the effect of rupture complexity on estimates of source size a general technique is proposed for estimating rupture geometry from measurements of body wave durations wherein measurements of the overall signal duration or the duration of a single pulse identified in all of the arrivals are inverted to estimate the geometry of the overall rupture or of a specific subevent respectively the complexity of a waveform is determined by comparing the overall signal duration to the duration of the most prominent pulse in the waveform this complexity is used to estimate the ratio of the average rupture velocity to the subevent rupture velocity the shear waves radiated by eight moderate 3 6 ml 4 9 multiply recorded aftershocks of the 1975 oroville california earthquake are analyzed using measurements of the corner frequency the characteristic frequency the pulse duration and the signal duration comparison of these four different estimates of source size indicates that the corner frequency and the characteristic frequency are more sensitive to the dominant subevent size than to the overall event size the difference between the estimates of source size determined from the signal duration measurements and the spectral measurements increases as the rupture complexity increases

space time description of nonstationary trapped lee waves using st radars aircraft and constant volume balloons during the pyrex experiment abstract the third intensive observation period iop3 of pyrex was a case of strong lee waves generated by a southerly wind crossing the pyrenees chain upstream radiosounds and measurements obtained by aircraft along the chain transect and by constant volume balloons launched near the crest provided spatial characteristics of the lee wave at different times and heights values ranging from 7 to 14 km for the horizontal wavelength and from 3 to 5 m s 1 for the maximum amplitude of the air vertical velocity were observed the lee wave horizontal extent measured from the crest line reached 30 to 55 km in addition two very high frequency stratosphere troposphere vhf st radars one on the mountain mean axis and another downstream in the lee wave field observed the temporal variations of the vertical profiles of the vertical velocity the analysis of those observed variations and their vertical distribution allowed the stationarity of the wave to be studied the lee wave was found to be far from stat

ice record of a large eruption of deception island volcano antarctica in the xviith century a well marked volcanic ash layer was found at 145 9 m depth in a 154 3 m ice core recovered in 1981 on james ross island antarctic peninsula ash composition analysis indicates that we are dealing with an eruption of the deception island volcano located some 200 km northwestward from james ross island regional lake sediments seem also to have recorded the eruption its date some 350 years ago has been determined precisely by comparison with a well dated south pole station ice core the strength and regional to global impact of the event are discussed it is concluded it was most probably the largest eruption of this volcano over the studied time period this exceptional layer was used to adjust the dating of the core

gravity wave and equatorial wave morphology of the stratosphere derived from long term rocket soundings fluctuations in vertical profiles of atmospheric temperature and horizontal wind in the 20 60 km altitude range have been isolated from meteorological rocket measurements during 1977 87 at 15 widely separated sites the seasonal geographical and vertical variability of the variance of horizontal velocities u 2 2 and relative temperature perturbations t 2 were studied the bulk of the variance of both quantities in the 2 10 km and 2 20 km vertical wavelength bands was associated with gravity wave motions although in depth study of the wave polarization shows that planetary scale equatorial wave modes contribute to the variance at equatorial sites annual mean variances varied widely among the 15 stations suggesting appreciable geographical variability in stratospheric wave activity

the bering sea and paleoceanography abstract this paper serves as an introduction to the bering sea preceding the 14 contributed papers contained in this volume several parts of the paper are allocated for current reviews of the bering sea included in the review topics are geomorphology surface water circulation and the importance of the formation of intermediate waters representative results of previous paleoceanographic studies are also presented in particular focusing on spatial and temporal distributions of biosiliceous microfossils as well as isotopic analyses of carbon and nitrogen concerning changes in productivity and nutrients motivations behind the scientific expeditions conducted which resulted in the many papers included here are briefly discussed in order to illustrate the recent trend in paleoceanography in the bering sea and the adjacent regions brief summaries or highlights of each of the contributed papers are given in order to provide an overview of the volume

