Changes In Vertical Velocity Research Articles

Finescale Structure and Microphysics of Coastal Stratus

Observations were made of unbroken marine stratus off the coast of Oregon using the combined capabilities of in situ probes and a 95-GHz radar mounted on an aircraft. Reflectivity and Doppler velocity measurements were obtained in vertical and horizontal planes that extend from the flight lines. Data from three consecutive days were used to examine echo structure and microphysics characteristics. The clouds appeared horizontally homogeneous and light drizzle reached the surface in all three cases. Radar reflectivity is dominated by drizzle drops over the lower two-thirds to four-fifths of the clouds and by cloud droplets above that. Cells with above-average drizzle concentrations exist in all cases and exhibit a large range of sizes. The cells have irregular horizontal cross sections but occur with a dominant spacing that is roughly 1.2–1.5 times the depth of the cloud layer. Doppler velocities in the vertical are downward in all but a very small fraction of the cloud volumes. The cross correlation between reflectivity and vertical Doppler velocity changes sign at or below the midpoint of the cloud, indicating that in the upper parts of the clouds above-average reflectivities are associated with smaller downward velocities. This correlation and related observations are interpreted as the combined results of upward transport of drizzle drops and of downward motion of regions diluted by entrainment. The in situ measurements support these conclusions.

Age of air in a zonally averaged two‐dimensional model

The distribution of age‐of‐air in a two‐dimensional, zonally averaged model of the atmosphere is examined. The age‐of‐air is determined from mixing ratios of a fictitious tracer with a linearly increasing tropospheric source. The impact of horizontal mixing is isolated by performing parallel calculations with and without horizontal mixing terms in the tracer evolution equation. We examine the evolution of the tracer over several model years, using different tropical heat sources as well as different amounts of planetary wave mixing and drag. Typical ages in the midstratosphere when horizontal mixing is included range from 3 to over 5 years, depending primarily on the strength of the model's prescribed tropical heat source. These values of age are within the range of observational estimates based on long‐lived tracers with increasing tropospheric mixing ratios, such as HF, CO2 and SF6. Age determined from the horizontally unmixed tracer is reduced by 1 to 2 years. However, the evolution of the unmixed tracer is consistent with observed behavior of tropical water vapor oscillations in data from the Halogen Occultation Experiment (HALOE). We found stronger than expected sensitivity of middle atmospheric age to prescribed heating in the tropical troposphere. This sensitivity in our model arises from small resulting changes to the residual vertical velocity in the tropics. These vertical velocity changes are in turn associated with net heating changes of 0.05–0.10 K d−1 in the tropical lower stratosphere. We argue that changes of this magnitude are within the uncertainties imposed by natural variations in the tropics.

An evaluation of the temperature, water vapor, and vertical velocity structure of aircraft contrails

Measurements made in contrails formed in the wake of a Lear 35 have been analyzed with respect to their temperature, water vapor, and vertical velocity structure. The National Center for Atmospheric Research (NCAR) Sabreliner traversed the Lear's wake at distances varying from 150 m to 5 km and penetrated the contrails 243 times over the course of seven flights. The width of the plume is documented as a function of the distance between the leading and chase aircraft and the temperature, humidity and vertical motion components inside the plume have been analyzed and compared with a three dimensional wake vortex model. The analysis shows that the width increases very little within the first 5 km, in agreement with the vortex model. The increases in temperature and water vapor in the contrail 500 m from the exhaust were ≈0.6° and 8 ppmv, respectively. The vertical velocity change across the contrail was ≈4 m s−1. The agreement between observations and model predictions is quite good in comparisons of temperature. The model predicts larger water vapor mixing ratios, but the differences can be explained within the expected measurement uncertainties and lack of particle condensation in the vortex model. The model predicts larger excursions in vertical velocity but the trends are in excellent agreement between model and observations.

