inertia gravity waves observed in the lower stratosphere over macquarie island abstract this study examines the properties of inertia gravity waves observed in the lower stratosphere over macquarie island how these properties vary with season and the likely source of the waves the waves are observed in high resolution upper air ozonesonde soundings of wind and temperature released from macquarie island during the 1994 ashoe maesa program the properties of the inertia gravity waves observed in the soundings are quantified using hodograph and rotary spectral analyses the analyzed waves have horizontal wavelengths between 100 and 1000 km vertical wavelengths between about 1 and 7 km intrinsic frequencies between f and 2f and horizontal trace speeds between 50 and 30 m s 1 there appears to be a seasonal cycle in the inertia gravity wave activity in the lower stratosphere the minimum being in the austral winter when the background zonal flow is strong and westerly and its vertical shear is positive in contrast the variance of the horizontal perturbation winds does not show a

gravity wave generation around the polar vortex in the stratosphere revealed by 3 hourly radiosonde observations at syowa station intensive radiosonde observations were performed at syowa station 69 0 s 39 6 e over about 10 days in each of march june october and december 2002 to examine inertia gravity wave characteristics in the antarctic lower stratosphere based on the 3 hourly observation data two dimensional i e vertical wavenumber versus frequency spectra of wind fluctuations were examined utilizing a double fourier transform method clear signals of gravity waves whose phases propagate upward suggesting downward energy propagation are detected in june and october when the polar night jet pnj was present on the other hand downward phase propagation i e upward energy propagation components are dominant in all months there is a spectral peak around the inertial frequency in a wide range of vertical wavenumbers in december when the background wind was weak whereas large spectral densities are distributed over lower frequency regions in june and october these spectral characteristics are consistent with the results obtained using a gravity wave resolving global circulation model gcm by sato et al dynamical characteristics are examined separately for upward and downward propagating gravity waves in june using a hodograph analysis method as a result it is found that upward and downward propagating wave packets observed simultaneously in the same height regions have similar horizontal wavelengths and phase velocities this fact suggests that these gravity waves are generated from the same source with a similar mechanism when the wave packets were observed both the local rossby number and the residual in the nonlinear balance equation estimated using ncep ncar reanalysis data are large around the pnj situated slightly to the lower latitudes of syowa station therefore it is likely that the observed inertia gravity waves are generated by a spontaneous adjustment around the geostrophically unbalanced pnj and propagate toward syowa station the possibility of spontaneous gravity wave generation around the pnj is confirmed by comparison with the gcm simulation by sato et al

inertia gravity waves revealed in radiosonde data at jang bogo station antarctica 74 37 s 164 13 e 2 potential sources and their relation to inertia gravity waves

a statistical study of inertia gravity waves in the troposphere based on the measurements of wuhan atmosphere radio exploration ware radar wuhan atmosphere radio exploration ware radar is the first mesosphere stratosphere troposphere radar to have become operative in the mainland of china and is dedicated to real time atmospheric observations based on the ware radar data collected for the period from september 2011 to february 2013 2666 downward and 1735 upward inertia gravity waves igws are identified from three dimensional 3 d wind fields observed in the troposphere and subsequently analyzed in a statistical manner wave characteristics including intrinsic frequencies vertical wavelengths horizontal wavelengths vertical wave number spectra energy density spectra and wave sources are investigated using a combination of the lomb scargle spectral analysis the quasi monochromatic gravity waves model and the hodograph method our results demonstrate that the characteristic parameters of upward and downward tropospheric igws are not significantly different these results indicate that the tropospheric igws parameters are not directly correlated with propagation directions combining with the information of statistical 3 d wind field and some climatic characteristics of hubei province atmospheric moist convection will contribute most in summer whereas jet front systems will contribute most in winter one may expect seasonal variations to be tied to the varying importance of these sources

