small scale waves encountered during aase variability on scales of 200 km or less in the lower stratosphere is examined using potential temperature data collected during the aase campaign enhanced variability is found over regions containing topography presumably due to gravity waves the effect of gravity wave critical levels on topographically induced variability is examined a significant reduction in variability is found when a critical level is present

flux and fate of small mountainous rivers derived sediments into the taiwan strait article i nfo high resolution chirp sonar profiles across the taiwan strait reveal a large silt sand dominated deltaic clinoform up to 50 m thick overlying the postglacial transgressive sea floor across the southeastern central and northern strait delta like configuration and internal depositional sequences indicate a northwestward progradation from western taiwan primarily from the choshui zhuoshui river grain size and mineral data confirm the sediment s taiwanese derivation the chirp profiles together with existing radiocarbon and geomagnetic dates suggest that the clinoform has formed over the past 10 kyr the estimated volume of 375 km 3 of sediment mainly sand and silt suggests a mean annual accumulation of 60 10 6 t yr presumably much of fine mud delivered by taiwanese rivers has been washed away by the local currents and escaped either northeastward into the southern okinawa trough or southward into the south china sea numerous shallow borings onshore over the central western taiwan coastal plain reveal an additional 350 km 3

climatology of upper tropospheric lower stratospheric utls jets and tropopauses in merra abstracta global climatology 1979 2012 from the modern era retrospective analysis for research and applications merra shows distributions and seasonal evolution of upper tropospheric jets and their relationships to the stratospheric subvortex and multiple tropopauses the overall climatological patterns of upper tropospheric jets confirm those seen in previous studies indicating accurate representation of jet stream dynamics in merra the analysis shows a northern hemisphere nh upper tropospheric jet stretching nearly zonally from the mid atlantic across africa and asia in winter spring this jet splits over the eastern pacific merges again over eastern north america and then shifts poleward over the north atlantic the jets associated with tropical circulations are also captured with upper tropospheric westerlies demarking cyclonic flow downstream from the australian and asian monsoon anticyclones and associated easterly jets multiple tropopauses associated with the thermal tropopause break

a high resolution one layer model of breaking planetary waves in the stratosphere numerical integrations of a one layer hemispheric model of the winter stratosphere have been carried out at very high resolution of the order of a fraction of a degree of latitude the numerical experiments simulate planetary wave breaking and polar vortex erosion under conditions far closer to the real winter stratosphere than those assumed in earlier critical layer models the model has implications for stratospheric photochemistry and the antarctic ozone hole problem

bottom currents and sediment transport on san pedro shelf california abstract geoprobe geological processes bottom environmental tripods were used to measure bottom currents pressure and light transmission and scattering and to obtain time series photographs of the sea floor at depths of 23 m and 67 m on san pedro shelf between 18 april and 6 june 1978 winds were light 5 m s with a mean direction from the southwest throughout the measurement period hourly averaged currents 1 m above the bottom never exceeded 21 cm s average speeds were about 5 cm s at the 23 m site and 6 8 cm s at 67 m and the strongest currents were produced by the tides the mean flow of bottom water was less than 3 cm s at both geoprobes and was rather persistently southward offshelf wave generated bottom currents and bottom pressure variations were sampled at hourly intervals average wave period and wave height were 12 8 s and 0 44 m respectively at the 23 m site wave orbital velocities ranged from about 5 to 30 cm s at 23 m and from 2 to 8 cm s at 67 m bottom photographs at 67 m show that the relatively sluggish tide generated and mean currents were below threshold velocity for the silty very fine sand throughout the observational period threshold depth for wave rippling of very fine sand averaged about 28 m with a range from about 12 m to 50 m wave generated currents were the only currents that exceeded threshold levels the wave currents maintained relatively high concentrations of sediment in suspension near the bottom over the inner shelf 25 m and this material principally silt and clay was transported offshore by the weak mean flow approximately 50 of this material was deposited as the bottom orbital velocities decreased to subthreshold values 10 15 cm s the o served movement of fine sediment across the inner shelf can account for a portion of the mud content of the modern silty sands on the central shelf and on the outer shelf however it is clear that the sand fractions which constitute greater than 70 of the central shelf substrate must be transported during high energy winter storms

intra event and inter seasonal behaviour of suspended sediment in flash floods of the semi arid northern negev israel abstract a better understanding of the relation between suspended sediment concentration and water discharge is gained by recognizing amongst other things the different impacts of two types of rainfall event wandering discrete convective or convectively enhanced high intensity storms and ubiquitous multi celled low intensity frontal storms in the levant the first type is characteristic of autumn and spring and the flushing of sediment by the instant onset of high intensity rainfall produces a clockwise hysteresis in the suspended sediment water discharge relation the second type is characteristic of winter and can be marked by either anticlockwise or no hysteresis in the suspended sediment water discharge relation sedimentary flushing is rarely apparent suspended sediment concentrations in flash floods resulting from convective storms are high typically 10 4 10 5 mg l 1 but correlation with water discharge is low r 0 57 in contrast frontal storm runoff carries lower suspended sediment concentrations typically 10 3 10 4 mg l 1 and correlation with water discharge is better r 0 78 this division assists in interpreting the high degree of scatter evident in the overall suspended sediment concentration water discharge relation but it reveals that much is yet to be learned about the interplay of the disposition of cellular storm tracks and sediment source areas

polar stratospheric cloud processed air and potential voracity in the northern hemisphere lower stratosphere at mid latitudes during winter small scale 1000 km features in er 2 measurements of clo o3 h2o n2o and noy outside the lower stratospheric arctic vortex of 1988 1989 are compared with features on potential vorticity maps from the european centre for medium range weather forecasts ecmwf the potential vorticity maps are obtained from tl06 analyses and forecasts some of the plots have been truncated to lower resolution t63 or t42 which smooths out the finer scale structure comparison of these lower resolution plots shows how much detail is lost by excessive smoothing it is also evident that the forecast plots lose fine scale structure due to dissipation in the model resulting mainly from horizontal diffusion we conclude that blobs of air on the maps at latitudes between the vortex edge and 25 n having potential vorticities characteristic of the vortex did indeed originate from the vortex but that the real atmosphere is more sharply differentiated inhomogeneous than the meteorological analyses implying that the potential vorticity maps underestimate the amount of peeled off material areal budgets of the ex vortex air are considered for er 2 flight days and are performed for 24 hour forecasts at t63 and analyses at t42 t63 and t106 resolution at 475 k finally it is concluded that the lower stratospheric arctic vortex of 1988 1989 spread considerable amounts of air to mid latitudes which had been processed by polar stratospheric clouds and that this mechanism is a realistic explanation for the wintertime loss of ozone observed over northern mid latitudes during the last decade

ftir measurements of hf n2o and cfcs during the arctic polar night with the moon as light source subsidence during winter 1992 93 ground based ftir absorption measurements have been performed to study the zenith column densities of hf n2o cfc 12 and cfc 22 the spectra were recorded in the arctic ny alesund spitsbergen 79 n 12 e during winter 1992 93 and spring summer 1993 during the polar night the moon served as light source the analysis of the spectra has been performed in the way to study vertical motions in the atmosphere compared to the summer observations a subsidence of 1 4 km at 12 km altitude and 4 9 km at about 15 km has been calculated for december 1992 for february 1993 the data yield a subsidence of 2 5 km at 12 km altitude and 6 3 km at about 15 km altitude

rapid and widespread dispersal of flood sediment on the northern california margin the dispersal of flood sediment from small river systems is a poorly studied yet potentially important aspect of active continental margin sedimentation in january 1995 during a flood with a 30 yr return period the eel river northern california delivered an estimated 25 3 106 t metric tons of fine grained 62 m sediment to the ocean the flood formed a distinct layer on the sea bed that was centered on the 70 m isobath extended for 30 km along shelf and 8 km across shelf and was as thick as 8 5 cm but contained only 6 106 t of sediment thus 75 of the flood derived sediment did not form a recognizable deposit but was instead rapidly and widely dispersed over the continental margin stratigraphic models of and compilations of sediment flux to active continental margins need to take the dispersive nature of small river systems into account