On frontal and ventilated models of the main thermocline

A new similarity approach is applied to the thermocline equations in order to examine contrasting frontal and ventilated models of the main thermocline. The method of solution involves reducing the number of independent variables of the controlling partial differential equation, leading to a particular form for the solutions which satisfy appropriate boundary conditions. A frontal model of the thermocline is obtained following the study of Salmon and Hollerbach (1991). When the vertical diffusivity becomes vanishingly small, an interior front in the subtropical gyre appears at the depth where the vertical velocity changes sign. The front separates downwelling warm water in the subtropical gyre from the underlying upwelling of cold, deep water. These solutions appear to be robust to changes in the vertical diffusivity profile, as long as there is a small, nonzero value in the interior. However, when there is uniform diffusivity, there is no implied surface heat flux and surface isotherms are coincident with streamlines. As the diffusivity increases toward the surface, the surface heat input increases in magnitude and the temperature field becomes more plausible. A ventilated model of the thermocline is formed using the similarity approach with a diffusive surface boundary-layer overlying an adiabatic interior. In this case, the temperature and velocity fields are solved for in the limit of uniform potential vorticity. There is now a more plausible cross-isothermal flow in the surface layer with a polewards decrease in temperature, and the implied surface heat input increases equatorwards. Fluid is subducted from the surface boundary layer into the adiabatic interior and forms a continuous thermocline. In conclusion, the contrasting frontal and ventilated solutions arise from modeling different aspects of the circulation, rather than depending on the type of model employed. The ventilated solutions form a thermocline by advecting the surface temperature field into the interior of a subtropical gyre, whereas the frontal solutions create a thermocline from the interaction of the wind-driven gyre and the underlying thermohaline circulation. These thermocline solutions might occur separately or together in the real ocean, although both solutions might be modified by higher-order processes or more complicated forcing.

Microphysical modeling of cirrus: 2. Sensitivity studies

The one‐dimensional cirrus model described in part 1 of this issue has been used to study the sensitivity of simulated cirrus microphysical and radiative properties to poorly known model parameters, poorly understood physical processes, and environmental conditions. Model parameters and physical processes investigated include nucleation rate, mode of nucleation (e.g., homogeneous freezing of aerosols and liquid droplets or heterogeneous deposition), ice crystal shape, and coagulation. These studies suggest that the leading sources of uncertainty in the model are the phase change (liquid‐solid) energy barrier and the ice‐water surface energy which dominate the homogeneous freezing nucleation rate and the coagulation sticking efficiency at low temperatures which controls the production of large ice crystals (radii greater than 100 μm). Environmental conditions considered in sensitivity tests were CN size distribution, vertical wind speed, and cloud height. We found that (unlike stratus clouds) variations in the total number of condensation nuclei (CN) have little effect on cirrus microphysical and radiative properties, since nucleation occurs only on the largest CN at the tail of the size distribution. The total number of ice crystals which nucleate has little or no relationship to the number of CN present and depends primarily on the temperature and the cooling rate. Stronger updrafts (more rapid cooling) generate higher ice number densities, ice water content, cloud optical depth, and net radiative forcing. Increasing the height of the clouds in the model leads to an increase in ice number density, a decrease in effective radius, and a decrease in ice water content. The most prominent effect of increasing cloud height was a rapid increase in the net cloud radiative forcing which can be attributed to the change in cloud temperature as well as change in cloud ice crystal size distributions, It has long been recognized that changes in cloud height or cloud area have the greatest potential for causing feedbacks on climate change. Our results suggest that variations in vertical velocity or cloud microphysical changes associated with cloud height changes may also be important.

