantitative evaluation of convectively coupled kelvin waves cckws over the indian ocean and the pacific ocean simulated by 20 coupled climate models that participated in coupled model intercomparison project phase 5 the two leading empirical orthogonal function eof modes of filtered daily precipitation anomalies are used to represent the eastward propagating cckws in both observations and simulations the eigenvectors and eigenvalues of the eof modes represent the spatial patterns and intensity of cckws respectively and the lead lag relationship between the two eof principle components describe the phase propagation of cckws a non dimensional metric was designed in consideration of all the three factors i e pattern amplitude and phase propagation for evaluation the relative rankings of the models based on the skill scores calculated by the metric are conducted for the indian ocean and the pacific ocean respectively two models noresm1 m and mpi esm lr are ranked among the best 20 for both the regions three models inmcm4 mri cgcm3 and hadgem2 es are ranked among the worst 20 for both the regions while the observed cckw amplitude is greater north of the equator in the pacific some models overestimate the cckw ampliutde in the southern hemisphere this bias is related to the mean state precipitation bias along the south pacific convergence zone

drumlins and the dynamics of the subglacial environment abstract this volume contains a selection of papers presented at the vii international drumlin symposium westport ireland in may 2009 this introduction to the volume first outlines the significance of drumlins as a key subglacial bedform gives a brief history of drumlin research and identifies the major themes of subglacial research namely mapping and morphometry sedimentary and ice bed processes and glacier dynamics it then summarises in turn the major findings of the papers in this volume linking them to each other and to the wider literature finally this introductory paper considers future developments in studies of drumlins and the subglacial environment

mesoscale convective systems in relation to african and tropical easterly jets abstractthis paper documents the interaction processes between mesoscale convective systems mcs the tropical easterly jet tej and the african easterly jet aej over west africa during the monsoon peak of 2006 observed during the african monsoon multidisciplinary analyses amma project the results highlight the importance of the cloud system localization relative to the jets in order to explain their duration and life cycle a systematical study reveals that intense and long lived mcss correspond to a particular pattern where clouds associated with deep convection are located in entrance regions of tej and in exit regions of aej a case study on a particularly well documented convective event characterizes this link and infers the importance of jet streaks in promoting areas of divergence favoring the persistence of mcss

a climatology of waves in the equatorial region abstract propagating anomalies of moisture and moist deep convection in the tropics are organized into a variety of large scale modes these include but are not limited to the so called intraseasonal oscillations convectively coupled waves similar to those predicted by shallow water theory on the equatorial beta plane and tropical depression type disturbances along with the annual and diurnal cycles these modes act and interact to control much of the variance of tropical convection analyses of 10 yr of outgoing longwave radiation olr and precipitable water pw data are carried out to develop comparative climatologies of these wavelike modes the analysis relaxes the commonly used cross equatorial symmetry constraints which allows study of the portions of the wavelike processes that are asymmetric across the equator mean background states are found for olr and for pw as functions of day of the year examination of anomalies together with the background reveals much about how the waves are affec

abrupt early holocene 9 9 9 6 ka ice stream advance at the mouth of hudson strait arctic canada radiocarbon dated glacial geologic evidence documents an abrupt advance of the northern margin of the labrador sector of the laurentide ice sheet during the last deglaciation ice flow directional indicators together with ice marginal features found onshore and offshore delimit an ice stream that advanced north northeast 300 km crossed the mouth of hudson strait and outer frobisher bay and overran summits 400 m above sea level on outer hall peninsula southeast baffin island fifty eight 14 c ages including 27 accelerator mass spectrometry ages on single shells indicate that the advance was extremely rapid the entire advance retreat cycle took place in an 300 yr 14 c interval 9 9 9 6 ka at its maximum extent the ice stream supported a calving margin 200 km long terminating in open water 500 m deep implying a massive iceberg release marine evidence for the outflow is preserved along the labrador sea shelf as thick carbonate rich glacial marine drift but has not been recognized farther east in the north atlantic either the discharge of icebergs was insufficient to produce a trans north atlantic carbonate rich heinrich layer or the icebergs tracked southward where they encountered warming sea surface temperatures although the advance seems to have been coincident with a brief interval of minor regional cooling it failed to trigger a significant climate perturbation suggesting that the ocean atmosphere system had attained its stable interglacial condition by that time

