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

the proportionality between relative plate velocity and seismicity in subduction zones the magnitude and rate of seismicity differ between subduction zones calculations of background seismicity rates based on a global model of subduction zone seismicity reveal a positive correlation between relative plate velocity and background seismicity yet only the seismically quieter zones seem capable of generating magnitude 9 earthquakes

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

a global morphology of gravity wave activity in the stratosphere revealed by the gps occultation data gps met using temperature profiles obtained by the gps met gps meteorology experiment from april 1995 to february 1997 we have extracted mesoscale temperature perturbations with vertical wavelengths ranging from 2 to 10 km and background brunt vaisala frequency squared n2 for each occultation event we can evaluate a potential energy ep which is assumed to be caused by atmospheric gravity waves the monthly mean values of ep at 15 20 km around japan showed an annual variation with an enhancement in winter which is consistent with the climatological behavior of the kinetic energy of gravity waves observed with the mu middle and upper atmosphere radar 34 9 n 136 0 e from 1985 to 1989 we have then derived the global distribution of ep at 20 30 km during northern hemisphere winter from november to february our analysis shows that the largest ep values are generally centered around the equator between 25 n and 25 s with considerable longitude variations longitudinal variations of ep at 20 30 km in a latitude range of 30 60 n are also analyzed resulting in larger ep values over the continents than over the pacific ocean using gps met data without antispoofing latitudinal variations of ep are determined in 15 45 km although large ep values are concentrated near the equator at 20 30 km ep tends to become larger at midlatitudes at 30 40 km and higher altitude regions at midlatitudes ep is found to be larger in winter months in both hemispheres height variations of ep indicate a decrease at 25 30 km and a monotonic increase above 30 km

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

vhf radar observations of convectively generated gravity waves some new insights 1 vhf radar observations of tropical mesoscale convective systems have provided some new insights on convectively generated gravity waves over gadanki 13 5 n 79 2 e a tropical station in india present observations revealed disturbed tropopause structures and enhanced mass fluxes across the tropopause during the passage of deep convective systems the analysis suggest that during disturbed tropopause conditions not only the direct intrusion across the tropopause takes place but also the gravity wave activity associated with convection enhances in the lower stratosphere as compared to the stable tropopause conditions this result is a major outcome of the present study another noteworthy result from the present observations is the phase profile of convectively generated gravity waves which for the first time provided an opportunity to localize the source region of gravity waves

satellite observations of atmospheric variances a possible indication of gravity waves the microwave limb sounder mls on the upper atmosphere research satellite has now produced the first global maps of small scale variances in the middle atmosphere initial analyses are presented here that suggest these variances are due to gravity waves and the technique used to extract gravity wave information from saturated radiance measurements is described observations at 30 80km altitudes show that the variances of horizontal scales less than 100km are strongly correlated with upper tropospheric convection surface topography and stratospheric jetstreams mls monthly averages during solstice periods suggest that the normalized variance amplitude grows exponentially with height in the stratosphere and saturates in the mesosphere as expected from wave breaking and dissipation at these altitudes

secondary gravity wave generation over new zealand during the deepwave campaign multiple events during the deep propagating gravity wave experiment measurement program revealed mountain wave mw breaking at multiple altitudes over the southern island of new zealand these events were measured during several research flights from the national science foundation national center for atmospheric research gulfstream v aircraft utilizing a rayleigh lidar an na lidar and an advanced mesospheric temperature mapper simultaneously a flight on 29 june 2014 observed mws with horizontal wavelengths of 80 120 km breaking in the stratosphere from 10 to 50 km altitude a flight on 13 july 2014 observed a horizontal wavelength of 200 240 km mw extending from 20 to 90 km in altitude before breaking data from these flights show evidence for secondary gravity wave sgw generation near the breaking regions the horizontal wavelengths of these sgws are smaller than those of the breaking mws indicating a nonlinear generation mechanism these observations reveal some of the complexities associated with mw breaking and the implications this can have on momentum fluxes accompanying sgws over mw breaking regions

