lagrangian exploration of the california undercurrent 1992 95 abstract during the period 1992 95 nineteen isobaric rafos floats placed in the california undercurrent at intermediate depths 150 600 m off monterey and san francisco california reveal a region of varying width of subsurface poleward flow adjacent to the continental margin the float trajectories exhibit three patterns poleward flow in the undercurrent reversing but predominately alongshore flow adjacent to the continental margin and farther offshore anticyclonic motion accompanied by slow westward drift flow continuity of the undercurrent exists between pt reyes and at least cape mendocino with an average speed dependent on the float depth speeds were variable but common features were acceleration occurring to the south of pt arena and deceleration to the north of cape mendocino an important mechanism for floats and water to enter the ocean interior from the undercurrent is through the formation of submesoscale coherent vortices

gravity waves generated by a tropical cyclone during the step tropical field program a case study overflights of a tropical cyclone during the australian winter monsoon field experiment of the stratosphere troposphere exchange project step show the presence of two mesoscale phenomena a vertically propagating gravity wave with a horizontal wavelength of about 110 km and a feature with a horizontal scale comparable to that of the cyclone s entire cloud shield wavelength of 250 km or greater the larger feature is fairly steady though its physical interpretation is ambiguous the 110 km gravity wave is transient having maximum amplitude early in the flight and decreasing in amplitude thereafter its scale is comparable to that of 100 to 150 km diameter cells of low satellite brightness temperatures within the overall cyclone cloud shield these cells have lifetimes of 4 5 to 6 hours aircraft flights through the anvil show that these cells correspond to regions of enhanced convection higher cloud altitude and upwardly displaced potential temperature surfaces a three dimensional transient linear gravity wave simulation shows that the temporal and spatial distribution of meteorological variables associated with the 110 km gravity wave can be simulated by a slowly moving transient forcing at the anvil top having an amplitude of 400 600 m a lifetime of 4 5 6 hours and a size comparable to the cells of low brightness temperature the forcing amplitudes indicate that the zonal drag due to breaking mesoscale transient convective gravity waves is definitely important to the westerly phase of the stratopause semiannual oscillation and possibly important to the easterly phase of the quasi biennial oscillation there is strong evidence that some of the mesoscale gravity waves break below 20 km as well the effect of this wave breaking on the diabatic circulation below 20 km may be comparable to that of above cloud diabatic cooling

california undercurrent variability and eddy transport estimated from rafos float observations 1 rafos float observations collected between 1992 and 2002 were analyzed to identify the seasonal variability of circulation in four geographical boxes which extended along the central and northern california coast and were successively located farther offshore the mean pressure of the floats was 375 dbar poleward flow associated with the california undercurrent dominated the two boxes closest to shore extending from the 400 m isobath to a distance of 190 km offshore for the box closest to shore the monthly mean alongshore velocity was maximum minimum 5 4 cm s 1 7 cm s in may june february while the eddy kinetic energy eke was minimum was 33 cm2 s2 21 cm2 s2 in september december february the mean eke in the coastal region was 28 cm2 s2 increasing to 50 cm2 s2 for the region farthest offshore a distance of about 400 km for that region farthest offshore eke had a broad maximum from june to november and a minimum in april lagrangian correlation and dispersion tensors were estimated for floats that left the coastal region three different dispersive regimes of float motion were identified as ballistic transport normal diffusion and anomalous sub diffusion westward sub diffusion was induced by rossby wave like structures with a periodicity of 100 120 days

