DSD Model Research Articles

Characterization of rain microphysics on the leeside of the Western Ghats

AbstractThis study evaluates the performance of four impact‐type disdrometers installed at the Indian Institute of Tropical Meteorology, Pune, located on the leeside of the Western Ghats (WG). Further, seasonal variation of rain microphysical properties is studied during premonsoon (March–May), monsoon (June–September), postmonsoon (October–November), and winter (December–February). The four disdrometers exhibit comparable raindrop size distribution (DSD) patterns, though negligible differences are found at smaller drop diameters. The DSD shows higher concentrations of smaller (large‐size) drops during monsoon (premonsoon and postmonsoon). Principal component analysis revealed three distinct modes of DSD characteristics. Monsoon DSDs are associated with a group of numerous smaller drops allied with shallow storm heights (warm rain). The premonsoon and postmonsoon DSDs are clustered in a group where ice‐based processes dominate, resulting in higher median drop diameters (D0) and smaller normalized intercept parameters (Nw). The fitted gamma DSD model indicates higher mass‐weighted mean diameter (Dm) during premonsoon, and higher intercept parameter during monsoon, whereas postmonsoon and winter have intermediate values. DSD stratified with rain rate shows that the Dm values increase with an increase in rain rate during winter, monsoon and postmonsoon, whereas in premonsoon, Dm increases initially and then decreases. Higher Dm and lower Nw are observed during convective rain in all seasons. The fitted slope–shape parameter relationships show a considerable seasonal variation. The DSD on the WG's leeside is notably different from the windward slopes and other WG locations. Different microphysical and dynamical mechanisms lead to seasonal differences in DSD characteristics. In monsoon, a considerable volume of water vapour advected from the Arabian Sea promotes the formation of raindrops through collision–coalescence processes, which may result in a higher proportion of smaller and midsized raindrops. The deeper clouds during premonsoon and postmonsoon indicate mixed‐phase processes, which lead to mid and large‐sized raindrops.

The SENTINEL study of differentiated service delivery models for HIV treatment in Malawi, South Africa, and Zambia: research protocol for a prospective cohort study

BackgroundMany countries in sub-Saharan Africa are rapidly scaling up “differentiated service delivery” (DSD) models for HIV treatment to improve the quality of care, increase access, reduce costs, and support the continued expansion and sustainability of antiretroviral therapy (ART) programs. Although there is some published evidence about the health outcomes of patients in DSD models, little is known about their impacts on healthcare providers’ job satisfaction, patients’ quality of life, costs to providers or patients, or how DSD models affect resource allocation at the facility level.MethodsSENTINEL is a multi-year observational study that will collect detailed data about DSD models for ART delivery and related services from 12 healthcare facilities in Malawi, 24 in South Africa, and 12 in Zambia. The first round of SENTINEL included a patient survey, provider survey, provider time-and-motion observations, and facility resource use inventory. A survey of clients testing for HIV and a supplement to the facility resource use component to describe service delivery integration will be added for the second round. The patient survey will ask up to 10 patients enrolled in each DSD model at each study site about their experiences in HIV care and in DSD models, costs incurred seeking treatment, and preferences for HIV service delivery. The provider survey will ask up to 10 providers per site about the impact of DSD models on their positions and clinics. The time-and-motion component will directly observe the time use of a sample of providers implementing DSD models. Finally, the resource utilization component will collect facility-level data about DSD model availability and enrollment and the human and other resources needed to implement them. SENTINEL is planned to include four or more approximately annual rounds of data collection between 2021 and 2026.DiscussionAs national DSD programs for HIV treatment mature, it is important to understand how individual healthcare facilities are interpreting and implementing national guidelines and how healthcare workers and clients are adapting to new models of service delivery. SENTINEL will help policy makers and program managers understand the benefits and costs of differentiated service delivery and improve resource allocation going forward.

