Showing papers on "Disdrometer published in 2009"

Impact of Cloud Microphysics on the Development of Trailing Stratiform Precipitation in a Simulated Squall Line: Comparison of One- and Two-Moment Schemes

Abstract: A new two-moment cloud microphysics scheme predicting the mixing ratios and number concentrations of five species (i.e., cloud droplets, cloud ice, snow, rain, and graupel) has been implemented into the Weather Research and Forecasting model (WRF). This scheme is used to investigate the formation and evolution of trailing stratiform precipitation in an idealized two-dimensional squall line. Results are compared to those using a one-moment version of the scheme that predicts only the mixing ratios of the species, and diagnoses the number concentrations from the specified size distribution intercept parameter and predicted mixing ratio. The overall structure of the storm is similar using either the one- or two-moment schemes, although there are notable differences. The two-moment (2-M) scheme produces a widespread region of trailing stratiform precipitation within several hours of the storm formation. In contrast, there is negligible trailing stratiform precipitation using the one-moment (1-M) scheme. The primary reason for this difference are reduced rain evaporation rates in 2-M compared to 1-M in the trailing stratiform region, leading directly to greater rain mixing ratios and surface rainfall rates. Second, increased rain evaporation rates in 2-M compared to 1-M in the convective region at midlevels result in weaker convective updraft cells and increased midlevel detrainment and flux of positively buoyant air from the convective into the stratiform region. This flux is in turn associated with a stronger mesoscale updraft in the stratiform region and enhanced ice growth rates. The reduced (increased) rates of rain evaporation in the stratiform (convective) regions in 2-M are associated with differences in the predicted rain size distribution intercept parameter (which was specified as a constant in 1-M) between the two regions. This variability is consistent with surface disdrometer measurements in previous studies that show a rapid decrease of the rain intercept parameter during the transition from convective to stratiform rainfall.

Using Dual-Polarized Radar and Dual-Frequency Profiler for DSD Characterization: A Case Study from Darwin, Australia

Abstract: Comparisons are made between the reflectivity Z, median volume diameter D0, and rain rate R from a dual-frequency profiler and the C-band polarimetric radar (C-POL), which are both located near Darwin, Australia. Examples from the premonsoon “buildup” regime and the monsoon (oceanic) regime are used to illustrate the excellent agreement between the dual-profiler retrievals and the polarimetric radar-based retrievals. This work builds on similar works that were limited in scope to shallow tropical showers and predominantly stratiform rain events. The dual-frequency profiler retrievals of D0 and R herein are based on ensemble statistics, whereas the polarimetric radar retrievals are based on algorithms derived by using one season of disdrometer data from Darwin along with scattering simulations. The latest drop shape versus D relation is used as well as the canting angle distribution results obtained from the 80-m fall bridge experiment in the scattering simulations. The scatterplot of D0 from dual...

Characteristics of the Raindrop Size Distribution and Drop Shape Relation in Typhoon Systems in the Western Pacific from the 2D Video Disdrometer and NCU C-Band Polarimetric Radar

Abstract: The drop size distribution (DSD) and drop shape relation (DSR) characteristics that were observed by a ground-based 2D video disdrometer and retrieved from a C-band polarimetric radar in the typhoon systems during landfall in the western Pacific, near northern Taiwan, were analyzed. The evolution of the DSD and its relation with the vertical development of the reflectivity of two rainband cases are fully illustrated. Three different types of precipitation systems were classified—weak stratiform, stratiform, and convective—according to characteristics of the mass-weighted diameter Dm, the maximum diameter, and the vertical structure of reflectivity. Further study of the relationship between the height H of the 15-dBZ contour of the vertical reflectivity profile, surface reflectivity Z, and the mass-weighted diameter Dm showed that Dm increased with a corresponding increase in the system depth H and reflectivity Z. An analysis of DSDs retrieved from the National Central University (NCU) C-band pola...