a mesoscale gravity wave event observed during ccope iii wave environment and probable source mechanisms abstract synoptic and special mesoscale observations taken during the cooperative convective precipitation experiment ccope are used to describe the multiscale environment of a gravity wave event understand the wave environment interactions that led to the development of severe thunderstorms and asses possible wave generation mechanisms the storms formed sequentially as a packet of gravity waves propagated across a stationary thunderstorm outflow boundary convection developed most rapidly in that part of the mesonetwork in which existed the combination of relatively high parcel buoyant energy weak restraining inversion strong storm downdraft potential and substantial vertical wind shear associated with a mesoscale jet streak synoptic scale analysis reveals that the waves were excited north of a stationary front and within the right exit region of the jet streak as it approached a stationary ridge in the 300 mb height field strong indications of unbalanced flow were diagnosed within the gravit

model simulation of the cretaceous ocean circulation three dimensional numerical ocean circulation model experiments that were designed to evaluate the circulation characteristics for the mid cretaceous 100 million years ago show that the primary direction of flow through the tethys ocean was eastward in contrast a westward flowing circumglobal tethys current has been a consistent feature of earlier reconstructions of cretaceous ocean circulation the model studies demonstrate that i ocean circulation is sufficiently sensitive to the role of continental positions sea level and climate to limit the application of modern analogs to past circulations and ii reconstructions based on limited biogeographic data may not provide unique surface circulation patterns

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

case studies of nonorographic gravity waves over the southern ocean emphasize the role of moisture two case studies of nonorographic gravity waves are carried out for wave events that occurred over the southern ocean in november 2005 mesoscale simulations were carried out with the weather and research forecast model the simulated waves were compared to observations from superpressure balloons of the vorcore campaign and from the high resolution dynamic limb sounder satellite satisfactory agreement is found giving confidence in the estimations of wave parameters and amplitudes for the amplitudes both the model and observations provide a lower bound for different reasons waves are found in the lower stratosphere with horizontal wavelengths of the order of 150 200 km in the horizontal 5 8 km in the vertical corresponding to intrinsic frequencies between 5 and 10 f where f is the coriolis parameter although the tropospheric flow is very different between the two cases there are features which are common and appear significant for the gravity waves these include intense localized updrafts associated with convection in the troposphere and a displaced polar vortex inducing strong winds in the stratosphere above the frontal region relative to theoretical expectations the simulations emphasize the role of moisture intrinsic frequencies are significantly higher than those expected for waves produced by dry spontaneous generation from jets to quantify the contribution of moisture dry simulations were carried out yielding momentum fluxes over oceanic regions that were 2 5 times weaker identification of the generation mechanisms in these complex flows calls for further study and these should include moisture and a realistic stratospheric jet

meteorological tsunami of 19 march 2017 in the persian gulf observations and analyses on 19 march 2017 destructive tsunami like waves impacted the northeast shore of the persian gulf pg the maximum surveyed runup of about 3 m was observed at dayyer in southern iran where damaging waves inundated the land for a distance of 1 km and resulted in the deaths of five people because the pg has always been considered safe from extreme oceanic waves the event was totally unexpected in this study we examined sea level data from 12 stations across the pg and a variety of meteorological information including satellite imagery high altitude isohypse maps and high resolution air pressure records from 47 instruments along the pg our results show that the event was very local with recorded maximum trough to crest wave heights of 197 cm at dayyer and 234 cm at asaluyeh near field cities in iran located 80 km apart the dominant wave periods were in the range of 15 20 min at all distant tide gauges the observed wave heights were 35 cm no earthquakes or landslides were evident at the time of the event on the other hand atmospheric processes during 18 22 march were very active and 10 distinctive tsunamigenic air pressure disturbances were observed propagating over the pg suggesting that the event of 19 march 2017 was a meteorological tsunami atmospheric conditions over the pg were highly favourable for the generation of meteotsunamis and very similar to those that caused a chain of strong meteotsunamis in the mediterranean and black sea regions during 23 27 june 2014 based on the 500 hpa wind we evaluated that the disturbances had propagation speeds of 21 38 m s with the disturbance at dayyer having a speed of 26 m s toward 77 true the froude number fr estimated as the ratio of the air disturbance speed to the long wave speed on 19 march 2017 in the dayyer asaluyeh region was close to resonance fr 0 9 to 1 1 which is highly favourable for meteotsunami generation our findings indicate that the dayyer asaluyeh area is a hot spot that is highly vulnerable to extreme weather induced tsunami like waves

