a wind forced ekman spiral as a good statistical fit to low frequency currents in a coastal strait ekman s classical analysis of wind driven currents is a fundamental component of the modern circulation theory of the oceans but there have been few good observations of the predicted ekman spiral where the velocity vector rotates clockwise in direction in the northern hemisphere and decays exponentially in magnitude with increasing depth an analysis of recent cyclesonde velocity measurements based on the use of empirical orthogonal functions however suggests that a classical ekman spiral was a good statistical fit to a significant portion of the low frequency current fluctuations in the strait of georgia british columbia for fluctuation periods of about 5 to 10 days

a gcm investigation into the nature of baroclinic adjustment abstract spindown experiments have been conducted using an atmospheric general circulation model to determine the nature and timescale of adjustment to a baroclinically neutral state the spindown was obtained by turning off the radiative cooling of the atmosphere a procedure the authors argue that retains all the relevant constraints on the atmospheric motions a further experiment with radiation and all other physical parameterizations turned off was performed for comparison the neutral state was characterized by increased static stability but little reduction in meridional temperature gradient in the main baroclinic zones however the zones were observed to narrow and were flanked by regions where the meridional temperature gradient was reduced significantly this pattern was repeated in the no physics spin down experiment but in the absence of surface friction and strong orographic drag the flow also appeared to be stabilized by enhanced barotropic shear the neutral states from these two expe

a comparison of measured and wind derived ekman transport at 11 n in the atlantic ocean abstract a comparison of measured and wind derived ageostrophic transport is presented from a zonal transect spanning the atlantic ocean along 11 n the transport per unit depth shows a striking surface maximum that decays to nearly zero at a depth of approximately 100 m we identify this flow in the upper 100 m as the ekman transport the sustained values of wind stress and the penetration depth of the ekman transport reported here are considerably greater than in previous observations which were made in conditions of light winds the transport of 12 0 5 5 106 m3 s 1 calculated from the difference of geostrophic shear and shear measured by an acoustic doppler current profiler is in good agreement with that estimated from the shipboard winds 8 8 1 9 106 m3 s 1 and from climatology 13 5 0 3 106 m3 s 1 qualitatively the horizontal distribution of the wind driven flow was best predicted by the shipboard winds the cumulative transport increased linearly over the western three fourths of t

direct evidence for an ekman balance in the california current moored acoustic doppler current profiler velocity estimates and buoy wind observations made during a period of moderate southward winds were used to test the ekman balance at a site in the california current as in prior studies the wind driven flow was separated from the total flow by subtraction of a deep reference current the wind driven flow was shown to be in an ekman balance on daily timescales over a period of several months the mean observed transport was to the right of the wind and agreed to within 3 in magnitude and 4 in phase with the predicted ekman transport although the error bar was about 20 the mean velocity profile was a smooth spiral qualitatively similar although flatter than the theoretical ekman spiral prom the observed mean momentum balance profiles of the turbulent stress and eddy viscosity were inferred eddy viscosity estimates within the wind mixed layer were o 100 cm2 s 1

the late spring maximum of rainfall over the u s central plains and the role of the low level jet abstract the seasonal rainfall over the u s central plains features a late spring maximum a spring fall annual mode revealed from the empirical orthogonal function analysis on rainfall delineates a maximum center over the central plains that coincides with the large late spring rainfall this paper examines the large scale dynamical and hydrological processes in forming the rainfall center the ncep department of energy doe reanalysis 2 data reveal that the baroclinic structure of the continental scale circulation during late spring may and june induces a vertically out of phase divergent circulation forming strong convergence of water vapor flux over the central plains such circulation features generate concentrated convective activity in this region the upper level anticyclone development with the north american monsoon in july replaces the late spring baroclinic structure and in turn reduces the convective activity the great plains low level jet llj plays a role in the downscaling process

estimation of elastic stiffness coefficients of an orthorhombic physical model using group velocity analysis on transmission data abstractwe acquired 3c ultrasonic transmission seismograms measured group velocities associated with the three quasi body wave types and determined density normalized stiffness coefficients aij cij over an orthorhombic physical laboratory model the estimation of aij is based on an approximate relationship between the nine orthorhombic aij and group velocities estimation of the anisotropic aij is usually done using phase velocities with well known formulas expressing their theoretical dependence on aij however on time domain seismograms arrivals are observed traveling with group velocities group velocity measurements are found to be straightforward reasonably accurate and independent of the size of the transducers used in contrast the accuracy of phase velocities derived from the p transform analysis was found to be very sensitive to small differences in picked arrival times and to transducer size theoretical phase and group velocities calculated in a forward manner from the aij est