Photocatalytic Degradation of Magenta Effluent Using Magnetite Doped TiO2 in Solar Parabolic Trough Concentrator

Due to population growth and industrial development consumption of non-renewable energy sources, and consequently pollution, has increased. In order to reduce energy utilisation and preserve the environment, developed and developing countries are increasingly trying to find solutions based on renewable energy sources. Cost-effective wastewater treatment methods using solar energy would significantly ensure effective water source utilisation, thereby contributing towards sustainable development goals. In this paper, special emphasis is given to the use of solar energy as the driving force of the process, as well as the use of highly active magnetic TiO2-based catalysts. Therefore, in this study, we investigated the possibility of photocatalytic degradation of aqueous magenta graphic dye using titanium dioxide as a catalyst and DSD model in order to achieve the best process optimisation. TiO2 was successfully coated with magnetic nanoparticles by one step process and characterized using different techniques (BET, SEM/EDS, FTIR, XRD). Based on DSD statistical method optimal reaction conditions were pH = 6.5; dye concentration 100 mg/L; TiO2–Fe3O4 0.6 g/L, at which the highest degree of magenta dye decolourisation was achieved (85%). Application of solar energy coupled with magnetic TiO2 catalyst which could be recovered and reused makes this approach a promising alternative in green wastewater treatment.

Retrieval of Vertical Structure of Raindrop Size Distribution from Equatorial Atmosphere Radar and Boundary Layer Radar

This work develops an algorithm to retrieve the vertical structure of the raindrop size distribution (DSD) of rain from simultaneous observations of 47 MHz Equatorial Atmosphere Radar (EAR) and 1.3 GHz Boundary Layer Radar (BLR) at Koto Tabang, West Sumatra, Indonesia (0.20°S, 100.32°E, 865 m above sea level). EAR is sensitive to the detection of turbulence, and BLR is susceptible to identifying precipitation echo. The EAR Doppler spectrum broadening effects due to turbulence and finite radar beam width were reduced using the convolution process. The Gaussian function was used to model the turbulence Doppler spectrum. A non-linear least-squares fitting method was applied to retrieve DSD parameters. Subsequently, the equations to estimate DSD using this dual-frequency algorithm assume the gamma DSD model to retrieve the distribution from the Doppler spectrum of precipitation echo. The precipitation events on April 23, 2004 on the Coupling Processes in the Equatorial Atmosphere (CPEA-I) project have been analyzed. Results show that the precipitation spectrum obtained using the dual-frequency method is higher, more precise, and well-fitted than the single-frequency method, meaning the dual-frequency method has great potential to be used in observing the microphysical process and remote sensing application analysis of DSD in Indonesia, particularly at Koto Tabang. The analyses show various microphysical processes that occur in the rain, such as coalescence, evaporation, break-up, and condensation. Furthermore, for the purpose of easier remote sensing application analysis of profile DSD characteristics, we use a DSD ΔΖMP parameter. ΔΖMP is a rain rate insensitive DSD parameter representing mean drop size. The trend of ΔZMP is not totally uniform with regards to rain rate and reflectivity factors, with ΔZMP higher in the first half of the event and becoming lower toward the end. This suggests that we have to use different Z-R relations within the event. Doi: 10.28991/ESJ-2022-06-03-02 Full Text: PDF

Do differentiated service delivery models for HIV treatment in sub-Saharan Africa save money? Synthesis of evidence from field studies conducted in sub-Saharan Africa in 2017-2019.

Introduction: "Differentiated service delivery" (DSD) for antiretroviral therapy (ART) for HIV is rapidly being scaled up throughout sub-Saharan Africa, but only recently have data become available on the costs of DSD models to healthcare providers and to patients. We synthesized recent studies of DSD model costs in five African countries. Methods: The studies included cluster randomized trials in Lesotho, Malawi, Zambia, and Zimbabwe and observational studies in Uganda and Zambia. For 3-5 models per country, studies collected patient-level data on clinical outcomes and provider costs for 12 months. We compared costs of differentiated models to those of conventional care, identified drivers of cost differences, and summarized patient costs of seeking care. Results: The studies described 22 models, including conventional care. Of these, 13 were facility-based and 9 community-based models; 15 were individual and 7 group models. Average provider cost/patient/year ranged from $100 for conventional care in Zambia to $187 for conventional care with 3-month dispensing in Zimbabwe. Most DSD models had comparable costs to conventional care, with a difference in mean annual cost per patient ranging from 11.4% less to 9.2% more, though some models in Zambia cost substantially more. Compared to all other models, models incorporating 6-month dispensing were consistently slightly less expensive to the provider per patient treated. Savings to patients were substantial for most models, with patients' costs roughly halved. Conclusion: In five field studies of the costs of DSD models for HIV treatment, most models within each country had relatively similar costs to one another and to conventional care. 6-month dispensing models were slightly less expensive, and most models provided substantial savings to patients. Limitations of our analysis included differences in costs included in each study. Research is needed to understand the effect of DSD models on the costs of ART programmes as a whole.