numerical simulations of a gravity wave event over ccope part iii the role of a mountain plains solenoid in the generation of the second wave episode abstract mesoscale model simulations have been performed of the second episode of gravity waves observed in great detail in previous studies on 11 12 july 1981 during the cooperative convective precipitation experiment the dominant wave simulated by the model was mechanically forced by the strong updraft associated with a mountain plains solenoid mps as this updraft impinged upon a stratified shear layer above the deep well mixed boundary layer that developed due to strong sensible heating over the absaroka mountains the gravity wave was created this wave rapidly weakened as it propagated eastward however explosive convection developed directly over the remnant gravity wave as an eastward propagating density current produced by a rainband generated within the mps leeside convergence zone merged with a westward propagating density current in eastern montana the greatly strengthened cool pool resulting from this new convection then generated a bore wave that appeared to be continuous with the move

mesoscale gravity waves in the mei yu front system abstracthigh resolution cloud permitting simulations with the weather research and forecasting wrf model are performed to study the generation structure and characteristics of mesoscale gravity waves in an idealized mei yu front system two classes of waves are generated successively during the control simulation the first class of waves which is typical of vertically propagating waves excited by the front itself appears as the front develops before the generation of the prefrontal moist convection and has a coherent fanlike pattern from the troposphere to the lower stratosphere the second class of waves which is much stronger than the fanlike waves appears accompanied by the generation of the moist convection it is nearly vertically trapped in the troposphere while it propagates vertically upstream and downstream in the lower stratosphere the source function analysis is introduced to demonstrate that the mechanical oscillator mechanism plays a dominant role in the generation of convective gr

numerical simulations of a gravity wave event over ccope part ii waves generated by an orographic density current a mesoscale numerical model and detailed observations are used to investigate the generation and maintenance of a mesoscale gravity wave event observed in eastern montana on 11 july 1981 during the cooperative convective precipitation experiment ccope it is shown that the interaction between an orographic density current and a mountain barrier leads to the generation of the gravity waves the simulation results suggest the following four stage conceptual model during stage i shortly after sunset the remnant up branch of a thermally driven upslope flow east of the rockies was driven back toward the mountain by the pressure gradient force associated with a cool pool over north dakota the nocturnal stable layer over eastern montana was strengthened during passage of this density current during the 1 2 h transition period of stage ii the advancing density current became blocked as it encountered the higher terrain an isentropic ridge developed above the original warm lee trough due to strong adiabatic cooling caused by the sustained upward motion in the presence of orographic blocking during stage iii an even stronger upward motion center formed to the east of the density current head updraft in response to an eastward horizontal pressure gradient force produced by the isentropic ridge in stage iv as the density current head collapsed and downward motion developed to the west of the original updraft in quadrature phase with the isentropic perturbation a gravity wave was generated this wave propagated eastward with the mean wind opposite to the motion of the earlier density current and was maintained by the strong wave duct established earlier by the density current thus the mountain plains circulation may at times generate mesoscale gravity waves and deep convection hours after diurnal heating has ended

an analysis of frontogenesis in numerical simulations of baroclinic waves abstract using a primitive equation pe model we revisit two canonical flows that were previously studied using a semigeostrophic equation sg model in a previous paper the authors showed that the pe and the sg models can have significantly different versions of the large scale dynamics here they report on the implications of this difference for frontogenesis the program for the study of frontogenesis developed by b j hoskins and collaborators is followed to show how in the pe version of the canonical cases the surface warm front develops before the cold front and why the upper level front is a long nearly continuous feature going from ridge to trough the frontogenesis experienced by an air parcel is computed following the parcel to illustrate better the mechanisms involved as the present calculations are carried out longer than most previous ones the relation of the upper frontogenesis to the formation of the upper level cutoff cyclone is also examined trajectory and three dimensional g