Registration of wave disturbances over Yakutia

The results of investigations of wave processes with periods 2 hours on their influence and on the night sky airglow intensity are given. The observations were carried out by multichannel spectrometer for three seasons of 1985–1988 at the optical testing ground Maimaga ( γ = 63°N; λ = 129, 5°E). The synchronous detection of two and sometimes of three emissions of night sky airglow yielded the oppotunity to track a vertical travel of waves and to estimate their parameters. In most cases the waves propagate upward, i.e. the sources of waves were below mesosphere. The estimated vertical velocity change within 0,9-3,3 m/s and vertical wave length - within 18–85 km. A horizontal velocity varies from 83 to 330 m/s. The wave activity (the occurence frequency) and their amplitude in winter is higher than in spring. The estimated energies transfered by waves to the upper atmosphere are in winter 3.8·10 −3 W/m 2 and in spring 2.7·10 −3 W/m 2.

Effects of Small-Scale Vertical Motion on Radar Measurements of Wind and Temperature Profiles

Abstract Vertical velocities were observed during the month of June 1990 with two side-by-side wind profilers at Platteville, Colorado. Many of the observations reveal strong wave motion, probably mountain lee waves, that sometimes caused vertical velocity changes of several meters per second in less than an hour. It is demonstrated that, under these conditions, hourly averages cannot always be used to accurately account for the effects of vertical motion on the profiler measurements. It is also shown that it is impossible to accurately remove the effects of vertical motion from the horizontal wind component estimates when the horizontal scale of vertical-motion variability is comparable to the horizontal separation distance between antenna beams. The Radio Acoustic Sounding System (RASS) temperature measurements, however, are not affected by the small spatial scales because those measurements are made on the same vertical antenna beam as the vertical velocity measurements. Nevertheless, it is important t...

An anti -spatial -aliasing filter for explicit modeling and imaging in inhomogeneous media

An explicit finite difference solution to the scalar wave equation in isotropic, inhomogeneous media is completed by filtering out non-physical contributions to the data. This digital, anti -spatial -aliasing filter and some associated limits on angular frequency are determined. The filter is a projection operator determined from a constrained least-squares fit and can be implemented in the computer algorithm at either of two places. Furthermore, the filter should be applicable to any explicit finite difference solution to the wave equation. Unlike a standard dip filter, this filter is computationally flexible, efficient, and necessary in inhomogeneous media with rapid lateral and vertical velocity changes.

A Comparison of Techniques Used in Performing the Men’s Compulsory Gymnastic Vault at the 1988 Olympics

It was hypothesized that the techniques employed by two groups of male gymnasts in performing the handspring and salto forward tucked vault at the 1988 Olympics were not significantly different. The 11 highest scored vaults (Gl) of the 51 subjects filmed during the competition were compared with the 11 lowest scored vaults (G2). The G1 had (a) significantly greater horizontal velocity of hurdle and preflight and (b) significantly greater vertical reaction forces exerted on them by the horse, which in turn produced a significantly greater change of vertical velocity while on horse. Consequently, the better gymnasts departed from the horse with significantly greater vertical velocity, which resulted in significantly greater height, larger distance, and longer time of postflight than the gymnasts in G2. The better gymnasts had the instant of the tightest tuck position while significantly nearer the instant of peak postflight than the G2 gymnasts, which caused the height of CG at the tightest tuck position to be significantly greater for the better gymnasts. During the subsequent phase of the vault, the better gymnasts moved out of the tuck position higher in midair, extended the body more fully, and held this extended position longer to a controlled landing on the mat, all of which the judges are seeking.

Techniques Used in Performing the Handspring and Salto Forward Tucked Vault at the 1988 Olympic Games

The purposes of this study were to (a) determine the mechanical factors associated with successful performance of the handspring and salto forward vault at the 1988 Olympic Games, and (b) contrast the findings in this study to those from the 1986 USA Championships to gain additional insight for the improvement of performance. The subjects were 51 male gymnasts in the 1988 Olympic Games. Significant correlations indicated that the following were important determinants for successful results: (a) large horizontal velocity (VH) at takeoff (TO) from floor and board resulting from a fast sprint in the approach run; (b) a large change of vertical velocity (Vv) during the horse contact by means of blocking with arms and shoulders; and (c) large VH and Vv at TO from horse, which ensures great distance and height and a long time of postflight, which the judges are seeking. Comparison of the techniques between the two groups revealed that the Olympic gymnasts achieved significantly greater horizontal velocity in preflight, change of vertical velocity while on horse, and vertical velocity at takeoff from horse, which resulted in a significantly longer time of postflight than for the USA gymnasts. An analysis of the aspect of form in postflight, possibly by means of mechanical variables, should be conducted because it may provide additional insight for improvement for performance of this vault.