Do differentiated service delivery models for HIV treatment in sub-Saharan Africa save money? Synthesis of evidence from field studies conducted in sub-Saharan Africa in 2017-2019

Introduction: “Differentiated service delivery” (DSD) for antiretroviral therapy (ART) for HIV is rapidly being scaled up throughout sub-Saharan Africa, but only recently have data become available on the costs of DSD models to healthcare providers and to patients. We synthesized recent studies of DSD model costs in five African countries. Methods: The studies included cluster randomized trials in Lesotho, Malawi, Zambia, and Zimbabwe and observational studies in Uganda and Zambia. For 3-5 models per country, studies collected patient-level data on clinical outcomes and provider costs for 12 months. We compared costs of differentiated models to those of conventional care, identified drivers of cost differences, and summarized patient costs of seeking care. Results: The studies described 22 models, including conventional care. Of these, 13 were facility-based and 9 community-based models; 15 were individual and 7 group models. Average provider cost/patient/year ranged from $100 for conventional care in Zambia to $187 for conventional care with 3-month dispensing in Zimbabwe. Most DSD models had comparable costs to conventional care, with a difference in mean annual cost per patient ranging from 11.4% less to 9.2% more, though some models in Zambia cost substantially more. Compared to all other models, models incorporating 6-month dispensing were consistently slightly less expensive to the provider per patient treated. Savings to patients were substantial for most models, with patients’ costs roughly halved. Conclusion: In five field studies of the costs of DSD models for HIV treatment, most models within each country had relatively similar costs to one another and to conventional care. 6-month dispensing models were slightly less expensive, and most models provided substantial savings to patients. Limitations of our analysis included differences in costs included in each study. Research is needed to understand the effect of DSD models on the costs of ART programmes as a whole.

Three-Parameter Rain Drop Size Distributions From GPM Dual-Frequency Precipitation Radar Measurements: Techniques and Validation With Ground-Based Observations

Raindrop size distribution (DSD) parameters need to be estimated to determine rainfall from radar measurements of backscattered signals in the precipitating medium and to study microphysics of precipitation under varying atmospheric conditions. A technique is proposed to estimate the DSD parameters from Global Precipitation Measurement (GPM) dual-frequency products at Ku and Ka bands, which has been validated with ground-based disdrometer measurements obtained during the five-year period 2014-2018 over a tropical location, Kolkata (22°54’N, 88°35’E), India. The present method yields the three parameters of the DSD model in terms of a gamma function namely, intercept ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N₀</i> ), shape (μ) and slope (Λ). Based on a proposed optimization technique, the most appropriate μ-Λ relationship is determined during a GPM satellite pass to obtain the DSD parameters. The derived parameters have yielded mass-weighted mean diameter ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D_m</i> ) data that show much better agreement with ground-based DSD measurements than that provided by GPM DPR product. This method has also been used to obtain the height profiles of DSD that broadly correlate with ground-based micro rain radar (MRR) observations, showing how DSD varies at different altitudes. The present results demonstrate that the proposed technique is effective in obtaining three-parameter DSDs over a tropical location, and offers a useful method to study the microstructure of rain using space-borne radar.

Do differentiated service delivery models for HIV treatment in sub-Saharan Africa save money? Synthesis of evidence from field studies conducted in sub-Saharan Africa in 2017-2019.

Introduction: "Differentiated service delivery" (DSD) for antiretroviral therapy (ART) for HIV is rapidly being scaled up throughout sub-Saharan Africa, but only recently have data become available on the costs of DSD models to providers and patients. We synthesized recent studies of DSD model costs in five African countries. Methods: The studies included cluster randomized trials in Lesotho, Malawi, Zambia, and Zimbabwe and observational studies in Uganda and Zambia. For 3-5 models per country, studies collected patient-level data on clinical outcomes and provider costs for 12 months, and some studies surveyed patients about costs they incurred. We compared costs of differentiated models to those of conventional care and identified drivers of cost differences. We also report patient costs of seeking care. Results: The studies described 22 models, including facility-based conventional care. Of these, 13 were facility-based and 9 community-based models; 15 were individual and 7 group models. Average provider cost/patient/year ranged from $100 in Zambia to $187 in Zimbabwe, in both cases for facility-based conventional care. Conventional care was less expensive than any other model in the Zambia observational study, more expensive than any other model in Lesotho, Malawi, and Zimbabwe, and in the middle of the range in the Zambia trial and the observational study in Uganda. Models incorporating 6-month dispensing were consistently less expensive to the provider per patient treated. Savings to patients were substantial for most models, with patients' costs roughly halved. Conclusion: In five field studies of the costs of DSD models for HIV treatment, most models within each country had relatively similar costs, except for 6-month dispensing models, which were slightly less expensive. Most models provided substantial savings to patients. Research is needed to understand the effect of DSD models on the costs of ART programmes as a whole.