sharpness of the extratropical tropopause in baroclinic life cycle experiments 1 the sharpness of the extratropical tropopause is investigated using baroclinic life cycle experiments in these simulations slow synoptic scale dynamics leads to a net tropopause sharpening the mechanism involves vertical convergence of the ageostrophic wind the results support earlier suggestions from idealized theoretical studies

wind driven ocean currents and ekman transport oceanographic engineering of the woods hole oceanographic institution and the massachusetts institute of technology woods hole ma 02543 oceanographers have long sought to verify the theoretical ekman transport relation which predicts that a steady wind stress acting together with the coriolis force will produce a transport of water to the right of the wind in situ measurements of wind and ocean currents provide a detailed view of this phenomenon by separating the wind driven current from the measured total current and by averaging over a long record it is found that the observed transport is consistent with theoretical ekman transport to within about 10 percent in this case the wind driven transport is strongly surface trapped with 95 percent occurring in the upper 25 meters as a result of fair summer weather

detection and prediction of warm season midtropospheric vortices by the rapid update cycle the authors perform a statistical and dynamical analysis of midtropospheric mesoscale vortices captured by analyses from the rapid update cycle version 2 ruc 2 during the period 1 may to 31 august 1999 a total of 203 vortices meeting conditions of an automated algorithm were found of these 86 were observed to form within organized convection and were termed mesoscale convective vortices mcvs mcvs were favored over a broad area from eastern colorado and western nebraska to the mississippi river valley essentially collocated with the loci of organized convection the remaining 117 vortices termed dry vortices clustered in the immediate lee of the rocky mountains and over the southeastern united states vortices arising from convection had considerably greater intensity and longevity than dry vortices they were roughly five times more likely to be involved with the triggering of new convection a relationship was found between intensity and longevity such that there appears to be a maximum vortex lifetime that can be estimated from its maximum intensity vortices arising from convection had markedly greater humidity and water vapor mixing ratio underneath their centers compared to dry vortices consistent with many dry vortices having a topographic origin and mcvs arising from organized convection parameters such as horizontal scale background vertical wind shear and horizontal deformation were not systematically related to intensity or longevity prediction of mesoscale vortices by the ruc 2 was examined for a subsample of all cases in general the ruc 2 was able to predict the evolution of vortices once analyzed but had virtually no skill at predicting 12 h in advance the formation of the vortices however forecasts of organized convection should still benefit from accurate predictions of long lived vortex tracks

ekman drift in homogeneous water measurements made with satellite tracked buoys drogued in different layers between the sea surface and 30 m depth under homogeneous winter conditions in the north sea allow analysis of the ekman currents under a large variety of wind conditions the experiment lasted from november 20 1991 until february 29 1992 the first 4 weeks of this period during which the buoys stayed close together are used to determine the ekman stresses the total current field is a superposition of barotropic currents due to sea level variations and ekman currents the classical ekman theory is not able to describe properly the observed deflection of the currents to the right of the wind direction and their decay with depth this deflection is 10 near the sea surface and increases to approximately 50 in 25 m depth the relation between wind stress and the stress field in the interior of the water is given by a tensor which describes the rotation and the variation of the stress with increasing depth the concept of eddy viscosity is applicable if a viscosity tensor is used to relate stress and vertical shear the viscosity tensor is a function of the vertical coordinate only and is independent from the wind stress it shows maximum values in 15 to 20 m depth and may be due to langmuir circulation cells further studies are needed to determine the physics of this tensor its magnitude in the interior of the mixed layer exceeds 1000 cgs units consequently ekman currents are weak and may not be the dominant currents within the mixed layer

horizontal dispersion in the sea caused by recurring changes of the depth of the wind drift 1 this paper explores a new horizontal dispersion mechanism due to recurrent changes of the depth of the wind drift in the shallow mode the wind drift moves the upper part of the surface layer relative to the lower part giving an increased horizontal area being covered by a tracer present in the layer when returning to the deep mode the accompanying vertical mixing increases the volume of the cloud the rate of increase of the tracer cloud area is proportional to the wind drift velocity in the shallow mode and the area itself and therefore proportional to the elapsed time squared t2 the t2 law is demonstrated by a numerical experiment and supported by published experimental results the quadratic dependence is explained by the larger and larger exposure to wind driven advection and not by larger and larger scales of motions taking part in the process known from eddy dispersion