evidence of gravity wave ducting in the mesopause region from airglow network observations 1 we present observational evidence of gravity wave ducting and show for the first time that the ducting occurs over large horizontal distances in the mesopause region an optical network of four all sky imagers in japan identified two dimensional patterns of small scale gravity wave bands in oh airglow images on 13 june 2004 the wave signatures clearly showed northward propagation of more than 1800 km over a wide range of latitudes the horizontal wavelength horizontal phase speed and wave period were estimated from the airglow data as 33 4 km 42 8 m s 1 and 13 4 min respectively the wave structure lasted for the whole 5 h airglow observation period simultaneous mf radar wind data and timed saber measurements suggested that the wave was trapped and ducted at the airglow height the ducting likely contributed to the remarkable coherence of the wave as it propagated northward

structure and geodynamic evolution of the central bransfield basin nw antarctica from seismic reflection data abstract the bransfield basin is a young active rift basin located between the northern margin of the antarctic peninsula and the south shetland islands margin deception and bridgeman islands divide the bransfield basin in three subbasins the western central and eastern specific morpho tectonic features and sediment fill differentiate each subbasin the structure and geodynamic evolution of the central bransfield basin which is in a stage of incipient seafloor spreading have been investigated in detail from a dense grid of single channel seismic reflection data the central bransfield basin is dominated by two families of normal faults which are oriented northeast and northwest the ne trending faults define three graben systems that are roughly parallel to the basin axis in an across basin direction the mean trend of this family of faults ranges from n71 the graben system nearest to the antarctic peninsula over n64 the intermediate graben system to n53 the graben system nearest to the south shetland islands the nw trending family of faults is responsible for the deepening of the basin from southwest to northeast both families of faults define the overall central bransfield basin structure resulting in a complex division of the basin floor additionally tens of volcanic edifices are located on the basin floor the larger ones being associated to the nw trending faults interaction of tectonics and sedimentation give place to the differentiation of three tectonostratigraphic units tu1 tu2 and tu3 from oldest to youngest tu1 occupies the southernmost graben system and it is affected by the ne trending bounding normal faults tu2 extends further northwestwards than tu1 and essentially fills the intermediate graben system tu3 represents a further extension of the sediment infill over most of the central bransfield basin and marks the initiation of the infill of the northernmost graben system faults bounding this graben also determine the straight and abrupt morphology of the south shetland islands margin the observed arrangement of the graben systems and the filling tectonostratigraphic units reveal a migration of extensional tectonics and associated depocentres from the antarctic peninsula margin to the south shetland island margin the left lateral rotation from n71 to n53 in the mean trend of the three successive graben systems could have been produced by the oblique subduction of the phoenix plate and the effect of the sinistral strike slip movement of the south scotia ridge 200 km northeastwards of the central bransfield basin

spatial extent of a hydrothermal system at kilauea volcano hawaii determined from array analyses of shallow long period seismicity 2 results we present a probabilistic method to locate the source of seismic events using seismic antennas the method is based on a comparison of the event azimuths and slownesses derived from frequency slowness analyses of array data with a slowness vector model several slowness vector models are considered including both homogeneous and horizontally layered half spaces and also a more complex medium representing the actual topography and three dimensional velocity structure of the region under study in this latter model the slowness vector is obtained from frequency slowness analyses of synthetic signals these signals are generated using the finite difference method and include the effects of topography and velocity structure to reproduce as closely as possible the behavior of the observed wave fields a comparison of these results with those obtained with a homogeneous half space demonstrates the importance of structural and topographic effects which if ignored lead to a bias in the source location we use synthetic seismograms to test the accuracy and stability of the method and to investigate the effect of our choice of probability distributions we conclude that this location method can provide the source position of shallow events within a complex volcanic structure such as kilauea volcano with an error of 200 m

analysis of ducted motions in the stable nocturnal boundary layer during cases 99 abstract data obtained with multiple instruments at the main site of the 1999 cooperative atmosphere surface exchange study cases 99 are employed to examine the character and variability of wave motions occurring in the stable nocturnal boundary layer during the night of 14 october 1999 the predominant motions are surprisingly similar in character throughout the night exhibiting largely westward propagation horizontal wavelengths of 1 to 10 km phase speeds slightly greater than the mean wind in the direction of propagation and highly coherent vertical motions with no apparent phase progression with altitude additionally vertical and horizontal velocities are in approximate quadrature and the largest amplitudes occur at elevated altitudes of maximum stratification these motions are interpreted as ducted gravity waves that propagate along maxima of stratification and mean wind and that are evanescent above and occasionally below the altitudes at which they are ducted modal structures for ducte