kinetics of pressure solution at halite silica interfaces and intergranular clay films pressure solution is widely regarded as a potentially important deformation mechanism along crustal faults and during aliagenesis yet the mechanisms and kinetics of this process remain highly controversial to better understand the fundamental factors controwing the rates of pressure solution at the grain to grain scale we conducted experiments in which convex halite lenses were pressed against fiats of fused silica in brine fluid pressures were maintained at 0 1 mpa temperatures and mean contact normal stresses ranged from 8 3 o to 90 2oc and 0 5 to 13 5 mpa respectively the geometry and growth rate of the contact spot between the two lenses and the rate at which the lenses approached one another convergence were monitored using reflected light interferometry and transmitted light photomicrography convergence occurred when halite and silica lenses were pressed together in brine halite silica experiments no undercutting was observed and dry control experiments indicated negligible dislocation creep convergence rates in experiments at 50 2oc ranged from 0 01 to 0 05 m d depending on mean normal stress and contact spot radius the data are consistent with intergranular pressure solution ips rate limited by diffusion through an intergranular film with a very high diffusion coefficient 10 5 10 7 cm2 s the data further suggest that the diffusion coefficient and or thickness of this film increases with decreasing normal stresses at least for normal stresses less than about 4 mpa as no island channel boundary structures were observed we propose that this film consists of a continuous layer of strongly adsorbed i e structured water that is maintained between the halite and silica lenses during deformation convergence rates in similar experiments conducted at a constant load of 0 11 n but at 8 3 o 50 2 o and 90 2oc were approximately constant at a given normal stress and contact spot size the cause of this temperature insensitivity is unknown but might result from changes in interphase boundary structure or thickness with increasing temperature that are sufficient to offset the expected thermal activation an experiment was also conducted in which a halite lens was pressed against a fused silica fiat coated with an 0 8 m thick film of na montmorillonite in brine this clay film produced an approximately fivefold increase in convergence rates over those observed in a halite silica experiment conducted without clay at the same load and temperature the strong sensitivity of ips rates both to contact spot radius and to the presence of second phases along grain boundaries suggests that fine grained clay rich fault gouges and multiphase granular aggregates should be particularly susceptible to pressure solution creep in the middle to upper crust

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

a study of mesoscale gravity waves over the north atlantic with satellite observations and a mesoscale model satellite microwave data are used to study gravity wave properties and variabilities over the northeastern united states and the north atlantic in the december january periods the gravity waves in this region found in many winters can reach the stratopause with growing amplitude the advanced microwave sounding unit a amsu a observations show that the wave occurrences are correlated well with the intensity and location of the tropospheric baroclinic jet front systems to further investigate the cause s and properties of the north atlantic gravity waves we focus on a series of wave events during 19 21 january 2003 and compare amsu a observations to simulations from a mesoscale model mm5 the simulated gravity waves compare qualitatively well with the satellite observations in terms of wave structures timing and overall morphology excitation mechanisms of these large amplitude waves in the troposphere are complex and subject to further investigations

the california current system off monterey california physical and biological coupling repeated hydrobiological surveys over the period 1988 2002 perpendicular to the central california coast indicate strong coupling between physical circulation and biological production an equatorward flowing jet about 100 200 km from shore marked the inshore edge of the california current cc this cc jet had its highest velocities during late winter and spring the jet divided inshore biologicallyproductive waters from offshore low production waters mean flow in the inshore waters is poleward however this flow is interrupted in late spring and summer bya surfaceenhanced equatorward flowing coastal upwelling jet the upwelling jet coincides with maxima of nutrients chlorophyll a and primaryproduction annual variabilityin the inshore zone is related to 1 vertical py cnocline movements associated with geostrophic adjustments to accelerations of the california current system and 2 coastal upwelling in offshore waters the annual cycle accounted for a small fraction of the variability indicating the dominance of eddies and meanders in this zone j geophys res 92 1987 12 947 the offshore regime was mesotrophic to oligotrophic with a subsurface chlorophyll a maximum above the nutricline considerable subduction mayoccur under the california current jet and be an important process in the export of biogenic material to the deep sea published byelsevier ltd

statistical analysis of the surface circulation in the california current system using satellite tracked drifters abstract a kinematic description of the surface circulation in the southern california current system is presented using the statistics of the 7 11 month long trajectories of 29 satellite tracked mixed layer drifters the drifters were released north of 30 n and traveled southward at an average speed of 3 4 cm s 1 along baja california through an inhomogeneous field of mesoscale eddies of 15 cm s 1 rms variability lagrangian and eulerian statistics of the variations about this mean southward drift are computed the drifter ensemble mean lagrangian decorrelation time scale is 4 5 days and the lagrangian decorrelation space scale is 40 50 km the computation of dispersion of single particles about the mean drift shows that the theory of diffusion by homogeneous random motion taylor s theory describes these dispersive motions well ensemble mean diffusivities of about 4 107 cm2 s 1 are found on a 200 200 km2 spatial average single partial diffusivities are found to be proportional to the kinetic ene

