The availability of radar-based rainfall products at high space-time resolutions and over contine... more The availability of radar-based rainfall products at high space-time resolutions and over continental scales has greatly advanced our understanding of the rainfall process and its interactions with other hydrological processes across a wide range of scales. However, it is well known that radars provide areal estimates of the rainfall, which are affected by systematic and random errors from various sources. Some of these errors are inherent to the observation system and unavoidable. Therefore, it is important to quantify the uncertainty associated with the radar-based rainfall products and to provide a strong basis for probabilistic quantitative precipitation estimation. Literature in the last four decades abounds with several studies comparing the radar estimates with estimates from other instruments, identifying the radar-rainfall error sources, minimizing the errors, and modeling the uncertainties. This chapter reviews key literature related to the characterization of errors for different space-time scales, rainfall regimes, and geographical settings. The emphasis is on the error models that can be utilized to represent the uncertainty in the form of ensembles. The chapter also lists a few open questions and challenges concerning the statistical structure of radarrainfall errors and the generation of the ensembles.
The electromagnetic power that arrives from the Sun in the C-band has been used to check the qual... more The electromagnetic power that arrives from the Sun in the C-band has been used to check the quality of the polarimetric, Doppler weather radar network that has recently been installed in Switzerland. The operational monitoring of this network is based on the analysis of Sun signals in the polar volume data produced during the MeteoSwiss scan program. It relies on a method that has been developed to: (1) determine electromagnetic antenna pointing; (2) monitor receiver stability; and (3) assess the differential reflectivity offset. Most of the results from such a method had been derived using data acquired in 2008, which was a period of quiet solar flux activity. Here, it has been applied, in simplified form, to the currently active Sun period. This note describes the results that have been obtained recently thanks to an inter-comparison of three polarimetric operational radars and the Sun's reference signal observed in Canada in the S-band by the Dominion Radio Astrophysical Observatory (DRAO). The focus is on relative calibration: horizontal and vertical polarization are evaluated versus the DRAO reference and mutually compared. All six radar receivers (three systems, two polarizations) are able to capture and describe the monthly variability of the microwave signal emitted by the Sun. It can be concluded that even this simplified form of the method has the potential to routinely monitor dual-polarization weather radar networks during periods of intense Sun activity.
Journal of Applied Meteorology and Climatology, 2011
... E-mail: [email protected]. 1. Introduction. ... REFERENCES. Ahijevych, DA, CA Davis,... more ... E-mail: [email protected]. 1. Introduction. ... REFERENCES. Ahijevych, DA, CA Davis, RE Carbone, and JD Tuttle, 2004: Initiation of precipitation episodes relative to elevated terrain. J. Atmos. Sci., 61, 2763–2769. [Abstract]. ...
The influence of ground clutter contamination on the estimation of polarimetric radar parameters,... more The influence of ground clutter contamination on the estimation of polarimetric radar parameters, horizontal reflectivity (Z h ), differential reflectivity (Z dr ), correlation coefficient (ρ hυ ), and differential propagation phase (ϕ dp ) was examined. This study aims to derive ...
Eulerian and Lagrangian persistence of precipitation patterns derived from continental-scale rada... more Eulerian and Lagrangian persistence of precipitation patterns derived from continental-scale radar composite images are used as a measure of predictability and for nowcasting [the McGill algorithm for precipitation nowcasting by Lagrangian extrapolation (MAPLE)]. A previous paper introduced the method and focused on the lifetime of patterns of rainfall rates and the scale dependence of predictability. This paper shows how the method of persistence of radar precipitation patterns can be extended to produce probabilistic forecasts. For many applications, probabilistic information is at least as important as the expected point value. Four techniques are presented and compared. One is entirely new and makes use of the intrinsic relationship between scale and predictability. The results with this technique suggest potential use for downscaling of numerical model output. For the 143 h of precipitation analyzed so far, roughly a factor of 2 was obtained between lead times of Eulerian and Lagrangian techniques. Three of the four techniques involve a scale parameter. The slope of the relationship between optimum scale and lead time is about 1 and 2 km min Ϫ1 for Lagrangian and Eulerian techniques, respectively. The skill scores obtained for the four techniques can be used as a measure of predictability in terms of probabilistic rainfall rates. The progress of other probabilistic forecasting methods, such as expert systems or numerical models, can be evaluated against the standard set by simple persistence.
