Weather Radar and Hydrology Edited by

Key words rainfall-rate-reflectivity relationships; optimization; genetic algorithms; precipitation; South Florida, USA
Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012),81-86

Radar hydrology: new Z-R relationships over the Klang River Basin, Malaysia for monsoon season rainfall
Suzana Ramli & Wardah Tahir

Faculty of Civil Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia

[e-mail]
Abstract The use of Quantitative Precipitation Estimation (QPE) in radar–rainfall measurement for hydrological purposes is significantly important. For several decades radars have been deployed to monitor and estimate precipitation routinely in several countries. However, in Malaysia, radar application for QPE is still new and needs to be explored. This paper focuses on the Z-R derivation work of radar-rainfall estimation. The work develops new Z-R relationships for the Klang River in the Selangor area for the monsoon season; namely southwest monsoon rain, northeast monsoon rain and two inter-monsoon rains which distribute heavy rain (>30 mm/h). Looking at the high potential of Doppler radar for QPE, the newly formulated Z-R equations will be useful in improving the measurement of rainfall for any hydrological application, especially for flood forecasting.

Key words radar; Quantitative Precipitation Estimation; Z-R development; monsoon; flood forecasting
Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 87-92

Simultaneous measurements of precipitation using
S-band and C-band polarimetric radars
Alexander Ryzhkov^1,2,3, Pengfei Zhang^1,2, John Krause^1,2,
Terry Schuur^1,2, Robert Palmer³ & Dusan Zrnic²

1 Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, 120 David L. Boren Blvd,
Norman, Oklahoma 73072, USA

[e-mail]

2 National Severe Storms Laboratory, Norman, Oklahoma, USA

3 Atmospheric Radar Research Center, University of Oklahoma, Norman, Oklahoma, USA
Abstract Simultaneous measurements of heavy tropical rain made by closely located S- and C-band polarimetric radars are examined. The performance of different algorithms for rainfall estimation is discussed. It is demonstrated that the polarimetric algorithm based on the combined use of specific differential phase and differential reflectivity yields the least biased estimate of rainfall at S-band. Similar estimation at C-band faces challenges.

Key words polarimetric radar; flash flood; tropical rain

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 93-98

French-Italian X- and C-band dual-polarized radar network for monitoring South Alps catchments
E. Moreau¹, E. Le Bouar¹, J. Testud¹ & R. Cremonini²

1 NOVIMET, 11 bd d’Alembert, 78280, Guyancourt, France

[e-mail]

2 ARPA Piemonte – Sistemi Previsionali, Torino, Italy
Abstract In the framework of the CRISTAL (CRues par l’Integration des Systèmes Transfrontaliers Alpins) project, two dual-polarized X-band radars have been deployed for monitoring the catchment of the Roya, located in the south Alps at the French-Italian border. The French radar (Hydrix) has been installed in the Maritime Alps (Mt-Vial, 1500 m) and the Italian radar was installed at Col de Tende at 1800 m altitude during the summer of 2010. Two Italian C-band dual-polarized radars complete the network, ensuring a full monitoring of the Roya catchment. This paper focuses on the capability of the two operational X-band radars to complement each other when monitoring rain/flood events in a mountainous area. Also illustrated is their ability for gap-filling neighbouring C-band radars which are blinded by orography. The ZPHI® algorithm is applied to the whole set of radar data, correcting for signal attenuation and estimating drop-size distribution and surface rainfall without any use of raingauge information. A case study from summer 2010 is shown, by comparing various radar-derived rainfall mosaics.

Key words radar network; dual-polarized radar; catchment

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 99-104.

Hail events observed by an X-band polarimetric radar along the French Mediterranean coast
ERWAN LE BOUAR, EMMANUEL Moreau & JACQUES TESTUD

NOVIMET – 11, Bd d’Alembert, 78280 Guyancourt, France

[e-mail]
Abstract During summer 2010, in a mountainous and Mediterranean context, very strong reflectivities were observed by the Hydrix™ radar located at Mount Vial (1500 m height, near Nice, France), suggesting hail occurrences. However, the operational product processing failed to provide good results since no hail detection procedure was implemented. Thus, it expectedly produced very strong rainfall rates when gauge measurements showed very weak ones. A hail detection procedure taking advantage of the radar polarimetric capabilities has been tested in off-line processing, showing much better output performances, encouraging its operational implementation. This paper presents the obtained results, and describes the approach chosen for detecting the presence of hail.