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

velocity dependence of strength and healing behaviour in simulated phyllosilicate bearing fault gouge abstract despite the fact that phyllosilicates are widespread in fault zones little is known about the strength of phyllosilicate bearing fault rocks under brittle ductile transitional conditions in this study we explored the steady state strength and healing behaviour of a simulated phyllosilicate bearing fault rock i e muscovite plus halite and brine at room temperature normal stresses of 1 9 mpa atmospheric fluid pressure and sliding velocities of 0 001 13 m s using a rotary shear apparatus while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behaviour the strength of mixtures containing 10 50 muscovite is both normal stress and sliding velocity dependent at low velocities 1 m s velocity weakening frictional behaviour occurs along with the development of a structureless intermixed cataclastic microstructure the steady state porosity of samples deformed in this regime increases with increasing sliding velocity we propose that this behaviour involves competition between dilatation due to granular flow and compaction due to pressure solution towards higher sliding velocities dilatation increasingly dominates over pressure solution compaction so that porosity increases and frictional strength decreases during periods of zero slip pressure solution compaction occurs causing a significant strength increase on reshearing our results imply that cataclastic overprinting of mylonitic rocks in natural fault zones does not require any changes in temperature or effective pressure conditions but can simply result from oscillating fault motion rates our healing data suggest that foliated aseismically creeping fault segments will remain weak and aseismic whereas segments that have slipped seismically will rapidly re strengthen and remain in the unstable velocity weakening regime

annual and interannual variations in global 6 5dws from 20 to 110 km during 2002 2016 observed by timed saber

gravity waves resolved in ecmwf and measured by saber 1 the limited resolution of most general circulation models gcms is not sufficient to simulate gravity waves gws explicitly ecmwf european center for medium range weather forecasts data have now a horizontal resolution of so parts of the mesoscale gws can be resolved although most source processes still contain sub grid phenomena we validate the gws resolved in ecmwf by comparison with corresponding results obtained from global saber sounding of the atmosphere using broadband emission radiometry satellite observations for this comparison effects of the radiative transfer and satellite retrieval procedure are accounted for globally gws can be attributed to various gw sources and the gw spectrum is modulated by the background winds correlation analysis comparing saber and ecmwf temperature fluctuations indicate good agreement with respect to mountain waves for example over the southern tip of south america or over scandinavia as well as gws at the edge of the winter polar vortex

low friction and fault weakening revealed by rising sensitivity of tremor to tidal stress at subduction zones deep parts of the fault can slip slowly generating tremor analysis of tremor in cascadia reveals increasing sensitivity of slip to tidal stresses over several days implying that the fault is weak and weakens as it slips

lidar observations of gravity waves and their spectra near the mesopause and stratopause at arecibo abstract the uiuc cedar rayleigh na lidar was operated for approximately 160 h on 30 nights in january march and april 1989 at the arecibo observatory 18 n 67 w as part of the aida act 89 campaign during this period 38 quasi monochromatic gravity waves were observed in the stratopause region 25 55 km and 62 waves were observed in the mesopause region 80 105 km the event rates in both regions are approximately half those observed at the midlatitude site of urbana the characteristics of the waves in both regions are similar measured vertical wavelengths range from 1 1 to 17 km vertical phase velocities from 6 to 270 cm s 1 observed periods from 5 min to 65 h and amplitudes relative atmospheric density variations 0 4 to 17 the wave amplitudes in the stratopause region are on average half the values for waves in the mesopause region with similar periods and vertical wavelengths vertical wavenumber spectra of density perturbations in both regions exhibit power law dependencies with slo

saber observations of gravity wave responses to the madden julian oscillation from the stratosphere to the lower thermosphere in tropics and extratropics

