migrating and nonmigrating semidiurnal tides in the upper atmosphere excited by tropospheric latent heat release migrating and nonmigrating semidiurnal tides

climatology of mesopause region temperature zonal wind and meridional wind over fort collins colorado 41 n 105 w and comparison with model simulations 1 between may 2002 and april 2006 many continuous observations of mesopause region temperature and horizontal wind each lasting longer than 24 h termed full diurnal cycle observations were completed at the colorado state university na lidar facility in fort collins colorado 41 n 105 w the combined data set consists of 120 full diurnal cycle observations binned on a monthly basis with a minimum of 7 cycles in april and a maximum of 18 cycles in august each monthly data set was analyzed to deduce mean values and tidal period perturbations after removal of tidal signals monthly mean values are used for the study of seasonal variations in mesopause region temperature zonal and meridional winds the results are in qualitative agreement with our current understanding of mean temperature and wind structures in the midlatitude mesopause region with an observed summer mesopause of 167 k at 84 km summer peak eastward zonal wind of 48 m s at 94 km winter zonal wind reversal at 95 km and peak summer pole to winter pole meridional flow of 17 m s at 86 km the observed mean state in temperature zonal and meridional winds are compared with the predictions of three current general circulation models i e the whole atmosphere community climate model version 3 waccm3 with two different simulations of gravity wavefields the hamburg model of the neutral and ionized atmosphere hammonia and the 2003 simulation of the thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm while general agreement is found between observation and model predictions there exist discrepancies between model prediction and observation as well as among predictions from different models specifically the predicted summer mesopause altitude is lower by 3 km 8 km 3 km and 1 km for waccm3 the two waccm runs hammonia and time gcm respectively and the corresponding temperatures are 169 k 170 k 158 k and 161 k the model predicted summer eastward zonal wind peaks to 71 m s at 102 km to 48 m s at 84 km to 75 m s at 93 km and to 29 m s at 94 km in the same order the altitude of the winter zonal wind reversal and seasonal asymmetry of the pole to pole meridional flow are also compared and the importance of full diurnal cycle observations for the determination of mean states is discussed

a comparison of mesospheric and low thermospheric winds measured by fabry perot interferometer and meteor radar over central china wind data observed by a fabry perot interferometer fpi and a meteor radar mr deployed in two stations which are 430 km apart in ground distance are used to study wind climatology in mlt over central china and compare between the measurements a general morphologic similarity of the fpi winds and mr winds is identified with four years data since november 2011 at 87 km the wind vector plots show the fpi and mr winds agree with each other very well in all months the zonal winds of both instruments have an apparent semi annual variation with a maximal strength of 20 m s at around 18 ut in equinoctial months and the meridional winds from both instruments have an apparent annual variation with a maximal strength of 40 m s at around 15 ut in summer months the correlation coefficients between the measurements of the two instruments are about 0 95 for meridional wind and 0 90 for zonal wind at 97 km the wind vector plots show that fpi and mr winds agree with each other from may to october and are obviously different in the rest months there are very weak semi annual variation at around 18 ut for both zonal winds and pronounced annual variation at around 13 ut for both meridional winds the correlation coefficients between the fpi and mr winds are 0 73 for zonal wind and 0 86 for meridional wind which are overall smaller than that at 87 km a gaussian distribution of airglow profile is used to investigate the deviations associated with peak height and full width half maximum fwhm of airglow layer it is found that the variation of peak height could lead to about 20 variation of correlation coefficients between measurements at the height of 87 km and about 14 8 at the height of 97 km on average the variation of fwhm could lead to a correlation coefficient variation of about 2 4 and 3 5 at the height of 87 km and 97 km respectively some other reasons such as the influence of geomagnetic field on meteor trail the propagation of gravity waves could also contribute to these differences between measurements

in situ measurements of velocity dispersion and attenuation in new jersey shelf sediments the existence of acoustic velocity dispersion and frequency dependence of attenuation in marine sediments is investigated using in situ measurements from a wideband acoustic probe system during the shallow water 2006 experiment direct path pulse propagation measurements show evidence of velocity dispersion within the 10 80khz frequency band at two silty sand sites on the new jersey shelf the measured attenuation in db m shows linear frequency dependency within the 10 80khz frequency band the measured velocity dispersion and attenuation curves are in good agreement with those predicted by an extended biot theory yamamoto and turgut j acoust soc am 83 1744 1751 1988 for sediments with a distribution of pore sizes

contourite erosive features caused by the mediterranean outflow water in the gulf of cadiz quaternary tectonic and oceanographic implications abstract contourite depositional systems have been the focus of much recent research but still relatively little is known about contourite erosive features and their associated processes based on multibeam bathymetry side scan imagery and different resolution seismic records a detailed description and classification of the major erosive submarine valley features of the contourite depositional system of the gulf of cadiz middle slope is presented for the first time four types of erosive features have been differentiated including contourite moats contourite channels marginal valleys and large isolated furrows and interpreted in terms of their tectonic and oceanographic implications during the quaternary the study of the distribution and characteristics of erosive features is essential to better understand the present and past interaction of the mediterranean outflow water mow with the middle slope seafloor and allows us to propose a new and more precise scheme for the mow circulation patterns this scheme includes a main along slope circulation responsible for the excavation of the contourite moat and channels and a secondary down slope circulation responsible for the erosion of marginal valleys and isolated furrows three evolutionary stages have been observed in the development of the erosive system during the quaternary that can be related to changes in the distribution and splitting of the mow as a consequence of the segmentation of the ne sw diapiric ridges by neotectonic effects 1 early pleistocene to mid pleistocene linear diapiric ridges 2 mid pleistocene to late pleistocene diapiric reactivation and 3 late pleistocene to holocene main recent phase of diapiric ridges segmentation and rotation this study provides important regional clues for establishing the evolution of the erosive features in relation with neotectonic effects and represents a good example of the potential of erosive features as evidences for the reconstruction of the paleoceanography and recent tectonic changes

shallowly buried enigmatic seismic stratigraphy on the new jersey outer shelf evidence for latest pleistocene catastrophic erosion chirp seismic profiles reveal a prominent seismic facies boundary 0 20 m below the seafloor within an 8 6 10 2 km area of the new jersey outer shelf this irregular boundary separates seismically transparent facies from underlying stratified facies the irregularities form two populations of incisions trending northeast and east northeast stratified blocks within the transparent facies occasionally within presumed incisions together with lithologic evidence indicate that some of the transparent facies was formed by disruption of the stratified facies preservation of steep 50 90 incision flanks implies that deposition of the transparent facies closely followed disruption catastrophic erosion and redeposition following the multiple breaching of glacial lake dams to the north ca 19 12 ka constitute the likeliest mechanisms both for producing facies boundary incisions and emplacing the transparent facies implying that local forcing can generate erosional unconformities on periglacial shelves in the absence of base level change this facies boundary adds complexity to the already complex shallowly buried stratigraphic record of the last glacio eustatic cycle on the new jersey continental shelf long considered typical of periglacial shelves worldwide

stationary planetary waves inferred from windii wind data taken within altitudes 90 120 km during 1991 96 abstract a climatology of stationary planetary waves spws in horizontal winds at latitudes 70 s 70 n and altitudes 90 120 km is obtained from wind imaging interferometer windii green line measurements in december january and march april of 1991 96 the observed solstitial spw fields are relatively stronger and dominated by zonal wavenumber 1 variations in contrast the equinoctial spw fields are weaker and characterized by zonal wavenumber 2 variations the zonal amplitude maxima of 10 25 m s 1 are generally centered at the midlatitudes of 35 40 in both hemispheres around 96 km with the eastward perturbation velocity maxima around 90 e for wavenumber 1 and 60 and 240 e for wavenumber 2 the meridional amplitude maxima are about 5 15 m s 1 and show more variabilities in their latitude height distributions the meridional phases indicated that eliassen palm ep fluxes were downward poleward for the winter maxima vertically varying poleward for the summer maxima and more variable during march apr

large winds and wind shears caused by the nonlinear interactions between gravity waves and tidal backgrounds in the mesosphere and lower thermosphere a two dimensional nonlinear numerical model was used to simulate large winds 100m s 1 and wind shears 40m s 1 km 1 in the mesosphere and lower thermosphere mlt that are caused by the interaction between gravity waves gws and migrating tidal background by varying the wavelengths of gws and the phases of diurnal and semidiurnal tides 64 numerical experiments were performed our numerical experiments indicate that both migrating diurnal and semidiurnal tides strongly modulate the occurrence of gw breaking and the resulted large winds and wind shears the simulated large winds and wind shears are in good agreement with those from the rocket sounding chemical release measurements moreover the occurrence of large wind shears highly depends on the phases of migrating tides in local time which is in agreement with the reported lidar observations the local time dependence of large wind shears is mainly attributed to the filtering and or hindering effects of diurnal and semidiurnal tidal winds on gws our simulation reveals that the nonlinear interactions between gws breaking and the migrating diurnal and semidiurnal tides may play an important role in driving the large winds and wind shears in the mlt region and their local time dependence

stochastic sediment property inversion in shallow water 06 received time series at a short distance from the source allow the identification of distinct paths four of these are direct surface and bottom reflections and sediment reflection in this work a gibbs sampling method is used for the estimation of the arrival times of these paths and the corresponding probability density functions the arrival times for the first three paths are then employed along with linearization for the estimation of source range and depth water column depth and sound speed in the water propagating densities of arrival times through the linearized inverse problem densities are also obtained for the above parameters providing maximum a posteriori estimates these estimates are employed to calculate densities and point estimates of sediment sound speed and thickness using a non linear grid based model density computation is an important aspect of this work because those densities express the uncertainty in the inversion for sediment properties

