a model study of gravity waves over hurricane humberto 2001 abstract atmospheric gravity waves are known to influence global circulations understanding these waves and their sources help to develop parameterizations that include their effects in climate and weather forecasting models deep convection is believed to be a major source for these waves and hurricanes may be particularly intense sources simulations of hurricane humberto 2001 are studied using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 humberto is simulated at both tropical storm and hurricane stages fourier transform and wavelet analysis are employed to investigate wave characteristics and their behavior in the lower stratosphere the fourier analysis gives a regional view of storm affects whereas wavelet analysis gives a local picture of isolated events analysis of the movement of convective sources and local winds gives further insight into the mechanisms that can cause gravity waves convectively generated grav

collective effects of organized convection and their approximation in general circulation models abstract the collective effects of organized convection the environment were estimated using a two dimensional two way nested cloud resolving numerical model with a large outer domain 4500 km as initial conditions the authors used an idealized environment of the onset stage of the december 1992 westerly wind burst that occurred during the tropical oceans global atmosphere coupled ocean atmosphere response experiment two key aspects relating to convective parameterization were examined first the transports sources and sinks of heat moisture and momentum were derived using the model produced dataset in particular the total momentum flux compares well with moncrieff s dynamical theory second the bulk energetics of the cloud system were examined using the model produced dataset the authors found that the shear generation of kinetic energy is comparable to the buoyancy generation and dominates the sum of the buoyancy and water loading generation this means that in addition to the thermodynam

a numerical study of three dimensional gravity waves triggered by deep tropical convection and their role in the dynamics of the qbo abstract a 3d mesoscale model is used to study the structure of convectively triggered gravity waves in the tropics and their role in the dynamics of the middle atmosphere simulations with three stratospheric background zonal wind cases are examined in the first case the background wind profile is constant the other two are representative of the easterly and westerly phases of the quasi biennial oscillation qbo spectral analysis is used to link the structure of the triggered gravity waves to the dominant vertical wavelength of the latent heating within the convection in the qbo wind shear cases upward propagating gravity waves are damped as they approach their critical layer the signature of critical layer absorption is clearly visible in the profiles of vertical momentum flux divergence in the simulations with open boundary conditions the response to vertical momentum flux divergence takes the form of large dynamic pressure differences between the east and west boundaries together with acceler

the statistical characteristics of convective cells in a monsoon regime darwin northern australia abstract a season of operational cell and track data from darwin australia has been analyzed to explore the statistical characteristics of the convective cell heights the statistics for the monsoon and break regimes are significantly different with the break season cells being higher for a given reflectivity threshold the monsoon cells produce more rain but there are fewer intense cells and there is a much larger contribution from stratiform rain the monsoon cells are also slightly larger but shorter lived than the breaks the shorter lifetime may reflect a more rapid transition to a longer lived stratiform character the monsoon regime is shown to be associated with large scale ascent and higher humidity that may lead to more frequent but weaker cells within regimes the subset of intense cells generally reach near the tropopause or overshoot however there is little evidence in the data for a multimodal distribution of cell heights except perhaps for the intense monsoon cases instead the pi

sand transport on an estuarine submarine dune field abstract by means of surveys carried out with a phase measuring bathymetric system and current profiles obtained through an adcp of the internal area of the bahia blanca estuary a field of large dunes was analysed there are two different and well defined zones characterized by particular dune morphology and differing hydrodynamics the reduction in the channel cross section by a geological control leads to the increase in tidal current velocity which together with the available sediment leads to the formation of very large dunes h 4 m and l 100 m with the typical morphology of a limited amount of sediment overlying a rigid substrate the migration rate of these dunes between 65 and 130 m year 1 decreases as the bedform height increases differing sediment transport rates across the channel result in a non uniform migration rate which is responsible for the formation of dunes with linear crests oblique to the tidal current direction this fact indicates that determination of the sediment transport direction by using only large bedform orientation may be subject to a significant error

