interpretations of observed climatological patterns in stratospheric gravity wave variance observational analyses of gravity waves in the stratosphere have revealed various climatological patterns in gravity wave activity seasonal geographical and vertical variations have all been observed in this work a linear model of gravity wave propagation is applied to investigate the underlying causes of some of the observed patterns a collection of monochromatic gravity waves that represent a broad spectrum of wavenumbers and frequencies is input at 6 km altitude in the model propagation of the waves through realistic background atmospheric wind and stability fields is treated with linear ray theory and a simple saturation condition to limit amplitudes to stable values the wave spectrum at the 6 km source height is specified to be constant at all latitudes longitudes and times so the variability that appears at higher altitudes is due entirely to background atmosphere variations before the model results are compared to the observations the spectrum of waves is filtered in a way that mimics the limitations of each of the observation techniques the filtering is described in terms of vertical wavelength and is referred to as the observational filter in a vertically varying background wind gravity waves are doppler shifted in intrinsic frequency and refracted to different vertical wavelengths as they propagate vertically through the atmosphere the observational filter and the wave refraction effects can thus couple in interesting ways that have not been explicitly considered in previous work the model shows that this coupling can give rise to geographical seasonal and vertical variations in gravity wave observations without any variations in the spectrum or amplitude of gravity wave sources in the troposphere thus careful consideration of both the background wind profile and observational filter can greatly affect the interpretation of the observed climatological patterns in gravity wave activity

detection of miocene saucer shaped sills offshore senegal via integrated interpretation of seismic magnetic and gravity data the atlantic margin offshore senegal has been explored by seismic reflection and grav mag surveys high amplitude laterally transgressive seismic reflectors are found to coincide with gravimetric and magnetic highs once seismic data are integrated with potential fields modelling these reflectors can be safely interpreted as saucer shaped igneous sills up to some hundreds of metres thick some km wide the occurrence of hydrothermal vent complexes and forced folds in the stratigraphic sequence above the sills constrain the intrusion age to the miocene field observations and in situ magnetic susceptibility measurements of oligocene miocene and quaternary igneous rocks emplaced in coastal senegal support this interpretation

gravity wave propagation and dissipation from the stratosphere to the lower thermosphere 1 one night 28 october 2003 temperature and horizontal wind measurements by a resonance sodium na wind temperature lidar at maui 20 7 n 156 3 w and temperature measurement by a rayleigh lidar at mauna loa observatory mlo 19 5 n 155 6 w hawaii were used to study gravity wave gw propagation from the lower stratosphere to the lower thermosphere a dominant wave mode was identified from 35 to 103 km the wave was partially dissipated and propagating upward with a scale height of temperature amplitude at 14 km a damping layer was present around the stratopause where the wave amplitude was small which also corresponded to a low static stability layer the vertical wavelengths were larger in the mesosphere 12 13 km than in the stratosphere 6 7 km consistent with the decreasing static stability with altitude hodograph analysis of the na lidar wind data showed that the wave was propagating northward and the horizontal wavelength was 2140 km and intrinsic period was 15 h in the region 84 103 km the apparent period was 6 h and consistent with doppler shift of the background wind it is suggested that the convective zone over the equator to the south of hawaii provided a constant gw source that is responsible for the observed gw throughout the night

climatology of short period gravity waves observed over northern australia during the darwin area wave experiment dawex and their dominant source regions 1 the darwin area wave experiment dawex was designed to investigate the generation and propagation of gravity waves from intense regions of localized convection that occur regularly over northern australia in the vicinity of darwin during the premonsoon period this multinational program was conducted during the austral spring 2001 using a range of coordinated optical radar and in situ balloon measurements as part of this program all sky image observations of short period gravity wave events in the near infrared oh nightglow emission altitude 87 km were made from two well separated sites in northern australia wyndham 15 5 s 128 1 e and katherine 14 5 s 132 3 e over a 10 day period during november 2001 a total of 25 extensive wave events were observed during this period from which the dominant horizontal wave characteristics were determined to be wavelength 25 35 km and observed phase speed 27 75 m s yielding observed periods from 7 to 14 min consistent with previous measurements at other low latitude sites a key finding of this study was a marked anisotropy in the wave propagation headings with over 3 4 of the events exhibiting a strong southward component of motion and a clear preference for wave progression over the azimuthal range se to ssw although this range encompasses gravity waves originating locally from the darwin area the majority of the wave events exhibited propagation headings consistent with more distant sources located to the north and northwest of australia assuming deep convection was the dominant mechanism for the waves the strong asymmetry in their velocity distribution appears to result from a combination of nonuniformity in the geographic occurrence of thunderstorms coupled together with significant wind filtering effects at the source altitude and within the middle atmosphere these results are consistent with long range short period wave propagation most probably in the form of ducted waves possibly from intense convective regions located 1000 km to the north over the indonesian island chain

three field photometer observations of short period gravity wave intrinsic parameters in the 80 to 100 km height region 1 a three field photometer 3fp for making observations of airglow in the mesosphere lower thermosphere mlt region has been operated at the center of the large mf aerial array located near adelaide 138 e 35 s since 1993 observations of the 557 7 nm airglow intensity emitted by atomic oxygen oi at heights near 97 km and the 730 0 nm airglow intensity emitted by hydroxyl oh near 87 km have been made simultaneously with mf spaced antenna observations of wind velocities in the 80 100 km height region the 3fp measures the intensity of the 557 7 nm airglow in three fields separated by about 13 km at heights near 97 km and then the intensity of the 730 nm airglow in three fields separated by about 12 km at heights near 87 km on a 60 s cycle these data have been analyzed to yield gravity wave observed phase speeds and horizontal wavelengths simultaneous mf radar data have been analyzed to yield measurements of the neutral wind velocity in 2 km height steps in the 80 100 km height interval every 2 min and these have been used together with the observed wave parameters to calculate intrinsic gravity wave parameters this paper presents a very brief overview of the system the motivation for the work and preliminary analysis of the data from 1995 until 2000

global gravity wave variances from aura mls characteristics and interpretation abstract the gravity wave gw resolving capabilities of 118 ghz saturated thermal radiances acquired throughout the stratosphere by the microwave limb sounder mls on the aura satellite are investigated and initial results presented because the saturated optically thick radiances resolve gw perturbations from a given altitude at different horizontal locations variances are evaluated at 12 pressure altitudes between 21 and 51 km using the 40 saturated radiances found at the bottom of each limb scan forward modeling simulations show that these variances are controlled mostly by gws with vertical wavelengths z 5 km and horizontal along track wavelengths of y 100 200 km the tilted cigar shaped three dimensional weighting functions yield highly selective responses to gws of high intrinsic frequency that propagate toward the instrument the latter property is used to infer the net meridional component of gw propagation by differencing the variances acquired from ascending a and descending d o