seismic and bathymetric evidence for four different episodes of iceberg scouring on the new jersey outer shelf possible correlation to heinrich events abstract re analysis of dense chirp seismic surveys on the outer new jersey shelf reveals two sets of shallowly buried incisions the incisions are linear to slightly sinuous oriented ne sw and exhibit cross cutting relationships we interpret both sets as paleo iceberg scours one set cuts into the r horizon a regional unconformity that formed 45 40 ka and which was subsequently buried by the finer grained outer shelf sediment wedge osw the second set is part of an erose boundary between a layered lower unit of the osw and an upper more transparent unit the erose boundary scours are deeper and have steeper slopes than the r horizon scours the latter often exhibit bermed edges whereas the former do not these differences in cross sectional morphology are likely determined by the material properties of the sediments being scoured sand at the r horizon and clay at the erose boundary the orientation of both sets of scours is consistent with previously recognized iceberg scours in stratigraphically younger seafloor on the outer new jersey shelf in 110 150 m water depths located 40 km to the northeast we argue that heinrich events recurring periods of massive iceberg flux into the north atlantic represent the most likely times for transporting icebergs to these latitudes based on stratigraphic relationships a recently published ambient sea level curve and radiocarbon age constraints we attribute the r horizon scours to heinrich event h4 37 cal ka the erose boundary scours to h3 30 cal ka and the seafloor scours to h2 23 cal ka and or h1 17 cal ka facies changes immediately following the r horizon and erose boundary scours may be related to heinrich event forced climate changes perhaps the onset of interstadial conditions and associated melt water pulses floods these pulses floods repeatedly carried fine grained rock flour produced by widespread glacial erosion to the new jersey shelf

a coordinated investigation of the gravity wave breaking and the associated dynamical instability by a na lidar and an advanced mesosphere temperature mapper over logan ut 41 7 n 111 8 w the impacts of gravity wave gw on the thermal and dynamic characteristics within the mesosphere lower thermosphere especially on the atmospheric instabilities are still not fully understood in this paper we conduct a comprehensive and detailed investigation on one gw breaking event during a collaborative campaign between the utah state university na lidar and the advanced mesospheric temperature mapper amtm on 9 september 2012 the amtm provides direct evidence of the gw breaking as well as the horizontal parameters of the gws involved while the na lidar s full diurnal cycle observations are utilized to uncover the roles of tide and gws in generating a dynamical instability layer by studying the changes of the oh layer peak altitude we located the wave breaking altitude as well as the significance of a 2 h wave that are essential to this instability formation by reconstructing the mean fields tidal and gw variations during the wave breaking event we find that the large amplitude gws significantly changed the brunt vaisala frequency square and the horizontal wind shear when superimposed on the tidal wind producing a transient dynamic unstable region between 84 km and 87 km around 11 00 ut that caused a subsequent small scale gw breaking

increased contribution of terrigenous supply from taiwan to the northern south china sea since 3 ma seismic profiles provide evidence that there has been strong transport by deep water bottom currents and drift deposition on the northern slope of the south china sea earlier geochemical studies suggest that the drift sediments originated primarily from taiwan however the transport process history and origin of the deep water bottom deposition in the northern south china sea on both glacial interglacial and tectonic time scales remain unclear here we show new high resolution records of clay minerals grain size and mass accumulation rate mar of terrigenous materials from ocean drilling program odp site 1144 together with trace element concentrations in siliciclastic sediments from odp site 1146 combined with other published data we find that the primary source for sediments at odp sites 1144 1148 since 3 ma is from taiwan and not from pearl river as previously thought before 3 ma however sediment source to odp sites 1146 and 1148 was mainly from the pearl river increased contribution of terrigenous supply from taiwan to the northern south china sea since similar to 3 ma may be related to the formation of the taiwan orogen and strengthening of deep water bottom current transport in the northern south china sea variations in clay mineralogy and sedimentology at odp site 1144 located on a sediment drift shows strong glacial interglacial cyclicity this suggests that bottom current deposition is highly dependent on sea level fluctuations which control the terrigenous supply to the deep sea c 2010 elsevier b v all rights reserved

particle filtering for passive fathometer tracking seabed interface depths and fathometer amplitudes are tracked for an unknown and changing number of sub bottom reflectors this is achieved by incorporating conventional and adaptive fathometer processors into sequential monte carlo methods for a moving vertical line array sediment layering information and time varying fathometer response amplitudes are tracked by using a multiple model particle filter with an uncertain number of reflectors results are compared to a classical particle filter where the number of reflectors is considered to be known reflector tracking is demonstrated for both conventional and adaptive processing applied to the drifting array data from the boundary 2003 experiment the layering information is successfully tracked by the multiple model particle filter even for noisy fathometer outputs

a geophysical study of the manila trench luzon philippines 1 crustal structure gravity and regional tectonic evolution the manila trench subduction zone is an active convergent plate margin between the south china sea and the northern philippines the trench trends northerly and is associated with a volcanic arc an east dipping benioff zone beneath luzon and a well developed fore arc basin system the luzon trough fore arc basins lie landward of the manila trench and contain up to 4 5 km of cenozoic sediments offscraping and accretion of turbidite sediments deposited in the manila trench have resulted in the upbuilding and outbuilding of an accretionary prism which forms the seaward margin of the fore arc basin system the uplifted zambales ophiolite and its offshore extension form the landward side of the fore arc basin multichannel seismic reflection profiles reveal that folding and thrust faulting of trench strata occur at the base of the trench slope the major structural decollement at the manila trench usually forms near the unconformity separating the hemipelagic sediments from the turbidite sediments subduction and perhaps underplating of the basal hemipelagic trench sediments accompany the deformation and accretion of the overlying clastic deposits faulting and uplift occur within a narrow zone of the fore arc where seamounts associated with the relict spreading center of the south china sea basin have presumably been subducted north of lingayan gulf the fore arc is disrupted by active fault systems that trend north and northwest offshore from the luzon central valley and from the southern cordillera central based on regional geological and tectonic observations we infer that subduction probably began at the manila trench in late oligocene to middle miocene time the long term average convergence rate at the manila trench is estimated to be between 10 and 20 mm yr and may be slowing in the north owing to the collision of taiwan with eurasia

new lunar meteorite northwest africa 2996 a window into farside lithologies and petrogenesis the northwest africa nwa 2996 meteorite is a lunar regolith breccia with a mingled bulk composition and slightly elevated incompatible element content nwa 2996 is dominated by clasts of coarse grained noritic and troctolitic anorthosite containing calcic plagioclase an 98 and magnesian mafic minerals mg 75 distinguishing it from apollo ferroan anorthosites and magnesian suite rocks this meteorite lacks basalt and owes its mingled composition to a significant proportion of coarse grained mafic clasts one group of mafic clasts has pyroxenes similar to anorthosites but contains more sodic plagioclase an 94 distinguishing it as a separate lithology another group contains mg rich very low titanium pyroxenes and could represent an intrusion parental to regional basalts other clasts include granophyric k feldspar disaggregated phosphate bearing quartz monzodiorites and alkali suite fragments an 65 these evolved lithics are a minor component but contain minerals rich in incompatible elements several anorthosite clasts contain clusters of apatite suggesting that the anorthosites either assimilated evolved rocks or were metasomatized by a liquid rich in incompatible elements we used lunar prospector gamma ray spectrometer remote sensing data to show that nwa 2996 is most similar to regoliths in and around the south pole aitken spa basin peripheral regions of eastern mare nectaris crisium and southern areas of mare humorum however the mineralogy of nwa 2996 is distinctive compared with apollo and luna mission samples and is likely consistent with an origin near the spa basin anorthosite clasts could represent local crustal material mafic clasts could represent intrusions beneath basalt flows and apatite bearing rocks could carry the spa kreep signature

geoacoustic inversion using combustive sound source signals in the summer of 2006 combustive sound sources css were deployed in shallow waters off new jersey during the shallow water experiment sw 06 the depth of these sources were 26 m in water depths of the order of 100 m css are low frequency broadband sound sources and suitable for modal dispersion based inversion css data collected on various receivers single hydrophone receiving units shru vertical line array etc will be used for the inversions the inversions are based on an iterative scheme using a new time frequency analysis technique dispersion based short time fourier transform in which each time frequency tiling is adaptively rotated in the time frequency plane depending on the local wave dispersion data from various receivers will be used to investigate the spatial variation in compressional wave speed compressional wave attenuation will also be estimated using modal amplitude ratios inversion results will be validated by comparing the data with model predictions work supported by the office of naval research

a mesoscale eddy pair southwest of taiwan and its influence on deep circulation 1 a pair of mesoscale eddies namely an anticyclonic eddy ae and a cyclonic eddy ce generated southwest of taiwan was investigated using long term moored observations augmented with satellite and reanalysis data ae ce increased the upper ocean current to 100 cm s 50 cm s and generated temperature anomaly t up to 7 5 c 3 0 c the vertical structure of ae presented a phase difference between t and velocity with the core of t located south of the zero velocity line this phase difference induced a 28 5 12 0 tw 1 tw 1012 w westward eddy heat transport southwest of taiwan ae also presented strong nonlinearity in the upper ocean and yielded an annual mean volume transport of 0 86 0 15 sv energy analysis showed that both baroclinic and barotropic instabilities were important for the generation and growth of the eddy pair and contribution from wind work was relative small in the deep sea ae ce intensified the deep currents and generated large positive negative t the deep and surface currents flowed in opposite directions during the eddy events which is consistent with the interpretation that the eddy pair is dominated by the first baroclinic mode the observed deep penetrating eddy pair could greatly influence the deep circulation of the northeastern south china sea