25 day period large scale oscillations in the argentine basin revealed by the topex poseidon altimeter the measurement of the global sea surface height made by the topex poseidon satellite has provided the first synoptic view of large scale oceanic variability at intraseasonal scales from weeks to months areas of significant intraseasonal variability were found primarily in the tropics and the high latitude oceans the southern ocean in particular the focus of the paper is the finding of large scale oscillations at a period of 25 days in the argentine basin of the south atlantic ocean these oscillations exhibit a dipole pattern of counterclockwise rotational propagation centered at 458s 3178e over the zapiola rise the scale of the dipole is about 1000 km the peak to trough amplitude is on the order of 10 cm the amplitude of these oscillations has large seasonalto interannual variations these oscillations are shown to be associated with a free barotropic mode of the basin as a solution to a linearized barotropic vorticity equation closed f h contours provide a mechanism for the confinement of the waves to the topographic feature of the zapiola rise results from a numerical model simulation reproduced the patterns of the observed oscillations the resultant mass transport variability is on the order of 50 sv sv 106 m3 s21 deep current meters in the argentine basin reveal signals consistent with the altimetry observations

bottom currents derived from a shipborne adcp on woce cruise a11 in the south atlantic abstract this paper is divided into two parts the first describing an enhancement of the shipborne adcp system and the second describing information about bottom currents that have been obtained therefrom on woce cruise a11 in the south atlantic punta arenas to cape town rrs discovery has been fitted with a gps3df receiver and an array of antennas about its bridge which determine the instantaneous attitude of the ship the heading record from this instrument has been compared with the ship s gyrocompass throughout the 40 day cruise differences have been calculated and examined according to heading speed and movements underway differences are found insensitive to heading except in a southerly sector but on station differences exhibit a sinusoidal dependence on heading with range 3 steaming from a station led to transient behavior with recognizable effects for 1 hour the results are generally consistent with earlier reports and are attributed to gyro error an improved heading measurement has a

a high resolution satellite only grace based mean dynamic topography of the south atlantic ocean 1 a new filtering method based on singular spectrum analysis has been devised to extract high resolution 0 25 0 25 grid satellite only mean dynamic ocean topography mdt constructed by differencing of the ggm02 grace gravity model from the gsfcmss00 mean sea surface this data adaptive interpolation type filter is adequate for the finite domain mdt processing since it minimizes smoothing and does not lose boundary points it is applied to the computation of two new mdts and mdt derived mean geostrophic circulation maps of the south atlantic region from 15 n to 50 s advantages of these new maps are clarified when contrasted with the rio 2005 chambers zlotnicki 2004 and adcp cruise transect data

model study of waves generated by convection with direct validation via satellite abstract atmospheric gravity waves have a major effect on atmospheric circulation structure and stability on a global scale gravity waves can be generated by convection but in many cases it is difficult to link convection directly to a specific wave event in this research the authors examine an event on 12 january 2003 when convective waves were clearly generated by a period of extremely intense rainfall in the region of darwin australia during the early morning the waves were observed by the atmospheric infrared sounder airs instrument on board the aqua satellite and a dry version of a nonlinear three dimensional mesoscale cloud resolving model is used to generate a comparable wave field the model is forced by a spatially and temporally varying heating field obtained from a scanning radar located north of darwin at gunn point with typical cloud resolving model studies it is generally not possible to compare the model results feature for feature with observations since although the model pr

msx satellite observations of thunderstorm generated gravity waves in mid wave infrared images of the upper stratosphere data from the midcourse space experiment msx has provided the first observations of thunderstorm generated gravity waves imaged from space gravity wave theory predicts that isolated sufficiently convective thunderstorms can launch waves and create a unique intensity pattern of concentric circles on a radiating surface of constant altitude above such a storm among the msx constant nadir angle mid wave infrared mwir observations two instances of such patterns have been identified it was confirmed from meteorological satellite images that highly convective isolated thunderstorms occurred at the locations and times expected