volcanism and aseismic slip in subduction zones the spatial and temporal relationship of volcanism to the occurrence of large earthquakes and convergent plate motion is examined the number of volcanic eruptions per year in a convergent zone is found to be linearly related to the aseismic slip component of plate motion if the aseismic slip rate is low coupling between converging plates is strong then the primary manifestation of tectonic activity is the occurrence of large earthquakes with only infrequent volcanic activity if however the aseismic slip rate is high coupling is weak then there are few large earthquakes and volcanism is the principal manifestation of tectonic activity this model is consistent with the spatial distribution of large earthquakes and active volcanoes in the circum pacific area it is tested by examining the extent of volcanic activity in the rupture zones of the 1952 1973 sequence of earthquakes in the japan kurile islands area the number of volcanic euptions along these zones during the interval between large earthquakes is used to compute the aseismic slip rates for these segments based on the relationship developed in this study the aseismic slip rates so computed agree with those determined from the earthquake history of the area and rates of plate motion themore agreement suggests that in the interval between large earthquakes the aseismic plate motion is manifested in a specific number of volcanic eruptions therefore in areas with adequate historial data it should be possible to use the model developed in this study to monitor volcanic eruptions for long term prediction of large earthquakes less

global ray tracing simulations of the saber gravity wave climatology 1 since february 2002 the saber sounding of the atmosphere using broadband emission radiometry satellite instrument has measured temperatures throughout the entire middle atmosphere employing the same techniques as previously used for crista cryogenic infrared spectrometers and telescopes for the atmosphere we deduce from saber v1 06 data 5 years of gravity wave gw temperature variances from altitudes of 20 to 100 km a typical annual cycle is presented by calculating averages for the individual calendar months findings are consistent with previous results from various satellite missions based on zonal mean saber data for july and zonal mean gw momentum flux from crista a homogeneous and isotropic launch distribution for the grograt gravity wave regional or global ray tracer is tuned the launch distribution contains different phase speed mesoscale waves some of very high phase speed and extremely low amplitudes as well as waves with horizontal wavelengths of several thousand kilometers global maps for different seasons and altitudes as well as time series of zonal mean gw squared amplitudes based on this launch distribution match the observations well based on this realistic observation tuned model run we calculate quantities that cannot be measured directly and are speculated to be major sources of uncertainty in current gw parameterization schemes two examples presented in this paper are the average cross latitude propagation of gws and the relative acceleration contributions provided by saturation and dissipation on the one hand and the horizontal refraction of gws by horizontal gradients of the mean flow on the other hand

airglow imager observations of atmospheric gravity waves at alice springs and adelaide australia during the darwin area wave experiment dawex 1 the darwin area wave experiment occurred in australia from october to december 2001 an objective was to characterize the atmospheric gravity wave field produced from intense convective activity that is routinely observed around darwin during november and december two airglow imagers were sited at adelaide and at alice springs each located over 1000 km south of darwin waves were observed at the mesopause region propagating predominantly toward the southeast with some going to the northwest but with none observed going from east to west the lack of waves propagating toward the west suggests some wind filtering mechanism below 80 km altitude waves observed over alice springs were analyzed in detail on three nights on 16 november they were seen propagating toward the northwest it is proposed that they were generated by dynamical events associated with a cutoff low pressure system present over southwest australia on 17 and 19 november the observations are consistent with wave generation by convective activity present in the darwin area thus as proposed by walterscheid et al 1999 and hecht et al 2001a the ducting of waves from distant sources is shown to be a viable explanation for the quasi monochromatic waves frequently observed in airglow observations walterscheid et al 1999 suggested that ducting of waves from the extensive region of deep cumulus convection over northern australia explained the strong poleward directionality seen in the summer months the present study suggests that propagation from northern australia is selective and ducted waves from this region may not be the primary source of waves over adelaide when convection is occurring over central australia

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

analysis of large amplitude stratospheric mountain wave event observed from the airs and mls sounders over the western himalayan region mountain waves in the stratosphere have been observed over elevated topographies using both nadir looking and limb viewing satellites however the characteristics of mountain waves generated over the himalayan mountain range and the adjacent tibetan plateau are relatively less explored the present study reports on three dimensional 3 d properties of a mountain wave event that occurred over the western himalayan region on 9 december 2008 observations made by the atmospheric infrared sounder on board the aqua and microwave limb sounder on board the aura satellites are used to delineate the wave properties the observed wave properties such as horizontal lambda x lambda y and vertical lambda z wavelengths are 276 km zonal 289 km meridional and 25 km respectively a good agreement is found between the observed and modeled analyzed vertical wavelength for a stationary gravity wave determined using the modern era retrospective analysis for research and applications merra reanalysis winds the analysis of both the national centers for environmental prediction national center for atmospheric research reanalysis and merra winds shows that the waves are primarily forced by strong flow across the topography using the 3 d properties of waves and the corrected temperature amplitudes we estimated wave momentum fluxes of the order of similar to 0 05 pa which is in agreement with large amplitude mountain wave events reported elsewhere in this regard the present study is considered to be very much informative to the gravity wave drag schemes employed in current general circulation models for this region

the effect of varying the source spectrum of a gravity wave parameterization in a middle atmosphere general circulation model climate simulations of the middle atmosphere circulation with general circulation models are now starting to include parameterizations of the momentum flux deposition due to unresolved gravity wave spectra a current uncertainty in the application of such parameterizations is the specification of the imposed gravity wave spectrum the aim of this work is to quantify the effect of varying within a realistic range the source spectrum of a gravity wave parameterization in a general circulation model results from two simulations with the gravity wave spectrum launched at two different heights the surface and the 110 hpa pressure level respectively are compared noteworthy differences found in the simulated middle atmosphere response include the following 1 the average temperature in the southern winter upper stratosphere is about 40 k warmer in the experiment with the surface as the launching height virtually eliminating the typical cold polar bias that affects many general circulation models 2 stronger easterlies in the subtropical summer mesosphere again in the experiment with the surface as the launching height diagnostics of the parameterized gravity waves indicate that in the experiment with the surface as the launching height the net zonal momentum flux transported by the gravity waves is negative just above the troposphere at middle latitudes this negative net momentum flux facilitates the deceleration of the mesospheric winter westerlies the meridional circulation induced by such deceleration is thereafter responsible for the substantial polar winter warming in contrast in summer the negative net momentum flux limits the upper mesospheric deceleration of the easterlies in the experiment with launching height at 110 hpa the gravity wave net momentum flux is instead zero by construction at the launching height

airglow imaging observations of small scale structures driven by convective instability in the upper mesosphere over tirunelveli 8 7 n 1 airglow imaging observations of broadband oh meinel band emissions made on the night of 20 january 2007 from the tropical indian site tirunelveli 8 7 n 77 8 e reveal large and small scale wave features that are aligned perpendicular to each other and that are associated with gravity wave dynamics the large scale waves were the signatures of propagating quasi monochromatic qm waves whereas the small scale features were identified to be ripples generated by convective instability in the mesosphere lower thermosphere mlt region the qm waves showed consistent propagation toward the northwest direction throughout the observation period of 4 5 hr whereas the ripples that manifested as short lived patches in the airglow images were transient and did not show any prominent phase propagation in addition to these well resolved structures in images we infer the presence of waves with relatively longer observed time periods compared with the observed time period of qm waves from the spectrum of the time series generated with zenith intensity values derived from the images from the complementary wind and temperature data obtained with co located mf radar and sounding of atmosphere with broad band emission radiometry on the thermosphere ionosphere mesosphere energetics and dynamics mission an attempt is made to understand the dynamic processes occurring in the vicinity of the mesopause during the night of 20 january 2007 the uniqueness of the present observations is that there were short lived ripple patches seen in various parts of the sky during the entire observation period of 4 5 hr the precipitation rates obtained by the tropical rainfall measuring mission satellite mission suggest that the deep convective activity occurring over the equatorial eastern indian ocean provided a plausible source mechanism for sustained generation of the waves observed over tirunelveli during this night

