Showing papers on "Wind shear published in 1989"
TL;DR: In this paper, the effect of wind-generated, long gravity waves on the air flow was studied using the quasilinear theory of wind wave generation, which is an extension of the Miles' shear flow instability.
Abstract: In this paper we are concerned with the effect of wind-generated, long gravity waves on the air flow. We study this example of resonant wave-mean flow interaction using the quasilinear theory of wind-wave generation. This theory is an extension of the Miles' shear flow instability in that the effect of the gravity waves on the mean wind profile is taken into account as well. The direct effect of air turbulence on the mean wind profile is modeled by a mixing length model. We present results of the numerical calculation of the steady state wind profile for given wave spectra. Results are found to be sensitive for the parameterization of the high-frequency tail of the wave spectrum. Following a proposal by Snyder on the fetch or wave age dependence of the Phillips constant, a strong dependence of the drag of air flow over sea waves on the wave age is found. For young wind sea (small wave age) a strong coupling between wind and waves is found, whereas there is hardly no coupling for old wind sea. Thi...
572 citations
TL;DR: In this article, it was shown that sporadic-E is most likely due to a vertical shear in the horizontal east-west wind and this theory accounts for the detailed observations of the wind and electron density profiles.
427 citations
TL;DR: In this paper, a strictly two-dimensional cloud model was used to gauge the effect of vertical wind shear on the mature phase behavior of model-simulated multicellular storms, extending the previous work of the authors.
Abstract: A strictly two-dimensional cloud model was used to gauge the effect of vertical wind shear on the mature phase behavior of model-simulated multicellular storms, extending the previous work of the authors. We specifically examined the propagation speed, quasi-equilibrium behavior, storm scale and updraft orientation of the model storms as a function of shear intensity. We also considered the precipitation efficiencies of our. model storms and applied density current and Rotunno–Klemp–Weisman theories to our results. Our previous work revealed that model storms could achieve a mature phase consisting of repetitive multicellular development when certain numerical obstacles were overcome. This was referred to as a “quasi-equilibrium state.” We found herein that this state was also reached by model storms even when subjected to a very wide range of low-level wind shear intensities, although the temporal behavior during this stage was clearly dependent on the shear. We also found a very systematic rela...
111 citations
TL;DR: The SOUSY VHF (53.5 MHz) radar has been operated on a campaign basis on the island of Andoya in Northern Norway (69°17′N, 16°01′E), with the aim of investigating the backseattering structures and dynamics of the polar middle atmosphere, since November 1983 as mentioned in this paper.
Abstract: The mobile SOUSY VHF (53.5 MHz) Radar has been operated on a campaign basis on the island of Andoya in Northern Norway (69°17′N, 16°01′E), with the aim of investigating the backseattering structures and dynamics of the polar middle atmosphere, since November 1983. During winter the occurrence of mesospheric echoes at altitudes from 50 to 90 km is strongly correlated with radio wave absorption events measured with a riometer on 32.5 MHz. Individual structures are observed for up to 8 hours and, in general, appear as thin layers separated by 3–5 km, with typical maximum signal-to-noise ratios (SNRs) of 5–25 dB. Many of these are related to variations in the background wind produced by long-period gravity waves and tidal period motions and, in as much, are similar to mesospheric layers at middle and low latitudes. In summer the echo region is largely restricted to a height interval from 75 to 95 km, with 80% of the echoes occurring in the 80- to 93-km height range, and on average, it has a distinct maximum in SNR near 86 km. In the 83- to 91-km height region, echoes are detected almost continuously, with a minimum occurrence rate of 85%. There is a low correlation (∼0.26) between echo strength and absorption. Many of the weaker echoing regions, those with SNRs up to 30 dB, are related to the background wind shear. Spectral analysis of time series of both SNR and zonal velocity for a period of 9 days reveals 54-, 24-, 12-, and 8-hour components, with the 12-hour component dominating. Strong bursts in backscattered power tend to occur in the late afternoon and early morning hours, so they coincide with the time of maximum westward velocity of the semidiurnal tide. This suggests that the bursts are due to an increase in the turbulent intensity produced by dynamical instability of this mode. Layers consistent with dynamically unstable upward propagating inertio-gravity waves are also often observed to move down through the 93- to 80-km height range. Thus dynamical instability of the semidiurnal tide and long-period gravity waves appears to play a major role in determining much of the structure observed in the backscatter region. However, the strongest summer polar mesopause echoes, those with peak SNRs greater than 30 dB, while showing modulation due to the background winds, often show no clear relation to the background wind shear. This supports the view that the production mechanism of the very strong SNRs associated with this layer is different in character from that of winter echoes observed in the polar mesosphere by VHF radars, and to those mesospheric layers observed at mid-latitudes using the same technique.