interhemispheric differences in stratospheric water vapour during late winter in version 4 mls measurements observations of stratospheric water vapour made by the microwave limb sounder mls during the 1992 and 1993 arctic and 1992 antarctic late winters have now been produced using version 4 of the retrieval software these improved measurements are analysed as equivalent latitude zonal means major interhemispheric differences are revealed in the water vapour content of the vortex in the lower stratosphere this technique emphasises mixing ratio gradients at the edges of both polar vortices and a local maximum at the edge of the antarctic vortex there are some small interhemispheric differences in mixing ratios in mid latitudes but they are not strongly related to the dehydration of the antarctic vortex a mixing ratio gradient across the interior of the antarctic vortex at 530k indicates it is not isentropically mixed a strong local maximum in mixing ratio at the centre of the antarctic vortex in the mid stratosphere indicates it is not well mixed in the mid stratosphere also there is little evidence of significant structure inside the arctic vortex

dust transport and synoptic conditions over the sahara arabia deserts during the mis6 5 and 2 1 transitions from grain size chemical and isotopic properties of red sea cores abstract the red sea situated between the sahara and arabia deserts is a natural trap for fine grained particles transported by winds and floods from weathered materials in these deserts derived from the proterozoic crustal granitic and basaltic terrains and phanerozoic carbonates the accumulated fine particles provide valuable information on the climate conditions in the source regions and modes of atmospheric circulation over the red sea region here we report on the grain size mineralogy chemical composition and nd and sr isotope ratios of fine grained insoluble residues ir from acid leaching that were recovered from two deep sea cores kl23 and kl11 drilled in the northern and central red sea respectively we focus on the mis6 5 and mis2 1 transitions kl23 samples are closer to the sahara granitoids field and display significant variations during the mis6 5 transition between end of 7 to 2 and 87sr 86sr of 0 7096 to 0 7114 smaller variations occurred during the mis2 1 transition between end of 5 to 6 and 87sr 86sr of 0 7104 to 0 7118 the kl11 values are closer to the blue nile field which comprises mixtures of granitoid and basalt derived particles during the mis6 5 transition their end varies from 4 to 1 and in 87sr 86sr from 0 7059 to 0 7091 during periods equivalent to sapropels s5 and s1 both cores appear to converge to similar isotope ratios of e nd 2 and 87sr 86sr 0 7095 indicating derivation from the granitoid terrains of the arabian nubian shield occurring adjacent to the red sea and possibly distributed by runoff in terms of synoptic conditions the data indicate that during glacials dust was blown to the northern red sea from the northern sahara desert in association with the mediterranean winter cyclones and to the central red sea from the ethiopian plateau by southern winds that are associated with monsoonal circulation during interglacials especially sapropel intervals monsoonal rains caused erosion and flooding at the arabian nubian shield margins of the red sea during the heinrich events associated with the studied intervals h11 and h1 dust from mixed basaltic granitic terrains was blown from all of the regional sources in the red sea region reflecting severe regional aridity and transport of dust by regional winds when monsoonal activity and mediterranean cyclone activity were weak

millimeter wave spectroscopic measurements over the south pole 1 a study of stratospheric dynamics using n2o observations millimeter wave measurements of n2o and o3 cheng et al 1995 along with several other trace gases have been made nearly continuously from february 1993 through early january 1994 at the amundsen scott station south pole in order to separate chemical and dynamical effects this paper uses the observations of the long lived tracer n2o to study stratospheric dynamics the main emphasis is on the synoptic evolution of the polar vortex over an entire winter period and quantitative results are given for various times and altitudes diabatic descent rates derived for different altitude levels showed the strongest descent in austral fall at high altitudes agreeing fairly well with model predictions by rosenfield et al 1994 subsidence was observed to continue until late october well after polar sunrise the breakdown of the vortex occurred first in the upper stratosphere marked in the intrusion of n2o rich air at these altitudes consistent with trajectory calculations our calculated descent rates are not consistent with the idea that the polar vortex is a flowing processor but instead should be viewed as an isolated system

a new chemical lagrangian model of the stratosphere clams 1 formulation of advection and mixing 1 recent satellite observations and dynamical studies have demonstrated the existence of filamentary structures in chemical tracer fields in the stratosphere it is also evident that such features are often below the spatial resolution of the highest resolution eulerian models that have been used up to the present time these observations have motivated the development of a novel chemical lagranigan model of the stratosphere clams that is based on a lagrangian transport of tracers the description of clams is divided into two parts part 1 this paper concentrates on the lagrangian dynamics i e on the calculation of trajectories and on a completely new mixing algorithm based on a dynamically adaptive grid while part 2 describes the chemical integration and initialization procedure the mixing of different air masses in clams is driven by the large scale horizontal flow deformation and takes into account the mass exchange between the nearest neighbors determined by delaunay triangulation here we formulate an isentropic i e two dimensional version of the model and verify the mixing algorithm using tracer distributions measured during the space shuttle crista 1 experiment where highly resolved stratospheric structures were observed in early november 1994 a comparison of the measured southern hemispheric n2o distribution with clams results allows the intensity of simulated mixing to be optimized the long term robustness of the transport scheme is investigated in a case study of the 1996 1997 northern hemisphere polar vortex this study further provides a dynamical framework for investigations of chemical arctic ozone destruction discussed in part 2

late quaternary history of the ventura mainland shelf california abstract the ventura mainland shelf off california provides an interesting example of sedimentary response to tectonic activity and eustatic sea level fluctuations during the late quaternary a network of 370 km of high resolution seismic reflection profiles provides the basis for the study the high local rates of uplift as well as local basin subsidence have resulted in two distinct styles of sedimentation a late pleistocene angular unconformity separates folded plio pleistocene strata from undeformed upper pleistocene and holocene strata on the northern shelf in contrast the southern shelf is characterized by a thick section of stacked progradational deltaic sequences containing a well preserved record of late quaternary sedimentation sediment overlying the unconformity north of the pitas point fault ranges from 10 to 40 m in thickness whereas the equivalent sequence in the adjacent southern shelf is 80 85 m thick the distribution of upper pleistocene and holocene deposits is controlled by structural features including the pitas point and oak ridge faults and the ventura avenue anticline as well as proximity to fluvial input from the santa clara and ventura rivers within upper pleistocene deposits a pair of buried marine terraces occur at depths of 33 and 50 m below present sea level b p s l terrace deposits consist of a basal coarse grained transgressive deposit which is transitional into a finer grained marine facies these deposits are associated with a period of aggradation during minor late wisconsinan sea level cycles deltaic deposits beneath the southern shelf 4 km north of hueneme submarine canyon suggest that the santa clara river debouched into the sea at this location during the late pleistocene the santa clara river shifted southward during the late wisconsinan and cut a large channel now buried near hueneme canyon this channel indicates that relative sea level was at least 113 m b p s l during the late wisconsinan a smaller channel indicates a fall in sea level to 46 m b p s l during the holocene the oak ridge fault displays a general increase in offset seaward across the shelf with a maximum vertical displacement of 17 m on the saugus upper pleistocene contact displacements on the pitas point fault increase shoreward attaining as much as 40 m of vertical displacement of the late pleistocene unconformity nearshore the pitas point fault vertically displaces the seafloor by 4 m

the spatial and temporal variability of sand erosion across a stabilizing coastal dune field this study aimed at quantifying the temporal and spatial variability in sand erosion and deposition over a coastal dune field in israel these were measured monthly over 2 years using 315 erosion pins over four transects that were placed perpendicular to the coastline vegetation cover was estimated based on aerial photographs and landsat satellite images whereas the relative height was based on a digital elevation model these variables were calculated for the area upwind south west of the erosion pins at various lengths ranging from 15 to 400 m nine geomorphologic units were defined five related to active units and four to stabilized units in active units at least 65 of the temporal variance in the annual absolute changes in sand level was explained by the index of resultant drift potential with most of the sand movement occurring during winter storms local rainfall had no apparent impact on sand mobility due to the low coincidence of sand carrying winds and rainfall in israel during the passage of frontal cyclones as for the spatial variables only a weak correlation was found between sand mobility with the distance from the coastline r 2 18 rather sand erosion and deposition were influenced by vegetation cover and the relative height of an area of 100 200 m upwind the values of soil adjusted vegetation index were significantly negatively correlated with annual absolute changes r 2 40 whereas the relative height was significantly positively correlated r 2 36 applying a multiple regression model 68 of the spatial variability in sand mobility was explained the resulting map of sand activity clearly shows that at this stage of the stabilization process most of the dunes are now disconnected and movement of sand grains from the beach or between the dunes is very limited these methods can be applied into spatial and temporal models of sand mobility thus assessing the impact of different management practices on coastal dunes

