Rain rates, drop size information, and precipitation type, obtained from one-way differential propagation phase and attenuation along a microwave link

AbstractTo date, one of the most widely used parametric forms for modeling raindrop size distribution (DSD) is the three-parameter gamma. The aim of this paper is to analyze the error of assuming such parametric form to model the natural DSDs. To achieve this goal, a methodology is set up to compare the rain rate obtained from a disdrometer-measured drop size distribution with the rain rate of a gamma drop size distribution that produces the same triplets of dual-polarization radar measurements, namely reflectivity factor, differential reflectivity, and specific differential phase shift. In such a way, any differences between the values of the two rain rates will provide information about how well the gamma distribution fits the measured precipitation. The difference between rain rates is analyzed in terms of normalized standard error and normalized bias using different radar frequencies, drop shape–size relations, and disdrometer integration time. The study is performed using four datasets of DSDs collected by two-dimensional video disdrometers deployed in Huntsville (Alabama) and in three different prelaunch campaigns of the NASA–Japan Aerospace Exploration Agency (JAXA) Global Precipitation Measurement (GPM) ground validation program including the Hydrological Cycle in Mediterranean Experiment (HyMeX) special observation period (SOP) 1 field campaign in Rome. The results show that differences in rain rates of the disdrometer DSD and the gamma DSD determining the same dual-polarization radar measurements exist and exceed those related to the methodology itself and to the disdrometer sampling error, supporting the finding that there is an error associated with the gamma DSD assumption.

Download Full-text

Atmospheric observations with E-band microwave links – challenges and opportunities

10.5194/amt-2020-28 ◽

2020 ◽

Cited By ~ 2

Author(s):

Martin Fencl ◽

Michal Dohnal ◽

Pavel Valtr ◽

Martin Grabner ◽

Vojtěch Bareš

Keyword(s):

Water Vapor ◽

Size Distribution ◽

Drop Size ◽

Drop Size Distribution ◽

Distribution Data ◽

Vapor Sensing ◽

Challenges And Opportunities ◽

Atmospheric Observations ◽

Order Of Magnitude ◽

Microwave Link

Abstract. Opportunistic sensing of rainfall and water vapor using commercial microwave links operated within cellular networks was conceived more than a decade ago. It has since been further investigated in numerous studies predominantly concentrating on the frequency region of 15–40 GHz. This manuscript provides the first evaluation of rainfall and water vapor sensing with microwave links operating at an E band (specifically, 71–76 GHz and 81–86 GHz), which are increasingly updating, and frequently replacing, older communication infrastructure. Attenuation-rainfall relations are investigated theoretically on drop size distribution data. Furthermore, quantitative rainfall estimates from six microwave links, operated within cellular backhaul, are compared with observed rainfall intensities. Finally, the capability to detect water vapor is demonstrated on the longest microwave link measuring 4.86 km in path length. The results show that E-band microwave links are by one order of magnitude more sensitive to rainfall than devices operating in the 15–40 GHz range and are thus able to observe even light rainfalls, a feat practically impossible to achieve previously. The E-band links are, however, substantially more affected by errors related to variable drop size distribution. Water vapor retrieval might be possible from long E band microwave links, nevertheless, the efficient separation of gaseous attenuation from other signal losses will be challenging in practice.

Download Full-text

Statistics of Drop Size Distribution Parameters and Rain Rates for Stratiform and Convective Precipitation during the North Australian Wet Season

Monthly Weather Review ◽

10.1175/mwr-d-12-00262.1 ◽

2013 ◽

Vol 141 (9) ◽

pp. 3222-3237 ◽

Cited By ~ 32

Author(s):

Guillaume Penide ◽

Vickal V. Kumar ◽

Alain Protat ◽

Peter T. May

Keyword(s):