Key words hail; X-band; dual-polarisation; classification

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 105-110.

technology and multifractal drop distribution
D. Schertzer¹, I. Tchiguirinskaia¹ & S. Lovejoy²

1 Université Paris-Est Ecole des Ponts ParisTech LEESU, 6-8 Av Blaise Pascal Cité Descartes, Marne-la-Vallée,
77455 Cx2, France

[e-mail]

2 McGill University, Physics Dept., Montreal, PQ, Canada
Abstract Hydrologists have been waiting for some time to have radar data with a resolution higher than the kilometre scale, especially for urban applications. This is now achievable with the help of polarimetric
X-band radars, not only because of their higher frequency, but also because they are much more affordable and versatile. X-band radar networks are thus planned around megalopolises. However, to fully take advantage of the sophisticated polarimetric “self-calibration” requires further investigations of fundamental questions. For instance, ad-hoc homogeneity approximations and/or factorization of the drop distribution have led to the common practice to average several scans, and therefore to degrade the measurement resolution in an attempt to reduce the coherent backscattering due to heterogeneity of the drop distribution. With the help of high-resolution data from an infrared optical spectro-pluviometer, we come back to the question of the insights brought by multifractals on the corresponding statistical bias.

Key words X-band radar; urban hydrology; drop distribution; multifractals

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 111-116.

Improvement of the dual-frequency precipitation retrieval method for a global estimation of Z-R relations
SHINTA SETO¹ & TOSHIO IGUCHI²

1 Institute of Industrial Science, the University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505, Japan

[e-mail]

2 National Institute of Information and Communications Technology, 4-2-1, Nukui-kita-machi, Koganei 184-8795, Japan
Abstract Z-R relations between radar reflectivity factor Z and precipitation rate R have been used for operational radar measurements, but the relations are known to be highly variable in time and space and also to be dependent on precipitation types. The Dual-frequency Precipitation Radar (DPR), which will be carried on the core satellite of the Global Precipitation Measurement (GPM) mission hopefully from 2013, is expected to instantaneously estimate the 2-moment drop size distribution function and to finally derive global maps of the coefficients of Z-R relations. For this big goal, it is necessary to develop an accurate retrieval method for DPR. Mardiana et al. developed the iterative backward retrieval method (MA04) without the use of surface reference technique, which may cause significant errors over land. Some previous studies tested MA04 with simple settings of precipitation measurement, and found that MA04 cannot derive the true solution when the precipitation rate is relatively high. In the first part of this study, MA04 was tested with a simulated DPR measurement dataset, which is more realistic than those used in the previous studies. The retrieved surface precipitation rate is evaluated, and it is shown that MA04 has a negative bias which corresponds to 40% of the true precipitation rate. It is also shown that the estimated Z_e (equivalent radar reflectivity factor) by MA04 tends to be smaller at lower range bins, while the true Z_e does not change largely along the range. In the second part of this study, based on MA04, three modified retrieval methods are developed and they are tested with the same simulated DPR measurement dataset. To overcome the shortcomings of MA04, constraints to make vertically stable profiles of Z_e are introduced in the modified methods. In the best method, the bias is limited to 12% of the true precipitation rate.

Key words Z-R relation; drop size distribution; spaceborne radar; DPR; GPM

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 117-122.

Dual-frequency measurement of rain using millimetre-wave radars: initial results
Peter Speirs & Duncan Robertson

School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK

[e-mail]
Abstract This paper presents initial results from an investigation into the feasibility of measuring rain using a pair of horizontally-pointed FMCW radars operating at 38 and 94 GHz. Such a system could potentially offer data complementary to that provided by existing networks of meteorological radars. It may find application where higher resolutions are required, or where a small, portable, low-power system is desirable. The technique used is a variation on the well known dual-frequency extinction technique. Radar-measured rainfall rates and drop-size distributions are compared with data gathered from a disdrometer.