a comparative study of large amplitude gravity wave events abstract two large amplitude gravity waves were observed over the midwestern united states on 5 and 14 january 1989 during the university of illinois winter precipitation program on both days an extensive amount of data was recorded including data from two radars and a radiosonde facility the waves originated near missouri registered pressure fluctuations as large as 10 mb and produced distinct precipitation bands along their updraft regions the waves were long lived and maintained their identity over 1000 km a distance several times their wave lengths the synoptic features at the surface were dissimilar a deep cyclone was present on 5 january while a leeside trough was present on 14 january however the middle and upper tropospheric flow patterns were similar in both cases the axis of a trough was immediately upstream of the gravity wave genesis area and a jet streak had just propagated through the base of the trough toward a downstream ridge soundings taken near the gravity waves were re

a case study of cyclogenesis using a model hierarchy abstract it is universally agreed that cyclogenesis in midlatitudes occurs through baroclinic conversion of the potential energy available from an initial state the mechanical process by which that conversion takes place is a perennial subject of discussion at least as far back as the 1950s it was recognized that in any practical forecast problem the initial condition is influential observational research continues to confirm the prevalence of tropopause level perturbations preceding surface cyclogenesis the observations also suggest that the growing disturbances have time varying vertical structures relating these observations to the classical linear theory of baroclinic instability is not immediately obvious since in the latter the precise form of the initial condition is not important and the theory predicts cyclogenesis with a fixed in time vertical structure these differences between theory and observations are but a few of the many that have been recognized and treated in modified theorie

generation of mesoscale gravity waves in upper tropospheric jet front systems abstract multiply nested mesoscale numerical simulations with horizontal resolution up to 3 3 km are performed to study the generation of mesoscale gravity waves during the life cycle of idealized baroclinic jet front systems long lived vertically propagating mesoscale gravity waves with horizontal wavelengths 100 200 km are simulated originating from the exit region of the upper tropospheric jet streak in a manner consistent with past observational studies the residual of the nonlinear balance equation is found to be a useful index in diagnosing flow imbalance and predicting wave generation the imbalance diagnosis and model simulations suggest that balance adjustment as a generalization of geostrophic adjustment is likely responsible for generating these mesoscale gravity waves it is hypothesized that through balance adjustment the continuous generation of flow imbalance from the developing baroclinic wave will lead to the continuous radiation of gravity waves

a study of cyclone mesoscale structure with emphasis on a large amplitude inertia gravity wave abstract an analysis is presented of prominent mesoscale structure in a moderately intense cyclone with emphasis on a long lived large amplitude inertia gravity wave igw that moved through the northeastern united states on 4 january 1994 available national weather service wsr 88d doppler radar and wind profiler observations are employed to illustrate the rich time dependent three dimensional structure of the igw as the igw amplified peak crest to trough pressure falls exceeded 13 hpa 30 min 1 it also accelerated away from the cyclone reaching a peak forward speed of 35 40 m s 1 across eastern new england the igw was one of three prominent mesoscale features associated with the cyclone the others being a weak offshore precursor warm frontal wave and an onshore band of heavy snow snow bomb in which peak hourly snowfalls of 10 15 cm were observed none of these three prominent mesoscale features were well forecast by existing operational prediction models particularly with regard to preci

sensitivity of mesoscale gravity waves to the baroclinicity of jet front systems abstract this study investigates the sensitivity of mesoscale gravity waves to the baroclinicity of the background jet front systems by simulating different life cycles of baroclinic waves with a high resolution mesoscale model four simulations are made starting from two dimensional baroclinic jets having different static stability and wind shear in order to obtain baroclinic waves with significantly different growth rates in all experiments vertically propagating mesoscale gravity waves are simulated in the exit region of upper tropospheric jet streaks a two dimensional spectral analysis demonstrates that these gravity waves have multiple components with different wave characteristics the short scale wave components that are preserved by a high pass filter with a cutoff wavelength of 200 km have horizontal wavelengths of 85 161 km and intrinsic frequencies of 3 11 times the coriolis parameter the medium scale waves that are preserved by a bandpass filter with 200 and 600 km cutoff wavelengths ha

orographic wave drag over the southern ocean a linear theory perspective abstractrecent studies suggest that stratospheric wind biases in global and climate models in the southern hemisphere may result from insufficient orographic wave drag particularly over the southern ocean in the latitude belt centered near 60 s in this study contributions to the stratospheric wave drag along 60 s from three neighboring orographic wave sources are evaluated using a multiple layer linear wave model with large scale wind and stratification profiles derived from the interim ecmwf re analysis era interim between the years 1991 and 2010 the orographic wave sources include the patagonian peaks in the southern andes the antarctic peninsula and the island of south georgia the climatological and dynamical aspects of the wave drag and its dependence on tropospheric winds are investigated the results suggest that these orographic wave sources may have significant contributions to the stratospheric drag over the southern ocean through meridional spreading of the wave momentum flux aloft assoc