late pleistocene tidewater glaciers and glaciomarine sequences from north county mayo republic of ireland late pleistocene deposits in north county mayo were deposited in three main glacigenic environments 1 drumlins and basal tills were formed when ice moved from the irish lowlands and local mountain catchments into donegal bay 2 gilbert type deltas accumulated up to 80m i o d on the lowlands and subaqueous moraines formed across minor valleys when marine based ice grounded inland 3 a thick drape of fossiliferous glaciomarine mud along the coastal fringe was deposited from meltwater plumes and by ice rafting immediately outside of these ice limits the muds contain an elphidium clavatum dominated low diversity microfauna which is characteristic of cold water conditions adjacent to glacier termini valves of macoma calcarea from the mud have been 14c dated at 16940 120 and 17300 100 bp the high level delta complex was deposited from tidewater glaciers in a peripheral depression adjacent to the drumlin ice limits of north county mayo although the field evidence cannot be used to determine former sea level history with any accuracy it poses general problems for sea level history and isostatic effects of the last major ice sheet in the west of ireland raised glaciomarine sequences commonly occur in close association with drumlin ice limits elsewhere in ireland and represent marine transgressions prior to glacial unloading it is suggested that the magnitudes and patterns of crustal depression are greater and geometrically more complex at the margins of ice sheets in ireland than hitherto realised

temporal changes in subglacial meltwater activity field evidence from the late devensian in the north of ireland abstract temporal changes in meltwater abundance distribution and characteristics controlling subglacial processes and ice sheet dynamics can be inferred from subglacial sediment successions field evidence for changes in subglacial meltwater characteristics over time is presented from two sites doonan drummee near a former late weichselian devensian ice centre in the north of ireland on a macroscale both sites investigated show subglacial diamicton overlying glacially planated bedrock platforms in more detail primary sedimentary structures and facies variability show a complex relationship between depositional processes and meltwater characteristics at the ice bed interface ibi sedimentary evidence suggests sediment transport and deposition took place by low viscosity subglacial slurries mobile sediment meltwater admixtures which are part of a continuum between the processes of subglacial sediment deformation and subglacial meltwater flooding subtle changes in meltwater abundance and distribution at the ibi controlled slurry rheology mechanisms of particle support and detailed sediment depositional processes

horizontal structure and seasonality of large scale circulations associated with submonthly tropical convection the relationship between deep tropical convection and large scale atmospheric circulation in the 6 30 day period range is examined regression relationships between filtered outgoing longwave radiation at various locations in the tropics and 200 and 850 mb circulation are mapped for the standard seasons and the spatial structure and seasonal dependence of the results are interpreted in view of the basic state circulation in regions where the convection is embedded in upper level easterlies anomalous equatorial easterly flow is typically present at 200 mb within and to the west of the convective signal along with patterns of meridional outflow into subtropical anticyclonic perturbations lagged relationships suggest that the convection is forcing the circulation in many of these cases the outflow and subtropical circulations are strongest into the winter hemisphere during the solstitial seasons with more symmetric signals about the equator seen in the equinoctial seasons the longitudinal positioning of the subtropical features with respect to the convection varies but is generally located due poleward or just to the east of the convection there tends to be a first baroclinic mode vertical structure to these circulations such that equatorial westerlies are present at 850 mb within the convection with closed circulations on either side of the equator resembling equatorial rossby modes especially common over the atlantic and pacific sectors as a contrast in regions located within upper level westerlies or along the margin of influence of upper westerly disturbances convection appears to be forced by upper level wave energy propagating into the deep tropics with the heating located in the upward motion region ahead of upper level troughs this occurs over the atlantic and eastern pacific sectors during northern winter and spring and over australia the south pacific and south america during southern summer when upper westerlies are at relatively low latitudes where they can interact with deep tropical convection the results confirm theoretical and modeling ideas that suggest that rossby wave energy is able to propagate into the deep tropics in regions where upper level westerlies exist in the tropics

do subglacial bedforms comprise a size and shape continuum understanding the evolution of the ice bed interface is fundamentally important for gaining insight into the dynamics of ice masses and how subglacial landforms are created however the formation of the suite of landforms generated at this boundary subglacial bedforms is a contentious issue that is yet to be fully resolved bedforms formed in aeolian fluvial and marine environments either belong to separate morphological populations or are thought to represent a continuum of forms generated by the same governing processes for subglacial bedforms a size and shape continuum has been hypothesised yet it has not been fully tested here we analyse the largest data set of subglacial bedform size and shape measurements ever collated 96 900 bedforms our results show that flutes form a distinct population of narrow bedforms however no clear distinction was found between drumlins and megascale glacial lineations msgls which form a continuum of subglacial lineations a continuum of subglacial ribs also exists with no clear size or shape distinctions indicating separate populations furthermore an underreported class of bedform with no clear orientation to ice flow quasi circular bedforms overlaps with the ribbed and lineation continua and typically occurs in spatial transition zones between the two potentially merging these three bedform types into a larger continuum