preslip and cascade processes initiating laboratory stick slip recent modeling studies have explored whether earthquakes begin with a large aseismic nucleation process or initiate dynamically from the rapid growth of a smaller instability in a cascade up process to explore such a case in the laboratory we study the initiation of dynamic rupture stick slip of a smooth saw cut fault in a 76 mm diameter cylindrical granite laboratory sample at 40 120 mpa confining pressure we use a high dynamic range recording system to directly compare the seismic waves radiated during the stick slip event to those radiated from tiny m 6 discrete seismic events commonly known as acoustic emissions aes that occur in the seconds prior to each large stick slip the seismic moments focal mechanisms locations and timing of the aes all contribute to our understanding of their mechanics and provide us with information about the stick slip nucleation process in a sequence of 10 stick slips the first few microseconds of the signals recorded from stick slip instabilities are nearly indistinguishable from those of premonitory aes in this sense it appears that each stick slip begins as an ae event that rapidly 20 s grows about 2 orders of magnitude in linear dimension and ruptures the entire 150 mm length of the simulated fault we also measure accelerating fault slip in the final seconds before stick slip we estimate that this slip is at least 98 aseismic and that it both weakens the fault and produces aes that will eventually cascade up to initiate the larger dynamic rupture

meteor wind radar observations of gravity wave momentum fluxes and their forcing toward the mesospheric semiannual oscillation 1 wind measurements from continuous meteor radar observations during june 2004 may 2007 are used to estimate the gravity wave momentum fluxes in the mesosphere lower thermosphere mlt region over trivandrum 8 5 n 76 9 e a low latitude station in india the radial velocity variances in the 82 98 km height region which are mainly caused by gravity waves measured by the meteor radar are used to determine the gravity wave momentum fluxes using a novel method proposed by hocking 2005 altitude profiles of momentum fluxes of short period less than 2 3 h gravity waves are estimated for three continuous years seasonal variation in the gravity wave momentum fluxes showed semi annual variation with equinoctial maximum and solstitial minimum by using estimated gravity wave momentum fluxes an attempt is made to quantify their contribution in driving the mesospheric semi annual oscillation msao the mean flow acceleration estimated from the divergence of gravity wave momentum fluxes is compared with the observed mean flow acceleration computed from monthly mean zonal winds during six msao cycles over three years this comparison reveled that the gravity wave contribution toward the westerly phase of msao varies from 20 60 while that toward the easterly phase varies from 30 70 variations are observed from cycle to cycle in the gravity wave forcing toward both phases of msao the significance of the present study lies in estimating the gravity wave momentum fluxes in the mlt region and quantifying their contribution toward the generation of msao over the low latitude for the first time

sources of gravity waves in the lower stratosphere above south pole 1 five year 2001 2005 high resolution radiosonde data were processed to obtain the gravity wave gw variabilities in the lower stratosphere over south pole sp our results show that gw activities in the lowermost section 10 15 km are strongest in may and september and weakest in the austral summer whereas in the altitude range of 15 25 km strongest weakest gw kinetic energy is observed around september january we also explored the relationships of gws to the synoptic scale variations in the troposphere and the ageostrophic motions in the upper troposphere over the antarctic which are expected to be significant mechanisms for gw generation a ray tracing model grograt was used to explore the relationship between gw propagation and the background field in the altitude of 15 25 km the annual cycle of gw activity resembles that of adjustment process below 15 km the annual cycle of gw activity has two peaks in may and september our analysis suggests that these two peaks are due to the variation of topographic gw generation and filtering of background atmosphere due to critical level filtering in the lowermost section topographic gws cannot propagate upward which makes the shape of gw annual cycle at higher altitudes closer to the annual cycle of adjustment processes the analysis suggests that the minimum of gw activity at sp during the austral summer may be due to the combination of weaker wave generation from adjustment processes associated with synoptic scale systems flow over topography and unfavorable background field for gw propagation