potential vorticity anomalies associated with squall lines abstract this study involves observations and model simulations of potential vorticity anomalies in the wake of midlatitude squall lines using data from the oklahoma kansas pre storm experiment we analyze potential vorticity fields near two squall lines one with and one without a trailing stratiform region from this observational analysis we suggest that squall lines with trailing stratiform regions can leave large positive midtropospheric potential vorticity anomalies in their wake to further interpret these observations we consider a two dimensional version of semigeostrophic theory formulated in isentropic and geostrophic coordinates which results in a simple potential pseudodensity inverse potential vorticity equation using apparent heat source fields that model those computed diagnostically from pre storm data we find that theory does indeed predict large midtropospheric potential vorticity anomalies for model squall lines with a trailing stratiform region but not for model squall lines t

observations of the deepwater flow into the baltic sea it has earlier been hypothesized that the deep water flowing into the baltic sea forms a bottom pool in the arkona sea just inside the entrance sills the flow from the pool farther into the baltic sea was assumed to be baroclinic geostrophic and controlled by the pool stratification this was supported by a realistic statistical description of the deepwater flow into the baltic sea computed using historical vertical density profiles from a hydrographical station in the arkona sea however basin wide synoptic measurements of density and currents were not available for a direct verification of the pool model a hydrographic survey was undertaken in the arkona sea shortly after a major inflow event in the beginning of 1993 the conductivity temperature depth sections reveal a thick bottom pool of deep water separated by a halocline from the surface water of baltic origin approaching the northern coastal boundary from the central parts of the pool the halocline sank by about 20 m before hitting the bottom the ship mounted acoustic doppler current profiler recorded a complicated current field however subtraction of the assumed barotropic part gives a current field quite similar to the baroclinic geostrophic current field computed from the density distribution thus a dense bottom pool including a baroclinic geostrophic boundary current along the northern flank of the pool is quite evident from our measurements

on the influence of buoyancy fluxes on wind drift currents abstract data from a moored buoy in the baltic proper have been analyzed to study the ageostrophic wind driven ekman transport accounting for buoyancy fluxes in a stratified ocean a model considering different dynamical regimes governed by wind stress buoyancy fluxes stratification and rotation is used to determine the thickness of the mixed layer for shallow layers in the regime of positive buoyancy fluxes 35 of the time a transport of about 0 77 f directed about 30 to the right of the wind is observed this is far from 1 0 f and 90 given by the classical ekman solution for homogeneous water the result can be understood qualitatively as caused by drag between the well mixed surface layer and the underlying layer if the time scale of decay is about 2 h 1 for negative buoyancy fluxes through the sea surface 53 of the time the mean observed transport was 1 69 f directed about 60 to the right of the wind finite depth equations for homogeneous water cannot explain this result no s

wind energy input to the ekman layer wind stress energy input through the surface ageostrophic currents is studied the surface ageostrophic velocity is calculated using the classical formula of the ekman spiral with the ekman depth determined from an empirical formula the total amount of energy input over the global oceans for subinertial frequency is estimated as 2 4 tw averaged over a period from 1997 to 2002 or 2 3 tw averaged over a period from 1948 to 2002 based on daily wind stress data from ncep ncar thus in addition to the energy input to the near inertial waves of 0 5 0 7 tw reported by alford and by watanabe and hibiya the total energy input to the ekman layer is estimated as 3 tw this input is concentrated primarily over the southern ocean and the storm track in both the north pacific and north atlantic oceans

wind driven motions in the northeast pacific as measured by lagrangian drifters abstract analysis is presented of the time dependent motion of 47 surface drifters in the northeast pacific during fall 1987 and 16 drifters in fall and winter 1989 90 the drifters were designed at 15 m depth and were designed to have wind produced slips less than 2 cm s 1 for wind speeds up to 20 m s 1 the coherence of velocity and local wind is presented for motions with periods between 1 day and 40 days for periods between 5 and 20 days drogue motion at 15 m depth is found to be highly coherent with local wind with an average phase of 70 to the right of the rotating wind vector these results differ from analyses of fgge type drifters as reported by mcnally et al and niiler in the same area a model of wind produced slip as a function of drifter design is used to provide a possible explanation of the differences a linear regression which accounts for 20 40 of the current variance gives water motion al 0 5 of wind speed and 68 to the right of the wind vector assuming an ekman type balance

