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Thomas G. Konrad and John C. Howard

Abstract

An unusual case of multiple streamers or filaments with the characteristic mare's tail pattern in vertical section has been observed by radar where the generating elements were condensation trails laid by high-altitude aircraft. The contrails were laid perpendicular to the wind and as they drifted a multitude of streamers formed along each trail. The streamers extended from 9 km to the ground. Numerous contrails were observed, each of which produced a sheet of streamers. RHI and PPI photographs at X and S band taken over a 2-hr period show the three-dimensional shape of the streamers due to the wind shear. Doppler measurements were also taken. The resulting velocity spectra are very narrow indicating little or no turbulence. Reflectivity factors were measured at various altitudes and show a decrease in reflectivity with distance from the generating line. Fall velocities based on the slopes of the streamer patterns varied from 0.4 to 1.4 m sec−1. In general, the characteristics of the precipitation streamers were quite similar to those previously measured in naturally occurring cloud forms such as cirrus uncinus.

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John S. Irwin, William B. Petersen, and Steven C. Howard

Abstract

The observed scatter of observations about air quality model predictions stems from a combination of naturally occurring stochastic variations that are impossible for any model to simulate explicitly and variations arising from limitations in knowledge and from imperfect input data. In this paper, historical tracer experiments of atmospheric dispersion were analyzed to develop algorithms to characterize the observed stochastic variability in the ground-level crosswind concentration profile. The algorithms were incorporated into a Lagrangian puff model (“INPUFF”) so that the consequences of variability in the dispersion could be simulated using Monte Carlo methods. The variability in the plume trajectory was investigated in a preliminary sense by tracking the divergence in trajectories from releases adjacent to the actual release location. The variability in the near-centerline concentration values not described by the Gaussian crosswind profile was determined to be on the order of a factor of 2. The variability in the trajectory was determined as likely to be larger than the plume width, even with local wind observations for use in characterizing the transport. Two examples are provided to illustrate how estimates of variability 1) can provide useful information to inform decisions for emergency response and 2) can provide a basis for sound statistical designs for model performance assessments.

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Howard B. Bluestein, Andrew L. Pazmany, John C. Galloway, and Robert E. McIntosh

An experiment whose objective was to determine the wind and reflectivity substructure of severe convective storms is detailed. A 3-mm-wavelength (95 GHz) pulsed Doppler radar was installed in a van and operated in the Southern Plains of the United States during May and early June of 1993 and 1994. Using a narrow-beam antenna with computer-controlled scanning and positioning the van several kilometers from targets in severe thunderstorms, the authors were able to achieve 30-m spatial resolution and also obtain video documentation. A dual-polarization pulse-pair technique was used to realize a maximum unambiguous velocity of ±80 m s−1. Analyses of data collected in a mesocyclone near the intersection of two squall lines, in a low-precipitation storm, and in a hook echo in a supercell are discussed. A strategy to achieve 10-m spatial resolution and obtain analyses of the internal structure of tornadoes is proposed.

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Arthur Witt, Donald W. Burgess, Anton Seimon, John T. Allen, Jeffrey C. Snyder, and Howard B. Bluestein

Abstract

Rapid-scan radar observations of a supercell that produced near-record size hail in Oklahoma are examined. Data from the National Weather Radar Testbed Phased Array Radar (PAR) in Norman, Oklahoma, are used to study the overall character and evolution of the storm. Data from the nearby polarimetric KOUN WSR-88D and rapid-scanning X-band polarimetric (RaXPol) mobile radar are used to study the evolution of low- to midaltitude dual-polarization parameters above two locations where giant hailstones up to 16 cm in diameter were observed. The PAR observation of the supercell’s maximum storm-top divergent outflow is similar to the strongest previously documented value. The storm’s mesocyclone rotational velocity at midaltitudes reached a maximum that is more than double the median value for similar observations from other storms producing giant hail. For the two storm-relative areas where giant hail was observed, noteworthy findings include 1) the giant hail occurred outside the main precipitation core, in areas with low-altitude reflectivities of 40–50 dBZ; 2) the giant hail was associated with dual-polarization signatures consistent with past observations of large hail at 10-cm wavelength, namely, low Z DR, low ρ HV, and low K DP; 3) the giant hail fell along both the northeast and southwest edges of the primary updraft at ranges of 6–10 km from the updraft center; and 4) with the exception of one isolated report, the giant hail fell to the northeast and northwest of the large tornado and the parent mesocyclone.