wavelet analysis and the governing dynamics of a large amplitude mesoscale gravity wave event along the east coast of the united states detailed diagnostic analyses are performed upon a mesoscale numerical simulation of a well observed gravity wave event that occurred on 4 january 1994 along the east coast of the united states the value of using wavelet analysis to investigate the evolving gravity wave structure and of using potential vorticity pv inversion to study the nature of the flow imbalance in the wave generation region is demonstrated the cross stream lagrangian rossby number the residual in the nonlinear balance equation and the unbalanced geopotential height field obtained from pv inversion are each evaluated for their usefulness in diagnosing the flow imbalance all of these fields showed clear evidence of strong imbalance associated with a middle to upper tropospheric jet streak and tropopause fold upstream of the large amplitude gravity wave several hours before the wave became apparent at the surface analysis indicates that a train of gravity waves was continuously generated by geostrophic adjustment in the exit region of the unbalanced upper level jet streak as it approached the inflection axis in the height field immediately downstream of the maximum imbalance associated with the tropopause fold a split front in the middle troposphere characterized by the advance of the dry conveyor belt above the warm front was overtaken by one of these propagating waves during this merger process a resonant interaction resulted which promoted the rapid amplification and scale contraction of both the incipient wave nonlinear wave development and the split front frontogenesis the gravity wave and front aloft became inseparable following this merger the situation became even more complex within a few hours as the vertical motion enhanced by this front wave interaction acted upon a saturated potentially unstable layer to produce elevated moist convection an analysis of the temporal changes in the vertical profile of wave energy flux suggests that moist convective downdraughts efficiently transported the wave energy from the midlevels downward beneath the warm front surface where the wave became ducted however pure ducting was not sufficient for maintaining and amplifying the waves rather wave cisk conditional instability of the second kind was crucial this complex sequence of nonlinear interactions produced a long lived large amplitude gravity wave that created hazardous winter weather and disrupted society over a broad and highly populated area although gravity waves with similar appearance to this large amplitude wave of depression occasionally have been seen in other strong cyclogenesis cases involving a jet streak ahead of the upper level trough axis it is unknown whether other such events share this same sequence of interactions

comparison of a large scale inertia gravity wave as seen in the ecmwf analyses and from radiosondes 1 the location characteristics and evolution of a large scale inertia gravity wave that occurred in the lower stratosphere over the north of the british isles on february 6 1997 are studied numerous high resolution radiosondes were available at that time and in that region as part of the fastex database they reveal an intense large scale inertia gravity wave igw propagating upwards above the tropopause maps of the divergence of the horizontal wind on isentropic surfaces were obtained from the ecmwf analyses and showed a clear pattern of alternating bands of convergence and divergence at the lower stratospheric heights in the same geographical region and starting at the same time the comparison of the characteristics of this igw in the analyses and in the observations suggests that the ecmwf analyses can be used for qualitative indications regarding the locations most favorable to large scale igw generation and the corresponding orientation of the waves

tracking gravity waves in baroclinic jet front systems abstract using a two dimensional fourier decomposition and a four dimensional ray tracing technique the propagating characteristics and source mechanisms of mesoscale gravity waves simulated in idealized baroclinic jet front systems are investigated the fourier decomposition successfully separates the simulated gravity waves from a complex background flow in the troposphere four groups of gravity waves in the lower stratosphere are identified from the spectral decomposition one is a northward propagating short scale wave packet with horizontal wavelength of 150 km and another is a northeastward propagating medium scale wave packet with horizontal wavelength of 350 km both of these are most pronounced in the exit region of the upper tropospheric jet a third group exists in the deep trough region above and nearly perpendicular to the jet and a fourth group far to the south of the jet right above the surface cold front both of which are short scale waves and have a horizontal wavelength of 100

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