geoacoustic and source tracking using particle filtering experimental results a particle filtering pf approach is presented for performing sequential geoacoustic inversion of a complex ocean acoustic environment using a moving acoustic source this approach treats both the environmental parameters e g water column sound speed profile ssp water depth sediment and bottom parameters at the source location and the source parameters e g source depth range and speed as unknown random variables that evolve as the source moves this allows real time updating of the environment and accurate tracking of the moving source as a sequential monte carlo technique that operates on nonlinear systems with non gaussian probability densities the pf is an ideal algorithm to perform tracking of environmental and source parameters and their uncertainties via the evolving posterior probability densities the approach is demonstrated on both simulated data in a shallow water environment with a sloping bottom and experimental data collected during the swellex 96 experiment

seafloor evidence for the interaction between cascading and along slope bottom water masses 1 the steep slope of the sw adriatic margin central mediterranean is impacted today by two water masses having markedly different origin but a similar southward flow component the levantine intermediate water liw and the north adriatic deep water naddw the liw forms through evaporation in the eastern mediterranean and enters the adriatic along a counterclockwise path the naddw forms through winter cooling on the north adriatic shelf and cascades across the western slope of the south adriatic basin bathymetric and side scan sonar tobi images of the sw adriatic margin accompanied by chirp sonar profiles define an area of extreme seafloor complexity characterized by a variety of sediment waves erosional scours longitudinal furrows and giant comet marks these distinctive bottom current features are not randomly distributed but appear genetically linked and have a consistent down current arrangement we ascribe this seafloor pattern to the constructive interference of the highly saline liw flowing along the slope between 200 and 600 m water depth and the cold naddw plunging off shelf obliquely to the slope stratigraphic data indicate that this oceanographic regime has been active since the last glacial interglacial transition the cascading naddw is density driven but is not short lived as a turbidity current would be consequently the interaction between downslope and along slope currents is here more dynamical as two water masses act simultaneously over a prolonged interval somewhat diverting their paths and leading to locally enhanced energetic conditions at the seafloor

coordinated investigation of summer time mid latitude descending e layer es perturbations using na lidar ionosonde and meteor wind radar observations over logan utah 41 7 n 111 8 w 1 it is well known that there is a strong correlation between the formation of a descending sporadic e layer es and the occurrence of large upper atmospheric zonal wind shears most likely driven by solar thermal tides and or gravity waves we present new results of es perturbation events captured between 13 and 17 july 2011 ut days 194 198 as part of a coordinated campaign using a wind temperature na lidar at utah state university 41 7on 111 8 w and a canadian advanced digital ionosonde cadi scientific instrumentation ltd saskatoon saskatchewan canada and skiymet meteor wind radar both located at nearby bear lake observatory 41 9 n 111 4 w during this period the cadi detected strong descending es on 2 days 195 and 197 when large modulations of the top side mesospheric na layer occurred in synchronism with strong oscillations in the ionosonde e region echoes a weakening in the descending e layer echoes was observed on the other 2 days 196 and 198 coincident with a large reduction in the zonal diurnal and semidiurnal amplitudes above 95 km both tidal components were found to have comparable contributions to the total zonal wind shear that was critical for es formation and its downward propagation further investigation indicates that the weakening tidal amplitudes and the occurrence of the es events were also influenced by a strong quasi two day period modulation suggesting significant quasi two day wave qtdw interactions with the tides indeed a nonlinear wave wave interaction induced 16 hour period child wave was also detected with amplitude comparable to that of the prevailing tides these interaction processes and their associated effects are consistent with earlier thermosphere ionosphere mesosphere electrodynamics general circulation model studies of nonlinear interactions between the migrating tidal waves and the qtdw and were probably responsible for the observed damping of the tidal amplitudes resulting in the disruption of the es

characteristics of semidiurnal tides observed by the kyoto meteor radar and saskatoon medium frequency radar we have compared seasonal variations of semidiurnal tides in the upper middle atmosphere observed by the kyoto meteor radar and the saskatoon medium frequency partial reflection radar in 1983 1985 amplitudes of semidiurnal tides are generally larger at saskatoon than at kyoto seasonal variations of phases at 90 km agree fairly well for both zonal and meridional components between kyoto and saskatoon the seasonal variation is mainly composed of two fundamental states appearing in summer centered april may september october and winter centered months november february march which are characterized by long and relatively short vertical wavelengths respectively clear transitions between the two states occur in equinoxes february april and october november using determinations at kyoto and saskatoon with 4 to 5 day observation intervals we have studied the behavior of semidiurnal tides during the transitions in october november in 1983 1985 and february april in 1985 precise comparisons have shown that the transitions are slightly delayed at saskatoon in both vernal and autumnal equinoxes abrupt changes in phases of semidiurnal tides coincide with reduction and pulsating fluctuations of their amplitudes suggesting the existence of interference between fundamental and higher modes which are dominant in summerlike and winterlike months respectively

oceanic eddy formation and propagation southwest of taiwan 1 oceanic eddies are active and energetic southwest of taiwan the formation and propagation of eddies in this area were investigated using 17 year satellite altimeter data cyclonic eddies ces and anticyclonic eddies aces often coexisted but there were more ces than aces generated during the period from october 1992 to october 2009 aces were stronger and in general lived longer than ces aces occurred more often in winter than in other seasons while ces were more frequent in summer compared with the direct local wind forcing the kuroshio path variability appears to be a dominant factor for eddy formation in this area a conceptual model of an eddy kuroshio interaction is proposed in summer there exists an outflow northwest of luzon island and the kuroshio likely leaps across the luzon strait to the north of the outflow and left of the kuroshio axis ces are often formed which in turn induce aces to the west of ces in winter under the influence of northeasterly monsoon the kuroshio current loop kcl appears southwest of taiwan more frequently than in other seasons and aces are frequently shed from the kcl most of the aces propagate westward and as a result ces are often spun up to the east of the aces the surface south china sea outflow in summer and the kcl in winter are however likely related to the monsoons therefore the indirect effects of monsoon winds are also evident in the seasonal variations of eddy occurrence

mean winds and tides in the upper middle atmosphere at urbana 40 n 88 w during 1991 1992 a summary of the first 18 months of continuous wind observations using the urbana medium frequency mf radar is presented emphasis is placed on height time contours of monthly mean winds and on amplitudes and phases of 24 hour and 12 hour tides results are compared with data from other midlatitude stations and models below 85 km monthly mean winds are shown to agree closely with the zonal mean geostrophic wind model cira86 significant discrepancies above 85 km have been noted in comparisons between cira86 and the other mesosphere lower thermosphere mlt radar stations including mf meteor and low frequency lf radars and are also sustained in the observations reported here tidal characteristics are generally consistent with other midlatitude observations although significant differences are noted between urbana and its closest mlt network neighbor station durham 43 n 71 w the mean wind observations provide a context for the gravity wave climatology derived from na lidar observations at urbana and promise to contribute toward improvements of middle atmosphere wind and tidal models

characteristics of ripple structures revealed in oh airglow images small scale ripple structures observed in oh airglow images are most likely induced by either dynamic instability due to large wind shear or convective instability due to superadiabatic lapse rate using the data set taken in the mesopause region with an oh all sky imager at yucca ridge field station colorado 40 7 n 104 9 w from september 2003 to december 2005 we study the characteristics and seasonal variations of ripple structures by analyzing the simultaneous background wind and temperature observed by the nearby sodium temperature wind lidar at fort collins colorado 40 6 n 105 w and a nearby medium frequency radar at platteville colorado 40 2 n 105 8 w we are able to statistically study the possible relation between ripples and the background atmosphere conditions characteristics and seasonal variations of ripples are presented in detail in this study the occurrence frequency of ripples exhibits clear seasonal variability with peak in autumn the occurrence of ripples shows a local time dependence which is most likely associated with the solar tides the lifetime and spatial scale of these ripples are typically 5 20 min and 5 10 km respectively and most of the ripples move preferentially either southward or northward however more than half of the observed ripples do not advect with background flow they have higher richardson numbers than those ripples that advect with background flow it is possible that they are not instability features but wave structures that are hard to be distinguished from the real instability features

geoacoustic inversion on the new jersey margin along and across the shelf this paper presents results of a range independent perturbative inverse approach applied to data from the shallow water experiment 2006 the inversion technique is based on a linearized relationship between sound speed in the sediment and modal eigenvalues horizontal wave numbers were estimated from data collected from two distinct source receiver tracks oriented along and across the shelf the specific inversion algorithm used is based on qualitative regularization and uses known information about the environment to constrain the solution locations of the r reflector and other layering information are used as a priori information for the inversion to emphasize the layered structure of the sediment

seasonal variation of diurnal perturbations in mesopause region temperature zonal and meridional winds above fort collins colorado 40 6 n 105 w 1 on the basis of lidar observations from may 2002 through april 2003 covering both day and night we performed a harmonic analysis to extract the diurnal perturbations in mesopause region temperature zonal and meridional winds over fort collins colorado 40 6 n 105 w binned every 2 months the results were compared to predictions of the 2000 and 2002 versions of global scale wave model gswm00 and gswm02 the diurnal tidal period oscillations showed a mixture of propagating and evanescent trapped modes but the propagating modes dominated for most of the year the agreement in temperature diurnal phases between observation and gswm prediction is marginal on the other hand other than july august meridional winds the observed diurnal phases in both wind components are in good agreement with gswm predictions for most of the altitude range reported the diurnal amplitude predictions of gswm00 were reasonably close to lidar observations while other than january february the gswm02 amplitude prediction overestimated the observations typically by a factor of two we also conducted comparisons on tidal perturbations in zonal wind between radar campaigns and our lidar observations the lidar data agreed reasonably well with the mf radar data from 2000 to 2001 at nearby platteville colorado 40 2 n 104 7 w but showed considerable differences with the data from other midlatitude stations from 1992 to 1993 the dominance of the evanescent mode in the temperature diurnal tidal oscillation during the early winter november and december which reached a peak value at midnight was interesting and anomalous by invoking the more recent data november and december in 2003 as well as the diurnal temperature observations from december 1998 we report that the evanescent trapped diurnal tidal perturbations were robust and persisted from one year to the next