Replicating the discovery, scrutiny, and decline model of media coverage in presidential primaries

ABSTRACT Media coverage has long been thought crucial to shaping the electoral fortunes of presidential primary candidates in the post-reform era, making how the media allot coverage a topic of paramount importance. Sides and Vavreck (2013. The Gamble: Choice and Change in the 2012 Presidential Election. Princeton, NJ: Princeton University Press) make a notable contribution to the study of media coverage in primaries with their “discovery, scrutiny, and decline” (DSD) model. This model, based on the 2012 Republican primary, suggests that the media’s preference for novelty leads to a cyclical identification of new and interesting candidates, a surge in coverage of that candidate, and a culminating drop of coverage back to baseline levels. But the generalizability of the DSD model beyond the 2012 GOP primary has not yet been thoroughly tested. This paper conducts such a test using the Presidential Primary Communication Corpus (PPCC) which contains news stories by The New York Times and the Washington Post of each candidate in the nine primaries from 2000 to 2020. The evidence is most supportive of the DSD model in the 2008 and 2012 Republican primaries and the 2004 and 2020 Democratic primaries but less supportive in the remaining five. This paper concludes with a discussion of why some campaigns don’t match the DSD model’s expectations.

Client and provider preferences for HIV care: Implications for implementing differentiated service delivery in Thailand.

IntroductionDifferentiated service delivery (DSD) for antiretroviral therapy (ART) maintenance embodies the client‐centred approach to tailor services to support people living with HIV in adhering to treatment and achieving viral suppression. We aimed to assess the preferences for HIV care and attitudes towards DSD for ART maintenance among ART clients and providers at healthcare facilities in Thailand.MethodsA cross‐sectional study using self‐administered questionnaires was conducted in September‐November 2018 at five healthcare facilities in four high HIV burden provinces in Thailand. Eligible participants who were ART clients aged ≥18 years and ART providers were recruited by consecutive sampling. Descriptive statistics were used to summarize demographic characteristics, preferences for HIV services and expectations and concerns towards DSD for ART maintenance.ResultsFive hundred clients and 52 providers completed the questionnaires. Their median ages (interquartile range; IQR) were 38.6 (29.8 to 45.5) and 37.3 (27.3 to 45.1); 48.5% and 78.9% were females, 16.8% and 1.9% were men who have sex with men, and 2.4% and 7.7% were transgender women, respectively. Most clients and providers agreed that ART maintenance tasks, including ART refill, viral load testing, HIV/sexually transmitted infection monitoring, and psychosocial support should be provided at ART clinics (85.2% to 90.8% vs. 76.9% to 84.6%), by physicians (77.0% to 94.6% vs. 71.2% to 100.0%), every three months (26.7% to 40.8% vs. 17.3% to 55.8%) or six months (33.0% to 56.7% vs. 28.9% to 80.8%). Clients agreed that DSD would encourage their autonomy (84.9%) and empower responsibility for their health (87.7%). Some clients and providers disagreed that DSD would lead to poor ART retention (54.0% vs. 40.4%), increased loss to follow‐up (52.5% vs. 42.3%), and delayed detection of treatment failure (48.3% vs. 44.2%), whereas 31.4% to 50.0% of providers were unsure about these expectations and concerns.ConclusionsPhysician‐led, facility‐based clinical consultation visit spacing in combination with multi‐month ART refill was identified as one promising DSD model in Thailand. However, low preference for decentralization and task shifting may prove challenging to implement other models, especially since many providers were unsure about DSD benefits. This calls for local implementation studies to prove feasibility and governmental and social support to legitimize and normalize DSD in order to gain acceptance among clients and providers.

Improving Radar Rainfall Estimations with Scaled Raindrop Size Spectra in Mei-Yu Frontal Rainstorms.