Errors in Estimating Raindrop Size Distribution Parameters Employing Disdrometer and Simulated Raindrop Spectra

Abstract: There have been debates and differences of opinion over the validity of using drop size distribution (DSD) models to characterize precipitation microphysics and to retrieve DSD parameters from multiparameter radar measurements. In this paper, simulated and observed rain DSDs are used to evaluate moment estimators. Seven estimators for gamma DSD parameters are evaluated in terms of the biases and fractional errors of five integral parameters: radar reflectivity (ZH), differential reflectivity (ZDR), rainfall rate (R), mean volume diameter (Dm), and total number concentration (NT). It is shown that middle-moment estimators such as M234 (using the second-third-fourth moments) produce smaller errors than lower- and higher-moment estimators if the DSD follows the gamma distribution. However, if there are model errors, the performance of M234 degrades. Even though the DSD parameters can be biased in moment estimators, integral parameters are usually not. Maximum likelihood (ML) and L-moment (LM) estima...

A Field Study of Reflectivity and Z–R Relations Using Vertically Pointing Radars and Disdrometers

Abstract: Observations from a 16-month field study using two vertically pointing radars and a disdrometer at Wallops Island are analyzed to examine the consistency of the multi-instrument observations with respect to reflectivity and Z–R relations. The vertically pointing radars were operated at S and K bands and had a very good agreement in reflectivity at a gate centered on 175 and 177 m above ground level over a variety of storms. This agreement occurred even though the sampling volumes were of different size and even though the S band measured the reflectivity factor directly, whereas the K-band radar deduced it from attenuated K-band measurements. Indeed, the radar agreement in reflectivity at the collocated range gates was superior to that between the disdrometer and either radar. This is attributed in large part to the spatial separation of the disdrometer and radar sample volumes, although the lesser agreement observed in a prior collocated disdrometer–disdrometer comparison suggests the larger siz...

Drop Shapes and Axis Ratio Distributions: Comparison between 2D Video Disdrometer and Wind-Tunnel Measurements

Abstract: Comparisons of drop shapes between measurements made using 2D video disdrometer (2DVD) and wind-tunnel experiments are presented. Comparisons are made in terms of the mean drop shapes and the axis ratio distributions. Very close agreement of the mean shapes is seen between the two sets of measurements; the same applies to the mean axis ratio versus drop diameter. Also, in both sets of measurements, an increase in the oscillation amplitudes with increasing drop diameter is observed. In the case of the 2DVD, a small increase in the skewness was also detected. Given that the two sets of measurements were conducted in very different conditions, the agreement between the two sets of data implies a certain “robustness” in the mean shape of oscillating drops that may be extended to natural raindrop oscillations, at least in steady rainfall and above the surface layer.

Calibration of simulated rainfall characteristics for the study of soil erosion on agricultural land.

Abstract: Rainfall simulation is a widely used method for soil erosion studies on agricultural land. Major problem of this experimental research method is the comparability between different simulators due to differences in simulated rainfall. Therefore the purpose of this study is to characterize the rainfall produced by a rainfall simulator which was widely used during the last decades. Four different calibration methods were used to assess the drop size distribution: (1) Indication Paper, (2) Plaster Micro Plot, (3) Joss–Waldvogel Disdrometer and (4) Laser Distrometer (Thies). Additionally, the latter one was used to measure drop fall velocity in combination with drop diameter. The spatial rainfall distribution pattern on the plot was measured with 100 rainfall gauges. The spatial rainfall distribution pattern clearly shows a heterogeneity, which is caused by the used nozzle configuration. Considerable differences in drop-size distribution can be observed depending on the used measurement technique. Laser Disdrometer and Plaster Micro Plot cover the whole produced drop size spectrum ranging from 3.0 mm, whereas Indication Paper as well as the Joss–Waldvogel Disdrometer primarily show drops smaller than 2.0 mm. Characterisation of rainfall is therefore strongly dependent on the used method and if different methods are used, may lead to contradictory results. The volume drop size distribution reflected by the Laser Distrometer is very similar to that one produced by rain with an intensity of 40 mm h −1 . Nevertheless, with maximum velocities above 10 m s −1 small drops are by far too fast and large drops with velocities dominantly below 5 m s −1 are too slow compared to natural rainfall. As an overall result, the simulator can be characterised as suitable for runoff and infiltration measurements, but with constraints due to the low reproducibility of the spatial rain distribution. As a consequence of the produced drop spectrum and fall velocity the erosion quantities may be underestimated systematically. For this, methodological development has to be focussed on homogeneous spatial rainfall distributions and on increasing the amount of large drops with higher fall velocities.