bedrock controls on subglacial landform distribution and geomorphological processes evidence from the late devensian irish sea ice stream abstract ice streams play an important role as regulators of the behaviour of modern ice sheets taking the form of corridors of fast flowing ice similar zones of fast moving ice have also been recognised draining the margins of the late devensian british and irish ice sheet although the geomorphological and sedimentary signatures of palaeo ice streams have received significant attention allowing the identification of these former ice streams the influence of bedrock geology on the processes occurring beneath these palaeo ice streams is less well understood even though subglacial geology has been shown to control the location ice streams within the west antarctic ice steam this paper highlights the role played by bedrock geology on landform distribution beneath a much older ice stream the late devensian irish sea ice stream the spatial relationships displayed between subglacial landforms and bedrock geology are described from anglesey northwest wales and the rhins of galloway southwest scotland both sites occur close to the eastern margin of this irish sea ice stream a link has been established between landform morphology and distribution and the disposition of the main tectonostratigraphical units within the bedrock changes in landform morphology are shown to have been locally controlled by large scale faults and or major lithological boundaries with less durable bedrock lithologies controlling the location and lateral extent of relatively faster flowing portions of the ice stream

video observations inside conduits of erupting geysers in kamchatka russia and their geological framework implications for the geyser mechanism several models have been proposed to explain periodic eruptions of geysers in essence the models all use two principally different types of geyser plumbing confi gurations dealing with two different physical mechanisms here we present data on direct video observations of interior conduit systems for four erupting geysers in geyser valley kamchatka russia the video footage reveals highly contorted water fi lled conduits that periodically discharge voluminous parcels of steam bubbles during eruptions these observations do not favor the models that use the most popular long vertical conduit type of plumbing where eruptions are caused by sudden fl ashing of superheated water into steam in contrast our data fi t the models using the less explored type of plumbing where pressurized steam gradually accumulates in an underground cavity bubble trap and periodically erupts through a water fi lled highly contorted conduit with the confi guration of an inverted siphon hydrodynamic calculations show that such a plumbing confi guration produces periodic eruptions when the volume of the bubble trap exceeds the volume of the conduit connecting it to the ground surface conduits of the studied geysers were developed from erosion by ascending geothermal water in landslide deposits chaotic internal structures of the deposits facilitated the formation of conduit systems with highly contorted confi gurations of the bubble trap type we suggest that geyser fi elds are rare on earth because they require the combination of hydrothermal discharge and geological formations having specifi c mechanical properties and structures that facilitate the generation of highly contorted conduits

basin scale patterns of subglacial sediment mobility implications for glaciological inversion modelling abstract patterns of glacial bedforms and their internal sediments are described from the omagh basin north central ireland here drumlins and ribbed moraines were variously formed preserved and remoulded during several late devensian ice flow stages and their patterns can be used as input into glaciological inversion models more detailed examination of the morphology and internal sediments of these bedforms shows a complex pattern of reworking driven by local scale basal thermal and hydrological regime sediment lithofacies associations and patterns of erratic carriage can be used to better evaluate ice bed conditions and basal processes than bedforms alone the sedimentary evidence suggests that bedforms were unlikely to have been formed during a single glacial episode as is implicit in glaciological inversion models and more likely formed during several episodes that cannot be resolved by crosscutting or superimposed bedform relationships alone

glaciofluvial erosional morphology and sediments of the coronation spondin scabland east central alberta spatially discontinuous meltwater channel networks on the canadian prairies are usually interpreted as having formed subaerially in front of the retreating laurentide ice sheet evidence in the coronation spondin scabland east central alberta supports an alternative formation by progressive channelization of a subglacial sheetflow of water the scabland is an integrated channel network with varying degrees of anabranching the channels having highly variable sizes shapes and orientations enhanced scour at some channel confluences reflects contemporaneous channel utilization channels also display convex up concave up and undulatory along channel profiles with some junctions at the same elevations longitudinal grooves in large scale channels are associated with numerous boulder deposits residual hills demarcated by channels display composite and streamlined forms superimposed on residuals are erosional transverse bedforms longitudinal grooves and undulating surfaces that indicate submergence

the global population of mesoscale convective complexes a global set of 714 mesoscale convective complexes is compiled and some of the common properties of the convective systems are identified and examined from a global perspective the data set includes date of occurrence time of first storms initiation maximum extent termination duration cold cloud shield areas and tracks from initiation to termination it is found that the typical convective complex is nocturnal generates a cold cloud shield area of approximately 350 000 km2 and persists for about 10 h the largest systems and most persistent systems tend to occur near the summer solstices for the globe about 400 systems occur each year primarily over land areas most systems develop in favoured zones although some activity occurs over every continent except antarctica and all major oceans the concentration of activity into favoured zones indicates that there must be special dynamic and or thermodynamic conditions necessary for convection to organize into convective complexes activity is strongly tied to the solar day and shifts from 35 s in early january to about 50 n during the boreal summer and back to 35 s by december within the northern hemisphere there is a pronounced poleward migration as the jet stream shifts northward relatively little migration occurs in the ocean dominated southern hemisphere where the subtropical jet remains quasi stationary over the convective complex regions the nocturnal life cycles copious rainfall large cloud shields and great frequency of mesoscale convective complexes suggest that they may be significant contributors to the global hydrologic cycle and earth system energy budget