recent developments in gravity wave effects in climate models and the global distribution of gravity wave momentum flux from observations and models recent observational and theoretical studies of the global properties of small scale atmospheric gravity waves have highlighted the global effects of these waves on the circulation from the surface to the middle atmosphere the effects of gravity waves on the large scale circulation have long been treated via parametrizations in both climate and weather forecasting applications in these parametrizations key parameters describe the global distributions of gravity wave momentum flux wavelengths and frequencies until recently global observations could not define the required parameters because the waves are small in scale and intermittent in occurrence recent satellite and other global datasets with improved resolution along with innovative analysis methods are now providing constraints for the parametrizations that can improve the treatment of these waves in climate prediction models research using very high resolution global models has also recently demonstrated the capability to resolve gravity waves and their circulation effects and when tested against observations these models show some very realistic properties here we review recent studies on gravity wave effects in stratosphere resolving climate models recent observations and analysis methods that reveal global patterns in gravity wave momentum fluxes and results of very high resolution model studies and we outline some future research requirements to improve the treatment of these waves in climate simulations copyright 2010 royal meteorological society and crown in the right of canada

a modeling study of orographic convection and mountain waves in the landfalling typhoon nari 2001 in this study the characteristics of mountain induced gravity waves mgws and orographic convection in typhoon nari 2001 and their impacts on the formation of orographic precipitation as nari moved across taiwan s central mountain range cmr are investigated by analyzing the cloud resolving model simulation results in the distant rain band convective cells were triggered frequently on the steep windward slope of cmr and advected downstream simultaneously mgws could exist on the lee side with stable environmental stratification three phases occurred in the mgws convection interaction including the enhancement of mgws and convection breaking and restoring of mgws when the convective cells and mgws were superposed in out of phase the amplitudes of both mgws and convective cells were increased decreased the vertical wavelength of mgws was also increased during the in phase superposition even inducing the further breaking of mgws for the formation of precipitation on the lee side mgws convection interaction contributes on a smaller scale to offset the reduction effect from the larger scale descending moreover convective cells on the windward slope could contribute a large amount of cloud ice and snow particles aloft to seed hydrometeors over the lee side more cloud water was produced by the mgws convection interaction when their amplitudes were increased during the in phase superposition riming and coalescence processes were responsible not only for the windward slope precipitation enhancement but also the secondary precipitation maximum over the lee side therefore the mgws convection interaction could modify the structure of vertical motion and hydrometeors over the lee side and then affect orographic precipitation when nari passed the cmr as nari s eyewall encountered the northern cmr the terrain generated long lasting strong updrafts at the upslope resulting in a doubled rainfall maximum to that in the no terrain sensitivity experiment the downdraft branch of the mgw produced a rain shadow on the lee side copyright 2011 royal meteorological society

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

eddy mean flow decomposition and eddy diffusivity estimates in the tropical pacific ocean 1 methodology 1 eddy diffusivity of the surface velocity field in the tropical pacific ocean was estimated using satellite tracked drifting buoys 1979 through mid 1996 the tropical pacific surface current system is characterized by nonstationarity strong meridional shear and an energetic mesoscale velocity field eddy diffusivity may be defined as the integral of the autocovariance of lagrangian eddy velocities requiring both stationary and homogeneous statistics of the eddy field eddy velocities were obtained by removing a splined mean field to eliminate mean shear from observations binned 1 spatially to group data that have similar dispersion characteristics and 2 temporally to create stationary eddy statistics zonal diffusivity estimates are up to 7 times larger than meridional diffusivity estimates in the high eddy energy regions this anisotropy is associated with the meridional mesoscale wave motion i e by equatorial and tropical instability waves that increases eddy variance but does not lead to a proportional increase in water parcel diffusion because of the coherent character of the trajectory motion at least for initial time lags simple autoregressive models of first and second order are used to describe and classify the resulting eddy statistics an independent confirmation of the diffusivity estimate in the central eastern pacific was obtained by comparing tracer flux divergence computed from a parameterization using diffusivity estimates of our analysis with that from direct eddy reynolds stress flux divergence our results show that diffusivity can be estimated for regions not considered previously either because of sparse data or the complexities of the velocity field