observations of intermediate scale diurnal waves in the equatorial mesosphere and lower thermosphere 1 the purpose of this study is to seek observational evidence for diurnal vertically propagating inertia gravity waves igws in the mesosphere and lower thermosphere mlt numerical modeling studies indicate that vertically propagating igws excited by tropical heating provide a significant source of momentum for the semiannual oscillation sao in the equatorial zonal mean winds the power spectrum of these waves has a strong diurnal component we analyze global patterns of ascending and descending node differences in mlt satellite temperatures which are assumed in this study to be proxies for waves of diurnal period juxtaposed upon the planetary scale features are localized variations with longitudinal wavelengths ranging from 25 to 50 and with vertical wavelengths between 13 and 25 km these intermediate scale variations are spatially coherent and persist for several weeks their amplitudes generally increase with altitude while their phase structures suggest both eastward and westward propagation the variance of wave numbers 9 17 in the mlt is examined in relation to the underlying stratospheric zonal mean zonal gradient winds stronger variances generally coincide with periods where the underlying zonal mean winds are relatively light or unidirectional the weak inverse association between variance strength and zonal wind magnitude is suggestive of a wave filtering mechanism

gravity wave variance in lims temperatures part i variability and comparison with background winds abstract small scale features in temperature data from the limb infrared monitor of the stratosphere satellite experiment are isolated by subtracting profiles of globally mapped temperatures containing zonal waves 0 6 from inverted temperature profiles these features are interpreted as internal gravity waves the preponderance of the variance is associated with the longest wavelengths corresponding to the lowest frequencies inertio gravity waves the data include approximately 2000 daily soundings between late october 1978 and late may 1979 all longitudes latitudes from about 65 s to 85 n and altitudes from the tropopause to the middle mesosphere pressures from 100 to 0 1 mb zonal mean gravity wave variance is compared with background winds and variance maps are presented for five one week periods early november early january early february late march and early may time height plots of zonal mean wave variance and background winds in the latitude bands 45 55 s 5 s 5 n and 45 55 n ar

juan de fuca plate aseismic subduction at 1 8 cm yr volcanic activity in the cascades in historic times suggests that the juan de fuca plate is underthrusting aseismically at about 1 8 cm yr this rate of underthrusting is identical to the rate computed from sediment studies

cenozoic volcanism in western senegal and its relationship to the opening of the central atlantic ocean abstract the westernmost part of the senegalese basin in west africa is characterized by an extensive magmatic event exposed in the form of sills and dykes mainly during the quaternary but beginning in the tertiary 35 0 1 ma miocene to 0 8 0 1 ma pleistocene the main exposures are located in the cap vert peninsula and thies plateau to the east of dakar this magmatic event postdated the opening of the central atlantic and displays chemical similarities to the tertiary quaternary magmatic centres within the african plate two main facies are distinguished among the flows microporphyric and doleritic textured olivine rich alkaline basalts the former often containing spinel lherzolite mantle inclusions the alkaline sodic affinity of the volcanic series and the ti k na nb p2o5 and zr content of the lavas are typical of magmas generated in a within continent plate tectonic setting this volcanism appears to have resulted from an active mantle hotspot over which the african plate migrated as the central atlantic ocean opened using reactivated faults contemporaneous with central atlantic opening as magmatic pathways

statistical study of atmospheric gravity waves in the mesopause region observed by a lidar chain in eastern china atmospheric gravity wave activities in the mesopause region have been observed and statistically investigated with a sodium lidar chain in eastern china in total there were 471 gravity waves identified from over 5400h of observations at hainan 19 99 degrees n 110 34 degrees e hefei 31 87 degrees n 117 23 degrees e and beijing 40 47 degrees n 115 97 degrees e these waves typically had vertical wavelengths of z 2 4km observed periods of t ob 1 4h amplitude growth factors of 0 025 similar to 0 05km 1 and wave amplitudes of ae 90km 1 5 6 strong systematic parameter relationships were found and they agree with the predictions of diffusive filtering theory statistical results show that the seasonal variability of gravity wave activity had a summer maximum and winter minimum characteristics in the mesopause region over eastern china a qualitative interpretation is proposed regarding the seasonal and geographic variability observed by the lidar chain based on analysis of source properties and influences from background wind which vary by season

mls observations of atmospheric gravity waves over antarctica 1 stratospheric gravity waves over antarctica are studied with the radiance variances observed by upper atmosphere research satellite microwave limb sounder uars mls strong wave activities are found during august and september in 1992 1994 over the drake passage region 290 315 longitude and 50 s 70 s latitude where the enhancement seems associated with the topography of both south america and antarctic peninsula tips during the same period significant gravity wave activities are also evident along the antarctic coastal region the vertical growth of the wave variance shows a scale height of 14 km at low altitudes for both drake passage and the coastal regions but reduces substantially at high altitudes the growth rate transition occurs at a lower altitude in the drake passage region where the variance is larger the gravity wave activities observed near the antarctic may contribute significantly to the formation of polar stratospheric clouds psc because of the overlapping with the vortex edge and with the psc activities as observed by claes cryogenic limb array etalon spectrometer

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

gravity waves in the tropical lower stratosphere an observational study of seasonal and interannual variability radiosonde observations made at cocos islands 12 s 97 e in the indian ocean between september 1992 and june 1998 are used to study seasonal and interannual variations in gravity wave activity in the lower stratosphere 18 25 km the islands are located in a region of generally strong convection that occurs at all times of the year with the period of strongest convective activity between december and july wet season the prevailing zonal winds during the observational period and height range are westward with a quasi biennial oscillation qbo superimposed time series of wave energy show that largest wave amplitudes occur during the wet season when convection is strongest but a qbo like variation is also apparent maximum energy densities of about 25 j kg 1 occur early 1993 1995 and 1997 at the times when the westward shears are largest wave energy is found to be propagating upward and in the horizontal there is considerable azimuthal anisotropy with predominate eastward propagation against the prevailing wind upward fluxes of zonal momentum flux u w are estimated by combining the temperature and wind information fluxes show a similar temporal behavior to the energy the motion and temperature fields are dominated by waves with vertical wavelengths 2 km using a stokes parameter analysis it is found that the intrinsic frequencies are on average 2 3 times the inertial frequency corresponding to intrinsic periods of 20 25 hours horizontal wavelengths between 200 and 2000 km are inferred with a mean value of about 1000 km the mean intrinsic phase speeds are about 10 ms 1 but ground based phase speeds are centered on 0 ms 1

imaging of atmospheric gravity waves in the stratosphere and upper mesosphere using satellite and ground based observations over australia during the twpice campaign 1 during the tropical warm pool international cloud experiment twpice an intense tropical low was situated between darwin and alice springs australia observations made on 31 january 2006 by the atmospheric infrared sounder instrument on the nasa aqua satellite imaged the presence of atmospheric gravity waves agws at approximately 40 km altitude with horizontal wavelengths between 200 and 400 km that were originating from the region of the storm airglow images obtained from alice springs about 600 km from the center of the low showed the presence of similar waves with observed periods of 1 to 2 h the images also revealed the presence of 30 to 45 km horizontal wavelength agws with shorter observed periods of near 15 to 25 min ray tracing calculations show that 1 some of the long wavelength waves traveled on rays without ducting to the altitudes where the observations were obtained and 2 shorter period waves rapidly reached 85 km altitude at a horizontal distance close to the storm thus occurring over alice springs only if they were trapped or ducted the mesospheric inversion layer seen in the measured temperature data almost forms such a trapped region the winds therefore critically control the formation of the trapped region wind profiles deduced from the available data show the plausibility for the formation of such a trapped region variations in the wind however would make ideal trapped region conditions short lived and this may account for the sporadic nature of the short period wave observations

