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Nambath K. Balachandran

disturbances produced by severe thunderstorms. Thesedisturbances are found to be due to acoustic wavesgenerated by thunderstorms. Rapi~l mesosphericheating over Wallops Island, Virginia during latesummer of 1976 is interpreted by Taylor (1979) asthe result of the dissipation of vertically propagating gravity waves generated by severe thunderstorms in the troposphere. Gravity waves from thunderstorms have beendetected at the ground level by a number ofworkers (e.g., Curry and Murty, 1974). The importance

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James D. Doyle and Nicholas A. Bond

analysis, notably time-dependent and diabatic effects. In the present case, the response of the incident flow to coastal terrain, particularly Vancouver Island, was also complicated by a preexisting mass of cool air along the coast. This air mass was constrained by the coastal terrain but had originated in the interior of the Pacific Northwest, and hence its characteristics were not solely controlled by orographic effects. The interactions between the above-mentioned factors make it very difficult to

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Tammy M. Weckwerth, Thomas W. Horst, and James W. Wilson

wind speed. Kristovich et al. (1999) identified the appearance of rolls in their wintertime lake-effect analysis region about an hour after an increase in low-level wind speed and speed shear, suggesting that increased shear was an impetus for roll formation. Other studies of rolls associated with cold air outbreak events over large bodies of water often had upstream measurements or observations within the spatial transition region between rolls and cellular convection but no measurements of the

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Claude Girard, Robert Benoit, and Michel Desgagné

along with modifications of (3) to take into account in particular the buoyancy effects of moisture and suspended hydrometeors. c. Change of thermodynamic variables and separation of terms It is always possible to subtract from the above equations a hydrostatic basic state. The step of identifying and separating advection and linear terms from the rest of nonlinear and source terms is a necessary one for the application of a SISL scheme. Here, we show how the scheme has been modified to allow for

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R. M. Raibin

radiosonde data and the vertical resolution of numerical prognostic models are not alwayssufficient to forecast these changes accurately on timescales of 0-12 hours. The development of new sensors (ground based andsatellite radiometers, Doppler radars with scannableand fixed antennas, Radio Acoustical Sounding Systems, RASS), with concomitant increase in horizontaland temporal resolution of data, gives hope to improveweather forecasts. In the United States for example,the NEXRAD network of about 100

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James K. Firestone and Bruce A. Albrecht

Weather Ex periment. II. The second Special Observing Period. Bull. Amer. Meteor. Soc., 60, 1316-1322.Gaynor, J. E., and P. A. Mandics, 1978: An analysis of the tropical marine boundary layer during GATE. Mon. Wea. Rev., 106, 223-232. , and C. F. Ropelewski, 1979: Analysis of the convectively mod ified GATE boundary layer using in situ and acoustic sounder data. Mon. Wea. Rev., 107, 985-993.Holland, J. S., and B. M. Rasmusson, 1973: Measurements of the atmospheric mass, energy and momentum

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L. Xin and G. W. Reuter

2828 MONTHLY WEATHER REVIEW VOLUME 124Numerical Simulation of the Effects of Mesoscale Convergence on Convective Rain Showers L. XtN AND G. W. REUTERDepartment of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada(Manuscript received 24 July 1995, in final form 16 May 1996)ABSTRACT A nonhydrostatic axisymmetric cloud model is

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Tracy Lorraine Smith, Stanley G. Benjamin, Seth I. Gutman, and Susan Sahm

1. Introduction Observational tracking of the often rapidly evolving moisture field is an essential component of weather forecasting and numerical weather prediction (NWP). Short-range numerical weather forecast accuracy often suffers from inadequate observational definition of the three-dimensional moisture field because of its high spatial and temporal variability. Currently, three observation systems provide most atmospheric water vapor measurements: rawinsondes, surface stations, and

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David P. Bacon, Nash’at N. Ahmad, Zafer Boybeyi, Thomas J. Dunn, Mary S. Hall, Pius C. S. Lee, R. Ananthakrishna Sarma, Mark D. Turner, Kenneth T. Waight III, Steve H. Young, and John W. Zack

uses a modified Kuo scheme to parameterize cumulus effects ( Kuo 1965 ; Anthes 1977 ), and an extensive bulk water microphysics package derived from Lin et al. (1983) . OMEGA models the shortwave absorption by water vapor and longwave emissivities of water vapor and carbon dioxide using the computationally efficient technique of Sasamori (1972) . OMEGA uses an optimum interpolation analysis scheme ( Daley 1991 ) to create initial and boundary conditions and supports piecewise four

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Shu-hua Chen and Wen-yih Sun

1. Introduction In the past, numerical weather prediction models had to use the governing equations with the hydrostatic approximation in order to avoid acoustic waves in the vertical direction. When high-frequency acoustic waves exist, an exceedingly small time step is required to prevent numerical instability of the explicit time-stepping scheme ( Mendez-Nunez and Carroll 1994 ; Hsu and Sun 2001 ). Fully compressible nonhydrostatic models, which include sound waves, have become more popular

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