Showing papers on "Disdrometer published in 1996"
TL;DR: In this article, an empirical stratiform-convective classification method based on N 0 and R (rainfall rate) is presented. But, the occurrence of precipitation was found to be 74% (stratiform) and 26% (convection) but total rainfall, on the other hand, was...
Abstract: An analysis of temporal variations in gamma parameters of raindrop spectra is presented utilizing surface-based observations from the Tropical Ocean Global Atmosphere Couple Ocean-Atmosphere Experiment. An observed dramatic change in the N0 parameter, found to occur during rainfall events with little change in rainfall rate, is suggestive of a transition from rain of convective origin to rain originating from the stratiform portion of tropical systems. An empirical stratiform-convective classification method based on N0 and R (rainfall rate) is presented. Properties of the drop size spectra from the stratiform classification are consistent with micro-physical processes occurring within an aggregation/melting layer aloft, which produces more large raindrops and fewer small to medium size raindrops than rain from the convective classification, at the same rainfall rate. The occurrence of precipitation was found to be 74% (stratiform) and 26% (convective), but total rainfall, on the other hand, was ...
685 citations
TL;DR: In this article, the size spectra of oscillating raindrops were determined from photographic measurements in Illinois showers at night using strobe lights, and the oscillations were detected from modulations in the fall streaks produced by backscattered light near the primary rainbow.
Abstract: The size spectra of oscillating raindrops were determined from photographic measurements in Illinois showers at night. The oscillations were detected from modulations in the fall streaks produced by backscattered light near the primary rainbow. Drop sizes were determined from the fall speed using strobe lights. A continuous record of raindrop size distributions was obtained from a disdrometer located beneath the camera sample volume. Results show that oscillations begin near 1-mm diameter, at the onset size for vortex shedding. This finding is consistent with the authors' recent laboratory and field studies for small raindrops. The size spectra show that all raindrops above 1 mm are oscillating, out to the largest size measured of 4.2-mm diameter. Extrinsic sources of drop oscillations were evaluated using a collision model with viscous decay and using the pressure forcing from turbulence and wind shear in the surface layer. Based on the disdrometer size distributions, the number of oscillating d...
66 citations
TL;DR: In this paper, six different types of automatic rain gauge systems have been collected for a set of summertime subtropical rain events at the University of South Florida and for a wintertime rain event at Miami, Florida.
Abstract: Automatic rain gauge systems are required to collect rainfall data at remote locations, especially oceanic sites where logistics prevent regular visits. Rainfall data from six different types of automatic rain gauge systems have been collected for a set of summertime subtropical rain events and for a set of wintertime rain events at Miami, Florida. The rain gauge systems include three types of collection gauges: weighing, capacitance, and tipping bucket; two gauges that inherently measure rainfall rate: optical scintillation and underwater acoustical inversion; and one gauge that detects individual raindrops: the disdrometer. All of these measurement techniques perform well; that is, they produce rainfall estimates that are highly correlated to one another. However, each method has limitations. The collection gauges are affected by flow irregularities between the catchment basin and the measurement chambers. This affects the accuracy of rainfall-rate measurements from these instruments, especiall...
64 citations
TL;DR: The relationship between raindrop size distribution, measured with a disdrometer, and a radar parameter of the melting-layer bright band is investigated in this article, where a good correlation (about −0.7) between the strength of the bright band (ΔZe) and the intercept and slope parameters of the Marshall-Palmer drop size distribution (N0, ∇) is observed for horizontally uniform precipitation of moderate intensity.
Abstract: The relationship between raindrop size distribution, measured with a disdrometer, and a radar parameter of the melting-layer bright band is investigated. The data, obtained in July 1993 in Switzerland, cover 120 h of precipitation. A good correlation (about −0.7) between the strength of the bright band (ΔZe) and the intercept and slope parameters of the Marshall-Palmer drop size distribution (N0, ∇) is observed for horizontally uniform precipitation of moderate intensity (one-third of total rainfall). Steep spectrum with many small drops and no large drops are associated with small values for ΔZe, whereas flat spectra with relatively few small drops and with large drops exhibit a well-defined bright band with a large ΔZe. Considering ΔZe allows a significantly better derivation of the rainfall rate from radar measurements than is possible with standard Z-R relationships. The rms errors of the 10-min averages of rainfall intensity can be reduced by 20%40%.