One of the less known aspects of operational flood forecasting systems in complex topographic are... more One of the less known aspects of operational flood forecasting systems in complex topographic areas is the way how the uncertainties of its components propagate and superpose when they are fed into a hydrological model. This paper describes an experimental framework for investigating the relative contribution of meteorological forcing uncertainties, initial conditions uncertainties and hydrological model parameter uncertainties in the realization of hydrological ensemble forecasts. Simulations were done for a representative small-scale basin of the Swiss Alps, the Verzasca river basin (186 km 2 ). For seven events in the time frame from June 2007 to November 2008 it was possible to quantify the uncertainty for a five-day forecast range yielded by inputs of an ensemble numerical weather prediction (NWP) model (COSMO-LEPS, 16 members), the uncertainty in real-time assimilation of weather radar precipitation fields expressed using an ensemble approach (REAL, 25 members), and the equifinal parameter realizations of the hydrological model adopted (PREVAH, 26 members). Combining the three kinds of uncertainty results in a hydrological ensemble of 10,400 members. Analyses of sub-samples from the ensemble provide insight in the contribution of each kind of uncertainty to the total uncertainty. The results confirm our expectations and show that for the operational simulation of peakrunoff events the hydrological model uncertainty is less pronounced than the uncertainty obtained by propagating radar precipitation fields (by a factor larger than 4 in our specific setup) and NWP forecasts through the hydrological model (by a factor larger than 10). The use of precipitation radar ensembles for generating ensembles of initial conditions shows that the uncertainty in initial conditions decays within the first 48 hours of the forecast. We also show that the total spread obtained when superposing two or more sources of uncertainty is larger than the cumulated spread of experiments when only one uncertainty source is propagated through the hydrological model. The full spread obtained from uncertainty superposition is growing non-linearly.
Predictability of precipitation is examined from storm to synoptic scales through an experimental... more Predictability of precipitation is examined from storm to synoptic scales through an experimental approach using continent-scale radar composite images. The lifetime of radar reflectivity patterns in Eulerian and Lagrangian coordinates is taken as a measure of predictability. The results are stratified according to scale, location, and time in order to determine how predictability depends on these parameters. Three companion papers
The availability of radar-based rainfall products at high space-time resolutions and over contine... more The availability of radar-based rainfall products at high space-time resolutions and over continental scales has greatly advanced our understanding of the rainfall process and its interactions with other hydrological processes across a wide range of scales. However, it is well known that radars provide areal estimates of the rainfall, which are affected by systematic and random errors from various sources. Some of these errors are inherent to the observation system and unavoidable. Therefore, it is important to quantify the uncertainty associated with the radar-based rainfall products and to provide a strong basis for probabilistic quantitative precipitation estimation. Literature in the last four decades abounds with several studies comparing the radar estimates with estimates from other instruments, identifying the radar-rainfall error sources, minimizing the errors, and modeling the uncertainties. This chapter reviews key literature related to the characterization of errors for different space-time scales, rainfall regimes, and geographical settings. The emphasis is on the error models that can be utilized to represent the uncertainty in the form of ensembles. The chapter also lists a few open questions and challenges concerning the statistical structure of radarrainfall errors and the generation of the ensembles.
The electromagnetic power that arrives from the Sun in the C-band has been used to check the qual... more The electromagnetic power that arrives from the Sun in the C-band has been used to check the quality of the polarimetric, Doppler weather radar network that has recently been installed in Switzerland. The operational monitoring of this network is based on the analysis of Sun signals in the polar volume data produced during the MeteoSwiss scan program. It relies on a method that has been developed to: (1) determine electromagnetic antenna pointing; (2) monitor receiver stability; and (3) assess the differential reflectivity offset. Most of the results from such a method had been derived using data acquired in 2008, which was a period of quiet solar flux activity. Here, it has been applied, in simplified form, to the currently active Sun period. This note describes the results that have been obtained recently thanks to an inter-comparison of three polarimetric operational radars and the Sun's reference signal observed in Canada in the S-band by the Dominion Radio Astrophysical Observatory (DRAO). The focus is on relative calibration: horizontal and vertical polarization are evaluated versus the DRAO reference and mutually compared. All six radar receivers (three systems, two polarizations) are able to capture and describe the monthly variability of the microwave signal emitted by the Sun. It can be concluded that even this simplified form of the method has the potential to routinely monitor dual-polarization weather radar networks during periods of intense Sun activity.