daytime boundary layer evolution over mountainous terrain part 1 observations of the dry circulations abstract this paper presents the boundary layer structure which accompanies the development of daytime local wind systems in a broad mountain valley as revealed by cross sections of potential temperature it describes how this structure leads to the occurrence of a region of convergence to the downwind side of mountains previous studies based primarily on one dimensional sounding of potential temperature and horizontal winds have shown that profiles of static stability and the presence of winds aloft have an important effect on the manner in which daytime thermally forced wind systems develop in the present study two dimensional cross sections obtained from aircraft data vertical soundings and surface mesonet data show several relevant features in mid to late morning near the surface for example upslope winds form in a shallow mixed layer at the underside of the nocturnal inversion layer cold pool at elevations above the top of this cold pool convectively mixed surface winds exist the spat

baroclinic eddy equilibration under specified seasonal forcing baroclinic eddy equilibration under a northern hemisphere like seasonal forcing is studied using a modified multilayer quasigeostrophic channel model to investigate the widely used quick baroclinic eddy equilibration assumption and to understand to what extent baroclinic adjustment can be applied to interpret the midlatitude climate under aslowly varyingseasonalforcing the eddyand meanflow seasonalbehavioris characterized by four clearly divided time intervals an eddy inactive time interval in summer a mainly dynamically determined eddy spinup time interval starting in midfall and lasting less than one month and a quasi equilibrium time interval for the zonal mean flow available potential energy from late fall to late spring with a mainly external forcing determined spindown time interval for eddy activity from late winter to late spring the baroclinic adjustment can be clearly observed from late fall to late spring the sensitivity studyof the eddyequilibrationto the time scale of the external forcing indicatesthat the time scale separation between the baroclinic adjustment and the external forcing in midlatitudes is only visible for external forcing cycles one year and longer in spite of the strong seasonality of the eddy activity similar to the observations a robust potential vorticity pv structureisstillobservedthroughalltheseasons however itisfoundthatbarocliniceddyisnottheonly candidatemechanismtomaintaintherobustpvstructure theroleoftheboundarylayerthermalforcingand the moistconvectionin maintaining the lower levelpv structureisdiscussed theadjustment and thevertical variation of the lower level stratification play an important role in all of these mechanisms

stratified ekman layers under fair weather conditions the time averaged wind driven current forms a spiral in which the current vector decays and turns clockwise with increasing depth these spirals resemble classical ekman spirals they differ in that their rotation depth scale exceeds the e folding depth of the speed by a factor of 2 to 4 and they are compressed in the downwind direction a related property is that the time averaged stress is evidently not parallel to the time averaged vertical shear we develop the hypothesis that the flat spiral structure may be a consequence of the temporal variability of stratification within the upper 10 20 m of the water column this variability is associated primarily with the diurnal cycle and can be treated by a time dependent diffusion model or a mixed layer model the latter can be simplified to yield a closed solution that gives an explicit account of stratified spirals and reasonable hindcasts of midlatitude cases at middle and higher latitudes the wind driven transport is found to be trapped mainly within the upper part of the ekman layer the diurnal warm layer at tropical latitudes the effects of diurnal cycling are in some ways less important and ekman layer currents are likely to be significant to much greater depths in that event the lower part of the ekman layer is likely to be affected by stratification variability that may be nonlocal

vertical seismic profile synthetics by dynamic ray tracing in laterally varying layered anisotropic structures dynamic ray tracing drt is important in evaluating high frequency seismic wave fields in complicated structures two formulations of the drt equations for inhomogeneous anisotropic media are presented one of them is represented by the classical drt system suggested by cerven 15 years ago both systems are specified in cartesian coordinates the drt equations are supplemented with formulae for the transformation of drt across a smoothly curved interface between two inhomogeneous anisotropic media cerven s formulation of the drt is applied to the computation of vertical seismic profile vsp synthetics the results of drt are used for the evaluation of the geometrical spreading and of the coefficients of the paraxial ray approximation for travel times and ray amplitudes in addition the drt is also used in the interval ray tracing procedure a procedure searching for rays starling from the source and terminating in a specified interval on a profile results of numerical modeling of vsp measurements in a three dimensional laterally varying structure consisting of isotropic and anisotropic layers separated by curved interfaces are presented ray diagrams of selected elementary waves time distance curves and multisource three component vsp synthetics generated for two different source locations calculated for the anisotropic model are compared with the results determined for a reference isotropic model the latter is obtained by averaging phase velocities of the anisotropic model this comparison clearly shows the effects of anisotropy and the lateral variation of the model on seismic wave fields the reliability of the ray synthetics is briefly discussed