60 citations
TL;DR: Application of the stochastic interception model may explain why interception losses from coniferous, fine-leaved forests in the temperate, low-intensity rainfall climate of the uplands of the U.K. are among the highest in the world, whereas interception Losses from tropical broad leaved forest in high- intensity rainfall climates of the tropics areamong the lowest.
Abstract: This paper reviews the development of the stochastic interception model from the original, single-layer, drop-size-dependent model to the two-layer model that recognizes that vegetation canopies are wetted through both the primary impact of raindrops to the top layer of the canopy and secondary impacts from drops falling from the vegetation to lower layers of the canopy. It is shown that drop volumes of primary raindrops can be calculated from the Marshall-Palmer distribution and drop volumes of secondary drops can be estimated from disdrometer measurements of the characteristic volume appropriate to the particular vegetation species. It is recognized that, in addition to the volume-dependent stochastic wetting effect, there is also another drop-size-dependent wetting effect that is related to the kinetic energy of the raindrops, which reduces the maximum storage that can be achieved on the canopy. The predicted wetting functions for canopies of different density are described and compared with observations made with the use of a rainfall simulator. It is also shown that the species-dependent model parameters can be determined from measurements made with the rainfall simulator. The improved performance of the model compared with conventional interception models is demonstrated for a tropical forest in Sri Lanka. Application of the two-layer model may explain why interception losses from coniferous, fine-leaved forests in the temperate, low-intensity rainfall climate of the uplands of the U.K. are among the highest in the world, whereas interception losses from tropical broad leaved forest in high-intensity rainfall climates of the tropics are among the lowest.
25 citations
TL;DR: In this paper, a new method is presented by which raindrop size spectra are determined from power spectra measured by an X-band Doppler radar, where bias caused by vertical wind, vw, is removed by an iterative process that uses a disdrometer-determined relation that is characteristic of the rainfall type.
Abstract: A new method is presented by which raindrop size spectra are determined from power spectra measured by an X-band Doppler radar. Prior to drop size spectrum calculation, bias caused by vertical wind, vw, is removed by an iterative process that uses a disdrometer-determined relation that is characteristic of the rainfall type. The specific relation (Z ≈ 507 R1.44) is determined from the best correlated data pair formed between Z or w with one of R, M, and vm. The vertical wind is estimated by shifting (rotating) the power spectrum along the velocity axis until this Z-R relation is satisfied. This method works for any shape of drop size spectrum. The power spectrum noise is studied by a computer simulation that indicates that smoothing of the spectra by a running average is not reliable for suppressing stochastic measurement noise. Consequently, a vertically pointing radar scanning strategy was designed to allow averaging of the power spectra prior to drop spectrum calculation. This scan was tested ...
17 citations
TL;DR: In this paper, the authors used a volume scanning strategy with a repetition cycle of 3.5 min to detect rain ensembles up to 3 km above the radar and at the ground by a disdrometer.
Abstract: During the Joint Tropical Rain Experiment of the Malaysian Meteorological Service and the University of Toronto, pulsating raindrop ensembles, hereafter pulses, were observed in and around Penang Island. Using a Doppler radar on 25 October 1990, a periodic variation of precipitation aloft 30 km from the radar site, with an approximate 8-min period, was established and seemed to be caused by the evolution and motion of horizontal inhomogeneities existing within the same cell. On 30 October 1990, using a new volume scanning strategy with a repetition cycle of 3.5 min, pulsations of the same frequency were observed up to 3 km above the radar and at the ground by a disdrometer. High concentrations of large drops were followed by high concentrations of successively smaller drops at the ground. This provides observational evidence to support the recent argument for using a time-varying release of precipitation-sized particles to model observed pulsating rainfall. Many cases of nonsteady rain from conve...
11 citations