104 citations
TL;DR: In this article, a long-lived mesoscale convectively generated vortex (MCV) associated with a convective complex (MCC) is documented, with a Rossby number of approximately 0.5, investigated as a feature intrinsic to the organization of the MCC.
Abstract: A long-lived mesoscale convectively-generated vortex (MCV) associated with a mesoscale convective complex (MCC) is documented. The MCV, with a Rossby number of approximately 0.5, is investigated as a feature intrinsic to the organization of the MCC. On 6–7 July 1982 a particularly large and intense MCC developed in a region of high convective available potential energy (CAPE) but weak vertical wind shear (bulk Richardson number ∼150), and weak advection of temperature and vorticity. Convection initially was organized in a narrow line with elements propagating relative to the mean environmental flow. These elements subsequently developed a large semicircular area of stratiform precipitation and a surface mesolow to the rear. Heavy rain fell over a broad area; amounts as great as 10.9 cm accompanied by flooding were reported in central Oklahoma. As the large semicircular rain area dissipated, a three layered structure became evident: a large upper tropospheric anticyclone, a rain cooled mesoscale h...
89 citations
TL;DR: In this paper, results from a computer simulation of wind flows around prismatic bodies using a k-ϵ model of turbulence are compared with full scale and wind tunnel tests done by others.
79 citations
TL;DR: In this article, the authors review the current knowledge of the turbulent structure of the upper part of the atmospheric boundary layer capped by a cloud deck, in the light of recent observations and model studies.
Abstract: Extended sheets of stratocumulus (Sc) in the upper part of the atmospheric boundary layer (ABL) often occur under appropriate meteorological conditions. These cloud decks are important both in climate studies and in weather forecasting. We review the current knowledge of the turbulent structure of the ABL capped by a cloud deck, in the light of recent observations and model studies. The most important physical processes determining this structure are longwave radiative cooling at cloud top, shortwave radiative wanning by absorption in the cloud, surface buoyancy flux, and wind shear in the ABL. As a result, turbulence can cause entrainment against the buoyancy jump at cloud top. In cases where only longwave radiative fluxes and surface buoyancy fluxes are important, the turbulent structure is relatively well understood. When shortwave radiative fluxes and/or wind shear are also important, the resulting turbulent structure may change considerably. A decoupling of the cloud from the sub-cloud layer or of the top of the cloud from the rest of the ABL is then regularly observed. In no cases are the details of the entrainment at cloud top understood well enough to derive a relatively simple formulation that is consistent with observations. Cloud-top entrainment instability may lead to the break-up of a cloud deck (but also to cloud deepening). The role of mesoscale circulations in determining fractional cloudiness is not yet well understood.
72 citations
TL;DR: In this paper, a second-moment turbulence-closure model was used to simulate nocturnal drainage flows observed during the 1984 ASCOT field expedition in Brush Creek, Colorado.
Abstract: A second-moment turbulence-closure model described in Yamada and Bunker is used to simulate nocturnal drainage flows observed during the 1984 ASCOT field expedition in Brush Creek, Colorado. In order to simulate the observed strong wind directional shear and temperature gradients, two modifications are added to the model. The strong wind directional shear was maintained by introducing a “nudging” term in the equation of motion to guide the modeled winds in the layers above the ridge top toward the observed wind direction. The second modification was accomplished by reformulating the conservation equation for the potential temperature in such a way that only the deviation from the horizontally averaged value was prognostically computed. The vegetation distribution used in this study is undoubtedly crude. Nevertheless, the present simulation suggests that tall tree canopy can play an important role in producing inhomogeneous wind distribution, particularly in the levels below the canopy top.