A Preliminary Analysis of Spatial Variability of Raindrop Size Distributions during Stratiform Rain Events

Abstract: The spatial variability of raindrop size distributions (DSDs) and precipitation fields is investigated utilizing disdrometric measurements from the four Precipitation Occurrence Sensor Systems (POSS) and radar reflectivity fields from S-band dual-polarization radar and vertically pointing X-band radar. The spatial cross correlation of the moments of DSDs, their ratio, error in rainfall estimate, and normalization parameters are quantified using a “noncentered” correlation function. The time-averaged spatial autocorrelation function of observed radar reflectivity factor (Ze) is smaller than that of estimated rainfall rate from Ze because of power-law R–Z transformation with its exponent larger than unity. The important spatial variability of DSDs and rain integral fields is revealed by the significant differences among average DSDs and leads to an average fractional error of 25% in estimating rainfall accumulation during an event. The spatial correlation of the reflectivity from POSS is larger tha...

Diurnal Variation of Rain Attenuation Obtained From Measurement of Raindrop Size Distribution in Equatorial Indonesia

Abstract: The measured rain rate, raindrop size distribution (DSD), and the ITU-R model over the frequency range from 1-100 GHz have been used to elucidate the cumulative rainfall rate and the variability of rain attenuation at Kototabang. Rain rate and DSD are recorded from ground-based optical rain gauge and disdrometer measurements, respectively. Considerable differences between the recorded data and the ITU-R model are observed at small time percentage. The specific rain attenuation obtained from the DSD measurement shows diurnal variation with the largest attenuation observed in the morning hours. This characteristic is due to the raindrop spectra of rain events in this period containing more small-sized drops (<2 mm) than at others as described by the largest contribution of these drops on the specific rain attenuation. The diurnal variation is serious for frequencies higher than 60 GHz especially in very extreme rain.

The Effect of Rain–No Rain Intermittency on the Estimation of the Universal Multifractals Model Parameters

Abstract: The multifractal properties of rain are investigated within the framework of universal multifractals. The database used in this study includes measurements performed over several months in different locations by means of a disdrometer, the dual-beam spectropluviometer (DBS). An assessment of the effect of the rain–no rain intermittency shows that the analysis of rain-rate time series may lead to a spurious break in the scaling and to erroneous parameters. The estimation of rain multifractal parameters is, therefore, performed on an event-by-event basis, and they are found to be significantly different from those proposed in scientific literature. In particular, the parameter H, which has often been estimated to be 0, is more likely to be 0.53, thus meaning that rain is a fractionally integrated flux (FIF). Finally, a new model is proposed that simulates high-resolution rain-rate time series based on these new parameters and on a simple threshold.

Variability of rainfall rate and raindrop size distributions in heavy rain

Abstract: [1] A stochastic model of rainfall rate is used to examine the temporal variability of rainfall during heavy convective rain periods. The model represents the microstructure of rainfall rate at time scales that are important for land surface processes associated with infiltration and runoff production. The representation of rainfall rate is based on a marked point process model of raindrop size distributions, which yields a gamma raindrop spectrum with parameters that are time-varying stochastic processes. Raindrop size distribution observations from a Joss-Waldvogel disdrometer in Princeton, New Jersey, during the period May–October 2006 are used along with the stochastic model to examine rainfall rate variability. Analyses focus on a sample of 60-min time periods in which heavy convective rainfall occurred. Central elements of the analyses entail examination of the relationships between rainfall rate and the time-varying model parameters that characterize the raindrop size distribution. We also examine the dependence structure among these processes. “Scaling law” formulations of raindrop size distributions are used to examine variability of raindrop size distributions. Analyses of the Princeton heavy rainfall periods also point to seasonal and diurnal heterogeneities as important elements of the distribution of extreme rainfall rates. Convective intensity, as reflected in cloud-to-ground lightning observations, plays an important role in the distribution of extreme rainfall rates and the evolution of raindrop size distributions associated with heavy rainfall.

