Search Results
You are looking at 1 - 10 of 24 items for
- Author or Editor: B. L. Weber x
- Refine by Access: All Content x
Abstract
A general hydrodynamic solution is derived for arbitrary gravity-wave fields on the ocean surface by extending Stokes' (1847) original perturbational analysis. The solution to the nonlinear equations of motion is made possible by assuming that the surface height is periodic in both space and time and thus can be described by a Fourier series. The assumption of periodicity does not limit the generality of the result because the series can be made to approach an integral representation by taking arbitrarily large fundamental periods with respect to periods of the dominant ocean waves actually present on the surface. The observation areas and times over which this analysis applies are assumed small, however, compared to the periods required for energy exchange processes; hence an “energy balance” (or steady-state) condition is assumed to exist within the observed space-time intervals. This in turn implies the condition of statistical stationarity of the Fourier height coefficients when one generalizes to a random surface. Part I confines itself to the formulation of a perturbation solution (valid to all orders) for the higher order terms resulting from a two-dimensional arbitrary periodic description of the surface height. The method is demonstrated by deriving (to second order) the height correction to the sea and (to third order) the first nonzero correction to the lowest order gravity-wave dispersion relation.
Abstract
A general hydrodynamic solution is derived for arbitrary gravity-wave fields on the ocean surface by extending Stokes' (1847) original perturbational analysis. The solution to the nonlinear equations of motion is made possible by assuming that the surface height is periodic in both space and time and thus can be described by a Fourier series. The assumption of periodicity does not limit the generality of the result because the series can be made to approach an integral representation by taking arbitrarily large fundamental periods with respect to periods of the dominant ocean waves actually present on the surface. The observation areas and times over which this analysis applies are assumed small, however, compared to the periods required for energy exchange processes; hence an “energy balance” (or steady-state) condition is assumed to exist within the observed space-time intervals. This in turn implies the condition of statistical stationarity of the Fourier height coefficients when one generalizes to a random surface. Part I confines itself to the formulation of a perturbation solution (valid to all orders) for the higher order terms resulting from a two-dimensional arbitrary periodic description of the surface height. The method is demonstrated by deriving (to second order) the height correction to the sea and (to third order) the first nonzero correction to the lowest order gravity-wave dispersion relation.
Abstract
Comparisons of horizontal wind component measurements from a rawinsonde and a UHF wind profiler radar, obtained twice daily over a period of nearly 2 years (from mid-January 1984 through October 1985), showed differences with a standard deviation of about 2.5 m s−1, mainly due to meteorological variability in the winds.
Abstract
Comparisons of horizontal wind component measurements from a rawinsonde and a UHF wind profiler radar, obtained twice daily over a period of nearly 2 years (from mid-January 1984 through October 1985), showed differences with a standard deviation of about 2.5 m s−1, mainly due to meteorological variability in the winds.
Abstract
In a previous paper (Weber and Barrick, 1977), a generalization of Stokes’ perturbational technique permitted us to obtain solutions to higher orders for gravity-wave parameters for an arbitrary, two-dimensional periodic surface. In particular, the second-order wave-height correction and the third-order dispersion relation correction were derived there. In this paper, we interpret and apply those solutions in a variety of ways. First of all, we interpret the dispersion relation (and its higher order corrections) physically, as they relate to the phase velocity of individual ocean wave trains. Second, the validity of the two results derived previously is established by comparisons in the appropriate limiting cases with classical results available from the literature. It is shown how the solutions—derived for periodic surface profiles—can be generalized to include random wave fields whose average properties are to be specified. Then a number of examples of averaged higher order wave parameters, are given, and in certain cases a Phillips’ one-dimensional wave-height spectral model is employed to yield a quantitative feel for the magnitudes of these higher order effects. Both the derivations and the examples have direct application to the sea echo observed with high-frequency radars, and relationships with the radar observables are established and discussed.
Abstract
In a previous paper (Weber and Barrick, 1977), a generalization of Stokes’ perturbational technique permitted us to obtain solutions to higher orders for gravity-wave parameters for an arbitrary, two-dimensional periodic surface. In particular, the second-order wave-height correction and the third-order dispersion relation correction were derived there. In this paper, we interpret and apply those solutions in a variety of ways. First of all, we interpret the dispersion relation (and its higher order corrections) physically, as they relate to the phase velocity of individual ocean wave trains. Second, the validity of the two results derived previously is established by comparisons in the appropriate limiting cases with classical results available from the literature. It is shown how the solutions—derived for periodic surface profiles—can be generalized to include random wave fields whose average properties are to be specified. Then a number of examples of averaged higher order wave parameters, are given, and in certain cases a Phillips’ one-dimensional wave-height spectral model is employed to yield a quantitative feel for the magnitudes of these higher order effects. Both the derivations and the examples have direct application to the sea echo observed with high-frequency radars, and relationships with the radar observables are established and discussed.
Abstract
The distribution of backscattered power was computed for three wind profilers in the Colorado network that operated at 50,405, and 915 MHz. Since the backscattered power is a function of fluctuations in the refractivity index, this power distribution also gives the relative distribution of C 2 n . Similar distributions were found for all three frequencies in the lower troposphere where the atmosphere is often well mixed. But near and above the tropopause the distributions for the three frequencies different, probably because they responded to different processes in the atmosphere.
Abstract
The distribution of backscattered power was computed for three wind profilers in the Colorado network that operated at 50,405, and 915 MHz. Since the backscattered power is a function of fluctuations in the refractivity index, this power distribution also gives the relative distribution of C 2 n . Similar distributions were found for all three frequencies in the lower troposphere where the atmosphere is often well mixed. But near and above the tropopause the distributions for the three frequencies different, probably because they responded to different processes in the atmosphere.