Key words millimetre-wave; radar; rainfall; dual frequency

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012)., 123-128

Adaptive phased array radar technology for urban hydrological forecasting
C. G. COLLIER¹, M. HOBBY¹, A. BLYTH¹, D. J. McLAUGHLIN²,
J. McGONIGAL³ & C. P. McCARROLL⁴

1 National Centre for Atmospheric Science, School of Earth & Environment, University of Leeds, Leeds LS2 9JT, UK

[e-mail]

2 University of Massachusetts, Amherst, Massachusetts, USA

3 Raytheon, UK

4 University of Massachusetts, Lowell, Massachusetts, USA
Abstract Current Water Companies Asset Management Programmes (AMP5 2010–2015) will address: sewer flooding and the pollution which may arise from it. Such floods can result in considerable damage and pose health hazards. Forecasting these events, often the result of heavy convective rainfall, to enable preventive action to be taken, is a major challenge. Convective precipitation patterns may change rapidly within a few minutes and improvements to the scanning technology are needed. Phased arrays are used in many defence radars, and are a desirable technology because they do not require maintenance of moving parts and allow flexibility in beam steering. They are also more robust in respect of component failure. An important additional feature is that such antennas can potentially be mounted to the sides of towers and buildings. Phased tilt technology, including its associated signal processing, has not been explored in the context of quantitative precipitation estimation for urban flood forecasting. This is the subject of this paper. Phased arrays are well suited to the application of adaptive scanning which offers great potential for this application.

Key words radar; phase tilt; urban flooding; adaptive scanning; quantitative precipitation estimation

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 129-134

Quantitative precipitation estimation using commercial microwave links
Aart overeem^1,2, Hidde leijnse¹ & remko uijlenhoet²

1 Royal Netherlands Meteorological Institute (KNMI), PO Box 201, 3730 AE De Bilt, the Netherlands

[e-mail]

2 Hydrology and Quantitative Water Management Group, Wageningen University, PO Box 47, 6700 AA, the Netherlands
Abstract There is an urgent need for high-quality rainfall observations with high spatial and temporal resolutions in catchment hydrology, particularly in urban hydrology. Weather radars are in principle well-suited for that purpose, but often need adjustment. Usually, only a few raingauge measurements are available as input for hydrological models or to adjust the radar data in real-time. X-band radar data, specifically interesting for urban hydrology, are often not available. Previous studies have shown that (commercial) microwave link data are suitable to calculate path-averaged rainfall intensities and, therefore, are a potentially valuable source of additional rainfall information. This is further explored in this study using data from 321 links from a commercial cellular telephone network in the Netherlands. Some preliminary results are presented concerning the derivation of rainfall maps and the correction of radar data using microwave link data.

Key words microwave link; rainfall measurement; weather radar; the Netherlands

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 135-140.

Off-the-grid weather radar network for precipitation monitoring in western Puerto Rico
Jorge M. Trabal^1,2, Gianni A. Pablos-Vega², José A. Ortiz²,
José G. Colom-Ustariz², Sandra Cruz-Pol², David J. McLaughlin¹, Michael Zink¹ & V. Chandrasekar³

1 University of Massachusetts, Amherst, Massachusetts, USA

[e-mail]

2 University of Puerto Rico, Mayagüez, Puerto Rico, USA

3 Colorado State University, Fort Collins, Colorado, USA
Abstract Operational weather radars are challenged in providing low-altitude observations of rainfall due to the Earth’s curvature and their deployment in “sparse” networks spaced hundreds of km apart. Given this limitation, work is underway to explore the feasibility of “dense” networks of small X-band radars. One approach uses low-cost networks of simple, single-polarization radars that are not dependent on existing infrastructure. This “Off-the-Grid” (OTG) concept is one that might provide a means to monitor rainfall and provide useful data where it is not feasible or cost-effective to deploy more costly and more accurate radars. This paper describes the OTG concept and design, and compares two data events from this network with measurements from an S-Band NEXRAD radar located in Puerto Rico, and rainfall data from a set of raingauges deployed in western Puerto Rico. Results show that OTG radar estimates were consistent with those from the S-band radar.

Key words X-band; radar network; off-the-grid; rainfall mapping and estimation

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 141-146.

Estimation of rain kinetic energy flux density from radar reflectivity factor and/or rain rate
Nan YU¹, Guy Delrieu¹, Brice Boudevillain¹, Pieter hazenberg² & Remko UIjlenhoet²

1 UJF – Grenoble 1 / CNRS / G-INP / IRD, LTHE UMR 5564, Grenoble, France

[e-mail]

2 Hydrology and Quantitative Water Management Group, Wageningen University, Wageningen, The Netherlands
Abstract This study offers an approach to estimate the rainfall kinetic energy (KE) by rain intensity (I) and radar reflectivity factor (Z) separately, or jointly, based on the one- or two-moment scaled raindrop size distribution (DSD) formulation, which contains (a) I and/or Z observations, (b) dimensionless probability density function (pdf) and (c) some intrinsic parameters. The key point of this formulation is to explain all variability of the DSD by the evolution of observations, hence the pdf and intrinsic parameters are considered as constants. A robust method is proposed to estimate the climatic values for these parameters, and our 28-month DSD data are used to test this estimation process. The results show that three relationships (KE-I, KE-Z and KE-IZ) which link the observations (I and/or Z) to rainfall kinetic energy (KE) are well established based on the climatic scaled DSD formulation. In particular, the combination of I and Z yields a significant improvement of estimation of KE.