the west african monsoon dynamics part iii the quasi biweekly zonal dipole abstract this paper presents an investigation of the mechanisms giving rise to the main intraseasonal mode of convection in the african monsoon during northern summer here identified as the quasi biweekly zonal dipole qbzd the qbzd is primarily characterized by a quasi stationary zonal dipole of convection whose dimension is larger than the west african monsoon domain with its two poles centered along the guinean coast and between 30 and 60 w in the equatorial atlantic the qbzd dynamical processes within the atlantic africa domain are examined in some detail the qbzd has a dipole pattern associated with a walker type circulation in the near equatorial zonal plane it is controlled both by equatorial atmospheric dynamics through a kelvin wave like disturbance propagating eastward between its two poles and by land surface processes over africa inducing combined fluctuations in surface temperatures surface pressure and low level zonal winds off the coast of west africa when convection is at a min

dating and rhythmicity from the last deglacial cycle in the british isles in northern britain glaciotectonically thickened sediment piles represent the sediment flux transferred to ice margins by phases of fast ice flow and drumlin streamlining during the last deglacial cycle radiocarbon dating of marine faunas within deglacial muds age constrain phases of drumlinisation shaping to between 19 and 14 5 ka bp individual phases of drumlinization can be correlated with millennial time scale discharge events documented from the circum north atlantic which are probably climate driven the overall deglacial cycle records at least five major millennial time scale ice margin oscillations and phases of sediment sequence rhythmicity

sedimentology of a glaciofluvial landsystem lough ree area central ireland implications for ice margin characteristics during devensian deglaciation eskers in a glaciofluvial landsystem in the lough ree area central ireland exhibit two orientations the most southerly esker in the area the athlone esker forms part of a dendritic esker system with paleocurrent directions indicating eastward drainage while the rooskagh esker and associated eskers and kames immediately to the north were formed during southward drainage sediments indicate that sharp crested steep sided sections of both ridges were formed within subglacial tunnels while fan shaped and flat topped areas were formed as subaqueous outwash fans and deltas in standing water immediately in front of an ice margin the deposition of ice marginal deposits indicating southward paleoflows against the side of the eastward flowing athlone esker indicates a 90 shift in the direction of ice surface slope and a similar shift in the likely orientation of the ice margin the absence of any evidence of intermediate ice or water flow directions indicates that the shift reflects a recession of ice followed by a readvance from the north

structural and depositional evidence for repeated ice marginal oscillation along the eastern margin of the late devensian irish sea ice stream abstract late devensian glacigenic sediments and landforms along the north west coast of wales document the advance and subsequent retreat of the eastern margin of an irish sea ice stream that met coalesced and ultimately uncoupled from ice radiating outwards from the adjacent welsh ice cap centred over snowdonia across the boundary between the two former ice masses is a set of sediment landform assemblages that reflect rapidly changing erosional and depositional conditions during ice interaction from the inner part of the ice stream the assemblages range outwards from a subglacial depositional assemblage characterised by drumlin swarms through a subglacial erosional assemblage marked by prominent bedrock scours and large subglacial rock channels through an ice marginal assemblage identified by closely spaced glaciotectonised push moraines and intervening marginal sandur troughs into a freely expanding proglacial sandur and lacustrine delta assemblage the ice marginal assemblage provides evidence for numerous oscillatory episodes during retreat and at least 20 ice marginal limits can be identified at least 11 of these display multiple criteria for identifying readvance and in the ideal case is characterised by a moraine form built by localised tectonic stacking of diamict to the rear fronted by a clastic wedge of ice front alluvial fan gravel and intercalated flow till the distribution of sediment landform assemblages suggests a highly dynamic convergent ice stream flow pattern with high ice velocity a sharply delineated lateral shear margin pervasive ice marginal glaciotectonic deformation and a tightly focused ice marginal sediment delivery system all signature characteristics of contemporary ice streams

irish ice sheet dynamics during deglaciation of the central irish midlands evidence of ice streaming and surging from airborne lidar abstract high resolution digital terrain models dtms generated from airborne lidar data and supplemented by field evidence are used to map glacial landform assemblages dating from the last glaciation midlandian glaciation oi stages 2 3 in the central irish midlands the dtms reveal previously unrecognised low amplitude landforms including crevasse squeeze ridges and mega scale glacial lineations overprinted by conduit fills leading to ice marginal subaqueous deposits we interpret this landform assemblage as evidence for surging behaviour during ice recession the data indicate that two separate phases of accelerated ice flow were followed by ice sheet stagnation during overall deglaciation the second surge event was followed by a subglacial outburst flood forming an intricate esker and crevasse fill network the data provide the first clear evidence that ice flow direction was eastward along the eastern watershed of the shannon river basin at odds with previous models and raise the possibility that an ice stream existed in this area our work demonstrates the potential for airborne lidar surveys to produce detailed paleoglaciological reconstructions and to enhance our understanding of complex palaeo ice sheet dynamics