role of eastward propagating convection systems in the diurnal cycle and seasonal mean of summertime rainfall over the u s great plains by diagnosing the 3 hourly north american regional reanalysis rainfall dataset for the 1979 2003 period it is illustrated that the eastward propagation of convection systems from the rockies to the great plains plays an essential role for the warm season climate over the central u s this eastward propagating mode could be the deciding factor for the observed nocturnal rainfall peak over the great plains the results also suggest that nearly half of the total summer mean rainfall over this region is associated with these propagating convection systems for instance the extreme wet condition of the 1993 summer may be attributed to the frequent occurrence of propagating convection events and enhanced diurnal rainfall amplitude over the great plains thus proper representation of this important propagating component in gcms is essential for simulating the diurnal and seasonal mean characteristics of summertime rainfall over the central us

3d velocity distribution of p and s waves in a biotite gneiss measured in oil as the pressure medium comparison with velocity measurements in a multi anvil pressure apparatus and with texture based calculated data abstract ultrasonic measurements of the 3d velocity distribution of p and s waves were performed on a spherical sample of a biotite gneiss from the outokumpu scientific drill hole measurements were done at room temperature and pressures up to 400 and 70 mpa respectively in a pressure vessel with oil as a pressure medium a modified transducer sample assembly and the installation of a new mechanical system allowed simultaneous measurements of p and s wave velocities in 132 independent directions of the sphere on a net in steps of 15 proper signals for p and s waves could be recorded by coating the sample surface with a high viscosity shear wave gel and by temporal point contacting of the transmitter and receiver transducers with the sample surface during the measurements the 3d seismic measurements revealed a strong foliation related directional dependence anisotropy of p and s wave velocities which is confirmed by measurements in a multi anvil apparatus on a cube shaped specimen of the same rock both experimental approaches show a marked pressure sensitivity of p and s wave velocities and velocity anisotropies with increasing pressure p and s wave velocities increase non linearly due to progressive closure of micro cracks the reverse is true for velocity anisotropy 3d velocity calculations based on neutron diffraction measurements of crystallographic preferred orientation cpo of major minerals show that the intrinsic bulk anisotropy is basically caused by the cpo of biotite constituting about 23 vol of the rock including the shape of biotite grains and oriented low aspect ratio microcracks into the modelling increases bulk anisotropy an important finding from this study is that the measurements on the sample sphere and on the sample cube displayed distinct differences particularly in shear wave velocities it is assumed that the differences are due to the different geometries of the samples and the configuration of the transducer sample assembly on the spherical sample with a point source and point receiver the first break at the velocity arrival time is suggested to define group velocities in most cases whereas the receivers in the multi anvil apparatus recorded the flat part of the wavefront that is phase velocities

the influence of the rocky mountains on the 13 14 april 1986 severe weather outbreak part ii evolution of a prefrontal bore and its role in triggering a squall line abstract in this paper part ii of a series the evolution of a prefrontal bore on the leeside of the rockies and its subsequent propagation and initiation of convection farther downstream over eastern colorado and western nebraska are investigated the observational evidence for this sequence of events was obtained from combined analyses of high resolution goes satellite imagery and program for regional observing and forecasting services mesonetwork data over the colorado region for the severe weather event that occurred during 13 14 april 1986 a 2d nonhydrostatic numerical model is used to further understand the initiation of the bore and its ability to propagate farther downstream and trigger convection analysis of satellite imagery and mesonet data indicated that an internal bore ahead of a cold front a moderate downslope windstorm and a quasi stationary hydraulic jump were generated within a few hours along the iceslope as a pacific cold front and its attendant upper level jet streak advanced o