Abstract
The effects of spatial, combined spatial and temporal sampling errors, and wind measurement errors on profiler-derived divergence estimates computed using the linear vector point function method are examined. Analysis indicates that divergence errors are minimized when the ratio between the spacing of the profilers and the sampled wavelength (Δx/Lx ) is between 0.15 and 0.24 and the ratio between the profiler sampling time to the timescale of the weather system (Δt/T) is less than 0.055.
When Δx/Lx ≤ 0.24, synoptic-scale divergence smaller than ±1.0 × 10−5 s−1 cannot be measured, because the error in the profiler wind estimates is larger than the horizontal velocity gradients. The expected errors in divergence calculations given typical profiler spatial and temporal sampling strategies are examined.
Abstract
The effects of spatial, combined spatial and temporal sampling errors, and wind measurement errors on profiler-derived divergence estimates computed using the linear vector point function method are examined. Analysis indicates that divergence errors are minimized when the ratio between the spacing of the profilers and the sampled wavelength (Δx/Lx ) is between 0.15 and 0.24 and the ratio between the profiler sampling time to the timescale of the weather system (Δt/T) is less than 0.055.
When Δx/Lx ≤ 0.24, synoptic-scale divergence smaller than ±1.0 × 10−5 s−1 cannot be measured, because the error in the profiler wind estimates is larger than the horizontal velocity gradients. The expected errors in divergence calculations given typical profiler spatial and temporal sampling strategies are examined.
Abstract
A new method for estimating winds and radio acoustic sounding system temperatures from radar Doppler measurements for the new NOAA wind profilers is described. This method emphasizes the quality of 6-min measurements prior to the computation of hourly averages. Compared with the older method currently being used, this new method provides measurements exhibiting better consistency and more complete coverage over height and time. Furthermore, it corrects aliased measurements.
Abstract
A new method for estimating winds and radio acoustic sounding system temperatures from radar Doppler measurements for the new NOAA wind profilers is described. This method emphasizes the quality of 6-min measurements prior to the computation of hourly averages. Compared with the older method currently being used, this new method provides measurements exhibiting better consistency and more complete coverage over height and time. Furthermore, it corrects aliased measurements.
Abstract
We computed the monthly average backscattered power over a five-year period for the Fleming 50 MHz wind profiler, which is proportional to CN 2. We found that in addition to seasonal cycle in CN 2 below the tropopause, there was a year-to-year variation as well. Above the tropopause, the seasonal variations were almost gone; however, there were significant changes with periods longer than one year. We examined a shorter back-scattered power record from the Stapleton wind profiler and found similar longer-term trends. These long-term trends will affect the performance of wind profilers.
Abstract
We computed the monthly average backscattered power over a five-year period for the Fleming 50 MHz wind profiler, which is proportional to CN 2. We found that in addition to seasonal cycle in CN 2 below the tropopause, there was a year-to-year variation as well. Above the tropopause, the seasonal variations were almost gone; however, there were significant changes with periods longer than one year. We examined a shorter back-scattered power record from the Stapleton wind profiler and found similar longer-term trends. These long-term trends will affect the performance of wind profilers.
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 that these temperature measurements be made simultaneously with vertical velocity measurements so that valid vertical velocity corrections can be made.
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 that these temperature measurements be made simultaneously with vertical velocity measurements so that valid vertical velocity corrections can be made.
Abstract
A study was undertaken to review international literature pertaining to people’s behavior in and around floodwater. The review focused on people’s voluntary entry of floodwater. From the literature, five predominant reasons for entering floodwater were identified, including undertaking a recreational activity; attempting to reach a destination; retrieving property, livestock, or pets; undertaking employment duties; and rescuing or assisting with evacuation. Two primary influences on entering floodwater were found, namely risk perception (i.e., being unaware of or underestimating the risk from flooding) and social influences (i.e., being influenced by others). Demographics and environmental and temporal factors also played a part in decision-making about whether to enter floodwater or not. Emergency managers should take account of such factors when devising future public education strategies. Further research, including comparisons with current theoretical models, could help identify additional influences on decision-making for floodwater entry.
Abstract
A study was undertaken to review international literature pertaining to people’s behavior in and around floodwater. The review focused on people’s voluntary entry of floodwater. From the literature, five predominant reasons for entering floodwater were identified, including undertaking a recreational activity; attempting to reach a destination; retrieving property, livestock, or pets; undertaking employment duties; and rescuing or assisting with evacuation. Two primary influences on entering floodwater were found, namely risk perception (i.e., being unaware of or underestimating the risk from flooding) and social influences (i.e., being influenced by others). Demographics and environmental and temporal factors also played a part in decision-making about whether to enter floodwater or not. Emergency managers should take account of such factors when devising future public education strategies. Further research, including comparisons with current theoretical models, could help identify additional influences on decision-making for floodwater entry.
Abstract
The maximum height performance of the 50, 405 nd 915 MHz Colorado wind profiles is computed from the wind profiler database. Results show that even though the 50 MHz profiler has the largest seasonal variation in the maximum height coverage, it also has the greatest height coverage. In addition, it also has a greater increase in height for the same increase in sensitivity. On the basis of thew measurements we predict the height coverage of the 405 MHz wind profiler for the proposed wind profiler network.
Abstract
The maximum height performance of the 50, 405 nd 915 MHz Colorado wind profiles is computed from the wind profiler database. Results show that even though the 50 MHz profiler has the largest seasonal variation in the maximum height coverage, it also has the greatest height coverage. In addition, it also has a greater increase in height for the same increase in sensitivity. On the basis of thew measurements we predict the height coverage of the 405 MHz wind profiler for the proposed wind profiler network.