detecting overlapping gravity waves using the s transform 1 we discuss an adaptation to the widely used stockwell transform based method for the detection of gravity waves to allow the detection of multiple overlapping waves this adjusted method is applied to data from the high resolution dynamics limb sounder for the period of may 2006 and is found to change the measured distribution of gravity wave momentum flux on a global scale an overall 68 increase in measured momentum flux is observed for the 20 30km altitude range with significant regional variability the largest absolute increase is over india the southern ocean and the antarctic peninsula regions previously known to exhibit high levels of momentum flux a strong relative increase is observed north of the equator particularly in the tropics analysis of the wavelength distribution of detected gravity waves shows that the majority of this increase is due to the detection of small vertical and horizontal scale waves which were presumably previously masked by higher amplitude events in the same profile

gravity waves generated by deep tropical convection estimates from balloon observations and mesoscale simulations 1 convective gravity waves in the tropics are studied by analyzing in situ measurements from long duration stratospheric balloons launched during the preconcordiasi campaign 2010 and mesoscale simulations an improved temporal resolution of the observations as well as the balloon quasi lagrangian behavior allow an unprecedented investigation of the whole gravity wave spectrum first a case study of gravity waves generated by a developing cyclone tropical storm gelane february 2010 is carried out using observations complemented by numerical simulations with the weather research and forecast model with a resolution down to 1 km distributions of momentum fluxes obtained from both data show reasonable agreement and emphasize waves with short wavelengths 15 km and short periods 20 min still some differences are also found which can likely be related to errors of the modeled background flow second observations from the whole preconcordiasi flights are analyzed with an emphasis on gravity wave momentum fluxes their phase speed distribution has a robust shape with maximum fluxes with near zero ground based phase speeds yet significant momentum fluxes are also found for larger values yielding a mean phase speed of about 27 ms 1 the momentum fluxes are concentrated in short episodes with intense values and their intermittency is quantified using probability distribution functions and the gini coefficient 0 5 0 6 the relative importance of convective and topographic sources are investigated suggesting comparable intensities but a greater occurrence frequency of convective events waves emitted by tropical storm gelane do not stand out relative to other convective events

lagrangian eddy scales in the northern atlantic ocean eddy time and length scales are calculated from surface drifter and subsurface float observations in the northern atlantic ocean outside the energetic gulf stream subsurface timescales are relatively constant at depths from 700 m to 2000 m length scale and the characteristic eddy speed decrease with increasing depth below 700 m but length scale stays relatively constant in the upper several hundred meters of the gulf stream it is suggested that this behavior is due to the lagrangian sampling of the mesoscale field in limits set by the eulerian eddy scales and the eddy kinetic energy in high energy regions of the surface and near surface north atlantic the eddy field is in the frozen field lagrangian sampling regime for which the lagrangian and eulerian length scales are proportional however throughout much of the deep ocean interior the eddy field may be in the fixed float regime for which the lagrangian and eulerian timescales are nearly equal this does not necessarily imply that the deep interior is nearly linear as fixed float sampling is possible in a flow field of o 1 nonlinearity

