Showing papers on "Disdrometer published in 2008"
TL;DR: In this paper, data from three 2D video disdrometers and an S-band polarimetric radar are used to characterize rain microphysics in Oklahoma and a method of sorting and averaging based on two parameters (SATP) is proposed.
Abstract: In this paper, data from three 2-dimensional video disdrometers (2DVDs) and an S-band polarimetric radar are used to characterize rain microphysics in Oklahoma. Sampling errors from the 2DVD measurements are quantified through side-by-side comparisons. In an attempt to minimize the sampling errors, a method of sorting and averaging based on two parameters (SATP) is proposed. The shape–slope (μ–Λ) relation of a constrained gamma (C-G) model is then refined for the retrieval of drop size distributions (DSDs) from polarimetric radar measurements. An adjustable term that is based on observed radar reflectivity and differential reflectivity is introduced to make the C-G DSD model more applicable. Radar retrievals using this improved DSD model are shown to provide good agreement with disdrometer observations and to give reasonable results, including in locations near the leading edge of convection where poorly sampled large drops are often observed.
219 citations
TL;DR: In this article, the authors studied the characteristics of raindrop size distribution in seven tropical cyclones through impact-type disdrometer measurements at three different sites during the 2004-06 Atlantic hurricane seasons.
Abstract: Characteristics of the raindrop size distribution in seven tropical cyclones have been studied through impact-type disdrometer measurements at three different sites during the 2004–06 Atlantic hurricane seasons. One of the cyclones has been observed at two different sites. High concentrations of small and/or midsize drops were observed in the presence or absence of large drops. Even in the presence of large drops, the maximum drop diameter rarely exceeded 4 mm. These characteristics of raindrop size distribution were observed in all stages of tropical cyclones, unless the storm was in the extratropical stage where the tropical cyclone and a midlatitude frontal system had merged. The presence of relatively high concentrations of large drops in extratropical cyclones resembled the size distribution in continental thunderstorms. The integral rain parameters of drop concentration, liquid water content, and rain rate at fixed reflectivity were therefore lower in extratropical cyclones than in tropical cyclones. In tropical cyclones, at a disdrometercalculated reflectivity of 40 dBZ, the number concentration was 700 100 drops m 3 , while the liquid water content and rain rate were 0.90 0.05 g m 3 and 18.5 0.5 mm h 1 , respectively. The mean mass diameter, on the other hand, was 1.67 0.3 mm. The comparison of raindrop size distributions between Atlantic tropical cyclones and storms that occurred in the central tropical Pacific island of Roi-Namur revealed that the number density is slightly shifted toward smaller drops, resulting in higher-integral rain parameters and lower mean mass and maximum drop diameters at the latter site. Considering parameterization of the raindrop size distribution in tropical cyclones, characteristics of the normalized gamma distribution parameters were examined with respect to reflectivity. The mean mass diameter increased rapidly with reflectivity, while the normalized intercept parameter had an increasing trend with reflectivity. The shape parameter, on the other hand, decreased in a reflectivity range from 10 to 20 dBZ and remained steady at higher reflectivities. Considering the repeatability of the characteristics of the raindrop size distribution, a second impact disdrometer that was located 5.3 km away from the primary site in Wallops Island, Virginia, had similar size spectra in selected tropical cyclones.
132 citations
TL;DR: In this article, the authors extend the earlier work by augmenting the profiling radar observations with collocated raindrop disdrometers to measure drop size distributions (DSD) at the surface.
Abstract: Recent studies using vertically pointing S-band profiling radars showed that coastal winter storms in California and Oregon frequently do not display a melting-layer radar bright band and inferred that these nonbrightband (NBB) periods are characterized by raindrop size spectra that differ markedly from those of brightband (BB) periods. Two coastal sites in northern California were revisited in the winter of 2003/04 in this study, which extends the earlier work by augmenting the profiling radar observations with collocated raindrop disdrometers to measure drop size distributions (DSD) at the surface. The disdrometer observations are analyzed for more than 320 h of nonconvective rainfall. The new measurements confirm the earlier inferences that NBB rainfall periods are characterized by greater concentrations of small drops and smaller concentrations of large drops than BB periods. Compared with their BB counterparts, NBB periods had mean values that were 40% smaller for mean-volume diameter, 32% s...
