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ROBERT L. SMITH and DAVID W. HOLMES

Abstract

The U.S. Weather Bureau has been experimenting with a radar operating on the Doppler principle to determine whether apparatus of this type would detect and uniquely identify tornadoes. The principles of Doppler radar as applied to meteorology and results of recent experiments with equipment of this type are discussed. Calculations of anomalous wind speeds of 206 m.p.h. in a funnel cloud and 94 m.p.h. in a dust devil are presented in detail. In addition, data have been gathered from squall lines and isolated thunderstorms. Recommendations are made for an optimum Doppler radar system for the detection of tornadoes.

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Christopher Daly, Jonathan W. Smith, Joseph I. Smith, and Robert B. McKane

Abstract

High-quality, daily meteorological data at high spatial resolution are essential for a variety of hydrologic and ecological modeling applications that support environmental risk assessments and decision making. This paper describes the development, application, and assessment of methods to construct daily high-resolution (∼50-m cell size) meteorological grids for the 2003 calendar year in the Upper South Santiam Watershed (USSW), a 500-km2 mountainous catchment draining the western slope of the Oregon Cascade Mountains. Elevations within the USSW ranged from 194 to 1650 m. Meteorological elements modeled were minimum and maximum temperature; total precipitation, rainfall, and snowfall; and solar radiation and radiation-adjusted maximum temperature. The Parameter–Elevation Regressions on Independent Slopes Model (PRISM) was used to interpolate minimum and maximum temperature and precipitation. The separation of precipitation into rainfall and snowfall components used a temperature-based regression function. Solar radiation was simulated with the Image-Processing Workbench. Radiation-based adjustments to maximum temperature employed equations developed from data in the nearby H. J. Andrews Experimental Forest. The restrictive terrain of the USSW promoted cold-air drainage and temperature inversions by reducing large-scale airflow. Inversions were prominent nearly all year for minimum temperature and were noticeable even for maximum temperature during the autumn and winter. Precipitation generally increased with elevation over the USSW. In 2003, precipitation was nearly always in the form of rain at the lowest elevations but was about 50% snow at the highest elevations. Solar radiation followed a complex pattern related to terrain slope, aspect, and position relative to other terrain features. Clear, sunny days with a large proportion of direct radiation exhibited the greatest contrast in radiation totals, whereas cloudy days with primarily diffuse radiation showed little contrast. Radiation-adjusted maximum temperatures showed similar patterns. The lack of a high-quality observed dataset was a major issue in the interpolation of precipitation and solar radiation. However, observed data available for the USSW were superior to those available for most mountainous regions in the western United States. In this sense, the methods and results presented here can inform others performing similar studies in other mountainous regions.

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Mark A. Donelan, Fred W. Dobson, Stuart D. Smith, and Robert J. Anderson

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Thomas M. Smith, Richard W. Reynolds, Robert E. Livezey, and Diane C. Stokes

Abstract

Studies of climate variability often rely on high quality sea surface temperature (SST) anomalies. Although the high-resolution National Centers for Environmental Prediction (formerly the National Meteorological Center) optimum interpolation (OI) SST analysis is satisfactory for these studies, the OI resolution cannot be maintained before November 1931 due to the lack of satellite data. Longer periods of SSTs have come from traditional analyses of in situ (ship and buoy) SST observations alone.

A new interpolation method is developed using spatial patterns from empirical orthogonal functions (E0Fs)—that is, a principal component analysis—to improve analyses of SST anomalies from 1950 to 1981. The method uses the more accurate OI analyses from 1982 to 1993 to produce the spatial EOFs. The dominant EOF modes (which correspond to the largest variance) are used as basis functions and are fit, in a least squares sense, to the in situ data to determine the time dependence of each mode. A complete field of SST anomalies is then reconstructed from these spatial and temporal modes. The use of EOF basis functions produces an improved in situ SST analysis that more realistically represents sparsely sampled, large-scale structures than traditional analyses.

The EOF reconstruction method is developed for the tropical Pacific for the period 1982–92 and compared to the OI. The method is then expanded to the globe and applied to a much longer period, 1950–92. The results show that the reconstructed fields generally have lower rms differences than the traditional in-situ-only analyses relative to the OI. In addition, the reconstructed fields were found to be smoother than the traditional analyses but with enhanced large-scale signals (e.g., ENSO). Regions where traditional analyses are adequate include some parts of the North Atlantic and the North Pacific, where in situ sampling is most dense. Although the shape of SST anomaly patterns can differ greatly between the reconstruction and traditional in situ analysis, area-averaged results from both analyses show similar anomalies.

