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  • Author or Editor: D. L. T. Anderson x
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E. E. Gossard, D. E. Wolfe, K. P. Moran, R. A. Paulus, K. D. Anderson, and L. T. Rogers

Abstract

An experiment comparing balloon and profiler observations was carried out to evaluate the capability of Doppler radar wind profilers to remotely measure useful meteorological quantities other than wind. The site chosen was in Southern California during a time of year when it offers a natural laboratory for investigating extreme contrasts in temperature and humidity. To evaluate the new capabilities, it was found that new and additional treatment of the radar data was necessary. For example, the adequacy of the usual radar wind observations obtained by editing the Doppler spectral moments was found to be very questionable for short-term observations, so the authors extended the editing to the raw spectra, and substantial improvement was found. The advantages of the redundancy in five-beam systems are investigated and are also found to be very necessary to obtain the accuracy needed. A technique for minimizing the variances of the differences of the four redundant pairs of radials is described. The resulting improved vertical velocity estimates substantially improve the agreement between radio acoustic sounding system (RASS) temperature retrievals and balloon-measured temperatures. The ability of the profilers to measure turbulence intensity was tested, and the accuracy of techniques using the spectral width to measure turbulent dissipation rate when complicated spectra are present is examined. Two different techniques for optimizing the calculation of spectral width are compared and the errors assessed. One technique integrates over the uncontaminated range of the chosen spectral peak and then extrapolates a Gaussian function to infinity. The other method uses the slope of the log least squares best fit of the uncontaminated points to a Gaussian function. Profiler-measured length scales of wind and scalar quantities are measured and compared. Profiles of radar-measured gradients of refractive index are compared with gradients measured by balloon. It is shown how gradients of humidity can be calculated to about the same accuracy as refractive-index gradients by combining the temperature gradients from RASS with the refractive-index gradient observations from the radar.

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T.L. Anderson, D.S. Covert, S.F. Marshall, M.L. Laucks, R.J. Charlson, A.P. Waggoner, J.A. Ogren, R. Caldow, R.L. Holm, F.R. Quant, G.J. Sem, A. Wiedensohler, N.A. Ahlquist, and T.S. Bates

Abstract

As designed in the 1940s by Beuttell and Brewer, the integrating nephelometer offers a direct method of measuring light scattering by airborne particles without assumptions about particle composition, shape, or physical state. A large number of such instruments have been deployed; however, only a limited number of validation experiments have been attempted. This paper reports a set of closure experiments in which a gas-calibrated nephelometer is used to measure the scattering coefficient of laboratory-generated particles of known size and refractive index.

Specifically, it evaluates the performance of a high-sensitivity, three-wavelength, total scatter/backscatter integrating nephelometer (TSI, Inc., model 3563). Sources of uncertainty associated with the gas-calibration procedure, with photon-counting statistics, and with nonidealities in wavelength and angular sensitivity are investigated. Tests with particle-free gases indicate that noise levels are well predicted by photon-counting statistics and that the nephelometer response is linear over a wide range of scattering coefficients. Tests with particles show average discrepancies between measured and predicted scattering of 4%–7%. Error analysis indicates that these discrepancies are within experimental uncertainty, which was dominated by particle generation uncertainty. The simulation of nephelometer response, which is validated by these tests, is used to show that errors arising from nephelometer nonidealities are less than 10% for accumulation-mode or smaller particles (i.e., size distributions for which the volume mean diameter is 0.4µm or less) and that significant differences exist between the total scatter and backscatter uncertainties. Based on these findings, appropriate applications of the model 3563 nephelometer am discussed.

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A. B. White, M. L. Anderson, M. D. Dettinger, F. M. Ralph, A. Hinojosa, D. R. Cayan, R. K. Hartman, D. W. Reynolds, L. E. Johnson, T. L. Schneider, R. Cifelli, Z. Toth, S. I. Gutman, C. W. King, F. Gehrke, P. E. Johnston, C. Walls, D. Mann, D. J. Gottas, and T. Coleman

Abstract

During Northern Hemisphere winters, the West Coast of North America is battered by extratropical storms. The impact of these storms is of paramount concern to California, where aging water supply and flood protection infrastructures are challenged by increased standards for urban flood protection, an unusually variable weather regime, and projections of climate change. Additionally, there are inherent conflicts between releasing water to provide flood protection and storing water to meet requirements for the water supply, water quality, hydropower generation, water temperature and flow for at-risk species, and recreation. To improve reservoir management and meet the increasing demands on water, improved forecasts of precipitation, especially during extreme events, are required. Here, the authors describe how California is addressing their most important and costliest environmental issue—water management—in part, by installing a state-of-the-art observing system to better track the area’s most severe wintertime storms.

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