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Michael D. Eilts and Steven D. Smith

Abstract

A Doppler velocity dealiasing algorithm is described that processes one radial at a time by comparing that radial with a previous radial. This technique has worked reliably on numerous Doppler radar datasets for clear air, thunderstorm, and severe thunderstorm situations. It was also tested on four volume mans from severe weather environments with difficult aliasing problems to determine statistically how well the algorithm performs in a worst case environment. Of some 1.2 million velocities in these severe storms, 0.2% were improperly dealiased, and 93% of those were above 13 km height in the storm-top divergent region where shears were extreme. Every tornado, mesocyclone, gust front, microburst, and storm-top divergent signature was preserved, and could be readily discerned by human analyst. No adverse impact was observed on the signature and automated signature detection algorithms would therefore be freed from contamination by velocity aliasing. The velocity dealiasing algorithms described is adaptive and therefore efficient because simple cheeks are made initially, and progressively more sophisticated and time-consuming checks are used only if they are needed.

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Steven D. Smith and Robert M. Rabin

Abstract

Applications of Doppler weather radar data to the analysis of wind fields are reviewed. Radial velocity measurements from a single radar are used to estimate horizontal wind vectors within small azimuthal sectors using two different models. One assumes a uniform wind, the other a linear wind within the sector. Errors in wind estimates owing to gradients of wind are derived using harmonic analysis. The radar data analysis techniques are tested on complex wind patterns which were reconstructed from dual-Doppler radar measurements.

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Steven D. Smith and Robert M. Rabin

Abstract

An analysis technique to derive wind field parameters from single-Doppler velocity measurements, known as Modified Velocity-Volume Processing (MVVP) is examined from both theoretical and operational perspectives. For this technique, radar data within limited spatial volumes are fit to a model which usually assumes linearity of the Cartesian wind components. The accuracies and limitations of this technique are illustrated with examples from a case study of a severe storm outbreak in central Oklahoma on 17 May 1981. Implications for use of the MVVP in convective storm forecasting are considered.

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Steven A. Ackerman, W. L. Smith, H. E. Revercomb, and J. D. Spinhirne

Abstract

Lidar and high spectral resolution infrared radiance observations taken on board the ER-2 on 28 October 1986 are used to study the radiative properties of cirrus cloud in the 8–12 μm window region. Measurements from the High-spectral resolution Interferometer Sounder (HIS) indicate that the spectral variation of the equivalent blackbody temperature across the window can be greater than 5°C for a given cirrus cloud. This difference is attributed to the presence of small particles.

A method for detecting cirrus clouds using 8 μm, 11 μm, and 12 μm bands is presented. The 8 μm band is centered on a weak water-vapor absorption line while the 11 μm and 12 μm bands are between absorption lines. The brightness temperature difference between the 8 and 11 μm bands is negative for clear regions, while for ice clouds it is positive. Differences in the 11 and 12 μm channels are positive, whether viewing a cirrus cloud or a clear region. Inclusion of the 8 μm channel therefore removes the ambiguity associated with the use of 11 and 12 μm channels alone. The method is based on the comparison of brightness temperatures observed in these three channels.

The HIS and lidar observations were combined to derive the spectral effective beam emissivity (ε) of the cirrus clouds. Fifty percent of clouds on this day displayed a spectral variation of ε from 2–10%. These differences, in conjunction with large differences in the HIS observed brightness temperatures, indicate that cirrus clouds cannot be considered gray in the 8–12 μm window region.

The derived spectral transmittance of the cloud is used to infer the effective radii of the particle size distribution, assuming ice spheres. For 28 October 1986 the effective radius of cirrus cloud particle size distribution (r eff) was generally within the 30–40 μm range with 8% of the cases where 10 < r eff < 30 μm and 12% of the cases corresponding to r ref > 40 μm.