modulation of the convectively coupled kelvin waves over south america and the tropical atlantic ocean in association with the madden julian oscillation abstractin this study evidence of the strong modulation of the convectively coupled kelvin wave cckw activity by the madden julian oscillation mjo is presented with a particular focus over the south america and tropical atlantic region the mjo impacts on cckws over this region as noted in anomalous fields of rainfall as well as vertical profiles of wind moisture and temperature are primarily through the modulation of kelvin wave amplitude with secondary effects on vertical structure and little impact on wavenumber cckw activity is enhanced during mjo phases 8 1 and 2 and damped during mjo phases 4 5 and 6 further analyses reveal that the strong modulation of the mjo on the cckw activity could be largely through two factors namely the vertical zonal wind shear and the lower to middle tropospheric specific humidity the cckw activity tends to be enhanced during mjo phases when the easterly vertical wind shear and positive low to midtroposphere moisture anomalies are present and vice ve

near surface westerly wind jet in the atlantic itcz 1 a suite of satellite data are used to study the near surface westerly winds developing during peak months july september of the west african monsoon in the atlantic intertropical convergence zone these new data show that the westerlies appear in the form of a westerly jet during peak years the daily near surface westerly wind speed may exceed 10 ms 1 the amplitude of the jet displays substantial decadal and interannual variability that corresponds to rainfall in the west african sahel and the frequency of african easterly waves observations and ocean model simulations show that the jet acts to cool sst through entrainment and latent heat loss and to intensify the north equatorial countercurrent by increasing the southward oceanic pressure gradient

the jakobshanvs effect the jakobshavns effect may have been a significant factor in hastening the collapse of palaeo ice sheets with the advent of climatic warming after 18 000 years ago and may precipitate partial collapse of the present day greenland and antarctic ice sheets following co2 induced climatic warming in the decades ahead the jakobshavns effect is observed today on jakobshavns glacier which is located at 69 10 n on the west coast of greenland the jakobshavns effect is a group of positive feedback mechanisms which allow jakobshavns glacier to literally pull ice out of the greenland ice sheet at a rate exceeding 7 km a across a floating terminus 800 m thick and 6 km wide the pulling power results from an imbalance of horizontal hydrostatic forces in ice and water columns at the grounding line of the floating terminus positive feedback mechanisms that sustain the rapid ice discharge rate are ubiquitous surface crevassing high summer rates of surface melting extending creep flow progressive basal uncoupling progressive lateral uncoupling and rapid iceberg calving

equatorial atmospheric waves and their association to convection equatorial wave systems and their relationships with convective activity are analyzed in the western and central pacific regions during the coupled ocean atmosphere response experiment coare intensive observation periods the study uses geostationary meteorological satellite infrared temperature observations and the operational european centre for medium range weather forecasts analyses supplemented with coare observations spectral and complex principal component analysis are applied to the data using the linear theory of equatorially trapped waves as a guideline the existence of three types of waves is detected in the 7 10 day period range n 5 1 rossby waves are found to the east of the date line in a region of weak convective activity over the western equatorial pacific where intense convection occurs the 7 10 day waves do not possess the general characteristics of linear rossby waves but they are strongly linked to the active phases of westerly wind bursts and of convection analysis of the meridional wind reveals intense mixed rossby gravity waves with a mean 5 day period and westward phase and eastward group velocities over the western pacific the convection is found to be strongly correlated with the antisymmetric structure of the divergent field as predicted by the linear theory in the 200 hpa divergence field n 5 1 gravity waves are visible having periods shorter than 2 5 days they rapidly propagate about 25 m s21 both westward and eastward and have strong correlations with convective clusters

converging ice streams a new paradigm for reconstructions of the laurentide ice sheet in southern ontario and deposition of the oak ridges moraine geomorphometric analyses of high resolution 5 m digital elevation datasets shows that the greater toronto area and its immediate environs is built across the former till beds of two fast flowing ice streams the newly named the simcoe ice stream sis and the halton ice stream ois within the last laurentide ice sheet lis these formed during regional deglaciation sometime around 13 000 ybp and are directly analogous to fast flowing 3 km yr 1 ice streams in today s antarctic and greenland ice sheets their subglacial footprint in southern ontario consists of flow sets of highly elongated flow parallel till ridges up to 4 km in length and 100 m in width megascale glacial lineations msgls that converge on the oak ridges moraine orm from the north sis and south his orm is southern ontario s largest glacial landform extending from the niagara escarpment to kingston over some 160 km and was deposited as a series of en echelon glaciolacustrine fan deltas in a complexly evolving glaciolacustr