doppler ducting of atmospheric gravity waves atmospheric gravity waves are subject to horizontal ducting in a stably stratified atmosphere that contains levels of wind maximum or minimum quite apart from any superimposed consequences of vertical variation of stability and quite apart from the existence or otherwise of critical levels the process doppler ducting is examined here for two prototype cases an isolated wind maximum and a wind minimum at ground level and for two more realistic model cases a strong tropospheric jet and a nocturnal boundary layer jet the wave structure modal behavior and dispersion curves of all four are very similar it is argued that doppler ducting is available to a part of the gravity wave spectrum in all real circumstances and that it should be considered as a possible candidate whenever observations indicate that some ducting process is operative one particular wave event is discussed in some detail and it is shown that doppler ducting in its simplest form provides a plausible alternative to a more complicated ducting process which involved critical levels and energy leakage previously inferred doppler ducting is available equally to gravity waves in the oceans when background currents vary with depth

on the nature of short period mesospheric gravity wave propagation over halley antarctica 1 as part of a collaborative program between british antarctic survey and utah state university measurements were made using an all sky airglow imager located at the u k halley station 76 s 27 w during the 2000 and 2001 austral winter seasons from april through to early september a co located imaging doppler interferometer was utilized to obtain coincident wind measurements for a total of 171 wave events this study comprises the first detailed climatological investigation of the propagation nature freely propagating doppler ducted or evanescent of individual quasi monochromatic short period wave events at a high southern latitude distributions of the derived vertical wavelength exhibit an interquartile range from 16 48 km with a median vertical wavelength of 21 km the majority of the wave events were found to be freely propagating waves with only 5 exhibiting a clear doppler ducted signature while 15 of the waves were found to be evanescent in nature although no coincident temperature measurements were available subsequent saber temperature measurements suggest that up to 28 of the measured temperature profiles are capable of providing a ducted environment for the observed wave field this is in sharp contrast to findings at mid and low latitudes where these waves have been shown to be prone to doppler ducted motion it is suggested that the relatively weak wind field and associated tidal wind amplitudes over halley are not capable of forming a significant doppler ducted region to sustain a substantial amount of ducted waves belonging to the detectable spectrum of the airglow imager as these wind fields are comparable to wind fields found at other polar latitudes we hypothesize that the majority of short period gravity waves observed in the polar mesosphere are freely propagating and thus an important source of energy transfer into the mlt region

climatology and modeling of quasi monochromatic atmospheric gravity waves observed over urbana illinois from analyzing nine months of airglow imaging observations of atmospheric gravity waves agws over adelaide australia 35 s walterscheid et al 1999 have proposed that many of the quasi monochromatic waves seen in the images were primarily thermally ducted here are presented 15 months of observations from february 1996 to may 1997 for agw frequency and propagation direction from a northern latitude site urbana illinois 40 n as adelaide urbana is geographically distant from large orographic features similar to what was found in adelaide the agws seem to originate from a preferred location during the time period around summer solstice in conjunction with these airglow data there exists mf radar data to provide winds in the 90 km region and near simultaneous lidar data which provide a temperature climatology the temperature data have previously been analyzed by states and gardner 2000 the temperature and wind data are used here in a full wave model analysis to determine the characteristics of the wave ducting and wave reflection during the 15 month observation period this model analysis is applied to this and another existing data set recently described by nakamura et al 1999 it is shown that the existence of a thermal duct around summer solstice can plausibly account for our observations however the characteristics of the thermal duct and the ability of waves to be ducted is also greatly dependent on the characteristics of the background wind a simple model is constructed to simulate the trapping of these waves by such a duct it is suggested that the waves seen over urbana originate no more than a few thousand kilometers from the observation site

