large scale dynamics of the mesosphere and lower thermosphere an analysis using the extended canadian middle atmosphere model the extended canadian middle atmosphere model is used to investigate the large scale dynamics of the mesosphere and lower thermosphere mlt it is shown that the 4 day wave is substantially amplified in southern polar winter in the presence of instabilities arising from strong vertical shears in the mlt zonal mean zonal winds brought about by parameterized nonorographic gravity wave drag a weaker 4 day wave in northern polar winter is attributed to the weaker wind shears that result from weaker parameterized wave drag the 2 day wave also exhibits a strong dependence on zonal wind shears in agreement with previous modeling studies in the equatorial upper mesosphere the migrating diurnal tide provides most of the resolved westward wave forcing which varies semiannually in conjunction with the tide itself resolved forcing by eastward traveling disturbances is dominated by smaller scales nonmigrating tides and other planetary scale waves play only a minor role in the zonal mean zonal momentum budget in the tropics at these heights resolved waves are shown to play a significant role in the zonal mean meridional momentum budget in the mlt impacting significantly on gradient wind balance balance fails at low latitudes as a result of a strong reynolds stress associated with the migrating diurnal tide an effect which is most pronounced at equinox when the tide is strongest resolved and parameterized waves account for most of the imbalance at higher latitudes in summer this results in the gradient wind underestimating the actual eastward wind reversal by up to 40

nonlinear horizontal diffusion for gcms abstract the mixing length based parameterization of horizontal diffusion which was originally proposed by smagorinsky is revisited the complete tendencies of horizontal momentum diffusion the associated frictional heating and horizontal diffusion of sensible heat in spherical geometry are derived the formulations are modified for the terrain following vertical hybrid coordinate system in a way that ensures energy and angular momentum conservation at each layer test simulations with a simple general circulation model run at t42 horizontal resolution and for permanent january conditions confirm the conservation properties and highlight the enhancement of nonlinear horizontal diffusion in areas of high baroclinic activity the simulated internal variability is dependent on the nature of the horizontal diffusion with high frequency variability being enhanced over the northern continents and low frequency variability being increased decreased over the pacific atlantic ocean when using nonlinear

eastward propagating planetary waves with periods of 1 5 days in the winter antarctic stratosphere as revealed by merra and lidar 1 this study presents the first report of planetary wave pw influences on significant temperature perturbations 10 20 k within a course of one day detected by an fe lidar from 35 to 51 km in the austral winter of 2011 at mcmurdo 77 8 s 166 7 e antarctica such large temperature perturbations are captured in the modern era retrospective analysis for research and applications merra data and correspond to various phases of eastward propagating pws with periods of 1 5 days as revealed in merra the strongest pw dominating the temperature perturbations has a period of 4 5 days with wavenumber 1 a 2 day wave with wavenumber 2 and a 1 25 day wave with wavenumber 3 also have significant influences we find that these eastward propagating pws are highly confined to winter high latitudes likely because negative refractive indices equatorward of 45 s result in evanescent wave characteristics and prevent the pws from propagating to lower latitudes the eliassen palm flux divergence and instability analyses suggest that barotropic baroclinic instability at 50 s 60 s induced by the stratospheric polar night jet and or the double jet structure is the most likely wave source such instability in the region poleward of 70 s is a complementary source for the 4 day wave where we find that the heat flux of the 4 day wave is large and transported from 70 s toward the pole above 40 km this transport direction is likely linked to the meridional gradient of background temperature the migrating diurnal tide near 78 s in the upper stratosphere is discernable but significantly smaller than that of the dominant 4 day wave

mesoscale eddies in the northeastern pacific tropical subtropical transition zone statistical characterization from satellite altimetry 1 mesoscale eddies in the northeastern pacific tropical subtropical transition zone 16 n 30 n 130 w 102 w are analyzed using nearly 18 years of satellite altimetry and an automated eddy identification algorithm eddies that lasted more than 10 weeks are described based on the analysis of 465 anticyclonic and 529 cyclonic eddy trajectories we found three near coastal eddy prolific areas 1 punta eugenia 2 cabo san lucas and 3 cabo corrientes these three areas are located in places where the coastal morphology changes abruptly and strong surface current intensification occurs at some phase of the seasonal cycle although mesoscale eddies in these areas have been previously reported this study provides their first statistically supported characterization punta eugenia showed the highest eddy production with more cyclones generated followed by cabo corrientes also with more cyclones and cabo san lucas with more anticyclones cabo corrientes eddies showed the highest mean values in propagation speed swirling speed and eddy kinetic energy whereas punta eugenia eddies showed the lowest values cyclonic eddies increased their distance traveled and duration from south to north in contrast anticyclonic eddies increased from north to south in average anticyclones tend to travel faster than cyclones in all the subregions these long lived eddies were mainly nonlinear and therefore can redistribute coastal waters relatively far into the open ocean the peaks in the seasonal signal of eddy generation can be associated with the peaks in the strength of the offshore currents and or in the coastal upwelling index no clear relationship could be established between el nino events and eddy generation