surface properties of stabilizing coastal dunes combining spectral and field analyses the coastal dunes of israel have been undergoing a process of stabilization since 1948 one of the major features of this process is a change in the surface properties of the dunes the development of a biological soil crust bsc and a change in the properties of the sand grains themselves in ashdod at the southern coastal plain of israel sand properties that include the bsc their fines silt and clay content and free iron oxide indicating their degree of rubification have been analysed in detail using field and lab spectroscopy methods in addition sand erosion and deposition were measured using erosion pins to determine their effect on the presence of the above mentioned factors it was found that the bsc over these dunes is comprised of green algae that differs in its reflectance spectra from cyanobacterial crust especially in the blue band the crust was found to be particularly developed in the stable areas mainly the interdunes and on the north facing slopes rather than on the south facing slopes a positive correlation was found between the crust fines and chlorophyll content with stable areas showing more developed bsc the stable areas showed also a lower albedo and slightly more developed reddish colour indicating a slightly higher rate of rubification this study demonstrates that the intensity of sand erosion deposition rates affects soil properties with the bsc being the fastest to react to the stabilization process months to several years followed by the content of fine particles several years to a decade whereas the rubification process is a much weaker marker and may need much longer time periods to develop decades to centuries

climatology and interannual variability of wave mean flow interaction in the southern hemisphere abstract the climatology and interannual variability of wave mean flow interaction in the southern hemisphere 20 80 s 0 55 km is described for the winter months of june september based on a sample of four years 1979 82 the stratospheric jet stream shifts downward and poleward over the course of the winter in response to seasonal variations in thermal forcing the shift occurs at different times in different years however so that the months of july and august show substantial interannual variability of monthly mean zonal winds the poleward and downward shift of the jet axis in an individual year is usually abrupt and occurs in association with a burst of upwardly propagating planetary waves the driving of the mean flow in the stratosphere generally has a dipolar structure with easterly accelerations near 40 s and westerly accelerations in polar latitudes the structure of the wave driving is consistent with the structure of the observed mean flow accelerations

the annual cycle of northern hemisphere storm tracks part i seasons abstractin this paper and part ii a comprehensive picture of the annual cycle of the northern hemisphere storm tracks is presented and discussed for the first time it is based on both feature trac

wavebreaking and mixing in the northern hemisphere summer stratosphere the cause of zonal ozone variations observed by the polar ozone and aerosol measurement ii poam ii instrument in the northern hemisphere summer stratosphere from 55 to 65 n and 20 to 30 km is investigated using united kingdom meteorological office ukmo stratospheric data eliassen palm e p flux vectors calculated from the ukmo data show that wave activity propagates vertically from the troposphere into the stratospheric easterlies during the northern hemisphere summer in the layer between 20 and 30 km the e p flux divergence is small but nonzero space time power spectra show that wave power shifts from eastward propagating waves in the upper troposphere to predominantly westward propagating waves in the middle stratosphere consistent with phase speed filtering following the charney drazin theorem air parcel trajectories and effective diffusivity calculations show substantial mixing due to breaking of westward propagating waves in the summer easterly wind regime changes in mixing properties during the summer season are consistent with changes in the mean state and the wave forcing we conclude that breaking of large scale westward propagating waves in the summer easterlies causes meridional transport and the observed local maximum in ozone variability

surface cyclones in the era 40 dataset 1958 2001 part i novel identification method and global climatology abstract a novel method is introduced to generate climatological frequency distributions of meteorological features from gridded datasets the method is used here to derive a climatology of extratropical cyclones from sea level pressure slp fields a simple and classical conception of cyclones is adopted where a cyclone is identified as the finite area that surrounds a local slp minimum and is enclosed by the outermost closed slp contour this cyclone identification procedure can be applied to individual time instants and climatologies of cyclone frequency fc are obtained by simple time averaging therefore unlike most other climatologies the method is not based on the application of a tracking algorithm and considers the size of cyclones in combination with a conventional cyclone center tracking algorithm that allows the determination of cyclone life times and the location of cyclogenesis and cyclolysis additional frequency fields can be obtained for special categories of cyclones that are gener

arctic and antarctic polar vortices 1957 2002 as seen from the era 40 reanalyses 1 we have studied the climatological structure interannual variability and interrelationship of various characteristics of the arctic and antarctic stratospheric vortices at several isentropic levels on the basis of the ecmwf era 40 reanalysis 1957 2002 because of suspect data in the presatellite period in the southern hemisphere only data from 1979 onward are used to study the climatology of the antarctic vortex the climatological structure of the vortices in both hemispheres is mainly consistent with previous climatologies obtained from other data sets a study of the interrelationship between the vortex characteristics suggests that in the arctic a larger vortex is usually colder and stronger whereas in the antarctic winter such a relationship is not established it is found that the arctic psc area has increased during the 1958 2002 period but in contrast to earlier studies no statistically significant trends in size coldness or longevity of the arctic lower stratospheric vortex since 1979 are found during the period 1979 2001 the antarctic spring vortex has become stronger and colder and it breaks up later however the antarctic vortex cooling has not affected the october vortex area which shows only little change for the same period it is found that the area of the antarctic vortex during late winter and spring depends on the planetary wave propagation to the stratosphere in the preceding period whereas the corresponding relationship between these waves and the psc area in october is destroyed by the trends in the psc area

the offshore export of sand during exceptional discharge from california rivers littoral cells along active tectonic margins receive large inputs of sand and gravel from coastal watersheds and commonly lose this sediment to submarine canyons one hypothesis is that the majority of coarse sand and gravel river sediment discharge will be emplaced within and immediately resupply local littoral cells a competing hypothesis is that the infrequent large floods that supply the majority of littoral sediment may discharge water sediment mixtures within negatively buoyant hyperpycnal plumes that transport sediment offshore of the littoral cell here we summarize pre and post flood surveys of two wave dominated california united states river deltas during record to near record floods to help evaluate these hypotheses the 1982 1983 delta at the san lorenzo river mouth and the 2005 delta at the santa clara river mouth flood sedimentation at both deltas resulted in several meters of aggradation and hundreds of meters of offshore displacement of isobaths one substantial difference between these deltas was the thick 2 m aggradation of sand on the inner shelf of the santa clara river delta that contained substantial amounts 50 of littoral grade sediment once deposited on the inner shelf only a fraction 20 of this river sand was observed to migrate toward the beach over the following 5 yr furthermore simple hypopycnal plume behavior could not explain deposition of this sand on the inner shelf thus during an exceptional flood a substantial amount of littoral grade sand was exported offshore of the littoral system at the santa clara river mouth likely from hyperpycnal plume processes and was deposited on the inner shelf

mobilization of fine detritus to the dead sea basin during the late glacial and early holocene abstract the mineralogical grain size and geochemical properties e g nd and sr isotopes mg al ratios of fine detritus that accumulated in the dead sea during the late glacial to early holocene time 22 7 ka are used to identify its sources and modes of transport and to reconstruct the hydroclimate conditions in the dead sea watershed samples were retrieved from the dsddp 5017 1a core that was drilled in the deep floor of the lake and from various exposures of surface cover in the lake s watershed the data show that during most of the late glacial detrital particles were either directly blown mostly from the north sahara desert or were washed from the surface cover loessial soils of the north negev desert and judea desert this picture changed during the end of the last glacial to the early holocene 14 7 ka when the fine detritus showed evidence for contribution from surface cover that contained basaltic soils the contribution of basaltic soils to the fine detritus inventory of the dead sea and to terraces in the jordan valley indicates a period of intense erosion in the northern highlands of the dead sea watershed at an interval that partly coincides with sapropel s1 in contrast during the last interglacial sapropel s5 fine detritus was mostly mobilized to the lake from southern and eastern region of the watershed the formation and accumulation of terraces from this basaltic derived material could be an important factor in the establishment of early agriculture settlements in the jordan valley

trace gas transport in the arctic vortex inferred from atmos atlas 2 observations during april 1993 measurements of the long lived tracers ch4 n2o and hf from the atmospheric trace molecule spectroscopy atmos instrument during the atmospheric laboratory for science and applications 2 atlas 2 space shuttle mission in april 1993 are used to infer average winter descent rates ranging from 0 8 km month at 20 km to 3 2 km month at 40 km in the arctic polar vortex during the 1992 93 winter descent rates in the mid stratosphere are similar to those deduced for the antarctic vortex using atmos atlas 3 measurements in november 1994 but the shorter time period of descent in the arctic leads to smaller total distances of descent strong horizontal gradients observed along the vortex edge indicate that the arctic vortex remains a significant barrier to transport at least until mid april in the lower to middle stratosphere