the concept of wave turbopause layer and its signature in the global mesosphere lower thermospheric gravity wave activity 1 the concept of the wave turbopause layer is introduced and discussed in this study which defines the wave turbopause as a layer having a lower and upper boundary where maximum dissipation of atmospheric waves happens the analysis is carried out using three years of saber temperature measurements 2004 2006 and seasonal and latitudinal variability of the wave turbopause layer is established on an average it is found that there is a maximum of 5 20 km difference in altitude between the lower and upper boundaries of the wave turbopause seasonally the winter hemispheric high latitudes have the highest wave turbopause which decreases toward the summer hemisphere with a secondary maximum at the summer hemisphere midlatitude moreover the monthly variability of the wave turbopause and mesopause is studied for 50 n 0 and 50 s latitudes on global scale the latitude height sections of zonal mean gravity wave potential energy of the mlt region is compared with the wave turbopause characteristics the wave turbopause pattern seems to be superposed on the potential energy transition pattern which exposes an intermediate layer sandwiched between low and high magnitudes of potential energy thus the present study proposes the concept of the wave turbopause layer and substantiates the same by discussing its latitudinal structure seasonal and monthly variability correlation with the cold point mesopause and gravity wave potential energy in the mlt region

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

sources of mesoscale variability of gravity waves part i topographic excitation abstract aircraft measurements of winds and temperatures collected during the gasp program are used to study the effects of topography as a source of mesoscale variability variances of fluctuations at the mesoscale over rough terrain are enhanced up to nearly two orders of magnitude compared to nonsource regions in some cases and are frequently enhanced by an order of magnitude the implications of these episodic enhancements of variances for the vertical transports of energy and momentum are considered in the framework of gravity wave theory the observed flight data are used to estimate the momentum flux u w on several flight segments results show that the flux is generally negative with mean value 0 26 m2 s 2 and with magnitudes ranging up to 1 5 m2 s 2 spectral analysis shows that the largest contributions to the net flux come from horizontal scales of 25 x 60 km finally the observed momentum fluxes are used to infer the anisotropy factor of gravity waves over rough terrain which is foun

global estimates of gravity wave momentum flux from high resolution dynamics limb sounder observations analyzed to derive global properties of gravity waves we describe a wavelet analysis technique that determines covarying wave temperature amplitude in adjacent temperature profile pairs the wave vertical wavelength as a function of height and the horizontal wave number along the line joining each profile pair the analysis allows a local estimate of the magnitude of gravity wave momentum flux as a function of geographic location and height on a daily basis we examine global distributions of these gravity wave properties in the monthly mean and on an individual day and we also show sample instantaneous wave events observed by hirdls the results are discussed in terms of previous satellite and radiosonde observational analyses and middle atmosphere general circulation model studies that parameterize gravity wave effects on the mean flow the high vertical and horizontal resolution afforded by the hirdls measurements allows the analysis of a wider range of wave vertical and horizontal wavelengths than previous studies and begins to show individual wave events associated with mountains and convection in high detail mountain wave observations show clear propagation to altitudes in the mesosphere

strain localization driven by thermal decomposition during seismic shear field and laboratory observations show that shear deformation is often extremely localized at seismic slip rates with a typical deforming zone width on the order of a few tens of microns this extreme localization can be understood in terms of thermally driven weakening mechanisms a zone of initially high strain rate will experience more shear heating and thus weaken faster making it more likely to accommodate subsequent deformation fault zones often contain thermally unstable minerals such as clays or carbonates which devolatilize at the high temperatures attained during seismic slip in this paper we investigate how these thermal decomposition reactions drive strain localization when coupled to a model for thermal pressurization of in situ groundwater building on rice et al 2014 we use a linear stability analysis to predict a localized zone thickness that depends on a combination of hydraulic frictional and thermochemical properties of the deforming fault rock numerical simulations show that the onset of thermal decomposition drives additional strain localization when compared with thermal pressurization alone and predict localized zone thicknesses of 7 and 13 m for lizardite and calcite respectively finally we show how thermal diffusion and the endothermic reaction combine to limit the peak temperature of the fault and that the pore fluid released by the reaction provides additional weakening of 20 40 of the initial strength

temperature profiles in the mlt region using radar meteor trail decay times comparison with timed saber observations 1 a method for obtaining the height profiles of the temperature in the mlt region using the radar meteor trail decay times is discussed the present method combines the two existing methods for estimating the temperature pressure parameter and the temperature from the meteor radar observations using these two measurements pressure is obtained around 90 km and subsequently the height profile of pressure is obtained in the mlt region by assuming a scale height of 5 7 km the height profile of the pressure is then used to obtain the temperature profile the real time pressure measurements are used to obtain the temperature profiles day to day variability of the pressure around 90 km is compared with the monthly mean pressure values of cira 86 model and the temperature pressure profiles are compared with the timed saber satellite measurements the comparison of radar and saber observations is very encouraging and reinforces the need of real time pressure measurements for estimation of temperature from radar meteor trail decay time technique