extended canadian middle atmosphere model zonal mean climatology and physical parameterizations 1 this paper describes the energetics and zonal mean state of the upward extension of the canadian middle atmosphere model which extends from the ground to 210 km the model includes realistic parameterizations of the major physical processes from the ground up to the lower thermosphere and exhibits a broad spectrum of geophysical variability the rationale for the extended model is to examine the nature of the physical and dynamical processes in the mesosphere lower thermosphere mlt region without the artificial effects of an imposed sponge layer which can modify the circulation in an unrealistic manner the zonal mean distributions of temperature and zonal wind are found to be in reasonable agreement with observations in most parts of the model domain below 150 km analysis of the global average energy and momentum budgets reveals a balance between solar extreme ultraviolet heating and molecular diffusion and a thermally direct viscous meridional circulation above 130 km with the viscosity coming from molecular diffusion and ion drag below 70 km radiative equilibrium prevails in the global mean in the mlt region between 70 and 120 km many processes contribute to the global energy budget at solstice there is a thermally indirect meridional circulation driven mainly by parameterized nonorographic gravity wave drag this circulation provides a net global cooling of up to 25 k d 1

gravity wave induced anomalous potential vorticity gradient generating planetary waves in the winter mesosphere abstractthis study shows that gravity wave gw forcing gwf plays a crucial role in the barotropic baroclinic instability that is frequently observed in the mesosphere and considered an origin of planetary waves pws such as quasi 2 day and quasi 4 day waves simulation data from a gw resolving general circulation model were analyzed focusing on the winter northern hemisphere where pws are active the unstable field is characterized by a significant potential vorticity pv maximum with an anomalous latitudinal gradient at higher latitudes that suddenly appears in the midlatitudes of the upper mesosphere this pv maximum is attributed to an enhanced static stability that develops through the following two processes 1 strong pws from the troposphere break in the middle stratosphere causing a poleward and downward shift of the westerly jet to higher latitudes and 2 strong gwf located above the jet simultaneously shifts and forms an upwelling in the midlatitudes causing a significant increase in

gravity wave characteristics in the southern hemisphere revealed by a high resolution middle atmosphere general circulation model abstractgravity wave characteristics in the middle to high latitude southern hemisphere are analyzed using simulation data over 3 yr from a high resolution middle atmosphere general circulation model without using any gravity wave parameterizations gravity waves have large amplitudes in winter and are mainly distributed in the region surrounding the polar vortex in the middle and upper stratosphere while the gravity wave energy is generally weak in summer the wave energy distribution in winter is not zonally uniform but it is large leeward of the southern andes and antarctic peninsula linear theory in the three dimensional framework indicates that orographic gravity waves are advected leeward significantly by the mean wind component perpendicular to the wavenumber vector results of ray tracing and cross correlation analyses are consistent with this theoretical expectation the leeward energy propagation extends to several thousand kilometers which explains part of the gravity wave distribution aro

general aspects of a t213l256 middle atmosphere general circulation model 1 a high resolution middle atmosphere general circulation model gcm developed for studying small scale atmospheric processes is presented and the general features of the model are discussed the gcm has t213 spectral horizontal resolution and 256 vertical levels extending from the surface to a height of 85 km with a uniform vertical spacing of 300 m gravity waves gws are spontaneously generated by convection topography instability and adjustment processes in the model and the gcm reproduces realistic general circulation in the extratropical stratosphere and mesosphere the oscillations similar to the stratopause semiannual oscillation and the quasi biennial oscillation qbo in the equatorial lower stratosphere are also spontaneously generated in the gcm although the period of the qbo like oscillation is short 15 months the relative roles of planetary waves large scale gws and small scale gws in maintenance of the meridional structures of the zonal wind jets in the middle atmosphere are evaluated by calculating eliassen palm diagnostics separately for each of these three groups of waves small scale gws are found to cause deceleration of the wintertime polar night jet and the summertime easterly jet in the mesosphere while extratropical planetary waves primarily cause deceleration of the polar night jet below a height of approximately 60 km the meridional distribution and propagation of small scale gws are shown to affect the shape of the upper part of mesospheric jets the phase structures of orographic gws over the south andes and gws emitted from the tropospheric jet stream are discussed as examples of realistic gws reproduced by the t213l256 gcm