Size Distribution ◽

Large Scale ◽

Drop Size ◽

Drop Size Distribution ◽

The Other ◽

Convective Precipitation ◽

Trade Wind ◽

High Concentration ◽

Wet Season ◽

Rain Rates

Abstract C-band polarimetric radar measurements spanning two wet seasons are used to study the effects of the large-scale environment on the statistical properties of stratiform and convective rainfall around Darwin, Australia. The rainfall physical properties presented herein are the reflectivity fields, daily rainfall accumulations and raining area, rain rates, and drop size distribution (DSD) parameters (median volume diameter and “normalized” intercept parameter). Each of these properties is then analyzed according to five different atmospheric regimes and further separated into stratiform or convective rain categories following a DSD-based approach. The regimes, objectively identified by radiosonde thermodynamic and wind measurements, represent typical wet-season atmospheric conditions: the active monsoon regime, the “break” periods, the “buildup” regime, the trade wind regime, and a mixture of inactive/break periods. The large-scale context is found to strongly modulate rainfall and cloud microphysical properties. For example, during the active monsoon regime, the daily rain accumulation is higher than in the other regimes, while this regime is associated with the lowest rain rates. Precipitation in this active monsoon regime is found to be widespread and mainly composed of small particles in high concentration compared to the other regimes. Vertical profiles of reflectivity and DSD parameters suggest that warm rain processes are dominant during this regime. In contrast, rainfall properties in the drier regimes (trade wind/buildup regimes) are mostly of continental origin, with rain rates higher than in the moister regimes. In these drier regimes, precipitation is mainly formed of large raindrops in relatively low concentration due to a larger contribution of the ice microphysical processes on the rainfall formation.

Download Full-text

Evaluation of the New Version of the Laser-Optical Disdrometer, OTT Parsivel2

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-13-00174.1 ◽

2014 ◽

Vol 31 (6) ◽

pp. 1276-1288 ◽

Cited By ~ 102

Author(s):

Ali Tokay ◽

David B. Wolff ◽

Walter A. Petersen

Keyword(s):

Drop Size ◽

Heavy Rain ◽

Rain Gauges ◽

Raindrop Size Distribution ◽

Goddard Space Flight Center ◽

Absolute Bias ◽

Fall Speed ◽

The Difference ◽

Raindrop Size ◽

Rain Rates

Abstract A comparative study of raindrop size distribution measurements has been conducted at NASA’s Goddard Space Flight Center where the focus was to evaluate the performance of the upgraded laser-optical OTT Particle Size Velocity (Parsivel2; P2) disdrometer. The experimental setup included a collocated pair of tipping-bucket rain gauges, OTT Parsivel (P1) and P2 disdrometers, and Joss–Waldvogel (JW) disdrometers. Excellent agreement between the two collocated rain gauges enabled their use as a relative reference for event rain totals. A comparison of event total showed that the P2 had a 6% absolute bias with respect to the reference gauges, considerably lower than the P1 and JW disdrometers. Good agreement was also evident between the JW and P2 in hourly raindrop spectra for drop diameters between 0.5 and 4 mm. The P2 drop concentrations mostly increased toward small sizes, and the peak concentrations were mostly observed in the first three measurable size bins. The P1, on the other hand, underestimated small drops and overestimated the large drops, particularly in heavy rain rates. From the analysis performed, it appears that the P2 is an improvement over the P1 model for both drop size and rainfall measurements. P2 mean fall velocities follow accepted terminal fall speed relationships at drop sizes less than 1 mm. As a caveat, the P2 had approximately 1 m s−1 slower mean fall speed with respect to the terminal fall speed near 1 mm, and the difference between the mean measured and terminal fall speeds reduced with increasing drop size. This caveat was recognized as a software bug by the manufacturer and is currently being investigated.

Download Full-text

Analysis of Measured Drop Size Spectra over Land and Sea

ISRN Meteorology ◽

10.5402/2012/296575 ◽

2012 ◽

Vol 2012 ◽

pp. 1-10 ◽

Cited By ~ 10

Author(s):

Karl Bumke ◽

Jörg Seltmann

Keyword(s):

Drop Size ◽

Rain Rate ◽

Exponential Model ◽

Coastal Areas ◽

Data Sets ◽

Size Spectra ◽

Stratiform Rain ◽

Open Sea ◽

Rain Rates

Drop size spectra were measured by using an optical disdrometer of type ODM 470 at different locations. They were subdivided in to four data sets: measurements over land, in coastal areas, over semienclosed seas, and over the open sea. Based on 1-minute measurement intervals, no differences were found in drop size spectra between continental and maritime areas. An exponential model with a rain rate depending on interception number and prefactor in the exponent fits well the spectra, and maximum drop sizes depend strongly on estimated rain rates. In contrast to other investigations, there are no significant differences between spectra of convective and stratiform rain based on 1-minute measurement intervals. However, spectra integrated over 10 minutes show the expected differences.