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

a fast propagating large scale atmospheric gravity wave observed in the wave2004 campaign 1 the waves in airglow campaign in 2004 wave2004 which aimed to elucidate the formation process of waves in airglow structures from both dynamical and chemical perspectives was conducted using rocket borne and ground based instruments in japan on 17 january 2004 in this experiment we observed a large scale atmospheric gravity wave agw which appeared in both the vertical profiles of sodium density obtained by a na lidar and the horizontal distributions of airglow emission obtained by an all sky imager asi vertical propagation of the agw accompanied by a shortening of its vertical wavelength was clearly visualized using the na lidar data the horizontal wavelength horizontal phase velocity period and propagation direction of the agw were estimated from the asi data as 673 774 km 107 122 m s 1 75 hours and north northeastward respectively using these parameters and the mf radar wind vertical wavelengths of the wave were calculated from the dispersion relation of gravity waves the calculated vertical wavelengths were comparable at altitudes of 85 5 km and 93 25 km to those estimated from the variation of the sodium density using a simple ray tracing technique the agw was traced back to the southern edge of the distorted jet stream near tropopause this result strongly suggests that an unstable baroclinic wave associated with ageostrophic motions in the jet stream was the wave source of the large scale agw observed in the wave2004

structure of the southern senegalo mauritanian basin west africa from geoelectrical studies abstract the southern part of the senegalo mauritanian basin is geologically featureless and little is known about the division of the sedimentary sequence and regional geological structure because of the scarcity of deep drillholes a magnetotelluric survey was therefore carried out in an attempt to obtain details concerning the electrical characteristics thickness and structure of the mesozoic cainozoic senegalo mauritanian basin from the surface down the interpretation of magnetotelluric data shows several distinct electrical boundaries the general trend shows a decrease in near surface resistivity from east to west the basin is characterized by water saturated unconsolidated low resistivity sediments with a westward sloping monoclinal style the combination of borehole and geological data with a geoelectrical cross section provides a simplified model of the geological electrical units of the basin this shows the distribution of strata above and below the base of the senonian conductive material 10 30 ohm m at depth in the central part of the profile may represent a northern extension of the palaeozoic sediments of the bove sequence which lies immediately south of the magnetotelluric line significant electrical contrasts between the sediments and basement rocks allow mapping of the top of the high resistivity basement which is characterized by progressively deeper burial to the west

gravity waves in the troposphere and stratosphere during the macwave midas summer rocket program 1 combining data taken during the macwave summer rocket campaign at the andoya rocket range 69 3 n 16 0 e with a lidar radiosondes falling spheres and vhf radars at andoya and at the esrange the gravity wave content of the troposphere and stratosphere during the campaign nights was analyzed the lidar yielded vertical wavelengths and periods of gravity waves in the stratosphere a stokes parameter analysis was performed for the radiosonde and falling sphere data to estimate propagation directions of the gravity waves the wave content in the troposphere was inferred by applying wavelet and cross spectral methods to the radar data we found propagation conditions and spectra of the waves to vary with height following the change in the background wind the waves were excited both at the ground and in the tropopause lower stratosphere region

latitudinal variations of the convective source and propagation condition of inertio gravity waves in the tropics latitudinal variations of the convective source and vertical propagation condition of inertio gravity waves igws in the tropical region 30 s 30 n are examined using high resolution global cloud imagery gci and 6 hourly ncep ncar reanalysis data respectively for 1 yr march 1985 february 1986 the convective source is estimated by calculating the deep convective heating dch rate using the brightness temperature of the gci data the latitudinal variation of dch is found to be significant throughout the year the ratio of the maximum to minimum values of dch in the annual mean is 3 2 and it is much larger in the june august jja and december february djf means spectral analyses show that dch has a dominant period of 1 day a zonal wavelength of about 1600 km and a gaussian type phase speed spectrum with a peak at the zero phase speed the vertical propagation condition of igws is determined in the zonal wavenumber and frequency domain by two factors i latitude which determines the coriolis parameter and ii the basic state wind structure in the target height range of wave propagation it was found that the basic state wind significantly influences the wave propagation condition in the lower stratosphere between 150 and 30 hpa and accordingly a large portion of the source spectrum is filtered out this is prominent not only in the latitudes higher than 15 where strong negative shear exists but also near the equator where strong positive shear associated with the westerly phase of the quasi biennial oscillation qbo filters out large portions of the lowfrequency components of the convective source there is no simple relationship between the ground based frequency and latitude lower latitudes are not always favorable for low frequency igws to be observed in the stratosphere the basic state wind in the tropics which has seasonal annual and interannual variations plays a major role not only in determining the wave propagation condition in the stratosphere but also in producing convective sources in the troposphere

measurements of superadiabatic lapse rates in the middle atmosphere a large power aperture product rayleigh scatter lidar system has been successfully built and over 175 nights of middle atmosphere temperature measurements have been obtained the high signal to noise ratio of these measurements allows the stability of the air in the upper stratosphere and mesosphere to be determined a detailed methodology has been developed to attempt to differentiate between lapse rate variations due to photon counting errors and actual geophysical variations on nights when the geophysical variations are large compared to the photon counting errors regions of convective stability and instability can be determined at a reasonably high confidence level both statistics of the layers and an image of the layers is presented for the night of may 31 1996 the measured percentage of unstable layers is in agreement with the predictions of hines 1991 as is the apparently sporadic formation and distribution of the unstable regions

lidar temperature measurements of gravity waves over kuhlungsborn 54 n from 1 to 105 km a winter summer comparison 1 since august 2002 temperature measurements from 1 to 105 km are performed at the leibniz institute of atmospheric physics in kuhlungsborn 54 n with a combination of different lidars results from 14 nights in winter and 31 in summer are presented nightly mean profiles and fluctuations with a temporal and vertical resolution of 15 min and 1 km respectively are derived in both seasons wave energy propagates upward phase propagates downward with vertical phase speeds of 0 25 to 1 9 m s phase speeds are generally larger in the mesosphere compared to the stratosphere because of decreasing static stability wave periods are found in the entire range of 1 8 hours given by experimental constraints with no preference for particular periods the observed vertical wavelengths cover the entire instrumental range of 5 50 km but the majority lies below 22 km in both seasons in single nights a few waves up to three dominate the wave spectrum and represent 45 65 of the entire variability wave amplitudes generally increase with altitude with a scale height of 18 22 km i e less than expected 14 km for propagation conserving momentum flux density the gravity wave energy loss changes with altitude and is different in both seasons local fluctuation minima nodes are often observed frequently colocated with convective instabilities temperature fluctuations are generally smaller in summer compared to winter maximum values are 10 and 25 k respectively applying gravity wave polarization relations to the mean winter and summer lidar temperature profiles the difference of fluctuations is basically determined by the background conditions especially at 60 80 km