71 citations
TL;DR: In this paper, the authors used a 3D model to generate several convective clouds randomly inside the model domain, and then observed and analyzed the interactions and merging between the simulated clouds.
Abstract: Cumulus processes involved in the interaction and merging of clouds under the influence of different imposed conditions (including large-scale lifting forcing, environmental wind shear, and cloud microphysical processes) were studied using simulations with a three-dimensional model. The design of the study was to generate several convective clouds randomly inside the model domain, and then to observe and analyze the interactions and merging between the simulated clouds. Ten merged clouds were identified. Seven of these, each involving two previously separated clouds, generally lie along a line parallel to the initial environmental wind shear vector, while one (also a two-cloud system) lies along a line perpendicular to the wind shear vector prior to merging. The remaining two merging systems involve three parent clouds each; they are a combination of parallel and perpendicular cells. The merging mechanisms associated with three-cloud merging cases are studied by examining the temperature, pressure, and wind fields prior to, during, and following the merging.
66 citations
TL;DR: In this paper, the authors used a non-hydrostatic anelastic model to simulate dry and moist convection and the associated gravity wave fields from three-dimensional numerical simulations using a very similar environmental speed-shear case.
Abstract: Results are presented of thermally forced dry and moist convection and the associated gravity wave fields from three-dimensional numerical simulations using a non-hydrostatic anelastic model. This paper extends earlier two-dimensional simulations to include effects of the third spatial dimension employing a very similar environmental speed-shear case for the study. The present simulations produce scattered fair weather cumuli in agreement with observations. In many important respects, the physical response is quite similar to that obtained in the earlier two-dimensional calculations. The near-uniform surface sensible heat flux results in Rayleigh modes filling the convective boundary layer (CBL) to begin with, whereas later, after convective motions start interacting with the overlying stable layer, larger horizontal scale deep modes become evident and in some cases dominant. The eigenfunction structure of these dominant forced normal modes consists of boundary layer eddies in the lower levels and gravity waves above. They are important organizers of the cumulus convection. As in the earlier two-dimensional simulations, the efficiency of gravity wave excitation was found to be very sensitive to the mean wind shear in the region spanning the CBL and the overlying stable layer. The dominant horizontal wavelength in the shear direction ranges between 10 and 15 km in the free atmosphere whereas it peaks at about 6 km in the CBL.
The strong difference between the preferred directions of alignment for the eddies in the CBL (rolls aligned with the mean shear) and the overlying waves (aligned with lines of constant phase normal to the shear) results in overall broken conditions. The boundary layer motions are organized in broken ‘varicose-like’ rolls aligned approximately with the mean shear. The overlying waves show a somewhat more scattered pattern. This scattered-type dominant forced modal response combined with the nonlinear effect of the clouds themselves results in a cloud pattern revealing a high degree of randomness. This cloud field randomness occurs in spite of a near-zero horizontal wavenumber structure to the surface sensible heat flux.
Exchanges of momentum between convective and mean motions in the CBL result in strongly curved stress profiles and a mixing out of the initial boundary layer shear. Sensitivity tests were performed where the mixing of momentum was partially compensated by the addition of low-level pressure gradient terms.
64 citations
TL;DR: In this paper, a quasi-stationary gravity wave induced orographically by airflow over the island and mountains of Puerto Rico is interpreted as a manifestation of inertia-gravity waves having intrinsic periods comparable to the local inertial period, and the ellipticity of the Viated halograph is attributed to an effect of background wind shears.
Abstract: Vertically variable horizontal winds observd over Arecibo by to and Woodman, which were previously interpreted as a manifestation of inertia-gravity waves having intrinsic periods comparable to the local inertial period, are reinterpreted as quasi-stationary gravity waves of much shqrter intrinsic period, induced orographically by airflow over the island and mountains of Puerto Rico. The ellipticity of the Viated halograph is attributed to an effect of background wind shears in the presence of such waves. This new interpretation carries implicationsboth for the study of similar wind patterns elsewhere and for the reproducibility ofwind fields at Arecibo, where a natural laboratory for the study of mountain waves, of critical-layer interactions and of associated turbulence appears to be available.
TL;DR: In this paper, a case study of the ocean radar backscatter dependence on near-surface wind and wind stress is presented using the data obtained on February 18, 1986 during the Frontal Air-Sea Interaction Experiment.