controls on sediment distribution in the coastal zone of the central california transform continental margin usa abstract we use 10 000 km of high resolution seismic reflection data together with multibeam bathymetry to document complex and highly variable post last glacial maximum lgm sediment distribution and thickness in the coastal zone 10 m isobath to 5 6 km offshore along a 800 km section of central california s transform continental margin sediment thickness ranges from 0 seafloor bedrock to 64 m with a mean of 8 7 m we delineate 25 coastal zone sediment domains and group them based on common geomorphology and sediment occurrence thickest sediment occurs in mountain front and large river domains which comprise 14 5 and 7 9 of the coastal zone and contain 30 1 and 18 2 of coastal zone sediment respectively in contrast small river domains and sediment poor shelf domains comprise 50 7 and 15 7 of the coastal zone and contain 18 4 and 12 7 of its sediment the distribution and thickness of post lgm sediment in the coastal zone is controlled by a combination of tectonics sediment supply and eustasy sediment is derived from a tectonically controlled coastal landscape of rapidly uplifting mountain fronts more slowly uplifting marine terraces and fault bounded headlands and alluvial estuarine troughs sediment supply is maximized along steep landslide prone mountain fronts and at the mouths of large watersheds and minimized along lower relief terraced coastal landscape drained by smaller rivers and creeks in the offshore coastal zone tectonics generates local uplifts and basins and influences shelf width and gradient as well as the locations of some shelf incised submarine canyons sea level rise raises base level drowns estuaries creates accommodation space on the shelf amount based on gradient and isolates the heads of many submarine canyons at or near the shelfbreak comparison of shelf sediment volumes with estimates of unaltered watershed sediment supply reveals that a relatively small proportion of post lgm sediment supply is preserved on the shelf offshore of some of the largest rivers sediments deposited in shoreline and shelf environments have limited preservation potential and the most complete long term geologic record of the post lgm transgression and highstand is likely represented in slope and submarine fan deposits

climatology of cyclogenesis mechanisms in the mediterranean abstract a general climatology of the main mechanisms involved in mediterranean cyclogenesis is presented a diagnostic study of both composite means and case studies is performed to analyze processes occurring in different seasons and in different cyclogenetic regions within the same season it is shown that cyclones that developed over the three most active areas in winter the gulf of genoa the aegean sea and the black sea are essentially subsynoptic lows triggered by the major north atlantic synoptic systems being affected by local orography and or low level baroclinicity over the northern mediterranean coast it is also suggested that cyclones in two or all three of these regions often occur consecutively linked to the same synoptic system in spring and summer thermally induced lows become progressively more important despite the existence of other factors such as the atlas mountains contributing to lee cyclogenesis in northern africa or the extension of the asian monsoon into the eastern

tropical mixing barriers in the lower stratosphere in the geophysical fluid dynamics laboratory skyhi model large scale isentropic mixing in the tropical lower stratosphere is investigated by computing lagrangian trajectories using winds from the geophysical fluid dynamics laboratory skyhi general circulation model the use of model simulated winds avoids some problems with analyzed winds in the tropics during the solstitial seasons a weak mixing zone is present in the tropics in the model simulations the weak mixing zone is relatively isolated from the midlatitude surf zones in the northern and southern hemispheres by two mixing barriers a strong one on the summer hemisphere side and a weak one on the winter side the mixing barriers vary seasonally in response to seasonal variations of the tropical zonal mean zonal flow and wave spectrum the roles of the zonal mean flow and of different parts of the wave spectrum in meridional transport are tested using filter techniques effective meridional diffusion coefficients are calculated by using filtered and antifiltered winds i e winds with selected spatial scales either attenuated or amplified the results suggest that mixing in the tropical easterlies occurs near the critical layers for the large scale zonal wavenumber 10 westward moving waves which is where the waves would be expected to break wave spectrum analysis indicates that during the solstitial seasons there is a zone in the tropics exactly matching the weak mixing zone where there is relatively little power in westward moving waves the tropical mixing barriers are a result of the relative lack of such waves

reconstructing precipitation changes in northeastern africa during the quaternary by clay mineralogical and geochemical investigations of nile deep sea fan sediments abstract clay mineralogy combined with high resolution element geochemistry of core md90 9064 located in the distal part of the nile deep sea fan levantine basin have been investigated to reconstruct rainfall changes in northeastern africa during the quaternary and to determine possible climatic controls clay minerals of core md90 964 are derived mainly from three sedimentary sources the sahara nile river and egyptian wadis and are characterized by contrasted mineralogical composition variations in illite content and logarithm ratios of si al and k al permit the tracking of eolian input from sahara to the mediterranean sea it is suggested that precipitation changes in the sahara are mainly dominated by glacial interglacial cycles such variations are owing to a shift of climatic conditions in the north atlantic from a nao positive like condition in glacial times to a nao negative like condition in interglacial times fe content in the levantine sediments is mostly derived from fe bearing heavy minerals brought by the nile river therefore variations of fe al ratios can be used to establish precipitation changes in the nile river basin long term variation in precipitation in the nile river basin is governed by precessional and eccentricity signals implying that the african monsoon is the most significant controlling factor for precipitation changes in this region precipitation changes in the northeastern coasts of africa are reconstructed using kaolinite contents provided by the egyptian wadis it is reported that precipitation in coastal northeastern africa is mainly of the mediterranean climate type long term variations in rainfall in this region are also affected by the nao like climatic variability and thus dominated by the glacial interglacial cycles

post glacial sediments of the californian shelf from cape san martin to the us mexico border abstract previous workers of the californian shelf from cape san martin to the us mexico border have assembled compilations of high resolution acoustic seismic profiling data from a number of primary sources to examine these data more effectively the region has been divided into four areas for convenience in mapping and partly in response to natural geographic divisions these data plus additional detailed profiling off san onofre south of dana point have made possible calculations of the total volume of unconsolidated post glacial sediments on this narrow active transform margin shelf the san onofre survey shows that there are several well defined buried terraces cut into the bedrock surface these occur at about 20 30 to 35 40 to 50 and 60 to 80 m below present datum dating reported in the literature suggests that the bulk of the sediments are holocene as sea level shifts from glacial to interglacial much of the sediment stored on the shelf at high stand is reworked to deeper water during the fall to the following low stand previous studies suggest that for the large deposits off the santa maria santa ynez and ventura santa clara rivers some sediment may remain after a sea level cycle the estimated total holocene past 10 000 years river discharge for the region based on records of the past century is about 130 km3 thus the total shelf deposit of ca 60 km3 represents about one half of the holocene siliciclastic contribution however the 60 km3 includes basal sediments in the three large river lenses that are probably pre holocene a more probable holocene contributed volume is about 30 km3 previous studies show that biogenic and fluvial contributions are generally little sediment from the areas of relatively high input passes to the starved areas which remain as non depositional low deposition rate or erosional surfaces the major portion of the shelf is sediment starved since only a few small ephemeral streams enter most of the cliffed coastal areas and rocky surfaces are exposed in the inner and outer shelf

persistence of polar stratospheric clouds in the southern polar region observations of antarctic polar stratospheric clouds pscs were examined using the 1 micron aerosol extinction ratio data from the sam ii satellite experiment for the years 1979 1982 and 1984 1987 pscs were sighted between 10 and 25 km and were usually first observed by mid june clouds disappeared earlier at higher altitudes late august near 24 km in most cases and later at lower altitudes late september or october near 16 km it was found that pscs persisted longer in 1985 and 1987 at 18 km and were more frequently observed in september and october 1987 than the other years inference of likely psc formation regions from national meteorological center temperature data indicated that clouds would begin forming in late may and usually disappear in september this analysis confirmed the persistence of colder conditions during the spring of 1987

monitoring the vertical structure of the arctic polar vortex over northern scandinavia during easoe regular n2o profile observations different whole air samplers were flown on large balloons launched from kiruna 67 9 n 21 1 e in the period from 30 november 1991 until 20 march 1992 thirteen vertical profiles of the n2o mixing ratio were obtained from the analyses of the stratospheric air samples collected at altitudes between about 10 km and 31 km the series of profile observations illustrates the temporal variation of the vertical structure of the arctic polar vortex over northern scandinavia during easoe already by mid december the n2o mixing ratios observed at the 600 k isentropic level about 24 25 km were as low as 20 ppbv due to the effect of diabatic subsidence in december subsidence rates of about 100 180 m day were observed dynamic wave activity at the edge of the vortex led to significant sideways erosion at lower altitudes however inside the vortex at altitudes above 600 k n2o mixing ratios of less than 10 ppbv were observed until the end of march