dynamics of the laurentide ice sheet in hudson bay canada abstract interpretation of sidescan sonar and high resolution sub bottom seismic data from hudson bay has led to the development of a model for final disintegration of the laurentide ice sheet the well preserved geomorphic features observed from the bay floor are similar to subaerially exposed glaciogenic features observed around the perimeter of hudson bay and can be related to the following three paleoenvironments subglacial erosion deposition ice margin deposition and reworking and post glacial reworking and burial subglacial features observed include fluted terrains with superimposed rogen moraines relief attributed to ice surging eskers subglacial channels and dead ice topography de geer moraines and recessional moraine complexes indicate the mechanism and orientation of ice breakup retreat the orientations of these features are locally consistent with regional trends indicating the overall direction of ice sheet flow and retreat during the last phase of the laurentide ice sheet subglacial channel complexes incised into the till and bedrock and high energy bedforms deposited on the till surface occur in present day water depths down to 160 m due to isostatic depression these could have been as much as 315 m deeper at the time of formation they indicate a wet based glacier with high energy subglacial drainage during the late phases of ice retreat the sidescan sonar data also reveal numerous zones of distinctive morphology attributed to ice breakup and post glacial processes cross cutting relationships allow the determination of the relative ages of these zones from oldest to youngest these zones are interpreted to represent scouring of the bedrock and overburden by the remnants of the ice sheet seafloor scouring by tabular icebergs which moved in a tidally induced arcuate pattern or under the influence of massive glacial lake outflows development of dead ice topography under residual ice masses and random iceberg scouring by smaller icebergs restricted to present day water depths of less than 180 m recently published reconstructions of the collapse of the laurentide ice sheet based on dated quaternary sections on land suggest that the bay was rapidly deglaciated in approximately 400 years the well preserved and distinctive glaciogenic and stratigraphic indicators observed from the bay floor suggest that they were formed by a succession of mechanisms which were too short lived to obliterate the underlying evidence of deglaciation this supports the interpretation of extremely rapid deglaciation of hudson bay and points out that subsequent marine processes have not been sufficient to obliterate the glacial features

lidar observations of stratospheric gravity waves from 2011 to 2015 at mcmurdo 77 84 s 166 69 e antarctica 1 vertical wavelengths periods and frequency and vertical wave number spectra five years of atmospheric temperature data collected with an fe boltzmann lidar by the university of colorado group from 2011 to 2015 at arrival heights are used to characterize the vertical wavelengths periods vertical phase speeds frequency spectra and vertical wave number spectra of stratospheric gravity waves from 30 to 50 km altitudes over 1000 dominant gravity wave events are identified from the data the seasonal spectral distributions of vertical wavelengths periods and vertical phase speeds in summer winter and spring fall are found obeying a lognormal distribution both the downward and upward phase progression gravity waves are observed by the lidar and the fractions of gravity waves with downward phase progression increase from summer 59 to winter 70

horizontal parameters of daytime thermospheric gravity waves and e region neutral winds over puerto rico we report on the electron density perturbation amplitudes periods up to 60 min horizontal and vertical wavelengths phase speeds and propagation directions of daytime traveling ionospheric disturbances tids from 115 to 300 km altitude using dual beam experiments at the arecibo observatory ao puerto rico as in previous studies we find a near continuum of waves above the ao while the tids propagate in nearly all directions except purely westward we find that most propagate southward southeastward we find that tid amplitudes increase nearly exponentially with increasing period although with a much smaller slope for periods 30 min tid amplitudes peak on the bottomside of the f region typical vertical wavelengths increase from less than 50 km at low altitudes to 100 300 km horizontal wavelengths increase from 70 100 km to 150 500 km over the same altitude range median vertical wavelengths horizontal wavelengths and periods increase with altitude up to z 100 150 m s we also measure the e region horizontal neutral winds and find that they peak at 150 m s near z 105 km in the middle of the day wave phase speeds are in general greater than these ambient winds in addition by tracing individual wave packets vertically in altitude we find that a packet s vertical wavelength generally peaks near the altitude where its inferred ion velocity amplitude is maximum the vertical wavelength generally decreases above this altitude an observation that is consistent with gravity wave packet theory

three dimensional properties of andes mountain waves observed by satellite a case study the southern andes region has been clearly identified in previous satellite and balloon observations and in global models as a hot spot of small scale gravity wave activity with monthly mean momentum fluxes exceeding 10 times background values in fall winter and spring seasons this makes this region a focus of interest for global circulation and climate studies we analyze a case study on 8 may 2006 combining observations from the atmospheric infrared sounder instrument on the aqua satellite and the high resolution dynamics limb sounder instrument of the aura satellite to form a three dimensional picture of the wave field the observations show a widespread wave pattern over the southern andes extending eastward over the south atlantic simulations with the weather research forecasting model clearly identify the waves as orographic in origin but the observed wave pattern is far from the simple two dimensional wave field forced by steady flow over a mountain ridge the morphology of the pattern is consistent with three dimensional linear theoretical calculations of downstream propagation and latitudinal focusing of mountain waves into the stratospheric jet the observations confirm the importance of this process in the stratosphere and we find the process also occurring in the global analysis and forecasts from the european centre for medium range weather forecasting our analysis evaluates some strengths and weaknesses of current orographic wave drag parameterizations in global models and the relevance of parameterization assumptions in global models with high resolution copyright 2011 by the american geophysical union

