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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
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
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.
Abstract
Radar wind profilers (RWPs) sense the mean and turbulent motion of the clear air through Doppler shifts induced along several (3–5) upward-looking beams. RWP signals, like all radars signals, are often contaminated. The contamination is clearly evident in the associated Doppler spectra, and automatic routines designed to extract meteorological quantities from these spectra often yield inaccurate results. Much of the observed contamination is due to an aliasing of higher frequency signals into the clear-air portion of the spectrum and a broadening of the spectral contaminants caused by the relatively short time series used to generate Doppler spectra. In the past, this source of contamination could not be avoided because of limitations on the size and speed of RWP processing computers. Today’s computers, however, are able to process larger amounts of data at greatly increased speeds. Here it is shown how standard and well-known spectral processing methods can be applied to significantly longer time series to reduce contamination in the radar spectra and thereby improve the accuracy and the reliability of meteorological products derived from RWP systems. In particular, spectral processing methods to identify and remove contamination that is often aliased into the clear-air portion of the spectrum are considered. Optimal techniques for combining multiple spectra to produce averaged spectra are also discussed.
Abstract
Radar wind profilers (RWPs) sense the mean and turbulent motion of the clear air through Doppler shifts induced along several (3–5) upward-looking beams. RWP signals, like all radars signals, are often contaminated. The contamination is clearly evident in the associated Doppler spectra, and automatic routines designed to extract meteorological quantities from these spectra often yield inaccurate results. Much of the observed contamination is due to an aliasing of higher frequency signals into the clear-air portion of the spectrum and a broadening of the spectral contaminants caused by the relatively short time series used to generate Doppler spectra. In the past, this source of contamination could not be avoided because of limitations on the size and speed of RWP processing computers. Today’s computers, however, are able to process larger amounts of data at greatly increased speeds. Here it is shown how standard and well-known spectral processing methods can be applied to significantly longer time series to reduce contamination in the radar spectra and thereby improve the accuracy and the reliability of meteorological products derived from RWP systems. In particular, spectral processing methods to identify and remove contamination that is often aliased into the clear-air portion of the spectrum are considered. Optimal techniques for combining multiple spectra to produce averaged spectra are also discussed.
Abstract
Through the integrated analysis of remote sensing and in situ data taken along the Front Range of Colorado, this study describes the interactions that occurred between a leeside arctic front and topographically modulated flows. These interactions resulted in nonclassical frontal behavior and structure across northeastern Colorado. The shallow arctic front initially advanced southwestward toward the Front Range foothills, before retreating eastward. Then, a secondary surge of arctic air migrated westward into the foothills. During its initial southwestward advance, the front exhibited obstacle-like, density-current characteristics. Its initial advance was interrupted by strong downslope northwesterly flow associated with a high-amplitude mountain wave downstream of the Continental Divide, and by a temporal decrease in the density contrast across the front due to diurnal heating in the cold air and weak cold advection in the warm air. The direction and depth of flow within the arctic air also influenced the frontal propagation.
The shallow, obstacle-like front actively generated both vertically propagating and vertically trapped gravity waves as it advanced into the downslope northwesterly flow, resulting in midtropospheric lenticular wave clouds aloft that tracked with the front. Because the front entered a region where strong downslope winds and mountain waves extended downstream over the high plains, the wave field in northeastern Colorado included both frontally forced and true mountain-forced gravity waves. A sequence of Scorer parameter profiles calculated from hourly observations reveals a sharp contrast between the prefrontal and postfrontal wave environments. Consequently, analytic resonant wave mode calculations based on the Scorer parameter profiles reveal that the waves supported in the postfrontal regime differed markedly from those supported in the prefrontal environment. This result is consistent with wind profiler observations that showed the amplitude of vertical motions decreasing substantially through 16 km above mean sea level (MSL) after the shallow frontal passage.