global distribution and interannual variations of mesospheric and lower thermospheric neutral wind diurnal tide 1 migrating tide 1 using the timed doppler interferometer tidi mesospheric and lower thermospheric neutral wind multiyear data set 2002 2007 and ncar time general circulation models gcm 1 2 annual run results 2002 2005 at the tidi sampling points we study the migrating diurnal tide s global distribution interannual and seasonal variations in connection with the mean zonal wind interannual variations a strong quasi biennial oscillation qbo effect on the diurnal tide was observed in the tidi data and reproduced to a lesser degree in the time gcm run the migrating diurnal tide amplitude is larger during the eastward phase of the stratospheric qbo and weaker during the westward phase westward mesospheric equatorial mean zonal winds appeared during the eastward phase of the stratospheric qbo in 2002 2004 and 2006 the strongest qbo effect on both the migrating diurnal tide and mean zonal winds was observed during the march equinox the stronger tides may be related to the weaker gravity wave filtering in the stratosphere during the eastward phase stratospheric qbo the tidi data also exhibit large interhemispheric asymmetry the westward mean zonal winds in the mesosphere appeared to be associated with the enhanced diurnal tide the time gcm 1 2 diurnal tide amplitudes are in general smaller than those observed by the tidi instrument limited vertical spatial resolution for the time cgm 1 2 is suggested as the cause future improvements are expected with a higher spatial resolution in the model

in situ observation of contour currents in the northern south china sea applications for deepwater sediment transport deepwater currents and related suspended sediment concentration were obtained by an acoustic doppler current profiler adcp mooring system in the northern south china sea from september 2011 to may 2013 to characterize the occurrence of contour currents and to evaluate their sediment transport capacity magnitude of the current velocity generally varied in the range of 0 2 cm s with a dominant flow direction of 250 southwestward the observed contour current defined as the along slope component of the deepwater currents has a tunnel like vertical structure with the largest velocity occurring in the middle of the tunnel and decreasing outwards both the magnitude and the depth range of the maximum velocity display evident inter seasonal variations with the strongest velocity in summer and the weakest in spring while the thickness of the contour currents was the highest in winter and the lowest in spring we also found that passing through of the deep reaching mesoscale eddies significantly affected the magnitude and direction of the contour currents the suspended sediment concentration ssc estimated from echo intensities of the adcp is the highest at the near bottom 400 g l and decreases upwards to 10 g l at water depth shallower than 1750 m high ssc is mostly observed during periods of low magnitude of the contour currents suggesting resuspension of sediment from the seafloor is not the major controlling factor of these high ssc events our observation also suggests that the major role that contour currents play is to transport sediment from the sources through keeping sediment suspended above the lower continental slope of the south china sea

oceanic density fronts steering bottom current induced sedimentation deduced from a 50 ka contourite drift record and numerical modeling off nw spain abstract how the various bottom near hydrographic and sedimentary processes control the formation of contourite drifts i e of bottom current related confined deep sea depocenters usually remains widely speculative this study uses a transect of six sediment cores and a sediment echosounder profile across a whole contourite system off nw spain to address the sediment dynamics responsible for the depositional pattern this mounded patch type contourite drift 18 km long 20 km wide with a 150 m deep channel moat has formed around an 800 m high structural obstacle deposition on the contourite drift in the past was characterized by alternating calm and high energy bottom flow conditions calm conditions last glacial period 27 17 cal ka bp late holocene times process based numerical modeling demonstrates that pulse like oceanic density fronts traveling within the transition zone of two water masses labrador sea water mediterranean outflow water provide a powerful mechanism for contouritic deposition rather than the core of a water mass itself these gravity driven density fronts lead to local re suspension of sands stored inside the drift s moat and to subsequent upward transport towards the drift s crest here the oceanic density fronts produce additional km scale eddies these migrating eddies provide an efficient mechanism for further widespread sediment re distribution in comparison with paleoceanographic reconstructions a downward migration or expansion of the mediterranean outflow water by about 300 m led most probably to such temporary contouritic sand deposition we finally propose a conceptual model to explain how seafloor obstacles redirect and perturbate bottom currents this model proposes not only a sharp contact between two water masses but also the transition zone between those as an important high energy regime offering oceanic density fronts a travel medium these fronts are strong enough to distribute fine sands across highly pronounced seabed topography on the respective time scale the moat itself seems to act as the main source for those sands making a remote source and a long distance sediment transport unnecessary

source to sink transport processes of fluvial sediments in the south china sea the south china sea offers an excellent case for studying source to sink transport processes of fluvial sediments among the global marginal seas this study synthesizes existing clay mineralogical and geochemical data from similar to 1500 samples from the seafloor and surrounding rivers deepwater mooring observation results and high resolution glacial cyclic clay mineralogy records from six high quality sediment cores source to sink sediment transport from the river mouth to the continental shelf and then to the abyssal basin is investigated at two time scales modern process and late quaternary glacial cycles the results firstly show the high diversity of clay mineralogical and geochemical compositions in riverbed surface sediments surrounding the south china sea e g dominant illite and chlorite in taiwan overwhelming majority of smectite in luzon dominant kaolinite in south china and similar amounts of the four clay mineral species in red and mekong river systems the formation of these fluvial sediments through chemical weathering in surrounding drainage systems is controlled principally by the east asian monsoon climate with warm temperature and high precipitation and subordinately by tectonic activity and specific lithological character the basin wide distribution of clay mineral assemblages combined with neodymium and strontium isotopic compositions reflects strong provenance control and differential settling effects the differential settling of kaolinite in slightly saline and proximal regions relative to smectite in more saline and distal regions is well demonstrated in the south china sea through combining clay mineralogical distributions on the seafloor with observed oceanic current systems the modern transport pathways can be well established e g in the northern south china sea illite and chlorite from taiwan are mainly carried by contour currents with the strong influence of mesoscale eddies high resolution sediment dynamic analysis for the late quaternary reveals different sediment transport patterns in the northern western and southern south china sea when the land sea configuration dramatically changed during glacial conditions in the north the terrigenous dispersal is mainly controlled by provenance supply and oceanic current transport in the west the clay mineral assemblage reflects variations of the prevailing surface current influenced by monsoon winds in the south the clay mineral input indicates intensive chemical weathering during interglacial periods and strengthened physical erosion during glacial periods the transport of terrigenous sediments since the last glaciation is quantitatively reconstructed through studying two deepwater sediment cores located in the northern south china sea the relative contributions from three provenances south china luzon and taiwan highlight their distinct variability over the last 28 ka implying that the southward shift of the inter tropical convergence zone itcz at 16 ka bp caused an increased sediment contribution from south china the intensified influence of the kuroshio current intrusion controls more efficient westward transport of luzon sediments and the stronger deepwater current transports taiwan sourced sediments further westward from the last glaciation to the holocene c 2015 elsevier b v all rights reserved

concurrent oh imager and sodium temperature wind lidar observation of localized ripples over northern colorado 1 on 3 and 5 september 2002 the oh all sky imager at platteville colorado 40 2 n 104 7 w observed small scale wavelike patterns known as ripples with horizontal wavelengths of 9 km and 7 km and lifetimes of 9 min and 15 min respectively the colorado state university sodium lidar at nearby fort collins colorado 40 6 n 105 w also made concurrent observations of temperature and zonal and meridional winds which allowed us to determine the nature of the ripples observed our observations suggest that the 3 september ripple was induced by a convective instability located at 87 5 km and the 5 september ripple was induced by a dynamic instability at 88 5 km the ripples clearly advected as packets with the background wind lidar measurements also allowed us to relate the directions of wind shear to the phase front alignments of both the ripples and the nearby short period atmospheric gravity waves these spatial relationships provided a meaningful comparison with previously observed ripples as well as with current theoretical models using the 16 hour continuous lidar data set for each case we deduced that long period waves created an unusually large temperature perturbation at the ripple times on 3 september and an unusually large wind shear perturbation on 5 september these perturbations prepared the background atmosphere to be near the verge of local instability but as revealed again by lidar observation it was the superposition of smaller scale perturbations at the time of the ripples that helped to actually reach the conditions required for instability and generation of the ripples

neotectonic regime on the passive continental margin of the northern south china sea abstract between 1989 and 1994 more than 6600 km of reflection seismic profiles were obtained in the south china sea off hong kong with the german research vessel sonne during cruises so 50b so 72a and so 95 a seismo stratigraphic interpretation of this data set leads to a new age assignment of the unconformity t0 which we place within the pleistocene both neogene unconformities t1 and t0 are generated by uplift of the dongsha rise and truncation of their overlying strata this uplift is caused by intrusion of magma into the upper crust our seismic profiles show plutons which have penetrated the sedimentary cover whereby their original stratification in the contact zone is eliminated these magmato tectonic events may be correlated to the two main collision phases between taiwan and the continental margin of east china 5 3 and 3 0 ma ago the collisional events subsequent to the nnw to wnw drift of taiwan transformed the compression into strike slip movements along the continental margin of southeastern china the accompanying stress regime is transtensional with subsidence of the cooling oceanic crust since the cessation of rifting and its consumption beneath the manila trench providing the extensional stress the strike slip movements remobilized many of the rift and drift faults providing pathways for magma ascent the tectonic framework of the northern south china sea is characterized by miocene faults trending ne sw these faults are scarce but are distributed throughout the study area pliocene faults striking ene wsw to ne sw are concentrated west of the dongsha islands and are mostly strike slip in character recent faults are generally oriented ne sw subparallel to the synrift faults they result in part from local uplifts where they are normal in character but strike slip motion also occurs most of the faults involve the basement and represent reactivated zones of weakness of the rift and drift phases

the origin of stationary planetary waves in the upper mesosphere abstract satellite observations indicate that quasi stationary planetary waves often exist to at least 100 km in the winter mesosphere waves are also seen in the summer upper mesosphere a three dimensional numerical model was used to simulate these waves and to diagnose the physical processes involved the waves simulated in the model closely resemble observed waves several model runs that isolate specific processes are used to determine the relative importance of two forcing mechanisms in the model planetary waves that propagate from below are significantly damped at the altitude where gravity wave drag becomes large about 75 km in the winter midlatitudes or below if a reversal in the mean wind is encountered momentum forcing associated with breaking gravity waves that have been filtered by planetary scale wind variations below acts to generate planetary waves in the middle and upper mesosphere the amplitude from in situ forcing by gravity wave breaking exceeds the amplitude from the upward prop