Journal of Applied Meteorology and Climatology, 2011
... E-mail: [email protected]. 1. Introduction. ... REFERENCES. Ahijevych, DA, CA Davis,... more ... E-mail: [email protected]. 1. Introduction. ... REFERENCES. Ahijevych, DA, CA Davis, RE Carbone, and JD Tuttle, 2004: Initiation of precipitation episodes relative to elevated terrain. J. Atmos. Sci., 61, 2763–2769. [Abstract]. ...
The influence of ground clutter contamination on the estimation of polarimetric radar parameters,... more The influence of ground clutter contamination on the estimation of polarimetric radar parameters, horizontal reflectivity (Z h ), differential reflectivity (Z dr ), correlation coefficient (ρ hυ ), and differential propagation phase (ϕ dp ) was examined. This study aims to derive ...
Eulerian and Lagrangian persistence of precipitation patterns derived from continental-scale rada... more Eulerian and Lagrangian persistence of precipitation patterns derived from continental-scale radar composite images are used as a measure of predictability and for nowcasting [the McGill algorithm for precipitation nowcasting by Lagrangian extrapolation (MAPLE)]. A previous paper introduced the method and focused on the lifetime of patterns of rainfall rates and the scale dependence of predictability. This paper shows how the method of persistence of radar precipitation patterns can be extended to produce probabilistic forecasts. For many applications, probabilistic information is at least as important as the expected point value. Four techniques are presented and compared. One is entirely new and makes use of the intrinsic relationship between scale and predictability. The results with this technique suggest potential use for downscaling of numerical model output. For the 143 h of precipitation analyzed so far, roughly a factor of 2 was obtained between lead times of Eulerian and Lagrangian techniques. Three of the four techniques involve a scale parameter. The slope of the relationship between optimum scale and lead time is about 1 and 2 km min Ϫ1 for Lagrangian and Eulerian techniques, respectively. The skill scores obtained for the four techniques can be used as a measure of predictability in terms of probabilistic rainfall rates. The progress of other probabilistic forecasting methods, such as expert systems or numerical models, can be evaluated against the standard set by simple persistence.
One of the less known aspects of operational flood forecasting systems in complex topographic are... more One of the less known aspects of operational flood forecasting systems in complex topographic areas is the way how the uncertainties of its components propagate and superpose when they are fed into a hydrological model. This paper describes an experimental framework for investigating the relative contribution of meteorological forcing uncertainties, initial conditions uncertainties and hydrological model parameter uncertainties in the realization of hydrological ensemble forecasts. Simulations were done for a representative small-scale basin of the Swiss Alps, the Verzasca river basin (186 km 2 ). For seven events in the time frame from June 2007 to November 2008 it was possible to quantify the uncertainty for a five-day forecast range yielded by inputs of an ensemble numerical weather prediction (NWP) model (COSMO-LEPS, 16 members), the uncertainty in real-time assimilation of weather radar precipitation fields expressed using an ensemble approach (REAL, 25 members), and the equifinal parameter realizations of the hydrological model adopted (PREVAH, 26 members). Combining the three kinds of uncertainty results in a hydrological ensemble of 10,400 members. Analyses of sub-samples from the ensemble provide insight in the contribution of each kind of uncertainty to the total uncertainty. The results confirm our expectations and show that for the operational simulation of peakrunoff events the hydrological model uncertainty is less pronounced than the uncertainty obtained by propagating radar precipitation fields (by a factor larger than 4 in our specific setup) and NWP forecasts through the hydrological model (by a factor larger than 10). The use of precipitation radar ensembles for generating ensembles of initial conditions shows that the uncertainty in initial conditions decays within the first 48 hours of the forecast. We also show that the total spread obtained when superposing two or more sources of uncertainty is larger than the cumulated spread of experiments when only one uncertainty source is propagated through the hydrological model. The full spread obtained from uncertainty superposition is growing non-linearly.
Predictability of precipitation is examined from storm to synoptic scales through an experimental... more Predictability of precipitation is examined from storm to synoptic scales through an experimental approach using continent-scale radar composite images. The lifetime of radar reflectivity patterns in Eulerian and Lagrangian coordinates is taken as a measure of predictability. The results are stratified according to scale, location, and time in order to determine how predictability depends on these parameters. Three companion papers
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