Geophysical structure of the broadlandsohaaki geothermal field (New zealand)

A retrofitting study of the geophysical anomalies of the Broadlands-Ohaaki field was undertaken after production drilling had been completed in 1984. This study uses all relevant information from earlier (1965–1970) geophysical exploration surveys, results from detailed seismic reflection and airborne magnetic surveys made in 1984, and information from 44 exploration and production wells. The seismic reflection survey (12 fold CMP) shows that reflections from the top and the bottom of concealed Quaternary volcanic extrusions and pyroclastic flows can be obtained inside a hot-water system down to about 1 km depth. Processing of the data yields a detailed seismic velocity structure showing significant horizontal and vertical velocity changes inside and outside the field which, in showing significant horizontal and vertical velocity changes inside and outside the field which, in than 1 km are seismically opaque inside the field. The seismic structures down to 1 km depth, together with the density data of all formations and the well data, were used to interpret, in detail, gravity anomalies. The interpretation models define the gross structure of major lithostratigraphic units down to the Mesozoic basement (2.5 km maximum depth) both inside and outside the geothermal field. Seismic structures and gravity models allow the interpretation of magnetic anomalies associated with several concealed, up to 0.6 km thick, Quaternary calc-alkaline lava extrusions. A structural contour map of the Mesozoic basement sediments and isopach maps of major volcanic units, including two productive layers within a sequence of pyroclastic flows, are presented. The results demonstrate the importance of a retrofitting study at the post-drilling phase of an explored hot-water system.

Effect of loss of balance on biomechanics platform measures of sway: Influence of stance and a method for adjustment

This paper describes a method for adjusting biomechanics platform measures of sway for loss of balance. Area and velocity measures of sway were determined in forty-seven elderly women, in double and single leg stance, first with their eyes open, then closed. Subjects were rarely able to complete 10 s trials during single leg stances. Therefore, a method was developed for eliminating data associated with loss of balance. Monitoring changes in vertical force and velocity by computer, those points exceeding trial specific thresholds associated with loss of balance were truncated. In double leg stances, loss of balance increased area measures by 0–3%, but did not effect velocity measures. In contrast, the loss of balance experienced by most subjects in single leg stance exaggerated area measures by 16–38%, and velocity measures by up to 10%. In double leg stances the correlations between unadjusted area measures and area measures adjusted for loss of balance ranged from 0.98 to 1.00. In single leg stances, the correlations for the area measures ranged from 0.69 to 0.89. The correlations between adjusted and unadjusted velocity measures were 1.00 and 0.93 for the double and single leg stances respectively. Although the question of which sway measure is best remains unanswered, this study provides useful data for future research. First, it demonstrates a method for modifying area representations of the center of pressure excursions for the effects of loss of balance. Second, it quantifies the effects of loss of balance in different stances; for the population studied the effects are minimal in double leg stances, but may be substantial when sway is measured in single leg stances.