Characteristics of Rain Integral Parameters during Tropical Convective, Transition, and Stratiform Rain at Gadanki and Its Application in Rain Retrieval

Abstract: In the present study the characteristics of rain integral parameters during tropical convective (C), transition (T), and stratiform (S) types of rain are studied with the help of Joss–Waldvogel disdrometer (JWD), L-band, and very-high-frequency wind profilers at Gadanki (13.5°N, 79.20°E). The classifications of three regimes are made with the help of an L-band wind profiler. For rain rate R C > S rain. During the three types of rain, correlations are found in the order of Z/Dm–R > Z–R > Dm–Z > Dm–R. Significant improvement is observed in rain retrieval by using the Z/Dm–R relation relative to the conventional Z–R relation. By utilizing the Z/Dm–R relations, the root-mean-square error was reduced by 19%–46%.

Estimation of Gamma Raindrop Size Distribution Parameters: Statistical Fluctuations and Estimation Errors

Abstract: The gamma distribution is often used to characterize raindrop size distributions (DSDs). However, the estimation of measured raindrop distributions suffers from the shortcomings of statistical sampling errors, which become increasingly significant when the collecting surface of the measuring instrument and the integration time are small. Different estimators of the three parameters (N0*, μ, and Dm) that characterize a normalized gamma distribution have been computed from simulated DSD. A database has been established, containing 22 950 simulated DSDs, corresponding to a wide set of various rainfall situations. Moment, least squares, and maximum likelihood estimators have been evaluated. Error measurement considerations are discussed, in particular the difficulty encountered in measuring small drops (diameter <0.5 mm) with a disdrometer. Modified estimation approaches are proposed to compensate for the lack of small drops accounted for by real measurements. For each of the different methods, syste...

Comparing methodologies for the characterization of water drops emitted by an irrigation sprinkler.

Abstract: A variety of techniques have been proposed for sprinkler drop characterization. Two of them, the disdrometer method (D) and the low-speed photographic method (P), have recently been applied in the literature. A statistical method for the improvement of disdrometer measurements (DM) has been proposed to improve D measurements. The aims of this study were: (1) to compare the disdrometer and photographic methods under indoor conditions, (2) to produce a drop characterization data set, (3) to assess the effect of the statistical treatment of disdrometer data, and (4) to gain insight into the relationship between drop variables. The drops resulting from an impact sprinkler operating at 200, 300, and 400 kPa were characterized at distances of 3, 6, 9, and 12 m from the sprinkler. In each method, diameters responded to operating pressure and distance from the sprinkler according to the expected trends. The difference in volumetric diameter estimation between methods P and D amounted to -4% of the average P volumetric diameter. The application of DM to this data set increased the difference in volumetric diameter with method P to 15%. Drop velocity and angle could be measured with method P and showed clear relationships with drop diameter. Finally, regression equations are presented relating the most relevant experimental variables. The disdrometer resulted in fast measurements of drop diameter, while the photographic method provided additional variables but required intense work in the laboratory and particularly in the office.