glacially streamlined hard and soft beds of the paleo ontario ice stream in southern ontario and new york state abstract an extensive tract of glacially streamlined terrain across a large part of southern ontario canada is recognized as the footprint of the paleo ontario ice stream ois within the easternmost great lakes sector of the last laurentide ice sheet the upstream part is a drumlinized and megagrooved hard bed underlain by cambro ordovician carbonates and sandstones subglacial plucking of jointed limestone on the lateral margins of drumlinized escarpment interfluves and rock drumlins generated a large flux of coarse debris within the ice base recorded by sporadic spreads of hummocky rubble moraine downstream the hard bed passes underneath a streamlined soft bed of till cored drift drumlins and megaridges of the classic peterborough and new york state drumlin fields the boundary between the two bed types is a 10 km wide mixed bed of isolated drift drumlins resting on drumlinized rock suggesting a common erosional origin spatial variation in the geomorphology of 2500 drift drumlins indicates that megaridges are clones resulting from the erosion and dissection of larger parent drumlins a large moraine system may mark the final collapse and melt of the ice stream accompanying abrupt flow switching of its margin

ams c 14 dating of deglacial events in the irish sea basin and other sectors of the british irish ice sheet sedimentary sequences deposited by the decaying marine margin of the british irish ice sheet biis record isostatic depression and successive ice sheet retreat towards centres of ice dispersion radiocarbon dating by accelerator mass spectrometry ams of in situ marine microfaunas that are commonly associated with these sequences constrain the timing of glacial and sea level fluctuations during the last deglaciation enabling us to evaluate the dynamics of the bus and its response to north atlantic climate change here we use our radiocarbon dated stratigraphy to define six major glacial and sea level events since the last glacial maximum 1 initial deglaciation may have occurred 18 3 kyr c 14 bp along the northwestern irish coast in agreement with a deglacial age of similar to 22 cl 36 kyr bp for southwestern ireland ice retreated to inland centres and areas of transverse moraine began to form across the north irish lowlands 2 channels cut into glaciomarine deglacial sediments along the western irish sea coast are graded to below present sea level identifying a fall of relative sea level rsl in response to isostatic emergence of the coast 3 marine mud that rapidly infilled these channels records an abrupt rise in global sea level of 10 15 m similar to 16 7 c 14 kyr bp that flooded the irish sea coast and may have triggered deglaciation of a marine based margin in donegal bay 4 intertidal boulder pavements in dundalk bay indicate that rsl similar to 15 0 c 14 kyr bp was similar to present 5 a major readvance of all sectors of the biis occurred between 14 and 15 kyr 14 c bp which overprinted subglacial transverse moraines and delivered a substantial sediment flux to tidewater ice sheet margins this event the killard point stadial indicates that the bus participated in heinrich event 1 6 subsequent deposition of marine muds on drumlins 12 7 c 14 kyr bp indicates isostatic depression and attendant high rsl resulting from the killard point readvance these events identify a dynamic biis during the last deglaciation as well as significant changes in rsl that reflect a combination of isostatic loading and eustatic changes in global sea level c 2005 elsevier ltd all rights reserved

characteristics and origins of lee side stratification sequences in late pleistocene drumlins northern ireland spindle and parabolic shaped drumlins examined at fifty five localities in northern ireland possess stratification sequences on their lee side flanks these forms lack the distinctive steep stoss and tapering lee ends of classical drumlins and tend to occur in linear zones transverse to late pleistocene ice flow in most cases 90 per cent the stratified deposits infill embayments excavated in the lee side of barkhanoid forms and in the remainder 10 per cent they are superimposed on the lee side of whaleback forms the stratification sequences developed as a result of sedimentation in interconnected subglacial water filled cavities and are unlike remanie proglacial sediments moulded by ice into drumlin form stratigraphic evidence indicates that the lee side sequences developed during drumlin streamlining which supports the view that subglacial hydraulic processes played an important role in drumlin formation

the influence of amazon rainfall on the atlantic itcz through convectively coupled kelvin waves abstract using outgoing longwave radiation olr and tropical rainfall measuring mission trmm daily rain rate data systematic changes in intensity and location of the atlantic intertropical convergence zone itcz were detected along the equator during boreal spring it is found that the changes in convection over the tropical atlantic may be induced by deep convection in equatorial south america lagged regression analyses demonstrate that the anomalies of convection developed over the land propagate eastward across the atlantic and then into africa the eastward propagating disturbances appear to be convectively coupled kelvin waves with a period of 6 7 5 days and a phase speed of around 15 m s 1 these waves modulate the intensity and location of the convection in the tropical atlantic and result in a zonal variation of the atlantic itcz on synoptic time scales the convectively coupled kelvin wave has substantial signals in both the lower and upper troposphere both a reanalysis dataset and the qui