comparison of global distributions of zonal mean gravity wave variance inferred from different satellite instruments gravity wave temperature fluctuations acquired by the crista instrument are compared to previous estimates of zonal mean gravity wave temperature variance inferred from the lims mls and gps met satellite instruments during northern winter careful attention is paid to the range of vertical wavelengths resolved by each instrument good agreement between crista data and previously published results from lims mls and gps met are found key latitudinal features in these variances are consistent with previous findings from ground based measurements and some simple models we conclude that all four satellite instruments provide reliable global data on zonal mean gravity wave temperature fluctuations throughout the middle atmosphere

comparison of seismicity parameters in different subduction zones and its implications for the cascadia subduction zone the cascadia subduction zone is a young subduction zone with associated volcanic activity but with no history of large thrust earthquakes associated with it as is characteristic of other subduction zones this has led to questions about the potential for great earthquakes associated with this subduction the seismic potential associated with this subduction has been investigated in this study by examining and comparing the number of shallow earthquakes with magnitude 6 which have occurred in different subduction zones since 1910 this examination shows that all subduction zones exhibit a higher level of activity than cascadia furthermore two of these zones with similar rates of plate motion and age at subduction the rivera plate and southwest japan have not only experienced great earthquakes but show a higher rate of activity than the cascadia zone the activity rate in subduction zones with predominantly aseismic slip is also higher than the activity rate in the cascadia zone earthquake activity in the rupture zones of great earthquakes both before and after the occurrence of great earthquakes is higher than the activity rate in the cascadia zone these results therefore suggest that the low rate of activity in the cascadia zone is unusual and supports the idea that the subduction here is different and that perhaps the potential for great earthquakes cannot be extrapolated simply on the basis of certain similarities between the cascadia zone and other subduction zones with a history of great earthquakes the low rate of earthquake activity in the cascadia zone can however be explained on the basis of the combined effect of low rate of plate motion significant aseismic subduction and young age at subduction the activity rate in the cascadia zone is consistent with the activity rates in other subduction zones if it is assumed that much of the plate motion is accommodated aseismically the seismic slip rate associated with this subduction zone is a small fraction of the rate of plate motion and therefore even if the potential for great earthquakes may exist the return period for great earthquakes will be much longer 2 or 3 times than in other zones with similar characteristics such as the rivera plate or southwest japan

characteristics of short period wavelike features near 87 km altitude from airglow and lidar observations over maui 1 small scale less than 15 km horizontal wavelength wavelike structures known as ripples are a common occurrence in oh airglow images recent case studies attribute their origin to the presence of either convective or dynamical instabilities however little is known about their frequency of occurrence and period the maui malt observatory located at mt haleakala is instrumented with a na wind temperature lidar which allows the determination of whether the atmosphere is dynamically or convectively unstable and a fast oh airglow camera which takes images every 3 s with a sensitivity high enough to see the ripples this study reports on 2 months of observations in october november 2003 and in august 2004 eight nights of which also included na lidar measurements the imager results suggest that instability features occur in the 85 to 90 km region of the atmosphere for around 20 of the time the nominal observed period for the ripples is between 2 and 4 min while there are clear night to night variations the average observed period is similar for both the 2003 and 2004 observations in addition a few of the small scale structures are not ripples caused by instabilities but rather have features consistent with their being short horizontal wavelength evanescent waves their fractional intensity fluctuations are as large or larger than those of the ripple instabilities unlike the instabilities the origin of the evanescent waves is not determined

global observations of gravity waves from high resolution dynamics limb sounder temperature measurements a yearlong record of temperature amplitude and vertical wavelength 1 global observations of gravity waves have been performed using the high resolution dynamics limb sounder hirdls temperature data a background field that was derived by dynamically calculating 31 day 15 day means to block the stationary component and the slowly varying planetary scale waves was first subtracted from the hirdls temperature measurements an additional step was then taken to remove rapidly moving planetary scale waves by developing an along track temperature filter which was created by averaging the profiles within a 1000 km along track window finally each individual temperature perturbation vertical profile was analyzed using a fast fourier transform to estimate gravity wave temperature amplitudes and vertical wavelengths the investigation of the monthly mean gravity wave temperature amplitudes for the year 2006 found that gravity wave activity in the stratosphere is highly variable with season and can be very orographically dependent especially in the winter extratropics the monthly zonal means show that the peak vertical wavelengths correspond closely to the peak amplitudes the increasing amplitudes and vertical wavelengths are faster and generated at lower altitudes in the winter extratropical and high latitude stratosphere than those in the summer tropical stratosphere this is consistent with the lower source altitudes of orographic gravity waves in the extratropics and high latitudes and the higher source altitudes of convectively generated gravity waves in the tropics three cases were studied for the observed gravity waves over large mountain ranges using the european centre for medium range weather forecasts wind data investigations of episodes of enhanced gravity wave activity over the southern andes the cascade range and the rockies in winter months of 2006 indicate that orographic gravity waves refract downwind from the mountains and propagate along the direction of the intense winds by way of contrast observations of gravity waves around the himalayas show a strong relationship with the cyclones in that region

wintertime temperature maximum at the subtropical stratopause in a t213l256 gcm 1 a wintertime temperature maximum can be observed at the subtropical stratopause but does not appear in the radiative equilibrium temperature distribution this structure was well simulated using a high resolution general circulation model and examined in detail the stratopause temperature is latitudinally maximized in the winter subtropics because of a strong downwelling of the meridional circulation from summer tropics to winter subtropics passing above the stratopause its strong meridional flow consists of two parts a strong poleward flow in the winter subtropics with nearly vertically aligned contours of absolute angular momentum m and a strong cross equatorial flow toward winter hemisphere above the tropical stratopause with nearly horizontally aligned m contours the strong poleward flow in the winter subtropics is driven by a large eliassen palm e p flux convergence in a small absolute vorticity region the large e p flux convergence is due to extratropical planetary waves and asymmetric inertial instability on the other hand the strong cross equatorial flow is induced along the m contour to satisfy mass continuity with the strong poleward flow in the winter subtropics and exists in the easterly phase of s sao with a small latitudinal gradient of m the easterly of s sao during its mature phase acts as a corridor for cross equatorial meridional circulation while cross equatorial meridional circulation contributes to driving the easterly of s sao in its development phase

estimation of gravity wave momentum flux and phase speeds from quasi lagrangian stratospheric balloon flights part i theory and simulations a methodology for estimating gravity wave characteristics from quasi lagrangian observations provided by long duration superpressure balloon flights in the stratosphere is reviewed wavelet analysis techniques are used to detect gravity wave packets in observations of pressure temperature and horizontal velocity an emphasis is put on the estimation of gravity wave momentum fluxes and intrinsic phase speeds which are generally poorly known on global scales in the atmosphere the methodology is validated using monte carlo simulations of time series that mimic the balloon measurements including the uncertainties associated with each of the meteorological parameters while the azimuths of the wave propagation direction are accurately retrieved the momentum fluxes are generally slightly underestimated especially when wave packets overlap in the time frequency domain or for short period waves a proxy is derived to estimate by how much momentum fluxes are reduced by the analysis retrievals of intrinsic phase speeds are less accurate especially for low phase speed waves a companion paper part ii implements the methodology to observations gathered during the vorcore campaign that took place in antarctica between september 2005 and february 2006