100 citations
TL;DR: In this paper, a cubic spline based operational system for the generation of the TRMM one-minute rain rate product 2A-56 from Tipping Bucket (TB) measurements is described.
Abstract: This paper describes the cubic spline based operational system for the generation of the TRMM one-minute rain rate product 2A-56 from Tipping Bucket (TB) gauge measurements. Methodological issues associated with applying the cubic spline to the TB gauge rain rate estimation are closely examined. A simulated TB gauge from a Joss-Waldvogel (JW) disdrometer is employed to evaluate effects of time scales and rain event definitions on errors of the rain rate estimation. The comparison between rain rates measured from the JW disdrometer and those estimated from the simulated TB gauge shows good overall agreement; however, the TB gauge suffers sampling problems, resulting in errors in the rain rate estimation. These errors are very sensitive to the time scale of rain rates. One-minute rain rates suffer substantial errors, especially at low rain rates. When one minute rain rates are averaged to 4-7 minute or longer time scales, the errors dramatically reduce. The rain event duration is very sensitive to the event definition but the event rain total is rather insensitive, provided that the events with less than 1 millimeter rain totals are excluded. Estimated lower rain rates are sensitive to the event definition whereas the higher rates are not. The median relative absolute errors are about 22% and 32% for 1-minute TB rain rates higher and lower than 3 mm per hour, respectively. These errors decrease to 5% and 14% when TB rain rates are used at 7-minute scale. The radar reflectivity-rainrate (Ze-R) distributions drawn from large amount of 7-minute TB rain rates and radar reflectivity data are mostly insensitive to the event definition.
89 citations
TL;DR: In this paper, the contribution of various physical sources of uncertainty affecting radar rainfall estimates at the ground is quantified toward deriving and understanding the error covariance matrix of these estimates.
Abstract: The contribution of various physical sources of uncertainty affecting radar rainfall estimates at the ground is quantified toward deriving and understanding the error covariance matrix of these estimates. The focus here is on stratiform precipitation at a resolution of 15 km, which is most relevant for data assimilation onto mesoscale numerical models. In the characterization of the error structure, the following contributions are considered: (i) the individual effect of the range-dependent error (associated with beam broadening and increasing height of radar measurements with range), (ii) the error associated with the transformation from reflectivity to rain rate due to the variability of drop size distributions, and (iii) the interaction of the first two, that is, the term resulting from the cross correlation between the effects of the range-dependent error and the uncertainty related to the variability of drop size distributions (DSDs). For this purpose a large database of S-band radar observations at short range (where reflectivity near the ground is measured and the beam is narrow) is used to characterize the range-dependent error within a simulation framework, and disdrometric measurements collocated with the radar data are used to assess the impact of the variability of DSDs. It is noted that these two sources of error are well correlated in the vicinity of the melting layer as result of the physical processes that determine the density of snow (e.g., riming), which affect both the DSD variability and the vertical profile of reflectivity.
64 citations
TL;DR: In this paper, a diagnostic relation of N0 as a function of rainwater content W is derived based on two-dimensional video disdrometer (2DVD) measurements, which reveals a clear correlation between N0 and W in which N0 increases as W increases.
Abstract: The exponential distribution N(D) = N0 exp(−ΛD) with a fixed intercept parameter N0 is most commonly used to represent raindrop size distribution (DSD) in rainfall estimation and in single-moment bulk microphysics parameterization schemes. Disdrometer observations show that the intercept parameter is far from constant and systematically depends on the rain type and intensity. In this study, a diagnostic relation of N0 as a function of rainwater content W is derived based on two-dimensional video disdrometer (2DVD) measurements. The data reveal a clear correlation between N0 and W in which N0 increases as W increases. To minimize the effects of sampling error, a relation between two middle moments is used to derive the N0–W relation. This diagnostic relation has the potential to improve rainfall estimation and bulk microphysics parameterizations. A parameterization scheme for warm rain processes based on the diagnostic N0 DSD model is formulated and presented. The diagnostic N0-based parameterizat...
61 citations
TL;DR: In this paper, the authors examined the terminal velocities of snow aggregates in storms along the Front Range in eastern Colorado with a ground-based two-dimensional video disdrometer.