sedimentation at the margins of a late pleistocene ice lobe terminating in shallow marine environments dundalk bay eastern ireland late pleistocene morainic sequences around dundalk bay eastern ireland were deposited in a variety of shallow glaciomarine environments at the margins of a grounded ice lobe the deposits are essentially ice proximal delta fan and apron sequences and are divided into two lithofacies associations lithofacies association 1 occurs as a series of morainal banks formed at the southern margin of the ice lobe in a body of water open to influences from the irish sea the morainal banks consist mainly of diamictic muds deposited from turbid plumes and by ice rafting with minor occurrences of turbidites cross bedded gravels subaqueous outwash and massive boulder gravels high density debris flows lithofacies association 2 was deposited in a narrow arm of the sea at the north eastern margin of the ice lobe the deposits consist mainly of a series of coalescing ice proximal gilbert type fan deltas which are interbedded distally with tabular and lens shaped subaqueous deposits the latter are mainly ice rafted diamictons debris flow deposits and subaqueous sands and gravels both lithofacies associations are draped by diamictons formed by a combination of rain out debris flow and traction current activity at a few localities the upper parts of the sequence have been sheared by minor oscillations of the ice sheet margin these sequences form part of an extensive belt of glaciomarine deposits which border the drumlin swarms of east central ireland lithostratigraphic variability is partially related to the arrival of large volumes of debris at the ice lobe margin when the main lowland ice sheet surged during drumlin formation complex depositional continua of this type lack any major erosional breaks and should not be used either as climatic proxies or for stratigraphic correlations

geological constraints on geophysical models of relative sea level change during deglaciation of the western irish sea basin numerical model predictions of low late devensian sea levels around britain are inconsistent with dated sea level indicators contained in the geological record stratigraphies from the western irish sea basin record high sea levels throughout the last deglacial cycle 21 13 ka bp and onshore ice marginal glaciomarine and marine sedimentation sedimentary evidence emphasizes the role played by delayed isostatic uplift coupled with rapid tidewater evacuation of ice from the basin drumlinization and marine downdraw in the northern irish sea basin records subglacial sediment transfer towards tidewater ice margins and headward extension of ice streams deep into the ice sheet around 14 ka bp

identification and significance of ice flow transverse subglacial ridges rogen moraines in northern central ireland in the omagh basin north central ireland subglacial diamict ridges lie transverse to southwestward late devensian ca 23 13 ka ice flow these ridges 0 5 2 5 km long 100 450 m wide 15 35 m high are similar morphologically to rogen moraines which have not been described previously from the british isles the crests of some transverse ridges are streamlined cross cut or overprinted by drumlins whereas other ridges are unmodified and were not affected by later drumlinisation at kilskeery west east trending eskers overlying unmodified transverse ridges post date drumlinisation 17 14 14c ka esker formation shows that the subglacial thermal regime changed from cold based favouring bedform preservation to warm based with meltwater flowing through enclosed subglacial channels patterns of flow transverse ridges and spatial variations in the degree of bedform modification record dynamic changes in regional subglacial environments during the last deglacial cycle this ice mass variability cannot be reconciled with current irish glacial models which are based on immobile ice centres and ordered stages of ice retreat in a wider context these changes in bedform patterns and basal ice regimes have a similar signature to millennial scale ice mass oscillations recorded by dated proxy evidence elsewhere in the amphi north atlantic 1997 john wiley sons ltd

atlantic tropical cyclogenesis a three way interaction between an african easterly wave diurnally varying convection and a convectively coupled atmospheric kelvin wave abstractthis paper explores a three way interaction between an african easterly wave aew the diurnal cycle of convection over the guinea highlands ghs and a convectively coupled atmospheric equatorial kelvin wave cckw these interactions resulted in the genesis of tropical storm debby over the eastern tropical atlantic during late august 2006 the diurnal cycle of convection downstream of the ghs during the month of august is explored convection associated with the coherent diurnal cycle is observed off the coast of west africa during the morning later convection initiates over and downstream of the ghs during the afternoon these convective features were pronounced during the passage of the pre debby aew the superposition between the convectively active phase of a strong cckw and the pre debby aew occurred shortly after merging with the diurnally varying convection downstream of the ghs the cckw aew interaction preceded tropical cyclogenesis by 18 h the cckw provided a favorable environment

analysis of the dominant mode of convectively coupled kelvin waves in the west african monsoon abstract the dominant mode of convectively coupled kelvin waves has been detected over the atlantic and africa during northern summer by performing composite analyses on observational fields based on an eof reconstructed convection index over west africa propagating eastward many waves originate from the pacific sector interact with deep convection of the marine itcz over the atlantic and the continental itcz over west and central africa and then weaken over east africa and the indian ocean it has been shown that they are able to modulate the life cycle and track of individual westward propagating convective systems their mean kinematic characteristics comprise a wavelength of 8000 km and a phase speed of 15 m s 1 leading to a period centered on 6 to 7 days the african kelvin wave activity displays large seasonal variability being highest outside of northern summer when the itcz is close to the equator facilitating the interactions between convection and these equatorially trapped waves the co