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Xiaoqian Zhang, David C. Smith IV, Steven F. DiMarco, and Robert D. Hetland

Abstract

Near the vicinity of 30° latitude, the coincidence of the period of sea breeze and the inertial period of the ocean leads to a maximum near-inertial ocean response to sea breeze. This produces a propagating inertial internal (Poincare) wave response that transfers energy laterally away from the coast and provides significant vertical mixing. In this paper, the latitudinal dependence of this wave propagation and its associated vertical mixing are investigated primarily using a nonlinear numerical ocean model. Three-dimensional idealized simulations show that the coastal oceanic response to sea breeze is trapped poleward of 30° latitude; however, it can propagate offshore as Poincare waves equatorward of 30° latitude. Near 30° latitude, the maximum oceanic response to sea breeze moves offshore slowly because of the near-zero group speed of Poincare waves at this latitude. The lateral energy flux convergence plus the energy input from the wind is maximum near the critical latitude, leading to increased local dissipation by vertical mixing. This local dissipation is greatly reduced at other latitudes. The implications of these results for the Gulf of Mexico (GOM) at ∼30°N is considered. Simulations with realistic bathymetry of the GOM confirm that a basinwide ocean response to coastal sea-breeze forcing is established in form of Poincare waves. Enhanced vertical mixing by the sea breeze is shown on the model northern shelf, consistent with observations on the Texas–Louisiana shelf. Comparison of the three-dimensional and one-dimensional models shows some significant limitations of one-dimensional simplified models for sea-breeze simulations near the critical latitude.

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Ronald B. Smith, Steven Skubis, James D. Doyle, Adrian S. Broad, Christoph Kiemle, and Hans Volkert

Abstract

A stationary mountain wave, embedded in southwesterly flow over Mont Blanc in the Alps, was observed simultaneously by three research aircraft and three types of remote sensing: GPS dropsondes, airborne light detecting and ranging (lidar), and rapid-scan satellite imagery. These observations provide a basis for testing linear and nonlinear theories of how mountain waves over complex terrain are controlled by the ambient wind profile, especially the effects of a low-level stagnant layer and the jet stream aloft. The layer of blocked flow near the ground reduced the amplitude of the wave generation. The strong wind and weak stability in the upper troposphere forced the wave into a decaying “evanescent” state. In spite of this evanescent condition, no lee waves were observed. The authors resolve this paradox by demonstrating that the stagnant layer below 3 km played an additional role. It was able to absorb downward reflected waves, preventing the formation of a resonant cavity. Linear theory, including this low-level absorption, predicts the observed wave structure quite well and captures the wave absorption process found in the fully nonlinear Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) model. In spite of wave decay through the upper troposphere, there is evidence from satellite images and model simulation that the waves reached the uppermost troposphere.

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Laurie G. Hermes, Arthur Witt, Steven D. Smith, Diana Klingle-Wilson, Dale Morris, Gregory J. Stumpf, and Michael D. Eilts

Abstract

The Federal Aviation Administration's Terminal Doppler Weather Radar (TDWR) system was primarily designed to address the operational needs of pilots in the avoidance of low-altitude wind shears upon takeoff and landing at airports. One of the primary methods of wind-shear detection for the TDWR system is the gust-front detection algorithm. The algorithm is designed to detect gust fronts that produce a wind-shear hazard and/or sustained wind shifts. It serves the hazard warning function by providing an estimate of the wind-speed gain for aircraft penetrating the gust front. The gust-front detection and wind-shift algorithms together serve a planning function by providing forecasted gust-front locations and estimates of the horizontal wind vector behind the front, respectively. This information is used by air traffic managers to determine arrival and departure runway configurations and aircraft movements to minimize the impact of wind shifts on airport capacity.

This paper describes the gust-front detection and wind-shift algorithms to be fielded in the initial TDWR systems. Results of a quantitative performance evaluation using Doppler radar data collected during TDWR operational demonstrations at the Denver, Kansas City, and Orlando airports are presented. The algorithms were found to be operationally useful by the FAA airport controllers and supervisors.