Abstract: Terminal velocities of snow aggregates in storms along the Front Range in eastern Colorado are examined with a ground-based two-dimensional video disdrometer. Power-law relationships for particles having equivalent volume diameters of 0.5–20 mm are computed for the temperatures −1°, −5°, and −10°C. Fall speeds increase with temperature. Comparison with relationships found in the literature suggests that temperature-dependent relations may be surrogates for relations based on aggregate composition (e.g., plates, columns, or dendrites) and the degree of riming.
57 citations
TL;DR: A new stochastic vector autoregressive semi-Markov model is proposed to randomly synthesize the temporal series of the three driving parameters of a normalized gamma RSD, modeled from disdrometer measurements using two-state analytical statistics of rain and dry period duration.
Abstract: Hydrometeorological and radio propagation applications can benefit from the capability to model the time evolution of raindrop size distribution (RSD). A new stochastic vector autoregressive semi-Markov model is proposed to randomly synthesize (generate) the temporal series of the three driving parameters of a normalized gamma RSD. Rainfall intermittence is reproduced through a discrete semi-Markov process, modeled from disdrometer measurements using two-state analytical statistics of rain and dry period duration. The overall model is set up by means of a large set of disdrometer measurements, collected from 2003 to 2005 at Chilbolton, U.K. The driving parameters of the retrieved RSD are estimated using three approaches: the Gamma moment method and the 1D and 3D maximum-likelihood methods. Interestingly, these methodologies lead to quite different results, particularly when one is interested in evaluating RSD higher order moments such as the rain rate. The accuracy of the proposed RSD time-series generation technique is evaluated against available disdrometer measurements, providing excellent statistical scores.
54 citations
TL;DR: In this article, a large number of different rain events were collected: they underwent microphysical analysis by computing the Z-R relationships, observing the average DSDs and DSD parameters, fitting the real distribution for different rainfall rate categories and applying convective (C) -stratiform (S) discrimination algorithms.
Abstract: . The drop size distribution (DSD) is a fundamental property of rainfall because the shape of the distribution reflects the physics of rain formation processes. Given the lack of studies on the DSD at mid-latitudes, the present work focuses on the microphysical characterization of precipitation events occurring in Italy, using two different types of disdrometer. A large number of different rain events was collected: they underwent microphysical analysis by computing the Z-R relationships, observing the average DSDs and DSD parameters, fitting the real distribution for different rainfall rate categories and applying convective (C) – stratiform (S) discrimination algorithms. A general agreement with past works at mid-latitudes is found both in the Z-R relationship and in DSD parameters. The rain distribution is well described by a gamma DSD and only in some cases (especially the light rain events) by an exponential DSD. Marked differences are observed in DSD parameters and Z-R relationships between C and S episodes. The use of disdrometers for areas covered by multiparametric radar is suggested and will be performed in the near future.
51 citations
TL;DR: In this article, the authors extracted DSD parameters from dual-frequency (UHF and VHF) wind profiler measurements made at Gadanki, India, in a summer monsoon season.
Abstract: Raindrop size distribution (DSD) parameters are retrieved from dual-frequency (UHF and VHF) wind profiler measurements made at Gadanki, India, in a summer monsoon season. The convoluted UHF spectra are first corrected for vertical air motion and spectral broadening (using VHF measurements) and later are used for deriving DSD parameters. Two distinctly different case studies, a mesoscale convective system and a pure stratiform precipitation system, have been considered for a detailed study. DSD parameters obtained in these case studies reveal systematic variations of DSD from case to case and also from one rain regime to another within the same precipitating system. A statistical study has been carried out using the profiler data collected during the passage of 16 rain events. The retrieved DSD profiles are divided into separate rain regimes (stratiform and convection), based on reflectivity, to examine salient microphysical characteristics and the vertical variability of DSD in different precipit...
50 citations
TL;DR: In this article, the authors present a new method that, while utilizing relations between moments, also takes account of the truncation, and the resulting estimates are simple functions of the observed data.
TL;DR: In this paper, two algorithms, the so-called beta () and constrained methods, were proposed for retrieving the governing parameters of the gamma drop size distribution (DSD) from dual-polarization radar measurements.