heat low over the saudi arabian desert during may 1979 summer monex abstract in may of 1979 a unique data set was obtained over the desert area in saudi arabia near the surface heat low as part of the garp monsoon experiment monex analysis of the data reveals that during the day a well mixed layer extends up to 650 mb while a stable layer forms above the desert surface during the night calculations of the divergence and kinematic vertical velocity show that the entire troposphere is dynamically active with strong descending motions during the day down to a 1 km deep surface layer which has ascending motion in it there is daytime surface convergence divergence around 850 mb and convergence above 700 mb during the pre sunrise hours there is descending motion down to the surface with divergence at nearly all levels from the surface up to 550 mb and convergence above this level the roles of vertical and horizontal advective as well as radiative processes in the thermal budget have been investigated during the pre sunrise hours the horizontal advective and longwav

interannual variability of the 4 day wave and isentropic mixing inside the polar vortex in midwinter of the southern hemisphere upper stratosphere 1 interannual variations of the flow field and large scale horizontal transport and mixing inside the wintertime polar vortex of the southern hemisphere upper stratosphere are investigated using isentropic winds obtained from the u k met office assimilated data for nine years of 1992 2000 we focused on the midwinter july when the polar vortex is not much distorted although an eastward propagating wave called the 4 day wave is observed in some years in the polar region finite time lyapunov exponents are computed and contour advections are done to examine stirring and mixing in the polar region when the 4 day wave has a large amplitude effective mixing through a stretching and folding process is seen inside the polar vortex finite time lyapunov exponents are sometimes as large as the midlatitudes and the material contours of small areas grow exponentially in time on the poleward side of 70 s such mixing properties are not uniform inside the vortex when the wave is not clearly seen on the other hand wind fields are close to a solid body rotation around the pole and mixing is very small lyapunov exponents are small and the material contours grow linearly in time by the stretching due to the meridional shear of the polar night jet such interannual variability of the strength of the mixing is correlated with the variability of the perturbation amplitude of potential vorticity in the polar region

lagrangian flow in the middle atmosphere the lagrangian view of air flow in the middle atmosphere is studied by computing tens of thousands of particle trajectories in a global primitive equation model this approach focuses attention on the long term fate of air and provides a high resolution view of air transport simulations are carried out for both the northern and southern winters to permit an inter hemispheric comparison the first part of the paper concentrates on transport in the meridional plane trajectories followed for many months show patterns which are well organized on a global scale ensembles of particles followed for a much shorter time are used to calculate a lagrangian mean meridional circulation which shows close similarities to published diabatic circulations calculated from observational data maps of meridional dispersion reveal a broad mid latitude band with well defined boundaries in which rapid dispersion occurs a more detailed visualization of transport in and around the southern polar vortex in late winter shows that small scales are generated in this mid latitude region but not in the vortex nor at low latitudes the ability of the vortex to retain a labelled air mass for many months is clearly demonstrated and the relevance of the results to understanding springtime ozone depletion is discussed

a quasi permeable barrier in the equatorial lower stratosphere analyses of global isentropic maps of potential vorticity from the united kingdom meteorological office ukmo data assimilation system reveal that there is a region of strong meridional potential vorticity pv gradients in the equatorial lower stratosphere a semi lagrangian tracer transport model is used to show that this region of strong pv gradients acts as a quasipermeable barrier to cross equator mass exchange on isentropic surfaces

subsidence of the arctic stratosphere determined from thermal emission of hydrogen fluoride we determine subsidence in the arctic stratospheric vortex from measurements of the column density of hydrogen fluoride using a rotational line in thermal emission the data were obtained with the far infrared spectrometer on board the nasa dc 8 aircraft during the arctic airborne stratospheric expedition from january through march 1992 a wide range of meteorological conditions was sampled both inside and outside the polar vortex region the measured values of subsidence are analyzed as a function of time of year and potential vorticity from this analysis we draw the following conclusions 1 subsidence is strongly correlated with potential vorticity however there appear to be other factors including meteorological conditions which play a lesser role 2 the gradient of subsidence with respect to potential vorticity is large and approximately constant across the vortex wall and is small elsewhere the gradient of subsidence with respect to horizontal distance is dramatically large across the vortex wall 3 there appears to be substantial descent in the early winter vortex from the evidence of the observed subsidence in january and the assumption of zero subsidence at the fall equinox 4 descent continues to occur in late winter with measured vertical velocities similar to that inferred for early winter the average early and late winter vertical velocity at a representative altitude of 18 km is 0 052 0 013 cm s 1 5 at the measured rate of subsidence the time required to flush the stratosphere by one scale height is about 6 months

sedimentary architecture of a low accumulation shelf since the late pleistocene nw iberia abstract continental shelves represent areas of highest economical and ecological importance nevertheless these sedimentary systems remain poorly understood due to a complex interplay of various factors and processes which results in highly individual construction schemes previous studies of sedimentary shelf systems have mainly focused on a limited number of cores retrieved from holocene fine grained depocentres as such the relation between shelf architecture and sedimentary history remains largely obscure here we present new data from the nw iberian shelf comprising shallow seismic profiles a large number of sediment cores and an extended set of radiocarbon dates to reveal the late quaternary evolution of a low accumulation shelf system in detail on the nw iberian shelf three main seismic units are identified these overly a prominent erosional unconformity on top of the basement the lowermost unit 1 is composed of maximal 75 m thick late tertiary to pleistocene deposits the youngest sediments of this unit are related to the last glacial sea level fall unit 2 was controlled by the deglacial sea level rise and shows a maximum thickness of 15 m finally unit 3 comprises deposits related to the late stage of sea level rise and the modern sea level highstand with a thickness of 4 m in mid shelf position two pronounced seismic reflectors separate these main units from each other their origin is related to 1 exposure and ravinement processes during lower sea level and 2 to reworking and re deposition of coarse sediments during subsequent sea level rise according to the sediment core ground truthing sediments of the late tertiary to pleistocene unit predominantly display homogenous fine sands with exceptional occurrences of palaeosols that indicate an ancient exposure surface fine sands which were deposited in the run of the last sea level rise show a time transgressive retrogradational development the seismic reflectors bounding the individual units appear in the cores as 0 1 to 1 m thick deposits consisting either of shell gravels or siliceous coarse sands with gravels the modern sea level highstand stage is characterised by zonal deposition of mud forming a mud belt in mid shelf position and sediment starvation on outer shelf zones radiocarbon ages indicate that this mud belt was the main depocentre for river supplied fine material on the nw iberian shelf at least over the past 5 32 ka bp the initial onset of this depocentre is proposed to be related to a shift in the balance between rate of sea level rise and amount of terrigenous sediment supply various other stratigraphical shelf reconstructions reveal analogies in architecture which indicate that timing and shaping of the individual units on low accumulation shelves is fundamentally controlled by eustatic sea level changes other factors of local importance such as differential elevation of the basement and the presence of morphological barriers formed by rocky outcrops on the seafloor have additionally modifying influence on the sedimentary processes

style and rate of holocene slip palos verdes fault southern california recent studies of the palos verdes fault in the los angeles outer harbor characterize the fault s holocene activity the studies included areal and local geophysical surveys as well as drilling sampling and dating of the subsurface materials the studies identify the fault s location in the shallow subsurface document evidence of holocene strike slip quantify dip slip versus sediment age and quantify the net slip where an early holocene paleochannel crosses the fault the slip rate for the palos verdes fault is constrained to between 2 7 and 3 mm yr for the past 7 8 to 8 ka because the new evidence shows that the palos verdes fault has one of the highest slip rates in the los angeles basin the studies provide significant new insight into the regional tectonics and the seismic risk of the los angeles region using this rate of slip and segmentation models for the fault the coastal los angeles region can expect an mw 7 to 7 2 event about every 400 to 900 years from this potential seismic source