inertia gravity waves in antarctica a case study using simultaneous lidar and radar measurements at mcmurdo scott base 77 8 s 166 7 e 1 this study presents the first coincident observation of inertia gravity waves igws by lidar and radar in the antarctic mesopause region this is also the first known observation of two simultaneous igws at the same location an fe boltzmann lidar at arrival heights 77 8 s 166 7 e provides high resolution temperature data and a co located mf radar provides wind data on 29 june 2011 coherent wave structures are observed in both the fe lidar temperature and mf radar winds two dominant waves are determined from the temperature data with apparent periods of 7 7 0 2 and 5 0 0 1 h and vertical wavelengths of 22 2 and 23 2 km respectively the simultaneous measurements of temperature and wind allow the intrinsic wave properties to be derived from hodograph analyses unambiguously the analysis shows that the longer period wave propagates northward with an azimuth of 11 5 clockwise from north this wave has a horizontal wavelength of h 2 2 0 2 103 km and an intrinsic period of i 7 9 0 3 h the intrinsic horizontal phase speed cih for this wave is 80 4 m s while the horizontal and vertical group velocities cgh and cgz are 48 3 m s and 0 5 0 1 m s respectively the shorter period wave has i 4 5 0 3 h and 100 4 with h 1 1 0 1 103 km and cih 68 5 m s its group velocities are cgh 58 5 m s and cgz 1 1 0 1 m s therefore both waves propagate with very shallow elevation angles from the horizon 0 6 0 1 and 1 1 0 1 for the longer and shorter period waves respectively but originate from different sources our analysis suggests that the longer period igw most likely originates from the stratosphere in a region of unbalanced flow

stratospheric gravity wave fluxes and scales during deepwave abstractduring the deep propagating gravity wave experiment deepwave project in june and july 2014 the gulfstream v research aircraft flew 97 legs over the southern alps of new zealand and 150 legs over the tasman sea and southern ocean mostly in the low stratosphere at 12 1 km altitude improved instrument calibration redundant sensors longer flight legs energy flux estimation and scale analysis revealed several new gravity wave properties over the sea flight level wave fluxes mostly fell below the detection threshold over terrain disturbances had characteristic mountain wave attributes of positive vertical energy flux efz negative zonal momentum flux and upwind horizontal energy flux in some cases the fluxes changed rapidly within an 8 h flight even though environmental conditions were nearly unchanged the largest observed zonal momentum and vertical energy fluxes were mfx 550 mpa and efz 22 w m 2 respectively a wide variety of disturbance scales were found at flight level over

recent developments in gravity wave effects in climate models and the global distribution of gravity wave momentum flux from observations and models recent observational and theoretical studies of the global properties of small scale atmospheric gravity waves have highlighted the global effects of these waves on the circulation from the surface to the middle atmosphere the effects of gravity waves on the large scale circulation have long been treated via parametrizations in both climate and weather forecasting applications in these parametrizations key parameters describe the global distributions of gravity wave momentum flux wavelengths and frequencies until recently global observations could not define the required parameters because the waves are small in scale and intermittent in occurrence recent satellite and other global datasets with improved resolution along with innovative analysis methods are now providing constraints for the parametrizations that can improve the treatment of these waves in climate prediction models research using very high resolution global models has also recently demonstrated the capability to resolve gravity waves and their circulation effects and when tested against observations these models show some very realistic properties here we review recent studies on gravity wave effects in stratosphere resolving climate models recent observations and analysis methods that reveal global patterns in gravity wave momentum fluxes and results of very high resolution model studies and we outline some future research requirements to improve the treatment of these waves in climate simulations copyright 2010 royal meteorological society and crown in the right of canada

first lidar observations of quasi biennial oscillation induced interannual variations of gravity wave potential energy density at mcmurdo via a modulation of the antarctic polar vortex

numerical modeling of the excitation propagation and dissipation of primary and secondary gravity waves during wintertime at mcmurdo station in the antarctic

large scale waves in the mesosphere and lower thermosphere observed by saber observations made by the sounding of the atmosphere using broadband emission radiometry saber instrument on board nasa s thermosphere ionosphere mesosphere energetics and dynamics timed satellite have been processed using salby s fast fourier synoptic mapping ffsm algorithm the mapped data provide a first synoptic look at the mean structure and traveling waves of the mesosphere and lower thermosphere mlt since the launch of the timed satellite in december 2001 the results show the presence of various wave modes in the mlt which reach largest amplitude above the mesopause and include kelvin and rossby gravity waves eastward propagating diurnal oscillations non sunsynchronous tides and a set of quasi normal modes associated with the so called 2 day wave the latter exhibits marked seasonal variability attaining large amplitudes during the solstices and all but disappearing at the equinoxes saber data also show a strong quasi stationary rossby wave signal throughout the middle atmosphere of the winter hemisphere the signal extends into the tropics and even into the summer hemisphere in the mlt suggesting ducting by westerly background zonal winds at certain times of the year the 5 day rossby normal mode and the 4 day wave associated with instability of the polar night jet are also prominent in saber data