Abstract: In this study the authors evaluate two algorithms, the so-called beta () and constrained methods, proposed for retrieving the governing parameters of the “normalized” gamma drop size distribution (DSD) from dual-polarization radar measurements. The method treats the drop axis ratio as a variable and computes drop shape and DSD parameters from radar reflectivity (ZH), differential reflectivity (ZDR), and specific differential phase shift (KDP). The constrained method assumes that the axis-ratio relation is fixed and computes DSD parameters from ZH, ZDR, and an empirical relation between the DSD slope and shape parameters. The two techniques are evaluated for polarimetric X-band radar observations by comparing retrieved DSD parameters with disdrometer observations and examining simulated radar parameters for consistency. Error effects on the method and constrained method retrievals are analyzed. The approach is found to be sensitive to errors in KDP and to be less consistent with observations. Large retrieved values are found to be associated with large retrieved DSD shape parameters and small median drop diameters. The constrained method provides reasonable rain DSD retrievals that agree better with disdrometer observations.
TL;DR: In this paper, disdrometer observations from a variety of climate regions are employed to develop constraints on the gamma distribution that are optimized for dual-frequency radar rainfall retrievals, and then gamma parameters are fit to the composites.
Abstract: Observations of raindrop size distributions (DSDs) have validated the use of three-parameter distribution functions in representing the observed spectra. However, dual-frequency radar measurements are limited to retrieving two independent parameters of the DSD, thus requiring a constraint on a three-parameter distribution. In this study, disdrometer observations from a variety of climate regions are employed to develop constraints on the gamma distribution that are optimized for dual-frequency radar rainfall retrievals. These observations are composited by reflectivity, and then gamma parameters are fit to the composites. The results show considerable variability in shape parameter between regions and within a region at different reflectivities. Most notable is that oceanic regions exhibit maxima in shape parameter at 13.6-GHz reflectivities between 40 and 50 dBZ, in contrast to continental regions. The shape parameter and slope parameter of all composite DSDs are poorly correlated. Thus, constra...
TL;DR: In this article, the canting angle distribution of raindrops derived separately from a 2D video disdrometer and from an S-band advanced polarimetric radar is presented.
Abstract: The canting angle distribution of raindrops derived separately from a 2-D video disdrometer and from an S-band advanced polarimetric radar are presented. In the former case, measurements were made in both natural and artificial rain. The canting angles showed a symmetric distribution about 0° with a standard deviation (σβ) of 7°–8° in low wind conditions and 12° in moderate wind conditions. In the radar-based estimates, the histogram of σβ derived from data obtained during a light stratiform rain event with embedded convection shows the mode to be around 7°, with a significant positive skewness. Around 16% of occurrences exceeded 10° and 3.3% exceeded 15°.
TL;DR: In this paper, the authors focus on the sensitivity of streamflow simulations to temporal variations in radar reflectivity-rainfall (i.e., Z-R ) relationships and derive the relationship at a series of temporal scales ranging from a climatological scale to a sub-event scale.
Abstract: This study focuses on the sensitivity of streamflow simulations to temporal variations in radar reflectivity–rainfall (i.e., Z–R ) relationships. The physically based continuous-mode distributed hydrologic model—gridded surface subsurface hydrologic analysis—is used to predict runoff during three major rainfall-runoff periods observed in a 35 km2 experimental watershed in southern Louisiana. Z–R relationships are derived at a series of temporal scales ranging from a climatological scale, where interstorm Z–R variations are ignored, down to a subevent scale, where variations in rainfall type (convective versus stratiform) are taken into account. The analysis is first performed using Z and R data pairs derived directly from disdrometer drop size distribution measurements, and then repeated using WSR-88D radar reflectivity data. The degree of sensitivity in runoff simulations to temporal variations in Z–R relationships depends largely on the method used to derive the parameters of these relationships. Using ...
TL;DR: In this paper, an attempt has been made to effectively utilize the synergy of various approaches providing microphysical information of precipitation to study short term variations in a Mesoscale Convective System (MCS).
Abstract: [1] An attempt has been made, for the first time, to effectively utilize the synergy of various approaches providing microphysical information of precipitation to study short term variations in a Mesoscale Convective System (MCS). A campaign has been conducted wherein rain samples are collected during the passage of MCSs over Gadanki, India, and simultaneously a powerful VHF radar and disdrometer have been operated to infer the characteristics of the vertical structure and rain drop size distribution (DSD) of precipitation. Besides the convection and transition rain, two distinctly different phases of the stratiform rain are identified. Evaporation of rain drops seems to be significant in both convection and stratiform portions of MCS. Observed changes in the temporal variation of the stable oxygen isotope ratios (δ18O) of precipitation are interpreted in terms of microphysical processes leading to isotopic fractionation. The pattern of variability in isotopic abundance is found to be different from convection to transition and to stratiform rain. The present analysis clearly shows that the height (or temperature) and the rain regime of condensation are of paramount importance in determining δ18O. Correlations of δ18O with rainfall integral parameters stress the need for caution in interpreting the depleted isotopic ratios are due to high rainfall and/or bigger drops.