observations of seasonal variation in the ekman layer abstract the seasonal variation in the ekman layer is examined using observations from the long term upper ocean study lotus including surface meteorology current and temperature the near surface current is found to be coherent with the wind at low frequencies periods greater than one day using a wind relative averaging method the authors find the observed near surface volume transport to be consistent with ekman transport the mean current profile has a spiral shape that is flat compared to the classic ekman spiral in that it rotates less with depth than does the ekman spiral the mean current e folds over 12 m in the summer and 25 m in the winter with a decay in amplitude that implies eddy viscosities of 60 10 4 and 250 10 4 m2 s 1 respectively diurnal cycling is the dominant mode of variability in the summer and it determines the vertical structure of the spiral in the winter diurnal cycling is almost nonexistent due to greatly reduced solar insolation and stronger winds a persisten

a baroclinic mechanism for the eddy feedback on the zonal index a baroclinic mechanism for the positive eddy feedback on the zonal index is proposed the author considers the quasigeostrophic response of the zonally averaged flow to forcing by baroclinic eddies the transient response to eddy forcing is a largely barotropic acceleration of the westerly flow and a reduction of the baroclinicity at the latitudes of eddy generation but over time the action of surface drag leads to enhanced baroclinicity at these latitudes the steady state response has positive baroclinicity at the latitude of eddy generation if the eddies propagate away from this latitude before they dissipate this reinforcement of the low level baroclinicity provides a positive feedback if it is assumed that baroclinic eddies are generated more vigorously in regions of stronger low level baroclinicity the proposed mechanism explains observed and modeled features of zonal index variations the frequency and drag dependence of eddy feedback the bandedness in latitude of zonal wind variations and the tendency for anomalies in the zonally averaged zonal wind to drift poleward over time

baroclinic adjustment a comparison between theory observations and models abstract isentropic slopes calculated from northern hemisphere analyses of the zonal mean state of the atmosphere are compared with isentropic slopes calculated from baroclinic adjustment theory in midlatitudes the isentropic slopes are relatively close to the adjusted values in the layer from 2 to 7 km 800 to 400 mb they also have very little variation in latitude and season which implies that baroclinic eddy fluxes supply a strong negative feedback to changes in isentropic slopes the vertical structure of the temperature field in the adjusted layers and the location of the layers suggest that vertical eddy heat fluxes play a significant role in this feedback process isentropic slopes are also calculated from simulations of the current climate by the giss model ii gcm and the ncar ccm2 both models have regions of apparent baroclinic adjustment similar to that in the northern hemisphere atmosphere however compared to the observations the agreement of the simulations with baroclinic adjustmen

elevated residual layers and their influence on surface boundary layer evolution abstract elevated mixed layers emls are an important factor in the development of springtime thunderstorms over the united states emls can be considered a subset of a larger class called residual layers since the mean state variables are the same at least initially as those of the boundary layers in which emls a formed it is possible however for boundary or residual layers that are not necessarily well mixed to be advected off regions of elevated terrain and overrun boundary layers forming over lower terrain these layers are called elevated residual layers erls erls may form frequently in regions near mountains where terrain gradients exist a simple slab mixed layer model is used to examine how idealized erl potential temperature profiles influence surface boundary layer development in addition several regionally generated erls were observed over phoenix arizona during the southwest area monsoon project these erls appear to have produced a change from moistening to entrainment drying s

oceanic restratification forced by surface frontogenesis potential vorticity pv conservation implies a strong constraint on the time evolution of the mean density at a given depth the authors show that on an f plane and in the absence of sources and sinks of pv it only depends on two terms namely the time evolution of the product between density anomaly and relative vorticity and the vertical pv flux this primitive equation result which applies at any depth suggests that the ageostrophic dynamics induced by baroclinic eddies strongly affect the mean oceanic stratification profile this result is illustrated for two simple initial value simulations of a baroclinic balanced jet for initial situations propitious to surface frontogenesis the simulations show a restratification over the whole water column characterized by the amplification in time of the brunt vaisala frequency in the upper oceanic layers in the absence of surface frontogenesis such as when the jet is initialized at the middepth of the water column the restratification is much weaker and slower because both simulations have similar kinetic energy and growth rate of baroclinic instability the results clearly reveal that the restratification is driven by surface frontogenesis in the first case and by vertical pv flux in the interior in the second case the authors also point out that the dynamics of the interior pv is tightly related to the surface dynamics because of total mass conservation