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

hudson bay river sediments and regional glaciation iii implications of mineralogical studies for wisconsinan and earlier ice flow patterns mineralogical studies of river sediments from the hudson bay and james bay lowlands suggest that the glacial erosion of pre devonian paleozoic carbonate rocks played an important role in the production of calcite enriched debris in the cape henrietta maria watershed ice flowing southwesterly across devonian basins in western hudson bay and the james bay lowlands would largely bypass the intervening cape area enrichment of iron in river sands of the cape watershed is attributed to proterozoic ferruginous sources now largely submerged under the waters of eastern hudson bay distributional patterns of carbonates and iron indicate that the dominant flow of ice from eastern hudson bay was southwesterly toward cape henrietta maria without major flow from the area of proterozoic bedrock into the nelson river watershed in the cape area iron enrichment due to proterozoic sources significantly overshadows possible contributions from siderite bearing devonian bedrock the fluvial sediment data are consistent with

the importance of spatial variability in the generation of secondary gravity waves from local body forces 1 we hypothesized earlier that the zonal mean body force required to close the mesospheric jets is sporadic in time and is composed of a large number of spatially and temporally localized body forces to explore the effects of such localization we randomly generate a series of localized 3d body forces in the mesosphere which create a mean acceleration of 100 m s 1 day 1 over this forcing volume secondary waves are also generated and because they have large vertical scales phase speeds and vertical group velocities they may induce important variabilities in the lower thermosphere where they dissipate we find that the secondary waves from spatially smoothed body forces have much smaller momentum fluxes frequencies and vertical group velocities thus global models having coarse resolution may be missing a significant source of sporadic wave drag and its effect throughout the middle atmosphere and lower thermosphere

reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the laurentide ice sheet abstract this paper reconstructs the deglaciation of the laurentide ice sheet lis including the innuitian ice sheet from the last glacial maximum lgm with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides we build on a recent inventory of laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the lis which we depict in a series of palaeogeographic maps results show that the drainage network at the lgm was similar to modern day antarctica the majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation until the ice sheet lost its marine margin ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build up peak phase and collapse of the cordilleran laurentide ice saddle the south eastern marine margin in atlantic canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the lgm in contrast the ice streams draining towards the north western and north eastern marine margins in the beaufort sea and in baffin bay appear to have remained stable throughout most of the late glacial and some of them continued to function until after the younger dryas yd the yd influenced the dynamics of the deglaciation but there remains uncertainty about the response of the ice sheet in several sectors we tentatively ascribe the switching on of some major ice streams during this period e g m clintock channel ice stream at the north west margin but for other large ice streams whose timing partially overlaps with the yd the drivers are less clear and ice dynamical processes rather than effects of climate and surface mass balance are viewed as more likely drivers retreat rates markedly increased after the yd and the ice sheet became limited to the canadian shield this hard bed substrate brought a change in the character of ice streaming which became less frequent but generated much broader terrestrial ice streams the final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around hudson bay our reconstruction indicates that the lis underwent a transition from a topographically controlled ice drainage network at the lgm to an ice drainage network characterised by less frequent broad ice streams during the later stages of deglaciation these deglacial ice streams are mostly interpreted as a reaction to localised ice dynamical forcing flotation and calving of the ice front in glacial lakes and transgressing sea basal de coupling due to large amount of meltwater reaching the bed debuttressing due to rapid changes in ice sheet geometry rather than as conveyors of excess mass from the accumulation area of the ice sheet at an ice sheet scale the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet the final elimination of which was mostly driven by surface melt

what is the source of the stratospheric gravity wave belt in austral winter abstractduring austral winter and away from orographic maxima or hot spots stratospheric gravity waves in both satellite observations and interim european centre for medium range weather forecasts ecmwf re analysis era interim data reveal enhanced amplitudes in a broad midlatitude belt extending across the southern ocean from east of the andes to south of new zealand the peak latitude of this feature slowly migrates poleward from 50 to 60 s wave amplitudes are much weaker across the midlatitude pacific ocean these features of the wave field are in striking agreement with diagnostics of baroclinic growth rates in the troposphere associated with midlatitude winter storm tracks and the climatology of the midlatitude jet this correlation suggests that these features of the stratospheric gravity wave field are controlled by geographical variations of tropospheric nonorographic gravity wave sources in winter storm tracks spontaneous adjustment emission from the midlatitude winter jet frontogenesi