Hydrological calibration of raw weather radar rainfall estimation relies on in situ rainfall measurements. Raindrop size distribution (DSD) was collected during three typical Mei-Yu rainstorms in July 2014 using three particle size velocity (Parsivel) DSD sensors along the Mei-Yu front in Nanjing, Chuzhou, and the western Pacific, respectively. To improve the radar precipitation estimation in different parts of the Mei-Yu front, a scaling method was adopted to formulate the DSD model and further derive the Z–R relations. The results suggest a distinct variation of DSDs in different parts of the Mei-Yu front. Compared with statistical radar Z–ARb relations obtained by mathematical fitting techniques, the use of a DSD model fitting based on a scaling law formulation theoretically shows a significant improvement in both stratiform (33.9%) and convective (2.8%) rainfall estimations of the Mei-Yu frontal system, which indicates that using a scaling law can better reflect the DSD variations in different parts of the Mei-Yu front. Polarimetric radar has indisputable advantages with multiparameter detection ability. Several dual-polarization radar estimators are also established by DSD sensor data, and the R(ZH, ZDR) estimator is proven to be more accurate than traditional Z–R relations in Mei-Yu frontal rainfall, with potential applications for operational C-band polarimetric radar.

Estimating Rain Microphysical Characteristics Using S-Band Dual-Polarization Radar in South Korea

AbstractRaindrop size distribution (DSD) observed using a disdrometer can be represented by a constrained-gamma (C-G) DSD model based on the empirical relationship between shape (µ) and slope (Λ). The C-G DSD model can be used to retrieve DSDs and rain microphysical parameters from dual-polarization radar measurements of reflectivity (ZH) and differential reflectivity (ZDR). This study presents a newµ–Λ relationship to characterize rain microphysics in South Korea using a two-dimensional video disdrometer (2DVD) and Yong-in S-band dual-polarization radar. To minimize sampling errors from the 2DVD and radar measurements, measured size distributions are truncated by particle size and velocity-based filtering and compared with rain gauge measurement. The calibration biases of radarZHandZDRwere calculated using the self-consistency constraint and vertical pointing measurements. The derivedµ–Λ relationship was verified using the mass-weighted mean diameter (Dm) and standard deviation of the size distribution (σm), calculated from the 2DVD, for comparison with existingµ–Λ relationships for Florida and Oklahoma. TheDm–σmrelationship derived from the 2DVD corresponded well with theµ–Λ relationship. Theµ–Λ relationship derived for the Korean Peninsula was similar to Florida, and both generally had largerµvalues than Oklahoma for the same Λ. The derivedµ–Λ relationship was applied to retrieve DSD parameters from polarimetric radar data, and the retrieved DSDs and derived physical parameters were evaluated and compared with the 2DVD measurements. The polarization radar-based C-G DSD model characterized rain microphysics more accurately than the exponential DSD model. The C-G DSD model based on the newly derivedµ–Λ relationship performed the best at retrieving rain microphysical parameters.

Uncertainties in retrieving microphysical properties of rain profiles using ground‐based dual‐frequency radar

AbstractDual‐frequency radar (DFR) could improve the accuracy of estimating the microphysical properties of rain profiles. Unfortunately, factors that cause inaccuracies in retrieved rain profiles include uncertainties in raindrop size distribution (DSD) parameterizations, DFR retrieval methods and radar measurement errors. The primary objective of this study was to assess the uncertainties in retrieving rain profiles to offer insight into application considerations for ground‐based DFRs in China. The uncertainties caused by DSD models are assessed by comparing attenuation coefficients and rain rates from DFR algorithms with those directly derived from DSD spectra from disdrometers. Then, based on a DSD model, the impacts of retrieval methods, radar range resolution, measurement error and errors in temperature on DFR retrievals are explored by comparing the rain profiles obtained using DFR algorithms with those directly output from the Weather Research and Forecasting model. Overall, the impact of measurement error on the DFR retrievals is relatively significant for both the forward retrieval method and the iterative backward retrieval method and should be eliminated in practical applications. At an individual uncertainty level, the impact of DSD parameterizations on the retrievals from the dual‐frequency technique is less than ±10% bias when the shape factor μ of the gamma distribution ranges from 2 to 4. The retrieved rain profiles from the forward retrieval method are relatively sensitive to radar range resolution and the retrieval performance can be improved with increasing the range resolution, while the iterative backward retrieval method exhibits stable retrieval performance. The impact of temperature errors on the retrieved rain profiles is negligible.