Abstract: A case study of the ocean radar backscatter dependence on near-surface wind and wind stress is presented using the data obtained on February 18, 1986 during the Frontal Air-Sea Interaction Experiment. The particular wind-wave conditions and their variations across a sharp sea surface temperature front are described. The small change in wind speed across the front cannot account for the large change in wind stress implying significant changes in the drag coefficient and surface roughness length. The results strengthen the hypothesis that radar backscatter is closely correlated to wind stress, and therefore, could be used for remote sensing of the wind stress itself over the global oceans.
TL;DR: In this paper, a simple one-dimensional boundary layer model, which includes the effects of stably-stratified air overlying a sloping surface, is able to reproduce some of the features of the observed profiles.
Abstract: Wind and temperature profiles in the lowest 2000 m of the atmosphere at Halley (75°35′S, 26°50′W) have been analysed. Surface winds blow most frequently from the sector 090° ± 45° but the 2000 m wind direction is much more evenly distributed and appears to be determined by synoptic-scale pressure gradients. A simple one-dimensional boundary layer model, which includes the effects of stably-stratified air overlying a sloping surface, is able to reproduce some of the features of the observed profiles.
Patent•
13 Nov 1989
TL;DR: In this paper, an apparatus and a method for detecting and indicating severe weather conditions such as wind shear and clear air turbulence includes a sensor for detecting the weather parameter of air temperature differential and a computer for comparing the parameter value with a stored constant value.
Abstract: An apparatus and a method for detecting and indicating severe weather conditions such as wind shear and clear air turbulence includes a sensor for detecting the weather parameter of air temperature differential and a computer for comparing the parameter value with a stored constant value. The sensor can be an infrared scanner in an aircraft or on the ground. When the parameter value exceeds the constant value, a severe weather condition warning indication is generated by the computer as a visual and/or audio signal. The method and apparatus can also include sensor modules for detecting wind speed and direction, barometric pressure and air temperature to be compared by the computer. A steam generator can generate steam bubbles for detecting winds aloft with the infrared scanner or weather radar.
TL;DR: The spatial coherence of the fit of analyses to observation is used as the basis for new diagnostics of the performance of any linear objective analysis system, and it is shown that a practical analysis system is efficient if the data are fitted to within observational error, and is inefficient otherwise.
Abstract: We use the spatial coherence of the fit of analyses to observation as the basis for new diagnostics of the performance of any linear objective analysis system. The diagnostics provide answers to such questions as:
Up to now these questions could only be answered indirectly, by evaluation of the forecasts resulting from the analyses, or by study of the changes made by the initialisation. The lack of simple objective methods to address these questions has sometimes resulted in controversy about the interpretation of data impact studies. Suppose, in a practical analysis system, that the observation errors are uniform and uncorrelated, and the observations are homogeneously distributed. We show (for any practical linear analysis system) that if the Observation-minus-Analysis (OmA) auto-correlations are positive when extrapolated to zero separation, then the analysis has certainly not extracted all the information from the observations, and does not fit the data to within the observational error. If however the extrapolated OmA correlations are negative, then the analysis system does fit the data to within observational accuracy. If, in addition, the weights given to the observations in the analysis of the observed values are known, one can derive useful estimates of the analysis error at the observation points. This last result leads to an estimate of the effective data density. Along with the new verifications of mass and wind analyses, methods are developed to estimate the effectiveness with which data on mass-wind balance have been used. The results for practical analysis systems are used to interpret empirical determinations of the OmA auto-correlations in the ECMWF analysis system, for data with uncorrelated errors. We shall say that a practical analysis system is efficient if the data are fitted to within observational error, and is inefficient otherwise. The methods demonstrate that operational mid-tropospheric wind analyses over North America are quite efficient, but that the windshear and thickness analyses near the tropopause over North America are inefficient. The analysis of mass wind balance over North America is efficient for any single level, but the analysis of thermal wind balance for thin layers near the tropopause is inefficient, most notably on short horizontal scales. The analysis of the wind shear near the tropical tropopause is somewhat better than over North America, probably because of the use of sharper vertical structure functions.
TL;DR: In this article, three cases of squall lines composed of strong to severe thunderstorms that formed over Arizona, and Sonora (Mexico) on July, 16-17 and 17-18, 1984, and August 2-3, 1986, are examined.