Rain microstructure retrievals using 2-D video disdrometer and C-band polarimetric radar

Abstract: . Measurements using the 2-D video disdrometer (2DVD) taken during a heavy rainfall event in Huntsville, Alabama, are analysed. The 2DVD images were processed to derive the rain microstructure parameters for each individual drop, which in turn were used as input to the T-matrix method to compute the forward and back scatter amplitudes of each drop at C-band. The polarimetric radar variables were then calculated from the individual drop contribution over a finite time period, e.g., 1 min. The calculated co-polar reflectivity, differential reflectivity, specific differential propagation phase and the co-polar correlation coefficient were compared with measurements from a C-band polarimetric radar located 15 km away. An attenuation-correction method based on the specific differential propagation phase was applied to the co-polar and differential reflectivity data from the C-band radar, after ensuring accurate radar calibration. Time series comparisons of the parameters derived from the 2DVD and C-band radar data show very good agreement for all four quantities, the agreement being sometimes better than the computations using the 1-min drop size distribution and bulk assumptions on rain microstructure (such as mean shapes and model-based assumptions for drop orientation). The agreement is particularly improved in the case of co-polar correlation coefficient since this parameter is very sensitive to variation of shapes as well as orientation angles. The calculations mark the first attempt at utilizing experimentally derived "drop- by-drop" rain microstructure information to compute the radar polarimetric parameters and to demonstrate the value of utilizing the 2-D video disdrometer for studying rain microstructure under various precipitation conditions. Histograms of drop orientation angles as well as the most probable drop shapes and the corresponding variations were also derived and compared with prior results from the 80 m fall "artificial rain" experiment.

A Method to Estimate Vertically Integrated Amounts of Cloud Ice and Liquid and Mean Rain Rate in Stratiform Precipitation from Radar and Auxiliary Data

Abstract: A method to retrieve total vertical amounts of cloud liquid and ice in stratiform precipitating systems is described. The retrievals use measurements from the vertically pointing Ka- and W-band cloud radars operated by the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program and auxiliary measurements from a scanning National Weather Service radar and a ground-based disdrometer. Separation between the cloud liquid and rain is based on estimations of the total attenuation of millimeter-wavelength radar signals in the liquid hydrometeor layer. Disdrometer measurements are used for the retrieval constraints. Because the liquid phase hydrometeor retrievals use only differential measurements, they are immune to the absolute radar calibration uncertainties. Estimates of the ice cloud phase are performed using empirical relations between absolute radar reflectivity and ice water content. Data from the nearby scanning weather-service radar, which operates at a lower frequency, are us...

Statistical Characteristics of Multipeak Raindrop Size Distributions at the Surface and Aloft in Different Rain Regimes

Abstract: Two years (∼672 h) of lower-atmospheric wind profiler (LAWP) and 4 yr (∼733 h) of Joss–Waldvogel disdrometer measurements are utilized to study the multipeak (MP) occurrence statistics at the surface and aloft. For the first time, an attempt has been made to address several key questions regarding MPs: their occurrence statistics and their dependency on height, season, and type of precipitation. MPs are not exceptional; rather, they are observed at all altitudes, albeit with different occurrence percentages. The occurrence of MPs seems to be height dependent, and this dependency varies with the type of rain system. The occurrence percentage of bimodal echo (two peaks) is high above (below) the melting level (ML) in convection (in other types of rain). The percentage occurrence of bimodal echo in warm rain is similar to that in cold rain, but only below the ML. The spectrum with more than two peaks appears to be predominantly in convection, particularly above 4 km. The MP statistics on the surface...

Disdrometer and Tipping Bucket Rain Gauge Handbook

Abstract: The Distromet disdrometer model RD-80 and NovaLynx tipping bucket rain gauge model 260-2500E-12 are two devices deployed a few meters apart to measure the character and amount of liquid precipitation. The main purpose of the disdrometer is to measure drop size distribution, which it does over 20 size classes from 0.3 mm to 5.4 mm. The data from both instruments can be used to determine rain rate. The disdrometer results can also be used to infer several properties including drop number density, radar reflectivity, liquid water content, and energy flux. Two coefficients, N0 and Λ, from an exponential fit between drop diameter and drop number density, are routinely calculated. Data are collected once a minute. The instruments make completely different kinds of measurements. Rain that falls on the disdrometer sensor moves a plunger on a vertical axis. The disdrometer transforms the plunger motion into electrical impulses whose strength is proportional to drop diameter. The rain gauge is the conventional tipping bucket type. Each tip collects an amount equivalent to 0.01 in. of water, and each tip is counted by a data acquisition system anchored by a Campbell CR1000 data logger.