across shelf sediment transport since the last glacial maximum southern california margin correlation of continental shelf slope stratigraphy in santa monica bay southern california with ocean drilling program records for nearby slope basin sites has illuminated the timing and scale of terrigenous sediment dispersal on margin since the last glacial maximum lgm marine flooding surfaces preserved in a transgressive sequence on the santa monica shelf provide a key link between base level elevation and sediment transport across shelf sediment accumulation rates at slope basin sites were maximal ca 15 10 ka well after the lgm decreased during the 12 9 ka transition from fluvial estuarine to fully marine conditions on the shelf and decelerated throughout the holocene to 30 75 of their values at the lgm the deceleration is interpreted to manifest a landward shift in the margin depocenter with the onset of transgressive sedimentation beginning when sea level surmounted the shelf edge ca 13 ka as predicted by sequence stratigraphic models however the records make clear that factors other than base level modulated slope basin accumulation rates during the deglaciation

early evolution of a stratospheric volcanic eruption cloud as observed with toms and avhrr this paper is a detailed study of remote sensing data from the total ozone mapping spectrometer toms and the advanced very high resolution radiometer avhrr satellite detectors of the 1982 eruption of el chichon mexico the volcanic cloud atmosphere interactions in the first four days of this eruption were investigated by combining ultraviolet retrievals to estimate the mass of sulfur dioxide in the volcanic cloud krueger et al 1995 with thermal infrared retrievals of the size optical depth and mass of fine grained 1 10 m radius volcanic ash wen and rose 1994 our study provides the first direct evidence of gravitational separation of ash from a stratospheric gas rich plinian eruption column and documents the marked differences in residence times of volcanic ash and sulfur dioxide in volcanic clouds the eruption column reached as high as 32 km carey and sigurdsson 1986 and was injected into an atmosphere with a strong wind shear which allowed for an observation of the separation of sulfur dioxide and volcanic ash the upper more sulfur dioxide rich part of the cloud was transported to the west in the stratosphere while the fine grained ash traveled to the south in the troposphere the mass of sulfur dioxide released was estimated at 7 1 109 kg with the mass decreasing by approximately 4 1 day after the peak the mass of fine grained volcanic ash detected was estimated at 6 5 109 kg amounting to about 0 7 of the estimated mass of the ash which fell out in the mapped ash blanket close to the volcano over the following days 98 of this remaining fine ash was removed from the volcanic cloud and the effective radius of ash in the volcanic cloud decreased from about 8 m to about 4 m

isentropic mixing in the arctic stratosphere during the 1992 1993 and 1993 1994 winters dynamic isolation of the winter arctic circumpolar vortex during 1992 1993 and 1993 1994 the second and third northern hemisphere winters of the uars mission is studied using quasi horizontal isentropic trajectories ejection of vortex air and entrainment of mid latitude air into the vortex are quantified and compared with climatological values obtained from the analysis of 16 arctic winters a number of unusual features of both winters are discussed the most notable features are the anomalous isolation experienced by the vortex during december 1992 and the unusual degree of isolation and persistence of the vortex during february and march of both years the 1992 1993 winter season is the most consistently isolated vortex on record only during january 1993 when entrainment is large is this pattern of extreme isolation broken 14 refs 3 tabs

holocene sea level curves for santa monica shelf california continental borderland a curve is constructed showing changes in sea level at the santa monica shelf over the past 18 000 years the curve is based on radiocarbon dates sedimentologic data and high resolution seismic stratigraphic analysis of late quaternary terrace deposits sea level was 117 meters below its present position about 18 000 years ago during the first 8000 years of the flandrian transgression sea level rose to at least 24 meters fell to about 46 meters and then rose to 20 meters all below present sea level subsequently sea level rose more slowly and without discernible interruption to its present position

the mean meridional transport circulation of the troposphere in an idealized gcm abstract large numbers of particle trajectories are used to characterize the mean meridional transport circulation of an idealized general circulation model gcm the gcm has a uniform land surface no topography or land sea contrasts and no seasonal cycle the trajectories are analyzed using both lagrangian mean statistics and an approach based on the green s function of the tracer transport equation it is shown that the distribution of particle trajectories provides an estimate of the ensemble mean green s function for the inviscid transport equation lagrangian means have a number of problems that render their interpretation difficult including boundary effects and selection of the appropriate averaging period the green s function on the other hand provides a quantitative description of the transport circulation that is easy to visualize and interpret the results demonstrate that within the idealized model the atmosphere can be divided into three parts the southern hemisphere extratropics the

geochemical characterization of contemporary fine detritus in the dead sea watershed abstract reconstruction of paleo synoptic conditions e g past atmospheric circulation involves tracing the origins and routes of transport of particles comprising eolian archives i e desert dust lacustrine deposits that accumulated in the quaternary lakes filling the dead sea basin include remobilized eolian desert dust that was washed to the lakes by floods here we analyze the mineralogical chemical compositions e g mg al ratios and 87sr 86sr and 143nd 144nd end values isotope ratios of fine siliciclastic particles that form the modern surface cover of the dead sea watershed e g loess mountain soils and flood particles that are mobilized to the lake during distinct synoptic conditions the data comprises reference data set that can be used for paleo synoptic interpretation enhancing our ability to decipher the paleoclimate history during the quaternary in the levant the end values and 87sr 86sr ratios of the fine detritus lie between 8 and 6 and 0 7035 to 0 7188 reflecting the values of erosional products of granitoids that are exposed in the sahara and arabia deserts and the unradiogenic sr from local soils in the dead sea watershed particles with low mg al ratios i e 0 17 0 31 are transported by the western winds associated with the mediterranean cyclones transporting dust from the sahara while particles with high mg al ratios 0 27 0 68 are associated with storms blowing dusts from east to the dead sea watershed saudi arabia and syrian deserts during red sea trough synoptic conditions fine particles blown from the sahara deserts during winter storms are rapidly washed to the lake by subsequent floods whereas the particles blown during dry storms associated with red sea trough synoptic conditions accumulate on the surface of the dead sea watershed and can be washed later to the lake during extensive rain events

north anatolian fault in the gulf of izmit turkey rapid vertical motion in response to minor bends of a nonvertical continental transform 1 the catastrophic rupture of the north anatolian fault east of the marmara sea on 17 august 1999 highlighted a need for mapping the underwater extension of that continental transform a new bathymetric map of izmit gulf indicates that the fault follows the axis of the gulf with a few minor bends submerged shorelines and shelf breaks that formed during the last glacial maximum provide markers to quantify vertical deformation variable tilting of these horizons reveals that vertical deformation is highest just south of the fault a correlation between vertical deformation of the southern fault block and distance to fault bends can be accounted for by a fault dipping steeply to the south hence subsidence uplift of the southern hanging wall block would be expected where the fault strikes at a slightly transtensional transpressional orientation to relative plate motion subsidence reaches about 8 mm yr west of the town of golcuk and might be accommodated in 1 2 m subsidence events during large earthquakes that scenario is compatible with the tsunami runups and the coseismic subsidence of the southern shore that occurred in 1999 seafloor morphology also suggests that earthquakes are accompanied by widespread gas and fluid release the periphery of the deepest basin displays a hummocky texture diagnostic of sediment fluidization and mud volcanoes occur west of hersek peninsula that might be activated by earthquakes finally the backscatter imagery reveals a series of lineaments midway through the gulf that are interpreted as products of the 1999 surface rupture the seafloor is undisturbed farther west suggesting that surface slip decreased to an insignificant level beyond hersek possibly the stress shadow from the 10 july 1894 earthquake which was felt strongly along the western izmit gulf contributed to arrest the 1999 surface rupture

soudano saharan depressions and their importance for precipitation and dust a new perspective on a classical synoptic concept according to a classical synoptic concept soudano saharan depressions ssds are surface lows that track westward over tropical west africa curve anticyclonically across the sahara and may then transform into eastward moving mediterranean cyclones occurrence frequency and track location undergo a marked seasonal cycle interactions between troughs in the upper level westerlies and mid level african easterly waves have been suggested as a mechanism for their formation ssds have been reported to be associated with dust storms and precipitation over northern africa this paper presents the first ever systematic investigation of ssds using re analysis and satellite data depressions are identified and tracked objectively based on closed contours in 0000 utc fields of 925 hpa geopotential height from the european centre for medium range weather forecasts era interim re analysis 1989 2008 to classify as potential ssds tracks must i start to the south of 20 n ii intersect 15 30 n 10 w 30 e iii cover a meridional distance of at least 10 latitude and iv have a minimum lifetime of 24 hours even with a relatively low threshold of 4 gpm only 50 potential ssds are found annual average 2 5 monthly range 0 6 lagrangian and eulerian composite analyses reveal that the identified systems i are mostly shallow lee troughs of the central saharan and atlas mountains during the warm season without a well defined cyclonic wind field ii do not show the seasonal track variation described in the literature iii mostly occur in association with high pressure anomalies over the mediterranean sea and iv are not associated with significant increases in dustiness and precipitation these results strongly suggest that the disturbances described as ssds do not manifest themselves as traceable low level depressions calling for a fundamental revision of the classical concept in the literature copyright 2011 royal meteorological society