Download Full-text

Variation of multimodality in rainfall drop size distribution with wind speeds and rain rates

The Journal of Engineering ◽

10.1049/joe.2016.0013 ◽

2016 ◽

Vol 2016 (6) ◽

pp. 203-209 ◽

Cited By ~ 1

Author(s):

K'ufre-Mfon E. Ekerete ◽

Francis Hunt ◽

Judith Jeffery ◽

Ifiok Otung

Keyword(s):

Size Distribution ◽

Drop Size ◽

Drop Size Distribution ◽

Wind Speeds ◽

Rain Rates

Download Full-text

Discrimination between Winter Precipitation Types Based on Spectral-Bin Microphysical Modeling

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-16-0044.1 ◽

2016 ◽

Vol 55 (8) ◽

pp. 1747-1761 ◽

Cited By ~ 13

Author(s):

Heather Dawn Reeves ◽

Alexander V. Ryzhkov ◽

J. Krause

Keyword(s):

Drop Size ◽

Winter Precipitation ◽

Horizontal Distribution ◽

Ensemble Model ◽

Freezing Rain ◽

New Approach ◽

Water Fraction ◽

Precipitation Type ◽

Microphysical Parameterization ◽

Microphysical Parameterization Scheme

AbstractA new approach for distinguishing precipitation types at the surface, the spectral bin classifier (SBC), is presented. This algorithm diagnoses six categories of precipitation: rain (RA), snow (SN), a rain–snow mix (RASN), freezing rain (FZRA), ice pellets (PL), and a freezing rain–ice pellet mix (FZRAPL). It works by calculating the liquid-water fraction fw for a spectrum of falling hydrometeors given a prescribed temperature T and relative humidity profile. Demonstrations of the SBC output show that it provides reasonable estimates of fw of various-sized hydrometeors for the different categories of precipitation. The SBC also faithfully represents the horizontal distribution of precipitation type inasmuch as the model analyses and surface observations are consistent with each other. When applied to a collection of observed soundings associated with RA, SN, FZRA, and PL, the classifier has probabilities of detection (PODs) that range from 62.4% to 98.3%. The PODs do decrease when the effects of model uncertainty are accounted for. This decrease is modest for RA, SN, and PL but is large for FZRA as a result of the fact that this form of precipitation is very sensitive to small changes in the thermal profile. The effects of the choice of the degree of riming above the melting layer, the drop size distribution, and the assumed temperature at which ice nucleates are also examined. Recommendations on how to mitigate all forms of uncertainty are discussed. These include the use of dual-polarized radar observations, incorporating output from the microphysical parameterization scheme, and the use of ensemble model forecasts.

Download Full-text

Estimation of path-average rain drop size distribution using the NASA/TRMM microwave link

IGARSS 2001. Scanning the Present and Resolving the Future. Proceedings. IEEE 2001 International Geoscience and Remote Sensing Symposium (Cat. No.01CH37217) ◽

10.1109/igarss.2001.976739 ◽

2002 ◽

Author(s):

R.F. Rincon ◽

R. Lang ◽

R. Meneghini ◽

S. Bidwell ◽

A. Tokay

Keyword(s):

Size Distribution ◽

Drop Size ◽

Drop Size Distribution ◽

Rain Drop ◽

Microwave Link ◽

Average Rain

Download Full-text

Rainfall Kinetic Energy in Denmark: Relationship with Drop Size, Wind Speed, and Rain Rate

Journal of Hydrometeorology ◽

10.1175/jhm-d-19-0251.1 ◽

2020 ◽

Vol 21 (7) ◽

pp. 1621-1637

Author(s):

Anna-Maria Tilg ◽

Flemming Vejen ◽

Charlotte Bay Hasager ◽

Morten Nielsen

Keyword(s):