Multipeak Raindrop Size Distribution Observed by UHF/VHF Wind Profilers during the Passage of a Mesoscale Convective System

Abstract: The Indian Mesosphere–Stratosphere–Troposphere radar (IMSTR), Lower Atmospheric Wind Profiler (LAWP), and Joss–Waldvogel (JW) disdrometer measurements during the passage of two distinctly different (in terms of total rain and rainfall rate) convective storms are utilized to understand the nature and origin of the multipeak raindrop size distribution (MRDSD). Important issues, such as the preferential stage and height at which bi- or multimodal rain distribution occurs in a mesoscale convective system (MCS) are addressed. For both of the storms, the MRDSD is observed during the transition period from convection to stratiform rain. The pattern and variation of the MRDSD during this period is strikingly similar in both of the storms. The MRDSD is first observed above the freezing level in the presence of heavy riming. The subsequent spectra have shown bimodal distribution below the freezing level, and the bimodality is attributed to the coexistence of ice and supercooled droplets. Interestingly, the...

Study of Z-R relationship over Gadanki for different rainfall rates

Abstract: In this paper, Z-R relationship for different rain fall rates over Gadanki has been studied over a period of four years 1998-2001. The basic data set consists of rainfall rates and reflectivities derived from disdrometer during this period. The study has been carried out for rainfall rates R� 0.5 mmh -1 , 0.5 50 mmh -1 . The study shows that Z-R relationship varies for different rainfall rates. The various functional relations

Analysis of the Variability in the Raindrop Size Distribution and Its Effect on Attenuation at 20-40 GHz

Abstract: A key problem in determining the level of attenuation from the rainfall rate is the considerable variability in the raindrop size distribution. This letter investigates the effects of the variability of the raindrop size distribution (DSD) on the estimation of specific attenuation. Disdrometer data from three sites in the U.K. were analyzed to derive the three parameters (Dm, mu, and Nw) of the normalized gamma distribution. The statistics of the parameters were analyzed as a function of time of year and rainfall intensity. From the raindrop size distribution data, the impact on attenuation at 20-40 GHz was investigated. A simple model to quantify the uncertainty of the raindrop size distribution has been created. Finally, we have shown qualitatively that differences between measured and modeled attenuation can partly be explained by uncertainty in the raindrop size distribution. Furthermore, we also show that although the model for mean attenuation is relatively constant, the standard deviation is much more variable even for sites in close proximity.

Classification of convective and stratiform types of rain and their characteristics features at a tropical location

Abstract: The effect of rain attenuation in high frequency signals need proper understanding of the variation of drop size distribution (DSD) separately in convective and stratiform rain due to different characteristics. This paper presents the analysis of variation of vertical rain rate profile for these two types from micro rain radar observations as well as the variation of DSD at ground using Disdrometer, of an event observed over Ahmedabad. The bright band signature in vertical rain rate profile is used for rain classification as well as the rain classification based on ground based DSD model is also attempted. The results highlight a rain classification scheme based on lognormal DSD parameter. It is also found that large drops size is more in convective cases associated with high rain rate. It is also observed that for lower rain rates, convective cases have smaller number of bigger drops than stratiform types of rain of same rain intensity. The information will be of importance for classification for rain and rain attenuation study.

Micro Rain Radar measurements of rainfall in Madrid

Abstract: A vertically pointing Doppler radar at 24.1 GHz, or Micro Rain Radar (MRR), has been installed at Universidad Politecnica de Madrid as part of the experimental set-up for propagation measurements that includes a tipping-bucket rain gauge and a disdrometer. The Doppler spectra measured by the MRR are converted into profiles of drop size density distributions. The MRR provides equally profiles of radar reflectivity, rainfall rate or terminal velocity, which can be useful to identify and analyse propagation effects produced by rain, once its behaviour has been assessed. With this aim, a study of MRR measurements is being performed. The analysis of MRR data corresponding to two different rainfall events, whose results are presented here, reveals characteristics in agreement with the stratiform or convective type of event.