3d data derived lithospheric structure of the central andes and its implications for deformation insights from gravity and geodynamic modelling abstract we present a new three dimensional density model of the central andes characterizing the structure and composition of the lithosphere together with a geodynamic simulation subjected to continental intraplate shortening the principal aim of this study is to assess the link between heterogeneities in the lithosphere and different deformation patterns and styles along the orogen foreland system of the central andes first we performed a 3d integration of new geological and geophysical data with previous models through forward modelling of bouguer anomalies subsequently a geodynamic model was set up and parametrized from the previously obtained 3d structure and composition we do not find a unambigous correlation between the resulting density configuration and terrane boundaries proposed by other authors our models reproduce the observed bouguer anomaly and deformation patterns in the foreland we find that thin skinned deformation in the subandean fold and thrust belt is controlled by a thick sedimentary layer and coeval underthrusting of thin crust of the foreland beneath the thick crust of the andean plateau in the adjacent thick skinned deformation province of the inverted cretaceous extensional santa barbara system sedimentary strata are much thinner and crustal thickness transitions from greater values in the andean to a more reduced thickness in the foreland our results show that deformation processes occur where the highest gradients of lithospheric strength are present between the orogen and the foreland thus suggesting a spatial correlation between deformation and lithospheric strength

longitude variations of the solar semidiurnal tides in the mesosphere and lower thermosphere at low latitudes observed from ground and space 1 we present an analysis of longitudinal variation in the solar semidiurnal tide observed in the nocturnal thermal structure of the low latitude mesopause region 83 103 km with a focus on two sites arecibo puerto rico 18 3 n 66 8 w and maui hawaii 20 7 n 156 3 w localized observations made by lidars are combined with longitudinal measurements by sounding of the atmosphere using broadband emission radiometry saber and compared with the global scale wave model 2002 gswm 02 for 6 months january april may july august and october in winter spring lidar measured amplitudes are larger than those recorded by saber whereas in summer the amplitudes are similar and in autumn the lidars observe smaller amplitudes than saber gswm amplitudes are between the lidar and saber measurements for january are comparable to the measurements in spring underpredict for summer and agree with the lidars in autumn the phase structure is consistent among lidars and saber for all of the months except january when there is a large phase shift and the local time of the temperature maximum is different between arecibo and maui gswm shows better agreement with phase measurements in winter spring than in summer autumn modal analysis of the saber data indicates that the 2 2 hough mode is present throughout the year in winter it is joined by the 2 4 mode while in summer it is accompanied by the 2 3 mode this change in the predominant hough modes may be related to the winter summer phase difference

southern argentina agile meteor radar system design and initial measurements of large scale winds and tides 1 the southern argentina agile meteor radar saamer was installed at rio grande on tierra del fuego 53 8 s 67 8 w in may 2008 and has been operational for 24 months this paper describes the motivations for the radar design and its placement at the southern tip of south america its operating modes and capabilities and observations of the mean winds planetary waves and tides during its first 20 months of operation saamer was specifically designed to provide very high resolution of large scale motions and hopefully enable direct measurements of the vertical momentum flux by gravity waves which have only been possible previously with dual or multiple beam radars and lidars or in situ measurements saamer was placed on tierra del fuego because it was a region devoid of similar measurements the latitude was anticipated to provide high sensitivity to an expected large semidiurnal tide and the region is now recognized to be a hot spot of small scale gravity wave activity extending from the troposphere into the mesosphere and lower thermosphere perhaps the most dynamically active location on earth saamer was also intended to permit simultaneous enhanced meteor studies including head echo and nonspecular measurements which were previously possible only with high power large aperture radars initial measurements have defined the mean circulation and structure exhibited planetary waves at various periods and revealed large semidiurnal tide amplitudes and variability with maximum amplitudes at higher altitudes often exceeding 60 m s 1 and amplitude modulations at periods from a few to 30 days

tidal perturbations and variability in the mesopause region over fort collins co 41n 105w continuous multi day temperature and wind lidar observations 1 an unusually long data set was acquired at the sodium lidar facility at colorado state university 41n 105w between sep 18 and oct 01 2003 including a 9 day continuous observation this time is long enough to average out the perturbations of gravity waves and short period planetary waves as such it can be used to define tidal period perturbations in temperature and horizontal wind assuming the sodium mixing ratio is a constant of motion the observed tidal period oscillation in sodium density follows that of vertical wind thus the data set defines tidal period perturbations of temperature and wind vector the observed amplitudes and phases were compared to global scale wave model predictions both gswm00 and gswm02 we found excellent agreement in diurnal phases and reasonable agreement in semidiurnal phases however gswm02 overestimates diurnal amplitudes and both model versions underestimate observed semidiurnal amplitudes since the data period is long enough for the study of planetary waves and of tidal variability we perform spectral analysis of the data revealing a strong quasi 3 day wave in meridional wind a 14 hour perturbation in zonal wind and both 14 hour and 10 hour periods in meridional wind likely the result of nonlinear interactions the observed semidiurnal amplitudes are much larger than the corresponding diurnal amplitudes above 85 km and over a few days the diurnal and semidiurnal amplitudes vary by factors of 2 3 causes for the observed tidal variability in terms of planetary wave modulation and tide gravity wave interaction are explored qualitatively

coordinated investigation of midlatitude upper mesospheric temperature inversion layers and the associated gravity wave forcing by na lidar and advanced mesospheric temperature mapper in logan utah mesospheric inversion layers mil are well studied in the literature but their relationship to the dynamic feature associated with the breaking of atmospheric waves in the mesosphere lower thermosphere mlt region are not well understood two strong mil events t 30 k were observed above 90 km during a 6 day full diurnal cycle na lidar campaign conducted from 6 august to 13 august logan utah 42 n 112 w colocated advanced mesospheric temperature mapper observations provided key information on concurrent gravity wave gw events and their characteristics during the nighttime observations the study found both mils were well correlated with the development and presence of an unstable region 2 km above the mil peak altitudes and a highly stable region below implicating the strengthening of mil is likely due to the increase of downward heat flux by the enhanced saturation of gravity wave when it propagates through a highly stable layer each mil event also exhibited distinct features one showed a downward progression most likely due to tidal gw interaction while the peak height of the other event remained constant during further investigation of atmospheric stability surrounding the mil structure lidar measurements indicate a sharp enhancement of the convective stability below the peak altitude of each mil we postulate that the sources of these stable layers were different one was potentially triggered by concurrent large tidal wave activity and the other during the passage of a strong mesospheric bore

observations of the r reflector and sediment interface reflection at the shallow water 06 central site acoustic bottom interacting measurements from the shallow water 06 experiment experiment frequency range 1 20khz are presented these are co located with coring and stratigraphic studies showing a thin 20cm higher sound speed layer overlaying a thicker 20m lower sound speed layer ending at a high impedance reflector r reflector reflections from the r reflector and analysis of the bottom reflection coefficient magnitude for the upper two sediment layers confirm both these features geoacoustic parameters are estimated dispersion effects addressed and forward modeling using the parabolic wave equation undertaken the reflection coefficient measurements suggest a nonlinear attenuation law for the thin layer of sandy sediments

short range travel time geoacoustic inversion with vertical line array this paper presents travel time geoacoustic inversion of broadband data collected on a vertical line array at short range of 230 m during the shallow water 2006 experiments a ray tracing method combined with a hybrid optimization algorithm that utilizes differential evolution and downhill simplex was used for the inversion of sediment properties the ocean sound speed profile and geometric parameters were inverted prior to the sea bottom properties to account for the temporally variable ocean environment the sediment sound speed and thickness estimates are consistent with in situ measurements and matched field inversion results of longer range data from the experiment

variability of the deep water overflow in the luzon strait abstractthe luzon strait with its deepest sills at the bashi channel and luzon trough is the only deep connection between the pacific ocean and the south china sea scs to investigate the deep water overflow through the luzon strait 3 5 yr of continuous mooring observations have been conducted in the deep bashi channel and luzon trough for the first time these observations enable us to assess the detailed variability of the deep water overflow from the pacific to the scs on average the along stream velocity of the overflow is at its maximum at about 120 m above the ocean bottom reaching 19 9 6 5 and 23 0 11 8 cm s 1 at the central bashi channel and luzon trough respectively the velocity measurements can be translated to a mean volume transport for the deep water overflow of 0 83 0 46 sverdrups sv 1 sv 106 m3 s 1 at the bashi channel and 0 88 0 77 sv at the luzon trough significant intraseasonal and seasonal variations are identified with their dominant time scales ranging between