interaction of mesoscale variability with large scale waves in the argentine basin abstract the argentine basin of the south atlantic ocean is a region of complicated ocean dynamics involving a wide range of spatial and temporal scales previous studies reported the existence of a basin mode of topographic barotropic rossby waves with a period close to 25 days in the region using observations of sea level anomalies from satellite altimeter measurements the present study provides evidence of interaction between the large scale 25 day waves and the energetic mesoscale variability of the region the amplitude of the 25 day waves is highly intermittent with dominant periods in the range of 110 150 days within this period band the wave amplitude is coherent with the energy level of the mesoscale variability when the mesoscale energy level goes down the wave amplitude goes up and vice versa suggesting an exchange of energy between the two scales this coherence is linked to the first three empirical orthogonal functions eofs of the sea level anomalies the spatial patterns of these

the influence of convectively generated thermal forcing on the mesoscale circulation around squall lines abstract the dynamical processes that determine the kinematic and thermodynamic structure of the mesoscale region around 2d squall lines are examined using a series of numerical simulations the features that develop in a realistic reference simulation of a squall line with trailing stratiform precipitation are compared to the features generated by a steady thermal forcing in a dry simulation with no microphysical parameterization the thermal forcing in the dry simulation is a scaled and smoothed time average of the latent heat released and absorbed in and near the leading convective line in the reference simulation the mesoscale circulation in the dry simulation resembles the mesoscale circulation in the reference simulation and around real squall lines it includes an ascending front to rear flow a midlevel rear inflow a mesoscale up and downdraft an upper level rear to front flow ahead of the thermal forcing and an upper level cold anomaly to the rear of the thermal forcing it is also shown t

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

the gravity wave response above deep convection in a squall line simulation abstract high frequency gravity waves generated by convective storms likely play an important role in the general circulation of the middle atmosphere yet little is known about waves from this source this work utilizes a fully compressible nonlinear numerical two dimensional simulation of a midlatitude squall line to study vertically propagating waves generated by deep convection the model includes a deep stratosphere layer with high enough resolution to characterize the wave motions at these altitudes a spectral analysis of the stratospheric waves provides an understanding of the necessary characteristics of the spectrum for future studies of their effects on the middle atmosphere in realistic mean wind scenarios the wave spectrum also displays specific characteristics that point to low physical mechanisms within the storm responsible for their forcing understanding these forcing mechanisms and the properties of the storm and atmosphere that control them are crucial first steps toward developing

on the dynamics of the zapiola anticyclone recent observations obtained in the south atlantic suggest the existence of a strong anticyclonic flow positioned over a major bottom topographic feature known as the zapiola drift here a numerical simulation of the south atlantic is described in which this anticyclone is reproduced and the model is used to diagnose the dynamics maintaining this flow with a mean barotropic transport of 140 sv and bottom velocities of 10 cm s 1 the simulated zapiola anticyclone compares well with in situ observations furthermore the model surface eddy kinetic energy shows a local minimum over the drift in agreement with observations from topex poseidon numerical experiments show that the circulation feature is sensitive to the intensity of the eddy field and to the particular value of the bottom friction both of these tendencies are in agreement with a theoretical explanation of the zapiola anticyclone that has recently appeared elsewhere thus we argue that the anticyclone is maintained by eddy driven potential vorticity fluxes accelerating flow within topographically closed ambient potential vorticity contours as far as we know this is the first south atlantic simulation to reproduce the zapiola anticyclone in a realistic fashion the quantitative success of this experiment is attributed to the use of a topography following sigma coordinate in a spatially well resolved model