Simultaneous estimates of cloud and rainfall parameters in the atmospheric vertical column above the Atmospheric Radiation Measurement Program southern Great Plains site

Abstract: [1] A novel remote sensing approach to simultaneously retrieve cloud liquid water paths (LWP) and ice water paths (IWP) and mean rainfall rate in a vertical atmospheric column was applied for stratiform-like precipitation events observed during the warm period of 2007 at the southern Great Plains site of the Atmospheric Radiation Measurement (ARM) Program. The retrieval method is based on multifrequency radar measurements at W, Ka, and S bands and raindrop size distribution estimates from a ground-based impact disdrometer. The radar measurements also provide a robust separation of the liquid, mixed, and ice hydrometeor layers. Characteristic values of LWP are about 300–400 g m−2, although values up to 1000 g m−2 and higher are not uncommon. There is on average insignificant correlation between cloud LWP and rainfall rates. IWP, which represents the precipitating cloud part of the atmospheric column that is observed above the freezing level, usually significantly exceeds cloud LWP in the liquid hydrometeor layer and can reach values of approximately 104 g m−2 and even higher. On average, mean rainfall in the liquid layer, Rm, increases with an increase in ice mass observed above the melting layer, although a corresponding mean correlation coefficient between Rm and IWP is only 0.32. There is noticeable variability in IWP-Rm relations between individual events. Storm dynamics is likely to influence the correlation between cloud and rainfall parameters as inferred from simultaneous columnar retrievals. Initial estimates indicate that IWP and rainfall are stronger related for events which exhibit lower vertical variability of wind.

CURIE: a low power X-band, low atmospheric Boundary Layer Doppler radar

Abstract: A new X-band Doppler miniradar, the CURIE radar (Canopy Urban Research on Interactions and Exchanges), mainly adapted to low Atmospheric Boundary Layer ABL sounding has been developed at LATMOS (Laboratoire Atmospheres, Milieux, Observations Spatiales) formerly CETP (Centre d'etude des Environnements Terrestre et Planetaires). After a brief description of the measurement conditions in a turbulent atmosphere, the main characteristics of the new sensor are presented. As an example, we compare CURIE vertical velocity fluctuations with UHF observations to show the vertical velocity measurement validity. As a prospective area of application in clear air, we focus on a first observation of vertical velocity variance which is supposed to be related to entrainment across the inversion layer. As our objective is to study low boundary layers during different atmospheric conditions and since the radar works in the presence of precipitation (as all X-band radar do), we also show vertical rain soundings in the lower part of the ABL and illustrate our findings with results demonstrating comparable reflectivity and precipitation rates as estimated with a disdrometer and with a rain gauge.

Calculations of cross‐polar discrimination spread for 20 GHz fixed satellite systems using rain microstructure information

Abstract: [1] Individual drop images in natural rain from a two-dimensional video disdrometer (2DVD) have been processed to obtain their shapes, sizes, and orientation angles, which, in turn, have been used to derive their complex forward scattering amplitudes at 19.701 GHz. Using these calculations, the specific attenuation for horizontal and vertical polarizations and the specific differential attenuation and the specific differential phase of all drops over 1 min are determined. A point-to-path scaling is used to derive the total rain attenuation for both polarizations as well as the total differential attenuation and the total differential phase. A 19.701 GHz experimental Earth-space link is simulated to determine the variation of cross-polar discrimination versus copolar attenuation (XPD-CPA) and the calculations are compared with 2 years of joint probability XPD-CPA beacon measurements. The comparisons indicate clearly that the variations in drop shape and drop orientation can give rise to significant spread in XPD.