Wind Speed ◽

Kinetic Energy ◽

Drop Size ◽

Rain Rate ◽

Turbine Blades ◽

Wind Turbine Blades ◽

Fall Velocity ◽

Wind Speeds ◽

Low Wind Speeds ◽

Rain Rates

AbstractRainfall kinetic energy is an important parameter to estimate erosion potential in connection to soil erosion or in the recent years to the erosion of the leading edges of wind turbine blades. Little is known about the seasonal drop size distribution and fall velocity dependence of rainfall kinetic energy as well as its relationship with wind speed. Therefore, 6 years of Thies Laser Precipitation Monitor disdrometer and wind measurements from Voulund, a field site in western Denmark, were analyzed. It was found that the rainfall kinetic energy was highest in summer due to higher drop concentrations and in autumn due to more time with rain. The rainfall kinetic energy peaked for drop diameters between 0.875 and 2.25 mm independent of the season. Rainfall kinetic energy decreased significantly with increasing wind speed, if considering the vertical fall speed of the drops for the calculation of the rainfall kinetic energy. However, it should be noted that the measurement uncertainty increases with increasing wind speed. As disdrometer observations are rarer than rain rate observations, the performance of empirical equations describing the relationship between rainfall kinetic energy rate and rain rate was investigated. It was found that an equation trained with an alternative method fulfilled the statistical requirements for linear regression and had a similar error compared to equations in the literature. Based on the analyses, it can be concluded that the erosion potential due to rainfall kinetic energy is highest between June and November at low wind speeds and high rain rates.

Download Full-text

Measurements of Rainfall Rate, Drop Size Distribution, and Variability at Middle and Higher Latitudes: Application to the Combined DPR-GMI Algorithm

Remote Sensing ◽

10.3390/rs13122412 ◽

2021 ◽

Vol 13 (12) ◽

pp. 2412

Author(s):

Viswanathan Bringi ◽

Mircea Grecu ◽

Alain Protat ◽

Merhala Thurai ◽

Christian Klepp

Keyword(s):

Size Distribution ◽

Drop Size ◽

Drop Size Distribution ◽

Retrieval Algorithm ◽

Lookup Tables ◽

Microwave Imager ◽

Statistical Relationships ◽

Rain Rates ◽

Global Precipitation ◽

Combined Algorithm

The Global Precipitation Measurement mission is a major U.S.–Japan joint mission to understand the physics of the Earth’s global precipitation as a key component of its weather, climate, and hydrological systems. The core satellite carries a dual-precipitation radar and an advanced microwave imager which provide measurements to retrieve the drop size distribution (DSD) and rain rates using a Combined Radar-Radiometer Algorithm (CORRA). Our objective is to validate key assumptions and parameterizations in CORRA and enable improved estimation of precipitation products, especially in the middle-to-higher latitudes in both hemispheres. The DSD parameters and statistical relationships between DSD parameters and radar measurements are a central part of the rainfall retrieval algorithm, which is complicated by regimes where DSD measurements are abysmally sparse (over the open ocean). In view of this, we have assembled optical disdrometer datasets gathered by research vessels, ground stations, and aircrafts to simulate radar observables and validate the scattering lookup tables used in CORRA. The joint use of all DSD datasets spans a large range of drop concentrations and characteristic drop diameters. The scaling normalization of DSDs defines an intercept parameter NW, which normalizes the concentrations, and a scaling diameter Dm, which compresses or stretches the diameter coordinate axis. A major finding of this study is that a single relationship between NW and Dm, on average, unifies all datasets included, from stratocumulus to heavier rainfall regimes. A comparison with the NW–Dm relation used as a constraint in versions 6 and 7 of CORRA highlights the scope for improvement of rainfall retrievals for small drops (Dm < 1 mm) and large drops (Dm > 2 mm). The normalized specific attenuation–reflectivity relationships used in the combined algorithm are also found to match well the equivalent relationships derived using DSDs from the three datasets, suggesting that the currently assumed lookup tables are not a major source of uncertainty in the combined algorithm rainfall estimates.

Download Full-text