the formation and fate of internal waves in the south china sea internal oceanic waves are subsurface gravity waves that can be enormous and travel thousands of kilometres before breaking but they are difficult to study here observations of such waves in the south china sea reveal their formation mechanism extreme turbulence relationship to the kuroshio current and energy budget internal waves are the underwater version of more familiar surface waves they can be enormous and travel thousands of kilometres before breaking the south china sea is known to be home to the largest internal waves in the world s oceans but their size generation mechanisms and role in the regional energy budget are unknown matthew alford and colleagues now present the results from the iwise observational campaign and reveal that internal waves more than 200 metres high break in the south china sea and create turbulence that is orders of magnitude larger than in the open ocean and that wave formation is influenced by the kuroshio current these results now allow for a complete energy budget of the south china sea and for a more accurate incorporation of internal waves into climate models internal gravity waves the subsurface analogue of the familiar surface gravity waves that break on beaches are ubiquitous in the ocean because of their strong vertical and horizontal currents and the turbulent mixing caused by their breaking they affect a panoply of ocean processes such as the supply of nutrients for photosynthesis1 sediment and pollutant transport2 and acoustic transmission3 they also pose hazards for man made structures in the ocean4 generated primarily by the wind and the tides internal waves can travel thousands of kilometres from their sources before breaking5 making it challenging to observe them and to include them in numerical climate models which are sensitive to their effects6 7 for over a decade studies8 9 10 11 have targeted the south china sea where the oceans most powerful known internal waves are generated in the luzon strait and steepen dramatically as they propagate west confusion has persisted regarding their mechanism of generation variability and energy budget however owing to the lack of in situ data from the luzon strait where extreme flow conditions make measurements difficult here we use new observations and numerical models to 1 show that the waves begin as sinusoidal disturbances rather than arising from sharp hydraulic phenomena 2 reveal the existence of 200 metre high breaking internal waves in the region of generation that give rise to turbulence levels 10 000 times that in the open ocean 3 determine that the kuroshio western boundary current noticeably refracts the internal wave field emanating from the luzon strait and 4 demonstrate a factor of two agreement between modelled and observed energy fluxes which allows us to produce an observationally supported energy budget of the region together these findings give a cradle to grave picture of internal waves on a basin scale which will support further improvements of their representation in numerical climate predictions

modeling and analysis of the structure and generation of the terdiurnal tide the terdiurnal or 8 h tide has been seen in a number of midlatitude radar measurements and has recently been mapped globally at 95 km a series of calculations and model simulations are used to examine the processes responsible for generating this tide and for its strong hemispheric asymmetry the model tidal structure deviates significantly from the structure of a single hough mode in contrast to the diurnal tide the dominant cause of the hemispheric asymmetry is the sensitivity of the propagation to the background state particularly the static stability several conceptual views of the tide are explored to give a heuristic view of this asymmetry this analysis predicts that particular modes are prohibited from propagating in large regions of the summer mesosphere the tide occurs naturally in a three dimensional nonlinear model extending from the tropopause to the lower thermosphere the model tide shows a number of features in common with observations including amplitude maxima in midlatitudes a wintertime peak and zonal winds larger than meridional winds the tidal amplitude in the model is weaker than observed at 95 km several interactive model integrations are performed to determine the forcing mechanism for the tide these calculations indicate that the direct solar forcing of the terdiurnal tide is the dominant mechanism occurring in the model at middle and high latitudes nonlinear interactions contribute to the low latitude tide

bayesian geoacoustic inversion in a dynamic shallow water environment this paper presents results for matched field bayesian geoacoustic inversion of multitonal continuous wave data collected on the new jersey continental shelf to account for effects of significant spatial and temporal variation of the water column sound speed the sound speed profile was represented by empirical orthogonal functions data error information for the inversion was estimated from multiple time windows of the data inversion results for the sediment sound speeds at three ranges are in excellent agreement with the ground truth

a contourite depositional system along the uruguayan continental margin sedimentary oceanographic and paleoceanographic implications abstract for the first time a multidisciplinary approach to evaluate the influence of bottom currents in the uruguayan continental margin is presented bathymetric data and multichannel 2d and 3d seismic reflection profiles were used to construct a morphosedimentary map to interpret and decode sedimentary and oceanographic processes along the uruguayan continental margin based on these results an extensive contourite depositional system on the margin is described which contains an impressive array of large erosive depositional drifts and mixed terrace features which have been generated primarily by the near bottom flows associated with water masses of antarctic and subantarctic origin from the eocene oligocene boundary up to present time the long term influence of water masses from higher southern latitudes in combination with down slope sedimentary processes have strongly controlled the overall margin morphology most of the features described here were formed during the middle late miocene epoch due to paleoceanographic shifts that include the arrival of antarctic intermediate water along the margin which in combination with deeper antarctic bottom water are fundamental in the margin evolution in combination with quaternary climatic and eustatic changes in sea level fluctuations of the brazil malvinas confluence influenced subsequently glacial and interglacial stages as recognized in sedimentary features defined here these paleoceanographic changes controlled the sedimentary stacking pattern and the locations of high amplitude reflections along the contourite terraces which could be associated with sandy deposits a more detailed understanding of the margin will improve interpretations of variations in the south atlantic subtropical gyre and further constrain general climatic and ocean circulation models

wind velocity and temperature fluctuations due to a 2 day wave observed with radio meteor echoes we study in this paper characteristics of both wind velocity and temperature fluctuations due to a 2 day wave near the mesopause by means of meteor echo measurements with the mu middle and upper atmosphere radar in shigaraki japan 35 n 136 e and a meteor wind radar newly constructed near jakarta indonesia 6 s 107 e a 2 day wave was conspicuously enhanced on july 12 19 1993 at both shigaraki and jakarta fluctuations of temperature and northward wind were inphase in shigaraki and they became antiphase in jakarta consistent with a prediction assuming a rossby gravity wave the phase lag of the fluctuations between the two sites suggested that this wave propagated westward with a zonal wavenumber of 3 seasonal variations of the 2 day wave in jakarta were examined by using a frequency spectrum and complex demodulation technique for temperature and wind fields finding clear enhancements during periods corresponding to summer months in each hemisphere especially in january 1993 the dominant wave period was fairly stable and was confined in a narrow range centered around 47 and 49 hours during summer months of the southern and northern hemispheres respectively the phase variations of temperature preceded those for the northward wind by 180 225 when an enhanced 2 day wave was seen in the northward component indicating their antiphase relation in the southern hemisphere these results strongly support the interpretation of the 2 day wave near the mesopause as the 3 0 mode of a rossby gravity wave with zonal wavenumber of 3

deepwater overflow through luzon strait 1 this study examines water property distributions in the deep south china sea and adjoining pacific ocean using all available hydrographic data our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the pacific into the south china sea through luzon strait applying hydraulic theory with assumptions of zero potential vorticity and flat bottom to the luzon strait yields a transport estimate of 2 5 sv 1 sv 106 m3 s 1 some implications of this result include 1 a residence time of less than 30 years in the deep south china sea 2 a mean diapycnal diffusivity as large as 10 3 m2 s 1 and 3 an abyssal upwelling rate of about 3 10 6 m s 1 these quantities are consistent with residence times based on oxygen consumption rates the fact that all of the inflowing water must warm up before leaving the basin implies that this marginal sea contributes to the water mass transformations that drive the meridional overturning circulation in the north pacific density distributions within the south china sea basin suggest a cyclonic deep boundary current system as might be expected for an overflow driven abyssal circulation

deep water exchanges between the south china sea and the pacific since the last glacial period deep ocean circulation is widely considered as one of the important factors for increasing co2 concentration and decreasing radiocarbon activity 14c of the atmosphere during the last deglaciation the ams 14c ages of benthic and planktonic foraminifers from 18 samples of core md05 2904 water depth of 2066 m in the northern south china sea scs and 15 samples of core md05 2896 water depth of 1657 m in the southern scs were analyzed in this study for reconstructing the intrabasin deep oceanic processes and hence exploring the deep water exchanges between the scs and the pacific since the last glacial period the results show that during the holocene the average apparent ventilation age of deep water was younger in the southern scs 1350 years than in the northern scs 1850 years due to relatively strong vertical mixing and advection consistent with modern observations however during the last glacial period and deglaciation the deep water was older in the southern scs 2050 years and 1800 to 1200 years respectively than in the northern scs 1600 years and 670 years respectively indicating reduced deep mixing and advection moreover the northern scs deep water was significantly younger during the last deglaciation than during the holocene and the last glacial period implying the existence of northern sourced newly formed and relatively young north pacific deep water our records do not support the intrusion of anomalously 14c depleted deep water to the middepth of the low latitude western pacific and the scs during the mystery interval 17 5 14 5 kyr b p

improved calibration of reflectance data from the lro lunar orbiter laser altimeter lola and implications for space weathering abstract the lunar orbiter laser altimeter lola experiment on lunar reconnaissance orbiter lro is a laser altimeter that also measures the strength of the return pulse from the lunar surface these data have been used to estimate the reflectance of the lunar surface including regions lacking direct solar illumination a new calibration of these data is presented that features lower uncertainties overall and more consistent results in the polar regions we use these data along with newly available maps of the distribution of lunar maria also derived from lro instrument data to investigate a newly discovered dependence of the albedo of the lunar maria on latitude hemingway et al 2015 we confirm that there is an increase in albedo with latitude in the lunar maria and confirm that this variation is not an artifact arising from the distribution of compositions within the lunar maria using data from the lunar prospector neutron spectrometer radiative transfer modeling of the albedo dependence within the lunar maria is consistent with the very weak to absent dependence of albedo on latitude in the lunar highlands the lower abundance of the iron source for space weathering products in the lunar highlands weakens the latitude dependence to the extent that it is only weakly detectable in current data in addition photometric models and normalization may take into account the fact that the lunar albedo is latitude dependent but this dependence can cause errors in normalized reflectance of at most 2 for the majority of near nadir geometries we also investigate whether the latitude dependent albedo may have obscured detection of small mare deposits at high latitudes we find that small regions at high latitudes with low roughness similar to the lunar maria are not mare deposits that may have been misclassified owing to high albedos imposed by the latitude dependence finally we suggest that the only modest correlations among space weathering indicators defined for the lunar samples may be due to mixing of soils from distinct latitudes