lack of precursory slip to the 1999 hector mine california earthquake as constrained by insar we looked for evidence of interseismic strain occurring between the 1992 landers earthquake and the 1999 hector mine earthquake near the lavic lake and bullion faults by using interferometric synthetic aperture radar insar interferograms covering the hector mine epicentral region were studied for possible slip along the bullion and lavic lake faults by both visual inspection and a matched filter technique intended to emphasize slip located at the nucleation point some indications of possible deformation associated with the 5 july 1992 m l 5 4 pisgah event was observed but high decorrelation prevented a conclusive determination we have seen no evidence for precursory slip in the epicentral region up to 30 days before the hector mine event we estimated that the slip equivalent to a m w 4 5 event would have been observable in the months before the hector mine event and this places an upper bound on the long term precursory slip had it occurred we have noted that insar is well suited for detecting precursory slip in general due to the high spatial resolution and the lack of ground instrumentation required but that the detection level depends on the depth and orientation of the slip back

quantification of gravity wave forcing in driving the stratospheric quasi biennial oscillation 1 using long term rayleigh lidar temperature observations during april 1998 april 2005 in the lower stratospheric region momentum flux divergence of the gravity waves of periods 0 5 1 and 2 4 hours are estimated over gadanki 13 5 n 79 2 e india monthly mean zonal winds from ncep ncar reanalysis data over gadanki at two pressure levels 10 and 20 hpa are used to study the characteristics of the quasi biennial oscillation qbo and its month to month acceleration this observed mean flow acceleration is compared with that estimated from the momentum flux divergence of gravity waves which led to a better insight into the role of gravity waves in driving the qbo the present analysis reveals that the contribution of gravity waves towards the westerly phase of qbo varies from 10 60 while that during easterly phase from 10 30 the present study thus quantifies the role of gravity waves in driving the easterly and westerly phases of qbo

using satellite observations to constrain parameterizations of gravity wave effects for global models abstract small scale gravity waves are common features in atmospheric temperature observations in satellite observations these waves have been traditionally difficult to resolve because the footprint or resolution of the measurements precluded their detection or clear identification recent advances in satellite instrument resolution coupled to innovative analysis techniques have led in the last decade to some new global datasets describing the temperature variance associated with these waves such satellite observations have been considered the best hope for quantifying the global properties of gravity waves needed to constrain parameterizations of their effects for global models although global maps of averaged gravity wave temperature variance have now been published from a variety of different instruments on earth orbiting platforms these maps have not provided the needed constraints the present paper first summarizes what has been learned from traditional temporally and spatially averaged analyse

characteristics of gravity waves with short vertical wavelengths observed with radiosonde and gps occultation during dawex darwin area wave experiment 1 we conducted radiosonde soundings during three intensive observation periods iop of the darwin area wave experiment dawex campaign in october to december 2001 and measured humidity temperature and wind velocity up to 30 35 km every 3 hours for 40 times at three sites in each iop we analyzed height profiles of kinetic ek and potential ep energy per unit mass caused by gravity waves with vertical wavelengths less than 3 km the wave energy was clearly enhanced between 15 20 km and 25 30 km and it was considerably depressed at 20 25 km between the two height regions this feature was seen at all the sites during the three iops different types of wave activity seem to contribute to the enhancement of ek and ep below 20 km and at 25 30 km height distribution of the wave energy at 20 30 km seems to correlate with the structure of the mean zonal wind shear we also analyzed a latitude height section of ep in october to december 2001 using gps occultation data with the champ satellite collected around the dawex sites 80 180 e and 30 n to 30 s compared with the latitude distribution of ep with gps the dawex results were slightly smaller and larger at 20 25 km and 25 30 km respectively the longitude variation of ep is also analyzed from the gps data at 10 15 s which generally agreed well with the dawex results at both 20 25 km and 25 30 km