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Howard B. Bluestein, Stephen G. Gaddy, David C. Dowell, Andrew L. Pazmany, John C. Galloway, Robert E. McIntosh, and Herbert Stein

Abstract

Counterrotating 500-m-scale vortices in the boundary layer are documented in the right-moving member of a splitting supercell thunderstorm in northeastern Oklahoma on 17 May 1995 during the Verification of the Origins of Rotation in Tornadoes Experiment. A description is given of these vortices based upon data collected at close range by a mobile, 3-mm wavelength (95 GHz), pulsed Doppler radar. The vortices are related to a storm-scale, pseudo-dual-Doppler analysis of airborne data collected by the Electra Doppler radar (ELDORA) using the fore–aft scanning technique and to a boresighted video of the cloud features with which the vortices were associated. The behavior of the storm is also documented from an analysis of WSR-88D Doppler radar data.

The counterrotating vortices, which were associated with nearly mirror image hook echoes in reflectivity, were separated by 1 km. The cyclonic member was associated with a cyclonically swirling cloud base. The vortices were located along the edge of a rear-flank downdraft gust front, southeast of a kink in the gust front boundary, a location previously found to be a secondary region for tornado formation. The kink was coincident with a notch in the radar echo reflectivity. A gust front located north of the kink, along the edge of the forward-flank downdraft, was characterized mainly by convergence and density current–like flow, while the rear-flank downdraft boundary was characterized mainly by cyclonic vorticity.

Previously documented vortices along gust fronts have had the same sense of rotation as the others in the group and are thought to have been associated with shearing instabilities. The symmetry of the two vortices suggests that they may have been formed through the tilting of ambient horizontal vorticity. Although the vortices did not develop into tornadoes, it is speculated that similar vortices could be the seeds from which some tornadoes form.

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William C. Macklin, Charles A. Knight, Howard E. Moore, Nancy C. Knight, Walter H. Pollock, John N. Carras, and Suszanne Thwaiters

Abstract

The deuterium, crystal and air bubble structures of 11 large hailstones from three severe storms have been examined. It is emphasized that there are a number of assumptions underlying the interpretation of such data and these are discussed. In seven of the hailstones the ambient temperatures at which they grew were inferred from the crystal size. The deuterium concentrations and ambient temperatures generally show similar variations and the crystal data thereby provide a useful way of placing an absolute temperature scale against the deuterium values. Throughout most of their growth, the hailstones grew in the updraft between about the ambient temperature levels of –17 to –30°C. The air bubble analyses showed that the hailstones grew near the wet growth limit or slightly wet and heat balance considerations give values of 2–3 g m−3 for the effective liquid water concentrations. On the assumption that the median volume radius of the cloud droplets is 10 µm, the actual liquid water concentrations are then about 4 to 5.5 g m−3.

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Andrew L. Pazmany, John C. Galloway, James B. Mead, Ivan Popstefanija, Robert E. McIntosh, and Howard W. Bluestein

Abstract

The Polarization Diversity Pulse-Pair (PDPP) technique can extend simultaneously the maximum unambiguous range and the maximum unambiguous velocity of a Doppler weather radar. This technique has been applied using a high-resolution 95-GHz radar to study the reflectivity and velocity structure in severe thunderstorms. This paper documents the technique, presents an analysis of the first two moments of the estimated mean velocity, and provides a comparison of the results with experimental data, including PDPP images of high-vorticity regions in supercell storms.