depleted deep south china sea δ13c paleoceanographic events in response to tectonic evolution in taiwan luzon strait since middle miocene abstract the most distinctive feature of the deep south china sea scs paleoceanography is the occurrence of long term depleted deep sea benthic foraminiferal 13c values they are lower than the global and the pacific composite records in the last 16 ma especially at 13 2 10 5 6 5 3 0 and 1 2 0 4 ma this distinct deep scs paleoceanograhic history coincides with the subduction collision history in the taiwan region where waters of the west pacific wp and the scs exchange the depleted deep sea benthic foraminiferal 13c events indicate that the scs deep basin became progressively a stagnant environment in the last 16 ma due to either closure of the connection with the wp bottom water or temporary reduction of the wp deep water flowing into the deep scs both the taiwan accretionary prism and the luzon arc became the main tectono morphological barriers for the wp bottom water flowing into the scs deep basin when eastward subduction of the scs oceanic lithosphere beneath the philippine sea plate started from the middle miocene 18 16 ma this began a long term trend of depleted scs deep sea benthic 13c values in the last 16 ma the oblique arc continent collision since 6 5 ma uplifted the taiwan accretionary prism rapidly above sea level and further isolated the scs from the open pacific the collision simultaneously causes backthrusting deformations in the north luzon trough forearc basin and sequentially closes interarc water gates between volcanic islands from north to south the loho and the taitung interarc water gates in the advanced collision zone were closed at 3 0 ma and 1 2 ma coinciding with the very low scs deep sea benthic 13c events at 3 0 and 1 2 0 4 ma respectively the taitung canyon between the lutao and lanyu volcanic islands in the incipient collision zone is semi closed presently these closure events also lead to the result that the wp deep water intrudes westward into the scs principally through the bashi channel between the lanyu and batan volcanic islands in the subduction zone

early interglacial carbonate dilution events in the south china sea implications for strengthened typhoon activities over subtropical east asia abstract a compilation of many late quaternary marine sediment records from the northern south china sea scs continental slope confirms 15 50 reductions in sedimentary calcium carbonate concentrations between 11 0 and 8 5 ka bp in the early holocene this low carbonate event occurred at a time when the regional sea level rose from 50 m to 10 m which drowned large areas of continental shelves especially those near and within the taiwan strait this event is associated with a significant increase in bulk sedimentation rates on the upper continental slope and the relative abundance of fine grained detritus sediment provenance analyses suggest a dominant terrigenous input from taiwan and a minor contribution from luzon during the low carbonate event similar to the background terrigenous deposition in other periods of the holocene two comparable low carbonate events respectively from the beginning of marine isotope stages 5 5 and 7 3 have also been recognized pointing to similar causal factors while carbonate dissolution and carbonate accumulation rate should not have been responsible increased terrigenous input and dilution is considered as the main cause for the recurrent low carbonate events in early interglacials we further hypothesize that during early interglacials fluvial sediment discharge from taiwan and luzon intensified due to stronger typhoon activities and massive fine grained sediments from these two end members may have been transported to the northern scs continental slope via surface and deep ocean currents the conjecture of strengthened typhoon activities over east asia during the early holocene is supported by high ocean heat contents in the west pacific warm pool area with the prevailing la nina like conditions

the eddy mean flow interaction and the intrusion of western boundary current into the south china sea type basin in an idealized model abstractin this paper an ideal model of the role of mesoscale eddies in the kuroshio intruding into the south china sea scs is developed which represents the northwestern pacific and the scs as two rectangular basins connected by a gap in the case of considering only intrinsic ocean variability a time dependent western boundary current wbc driven by steady wind is modeled under both eddy resolving and noneddy resolving resolutions almost all simulated wbcs intrude into the adjacent sea in the form of the loop current with multiple state transitions and eddy shedding processes which have aperiodic variations on intraseasonal or interannual scales determined by the eddy induced wbc variation for the parameters considered in this paper the wbc intrusion exhibits a 30 90 day cycle in the presence of the subgrid scale eddy forcing ssef but a 300 500 day cycle in the absence of ssef moreover the roles of the grid scale and subgrid scale eddies in the wbc intrusion are studied by using the dynam

quantifying the uncertainty of geoacoustic parameter estimates for the new jersey shelf by inverting air gun data this paper describes geoacoustic inversion of low frequency air gun data acquired during an experiment on the new jersey shelf hybrid optimization and bayesian inversion techniques based on matched field processing were applied to multiple shots from three air gun data sets recorded by a vertical line array in a long range shallow water geometry for the bayesian inversions full data error covariance matrix was estimated from a set of consecutive shots that had high temporal coherence and small spatial variation in source position the effect of different data error information on the geoacoustic parameter uncertainty estimates was investigated by using the full data error covariance matrix a diagonalized version of the full error covariance and a diagonal matrix with identical variances the comparison demonstrated that inversion using the full data error information provided the most reliable parameter uncertainty estimates the inversions were highly sensitive to the near sea floor geoacoustic parameters including sediment attenuation of a simple single layer geoacoustic model the estimated parameter values of the model were consistent with depth averaged values over wavelength scales of a high resolution geoacoustic model developed from extensive ground truth information the interpretation of the frequency dependence of the estimated attenuation is also discussed

seabed acoustics of a sand ridge on the new jersey continental shelf acoustic measurements were made on a sand ridge on the new jersey continental shelf data collected on two l arrays separated by 20km from a single multi frequency tow suggest small horizontal environmental variability values for the sound speed structure of the seabed are extracted by first applying a geo acoustic inversion method to broadband and narrowband acoustic data from short range sources then a parabolic equation algorithm is used to properly include the bathymetry and sub bottom layering finally the frequency dependence of the seabed attenuation is inferred by optimizing the model fit to long range transmission loss data in the 50 3000hz band

plio quaternary sedimentation processes and neotectonics of the northern continental margin of the south china sea abstract analyses of over 6600 km of reflection seismic profiles on the northern continental margin of the south china sea permit the recognition of four quaternary high frequency type 1 sequences of the 4th order deposited during the past ca 690 kyr at the present day shelf edge only lowstand systems tracts characterised by a prograding clinoformal internal reflection pattern are preserved the prograding complexes can be considered as regressive units accumulated during relative sea level falls they exhibit internal discontinuities which might point to minor sea level fluctuations of the 5th order a preliminary regional relative sea level curve for the past 630 kyr is established using the present positions of the delta fronts mapped the neotectonics curve derived by subtracting eustatic sea level changes from the relative sea level curve shows that the depths of the delta fronts today are controlled primarily by regional tectonic movements and the global sea level our seismo stratigraphic interpretation documents that the area off hong kong and around the dongsha islands experienced two uplift episodes during the past 5 ma namely at the miocene pliocene boundary and at the end of the lower middle pleistocene respectively these uplift events which are centred on the dongsha rise led to its subaerial exposure and to the erosion of the pliocene and most of the pleistocene strata the change from thermal subsidence of the continental margin initiated at the end of the drift phase to the phase of magmato tectonic uplift was caused by a reorientation of the tectonic regime the recent depositional environment on the northern continental margin of the south china sea is dominated by sediment accumulation within the inner shelf and the zhujiang pearl river estuary the outer shelf and upper slope especially around the dongsha islands are characterised by bypass of terrigenous material the sedimentary column in the deepsea basin has a thickness of more than 2 km and comprises 14 depositional units starting with terrestrial rift deposits it overlies oceanic as well as transitional crust

abrupt changes of intermediate water properties on the northeastern slope of the bering sea during the last glacial and deglacial period 1 millennial scale variability in the behavior of north pacific intermediate water during the last glacial and deglacial period and its association with dansgaard oeschger d o cycles and heinrich events are examined based on benthic foraminiferal oxygen and carbon isotopes 18obf and 13cbf and caco3 using a sediment core recovered from the northeastern slope of the bering sea a suite of positive 18obf excursions at intermediate depths of the bering sea which seem at least in part associated with increases in the 18obf gradients between the bering and okhotsk seas suggest the bering sea as a proximate source of intermediate water during several severe stadial episodes in the last glacial and deglacial period absence of such 18obf gradients during periods of high surface productivity in the bering and okhotsk seas which we correlate to d o interstadials suggests a reduction in intermediate water production in the bering sea and subsequent introduction of nutrient rich deep waters from the north pacific into intermediate depths of the bering sea we argue that a reorganization of atmospheric circulation in the high latitude north pacific during severe cold episodes in the last glacial and deglacial period created favorable conditions for brine rejection in the northeastern bering sea the resulting salinity increase in the cold surface waters could have initiated intermediate and deep water formation that spread out to the north pacific

bedform velocity matrix the estimation of bottom current velocity from bedform observations a wide variety of bedforms both depositional and erosional in origin has been recognized on the deep seafloor and attributed to the influence of bottom currents these range in scale from those visible in bottom photographs centimeter to decimeter to those recorded with seafloor bathymetric imaging meter to kilometer in many cases it has been possible to provide some quantification of substrate grain size and flow velocity responsible for each bedform type we have synthesized both our own and published data in order to present a bedform velocity matrix which facilitates the estimation of bottom current velocity based on bedform type despite imperfections we believe this to be a valuable model for assessing strength and variability of bottom currents that can have a significant influence on the siting of submarine cables pipelines and other seafloor installations