Ground reaction forces in running: A reexamination

Ground reaction force (GRF) data were collected on twenty adult males during running stance to establish normative standards to aid in assessment of the gait of atypical runners. Subjects ran between 30 and 40 trials across a Kistler 0.6 × 0.9 m force platform at self-selected speeds ranging from 2.5 to 5.5 m s −1. Best fit polynomials for a given descriptor variable were constructed for each subject and the polynomials were evaluated as a function of running speed. Predicted means and standard deviations (based on the polynomials) were calculated and multivariate analyses of variance were performed. The descriptor variables: impact peak, loading rate, thrust maximum, decay rate, average vertical GRF, change in vertical velocity, braking impulse, propulsive impulse and stance time were determined to be running speed dependent ( p < 0.001). Specific patterns associated with the breaking component of the antero-posterior GRF of heel-strikers included single, double and multiple peaks. Three dimensional graphic displays showed that, despite considerable group variability in medial-lateral GRF-time histories, consistency was evident in the patterns of individuals across speeds. Individual right-left asymmetries were clearly shown in these displays.

Simulation of laboratory vortex flow by axisymmetric similarity solutions

A similarity approach is utilized to investigate a simple axisymmetric steady-state model of the convergence region of a laboratory vortex. The resulting simplified set of equations are solved for a range of swirl angles by varying the tangential or radial velocity component at the outer rim. By increasing the swirl angle the flow is found to go from a one cell to a two cell configuration, i.e., the vertical velocity changes from everywhere positive to negative in the vicinity of the axis. Correspondingly the vertical vorticity maximum moves from the axis outward toward the radius of maximum tangential velocity, making the flow barotropically unstable with respect to unsymmetrical perturbations. DOI: 10.1111/j.2153-3490.1982.tb01847.x

Developments in exploration geophysics, 1975–1980

Advances in exploration geophysics have continued apace during the last six years. We have entered a new era of exploration maturity which will be characterized by the extension of our technologies to their ultimate limits of precision. In gravity and magnetics, new inertial navigation systems permit the very rapid helicopter‐supported land acquisition of precise surface gravity data which is cost‐effective in regions of severe topography. Considerable effort is being expended to obtain airborne gravity data via helicopter which is of exploration quality. Significant progress has also been made in processing and interpreting potential field data. The goal of deriving the maximum amount of accurate subsurface information from seismic data has led to much more densely sampled and precise 2- and 3-D land data acquisition techniques. Land surveying accuracy has been greatly improved. The number of individually recorded detector channels has been increased dramatically (up to 1024) in order to approximate much more accurately a point‐source, point‐detector system. Much more powerful compressional‐wave vibrators can now maintain full force while sweeping up or down from 5 Hz to over 200 Hz. In marine surveying, new streamer cables and shipboard instrumentation permit the recording and limited processing of 96 to 480 channels. Improvements have also been made in marine sources and arrays. The most important developments in seismic data processing—wave‐equation based imaging and inversion methods—may be the forerunners of a totally new processing methodology. Wave‐equation methods have been formulated for migration before and after stack, multiples suppression, datum and replacement statics, velocity estimation, and seismic inversion. Inversion techniques which provide detailed acoustic‐impedance or velocity estimates have found widespread commercial application. Wavelet processing has greatly expanded our stratigraphic analysis capabilities. Much more sophisticated 1-, 2-, and 3-D modeling techniques are being used effectively to guide data acquisition and processing, as direct interpretation aids, and to teach basic interpretation concepts. Some systems can now handle vertical and lateral velocity changes, inelastic attenuation, curved reflection horizons, transitional boundaries, time‐variant waveforms, ghosting, multiples, and array‐response effects. Improved seismic display formats and the extensive use of color have been valuable in data processing, modeling, and interpretation. Stratigraphic interpretation has evolved into three major categories: (1) macrostratigraphy, where regional and basinal depositional patterns are analyzed to describe the broad geologic depositional environment; (2) qualitative stratigraphy, where specific rock units and their properties are analyzed qualitatively to delineate lithology, porosity, structural setting, and areal extent and shape; and (3) quantitative stratigraphy, where anomalies are mapped at a specific facies level to define net porosity‐feet distribution, gas‐fluid contacts, and probable pore fill. In essence, what began as direct hydrocarbon‐indicator technology applicable primarily to Upper Tertiary clastics has now matured to utility in virtually every geologic province. Considerable effort has been expended on the direct generation and recording of shear waves in an attempt to obtain more information about stratigraphy, porosity, and oil and gas saturation. Seismic service companies now offer shear‐wave prospecting using vibrator, horizontal‐impact, or explosive sources. Well logging has seen the acceleration of computerization. Wellsite tape recorders and minicomputers with relatively simple interpretation algorithms are routinely available. More sophisticated computerized interpretation methods are offered as a service at data processing centers.