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James P. Kossin, John A. Knaff, Howard I. Berger, Derrick C. Herndon, Thomas A. Cram, Christopher S. Velden, Richard J. Murnane, and Jeffrey D. Hawkins

Abstract

New objective methods are introduced that use readily available data to estimate various aspects of the two-dimensional surface wind field structure in hurricanes. The methods correlate a variety of wind field metrics to combinations of storm intensity, storm position, storm age, and information derived from geostationary satellite infrared (IR) imagery. The first method estimates the radius of maximum wind (RMW) in special cases when a clear symmetric eye is identified in the IR imagery. The second method estimates RMW, and the additional critical wind radii of 34-, 50-, and 64-kt winds for the general case with no IR scene–type constraint. The third method estimates the entire two-dimensional surface wind field inside a storm-centered disk with a radius of 182 km. For each method, it is shown that the inclusion of infrared satellite data measurably reduces error. All of the methods can be transitioned to an operational setting or can be used as a postanalysis tool.

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Jesse E. Bell, Michael A. Palecki, C. Bruce Baker, William G. Collins, Jay H. Lawrimore, Ronald D. Leeper, Mark E. Hall, John Kochendorfer, Tilden P. Meyers, Tim Wilson, and Howard J. Diamond

Abstract

The U.S. Climate Reference Network (USCRN) is a network of climate-monitoring stations maintained and operated by the National Oceanic and Atmospheric Administration (NOAA) to provide climate-science-quality measurements of air temperature and precipitation. The stations in the network were designed to be extensible to other missions, and the National Integrated Drought Information System program determined that the USCRN could be augmented to provide observations that are more drought relevant. To increase the network’s capability of monitoring soil processes and drought, soil observations were added to USCRN instrumentation. In 2011, the USCRN team completed at each USCRN station in the conterminous United States the installation of triplicate-configuration soil moisture and soil temperature probes at five standards depths (5, 10, 20, 50, and 100 cm) as prescribed by the World Meteorological Organization; in addition, the project included the installation of a relative humidity sensor at each of the stations. Work is also under way to eventually install soil sensors at the expanding USCRN stations in Alaska. USCRN data are stewarded by the NOAA National Climatic Data Center, and instrument engineering and performance studies, installation, and maintenance are performed by the NOAA Atmospheric Turbulence and Diffusion Division. This article provides a technical description of the USCRN soil observations in the context of U.S. soil-climate–measurement efforts and discusses the advantage of the triple-redundancy approach applied by the USCRN.

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William P. Kustas, Martha C. Anderson, Joseph G. Alfieri, Kyle Knipper, Alfonso Torres-Rua, Christopher K. Parry, Hector Nieto, Nurit Agam, William A. White, Feng Gao, Lynn McKee, John H. Prueger, Lawrence E. Hipps, Sebastian Los, Maria Mar Alsina, Luis Sanchez, Brent Sams, Nick Dokoozlian, Mac McKee, Scott Jones, Yun Yang, Tiffany G. Wilson, Fangni Lei, Andrew McElrone, Josh L. Heitman, Adam M. Howard, Kirk Post, Forrest Melton, and Christopher Hain

Abstract

Particularly in light of California’s recent multiyear drought, there is a critical need for accurate and timely evapotranspiration (ET) and crop stress information to ensure long-term sustainability of high-value crops. Providing this information requires the development of tools applicable across the continuum from subfield scales to improve water management within individual fields up to watershed and regional scales to assess water resources at county and state levels. High-value perennial crops (vineyards and orchards) are major water users, and growers will need better tools to improve water-use efficiency to remain economically viable and sustainable during periods of prolonged drought. To develop these tools, government, university, and industry partners are evaluating a multiscale remote sensing–based modeling system for application over vineyards. During the 2013–17 growing seasons, the Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) project has collected micrometeorological and biophysical data within adjacent pinot noir vineyards in the Central Valley of California. Additionally, each year ground, airborne, and satellite remote sensing data were collected during intensive observation periods (IOPs) representing different vine phenological stages. An overview of the measurements and some initial results regarding the impact of vine canopy architecture on modeling ET and plant stress are presented here. Refinements to the ET modeling system based on GRAPEX are being implemented initially at the field scale for validation and then will be integrated into the regional modeling toolkit for large area assessment.

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