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Reed M. Maxwell, Julie K. Lundquist, Jeffrey D. Mirocha, Steven G. Smith, Carol S. Woodward, and Andrew F. B. Tompson

Abstract

Complete models of the hydrologic cycle have gained recent attention as research has shown interdependence between the coupled land and energy balance of the subsurface, land surface, and lower atmosphere. PF.WRF is a new model that is a combination of the Weather Research and Forecasting (WRF) atmospheric model and a parallel hydrology model (ParFlow) that fully integrates three-dimensional, variably saturated subsurface flow with overland flow. These models are coupled in an explicit, operator-splitting manner via the Noah land surface model (LSM). Here, the coupled model formulation and equations are presented and a balance of water between the subsurface, land surface, and atmosphere is verified. The improvement in important physical processes afforded by the coupled model using a number of semi-idealized simulations over the Little Washita watershed in the southern Great Plains is demonstrated. These simulations are initialized with a set of offline spinups to achieve a balanced state of initial conditions. To quantify the significance of subsurface physics, compared with other physical processes calculated in WRF, these simulations are carried out with two different surface spinups and three different microphysics parameterizations in WRF. These simulations illustrate enhancements to coupled model physics for two applications: water resources and wind-energy forecasting. For the water resources example, it is demonstrated how PF.WRF simulates explicit rainfall and water storage within the basin and runoff. Then the hydrographs predicted by different microphysics schemes within WRF are compared. Because soil moisture is expected to impact boundary layer winds, the applicability of the model to wind-energy applications is demonstrated by using PF.WRF and WRF simulations to provide estimates of wind and wind shear that are useful indicators of wind-power output.

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Xiaoqian Zhang, Steven F. DiMarco, David C. Smith IV, Matthew K. Howard, Ann E. Jochens, and Robert D. Hetland

Abstract

The spatial structure and temporal characteristics of sea breeze and the associated coastal ocean response in the northwest Gulf of Mexico are investigated using moored instruments, hydrographic stations, and wind measurements. Near the study area of 30°N, motions in the diurnal–inertial band (DIB) may be significantly enhanced by a near-resonant condition between local inertial and diurnal forcing frequencies. Wavelet analysis is used to quantify the results. Results indicate that diurnal sea-breeze variability peaks in summer and extends at least 300 km offshore with continuous seaward phase propagation. The maximum DIB oceanic response occurs in June when there is a shallow mixed layer, strong stratification, and an approximately 10-day period of continuous sea-breeze forcing. DIB current variance decreases in July and August as the consequence of the deepening of the mixed layer and a more variable phase relationship between the wind and current. River discharge varies interannually and can significantly alter the oceanic response during summer. The “great flood” of the Mississippi River in 1993 deepened the summer mixed layer and reduced the sea-breeze response during that year. Vertically, DIB currents are surface intensified, with a first baroclinic modal structure. The significance of these DIB motions on the shelf is that they can provide considerable vertical mixing in summer, as seen by the suppression of the bulk Richardson number (by a factor of 30) during strong DIB events. This provides a potential mechanism to ventilate seasonally occurring near-bottom hypoxic waters of the coastal ocean.

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James E. Hocker, Andrea D. Melvin, Kevin A. Kloesel, Christopher A. Fiebrich, Robert W. Hill, Richard D. Smith, and Steven F. Piltz

Abstract

Since 1997, the Oklahoma Mesonet (the state’s automated mesoscale weather station network) has served a community of more than 1,400 public safety officials (emergency managers, fire officials, law enforcement, etc.) across Oklahoma through a weather data and training program called Oklahoma’s First-Response Information Resource System using Telecommunications (OK-First). OK-First provides free weather and radar data interpretation classes to eligible public safety officials and, following successful completion of training, password-protected access to weather data tools including a website and software. The objective of OK-First when it began was to fill significant gaps in weather product training and data access for Oklahoma’s public safety community. Though the core mission remains the same 20 years later, many aspects of OK-First have evolved over time, including participant membership, training curriculum, formats of training, training requirements, website and software technology, and program feedback. The purpose of this paper is to provide an update on the Mesonet’s OK-First program, with a particular focus on training, tools, and the impact it has had on the public safety community.

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