hydrology of small tributary streams in a subarctic wetland rivers traversing subarctic wetlands are fed by numerous small tributary creeks which carry much of the wetland runoff into the rivers during the snow free season the wetlands being saturated generate abundant surface flow in the spring melt season this amount of water cannot be accommodated by the tributary creeks and together with general flooding of the rivers there is little distinction between overland flow and channelled flow across the wetland the feeder tributaries and the major rivers after snowmelt the water level subsides and most of the overland flow from the wetland is funnelled into the feeder creeks the feeders can usually respond quickly to rainstorms and recessions are short unless surface flow is sustained by extensive marshy depressions along the lower reaches of the major rivers the small tributary creeks are the main conveyors of wetland runoff to the rivers and therefore strongly modify the runoff characteristics of the rivers

gravity wave tidal interactions in the mesosphere and lower thermosphere over rothera antarctica 68 s 68 w 1 a simple technique for measuring gravity wave activity has been used to investigate gravity wave tidal interactions in the polar mesosphere and lower thermosphere mlt the technique uses the radial velocities of individual meteors recorded by meteor radar to derive a statistical measure variance of the activity of the high frequency gravity wave field this technique can measure gravity waves with horizontal wavelengths of up to about 400 km and periods up to approximately 3 hours interactions between the observed gravity wave field and the background wind are investigated using data collected between february 2005 and december 2008 by a meteor radar based at rothera antarctica 68 s 68 w the results reveal the presence of significant modulations of the observed gravity wave field at tidal periods of 12 and 24 hours correlations between the hourly zonal winds and the gravity wave field measured by the meteor radar reveal an in phase relationship between the hourly zonal winds and gravity wave variance in winter and an anti phase relationship in summer this is consistent with the theory of filtering by tidal winds acting on a zonally asymmetric gravity wave field in which westward waves dominate in winter and eastward waves dominate in summer the limitations of the technique and the effect this has on the interpretation of these results are also considered the effects of the diurnal cycles in meteor count rates the uncertainty in recorded radial velocities and the uncertainty in the measured heights of meteors are considered

secondary generation of gravity waves associated with the breaking of mountain waves abstract the generation of small scale gravity waves associated with the breaking of mountain waves in the stratosphere has been simulated within a fully compressible nonhydrostatic two dimensional numerical model the model includes the mesosphere and offers sufficiently high spatial resolution to characterize the breaking and generation of gravity waves in the stratosphere the mean flow is initialized by cira86 at 40 n in february a bell shaped mountain with 30 km half width and 1 5 km height is located in the bottom of the modeled domain the primary wave forced by the mountain propagates into the stratosphere with amplitude increasing with height and subsequently breaks in the lower stratosphere after the primary wave breaking significant wave activity is simulated in the stratosphere these secondary waves are generated at both the upstream and the downstream edges of the breaking zone analysis is mostly focused on downstream small scale waves the horizontal and vertical wavelengths of the se

traveling ionospheric disturbances over the united states induced by gravity waves from the 2011 tohoku tsunami and comparison with gravity wave dissipative theory

a general circulation model study of the orographic gravity waves over antarctica excited by katabatic winds 1 in this study we simulated orographic gravity waves ogws over antarctica using a t213l250 general circulation model gcm the gcm has a fine vertical resolution of 300 m throughout the middle atmosphere the simulation was run for a 1 year period results from 21 28 june were primarily considered ogws are excited by katabatic winds that travel down the surface slopes of the antarctic ice sheet a strong eastward katabatic wind blows over the west coast of the ross sea at the approach of the synoptic scale upper tropospheric westerly jets a quasi stationary ogw is then excited above the coast and propagates upward into the mesosphere an ogw appears sporadically during the antarctic winter and spring its amplitude is determined by the strength of the eastward katabatic wind dissipation of ogws within the middle atmosphere results in a localized deceleration of westerly winds greater than 30 m s 1 d 1 this in turn modifies the horizontal circulation in the polar vortex strong vertical mixing occurs within the mesosphere and is associated with wave breaking large temperature fluctuations associated with the ogws affect the formation or suppression of polar stratospheric clouds in the lower stratosphere katabatic wind excitation is the most powerful source of gravity waves over antarctica around the time of the winter solstice