baroclinic adjustment and midlatitude temperature profiles abstract an assessment is made of how baroclinically unstable waves might stabilize a zonal mean bow by adjusting vertical temperature profiles to this end temperature profiles for a continuous atmosphere an derived which are baroclinically stable features of these profiles of relevance to the atmosphere are discussed and a requirement is derived for the minimal amount of profile adjustment necessary to stabilize the zonal mean flow neither the atmosphere nor realistic models can perform the profile adjustment necessary to attain a rigorously stable state but a model used here which includes vertical heat fluxes from baroclinically unstable waves can attain an effectively stable state that is very similar to the rigorously stable state observed temperature profiles as well as model profiles that are not effectively stable also display features of the adjusted profiles indicating that much of the temperature variation with height in the midlatitude troposphere can be understood in terms of the ad

climatology of summer midtropospheric perturbations in the us northern plains part ii large scale effects of the rocky mountains on genesis propagating convective storms across the us northern plains are often coupled with preexisting midtropospheric perturbations mps initiated over the rocky mountains a companion study part i notes that such mps occur most commonly at 12 utc early morning and 00 utc late afternoon using a regional reanalysis and a general circulation model gcm this study investigates how such a bimodal distribution of the mp frequency is formed the results point to two possible mechanisms working together while each has a different timing in terms of maximum effect the diurnal evolutions between the midtropospheric flows over the rockies and over the great plains are nearly out of phase due to inertial oscillation during the nighttime the westerly flows at 700 500 mb over the rockies intensify while flows at the same level over the great plains turn easterly these two flows converge over the eastern rockies and induce cyclonic vorticity through vortex stretching after sunrise the convergence dissipates and the cyclonic vorticity is redistributed by horizontal vorticity advection moving it downstream this process creates a climatological zonally propagating vorticity signal which in turn facilitates the early morning mp genesis at 12 utc the analysis also reveals marked dynamic instability conducive to subsynoptic scale disturbances in the midtroposphere over the rockies strong meridional temperature gradients appear over the north facing slopes of the rockies due to terrain heating to the south and the presence of cooler air to the north this feature along with persistent vertical shear creates a charney stern type of instability i e sign changes of the meridional potential vorticity gradient meanwhile the development of terrain boundary layer reduces the rossby deformation radius which subsequently enhances the likelihood for baroclinic short waves such effects are most pronounced in the late afternoon and therefore are supportive to the mp genesis around 00 utc examination of gcm experiments with and without orography further supports the critical role of the rocky mountains and its associated boundary layer impacts on the formation of mps

elastic wave velocities chemistry and modal mineralogy of crustal rocks sampled by the outokumpu scientific drill hole evidence from lab measurements and modeling the outokumpu scientific deep drill hole intersects a 2500 m deep precambrian crustal section comprising a 1300 m thick biotite gneiss series mica schists at top followed by a 200 m thick meta ophiolite sequence underlain again by biotite gneisses mica schists 500 m thick with intercalations of amphibolite and meta pegmatoids pegmatitic granite from 2000 m downward the dominating rock types are meta pegmatoids pegmatitic granite average isotropic intrinsic p and s wave velocities and densities of rocks were calculated on the basis of the volume fraction of the constituent minerals and their single crystal properties for 29 core samples covering the depth range 198 2491 m the modal composition of the rocks is obtained from bulk rock xrf and mineral chemistry microprobe using least squares fitting laboratory seismic measurements on 13 selected samples representing the main lithologies revealed strong anisotropy of p and s wave velocities and shear wave splitting seismic anisotropy is strongly related to foliation and is in particular an important property of the biotite gneisses which dominate the upper and lower gneiss series at in situ conditions velocity anisotropy is largely caused by oriented microcracks which are not completely closed at the pressures corresponding to the relatively shallow depth drilled by the borehole in addition to crystallographic preferred orientation cpo of the phyllosilicates the contribution of cpo to bulk anisotropy is confirmed by 3d velocity calculations based on neutron diffraction texture measurements for vertical incidence of the wave train the in situ velocities derived from the lab measurements are significantly lower than the measured and calculated intrinsic velocities the experimental results give evidence that the strong reflective nature of the ophiolite derived rock assemblages is largely affected by oriented microcracks and preferred crystallographic orientation of major minerals in addition to the lithologic control c 2009 elsevier b v all rights reserved