Observations of internal wave vertical velocities by a free-fall vehicle

Abstract Slow variations, as great as ± 3 cm s −1 , have been found in the descent rates of free-fall vehicles operated in the ocean. Comparison with the much more uniform fall speeds measured in local fjords indicates that the variable descent rates reflect changes in the vertical water velocity rather than irregularities in the vehicle dynamics. A simple model shows that these vehicles fully respond to vertical velocity variations of the water that are in the internal wave frequency band. The observed spectrum can be derived from the Garrett and Munk internal wave model. It is shown that the instrument responds mostly to waves of relatively high frequency and low wavenumber. The phase velocity of these waves is much larger than the mean descent rate (=0.08 m s −1 ), so that the observed spectrum is essentially equivalent to a spectrum from a moored instrument. As these waves contain most of the variance, the r.m.s. vertival velocity can be estimated simply even in locations not amenable to other techniques. Data from the core of the Gulf Stream and from the seasonal thermocline had r.m.s. velocities much larger than those observed in the main thermocline, which were in rough agreement with the Garrett-Munk model.

Magnetic storm effects on the tropical ultraviolet airglow

Ogo 4 measurements of the UV equatorial airglow made during a period which included a major magnetic storm are analyzed and used as an indicator of wind direction and velocity as well as ExB drift magnitude and phase. Some features of the airglow intensity and distribution are explained in terms of storm-induced changes in vertical drift velocity, neutral composition, or both. The observations are shown to be consistent with an eastward neutral wind that transports ionization from the Southern to the Northern Hemisphere while raising the F layer in the South and lowering it in the North. Theoretical modeling of the low-latitude F-region ionosphere indicates that an eastward wind with velocity approaching 300 m/s at 2100 LT can qualitatively produce the observed hemispheric asymmetries in airglow emission rates.

Upwelling Layers in a Steady, Wind-Driven Stratified Ocean

Abstract A theoretical study is made of a region of steady upwelling adjacent to the eastern boundary of a stratified ocean. A multi-layered structure is required to satisfy all the boundary conditions. The velocity and temperature fields are found by matching to Ekman and thermal layers of the interior region. In the principal upwelling layer, vertical advection of heat is balanced by horizontal diffusion of heat. Very close to the coast a narrow mixing region is required to complete the solution. It is shown that the onshore flow and the vertical velocity change sign with depth.

The motion of a fluid in a cylindrical container with a free surface following vertical impact

The effect of a sudden change in vertical velocity of a vessel partially filled with fluid is considered. It is shown that very small free surface disturbances can be amplified so strongly by a velocity change that instability can occur. This instability frequently causes a jet to emanate from the free surface. Conditions causing free surface disturbances in a vessel in free fall are considered and it is shown that a contact angle between the fluid and the wall of the vessel different from ½π radians can distort the surface in such a way that the amplification and instability upon vertical impact results in a central jet. The results of experiments of this effect are shown. The generation of waves due to transient side wall motions, such as those that might result from fluid pressure at impact, are considered in the appendix. It is shown that such waves would have a different form than those observed in the experiments.

How to Make Velocity Corrections

The fundamental assumptions in regard to velocity distribution and the effect of these assumptions in the computation of reflection-seismograph data are discussed. Simple methods for adjusting reflection-seismograph information for lateral changes in vertical velocity are explained and illustrated.