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

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

limb sounders tracking topographic gravity wave activity from the stratosphere to the ionosphere around midlatitude andes several studies have shown that the surroundings of the highest andes mountains at mid latitudes in the southern hemisphere exhibit gravity waves gw generated by diverse sources which may traverse the troposphere and then penetrate the upper layers if conditions are favorable there is a specific latitude band where that mountain range is nearly perfectly aligned with the north south direction which favors the generation of wavefronts parallel to this orientation this fact may allow an optimization of procedures to identify topographic gw in some of the observations we analyze data per season to the east and west of these andes latitudes to find possible significant differences in gw activity between both sectors gw effects generated by topography and convection are expected essentially on the eastern side we use satellite data from two different limb sounding methods the global positioning system gps radio occultation ro technique and the sounding of the atmosphere using broadband emission radiometry saber instrument which are complementary with respect to the height intervals in order to study the effects of gw from the stratosphere to the ionosphere activity becomes quantified by the gw average potential energy in the stratosphere and mesosphere and by the electron density variance content in the ionosphere consistent larger gw activity on the eastern sector is observed from the stratosphere to the ionosphere night values however this fact remains statistically significant at the 90 significance level only during winter when gw generated by topography dominate the eastern sector on the contrary it is usually assumed that orographic gw have nearly zero horizontal phase speed and will therefore probably be filtered at some height in the neutral atmosphere however this scheme relies on the assumption that the wind is uniform and constant our results also suggest that it is advisable to separate night and day cases to study gw in the ionosphere as it is more difficult to find significant statistical differences during daytime this may happen because perturbations induced by gw during daytime are more likely to occur in a disturbed environment that may hinder the identification of the waves

rheological transitions facilitate fault spanning ruptures on seismically active and creeping faults the apparent stochastic nature of earthquakes poses major challenges for earthquake forecasting attempts physical constraints on the seismogenic potential of major fault zones may greatly aid in improving seismic hazard assessments but the mechanics of earthquake nucleation and rupture are obscured by the enormous complexity that natural faults display in this study we investigate the mechanisms behind giant earthquakes by employing a microphysically based seismic cycle simulator this microphysical approach is directly based on the mechanics of friction as inferred from laboratory tests and can explain a broad spectrum of fault slip behaviour we show that exceptionally large fault spanning earthquakes are governed by different micro scale mechanisms than regular small earthquakes more importantly the stress driven transition from ductile creep to granular flow facilitates the nucleation of giant earthquakes on faults that are otherwise seismically quiet this microphysically based approach offers new opportunities for investigating long term seismic cycle behaviour of natural faults

seismicity characteristics of a potentially active quaternary volcano the tatun volcano group northern taiwan the tatun volcano group tvg is located at the northern tip of taiwan near the capital taipei and close to two nuclear power plants because of lack of any activity in historical times it has been classified as an extinct volcano even though more recent studies suggestthattvgmighthavebeenactiveduringthelast20ka inmay2003aseismicmonitoringprojectatthetvgareawasinitiated by deploying eight three component seismic stations some of them equipped with both short period and broadband sensors during the 18 months observation period local seismicity mainly consisted of high frequency earthquakes either occurring as isolated events or as a continuous sequence in the form of spasmodic bursts mixed and low frequency events were also present during the same period eventhoughtheyoccurredonlyrarely arrivaltimesfromeventswithclearp s wavephaseswereinvertedinordertoobtaina minimum 1dvelocity modelwithstation corrections probabilistic nonlinear earthquakelocationswere calculated for allthese events using the newly derived velocity model most high frequency seismicity appeared to be concentrated near the areas of hydrothermal activity forming tight clusters at depths shallower than 4 km relative locations calculated using the double difference method and utilising catalogue and cross correlation differential traveltimes showed insignificant differences when compared to the nonlinear probabilistic locations in general seismicity in the tvg area seems to be primarily driven by circulation of hydrothermal fluids as indicated by the occurrence of spasmodic bursts mixed low frequency events and a b value 1 17 0 1 higher than in any other part of taiwan these observations that are similar to those reported in other dormant quaternary volcanoes indicate that a magma chamber may still exist beneath tvg and that a future eruption or period of unrest should not be considered unlikely