crustal model of the bransfield rift west antarctica from detailed obs refraction experiments summary the first detailed deep seismic refraction study in the bransfield strait west antarctica using sensitive obss ocean bottom seismographs was carried out successfully during the antarctic summer of 1990 1991 the experiment focused on the deep crustal structure beneath the axis of the bransfield rift seismic profile dss 20 was located exactly in the bransfield trough which is suspected to be a young rift system along the profile five obss were deployed at spacings of 50 70 km 51 shots were fired along the 310 km profile this paper gives the first presentation of the results a detailed model of the crustal structure was obtained by modelling the observed traveltimes and amplitudes using a 2 d ray tracing technique the uppermost sedimentary cover with velocities of 2 0 5 5 km s 1 reaches a depth of up to 8 km below this a complex with velocities of 6 4 6 8 km s 1 is observed the presence of a high velocity body with vp 7 3 7 7 km s 1 was detected in the 14 32 km depth range in the central part of the profile these inhomogeneities can be interpreted as a stage of back arc spreading and stretching of the continental crust coinciding with the deception bridgeman volcanic line velocities of 8 1 km s 1 characteristic of the moho are observed along the profile at a depth of 30 32 km

tidal variability of the geomagnetic polar cap mesopause above resolute bay variability in the geomagnetic polar cap neutral wind near the mesopause above resolute bay canada 74 9 n 94 9 w has been observed by a fabry perot interferometer using a circle to line detection technique fpi clio to observe the oh meinel emission we present an analysis of the first wind measurements obtained with the fpi clio from december 1995 to march 1996 the oh 7 3 892 0 nm doppler winds were analyzed for tidal oscillations defined herein as oscillations with periods which are sub harmonics of a solar day daily spectral analysis using 50 relatively clear days showed that oscillations between and including 12 h and 8 h were frequent throughout the winter season in both the meridional and the zonal winds a non linear least squares fit performed on the data from the jan 22 30 interval revealed that a 12 h tidal feature was dominant observations of the oh neutral winds show variations indicating strong tidal wave activity at the mesopause

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

seismovolcanic signals at deception island volcano antarctica wave field analysis and source modeling the seismovolcanic signals associated with the volcanic activity of deception island antarctica recorded during three antarctic summers 1994 1995 1995 1996 and 1996 1997 are analyzed using a dense small aperture 500 m seismic array the visual and spectral classification of the seismic events shows the existence of long period and hybrid isolated seismic events and of low frequency quasi monochromatic and spasmodic continuous tremors all spectra have the highest amplitudes in the frequency band between 1 and 4 hz while hybrids and spasmodic tremors have also significant amplitudes in the high frequency band 4 10 hz the array analysis indicates that almost all the well correlated low frequency signals share similar array parameters slowness and back azimuth and have the same source area close to the array site the polarization analysis shows that phases at high frequency are mostly composed of p waves and those phases dominated by low frequencies can be interpreted as surface waves no clear shear waves are evidenced from the energy evaluation we have found that the reduced displacement values for surface and body waves are confined in a narrow interval volcano tectonic seismicity is located close to the array at a depth shallower than 1 km the wave field properties of the seismovolcanic signals allow us to assume a unique source model a shallow resonating fluid filled crack system at a depth of some hundreds of meters all of the seismic activity is interpreted as the response of a reasonably stable stationary geothermal process the differences observed in the back azimuth between low and high frequencies are a near field effect a few episodes of the degassification process in an open conduit were observed and modeled with a simple organ pipe

intermediate focus earthquakes under south shetland islands antarctica this study is based on data from five field surveys 1992 1996 of seismic monitoring on deception island south shetland islands antarctica in the 1994 95 and 1995 96 surveys earthquakes were recorded by a seismic array in previous surveys data were collected by a high dynamic range short period station the analysis of the events shows evidence of intermediate focus seismicity 50 h 100 km related to the underplating zone of the south shetland plate because of poor station coverage we had to use unconventional techniques to locate the events such as zero lag cross correlation method that provide information about apparent velocity and back azimuth ray tracing procedure and particle motion patterns these criteria allowed us to identify 15 earthquakes that could be considered as intermediate focus events for which some focal parameters were estimated we conclude that the subduction zone between the drake plate and south shetland microplate has a moderate level of intermediate depth microseismicity