Sensitivity analysis of raindrop size distribution parameterizations in WRF rainfall simulation

Numerical weather models such as weather research and forecasting (WRF) are increasingly used in studies on water resources. However, they have suffered from relatively poor performance in rainfall estimation. Among the various influential factors, a critical parameter in the WRF model rainfall retrieval is raindrop size distribution (DSD), which has not been fully explored. The analysis of sensitivity and uncertainty of the DSD model accuracy is significant for rainfall forecasts based on mesoscale numerical weather prediction (NWP) models. A WRF-disdrometer integrated error assessment framework is developed to analyze the accuracy and sensitivity of DSD parameterizations of gamma distribution in WRF rainfall simulation. This study adopts three different microphysics parameterizations (Morrison, WDM6, and Thompson aerosol-aware) to simulate the DSD of approximately 100 rainfall events in Chilbolton, UK that are categorized into 12 scenarios based on the season, rainfall evenness, and rainfall rate. The Thompson aerosol-aware microphysics scheme shows the best performance among the three. In comparisons of WRF rainfall simulations across different scenarios of evenness and rainfall rate, a higher accuracy is obtained with more even rain and a higher rainfall rate. The sensitivity results of different DSD parameterizations indicate that the sensitivity to the intercept parameter N0 is pronouncedly higher than those to the shape parameter μ and slope parameter λ for all studied schemes. The overall WRF rainfall shows a trend of slight underestimation followed by overestimation as μ increases; further, the rainfall is overestimated when log10N0 or λ decreases and is underestimated when it increases and then remains constant. Comparisons of different scenarios reveal that variations of DSD parameters of even rain have a relatively high impact on rainfall recognizability, and the DSD parameterizations show a higher sensitivity for rainfall with a low rate. Moreover, the sensitivity discrimination is not clear among the rainfall of different seasons. The uncertainty assessment of the WRF rainfall retrieval caused by the shape parameter suggests that a gamma DSD model with a variable shape parameter should be developed according to the evenness, rainfall rate, and microphysics parameterizations by using the WRF model. Some modified algorithms of the WRF gamma DSD model for achieving better accuracy in WRF rainfall retrievals will be explored in future studies with various climatic regimes by adjusting the DSD parameterization based on the assimilation of measured data.

Attenuation relations for monsoonal rain at the X band from disdrometric measurements: Dependency on temperature, raindrop size distribution and drop shape models

Four years of disdrometric measurements made at Gadanki (13.5°N, 79.18°E), which receives rainfall during both southwest and northeast monsoons, have been used to (a) derive optimal attenuation relations for monsoonal rainfall at the X band, (b) study the impact of seasonal variation in raindrop size distribution (DSD) on attenuation relations and (c) analyze the dependency of these relations on the controlling parameters/models, such as temperature (T) and drop shape model. The results clearly show that the coefficients of these relations vary significantly with DSD (season and rain type), T and drop shape model, and are quite different for monsoonal rain than for those obtained elsewhere. The traditional relations that involve a specific attenuation (AH)‐reflectivity factor at horizontal polarization (ZH) and AH‐rain rate depend heavily on DSD and to some extent on T, while the relations involving a specific differential phase (KDP) and differential attenuation (ADP) show strong dependency on the drop shape model and DSD, but depend weakly on T. A detailed investigation has been carried out to decipher reasons for the observed intriguing seasonal variation in KDP‐based relations and their temperature dependency. The resonance scattering effects that are thought to be negligible at the X band in earlier studies appear to play a dominant role here and are primarily responsible for the observed features.

Retrieval of the raindrop size distribution from polarimetric radar data using double-moment normalisation

Abstract. A new technique for estimating the raindrop size distribution (DSD) from polarimetric radar data is proposed. Two statistical moments of the DSD are estimated from polarimetric variables, and the DSD is reconstructed using a double-moment normalisation. The technique takes advantage of the relative invariance of the double-moment normalised DSD. The method was tested using X-band radar data and networks of disdrometers in three different climatic regions. Radar-derived estimates of the DSD compare reasonably well to observations. In the three tested domains, in terms of DSD moments, rain rate, and characteristic drop diameter, the proposed method performs similarly to and often better than a state-of-the-art DSD-retrieval technique. The approach is flexible because no specific DSD model is prescribed. In addition, a method is proposed to treat noisy radar data to improve DSD-retrieval performance with radar measurements.