gravity waves appearing in a high resolution gcm simulation global characteristics of gravity waves in the lower stratosphere are examined using a gcm with high resolution in both the horizontal t106 corresponding to about 120 km and the vertical 600 m the bottom boundary condition of the model is that of an aquaplanet with perpetual february sea surface temperature the simulated gravity waves are in good agreement with mesosphere stratosphere troposphere mst radar observations at a middle latitude on the gravity wave structure and on the frequency spectra as a function of height the frequency spectra of simulated wind and temperature fluctuations are also examined as a function of latitude large values of spectral density are observed at frequencies higher than the inertial frequency f in a weak wind region around 20 km which is consistent with the characteristics of internal gravity waves an isolated peak is observed near f for horizontal wind spectra at latitudes higher than 108 while the energy is distributed in a wide range of frequency at lower latitudes where f approaches zero further analysis is performed of those fluctuations having periods shorter than 24 h and those having vertical wavelengths smaller than 5 km these are frequently analyzed as gravity waves using observation data the distribution of energy and momentum fluxes in the latitude height section is examined the result indicates that short period waves mostly propagate upward and poleward from the equatorial region the wave energy reaches about 508 lat at the 27 km altitude a negative positive maximum of vertical flux of meridional momentum y9w9 is seen above the subtropical jet in the northern southern hemisphere for small vertical scale gravity waves this is consistent with the preferred equatorward propagation of the wave indicated by a statistical analysis based on mst radar observations the ratio of potential to kinetic energy maximizes over the equator and decreases poleward the eliassen palm flux divergence associated with gravity waves is decelerative above the subtropical jet albeit small

rayleigh lidar observations of gravity wave activity in the upper stratosphere at urbana illinois abstract during 13 nights of rayleigh lidar measurements at urbana illinois in 1984 86 thirty six quasi monochromatic gravity waves were observed in the 35 50 km altitude region of the stratosphere the characteristics of the waves are compared with other lidar and radar measurements of gravity waves and with theoretical models of wave saturation and dissipation phenomena the measured vertical wavelengths 2 ranged from 2 to 11 5 km and the measured vertical phase velocities cz ranged from 10 to 85 cm s 1 the vertical wavelengths and vertical phase velocities were used to infer observed wave periods tob which ranged from 100 to 1000 min and horizontal wavelengths x which ranged firm 70 to 2000 km there may be errors in the inferred values of the horizontal wavelengths because they were calculated by assuming that the observed period inferred the intrinsic period dominant wave activity was found at vertical wavelengths between 2 4 km and 7 10 km no significant seasonal variations were evide

gravity waves generated by convection in the darwin area during the darwin area wave experiment 1 we describe a model study of gravity wave generation by convection near darwin during the darwin area wave experiment dawex we focus on an 7 hour period on 17 november 2001 for our study which included a major hector event over the tiwi islands followed by a continental convective outbreak that included a squall line to the southeast of darwin our model is a dry version of a three dimensional 3 d mesoscale cloud resolving model with horizontally uniform background wind and stability fields the model is forced with a spatially and temporally varying heating field representative of the convective latent heating in the area we derive this heating field from 3 d volumetric reflectivity from the precipitation radar located just north of darwin at gunn point during dawex the conversion from radar reflectivity to a 3 d latent heating field requires numerous assumptions that do not allow a quantitative heating estimate but which do provide a very realistic measure of the spatial morphology and temporal variations of the latent heating gravity waves generated by convective heating are known to be very sensitive to these characteristics of the heating so our resulting wave field is likely to be the most realistic possible description of the waves emitted from convection in the darwin area uncertainty in the wave amplitudes is large both because the input forcing heating is uncertain and because the use of heating as the sole proxy for wave forcing leads to additional wave amplitude errors we therefore compare the results of the model to other dawex measurements and previous modeling studies both to validate the waves in our model and to calibrate the wave amplitudes our study in turn aids in the interpretation of the other gravity wave measurements during dawex

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

simultaneous observations of the phase locked 2 day wave at adelaide cerro pachon and darwin the southern hemisphere summer 2 day wave tdw is the most dramatic large scale event of the upper mesosphere the winds accelerate over 1 week may attain 70 m s and are often accompanied by a near disappearance of the diurnal tide and stabilization of the period close to 48 h we denote this as the phase locked 2 day wave pl tdw we have examined airglow and meteor radar mr wind data from the andes lidar observatory cerro pachon chile 30 s 289 3 e mr data from darwin 12 5 s 131 e and airglow and medium frequency radar data from the university of adelaide 34 7 s 138 6 e for the behavior of the tdw during the austral summers of 2010 2012 and 2013 the cerro pachon and adelaide sites are located at similar latitudes separated in longitude by about 120 we find a remarkable coincidence between the tdw oscillations at chile and adelaide for the period january february 2010 the oscillations are nearly in phase in terms of local time and the minima and maxima repeat at nearly the same local time from cycle to cycle consistent with a phase locked wave number 3 tdw data for this and other years including darwin show that the amplitude of the diurnal tide decreases when the tdw is largest and that this occurs when the period is close to 48 h these observations support the proposal that the pl tdw is a subharmonic parametric instability wherein the diurnal tide transfers energy to a tdw that is resonant at nearly 48 h

rayleigh lidar observations of gravity wave activity in the winter upper stratosphere and lower mesosphere above davis antarctica 69 s 78 e 1 gravity wave activity in the upper stratosphere and lower mesosphere uslm is investigated using temperature data retrieved from a rayleigh lidar at davis antarctica 69 s 78 e during the 2007 and 2008 winters the temporal and height variabilities of waves with ground based periods greater than 2 h and vertical wavelengths between 4 km and 20 km are analyzed stratospheric gravity wave potential energy per unit mass shows a weaker correlation with stratospheric winds at davis than that reported in the arctic gravity waves dissipate above 40 km during winter while there is no dissipation in the autumn mesosphere a separate analysis of gravity waves with ground based periods of 2 6 h revealed lower dissipation in the winter mesosphere the seasonal cycle of gravity wave activity is evident throughout the uslm with peak activity observed during winter the gravity wave potential energy and vertical wavenumber power spectral density at davis are similar to that recorded at other high latitude sites

episodic tectonic subsidence of late holocene salt marshes northern oregon central cascadia margin salt marsh subsurface deposits 0 4 m depth in netarts bay a small coastal lagoon of northern oregon record six events of marsh burial in the last several thousand years five of the buried marsh surfaces show sharp nonerosional upper contacts with either anomalous sand layers tsunami deposits or tidal flat mud deposits these sequences indicate episodic abrupt subsidence of the marsh surfaces to low intertidal levels in contrast lower marsh contacts with underlying intertidal muds are gradational indicating gradual uplift and development of the marsh three independent measures of deposit elevation relative to mean tidal level percent organics diatom assemblages and percent eolian sand have been used to estimate vertical displacements of marsh surfaces abrupt subsidence displacements of 1 1 5 m alternate with gradual uplift displacements of the order of 0 5 1 0 m the vertical tectonic movements are interpreted to reflect coseismic strain release abrupt subsidence following interseismic strain accumulation gradual uplift associated with interplate coupling between the juan de fuca plate and the north american plate in the cascadia subduction zone recurrence intervals between subsidence events range from possibly less than 300 years to at least 1000 years with the last dated event likely occurring 300 400 radiocarbon years before present rcybp significant 14c age overlaps of at least four subsidence events recorded at netarts and reported for southern washington and other northern oregon bays at 300 500 1000 1300 1400 1800 and 3000 3300 rcybp suggest the potential for event synchroneity over at least 200 km of the central part of the cascadia subduction zone additional work is needed to test the synchroneity of these episodic events of coseismic subsidence