TL;DR: In this article, a model of rain shaft microphysics was used to simulate the evolution of a stratiform rainfall event during the Tropical Warm Pool-International Cloud Experiment (TWP-ICE) in Darwin, Australia.
Abstract: A model of rain shaft microphysics that solves the stochastic advection–coalescence–breakup equation in an atmospheric column was used to simulate the evolution of a stratiform rainfall event during the Tropical Warm Pool-International Cloud Experiment (TWP-ICE) in Darwin, Australia. For the first time, a dynamic simulation of the evolution of the drop spectra within a one-dimensional rain shaft is performed using realistic boundary conditions retrieved from real rain events. Droplet size distribution (DSD) retrieved from vertically pointing radar (VPR) measurements are sequentially imposed at the top of the rain shaft as boundary conditions to emulate a realistic rain event. Time series of model profiles of integral parameters such as reflectivity, rain rate, and liquid water content were subsequently compared with estimates retrieved from vertically pointing radars and Joss–Waldvogel disdrometer (JWD) observations. Results obtained are within the VPR retrieval uncertainty estimates. Besides eva...
TL;DR: In this paper, a preliminary method using the copolar reflectivity, differential reflectivity and ρco is given for estimating the broad drop size distributions (DSDs) parameters and validation is carried out by deriving the differential propagation phase from the estimated DSD parameters and comparing against measurements.
Abstract: A decrease in copolar correlation coefficient (ρco) at C band has been observed for several rain events with broad drop size distributions (DSDs). Observational evidence comes from simultaneous measurements with a C-band dual-polarization radar and a 2D video disdrometer. The possibility of utilizing the ρco decrease for DSD retrievals is discussed. A preliminary method using the copolar reflectivity, differential reflectivity, and ρco is given for estimating the DSD parameters. Validation is carried out by deriving the differential propagation phase (Φdp) from the estimated DSD parameters and comparing against measurements. The method presented here shows potential but needs to be further assessed in different rain climatologies.
TL;DR: In this article, concurrent data from two makes of laser disdrometer, fitting gamma distributions to each minute's data, was considered and it was shown that there does appear to be a relationship between the shape and slope parameters.
TL;DR: In this paper, an error analysis is presented to quantify the effect of atmospheric turbulence, vertical ambient air motion, selection of fall speed relationships, and velocity thresholding on rainfall rate.
Abstract: Vertically pointed wind profiling radars can be used to obtain measurements of the underlying drop size distribution (DSD) for a rain event by means of the Doppler velocity spectrum. Precipitation parameters such as rainfall rate, radar reflectivity factor, liquid water content, mass-weighted mean drop diameter, and median volume drop diameter can then be calculated from the retrieved DSD. The DSD retrieval process is complicated by the presence of atmospheric turbulence, vertical ambient air motion, selection of fall speed relationships, and velocity thresholding. In this note, error analysis is presented to quantify the effect of each of those factors on rainfall rate. The error analysis results are then applied to two precipitation events to better interpret the rainfall-rate retrievals. It was found that a large source of error in rain rate is due to unaccounted-for vertical air motion. For example, in stratiform rain with a rainfall rate of R = 10 mm h−1, a mesoscale downdraft of 0.6 m s−1 c...
01 Jan 2008
TL;DR: In this article, an error analysis is presented to quantify the effect of atmospheric turbulence, vertical ambient air motion, selection of fall speed relationships, and velocity thresholding on rainfall rate.