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

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

subtidal currents over the central california slope evidence for offshore veering of the undercurrent and for direct wind driven slope currents abstract in february 1991 an array of six current meter moorings was deployed for one year across the central california outer shelf and slope the main line of the array extended 30 km offshore of the shelf break out to water depths of 1400 m a more sparsely instrumented line displaced 30 km to the northwest extended 14 km offshore though shorter the northern line spanned similar water depths because the gradient of the topography steepened in the northern region a poleward flow pattern typical of the california undercurrent was seen across both lines in the array over most of the year the poleward flow was surface intensified in general the portion of the undercurrent that crossed the southern line had larger amplitudes and penetrated more deeply into the water column than the portion that crossed the northern line transport over the year ranged from 0 to 2 5 sverdrups sv poleward across the southern line 0 to 1 sv poleward across the northern line we suggest the difference in transport was caused by topographic constraints which tended to force the poleward flow offshore of the northern measurement sites the slope of the topography steepened too abruptly to allow the poleward flow to follow isobaths when currents were strong when current velocities lessened a more coherent flow pattern was seen across both lines in the array in general the poleward flow patterns in the undercurrent were not affected by local winds or by the local alongshore pressure gradient nor was a strong seasonal pattern evident rather unexpectedly a small but statistically significant fraction of the current variance over the mid and outer slope was driven by the surface wind stress an alongshelf wind stress caused currents to flow along the slope parallel to the wind field down to depths of 400 m below the surface and out to distances of 2 rossby radii past the shelf break the transfer functions were weak 3 4 cm s per dyn cm 2 but comparable to wind driven current amplitudes of 4 6 cm s per unit wind stress over the middle shelf equatorward alongshelf winds also caused water from 200 300 m over the slope to upwell onto the shelf as the surface water moved offshore

radiosonde observations of equatorial atmosphere dynamics over indonesia 2 characteristics of gravity waves this paper discusses the characteristics of gravity waves in the equatorial region revealed by analyzing radiosonde measurements of wind velocity and temperature fluctuations at 0 35 km with a height resolution of 150 m made every 5 7 hours between february 27 and march 22 1990 in east java indonesia we conducted hodograph analysis to delineate vertical and horizontal propagation characteristics and found that most gravity waves were generated in the middle of the troposphere and that they propagated upward into the stratosphere the amplitudes of wind velocity and temperature fluctuations due to gravity waves were larger in the stratosphere than in the troposphere the direction of horizontal propagation of gravity waves was rather uniformly distributed in the troposphere but it became eastward in the lower stratosphere being opposite to that of the mean winds because of quasi biennial oscillation the vertical wavenumber spectra of wind velocity were described fairly well by a saturated model spectrum although their amplitudes were smaller in the stratosphere a typical vertical wavelength was 2 2 5 km while the horizontal phase velocities were 5 7 and 12 m s in the troposphere and stratosphere respectively the amplitudes of small scale gravity waves were significantly larger in the equatorial stratosphere than at middle latitudes time height variation of the wind velocity variance due to gravity waves showed a clear correlation with that for high relative humidity which implies that cloud convection is an important mechanism of gravity wave generation in the equatorial region

gravity wave generation in the lower stratosphere due to passage of the typhoon 9426 orchid observed by the mu radar at shigaraki 34 85 n 136 10 e 1 intense gravity wave activities were investigated in the lower stratosphere during the typhoon 9426 strong vertical winds were observed just a few hours before the arrival of the typhoon center at the mu radar site about 30 min to 1 hour after the typhooncenter had passed a considerable reduction in vertical wind amplitude was detected dominant gravity waves showed time period in the range of 7 8 min 15 min and 40 60 min in the upper troposphere and lower stratosphere in the vicinity of the central region of the typhoon a gravity wave was observed which was monochromatic in nature with a vertical wavelength 3 km between 1 5 km and 23 km height in the lower stratosphere the horizontal wavelength for the prominent period was detected in the range of 10 15 km for 15 min wave period and 25 50 km for 40 60 min wave period the vertical wavelength of these waves was examined from 2 5 km to 4 0 km in the horizontal direction the intrinsic group velocity was estimated between 9 2 and 11 2 m s near the tropopause the average direction of group velocity was assessed at about 20 3 from the horizontal the generation of gravity wave like features in the lower stratosphere is believed induced by convection as the low temperature of the clouds indicates a deep penetration over the radar region as seen in the satellite gms images index terms 3314 meteorology and atmospheric dynamics convective processes 3334 meteorology and atmospheric dynamics middle atmosphere dynamics 0341 0342 3329 meteorology and atmospheric dynamics mesoscale meteorology 3384 meteorology and atmospheric dynamics waves and tides 6952 radio science radar atmospheric physics keywords convective updrafts gravity waves troposphere lower stratosphere