climatology of gravity waves in a forest the objectives of this study are to establish a climatology of gravity waves in a forest and to gain insights into the dynamics of this motion type the site is part of the boreas boreal ecosystem atmosphere study flux monitoring network the analysis relies mainly on 5 hz temperature time series observed with two arrays of fine wire thermocouples deployed in the vertical up to 40 m above the ground and horizontal separation up to 150 m from july to november 1996 supporting measurements include mean wind speed and direction at two heights above the forest waves of various intensities are found over 40 of the night time observations emphasizing the need to understand its role in transporting momentum and masses between the vegetation and the atmosphere these waves are shear generated they propagate in the direction of the mean wind at a speed that is most likely to fall between the mean wind speeds at z h 1 2 and 1 8 where z is the height above the ground and h is the mean tree height the median values of wave speed wavelength wave vertical displacement and wave frequency are 1 61 m s 1 75 m 10 m and 0 0214 hz respectively the wave motion remains coherent in the horizontal over less than one wavelength but is in general persistent in time

determination of horizontal and vertical structure of an unusual pattern of short period gravity waves imaged during aloha 93 an all sky ccd imager has been used to measure the properties of short period gravity waves present over the hawaiian islands during the aloha 93 campaign observations of emissions from four different altitudes provided a capability to describe the vertical as well as the horizontal structure of the wave field on several occasions during this campaign an unusual morphology wave pattern was detected that consisted of a group of small scale waves oriented in the same direction these were most noticeable in the oi 557 7 nm emission altitude 96 km and were usually observed in association with a larger scale gravity wave this paper presents a preliminary analysis of data recorded on the night of 22 october during which both types of waves were prominent the small scale waves exhibited highly coherent phase structures at each emission altitude consistent with a ducted wave motion the spatial intensity and phase modulation of this display is indicative of interference between two waves with similar characteristics and slightly different propagation directions the larger scale wave motion was observed to propagate perpendicular to the small scale waves and showed evidence of phase progression with altitude implying upward energy propagation these data have been interpreted in the context of simultaneous wind measurements from an mf radar

small scale gravity waves in the upper mesosphere and lower thermosphere generated by deep tropical convection a time dependent nonlinear fully compressible axisymmetric plane numerical model is used to simulate the generation of small scale gravity waves in the upper mesosphere and lower thermosphere by intense deep convection in the troposphere the simulations show that major convective storms in the tropics excite a broad spectrum of upper mesosphere lower thermosphere gravity waves above the storm centers the wave field includes a component that is guided in a thermal duct in the lower thermosphere and propagates horizontally outward from above the storm storms excite oscillations over the source which are initially confined to a stratospheric duct but leak into the thermospheric duct over time generating a long train of small scale ducted waves this ringing phenomenon persists for several hours after the storm has ended the ducted disturbances may propagate large distances from the source and explain observations of a strong summertime anisotropy favoring southward propagation of small scale waves observed in the airglow over adelaide more than 2000 km to the south of the storm events

mesospheric bore evolution and instability dynamics observed in pmc turbo imaging and rayleigh lidar profiling over northeastern canada on 13 july 2018 two successive mesospheric bores were observed over northeastern canada on 13 july 2018 in high resolution imaging and rayleigh lidar profiling of polar mesospheric clouds pmcs performed aboard the pmc turbo long duration balloon experiment four wide field of view cameras spanning an area of 75 150 km at pmc altitudes captured the two evolutions occurring over 2 hr and resolved bore and associated instability features as small as 100 m the rayleigh lidar provided pmc backscatter profiling that revealed vertical displacements evolving brightness distributions evidence of instability character and depths and insights into bore formation ducting and dissipation both bores exhibited variable structure along their phases suggesting variable gravity wave gw source and bore propagation conditions both bores also exhibited small scale instability dynamics at their leading and trailing edges those at the leading edges comprised apparent kelvin helmholtz instabilities that were advected downward and rearward beneath the bore descending phases extending into an apparently intensified shear layer instabilities at the trailing edges exhibited alignments approximately orthogonal to the bore phases that resembled those seen to accompany gw breaking or intrusions arising in high resolution modeling of gw instability dynamics collectively pmc turbo bore imaging and lidar profiling enabled enhanced definition of bore dynamics relative to what has been possible by previous ground based observations and a potential to guide new three dimensional modeling of bore dynamics the observed bore evolutions suggest potentially important roles for bores in the deposition of energy and momentum transported into the mesosphere and to higher altitudes by high frequency gws achieving large amplitudes