implementation of a gravity wave source spectrum parameterization dependent on the properties of convection in the whole atmosphere community climate model waccm 1 this article describes the implementation of a new source spectrum parameterization for convectively generated gravity waves in the whole atmosphere community climate model version 2 waccm2 this parameterization is active in the tropics and is interactive with the underlying convection the gravity wave spectrum at each model grid point and time step is determined based on the convective heating depth tropospheric wind and the convective heating rate this parameterization introduces more realistic spatial and temporal distributions of gravity wave activity and yields gravity wave characteristics related to the underlying wave source we present the estimated gravity wave momentum flux phase speed spectra at 100 hpa as well as the gravity wave drag in the middle and upper atmosphere using the new source spectrum representation we also show the effects of this more physically based parameterization on the structure of the stratospheric and mesospheric semi annual oscillations of the zonal wind compared to a simulation with uniform gravity wave distribution we conclude that the interaction of the gravity wave parameterization with tropospheric characteristics is a positive step toward a more physical representation of the middle and upper atmosphere

small scale wind disturbances observed by the mu radar during the passage of typhoon kelly abstract this paper describes small scale wind disturbances associated with typhoon kelly october 1987 that were observed by the mu radar one of the mst mesosphere stratosphere and troposphere radars continuously for about 60 hours with fine time and height resolution first in order to elucidate the background of small scale disturbances synoptic scale variation in atmospheric stability related to the typhoon structure during the observation is examined when the typhoon passed near the mu radar site the structure was no longer axisymmetric there is deep convection only in the front north northeast side of the typhoon while convection behind it is suppressed by a synoptic scale cold air mass moving eastward to the west of the typhoon a drastic change in atmospheric stability over the radar site as indicated by echo power profiles is likely due to the passage of the sharp transition zone of convection strong small scale wind disturbances were observed around the typhoon passage it is show

on deep current and hydrographic observations from a mudwave region and elsewhere in the argentine basin near bottom current measurements from both sides of a mudwave in an extensive mudwave region of the mid argentine basin are examined for evidence of lee waves such waves appear to exist when the across crest flow exceeds a critical value predicted by flood 1988 deep sea research 35 973 983 of about 9 cm s 1 the observations agree with the predictions of blumsack and weatherly 1989 deep sea research 36 155 172 in three of four cases however if it is assumed that the flow perturbations induced by lee waves are shifted slightly downcurrent from that predicted by the blumsack and weatherly model then there is agreement in all four cases the mudwave region is characterized as having a strong 10 cm s 1 steady eddy kinetic energy mean kinetic energy current the westward flow is consistent with the anticyclonic abyssal gyre centered about the zapiola drift inferred by flood and shor 1987 deep sea research 35 973 983 near bottom flow measurements made further to the west in the region of confluence of the brazil and malvinas current extensions reveal relatively energetic fluctuations and equatorward flowing deep western boundary currents along the continental slope along the continental rise a poleward flow is observed consistent with that inferred by reid 1989 progress in oceanography 23 149 244 too cold bottom layers were found to be common only on the lower continental slope 4000 m depth and at the mid basin mudwave site

the 25 day period large scale oscillations in the argentine basin revisited abstract from sea surface height measurements made by the ocean topography experiment topex poseidon satellite fu et al found and described large scale oscillations at the period of 25 days in the argentine basin of the south atlantic ocean these oscillations were previously hinted at by in situ observations only the extensive space time sampling capability of topex poseidon however was able to give a complete description of the phenomenon as a counterclockwise rotating dipole centered at 45 s 317 e over the zapiola rise fu et al also undertook theoretical and numerical studies to suggest that the phenomenon is a resonantly excited barotropic normal mode of the locally closed f h contour in a simulation study however they also found that the space time smoothing scheme employed would probably lower the amplitude of the estimated phenomenon by 30 40 by reprocessing the data using a different method and showing the amplitude to be almost 2 times as large in this note it is confirmed that t

variations of the argentine gyre observed in the grace time variable gravity and ocean altimetry measurements this work is supported by taiwan ministry of science and technology grants 105 2811 m 001 031 and 106 2116 m 001 013 and by national nature science foundation of china grants 41474019 41504014 and 41704012