Abstract: Vertically pointed wind profiling radars can be used to obtain measurements of the underlying drop size distribution (DSD) for a rain event by means of the Doppler velocity spectrum. Precipitation parameters such as rainfall rate, radar reflectivity factor, liquid water content, mass-weighted mean drop diameter, and median volume drop diameter can then be calculated from the retrieved DSD. The DSD retrieval process is complicated by the presence of atmospheric turbulence, vertical ambient air motion, selection of fall speed relationships, and velocity thresholding. In this note, error analysis is presented to quantify the effect of each of those factors on rainfall rate. The error analysis results are then applied to two precipitation events to better interpret the rainfall-rate retrievals. It was found that a large source of error in rain rate is due to unaccounted-for vertical air motion. For example, in stratiform rain with a rainfall rate of R 10 mm h 1 , a mesoscale downdraft of 0.6 m s 1 can result in a 34% underestimation of the estimated value of R. The fall speed relationship selection and source of air density information both caused negligible errors. Errors due to velocity thresholding become more important in the presence of significant contamination near 0 m s 1 , such as ground clutter. If particles having an equivalent volume diameter of 0.8 mm and smaller are rejected, rainfall rate errors from 4% to 10% are possible, although these estimates depend on DSD and rainfall rate.
TL;DR: In this article, a procedure to correct the reflectivity data from multiple radars is proposed, where the TRMM/PR (Tropical Rainfall Measurement Mission satellite/Precipitation Radar) is used as the standard calibrator.
Abstract: A procedure to correct the reflectivity data from multiple radars is proposed. The TRMM/PR (Tropical Rainfall Measurement Mission satellite/Precipitation Radar) is used as the standard calibrator. The data from a disdrometer is also used to account for the effects of rain attenuation at short wavelengths. The procedure is evaluated in the case of oceanic rain observed in MISMO (Mirai Indian Ocean cruise for the Study of the MJO-convection Onset), in which two radars were deployed; a C-band shipborne radar and an X-band ground-based radar.On the C-band radar, the traditional corrections for the factors such as rain attenuation, second-trip echos, shadows by obstacles, and noise, result in reflectivity data which closely matches that of the TRMM/PR. For the X-band radar, iterative matching to the TRMM/PR worked effectively to correct the reflectivity, with the aid of the disdrometer data to reflect the attenuation by the rain in the vicinity of the radar. The corrected reflectivity from both radars well matches that of TRMM/PR with negligible biases and reduced deviations.
TL;DR: In this article, the authors present results of a comparative analysis of rainfall data from several ground-based instruments, including two vertically pointing Doppler radars, S-band and X-band, an optical disdrometer, and a tipping-bucket rain gauge.
Abstract: . The authors present results of a comparative analysis of rainfall data from several ground-based instruments. The instruments include two vertically pointing Doppler radars, S-band and X-band, an optical disdrometer, and a tipping-bucket rain gauge. All instruments were collocated at the Iowa City Municipal Airport in Iowa City, Iowa, for a period of several months. The authors used the rainfall data derived from the four instruments to first study the temporal variability and scaling characteristics of rainfall and subsequently assess the instrumental effects on these derived properties. The results revealed obvious correspondence between the ground and remote sensors, which indicates the significance of the instrumental effect on the derived properties.
TL;DR: This study seeks to explore the differences of RSD-derived moments for distinct hydroclimate regions, and characterize the distribution of the inter-rain duration and rain duration to design a semi-Markov chain to represent the intermittency feature of the rainfall process in a climatological framework.
Abstract: A large data set of raindrop size distribution (RSD) measurements collected with the Joss-Waldvogel disdrometer (JWD) and the 2-D video disdrometer (2DVD) in the U.K., Greece, Japan, and the U.S. are analyzed and modeled. This work extends a previous effort devoted to the exploitation of U.K. data and the design of a stochastic procedure to randomly generate synthetic RSD intermittent time series. This study seeks to: (1) explore the differences of RSD-derived moments for distinct hydroclimate regions, ranging from tropics to subtropics and mid and northern latitudes; (2) compare the governing parameters of the normalized gamma RSD for both stratiform and convective events and perform a sensitivity analysis by using different best fitting techniques; (3) exploit the time-correlation structure of the estimated RSD parameters as the input of a vector autoregressive stationary model used to simulate time series (or horizontal profiles) of RSDs and, consequently, its moments as the rain rate and concentration; and (4) characterize the distribution of the inter-rain duration and rain duration to design a semi-Markov chain to represent the intermittency feature of the rainfall process in a climatological framework. This climatological analysis and the related stochastic RSD generation model may find useful applications within both hydrometeorology and radio propagation.
05 May 2008
TL;DR: Simulation of the synthetic storm technique applied to the rain rate time series measurements closely with results obtained from ITU-R P.530-10 shows that the incident direction of storm velocity and the assumption link location, influence rain attenuation statistic.