the recent seismo volcanic activity at deception island volcano abstract this paper reviews the recent seismic studies carried out at deception island south shetland islands antarctica which was monitored by the argentinean and spanish antarctic programs since 1986 several types of seismic network have been deployed temporarily during each antarctic summer these networks have consisted of a variety of instruments including radio telemetered stations autonomous digital seismic stations broadband seismometers and seismic arrays we have identified two main types of seismic signals generated by the volcano namely pure seismo volcanic signals such as volcanic tremor and long period lp events and volcano tectonic vt earthquakes their temporal distributions are far from homogeneous volcanic tremors and lp events usually occur in seismic swarms lasting from a few hours to some days the number of lp events in these swarms is highly variable from a background level of less than 30 day to a peak activity of about 100 events h the occurrence of vt earthquakes is even more irregular most vt earthquakes at deception island have been recorded during two intense seismic crises in 1992 and 1999 respectively some of these vt earthquakes were large enough to be felt by researchers working on the island analyses of both types of seismic events have allowed us to derive source locations establish seismic source models analyze seismic attenuation calculate the energy and stress drop of the seismic sources and relate the occurrence of seismicity to the volcanic activity pure seismo volcanic signals are modelled as the consequence of hydrothermal interactions between a shallow aquifer and deeper hot materials resulting in the resonance of fluid filled fractures vt earthquakes constitute the brittle response to changes in the distribution of stress in the volcanic edifice the two vt seismic series are probably related to uplift episodes due to deep injections of magma that did not reach the surface this evidence however indicates the high potential for future volcanic eruptions at deception island

high resolution measurements of vertical velocity with the european incoherent scatter vhf radar 1 motion field characteristics and measurement biases european incoherent scatter vhf radar measurements of vertical velocities were made under polar mesopause summer echo pmse conditions enabling spatial and temporal resolution of 300 m and 2 s and accuracies of 0 1 ms 1 or better our observations revealed vertical motions with periods ranging from hours to tens of seconds and vertical wave structure exhibiting both ducted and vertically propagating behavior significant correlations were found between the low pass vertical velocity and velocity uncertainties velocity variances at high frequencies radar backscatter power and radar spectral widths specifically upward motions at lower frequencies correlated with larger uncertainties high frequency variances and radar spectral widths while downward motions correlated best with larger backscatter power we show these correlations to lead to biases in the determination of mean vertical motions when data are thresholded by any of the above quantities we also suggest that these correlations arise from a tendency for turbulence to be associated primarily with the upward phase of wave motions at lower frequencies a companion paper by fritts and hoppe presents a spectral analysis of this same data set

propagating mesoscale cloud bands abstract banded cloud patterns are an often observed mesoscale phenomenon which may be produced under a variety of physical conditions and for a variety of reasons this paper concerns a detailed analysis of a propagating pattern which was observed with the noaa 2 satellite following a period of severe thunderstorm activity in the southwestern united states we review the local atmospheric conditions existing at the time the disturbance was observed and address the question concerning its mechanism of initiation and propagation we first test the hypothesis that the banded cloud formation could simply be a manifestation of a freely propagating packet of internal waves launched by earlier convective activity this hypothesis is shown to be unsatisfactory we next consider the modal structure of the atmosphere in the vicinity of the cloud bands and show that the slowest spatially decaying mode of the mean state has a horizontal wavelength and phase speed which match those of observed disturbance