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

generation and trapping of gravity waves from convection with comparison to parameterization some parameterizations of gravity wave mean flow forcing in global circulation models gcms add realism by describing wave generation by tropospheric convection because the convection in gcms is itself a parameterized process these convectively generated wave parameterizations necessarily use many simplifying assumptions in this work the authors use a realistic simulation of wave generation by convection described in previous work which was validated by observations from the darwin area wave experiment dawex to test these assumptions and to suggest some possible improvements to the parameterizations in particular the authors find that wave trapping in the troposphere significantly modifies the spectrum of vertically propagating waves entering the stratosphere above convective wave sources and offer a linear method for computing wave transmission and reflection effects on the spectrum suitable for inclusion in the parameterizations the wave fluxes originate from both a time varying heating mechanism and an obstacle effect mechanism acting in the simulation methods for including both mechanisms in the parameterizations are described waves emanating from the obstacle effect remain very sensitive to the depth of penetration of latent heating cells into an overlying shear zone which will continue to make it difficult to accurately parameterize in a gcm where the convective cells are not resolved

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

gregarious tropical convection abstract a beat source with a vertical profile like that of observed tropical mesoscale convective systems mcss is shown to cause through inviscid gravity wave dynamics upward displacement at low levels in a mesoscale region surrounding the heating typical values are 10 30 area contraction at the surface everywhere within 270 km of the heating 6 h after it starts as a result conditions near an existing mcs but beyond the area of mcs outflow become more favorable for the development of additional convection this theory predicts that cloud clusters should be gregarious infrared satellite imagery confirms that almost half of the cold cloudiness observed in a month over the oceanic warm pool region was contributed by just 14 objectively defined multiday supercluters

three forms of variability in argentine basin ocean bottom pressure ocean bottom pressure data are examined from a year long deployment of two bottom pressure recorders separated by 417 km in the argentine basin three forms of variability are found at high frequencies periods shorter than 2 hours the signal appears to be due to gravity wave propagation with the waves preferentially coming from the west at intermediate frequencies periods between 2 hours and 12 days the two records are highly coherent and in phase reflecting large scale coherent fluctuations which are well reproduced in a barotropic ocean model however the dominant mode is at a period of 20 days with a phase lag of about 90 100 degrees between the two records consistent with the a mode of variability previously inferred from satellite altimetry and current meters although the slightly shorter period is consistent with the suggestion that more than one mode contributes to the altimeter observations comparison with altimetry demonstrates that aliasing of higher frequency signals is not a significant source of error and confirms that a previously used altimetry mapping technique reduces the apparent amplitude of the mode the pressure records show a transport change of about 280 sv over one 12 day period and altimetry suggests that regions of higher variability exist the mode is only weakly excited in barotropic models but is strongly excited in a baroclinic model with a realistic eddy field suggesting that it is intrinsically linked to interactions between eddies mean flow and topography

multiple oscillatory modes of the argentine basin part i statistical analysis observations of the sea surface height in the argentine basin indicate that strong variability occurs on a time scale of 2030 days the aim of this study is to determine the physical processes responsible for this variability first results are presented from two statistical techniques applied to a decade of altimetric data a complex empirical orthogonal function ceof analysis identifies the recently discovered dipole mode as the dominant mode of variability a principal oscillation pattern pop analysis confirms the existence of this mode which has a period of 25 days the second ceof displays a propagating pattern in the northern argentine basin plus a rotating dipole in the southwest corner the pop analysis identifies both patterns as individual modes with periods of 30 and 20 days respectively second the barotropic normal modes of the argentine basin are studied using a shallow water model capturing the full bathymetry of the basin coherences between the spatial patterns of these modes and altimeter data suggest that several of the basin modes are involved in the observed variability this analysis implies that the 20 day mode detected by recent bottom pressure measurements is a true barotropic mode however the 25 day variability as found in altimeter data cannot be directly attributed to the excitation of a free rossby basin mode this study indicates that the results of several apparently conflicting observations of the flow variability in the argentine basin can be reconciled by assuming that multiple basin modes are involved