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

evidence for inertia gravity waves forming polar stratospheric clouds over scandinavia 1 at three successive days at the end of january 2000 the deutsches zentrum fur luft und raumfahrt dlr airborne lidar ozone lidar experiment explored mountain wave induced polar stratospheric clouds above the scandinavian mountain ridge global analyses and mesoscale modeling are applied to explain their complex internal structure and their day to day variability depending on the synoptical scale meteorological conditions stratospheric temperature anomalies of different amplitude and horizontal extent are generated by the upward propagating mountain waves short term excitation of about 6 hours resulted in localized stratospheric temperature anomalies directly above the mountain ridge as for 25 january 2000 in this case the elevation of the observed clouds differed not much from the synoptic scale clouds upstream above the norwegian sea on the other hand long lasting flow past the scandinavian mountain ridge formed huge 400 km horizontally extending stratospheric ice clouds in altitudes as much as 5 km above the elevation of the upstream clouds just 1 day later inertia gravity waves with horizontal wavelengths of about 350 km are responsible for their formation for the first time a predicted temperature minimum far downstream of the mountains could be proofed by the observation of an isolated stratospheric ice cloud above finland the observed particles are classified in terms of their measured optical properties such as backscatter ratio and depolarization in all cases mountain waves generated ice clouds in contrast to the nitric acid trihydrate tail of the ice cloud on 25 january the same classification results in a tail of liquid supercooled ternary solutions droplets 1 day later the particle structure downstream of the mountains is very complex and needs detailed microphyical modeling and interpretation

darwin area wave experiment dawex field campaign to study gravity wave generation and propagation 1 a field campaign studying aspects of the atmospheric dynamics from the ground to the lower thermosphere was conducted in australia during october to december 2001 this darwin area wave experiment dawex involved participation from nine institutions in the usa japan and australia and focused on studying wave perturbations in the middle atmosphere in conjunction with detailed observations of tropospheric moist convection the experiment involved extended deployment of six airglow imagers medium frequency radars and a boundary layer wind profiler tropospheric convection was observed by meteorological radars including the australian bureau of meteorology research centre c band polarized radar this paper provides an overview of the experimental setup and also discusses the basic meteorological fields during the experiment including some examples of convective activity near darwin wind and temperature fields extending up into the lower thermosphere were constructed on the basis of campaign observations and the ukmo global meteorological analysis these fields can be used for the modeling of gravity wave propagation through the middle atmosphere

timed saber observations of global gravity wave climatology and their interannual variability from stratosphere to mesosphere lower thermosphere the present study for the first time reports the global gravity wave activity in terms of their potential energy derived from timed saber observations right from the stratosphere to the mesosphere lower thermosphere mlt region the potential energy profiles obtained from saber temperature are validated by comparing them with ground based lidar observations over a low latitude site gadanki 13 5 n 79 2 e the stratospheric and mesospheric global maps of gravity wave energy showed pronounced maxima over high and polar latitudes of the winter hemisphere the interannual variability of the stratospheric gravity wave activity exhibited prominent annual oscillation over mid latitudes the equatorial gravity wave activity exhibited quasi biennial oscillation in the lower stratosphere and semi annual oscillation in the upper stratosphere the mlt region maps revealed summer hemispheric maxima over polar latitudes and secondary maxima over the equatorial region the results are discussed in the light of present understanding of global gravity wave observations the significance of the present study lies in emphasizing the importance of satellite measurements in elucidating gravity waves which is envisaged to have profound impact on parameterizing these waves

mesospheric gravity waves at saskatoon 52 n kyoto 35 n and adelaide 35 s the gravity waves with periods of 10 min to 8 hours in the mesosphere 67 80 km are studied using observations from the adelaide mf radar 35 s saskatoon mf radar 52 n and the middle and upper atmosphere mu radar at shigaraki near kyoto 35 n the seasonal variations of the gravity wave intensity deduced from the horizontal wind velocities showed semiannual variations with solstitial maxima and equinoctial minima at all three locations but the month of maximum intensity in the year depends on the locations and wave frequency the kinetic energy due to gravity waves showed similar amplitude between kyoto and adelaide but smaller at saskatoon which agrees well with the results of the preliminary comparison using a limited frequency range and limited observation periods by nakamura et al 1993a b the horizontal propagation direction of these gravity waves showed small seasonal variations and significant dependency with wave periods at saskatoon but showed more frequent variation without a large frequency dependency at kyoto and adelaide these characteristics indicate that at the lower latitudes gravity wave activity is larger as pointed out by tsuda et al 1994 from various observational techniques also the frequent changes of the gravity wave intensities at the lower latitudes suggest that there are strong influences of the background wind variation in the middle atmosphere such as semiannual oscillation mesospheric semiannual oscillation and other wind variations in the low latitudes

a search for mountain waves in mls stratospheric limb radiances from the winter northern hemisphere data analysis and global mountain wave modeling 1 despite evidence from ground based data that flow over mountains is a dominant source of gravity waves gws for the northern hemisphere winter middle atmosphere gw related signals in global limb radiances from the microwave limb sounder mls on the upper atmosphere research satellite uars have shown little direct evidence of mountain waves we address this issue by combining a renewed analysis of mls limb track and limb scan radiances with global mountain wave modeling using the naval research laboratory mountain wave forecast model mwfm mls radiance variances show characteristics consistent with mountain waves such as enhanced variance over specific mountain ranges and annual variations that peak strongly in winter however direct comparisons of mls variance maps with mwfm simulated mountain wave climatologies reveal limited agreement we further develop a detailed mls gw visibility function that accurately specifies the three dimensional in orbit sensitivity of the mls limb track radiance measurement to a spectrum of gws with different wavelengths and horizontal propagation directions on postprocessing mwfm generated mountain wave fields through these mls visibility filters we generate mwfm variance maps that agree substantially better with mls radiance variances this combined data analysis and mls filtered mwfm modeling leads us to conclude that many mls variance enhancements can be associated with mountain waves forced by flow over specific mountainous terrain these include mountain ranges in europe e g scandinavia alps scotland ural putoran altai hangay and sayan mountains yablonovyy stanovoy khingan verkhoyansk and central ranges north america e g brooks range mackenzie mountains colorado rockies southeastern greenland and iceland our results show that given careful consideration of the in orbit sensitivity of the instrument to gws middle atmospheric limb radiances measured from uars mls as well as from the new mls instrument on the earth observing system eos satellite can provide important global information on mountain waves in the extratropical northern hemisphere stratosphere and mesosphere