multi point observation of short period mesospheric gravity waves over japan during the front campaign simultaneous observations of short period gravity waves were carried out using three all sky cooled ccd imagers of oh airglow at moshiri northern edge of japan and at shigaraki and bisei middle part of japan during the front campaign of may 1998 these stations were separated by horizontal distances of 250 1300 km and they offered a unique opportunity to investigate the spatial extent of gravity waves in the mesopause region the images from shigaraki and bisei showed short period gravity waves horizontal wavelength 20 40 km phase front east west aligned moving northward phase velocity 20 40 m s on may 19 21 and 22 at moshiri similar east west waves moving northward were observed on may 19 and 21 indicating a broad horizontal extent of the gravity waves waves at moshiri were not evident on may 22 however the horizontal wind measured by the mf radar at wakkanai near moshiri showed height profiles that were similar to those at yamagawa southern edge of japan on may 19 and 21 but quite dissimilar on may 22 on the basis of these data we suggest that short period gravity waves in the mesopause region can have a broad spatial extent of more than 1000 km the generation and propagation of internal gravity waves are discussed as a cause of the spatial extent of the waves

first results from the meteor radar at south pole a large 12 hour oscillation with zonal wavenumber one the first mesopause region ca 92 5 km wind measurements from the meteor radar at amundsen scott station at south pole are described measurements are made along four orthogonal azimuth directions approximately 2 from the geographic south pole a large 20 ms 1 oscillation in the northward wind is observed with 12 hour period and zonal wavenumber one a similar wave was observed during august 1 13 1992 at south pole by hernandez et al 1993 using optical methods the predominant semidiurnal tide in the atmosphere is migrating with the apparent motion of the sun with s 2 the s 1 oscillation is interpreted here to result from the nonlinear interaction between the migrating semidiurnal tide and a stationary wave with s 1 the present mechanism represents an alternative to the gravity wave driven pseudotide theory put forth by walterscheid et al 1986 to explain the occurrence of unexpectedly large semidiurnal tidal oscillations at high latitudes

backscatter lidar observations of lower tropospheric dynamics during southern california wildfires abstract wavelike features suggesting gravity waves were revealed by lidar observations from el segundo california of smoke layers produced by large wildfires in the southern california region during a santa ana event unique features of the observations were multiple thin layers that enabled precise determinations of wave frequency amplitude and vertical structure the data revealed persistent wavelike oscillations that showed no phase variation with altitude an amplitude of 20 m and a period near 12 min the observations were averaged over 1 5 min with a vertical resolution of 3 m and were obtained over a period of 5 h on 25 october and 8 h on 26 october 2007 vertical profiles of temperature and winds from the aircraft communication addressing and reporting system acars of commercial aircraft departing los angeles international airport lax were selected for temporal and spatial coincidence with the lidar observations in addition satellite images of the smoke distribution over the los angel

meteorological source variability in atmospheric gravity wave parameters derived from a tropical infrasound station gravity waves are an important part of the momentum budget of the atmosphere despite this parameterizations of gravity wave spectra in atmospheric models are poorly constrained gravity waves are formed by jet streams flow over topography and convection all of which produce pressure perturbations as they propagate over the earth s surface detectable by microbarometer arrays used for sensing infrasound in this study observations of gravity waves between 2007 and 2011 at an infrasound station in the ivory coast west africa are combined with meteorological data to calculate parameters such as intrinsic phase speed and wavenumber through spectral analysis the seasonal and daily variations in all gravity wave parameters are examined the gravity wave back azimuth varies with the migration of the inter tropical convergence zone a region of intense convection supporting previous studies daily variations in gravity wave arrivals at the station can be linked to two distinct convective cycles over the land and ocean this was achieved by combining the gravity wave parameters with lightning strikes detected by the met office s arrival time difference lightning detection system noise generated by turbulence in the middle of the day was found to attenuate smaller pressure amplitude gravity waves artificially amplifying the daily variations in some gravity wave parameters detection of daily and seasonal variations in gravity wave parameters has the potential be used to improve the representation of gravity wave spectra in atmospheric models