Key words rain intensity; radar reflectivity factor; raindrop size distribution; kinetic energy

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 147-152

Variability of rain microphysics using long-term disdrometer observations
TANVIR ISLAM, MIGUEL A. RICO-RAMIREZ & DAWEI HAN

Department of Civil Engineering, University of Bristol, Bristol, UK

[e-mail]
Abstract This study explores variability of rain microphysics in terms of drop size distributions (DSD) using seven years of Joss-Waldvogel disdrometer data in a long-term perspective. Firstly, self-consistency evaluation of the disdrometer is performed against four raingauges. The result indicates that the disdrometer derived rain totals are in a good agreement to the raingauges with correlation coefficients ranging from 0.89 to 0.99. In addition, a total of 162 415 one-minute filtered raindrop spectra obtained from the disdrometer are fitted to the normalized gamma DSD model to understand DSD variability in different seasonal and atmospheric states. To characterize rain microphysics, four sets of DSDs are created from the entire raindrop spectra – two are based on seasonal “equinox” criteria and the other two are based on wet bulb temperature. It has been revealed that the normalized gamma DSD parameters, N_w, D_m, and μ vary from set to set because of seasonal and atmospheric variability. Finally, radar Z-R relations for the four DSD sets are developed and it is shown that coefficients differ meaningfully from state to state. In particular, the variability is found to be more substantial between those DSDs which have been separated using the wet bulb temperature.

Key words microphysics of precipitation; drop size distribution; radar remote sensing; reflectivity

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 153-160

Long-term diagnostics of precipitation estimates and radar hardware monitoring: two contrasting components of a radar data quality management system
DAWN HARRISON & ADAM CURTIS

Met Office, FitzRoy Road, Exeter EX1 3PB, UK

[e-mail]
Abstract Quality is key to ensuring that the potential offered by weather radar networks is realised. To help ensure optimum quality, a comprehensive radar data quality management system, designed to monitor the end-to-end radar data processing chain and evaluate product quality, is being developed at the Met Office. Two contrasting elements of the system, monitoring of key radar hardware performance indicators and generation of long-term integrations of radar products, are described. Examples for January 2011 are presented and ways in which the information has been used to identify problems and formulate solutions are given.

Key words quality monitoring; precipitation estimation

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 163-168.

NMQ/Q2: National Mosaic and Multi-sensor QPE System
Kenneth Howard¹ Jian Zhang¹, Carrie Langston²,
Steve Vasiloff¹, Brian Kaney² & Ami Arthur²

1 NOAA/National Severe Storms Laboratory, National Weather Center, 120 David L. Boren Blvd., Norman,
Oklahoma 73072, USA

[e-mail]

2 CIMMS/University of Oklahoma, National Weather Center, 120 David L. Boren Blvd., Norman, Oklahoma 73072, USA
Abstract Accurate quantitative precipitation estimates (QPE) are critical for monitoring and prediction of water-related hazards and water resources. While tremendous progress has been made in the last quarter century in many areas of QPE, significant gaps continue to exist in both knowledge and capabilities that are necessary to produce accurate high-resolution precipitation estimates on a national scale for a wide spectrum of users. Toward this goal, a national Next-Generation QPE (NMQ/Q2) system has been developed at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory (NSSL). The NMQ/Q2 system has been running in real-time in the USA since June 2006. The system generates a suite of QPE products for the Conterminous United States at a 1-km horizontal resolution and 2.5 minute update cycle. The experimental products are disseminated in real-time to users and have been utilized in various meteorological and hydrological applications. In 2006, working with the United States National Weather Service’s Office of Climate, Weather, and Water Services, NSSL began prototype testing of the high-resolution gridded NMQ/Q2 precipitation products as input into the Flash Flood Monitoring and Prediction program. Dissemination of Q2 products to selected River Forecast Centers (RFCs) began in 2007 with all RFCs currently having access through the Advanced Weather Interactive Processing System (AWIPS) Multi-sensor Precipitation Estimator (MPE).