sedimentary and structural evolution of a relict subglacial to subaerial drainage system and its hydrogeological implications an example from anglesey north wales uk subglacial drainage systems exert a major control on basal sliding rates and glacier dynamics however comparatively few studies have examined the sedimentary record of subglacial drainage this is due to the paucity of modern analogues the limited recognition and preservation of upper flow regime deposits within the geological record and the difficulty of distinguishing subglacial meltwater deposits from other meltwater sediments e g glacier outburst flood deposits within this study the sedimentological and structural evolution of a subglacial to subaerial ice marginal proglacial drainage system is examined particular emphasis is placed upon the genetic development and preservation of upper flow regime bedforms and specifically recognising them within a subglacial meltwater context facies are attributed to subglacial meltwater activity and record sedimentation within a confined but progressively enlargening subglacial channel system produced under dune to upper flow regime conditions bedforms include rare large scale sinusoidal bedding with syn depositional deformation produced by current induced traction and shearing within the channel margins subglacial sedimentation culminated with the abrupt change to a more ephemeral drainage regime indicating channel abandonment or a seasonal drainage regime retreat of the ice margin led to the establishment of subaerial drainage with phases of sheet flow punctuated by channel incision and anastomosing channel development under diurnal ablation related seasonal discharge the presence of extensive hydrofracture networks demonstrate that proglacial groundwater levels fluctuated markedly and this may have influenced later overriding of the site by an ice stream

teleconnections between the tropical pacific and the sahel a greater understanding of equatorial teleconnections is a key aspect of research into seasonal prediction and future climate change for tropical regions here the impact of pacific sea surface temperature sst anomalies on rainfall fluctuations over the semi arid sahel is explored using a combination of observed and model data the first key topic of this study is the identification of those aspects of anomalous pacific sst variability that are most strongly linked to the sahel one of these also illuminated by earlier studies is similar to the classic el nino southern oscillation pattern in the central and east pacific which in its el nino phase increases the likelihood of sahel drought it is shown here that although a part of this link is indirect operating via atlantic ssts its main effect appears to be through a direct atmospheric teleconnection the other critical pattern of equal importance and revealed here by a novel analysis technique is the large scale zonal gradient of ssts from the west pacific to the east indian ocean if weakened this too enhances the likelihood of sahel drought atmospheric general circulation model experiments forced either by observed or idealized ssts are used to confirm these two influences on the sahel crucially their sahelian impact is substantially reinforced when both are present and additionally further empirical analysis shows them to be largely independent the second key topic is an investigation of the mechanisms for this pacific sahel teleconnection these appear to involve anomalous stationary equatorial waves with communication occurring in both the eastward and westward directions in el nino years for example a kelvin wave emanates across the atlantic from east pacific convective heating anomalies and an equatorial rossby wave appears over the indian ocean in response to the anomalous west pacific indian ocean sst gradients via convective heating anomalies over the indian ocean these interact over africa to enhance large scale subsidence over the sahel thus reducing seasonal rainfall totals interannual changes in propagating equatorial waves or in the residence of subseasonal regimes appear not to play a substantial role

a late pleistocene intertidal boulder pavement from an isostatically emergent coast dundalk bay eastern ireland late pleistocene sequences around dundalk bay eastern ireland record glaciomarine sedimentation near the margin of a grounded ice lobe around 15 ka sp a coastal exposure at cooley point consists of four major facies deposited outside this ice limit 1 a basal mud facies deposited from sediment plumes accumulated following the initial ice marginal retreat inland it contains a well preserved arctic microfauna dominated by the foram elphidium clavatum and the ostracod roundstonia globulifera 2 a flat to undulating boulder facies pavement mostly one clast thick is found pressed into the mud and is characterized by bevelled and striated upper clast surfaces pavement attributes are a result of intertidal activity in a cold climate the boulder source is due to rafting by ice flees from glacigenic debris deposited during an ice advance 3 laminated sand facies drape the pavement and are a result of variable current activity 4 the overlying gravel facies is separated from the sand facies by a marine erosion surface the gravel facies is subaqueous channelized and is overlain by late glacial raised beach ridges locally the gravels have been deformed by ice pressure from partially floating ice flees facies changes record terrestrial submergence and provide evidence for changes in relative sea level during part of the last deglacial cycle the boulder pavement and deformed gravel facies suggest that ice flees and sea ice effects may be more common within stratigraphies along emergent coasts than previously thought though they have a low preservation potential extreme conditions during the deglacial favoured opportunistic microfaunas during mud deposition this event may be related to a major meltwater event within the irish sea basin