Abstract: Three cases of squall lines composed of strong to severe thunderstorms that formed over Arizona, and Sonora (Mexico) on July, 16-17 and 17-18, 1984, and August 2-3, 1986, are examined. Data, which included satellite imagery, VISSR-derived fields, surface data, and records or cloud-to-ground lightning strikes, indicate that the initiation, growth, and dissipation of all three squall lines were very similar. Results indicate that these mesoscale convective systems developed in an environment of relatively strong low-level shear with very weak shear aloft and that they possessed almost all the properties of a typical tropical squall line.
TL;DR: In the case of warm air flowing over cold water, the boundary layer appears to develop an internal boundary layer (IBL) in response to the sudden change in the sea surface temperature as discussed by the authors.
Abstract: Aircraft observations obtained during the Frontal Air–Sea Interaction Experiment (FASINEX) are used to investigate the structure of the marine atmospheric boundary layer in the vicinity of an ocean front. A quasi-stationary sea surface temperature (SST) discontinuity of 2°C was maintained across the frontal zone throughout the duration of the experiment The primary response of the atmosphere to changes in the SST was observed in the surface-related turbulence fluxes. In the case of warm air flowing over cold water, the boundary layer appears to develop an internal boundary layer (IBL) in response to the sudden change in the sea surface temperature. The organized updrafts and downdrafts within this layer collapse with entrainment–detrainment processes in these cells dominating the turbulence statistics. The IBL grows in response to the wind shear in this layer, although the surface shear stress is much smaller on the colder side of the front than on the warm. The depth of the IBL, and, in the abse...
TL;DR: A nonhydrostatic numerical mesoscale model has been applied to the study of an Oklahoma squall line with initial conditions taken from the Oklahoma-Kansas Preliminary Regional Experiment for STORM-Central (PRE-STORM) data for 7 May 1985 as mentioned in this paper.
Abstract: A nonhydrostatic numerical mesoscale model has been applied to the study of an Oklahoma squall line with initial conditions taken from the Oklahoma–Kansas Preliminary Regional Experiment for STORM-Central (PRE-STORM) data for 7 May 1985. The model reproduced features typical of organized propagating convection occurring during spring and summer in this region, namely a squall line/mesoscale convective system containing strong right-flank convection resembling many documented cases. The alignment and motion of the system change during its development and are determined by the ambient wind at three levels, the steering level of the mature cells, the level of free convection, and the surface layer. Three persistent right-flank cells had a characteristic rightward propagation relative to the mean wind shear vector. Their propagation occurred through successive mergers of cells that had formed at a downdraft outflow convergence front and were similar to the flanking line often seen to the south of str...
TL;DR: In this paper, a statistical analysis of series of maximum annual wind speeds, classified according to type of storm and wind direction, furnishes evidence concerning the following: a) for each type and orientation, the type I probability distribution showed a better fit to the data than either the type II or Log Normal distributions, b) the parameters of the extreme wind distributions for the two storm types are significantly different from each other.
TL;DR: In this article, a low-power, portable, continuous-wave (CW), 3-cm Doppler radar was used to obtain wind spectra in tornadoes from a distance of less than 10 km.
Abstract: A severe-storm intercept field program was held in Oklahoma and nearby parts of Texas during the 1987–38 spring seasons. The purpose of the experiment was to use, for the first time, a low-power, portable, continuous-wave (CW), 3-cm Doppler radar to obtain wind spectra in tornadoes from a distance of less than 10 km. We discuss measurements of spectra we recorded in a tornado, a funnel cloud, and two wall clouds. Photographic documentation is also given to aid in the interpretation of our data. Wind speeds as high as 60 m s−1 were measured in the tornado. It was found that deploying the portable Doppler radar from a storm-intercept vehicle may increase substantially the number of measurements of wind speeds in tornadoes. The radar has recently been modified so that it has frequency modulation (FM) capability, and hence can obtain wind spectra within range bins. A plan is presented for using the radar to find the source of vorticity in tornadoes.
TL;DR: In this paper, the problem of fitting a second-order pressure surface to both wind and pressure observations, with the aid of a boundary-layer formulation, is solved by locally fitting the secondorder surface to the wind data.