low latitude gravity wave variances in the mesosphere and lower thermosphere derived from saber temperature observation and compared with model simulation of waves generated by deep tropical convection a portion of waves generated by deep convection have scales and amplitudes large enough to be detected by space borne instruments we have analyzed temperature data from the sounding of the atmosphere using broadband emission radiometry saber instrument on the thermosphere ionosphere mesosphere energetics dynamics timed satellite for sub tidal scale fluctuations filtering was applied both vertically and horizontally to extract wave variances we have analyzed the altitude region between 70 and 130 km and focus on the variances at equatorial latitudes for the altitude region between 70 and 120 km as a function of season local time intervals geographical location and altitude we find significant variances where convection is particularly prolific intertropical convergence zone and at altitudes where wave trapping is known to be favored e g the lower thermospheric duct the locations of significant variances persist from year to year standard deviations of a few of tens of kelvins are found we have also performed simulations of the response to deep tropical convection with a time dependent high resolution fully compressible dynamical model our simulations give wave amplitudes that agree reasonably well with the observed amplitudes and show layering that is consistent with the observations our main finding is that significant variations seen in timed saber temperature data have a convective wave source and are concentrated in layers where thermal ducts occur

large scale waves in the upper mesosphere at antarctic high latitudes upper mesosphere combined optical measurements of wind and temperature fields at amundsen scott station south pole and wind radar measurements at scott base 78 s 167 e show the presence of large scale waves in this region of the atmosphere at amundsen scott the largest amplitude wave observed with sub diurnal periodicity appears with a frequency near 2 4 day 10 1 hour period with a westward phase progression of wavenumber one the presence of a wave with this periodicity is confirmed by the observations at scott base the combination of the experimentally found period phase progression associated small temperature oscillations and theoretical considerations lead to the interpretation of this wave as a lamb wave the present combination of spatially resolved optical measurements and radar measurements illustrates the value of multiple station and multiple technique observations in elucidating the upper mesosphere dynamical state as well as the properties of the waves propagating through the medium where the observations are being made

observational evidence of wave ducting and evanescence in the mesosphere a collaborative radar and imaging study of gravity waves over the hawaiian islands was performed during october 1993 as part of the airborne lidar and observations of hawaiian airglow 1993 coupling and dynamics of regions equatorial aloha 93 cadre campaign to investigate the propagation characteristics of short period 1 hour waves at nightglow altitudes the horizontal wavelengths and apparent phase speeds of quasi monochromatic wave events were measured in four separate nightglow emissions using data obtained by a high resolution ccd imager this information was correlated with simultaneous mf radar wind measurements over the same height interval 80 100 km to infer intrinsic wave parameters in each case correlating the two data sets allowed the determination of the local vertical wavenumber for each event in particular whether it be real indicative of freely propagating waves or imaginary indicative of ducted or evanescent waves the results of this study indicate a preponderance of ducted or evanescent waves at 80 100 km during the time of the observations with up to 75 of the events recorded exhibiting ducted or evanescent behavior also noted was a tendency for ducted behavior to be more prevalent among waves with shorter horizontal wavelengths in agreement with doppler ducting theory these results suggest that ducted waves are relatively common in the upper mesosphere and lower thermosphere region at least over the mid pacific ocean as small scale waves which are ducted have the potential to travel much longer horizontal distances than freely propagating waves the frequency of their occurrence should be taken into account in efforts to quantify gravity wave effects at these altitudes

vhf doppler radar observations of buoyancy waves associated with thunderstorms abstract the platteville vhf doppler radar located on the colorado piedmont near platteville colorado continuously measured the vertical wind velocity during a 12 day period in late july and early august 1981 measurements were made every 2 5 min on the average with range gates centered at 3 3 5 7 8 1 10 5 12 9 15 3 17 7 and 20 1 km above sea level periods of active thunderstorms were identified from the ppi maps from the national weather service 10 cm weather radar at limon colorado when no thunderstorm activity was present the vertical velocity fluctuations were small and erratic but a few hours after strong thunderstorm activity began large quasi sinusoidal wave trains with periods of about 40 min were observed power spectra of the vertical velocity time series showed enhancements at all frequencies during thunderstorm activity but for periods longer than 30 min the enhancements were larger particularly for the mid tropospheric range gates from 5 7 to 12 9 km some of the implication