modeling the quasi biennial oscillation s influence on isentropic tracer transport in the subtropics tracer transport in the lower stratosphere is investigated using an off line semi lagrangian transport model and winds from a mechanistic three dimensional middle atmosphere model interpolated to the 650 k isentropic surface over a winter season by comparing two simulations the effect of the quasi biennial oscillation s qbo s easterly or westerly wind phases on low latitude transport is examined especially regarding the formation of an apparent subtropical transport barrier at the equatorward edge of the surf zone the tracer field is diffused less than potential vorticity pv and shows sharper gradients and finer structures developing over the winter in both qbo phases the winter extratropical surf zone is bounded by large tracer gradients equatorward of about 15 latitude the inability of quasi stationary rossby waves to propagate into qbo easterlies leads to a much sharper edge forming between the rapidly stirred extratropical surf zone and the relatively unstirred tropics during the easterly qbo phase than occurs during the westerly qbo phase in the westerly phase some rossby wave activity can propagate across the equatorial westerlies and break on reaching the summer hemisphere easterly winds causing mixing there simulations using a tracer initially confined to the tropics show that more tropical air is mixed out to the winter extratropics by rossby wave stirring when the qbo phase is easterly despite the sharper band of stronger tracer or pv gradient which separates the tropics and the winter extratropics in this phase while air was mixed out of the tropics in both qbo phase simulations neither qbo phase simulation showed extratropical air being irreversibly mixed into the tropics these results are related to observations of the tropical reservoir of stratospheric aerosols especially the dynamics and transport of its winter hemisphere boundary

climate forcing of terrigenous sediment input to the central mediterranean sea since the early pleistocene clay mineralogy of odp site 964 in the ionian sea was investigated in order to reconstruct variations in detrital sediment input to the central mediterranean sea and to reconstruct the corresponding climatic processes over the last 1500 kyr the clay mineralogy of odp site 964 indicates a major shift in sedimentary sources from the saharan desert which is characterized by a clay mineral assemblage of palygorskite illite kaolinite to the apennine peninsula characterized by an illite smectite clay assemblage at 700 kyr prior to 700 kyr the low smectite content 10 20 and the strong precessional cycles in the variations of kaolinite illite and palygorskite indicate that terrigenous sediment to the central mediterranean sea mainly originated from saharan dust and was strongly affected by the african monsoon with a minor contribution of sediment deriving from the apennine peninsula an increase in the illite kaolinite ratio in the maxima of boreal summer insolation indicates a decreased dust input from the southern sahara as a result of the northward displacement of the african monsoon itcz system a gradual increase in smectite content has been identified between 1050 and 500 kyr probably associated with environmental vegetation and or hydrological changes in southern europe linked to the occurrence of the mpt and partly to tectonic uplift in the apennine peninsula a marked increase in terrigenous flux is observed at around 350 kyr coeval with a major phase of uplift in the calabrian arc

sr isotope record of quaternary marine terraces on the california coast and off hawaii abstract strontium isotopic ratios of dated corals have been obtained from submerged reefs formed during quaternary glacial periods off the hawaiian islands these data combined with data from deep sea sediments tightly constrain the secular variation of marine 87 sr 86 sr for the past 800 000 yr although long term trends are apparent no significant 0 02 rapid 87 sr 86 sr were resolved nor did we observe any samples with 87 sr 86 sr greater than that of modern seawater strontium in mollusks from elevated marine terraces formed during interglacial periods on the southern california coast show resolvable and consistent variations in 87 sr 86 sr which when compared to the trend of quaternary marine 87 sr 86 sr can be used to infer uplift rates and define approximate ages for the higher terraces the sr isotope age estimates indicate that uplift rates vary among crustal blocks and were not necessarily constant with time no contrast in sr isotopic ratios between similar age hawaiian and california fossils was observed confirming that any change in marine 87 sr 86 sr from glacial to interglacial periods must be small a realistic appraisal of the potential of sr isotope stratigraphy for chronometric applications in the quaternary suggests that the technique will be limited to relatively coarse distinctions in age

a 250 ka sedimentary record from a small karstic lake in the northern levant yammouneh lebanon paleoclimatic implications the levant influenced by both the mediterranean sea and the saharan arabian deserts is a key region for understanding climatic changes in response to glacial interglacial boundary conditions that have greatly affected regional hydrology here we present the first long term paleoenvironmental record from the northern levant presently much wetter than the southern levant our record derives from the multi proxy study of a sediment core 36 m long retrieved from the small intra mountainous tectonic basin of yammouneh lebanon which is mainly supplied by karstic springs sediments consist of a thick accumulation of brownish to greenish clayey silts interrupted by intervals of whitish marls composed of caco3 rich material the core chronology is based on radiometric dating 14c and u th and paleomagnetic techniques the sedimentary sequence spans approximately the last two glacial interglacial cycles 250 ka carbonate content is relatively high throughout the profile due to a perennial input of detrital calcite from the watershed but varies significantly the marls are mostly composed of authigenic and biogenic calcite and reflect lacustrine environments with high carbonate productivity during peaks of interglacial periods their occurrence suggests low physical erosion of the basin slopes which were covered by arboreal vegetation and intense karstic water circulation under warm and relatively wet conditions in agreement with pollen data the clayey silts are dominated by quartz and clay minerals and a few amounts of k feldspars and dolomite they are characterized by high concentration in magnetic particles and high relative concentrations of si al k and fe considered as strictly of detrital origin due to the carbonated nature of the watershed quartz and k feldspars are attributed to eolian origin from a distal source the clayey silt intervals generally suggest palustrine conditions with abrupt flows responsible for runoff derived material or subaerial environments and low local water availability in particular during the last glacial maximum high si al and k al ratios during interglacials are attributed to relatively high eolian dust contribution due to the decrease of local detrital inputs our study reveals significant differences between yammouneh and lake records from the dead sea basin southern levant the latter showing high low levels during glacial interglacial periods these hydrological differences might reflect either changes in the north south ns rainfall gradient in response to the development of the northern ice sheet and the southward migration of the westerly belt or local factors i e a decrease in efficient precipitation and water availability at yammouneh during the coldest glacial periods e g the last glacial maximum due to water storage by ice caps on the mount lebanon range and frozen soils in the yammouneh basin

the sharav cyclone observations and some theoretical considerations a special study of the sharav cyclones indicates that they are the result of large scale weak baroclinicity enhanced by vigorous boundary layer baroclinicity between the north african coast and the mediterranean it is illustrated how the jet stream plays a major role in the vertical circulation in producing a complex cyclonic circulation dominated by at least three mechanisms large scale interior baroclinicity boundary layer baroclinicity and jet stream related circulations the main characteristics of the sharav cyclone also called the saharan depression or khamsin depression in the mediterranean are reviewed unlike the cold winter cyclone the sharav cyclone is a spring cyclone its tracks lie mainly along the north african coast and turn to the north near the southeastern mediterranean its warm front is active and is sometimes associated with extremely high surface temperatures its cold front is shallow the sharav cyclone moves eastward relatively fast typically faster than 10 m s 1 and with a small speed variability in general there is an upper level trough to the west of the surface low and the surface horizontal scale is of the order of 500 1000 km finally it is frequently associated with heavy dust sand storms and low visibilities some of these features are illustrated in a case study of the april 28 30 1986 cyclone vertical cross sections indicate a deep circulation associated with the exit region of an upper level jet in addition to presenting evidence that the sharav cyclone is a deep tropospheric circulation it is shown that the transverse indirect circulation at the exit region of the jet is a major component of its circulation the classic two level baroclinic model phillips 1954 is applied the effects of the major diabatic heating due to the sensible heat flux above the north african desert and the large north to south temperature gradients are incorporated through the thermal wind of the basic state the model predicts the fast eastward motion the relatively smaller horizontal scale and the fast growth rate furthermore the model predicts an annual maximum growth rate in april and a secondary peak in october which agrees with the frequency of occurrences of the sharav cyclones

