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- Author or Editor: I. I. Zawadzki x
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Abstract
Spacial smoothing by the radar beam as well as post-detection integration reduce the variability of the distribution of rainfall rate in space. It is shown that when radar data are compared with instantaneous point rainfall rate a random error and a bias are introduced by the smoothing. This could account for some of the difficulties in the hydrological use of radars. It is shown that when raingage data are smoothed in time there is an optimum smoothing time interval such that the random error and the bias are reduced to a negligible level. A method is suggested for the optimum comparison of radar and raingage data and the possibility of a determination of Z-R relationships from such comparisons is discussed.
Abstract
Spacial smoothing by the radar beam as well as post-detection integration reduce the variability of the distribution of rainfall rate in space. It is shown that when radar data are compared with instantaneous point rainfall rate a random error and a bias are introduced by the smoothing. This could account for some of the difficulties in the hydrological use of radars. It is shown that when raingage data are smoothed in time there is an optimum smoothing time interval such that the random error and the bias are reduced to a negligible level. A method is suggested for the optimum comparison of radar and raingage data and the possibility of a determination of Z-R relationships from such comparisons is discussed.
Abstract
Space and time autocorrelation functions are defined for the precipitation process on a horizontal plane. An optical device was designed and used to measure these functions as well as the mean, the mean square, and the variance of the rainfall rate for a time sequence of precipitation patterns of a widespread convective storm. The input data were radar PPI records stored on film in which the transmittance was adjusted to be proportional to rainfall rate.
Abstract
Space and time autocorrelation functions are defined for the precipitation process on a horizontal plane. An optical device was designed and used to measure these functions as well as the mean, the mean square, and the variance of the rainfall rate for a time sequence of precipitation patterns of a widespread convective storm. The input data were radar PPI records stored on film in which the transmittance was adjusted to be proportional to rainfall rate.
Abstract
The decrease of the mean square and the variance of reflectivity due to radar beam smoothing and post-detection integration are studied in terms of the autocorrelation function of the field of reflectivity. An exponential form of this function is used to evaluate the results. Applications to the problem of radar beam resolution and design of radar displays are discussed.
Abstract
The decrease of the mean square and the variance of reflectivity due to radar beam smoothing and post-detection integration are studied in terms of the autocorrelation function of the field of reflectivity. An exponential form of this function is used to evaluate the results. Applications to the problem of radar beam resolution and design of radar displays are discussed.
Abstract
A critical review of the velocity-azimuth display (VAD) analysis for the retrieval of wind, divergence, and deformation from single-Doppler observations is presented. It is shown that in situations when the linear wind assumption is not valid the VAD analysis leads to incorrect conclusions. The range and height dependence of single-Doppler data contains information on the nonlinearity of the wind field and allows a generalized analysis by which vertical profiles of wind, divergence, and deformation at the radar site can in principle be obtained. These ideas are illustrated by two case analyses of single-Doppler observations in clear air.
Abstract
A critical review of the velocity-azimuth display (VAD) analysis for the retrieval of wind, divergence, and deformation from single-Doppler observations is presented. It is shown that in situations when the linear wind assumption is not valid the VAD analysis leads to incorrect conclusions. The range and height dependence of single-Doppler data contains information on the nonlinearity of the wind field and allows a generalized analysis by which vertical profiles of wind, divergence, and deformation at the radar site can in principle be obtained. These ideas are illustrated by two case analyses of single-Doppler observations in clear air.
Abstract
This study investigates whether part of the variability of rain rates not explained by the thermodynamic parameters could be explained by the vertical wind structure as revealed by standard aerological sounding observations. The correlation found between rain rates and vertical wind structure is at most marginally significant. Moreover, given the high degree of interdependence between the thermodynamic parameters and rain rates, the somewhat more significant correlation observed between the dynamic and thermodynamic variables may induce an automatic correlation between wind profiles and rain rates.
Abstract
This study investigates whether part of the variability of rain rates not explained by the thermodynamic parameters could be explained by the vertical wind structure as revealed by standard aerological sounding observations. The correlation found between rain rates and vertical wind structure is at most marginally significant. Moreover, given the high degree of interdependence between the thermodynamic parameters and rain rates, the somewhat more significant correlation observed between the dynamic and thermodynamic variables may induce an automatic correlation between wind profiles and rain rates.