lidar observations of persistent gravity waves with periods of 3 10 h in the antarctic middle and upper atmosphere at mcmurdo 77 83 s 166 67 e persistent dominant and large amplitude gravity waves with 3 10 h periods and vertical wavelengths 20 30 km are observed in temperatures from the stratosphere to lower thermosphere with an fe boltzmann lidar at mcmurdo antarctica these waves exhibit characteristics of inertia gravity waves in case studies yet they are extremely persistent and have been present during every lidar observation we characterize these 3 10 h waves in the mesosphere and lower thermosphere using lidar temperature data in june from 2011 to 2015 a new method is applied to identify the major wave events from every lidar run longer than 12 h a continuous 65 h lidar run on 28 30 june 2014 exhibits a 7 5 h wave spanning 60 h and 6 5 h and 3 4 h waves spanning 40 and 45 h respectively over the course of 5 years 323 h of data in june reveal that the major wave periods occur in several groups centered from 3 5 to 7 5 h with vertical phase speeds of 0 8 2 m s these 3 10 h waves possess more than half of the spectral energy for 93 of the time a rigorous prewhitening postcoloring technique is introduced for frequency power spectra investigation the resulting spectral slopes are unusually steep 2 7 below 100 km but gradually become shallower with increasing altitude reaching about 1 6 at 110 km two dimensional fast fourier transform spectra confirm that these waves have a uniform dominant vertical wavelength of 20 30 km across periods of 3 5 10 h these statistical features shed light on the wave source and pave the way for future research

towards a sediment and organic carbon budget for hudson bay abstract a preliminary sediment and organic carbon budget is constructed for the hudson bay marine system based on published literature and new data collected from nine rivers and 13 sediment boxcores the budget considers the main inputs of terrestrial and marine components of sediment and organic carbon and the main sinks sediment burial and losses oxidation export to hudson strait sedimentation rates 0 032 0 23 g cm 2 yr 1 were estimated from 210 pb profiles and a sediment advection diffusion model in our cores and in two cores collected previously by lockhart et al lockhart w l et al 1998 fluxes of mercury to lake sediments in central and northern canada inferred from dated sediment cores biogeochemistry 40 163 173 sedimentation rates implied by the 210 pb profiles were verified against profiles of 137 cs and for some of the cores contaminant pb the sediment sink in hudson bay was estimated at 138 64 10 6 t a 1 by applying the average sedimentation rate to the area of active sedimentation in the bay 15 of the seafloor calculated according to a regional sedimentation map developed from seismic data josenhans h w et al 1988 preliminary seismostratigraphic and geomorphic interpretations of the quaternary sediments of hudson bay natural resources canada the known sediment sources to hudson bay include river input 11 6 6 10 6 t a 1 subaerial coastal erosion 8 4 10 6 t a 1 marine primary production 24 2 17 10 6 t a 1 and atmospheric deposition 0 5 10 6 t a 1 based on the available data the modern sediment input 44 3 18 10 6 t a 1 represents only about one third of the apparent sediment sink in hudson bay resuspension and lateral transport of shallow water deposits primarily glacigenic and winnowing from topographic highs likely consequences of the exceptional continuous relative sea level rsl fall in hudson bay provides a plausible source for the 116 10 6 t a 1 imbalance using organic carbon and 13 c values in the cores we estimate the burial of particulate organic carbon poc in sediments at 1 3 0 6 10 6 t c a 1 of which 80 is marine the importance of reworked glaciomarine carbon to the burial flux is difficult to estimate because modern autochthonous primary production provides a large source of poc to the system 16 1 7 10 6 t c a 1 and its degradation is not well constrained the 0 58 10 6 t c a 1 terrestrial carbon estimated to be transported as part of the redistributed sediment load accounts for almost one half the total terrigenous poc inputs to the bay if sediment and oc supply and burial in the hudson bay system are presently responding to the history of isostatic rebound as proposed here the task of predicting and measuring the additional consequences of river diversions and climate change e g sea ice permafrost runoff is rendered considerably more difficult

secondary gravity waves generated by breaking mountain waves over europe a strong mountain wave observed over central europe on 12 january 2016 is simulated in 2d under two fixed background wind conditions representing opposite tidal phases the aim of the simulation is to investigate the breaking of the mountain wave and subsequent generation of nonprimary waves in the upper atmosphere the model results show that the mountain wave first breaks as it approaches a mesospheric critical level creating turbulence on horizontal scales of 8 30 km these turbulence scales couple directly to horizontal secondary waves scales but those scales are prevented from reaching the hermosphere by the tidal winds which act like a filter initial secondary waves that can reach the thermosphere range from 60 to 120 km in horizontal scale and are influenced by the scales of the horizontal and vertical forcing associated with wave breaking at mountain wave zonal phase width and horizontal wavelength scales large scale nonprimary waves dominate over the whole duration of the simulation with horizontal scales of 107 300 km and periods of 11 22 minutes the thermosphere winds heavily influence the time averaged spatial distribution of wave forcing in the thermosphere which peaks at 150 km altitude and occurs both westward and eastward of the source in the 2 ut background simulation and primarily eastward of the source in the 7 ut background simulation the forcing amplitude is 2 that of the primary mountain wave breaking and dissipation this suggests that nonprimary waves play a significant role in gravity waves dynamics and improved understanding of the thermospheric winds is crucial to understanding their forcing distribution