source characteristics of hypothetical subduction earthquakes in the northwestern united states historic earthquake sequences on subduction zones that are similar to the cascadia subduction zone are used to hypothesize the nature of shallow subduction earthquakes that might occur in the northwestern united states based on systematic comparisons of several physical characteristics including physiography and seismicity subduction zones that are deemed most similar to the cascadia subduction zone are those in southern chile southwestern japan and colombia these zones have all experienced very large earthquake sequences and if the cascadia subduction zone is also capable of storing elastic strain energy along its greater than 1000 km length then earthquakes of very large size m w 8 1 2 must be considered circumstantial evidence is presented that suggests but does not prove that large subduction earthquakes along the cascadia subduction zone may have an average repeat time of 400 to 500 yr

temperature tides and waves near the mesopause from lidar observations at two latitudes 1 daytime and nighttime temperature measurements covering several days enable the detection of tidal and wave perturbations in the mesopause region this study presents two potassium lidar observations from 28 n and 54 n which cover more than 100 hours each the temperature variations during this time show significant wave features and numerical analyses allow to separate those of tidal and nontidal origin the tidal activity under winter conditions is found to be dominated by upward propagating semidiurnal tides with amplitudes of about 10 k whereas a diurnal tide was also seen at 54 n it was not detectable at 28 n the data are discussed with respect to various available data sets and models comparisons with current numerical models show that especially the semidiurnal tide is clearly underestimated at both latitudes the tidal activity exhibits a strong variability this indicates nonlinear interactions with planetary waves which have also been observed

inertia gravity wave generation by the tropospheric midlatitude jet as given by the fronts and atlantic storm track experiment radio soundings 1 generation of inertia gravity waves by the midlatitude tropospheric jet is studied on the basis of the data obtained from the radio soundings over the north atlantic during the fronts and atlantic storm track experiment campaign a sample of 224 radio soundings is used to analyze the wave activity as a function of the distance to the jet it is shown that radio soundings displaying the most intense gravity wave activity both in the stratosphere and in the troposphere are the ones closest to the jet axis thus the jet region is the dominant source of gravity waves in this region far from orography further examination allows for identification of two specific regions of the flow that are associated with intense gravity wave activity the vicinity of the maximum of the jet velocity and the regions of strong curvature of the jet the detailed case studies we provide suggest that geostrophic adjustment is the dynamical mechanism responsible for the generation of large amplitude inertia gravity waves in the regions of the strong curvature of the wind the generation of waves in the vicinity of the regions where the wind veers in the deep troughs of the geopotential appears to be systematic

concentric gravity waves in the mesosphere generated by deep convective plumes in the lower atmosphere near fort collins colorado 1 gravity waves in the mesopause region 80 105 km may induce perturbations in oh meinal band emissions at 87 km these perturbations can be observed by ground based oh airglow imagers in this paper we present observations of concentric gravity waves cgw by the all sky oh imager at yucca ridge field station 40 7 n 104 9 w near fort collins colorado we find that expanding rings of concentric gravity waves were observed on 9 out of 723 clear nights from 2003 to 2008 in particular on 11 may 2004 concentric rings were observed for 1 5 h with nearly perfect circular rings entirely in the field of view during the first 30 min the centers of the concentric rings occurred at the geographic locations of two strong convective plumes which were active in the troposphere 1 h earlier we measured the horizontal wavelengths and periods of these gravity waves as functions of both radius and time these results agreed reasonably well with the internal boussinesq gravity wave dispersion relation with an assumed zero background wind similarly for the other 8 cases strong convective plumes occurred prior to the cgw observations near the apparent center of each of the arcs or rings for the 7 out of the 9 cases radiosonde data were available up to z 30 35 km these data showed that the wind speeds from the tropopause to 30 35 km were smaller than 20 30 m s because 8 of the 9 cases occurred when the total horizontal mean winds were weak and because the horizontal winds below 87 km were less than 20 m s on 11 may 2004 according to radiosonde and time gcm model data we postulate that weak background horizontal winds are likely a necessary condition for gravity waves excited from convective overshooting to be observed as concentric arcs or rings in the oh layer

the synoptic setting and possible energy sources for mesoscale wave disturbances abstract thirteen case studies of mesoscale wave disturbances characterized by either a singular wave of depression or wave packets with periods of 1 4 h horizontal wavelengths of 50 500 km and surface pressure perturbation amplitudes of 0 2 7 0 mb are reviewed to isolate common synoptic features for these cases and to shed light on possible energy sources for the waves a strong thermal inversion in the lower troposphere north of a frontal boundary and a jet streak propagating toward a ridge axis in the upper troposphere are commonly observed in all the cases in general the area of wave activity is bounded by the jet axis to the west or northwest a surface front to the southeast an inflection axis between the trough and ridge axes to the southwest and the ridge axis to the northeast the conditions specified by lindzen and tung as being necessary to form a wave duct which include the existence of the lower tropospheric inversion seem to be met in many of these cases this suggests that a du

observations of the phase locked 2 day wave over the australian sector using medium frequency radar and airglow data 1 the quasi 2 day wave with a nominal mean period just above 50 h is a significant feature of the 80 100 km altitude region in both hemispheres it becomes particularly prominent in the southern hemisphere summer at midlatitudes where a short time after summer solstice its amplitude rapidly increases and its mean period is found to be approximately 48 h producing an oscillation phase locked in local time this lasts for a few weeks presented here are observations of the meridional winds and airglow over two sites in australia for 4 years during the austral summers of 2003 2006 we show that during those times when the large amplitude phase locked 2 day wave pl tdw is present the diurnal tide greatly decreases this is consistent with the walterscheid and vincent 1996 model in which the pl tdw derives its energy from a parametric excitation by the diurnal tide these data also show that the diurnal tide is more suppressed and the pl tdw amplitude is larger in odd numbered years suggesting a biannual effect the airglow data indicated that for the pl tdw the winds and temperature are nearly out of phase when the pl tdw is present airglow amplitudes can become quite large a result dependent on the local time of the pl tdw maximum the airglow intensity response was in general much larger than what would be expected from the airglow temperature response suggesting that the pl tdw is causing a significant composition change possibly due to minor constituent transport

airglow observations of dynamical wind shear induced instabilities over adelaide australia associated with atmospheric gravity waves while several observations have been made in recent years of instability features in airglow images of atmospheric gravity waves agws such measurements are still rare to date these features are characterized by appearing to be aligned perpendicular to the agw wave fronts multi instrument observations confirm the theoretical prediction that such features are caused by convective instabilities where the agw induced temperature variation causes the total lapse rate to exceed the adiabatic lapse rate in february 2000 airglow observations were obtained at buckland park australia which showed instability features with a different characteristic these images showed small scale less than 10 km horizontal wavelength features aligned parallel to the larger scale agw wave fronts these features were only seen in oh images not in o2a images indicating that they originate below 90 km altitude simultaneous mf radar wind data reveal the presence of a mean wind shear which during the period of the small scale features was aligned nearly in the direction of agw propagation in addition the larger scale agw approached a critical level near 90 km altitude while the wind shear itself is not large enough to cause an instability an analysis of the data suggests that the small scale features are the result of a dynamic wind shear induced instability in the 87 90 km altitude region the instability was due to a combination of the background wind shear and the large shear induced by the passage of the larger scale agw as it approached the critical level