Abstract
The relationship between convective scales in the pre-storm environment and Doppler measurements of divergence is discussed with attention to problems inherent in radar measurements. A method is suggested to minimize the effects of beam smoothing and reflectivity weighting. A case study indicates the possibility of operational short-term forecasting of the onset time of precipitation from the radar measurements of divergence.
Abstract
The relationship between convective scales in the pre-storm environment and Doppler measurements of divergence is discussed with attention to problems inherent in radar measurements. A method is suggested to minimize the effects of beam smoothing and reflectivity weighting. A case study indicates the possibility of operational short-term forecasting of the onset time of precipitation from the radar measurements of divergence.
Abstract
Ten years of raingage data are processed in order to evaluate duration, average and maximum rate, mean square, variance, autocorrelation function and total amount for each rain storm. A spatial interpretation of these quantities is also given. Further, various rainfall rate probabilities are evaluated.
Abstract
Ten years of raingage data are processed in order to evaluate duration, average and maximum rate, mean square, variance, autocorrelation function and total amount for each rain storm. A spatial interpretation of these quantities is also given. Further, various rainfall rate probabilities are evaluated.
Abstract
Daily 5, 10 and 30 min maxima of precipitation rate determined from a raingage network and radar were correlated with parcel convective energies, upper air humidity, height of parcel convection and maxima of surface conditions. After a selection of 54 well-documented cases the correlation coefficient between the maximum of rain rate over 5 min and the maximum convective energy was ρ = 0.79 for all cases and ρ = 0.89 for 15 air mass cases. Introducing the upper air humidity further improves the correlations.
Abstract
Daily 5, 10 and 30 min maxima of precipitation rate determined from a raingage network and radar were correlated with parcel convective energies, upper air humidity, height of parcel convection and maxima of surface conditions. After a selection of 54 well-documented cases the correlation coefficient between the maximum of rain rate over 5 min and the maximum convective energy was ρ = 0.79 for all cases and ρ = 0.89 for 15 air mass cases. Introducing the upper air humidity further improves the correlations.
Abstract
A model of rain development based on the quasi-stochastic coalescence equation and including the sedimentation of drops has been used to study the formation of drop size distributions in conditions of weak updraft. Comparisons with “box model” results indicate that sedimentation effects are crucial in establishing the shapes of the distribution. Under realistic conditions of cloud droplet distribution with size, the raindrop size distributions as simulated by the model compare well with observations of orographic rain made in Hawaii. On the other hand, Doppler radar measurements of drop size distributions just below a bright band confirm that the Marshall-Palmer distribution results from processes affecting particles in the solid phase rather than from the interaction of raindrops.
Abstract
A model of rain development based on the quasi-stochastic coalescence equation and including the sedimentation of drops has been used to study the formation of drop size distributions in conditions of weak updraft. Comparisons with “box model” results indicate that sedimentation effects are crucial in establishing the shapes of the distribution. Under realistic conditions of cloud droplet distribution with size, the raindrop size distributions as simulated by the model compare well with observations of orographic rain made in Hawaii. On the other hand, Doppler radar measurements of drop size distributions just below a bright band confirm that the Marshall-Palmer distribution results from processes affecting particles in the solid phase rather than from the interaction of raindrops.
Abstract
Soundings. surface pressure, temperature and humidity obtained from a standard observation network were correlated with rain rates given by raingages and radar. The correlations indicate that a single thermodynamic parameter (static potential energy) explains ∼60% of the storm-to-storm variability of the mean and the maximum rain rates. During the evolution of a precipitating system the time variation of rain rate parameters follows closely the variation of the static energy. The entire distribution of rain rates is well stratified by the energy.
Abstract
Soundings. surface pressure, temperature and humidity obtained from a standard observation network were correlated with rain rates given by raingages and radar. The correlations indicate that a single thermodynamic parameter (static potential energy) explains ∼60% of the storm-to-storm variability of the mean and the maximum rain rates. During the evolution of a precipitating system the time variation of rain rate parameters follows closely the variation of the static energy. The entire distribution of rain rates is well stratified by the energy.