Abstract: For oceanographie studies, a high resolution description of the wind field at the sea surface is required. In order to estimate the air-sea interaction fluxes correctly, it is important that the derived wind field has the characteristics of actual surface winds. Ship synoptic observations are at irregular positions, while applications require boundary conditions at a regular grid. The problem is solved by locally fitting a second-order pressure surface to both wind and pressure observations, with the aid of a boundary-layer formulation. The results show that fitting wind and pressure data together provides better spatial resolution than using wind or pressure data alone, because more information is available. Wind data provide at least the same accuracy and less bias than pressure data, tested against independent wind observations. Also a stability and wind-dependent boundary-layer formulation results in less bias than a constant one. For the ship synoptic data available via GTS for the North Atlantic Ocean, spatial resolution, as expressed by an equivalent filter half-width, is 220 km, considerably improved compared to typical data assimilation schemes used in numerical forecast models.
TL;DR: In this paper, the airflow over the Cape of Three Points (Gulf of Guinea: 4.5°N, 2°W) has been simulated using a three-dimensional mesoscale model in order to investigate the sea breeze developing in synoptic vertical wind shears during the 1979 dry season.
Abstract: The airflow over Cape of Three Points (Gulf of Guinea: 4.5°N, 2°W) has been simulated using a three-dimensional mesoscale model in order to investigate the sea breeze developing in synoptic vertical wind shears during the 1979 dry season. Two different meteorological situations, characterized by two contrasted wind profiles between 500 and 2000 m have been studied, with two types of transitions between the lower circulation (SW monsoon) and the upper African easterly jet (AEJ). The first one is a veering case (6 January) and the second is a backing case (23 January). Calculations of CAPE (convective available potential energy) show that whereas instability is a maximum at both sides of the cape, the site of enhanced convection is determined by the wind shear in the 500–2000 m layer. Numerical results confirm satellite observations.
TL;DR: In this article, the structure of atmospheric boundary layer turbulence on either side of a well-developed sea surface temperature front southwest of Bermuda was determined using fast response data taken aboard the National Oceanic and Atmospheric Administration WP3D aircraft.
Abstract: Fast response data taken aboard the National Oceanic and Atmospheric Administration WP-3D aircraft are used to determine the structure of atmospheric boundary layer turbulence on either side of a well-developed sea surface temperature front southwest of Bermuda. The data were taken on February 17, 1986, as part of the Frontal Air-Sea Interaction Experiment (FASINEX). A broad region of low-humidity air extending from 15 km to 35 km south of the front is probably due to the presence of a frontally induced secondary circulation. Evidence for a secondary flow is found in both the time series of atmospheric variables and the statistics obtained from conditionally sampled updrafts and downdrafts in the transect across the SST front. Larger sea-air temperature and humidity differences on the warm (south) side of the front give rise to surface layer sensible and latent heat and buoyancy fluxes that are larger than those on the cold side. Turbulence structure appears to be influenced as much by the presence of strong wind shear at the top of the boundary layer as by differing conditions at the surface on either side of the front. A larger rate of entrainment on the warm side of the front is indicated by the greater influence of low-momentum air from the overlying shear layer on updrafts in the upper part of the mixed layer, as well as the more frequent overturning of cool/moist updrafts and warm/dry downdrafts. It is conjectured that the larger entrainment rate is due to the interaction between the inversion layer and more energetic updrafts produced by greater surface forcing on the warm side of the front.
TL;DR: In this article, a boundary-layer solitary wave sensed with the National Severe Storms Laboratory's Doppler weather radar and a 444m-tall instrumented tower suggest that solitary and other nonlinear waves are a source of significant wind shear hazard to safe flight.
Abstract: Observations of a boundary-layer solitary wave sensed with the National Severe Storms Laboratory's Doppler weather radar and a 444-m-tall instrumented tower suggest that solitary and other nonlinear waves are a source of significant wind shear hazard to safe flight and thus should be studied both experimentally and theoretically. Wave transport of the horizontal momentum of the vertically sheared ambient air contributed much to the observed wind perturbations and horizontal wind shear. Observations are compared with, and shown to agree fairly closely with, the waveform predicted by steady state, weakly nonlinear, internal wave theory.