Uncertainties of GPM DPR Rain Estimates Caused by DSD Parameterizations

AbstractA framework based on measured raindrop size distribution (DSD) data has been developed to assess uncertainties in DSD models employed in Ku- and Ka-band dual-wavelength radar retrievals. In this study, the rain rates and attenuation coefficients from DSD parameters derived by dual-wavelength algorithms are compared with those directly obtained from measured DSD spectra. The impact of the DSD gamma parameterizations on rain estimation from the Global Precipitation Measurement mission (GPM) Dual-Frequency Precipitation Radar (DPR) is examined for the cases of a fixed shape factor μ as well as for a constrained μ—that is, a μ–Λ relation (a relationship between the shape parameter and slope parameter Λ of the gamma DSD)—by using 11 Particle Size and Velocity (Parsivel) disdrometer measurements with a total number of about 50 000 one-minute spectra that were collected during the Iowa Flood Studies (IFloodS) experiment. It is found that the DPR-like dual-wavelength techniques provide fairly accurate estimates of rain rate and attenuation if a fixed-μ gamma DSD model is used, with the value of μ ranging from 3 to 6. Comparison of the results reveals that the retrieval errors from the μ–Λ relations are generally small, with biases of less than ±10%, and are comparable to the results from a fixed-μ gamma model with μ equal to 3 and 6. The DSD evaluation procedure is also applied to retrievals in which a lognormal DSD model is used.

A Variational Approach for Retrieving Raindrop Size Distribution from Polarimetric Radar Measurements in the Presence of Attenuation

AbstractThis study presents a two-dimensional variational approach to retrieving raindrop size distributions (DSDs) from polarimetric radar data in the presence of attenuation. A two-parameter DSD model, the constrained-gamma model, is used to represent rain DSDs. Three polarimetric radar measurements—reflectivity ZH, differential reflectivity ZDR, and specific differential phase KDP—are optimally used to correct for the attenuation and retrieve DSDs by taking into account measurement error effects. Retrieval results with simulated data demonstrate that the proposed algorithm performs well. Applications to real data collected by the X-band Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) radars and the C-band University of Oklahoma–Polarimetric Radar for Innovations in Meteorology and Engineering (OU-PRIME) also demonstrate the efficacy of this approach.

Comparison of the compact dopplar radar rain gauge and optical disdrometer

The operations of a compact Doppler radar rain gauge (R2S; Rufft, FRG) and optical disdrometer (LPM; THIES, FRG) are based on raindrop size distribution (DSD) measurements. We checked the instrumental error of these sensors and compared each sensor with a reference tipping-bucket rain gauge. This is because both rain gauges can detect fine particles and so they can function as rain sensors. The R2S has a measuring bias of rainfall intensity when the drop size distribution differs from the assumed statistical DSD model. The instrumental error on the LPM is small; in fact, the LPM shows good agreement with the reference rain gauge. Where the atmospheric density differs remarkably from the standard elevation, as is the case in highland areas, the R2S requires calibration using a reference rain gauge. The resultant calibration coefficient of the R2S to convert the reading into a reference tipping-bucket rain-gauge equivalent was 0.51 in a forest at an elevation of 1380 m. Further gathering of calibration coefficients obtained at different elevations will improve the R2S's applicability.

Estimation of N*0 for the Two-Scale Gamma Raindrop Size Distribution Model and Its Statistical Properties at Several Locations in Asia

Abstract An automatic estimation method is developed to detect stepwise changes in the amplitude parameter of the normalized raindrop size distribution (DSD) N*0. To estimate N*0, it is also assumed that the variation of three DSD parameters follows the two-scale gamma DSD model; this is defined as a DSD model in which one DSD parameter is fixed, the second is allowed to vary rapidly, and the third is constant over a certain space or time domain and sometimes exhibits stepwise transitions. For this study, it is assumed that N*0 is the third DSD parameter. To estimate this stepwise-varying parameter automatically, a non-Gaussian state-space model is used for the time series of log10N*0. The smoothed time series of log10N*0 fit well to the stepwise transition of log10N*0 when it was assumed that the state transition probability follows a Cauchy distribution. By analyzing the long-term disdrometer data using this state-space model, statistical properties for log10N*0 are obtained at several Asian locations. It is confirmed that the N*0 thus estimated is useful to improve the rain-rate estimation from the measurement of radar reflectivity factor.