Abstract: Results of rain attenuation statistics measurement in Surabaya using an optical disdrometer is reported. Rain attenuation statistic obtained simulation of the synthetic storm technique applied to the rain rate time series measurements closely with results obtained from ITU-R P.530-10 for outage probabilities 0.01-0.1%. For an outage probabilities less than 0.01% that predicted by SST have large rain attenuation than ITU-R P.530-10. The simulation results show that the incident direction of storm velocity and the assumption link location, influence rain attenuation statistic.
01 Jan 2008
01 Jun 2008
TL;DR: In this paper, a new approach is proposed to retrieve the rain drop size distribution (RDSD) by the combined use of velocity spectra of L-band and VHF wind profilers by taking into account of updrafts/downdrafts.
Abstract: A new approach is proposed to retrieve the rain drop size distribution (RDSD) by the combined use of velocity spectra of L–band and VHF wind profilers by taking into account of updrafts/downdrafts. The corrected velocity spectra during rain are fitted with the lognormal functional form by using the Marquerdt-Levenberg algorithm. The corrected velocity spectrum of the L-band profiler is converted to RDSD spectrum. On 22-23 June 2000, for convective and stratiform rain, the retrieved rain integral parameters from the wind profilers are compared with Joss-Waldovegel Disdrometer (JWD) measurements. Reasonably good agreement is found between the observations from these two systems, when the updrafts/downdrafts corrections are applied. During the convective rain, for rain rate, the root mean square (rmse) and correlation coefficients are found to be 5.0 mm/h and 0.74, respectively and for mean rain drop diameter (Dm) the rmse and correlation coefficient are 0.66 mm and 0.58. Similarly during stratiform rain, rmse and correlation coefficients for rain rate are found to be 1.01 mm/h and 0.71. For Dm, the rmse and correlation coefficient are 0.67 mm and 0.65, respectively. An inverse relationship is observed between profiler derived total number of drops (Nt) and Dm.
TL;DR: In this article, a ground-based 2D disdrometer was used to measure the terminal velocities of raindrops and their size distributions, and the relation between raindrop diameter and terminal velocity in terms of the Power-Law relation was analyzed.
Abstract: In this article, we take advantage of a terrestrial propagation link at Ka-band 19.5 GHz located on the campus of the National Central University in Chung-Li City to carry out a tropospheric radio propagation experiment. Data collected in 2004 were used in data analysis to provide a deeper understanding of the precipitation effect on tropospheric electromagnetic wave propagation at Ka-band. The results indicate that the relation between specific attenuation ĸe of 19.5 GHz radio wave amplitude and the measured rain fall rate R (in unit of mm hr -1 ) is of the form: ĸe = aR b (in unit dB km -1 ) with a = 0.0699 and b = 1.0984, which is fairly close to that obtained by assuming Laws-Parsons drop size distribution. In order to study the overall attenuation characteristics of Ka-band radio wave influenced by precipitation particles, we used a ground-based 2D disdrometer to measure the terminal velocities of raindrops and their size distributions. The result shows that the relation between raindrop diameter and terminal velocity in terms of the Power-Law relation, i.e., V(D) = AD B , and the drop size distribution can be expressed in the form of a Gamma distribution function, i.e., N(D) = N0D μ exp(-δD). With these results, the corresponding rain attenuation of the electromagnetic wave at Ka-band is estimated and discussed in this article.
01 Apr 2008
16 May 2008
TL;DR: In order to improve the precision of Radar rainfall estimates, the Parsivel was used for observation of rain drop spectra over Leizhou Peninsula from July to August, 2007 as discussed by the authors.
Abstract: In order to improve the precision of Radar rainfall estimates, the Parsivel was used for observation of rain drop spectra over Leizhou Peninsula from July to August, 2007. A total of 18070 size distributions were analyzed and the Z-R relationship of convective precipitation and mixtures of convective and stratocumulus cumulogenitus precipitation were obtained. These Z-R values were used for estimating areal rainfall and then compared with observations from automatic weather station. Cases with convective and mixtures of convective and stratocumulus cumulogenitus precipitation were selected for the evaluation. The precipitation studies were also used to evaluate the precision of the PARSIVEL measurements as compared to the rainfall data of automatic weather station.