gravity wave radiation and mean responses to local body forces in the atmosphere the authors determine the spectral linear solutions that arise in response to local 3d body forces and heatings in an idealized environment that turn on and off smoothly but not necessarily slowly over a finite interval in time the solutions include impulsive through slowly varying body forcings the forcings result in both a mean response which is typically significantly broadened spatially in one direction and a gravity wave response which allows the fluid to reach this state the gravity wave field depends on both the spatial attributes of the source and the forcing duration the frequency of the wave response is the characteristic source frequency formed from the source dimensions if the forcing frequency is greater than the characteristic frequency and is the forcing frequency otherwise the radiated gravity waves from zonal forcings have vertical wavelengths which are approximately twice the vertical extent of the forcing and horizontal wavelengths which are at least twice the horizontal extent of the forcing wave excitation is increasingly inefficient when the forcing frequency is smaller than the characteristic source frequency in addition the mean responses are not confined to the source region in general significant spatial broadening of the mean responses occurs if the source s frequency is high and low the responses are broadened horizontally and vertically respectively with the amount depending on the characteristic scales of the source if the body forcing is in the eastward direction then much or all of the ensuing zonal mean wind is eastward however for many realistic forcing scenarios a large percentage of the ensuing zonal wind flows westward these countersigned jets are displaced meridionally about the source thus spatially confined body forcings create both gravity wave and mean responses if the forcings are fast enough very slowly varying forcings create only mean responses

coordinated observations of 8 and 6 hr tides in the mesosphere and lower thermosphere by three meteor radars near 60 s latitude

quantification of the gravity wave forcing of the migrating diurnal tide in a gravity wave resolving general circulation model 1 the interaction of gravity waves gws and the migrating diurnal tide are studied in a gw resolving general circulation model gcm by calculating the tidal components of zonal wind accelerations and equivalent rayleigh friction due to tidal induced gw dissipation two 15 day periods for perpetual equinoctial and solstice simulations are analyzed which are performed with the japanese atmospheric general circulation model for upper atmosphere research jaguar high resolution gcm the model can directly simulate gws with horizontal wavelengths greater than about 190 km and thus reproduce the general features of the mean winds and temperatures from the surface to the mesosphere and lower thermosphere mlt the amplitudes of the migrating diurnal tide are successfully simulated during both seasons and the tidal winds affect the altitudes of gw dissipation in the low latitude mlt the tidal component of gw forcing has maximal values of about 15 m s 1 d 1 near the maximal vertical shears of the tidal winds and generally works to shorten the vertical wavelength of the migrating diurnal tide the phase relationship between the tidal winds and the tidal induced gw forcing is not exactly 90 out of phase causing amplification suppression of the tide the gw forcing amplifies the migrating diurnal tide during the equinox while during the solstice it suppresses the tidal winds in the upper mesosphere of both hemispheres this difference in behavior can be attributed to a seasonal variation of the mean zonal winds because combination of the mean and tidal winds affects the altitudes of gw dissipation

southern hemisphere extratropical gravity wave sources and intermittency revealed by a middle atmosphere general circulation model abstractsouthern hemisphere extratropical gravity wave activity is examined using simulations from a free running middle atmosphere general circulation model called kanto that contains no gravity wave parameterizations the total absolute gravity wave momentum flux mf and its intermittency diagnosed by the gini coefficient are examined during january and july the mf and intermittency results calculated from the kanto model agree well with results from satellite limb and superpressure balloon observations the analysis of the kanto model simulations indicates the following results nonorographic gravity waves are generated in kanto in the frontal regions of extratropical depressions and around tropopause level jets regions with lower higher intermittency in the july midstratosphere become more less intermittent by the mesosphere as a result of lower level wave removal the gravity wave intermittency is low and nearly homogeneous throughout the sh middle atmosphere during january this indicates t

solar related variations of the cloud top circulation above aphrodite terra from vmc venus express wind fields winds derived by a digital tracking technique from uv 365 nm images captured by the venus monitoring camera onboard the venus express spacecraft from 2006 through 2013 were used to study the atmospheric circulation at cloud top level 70 2 km this data set allows variations of the wind speed with both latitude and longitude to be studied and establishes their correlation with surface topography as well as local time dependence both zonal and meridional wind components show some correlation with topography the minimum zonal wind speed was found at noon above ovda regio 10 s 93 e the highest region of aphrodite terra one of the largest highlands in the equatorial region the area of slow zonal wind extends to at least 30 s and shifts in the direction of superrotation in the afternoon and with increasing latitude poleward the observed deceleration of cloud top wind was recently attributed to the interaction of the gravity mountain waves generated by aphrodite terra with the atmospheric circulation the present study was performed for different local time over the mountainous longitudes the deceleration pattern in the zonal wind field is mainly conserved within a few hours around noon systematic longitude shift is observed in the afternoon in the direction of the evening terminator another area of perturbation of both zonal and meridional wind components is observed in the equatorial region around lt 13 14 h and may be explained by the solar tide