interactions and triggering in a 3 d rate and state asperity model we present a 3 d continuous quasi dynamic rate and state model of multiple seismic asperities forced by surrounding aseismic creep and motivated by observations of coplanar multiplets our model allows to study the physics of interactions among a set of asperities first we show that the amount of interactions and clustering characterized by the omori law and interevent time distribution depends on how far the system is from a critical density of asperities which is related to the friction properties of the barriers separating the sources this threshold controls the ability of a population of asperities to destabilize the creeping barriers between them and therefore determines whether dynamic sequences including several asperities in the same event might occur in agreement with what is expected from observed magnitude frequency distributions therefore the concept of critical density of asperity provides a mechanical interpretation of statistical properties of seismicity as an illustration we used our numerical results in the specific case of parkfield in the period preceding the mw 6 2004 earthquake in order to infer the steady state friction parameter a b characterizing the creep of this part of the san andreas fault we estimate a value of a b that locally exceeds 0 001 which is in the upper range of what has already been proposed for the postseimic period of the mw 6 2004 parkfield earthquake

large nucleation before large earthquakes is sometimes skipped due to cascade up implications from a rate and state simulation of faults with hierarchical asperities 1 does a large earthquake have a large quasi static preparation a hierarchical asperity model in which a large tough patch patch l contains smaller fragile patches patch s enables a large earthquake to start with only small preparation because of cascade up rupture growth we realized such a model in a rate and state framework by heterogeneous distributions of the state evolution distance and its consequences are investigated by earthquake sequence simulations focus is put on elementary processes the interaction between two scales one patch l containing one patch s is simulated with their size ratio as a parameter if patch s is larger than the nucleation size of patch l the system falls into a limit cycle consisting of only one earthquake that starts with patch s nucleation and grows dynamically to rupture entire patch l if patch s is considerably smaller than the nucleation size of patch l small earthquakes never dynamically cascade up and the large earthquakes are initiated by large quasi static nucleation in between large earthquakes start in various ways by large nucleation dynamic cascade up or delayed cascade up in the final stage of quasi static nucleation the preseismic moment release rate increases roughly inversely proportional to the time to failure tf with its amplitude depending on the nucleation size for a patch s rupture to cascade up strength in the adjacent region must have been reduced manifested by a higher creep velocity before the patch s nucleation starts following 1 tf acceleration large nucleation sometimes has a precursory small earthquake characterized by larger afterslip than nonprecursory ones

physical characteristics of subduction interface type seismogenic zones revisited 1 based on global earthquake catalogs the hypocenters nodal planes and seismic moments of worldwide subduction plate interface earthquakes were extracted for the period between 1900 and 2007 assuming that the seismogenic zone coincides with the distribution of 5 5 m 7 earthquakes the subduction interface seismogenic zones were mapped for 80 of the trench systems and characterized with geometrical and mechanical parameters using this database correlations were isolated between significant parameters to identify cause effect relationships empirical laws obtained in previous studies were revisited in light of this more complete accurate and uniform description of the subduction interface seismogenic zone the seismogenic zone was usually found to end in a fore arc mantle rather than at a moho depth the subduction velocity was the first order controlling parameter for variations in the physical characteristics of plate interfaces determining both the geometry and mechanical behavior as such the fast subduction zones and cold slabs were associated with large and steep plate interfaces which in turn had large seismic rates the subduction velocity could not account for the potential earthquake magnitude diversity that was observed along the trenches events with mw 8 5 preferentially occurred in the vicinity of slab edges where the upper plate was continental and the back arc strain was neutral this observation was interpreted in terms of compressive normal stresses along the plate interface large lateral ruptures should be promoted in neutral subduction zones due to moderate compressive stresses along the plate interface that allow the rupture to propagate laterally