trace a trajectory intercomparison 2 isentropic and kinematic methods kinematic and isentropic trajectories are compared quantitatively during a single 5 day period october 13 18 1992 when several flights for the transport and atmospheric chemistry near the equator atlantic trace a experiment were conducted off the west coast of africa european centre for medium range weather forecasts ecmwf data are used to compute the 5 day backward trajectories arriving at locations over the south atlantic ocean and nearby parts of south america and southern africa two versions of kinematic trajectories are examined one version employs vertical motions supplied with the ecmwf data these trajectories often differ greatly from those based on the isentropic assumption the kinematic trajectories usually undergo considerably greater vertical displacements than their isentropic counterparts however most diabatic rates are consistent with those of synoptic scale systems ratios of acetylene to carbon monoxide are related to backward trajectories at various locations along a trace a flight a second version of kinematic trajectories employs vertical motions diagnosed from ecmwf horizontal wind components using the continuity equation these vertical motions are stronger than those supplied with the ecmwf data causing many of the trajectories to have larger vertical displacements and considerably different paths than the original kinematic versions many of these kinematic trajectories undergo diabatic rates that exceed generally accepted values on the synoptic scale this occurs in part because the diagnosed vertical motions are inconsistent with the ecmwf data the research indicates that the kinematic procedure yields realistic 5 day backward trajectories when the three dimensional wind data are available from a numerical model or other dynamically consistent data set such as provided by ecmwf

particles in the great pinatubo volcanic cloud of june 1991 the role of ice 1 pinatubo s 15 june 1991 eruption was earth s largest of the last 25 years and it formed a substantial volcanic cloud we present results of analysis of satellite based infrared remote sensing using advanced very high resolution radiometer avhrr and tiros operational vertical sounder high resolution infrared radiation sounder 2 tovs hirs 2 sensors during the first few days of atmospheric residence of the pinatubo volcanic cloud as it drifted from the philippines toward africa an so2 rich upper 25 km portion drifted westward slightly faster than an ash rich lower 22 km part though uncertainty exists due to difficulty in precisely locating the ash cloud the pinatubo clouds contained particles of ice ash and sulfate which could be sensed with infrared satellite data multispectral ir data from hirs 2 were most useful for sensing the pinatubo clouds because substantial amounts of both ice and ash were present ice and ash particles had peak masses of about 80 and 50 mt respectively within the first day of atmospheric residence and declined very rapidly to values that were 10 mt within 3 days ice and ash declined at a similar rate and it seems likely that ice and ash formed mixed aggregates which enhanced fallout sulfate particles were detected in the volcanic cloud by ir satellites very soon after eruption and their masses increased systematically at a rate consistent with their formation from so2 which was slowly decreasing in mass during the same period the initially detected sulfate mass was 4 mt equivalent to 3 mt so2 and after 5 days was 12 16 mt equivalent to 9 12 mt so2

mountain torques and synoptic systems in the mediterranean the mountains surrounding the mediterranean exert torques t during the passage of north atlantic systems which affect the angular momentum of the airflow passing over and around the massifs the alps the atlas range and the orographic block of asia minor are selected to investigate the typical flow conditions during torque events these mountain ranges are small enough to justify a local angular momentum analysis both the zonal and the meridional components of a mountain s torque t and t are used as stratification parameters in a statistical investigation of the interaction of large scale perturbations with this mountain how are these flows affected by the obstacle a simple scheme is tested which attempts to interpret results the torque analysis singles out eastward moving large scale systems their isobars are oriented from southwest northwest to northeast southeast near the mountain in zonal torque t t cases the massifs tend to generate a low level distortion of the pressure field such that the angular momentum of the flow over the mountain is reduced these results can be explained within the framework of the scheme the influence of the mountains on the pressure field is seen only at heights 4000 m the low level distortions of the pressure field contribute positively to the total torque for lags 0 in the alps and for all lags 2 2 days in asia minor where only t is evaluated the impact of the atlas mountains is seen only at 0

the glacial interglacial variation of seawater osmium isotopes as recorded in santa barbara basin abstract the pleistocene deposits of santa barbara basin sbb show laminations during interglacial periods typical of an anoxic or suboxic depositional environment and more sporadically laminated deposits during glacial times indicating a more oxic environment of deposition the 187os 188os value of sediment leaches varies as a function of climate consistent with a more radiogenic os signal during interglacial times and less radiogenic os values more typical of glacial times the signal is confounded by contributions from a high os detrital component with a variable 187os 188os value but generally agrees with prior result from deposits from other marine environments

the structure of the polar vortex reconstruction of the airborne antarctic ozone experiment and airborne arctic stratosphere expedition aircraft constituent observations radiative heating rate computations and trajectory calculations are used to generate comparative pictures of the 1987 southern hemisphere sh late winter and 1989 northern hemisphere nh mid winter lower stratospheric polar vortices overall both polar vortices define a region of highly isolated air where the exchange of trace gases occurs principally at the vortex edge through erosional wave activity aircraft measurement showed that 1 between 50 and 100 mbar horizontally stratified long lived tracers such as n20 are displaced downward 2 3 km on the cyclonic poleward side of the jet with the meridional tracer gradient sharpest at the jet core 2 eddy mixing rates computed using parcel ensemble statistics are an order of magnitude or more lower on the cyclonic side of the jet compared to those on the anticyclonic side 3 poleward zonal mean meridional flow on the anticyclonic side of the jet terminates in a descent zone at the jet core despite the similarities between the sh and nh winter vortices there are important differences during the aircraft campaign periods the sh vortex jet core was located roughly 8 o 10 o equatorward of its nh counterpart after pole centering as a result of the arger size of the sh vortex the dynamical heating associated with the jet core descent zone is displaced further from the pole the sh polar vortex can therefore approach radiative equilibrium temperatures over a comparatively larger area than the nh vortex the subsequent widespread formation of polar stratospheric clouds within the much colder sh vortex core gives rise to the interhemispheric differences in the reconstructed h20 noy c10 and 03 species which are affected by polar stratospheric clouds

terrestrial source to deep sea sink sediment budgets at high and low sea levels insights from tectonically active southern california sediment routing from terrestrial source areas to the deep sea influences landscapes and seascapes and supply and filling of sedimentary basins however a comprehensive assessment of land to deep sea sediment budgets over millennia with significant climate change is lacking we provide source to sink sediment budgets using cosmogenic radionuclide derived terrestrial denudation rates and submarine fan deposition rates through sea level fluctuations since oxygen isotope stage 3 younger than 40 ka in tectonically active spatially restricted sediment routing systems of southern california we show that source area denudation and deep sea deposition are balanced during a period of generally falling and low sea level 40 13 ka but that deep sea deposition exceeds terrestrial denudation during the subsequent period of rising and high sea level younger than 13 ka this additional supply of sediment is likely owed to enhanced dispersal of sediment across the shelf caused by seacliff erosion during postglacial shoreline transgression and initiation of submarine mass wasting during periods of both low and high sea level land and deep sea sediment fluxes do not show orders of magnitude imbalances that might be expected in the wake of major sea level changes thus sediment routing processes in a globally significant class of small tectonically active systems might be fundamentally different from those of larger systems that drain entire orogens in which sediment storage in coastal plains and wide continental shelves can exceed millions of years furthermore in such small systems depositional changes offshore can reflect onshore changes when viewed over time scales of several thousand years to more than 10 k y

invited review hydroclimatic changes in northern levant over the past 400 000 years the levant a transition zone between the temperate mediterranean domain and subtropical deserts is a key area to study the latitudinal migrations of zonal climatic belts in response to glacial interglacial conditions the region underwent large climatic shifts during the late quaternary with dramatic impacts on water resources and human populations this paper presents the unique long term hydro climatic record ca 400 ka from northern levant derived from a sediment core taken from a small tectonic basin of northern lebanon the currently wettest area of the levant combined biotic pollen biologic aquatic remains and abiotic proxies sediment properties carbonate oxygen isotopes reveal relatively high water availability during interglacials and generally drier glacials periods during the past four climate cycles these general trends are in line with pollen records from southeastern and near east mediterranean areas but differ from some paleohydrological records from the southern levant southward migrations of the rain bearing mid latitude westerlies during glacial periods and regional land topography are likely to explain the observed regional climate signatures in addition distinctive climate signatures of the successive wetter drier intervals reflect interactions between global forcing insolation atmospheric greenhouse gas concentration eastern mediterranean sea surface conditions intimately linked to north atlantic climate and to ice sheet and sea ice extent at high northern latitudes land topography and local hydrogeological processes our record brings new benchmarks for understanding the spatial heterogeneity of eastern mediterranean responses to global climate changes