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Mark A. Donelan, Fred W. Dobson, Stuart D. Smith, and Robert J. Anderson

Abstract

The aerodynamic roughness of the sea surface, z 0, is investigated using data from Lake Ontario, from the North Sea near the Dutch coast, and from an exposed site in the Atlantic Ocean off the coast of Nova Scotia. Scaling z 0 by rms wave height gives consistent results for all three datasets, except where wave heights in the Atlantic Ocean are dominated by swell. The normalized roughness depends strongly on wave age: younger waves (traveling slower than the wind) are rougher than mature waves. Alternatively, the roughness may be normalized using the friction velocity, u *, of the wind stress. Again, young waves are rougher than mature waves. This contradicts some recent deductions in the literature, but the contradiction arises from attempts to describe z 0 in laboratory tanks and in the field with a single simple parameterization. Here, it is demonstrated that laboratory waves are inappropriate for direct comparison with field data, being much smoother than their field equivalents. In the open ocean there is usually a mixture of swell and wind-driven sea, and more work is needed before the scaling of surface roughness in these complex conditions can be understood.

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Project ATMOSPHERE: AMS/NOAA 1991 Workshop for Teachers

This program was sponsored by the American Meteorological Society and funded by the National Oceanic and Atmospheric Administration with support from State University of New York, College at Brockport.

David R. Smith, Ira W. Geer, Robert S. Weinbeck, and Peter R. Chaston
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David R. Smith, Ira W. Geer, Robert S. Weinbeck, John T. Snow, and William H. Beasley

During the summer of 1993, Project ATMOSPHERE, in cooperation with the University of Oklahoma School of Meteorology, conducted a workshop to enhance both the meteorological background and leadership skills of AMS Atmospheric Education Resource Agents (AERAs). Fifty-eight teachers representing 39 states and the District of Columbia attended this workshop, which focused on atmospheric water processes and severe local storms. In addition to lectures and laboratory activities, AERAs also visited a variety of research and operational support facilities in the Norman area. This workshop was the third phase of training for AERAs, who represent the AMS in their local areas, providing instructional guidance for teachers and curricular input on the atmospheric sciences to their respective local and state educational agencies.

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Peter Black, Lee Harrison, Mark Beaubien, Robert Bluth, Roy Woods, Andrew Penny, Robert W. Smith, and James D. Doyle

Abstract

The High-Definition Sounding System (HDSS) is an automated system deploying the expendable digital dropsonde (XDD) designed to measure wind and pressure–temperature–humidity (PTH) profiles, and skin sea surface temperature (SST) within and around tropical cyclones (TCs) and other high-impact weather events needing high sampling density. Three experiments were conducted to validate the XDD.

On two successive days off the California coast, 10 XDDs and 14 Vaisala RD-94s were deployed from the navy’s Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft over offshore buoys. The Twin Otter made spiral descents from 4 km to 60 m at the same descent rate as the sondes. Differences between successive XDD and RD-94 profiles due to true meteorological variability were on the same order as the profile differences between the spirals, XDDs, and RD-94s. XDD SST measured via infrared microradiometer, referred to as infrared skin SST (SSTir), and surface wind measurements were within 0.5°C and 1.5 m s−1, respectively, of buoy and Twin Otter values.

A NASA DC-8 flight launched six XDDs from 12 km between ex-TC Cosme and the Baja California coast. Repeatability was shown with good agreement between features in successive profiles. XDD SSTir measurements from 18° to 28°C and surface winds agreed well with drifting buoy- and satellite-derived estimates.

Excellent agreement was found between PTH and wind profiles measured by XDDs deployed from a NASA WB-57 at 18-km altitude offshore from the Texas coast and NWS radiosonde profiles from Brownsville and Corpus Christi, Texas. Successful XDD profiles were obtained in the clear and within precipitation over an offshore squall line.

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James A. Brey, Elizabeth W. Mills, Ira W. Geer, Robert S. Weinbeck, Kira A. Nugnes, Katie L. O’Neill, Bernard A. Blair, David R. Smith, and Edward J. Hopkins
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Roy W. Spencer, Robbie E. Hood, Frank J. Lafontaine, Eric A. Smith, Robert Platt, Joe Galliano, Vanessa L. Griffin, and Elena Lobl

Abstract

An Advanced Microwave Precipitation Radiometer (AMPR) has been developed and flown in the NASA ER-2 high-altitude aircraft for imaging various atmospheric and surface processes, primarily the internal structure of rain clouds. The AMPR is a scanning four-frequency total power microwave radiometer that is externally calibrated with high-emissivity warm and cold loads. Separate antenna systems allow the sampling of the 10.7- and 19.35-GHz channels at the same spatial resolution, while the 37.1- and 85.5-GHz channels utilize the same multifrequency feedhorn as the 19.35-GHz channel. Spatial resolutions from an aircraft altitude of 20-km range from 0.6 km at 85.5 GHz to 2.8 km at 19.35 and 10.7 GHz. All channels are sampled every 0.6 km in both along-track and cross-track directions, leading to a contiguous sampling pattern ofthe 85.5-GHz 3-dB beamwidth footprints, 2.3 × oversampling of the 37.1-GHz data, and 4.4 × oversampling of the 19.35- and 10.7-GHz data. Radiometer temperature sensitivities range from 0.2° to 0.5°C. Details of the system are described, including two different calibration systems and their effect on the data collected. Examples of oceanic rain systems are presented from Florida and the tropical west Pacific that illustrate the wide variety of cloud water, rainwater, and precipitation-size ice combinations that are observable from aircraft altitudes.

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