TL;DR: In this article, the authors compare Geosat altimeter estimates of wind speed and nearly coincident estimates from NOAA data buoys to determine whether altimeter algorithms can be improved by using more of the information available from altimetry.
Abstract: Wind blowing across the ocean surface generates small, centimeter scale roughness. The radar cross section (RCS) measured by spaceborne, nadir-looking altimeters operating at about 13.5 GHz is responsive to this roughness. Present altimeter algorithms use RCS to infer wind speed. We compare Geosat altimeter estimates of wind speed and nearly coincident estimates from NOAA data buoys to determine whether altimeter algorithms can be improved by using more of the information available from altimetry. We find that a marginal improvement in wind speed retrievals can be obtained by including additional RCS information and significant wave height in the retrieval algorithm. Perhaps most important, results also suggest that wind-wave growth is suppressed in the presence of preexisting ocean swell.
TL;DR: In this paper, a modified Kolmogorov-Smirnov (KS) test was used to ascertain the extent of Weibull behavior for perpetual January and July model runs.
Abstract: The frequency distribution of the surface wind speeds at each 4.5°×7.5° latitude-longitude grid point produced by the National Center for Atmospheric Research community climate model is examined. A modified Kolmogorov-Smirnov (KS) test was used to ascertain the extent of Weibull behavior for perpetual January and July model runs. The modified KS test has been applied to 400 days of both perpetual January and July model runs using a 0.5-day time sample. A global map of the KS statistic for each of the January and July control runs has been generated. These maps are presented for both the ocean and land wind fields. For the January oceanic winds, 29.2% of the frequency distributions were non-Weibull at the 95% confidence level. Over land, 35.4% of the wind speed frequency distributions were judged to be non-Weibull. For the July wind speed data, 32.7% of the ocean data sets were judged to be non-Weibull, while for winds over land, 30.2% were found to be non-Weibull. Large areas of Eurasia experience non-Weibull behavior during the January run. The main oceanic latitudinal zones associated with a non-Weibull character are from 5° to 30° in each hemisphere, a feature that is most evident in the July run. The monsoonal winds over the Indian Ocean are almost entirely Weibull. The non-Weibull character of surface wind field frequency distributions may explain, in part, the apparent inability of some surface wind data sets to drive an ocean circulation model through inexact wind forcing.
TL;DR: In this article, a data set on wind shear, consisting of 24 frequency distributions of changes in headwind speed experienced by aircraft during landing phase, is modelled parsimoniously by means of the hyperbolic distribution.
Abstract: A data set on wind shear, consisting of 24 frequency distributions of changes in headwind speed experienced by aircraft during landing phase, is modelled parsimoniously by means of the hyperbolic distribution.
TL;DR: In this article, the authors show that the radar brightness of the streaks is modulated by the proportion of sand cover, vegetation, and exposed substrate, all of which relate to the local wind regime.
Abstract: Shuttle imaging radar (SIR-A) coverage across Bolivia shows the major physiographic provinces, including the Andean Altiplano. The Altiplano contains a variety of eolian features, many of which are visible as radar-dark, radar-mottled, and radar-bright streaks aligned parallel to the prevailing winds. The streaks form downwind from hills and are as much as 15 km long and 800 m wide. Dark streaks originate between closely spaced hills, whereas bright streaks form in the immediate lee of hills. The radar brightness of the streaks is modulated by the proportion of sand cover, vegetation, and exposed substrate, all of which relate to the local wind regime. In the radar-dark streaks, vegetation is sparse and the sand is organized into dune forms, some of which can be recognized as barchan dunes on the radar image by outlining of the dark dune by bright substrate. Radar-mottled zones are covered by numerous 0.5-2-m-high coppice dunes, and in radarbright streaks, the sand forms flat sheets but also includes sand mounds and abundant vegetation. Measurements indicate that winds are strongest and most turbulent in the region of active sand sheets and dunes, inhibiting the growth of vegetation and the formation of mounds and resulting in a radar-dark zone. These results are consistent with previous studies that have demonstrated the existence of turbulent eddies in the wake of topographic obstacles that produce zones of increased surface wind shear and enhanced sand mobility. The relation between the radar signature and the wind regime allows inferences to be drawn for the wind regime from image interpretation.