Disdrometer

About: Disdrometer is a research topic. Over the lifetime, 930 publications have been published within this topic receiving 23092 citations.

Measurements and Modeling of the Full Rain Drop Size Distribution

Abstract: The raindrop size distribution (DSD) is fundamental for quantitative precipitation estimation (QPE) and in numerical modeling of microphysical processes. Conventional disdrometers cannot capture the small drop end, in particular the drizzle mode which controls collisional processes as well as evaporation. To overcome this limitation, the DSD measurements were made using (i) a high-resolution (50 microns) meteorological particle spectrometer to capture the small drop end, and (ii) a 2D video disdrometer for larger drops. Measurements were made in two climatically different regions, namely Greeley, Colorado, and Huntsville, Alabama. To model the DSDs, a formulation based on (a) double-moment normalization and (b) the generalized gamma (GG) model to describe the generic shape with two shape parameters was used. A total of 4550 three-minute DSDs were used to assess the size-resolved fidelity of this model by direct comparison with the measurements demonstrating the suitability of the GG distribution. The shape stability of the normalized DSD was demonstrated across different rain types and intensities. Finally, for a tropical storm case, the co-variabilities of the two main DSD parameters (normalized intercept and mass-weighted mean diameter) were compared with those derived from the dual-frequency precipitation radar onboard the global precipitation mission satellite.

Improving Drop Size and Velocity Estimates of an Optical Disdrometer: Implications for Sprinkler Irrigation Simulation

Abstract: Optical disdrometers measure the attenuation of an infrared beam when water drops pass between the emitter and the receptor. The duration and intensity of the attenuation are used to estimate drop size and time of passage. These variables are used to calibrate and validate ballistic sprinkler simulation models. Two experimental problems affect the quality of the measurements: first, drops can pass to the side of the detector, so that only part of the drop attenuates the luminous flow; and second, several drops can overlap as they pass through the beam. This work presents a statistical treatment of the observed time of passage that can be used to eliminate a large part of the erroneous measurements, significantly improving the accuracy of disdrometer data. Furthermore, drop velocities can be estimated from the corrected times of passage. Simulation with the ballistic model shows that the minimum drop size accurately measured by the disdrometer is too large to characterize the fine diameters typical of drops landing close to the emitter. For farther landing distances, the discrepancies between measurements and simulations using ballistic theory can be large. Differences in drop velocity, drop size, and maximum sprinkler reach are discussed in this article. From our results, it can be concluded that the ballistic model (assuming independent movement of drops) constitutes an excessive simplification of reality. We believe that group displacement of the drops, resulting in a reduced air drag and in an increased probability of drop collision, is responsible for a relevant part of the reported differences.

Characterization of tropical precipitation using drop size distribution and rain rate-radar reflectivity relation

Abstract: Characterization of precipitation is important for proper interpretation of rain information from remotely sensed data. Rain attenuation and radar reflectivity (Z) depend directly on the drop size distribution (DSD). The relation between radar reflectivity/rain attenuation and rain rate (R) varies widely depending upon the origin, topography, and drop evolution mechanism and needs further understanding of the precipitation characteristics. The present work utilizes 2 years of concurrent measurements of DSD using a ground-based disdrometer at five diverse climatic conditions in Indian subcontinent and explores the possibility of rain classification based on microphysical characteristics of precipitation. It is observed that both gamma and lognormal distributions are performing almost similar for Indian region with a marginally better performance by one model than other depending upon the locations. It has also been found that shape-slope relationship of gamma distribution can be a good indicator of rain type. The Z-R relation, Z = ARb, is found to vary widely for different precipitation systems, with convective rain that has higher values of A than the stratiform rain for two locations, whereas the reverse is observed for the rest of the three locations. Further, the results indicate that the majority of rainfall (>50%) in Indian region is due to the convective rain although the occurrence time of convective rain is low (<10%).

The Green Ocean: precipitation insights from the GoAmazon2014/5 experiment

Abstract: This study summarizes the precipitation properties collected during the GoAmazon2014/5 campaign near Manaus in central Amazonia, Brazil Precipitation breakdowns, summary radar rainfall relationships and self-consistency concepts from a coupled disdrometer and radar wind profiler measurements are presented The properties of Amazon cumulus and associated stratiform precipitation are discussed, including segregations according to seasonal (wet or dry regime) variability, cloud echo-top height and possible aerosol influences on the apparent oceanic characteristics of the precipitation drop size distributions Overall, we observe that the Amazon precipitation straddles behaviors found during previous US Department of Energy Atmospheric Radiation Measurement (ARM) program tropical deployments, with distributions favoring higher concentrations of smaller drops than ARM continental examples Oceanic-type precipitation characteristics are predominantly observed during the Amazon wet seasons An exploration of the controls on wet season precipitation properties reveals that wind direction, compared with other standard radiosonde thermodynamic parameters or aerosol count/regime classifications performed at the ARM site, provides a good indicator for those wet season Amazon events having an oceanic character for their precipitation drop size distributions

On the Estimation of Surface Runoff through a New Plot Scale Rainfall Simulator in Sardinia, Italy☆

Abstract: Artificial rainfall is widely used to study the surface runoff process but several problems are related to the reproducibility of natural rainstorms. A new rainfall simulator and a collection system were designed and tested in the laboratory and in the field. The rainfall simulator consists of four independent lines of low-cost pressure washing nozzles operated at a pressure of 80 mbar which number and position causes the rainfall intensity delivered on the plot. The spatial rainfall distribution and his intensity were measured with 63 rainfall gauges covering the whole plot The Joss Waldvogel Disdrometer was used to characterize the rainfall produced by the rainfall simulator. The drop size distribution was obtained. The drop size spectrum ranges from 0.25 mm to 3.3 mm and its shape is the same to that one produced by a natural rainfall. The rainfall intensity varies from approximately 31 to 62 mm/h and it is sufficiently spatially uniform (Christiansen's coefficient of uniformity is 0.62 to 0.75) over the plot. Field tests were carried out in on a grassy field with silt-loam soil in Orroli, Sardinia in July and August 2010. The values of the mean rainfall intensities obtained from field data are in accord with the laboratory values. The field site measurement includes the surface runoff, evaluated using a dedicated tipping bucket flow meter, and the soil water content measured throughout the field experiments. The results showed the good performance of this new rainfall simulator that offers the possibility to reproduce natural rainfall to gather parameters needed for hydrologic modeling. The entire designed system offers the possibility to carry out reliable measurements of the surface runoff under different rain intensities and also allows one to measure this on different temporal scales by taking into account the differen environmental conditions.