Abstract
Through the integrated analysis of remote sensing and in situ data taken along the Front Range of Colorado, this study describes the interactions that occurred between a leeside arctic front and topographically modulated flows. These interactions resulted in nonclassical frontal behavior and structure across northeastern Colorado. The shallow arctic front initially advanced southwestward toward the Front Range foothills, before retreating eastward. Then, a secondary surge of arctic air migrated westward into the foothills. During its initial southwestward advance, the front exhibited obstacle-like, density-current characteristics. Its initial advance was interrupted by strong downslope northwesterly flow associated with a high-amplitude mountain wave downstream of the Continental Divide, and by a temporal decrease in the density contrast across the front due to diurnal heating in the cold air and weak cold advection in the warm air. The direction and depth of flow within the arctic air also influenced the frontal propagation.
The shallow, obstacle-like front actively generated both vertically propagating and vertically trapped gravity waves as it advanced into the downslope northwesterly flow, resulting in midtropospheric lenticular wave clouds aloft that tracked with the front. Because the front entered a region where strong downslope winds and mountain waves extended downstream over the high plains, the wave field in northeastern Colorado included both frontally forced and true mountain-forced gravity waves. A sequence of Scorer parameter profiles calculated from hourly observations reveals a sharp contrast between the prefrontal and postfrontal wave environments. Consequently, analytic resonant wave mode calculations based on the Scorer parameter profiles reveal that the waves supported in the postfrontal regime differed markedly from those supported in the prefrontal environment. This result is consistent with wind profiler observations that showed the amplitude of vertical motions decreasing substantially through 16 km above mean sea level (MSL) after the shallow frontal passage.
Abstract
An algorithm to compute the magnitude of humidity gradient profiles from the measurements of the zeroth, first, and second moments of wind profiling radar (WPR) Doppler spectra was developed and tested. The algorithm extends the National Oceanic and Atmospheric Administration (NOAA)/Environmental Technology Laboratory (ETL) Advanced Signal Processing System (SPS), which provides quality control of radar data in the spectral domain for wind profile retrievals, to include the retrieval of humidity gradient profiles. The algorithm uses a recently developed approximate formula for correcting Doppler spectral widths for the spatial and temporal filtering effects. Data collected by a 3-beam 915-MHz WPR onboard the NOAA research vessel Ronald H. Brown (RHB) and a 5-beam 449-MHz WPR developed at the ETL were used in this study. The two datasets cover vastly different atmospheric conditions, with the 915-MHz shipborne system probing the tropical ocean atmosphere and the 449-MHz WPR probing continental winter upslope icing storm in the Colorado Front Range. Vaisala radiosonde measurements of humidity and temperature profiles on board the RHB and the standard National Weather Service (NWS) radiosonde measurements at Stapleton, Colorado, were used for comparisons. The cases chosen represent typical atmospheric conditions and not special atmospheric situations. Results show that using SPS-obtained measurements of the zeroth, first, and second spectral moments provide radar-obtained humidity gradient profiles up to 3 km AGL.
Abstract
An algorithm to compute the magnitude of humidity gradient profiles from the measurements of the zeroth, first, and second moments of wind profiling radar (WPR) Doppler spectra was developed and tested. The algorithm extends the National Oceanic and Atmospheric Administration (NOAA)/Environmental Technology Laboratory (ETL) Advanced Signal Processing System (SPS), which provides quality control of radar data in the spectral domain for wind profile retrievals, to include the retrieval of humidity gradient profiles. The algorithm uses a recently developed approximate formula for correcting Doppler spectral widths for the spatial and temporal filtering effects. Data collected by a 3-beam 915-MHz WPR onboard the NOAA research vessel Ronald H. Brown (RHB) and a 5-beam 449-MHz WPR developed at the ETL were used in this study. The two datasets cover vastly different atmospheric conditions, with the 915-MHz shipborne system probing the tropical ocean atmosphere and the 449-MHz WPR probing continental winter upslope icing storm in the Colorado Front Range. Vaisala radiosonde measurements of humidity and temperature profiles on board the RHB and the standard National Weather Service (NWS) radiosonde measurements at Stapleton, Colorado, were used for comparisons. The cases chosen represent typical atmospheric conditions and not special atmospheric situations. Results show that using SPS-obtained measurements of the zeroth, first, and second spectral moments provide radar-obtained humidity gradient profiles up to 3 km AGL.