pliocene holocene contourite deposition under the antarctic circumpolar current western falkland trough south atlantic ocean the eastward flowing antarctic circumpolar current acc has influenced sedimentation on the slope and floor of the western falkland trough where the axis of the current is topographically constrained deep water flow below 3000 m has produced a symmetrical sediment drift on the trough floor with non depositional margins indicating higher current velocities at the base of slope to the southeast of the falkland islands there is a gap in the north scotia ridge north of which the floor of the trough is swept clean of sediment by the acc both echo character mapping and gloria side scan data indicate that currents follow the bathymetric contours along the slope redistributing sediment and locally eroding furrows from six cores on the drift and on the northern slope two styles of contourite deposition have been identified on the drift holocene biogenic sandy contourites overlie last glacial maximum muddy contourites and fine grained diatomaceous hemipelagites sedimentation rates here average 3 4 cm ka 1 the sandy contourites present in four of the cores from the sediment drift are sharply underlain by the finer grained diatomaceous hemipelagites the lack of a coarsening upward sequence commonly associated with an increase in current velocity may be indicative of high current activity eroding away the finer negative sequence pliocene and mid pleistocene glaucony rich sandy contourites containing radiolaria characterise the falkland plateau and the floor of the trough near the gap in the north scotia ridge we suggest that the glaucony is derived from a combination of authigenic formation and erosion of locally outcropping cretaceous and tertiary strata this is supported by dinoflagellate analysis sedimentation rates in these current swept areas average 1 cm ka 1

atmospheric tides in the low latitude e and f regions and their responses to a sudden stratospheric warming event in january 2010 an extensive analysis of atmospheric tides in the low latitude thermosphere and their responses to a major sudden stratospheric warming ssw event 18 23 january 2010 is presented the analysis is based on observational data from the arecibo dual beam incoherent scatter radar important findings of the present study are as follows 1 the diurnal tide with an evanescent phase structure dominates the f region meridional wind field the diurnal tide has a peak amplitude of 45 m s occurring at about 245 km and it is very stable throughout the nine consecutive days observation below 114 km the vertical structures of the diurnal tide in the meridional and zonal components are consistent which resemble the classical solar s 1 s 1 tidal mode 2 the f region semidiurnal tide is much weaker and has larger day to day variability than the diurnal tide in the e region the semidiurnal amplitudes in the meridional and zonal components grow continuously in the altitude ranges from 106 to 121 km and from 100 to 115 km respectively the vertical wavelength of the zonal component is estimated to be 45 km above 100 km which is close to the solar s 2 s 4 and s 2 s 5 tidal modes 3 the semidiurnal and terdiurnal tides respond strongly to the ssw while the impact that the ssw has on the diurnal tide in the meridional wind is limited during the ssw event the amplitudes of the semidiurnal and terdiurnal tides are enhanced in the f region but reduced in the upper e region

tides in the mesopause region over fort collins colorado 41 n 105 w based on lidar temperature observations covering full diurnal cycles 1 eighteen sets of 24 hour continuous lidar temperature observation well distributed throughout the year have been analyzed to reveal the mean amplitude and phase of oscillations with 24 12 8 and 6 hour periods for four seasons the amplitude and phase of both 24 and 12 hour components are compared to the prediction of the most recent global scale wave model gswm 00 the variability of diurnal and semidiurnal oscillations is examined by comparing the amplitude and phases of each observed day in autumn winter and spring even with the limited data sets reported here surprisingly good general agreement between the observed and model tidal phases can be established implicating the prevalence of migrating diurnal and semidiurnal tides compared to the diurnal and semidiurnal phases which typically show clear downward phase progression the 8 and 6 hour components exhibit small amplitude and show unorganized phase propagation as a function of altitude the advantage of having coverage over complete diurnal cycle and entire mesopause altitudes as demonstrated here would hopefully stimulate future tidal studies with lidar temperature and zonal and meridional wind observations

the role of non uniform roughness in the formation of sand ribbons abstract sand ribbons typically are shallow water sedimentary features characterized as thin elongate bands of sand overlying a coarser lag sediment which is exposed between them the ribbons are oriented along the direction of the dominant current and are formed by a secondary circulation pattern that includes a small component of the boundary shear stress directed toward the center of the sand ribbons a perturbation expansion coupled with flume experiments indicates that this circulation pattern is linked to differences in the bottom roughness between the sand ribbons and the adjacent coarser strips the non uniform turbulence field arising from this roughness distribution drives a secondary helical flow the expansion indicates that there is a preferred ratio of sand ribbon spacing to water depth 4 1 for unstratified channel flow conditions the secondary flow pattern forces the downstream flow to readjust so that the boundary shear stress over the smooth sand strips is considerably smaller than the mean stress this serves to retard the movement of sand through such a system

sequential geoacoustic inversion at the continental shelfbreak environmental parameters can have large spatial and temporal variability in shelfbreak regions the capability of sequential bayesian filters in tracking this variation is investigated particle filtering pf is used to extract the environmental parameters and their uncertainties the method tracks the environment with fewer particles relative to conventional geoacoustic inversion methods using successive independent inversions as an example data from the shallow water 2006 experiment are processed the pf approach first is used to track the source and the environment with little spatial variation just northwest of the shelfbreak then the strongly range dependent shelfbreak region is analyzed and the pf results are compared to previous geoacoustic inversion studies from the region

the influence of oceanographic processes on contourite features a multidisciplinary study of the northern south china sea abstract this study examines how multiscale oceanographic processes interact with the seafloor to influence the development of contourite features in northern part of the south china sea the multidisciplinary approach used in this study combines physical oceanographic monitoring numerical simulation multibeam echosounding seismic reflection profiling and sediment core interpretation the contourites detected and interpreted herein include depositional drifts and sediment waves erosional channels moats and furrows and mixed erosional and depositional features terraces and irregular depressions this study finds that climatic variation influences the intensity of quasi steady along slope regional water circulation which in turn influences the long term development of primary 10 100 km contourite depositional systems energetic but intermittent oceanographic processes such as eddies and internal waves generate smaller secondary features within the contourite depositional systems resulting in a complex local seafloor morphology westward to south westward migrating mesoscale eddies locally enhance regional water mass circulation and trigger sub mesoscale flows which can generate 1 10 km irregular depressions along their paths westward propagating internal solitary waves form sedimentary waves with the aid of numerical modelling results a sedimentary model is proposed to explain how oceanographic processes influence sedimentary processes and determine a hierarchy of associated feature formation this model can help advance understanding of how bottom currents influence sedimentary processes along continental margins and abyssal plains

effect of ocean sound speed uncertainty on matched field geoacoustic inversion the effect of ocean sound speed uncertainty on matched field geoacoustic inversion is investigated using data from the sw06 experiment along a nearly range independent bathymetric track significant sound speed differences were observed at the source and receiving array and several environmental parameterizations were investigated for the inversion including representing the ocean sound speed at both source and receivers with empirical orthogonal function eof coefficients a genetic algorithm based global optimization method was applied to the candidate environmental models then a bayesian inversion technique was used to quantify uncertainty in the environmental parameters for the best environmental model which included an eof description of the ocean sound speed

ionospheric and dynamical characteristics of the mesosphere lower thermosphere region over platteville 40 n 105 w and comparisons with the region over saskatoon 52 n 107 w 1 the newly installed medium frequency radar mfr at platteville provides unique opportunities to assess latitudinal effects in both the ionosphere and mesosphere lower thermosphere mlt by comparisons with the long established mfr at saskatoon the influence of the d region winter anomaly is evident in both ionospheres and descending sporadic layers 110 90 km are identified especially at 40 n for the first time for mf radar systems preliminary comparisons with the wind measurements are made and the processes are identified as complex contour plots of mean winds tides 12 and 24 hour and planetary waves pw 2 and 16 day demonstrate significant trends over 12 of latitude 1100 km the 24 hour tide dominates at 40 n the 12 hour tide dominates at 52 n and pw structures demonstrate spatial and temporal intermittency the two radars are now part of a new network canada u s japan opportunity cujo stretching from 81 w to 141 e

seasonal variations of semidiurnal tidal perturbations in mesopause region temperature and zonal and meridional winds above fort collins colorado 40 6 n 105 1 w 1 on the basis of colorado state university csu na lidar observations over full diurnal cycles from may 2002 to april 2006 a harmonic analysis was performed to extract semidiurnal perturbations in mesopause region temperature and zonal and meridional winds over fort collins colorado 40 6 n 105 1 w the observed monthly results are in good agreement with mf radar tidal climatology for urbana illinois and with predictions of the hamburg model of the neutral and ionized atmosphere hammonia sampled at the csu na lidar coordinates the observed semidiurnal tidal period perturbation within the mesopause region is found to be dominated by propagating modes in winter and equinoctial months with a combined vertical wavelength varying from 50 km to almost 90 km and by a mode with evanescent behavior and longer vertical wavelength 100 150 km in summer months most likely due to dominance of 2 2 and 2 3 tidal hough modes the observed semidiurnal tidal amplitude shows strong seasonal variation with a large amplitude during the winter months with a higher growth rate above 85 90 km and minimal amplitudes during the summer months maximum tidal amplitudes over 50 m s for wind and 12 k for temperature occur during fall equinox a detailed comparison with hammonia predictions shows excellent agreement in semidiurnal phases hammonia predicted semidiurnal amplitudes generally agree well with observations however hommonia underestimates temperature amplitudes in some of the nonsummer months as well as zonal wind and meridional wind amplitudes in april and september but overestimates them in february to reveal the effects of the atmospheric background on vertical propagation of tidal modes and their relative importance in the composite semidiurnal tide during different seasons we use the lidar observed monthly mean temperature and zonal wind from the same data set as well as hammonia output to calculate the vertical wave number seasonal variations of the major tidal modes of the migrating semidiurnal tide this leads to a qualitative understanding of the lidar observed and hammonia predicted seasonal variation of the semidiurnal tidal perturbation