Modelling of weather radar echoes from anomalous propagation using a hybrid parabolic equation method and NWP model data

Abstract

Abstract. Contamination of weather radar echoes by anomalous propagation (anaprop) mechanisms remains a serious issue in quality control of radar precipitation estimates. Although significant progress has been made identifying clutter due to anaprop there is no unique method that solves the question of data reliability without removing genuine data. The work described here relates to the development of a software application that uses a numerical weather prediction (NWP) model to obtain the temperature, humidity and pressure fields to calculate the three dimensional structure of the atmospheric refractive index structure, from which a physically based prediction of the incidence of clutter can be made. This technique can be used in conjunction with existing methods for clutter removal by modifying parameters of detectors or filters according to the physical evidence for anomalous propagation conditions. The parabolic equation method (PEM) is a well established technique for solving the equations for beam propagation in a non-uniformly stratified atmosphere, but although intrinsically very efficient, is not sufficiently fast to be practicable for near real-time modelling of clutter over the entire area observed by a typical weather radar. We demonstrate a fast hybrid PEM technique that is capable of providing acceptable results in conjunction with a high-resolution terrain elevation model, using a standard desktop personal computer. We discuss the performance of the method and approaches for the improvement of the model profiles in the lowest levels of the troposphere.

Radar Anomalous Propagation Associated with Foehn Winds Induced by Typhoon Krosa (2007)

“…(3). Previous studies had performed ray tracing using simulated data from high-resolution numerical weather prediction model data (Atkinson and Zhu 2006;Bebbington et al 2007) and produced nonisotropic distributions of AP echoes comparable to plan position indicator (PPI) radar observations. In the current study, 10-15-mresolution sounding data were interpolated vertically into 1-m resolution for calculating refractivity index.…”

Simulation of radio occultation measurements

“…The two differential equations are therefore called the outgoing and incoming parabolic wave equations, respectively. The wide-angle parabolic equation (WPE) for the forward travelling wave is given by (5) The operator in the wide-angle parabolic equation has been approximated by (6) This approximated operator is valid for a wide span of propagation angles. The corresponding split-step/sine transform solution for this wider angle parabolic equation (WPE) is given by (7) where {S} represents the sine transformation and p is the spatial frequency.…”

“…Ray tracers have in many cases the advantages of being faster than most wave propagators. A number of authors [5,7], have investigated the use of hybrid methods where a ray tracer is combined with a wave propagator based on a solution to the parabolic equation.…”

Quality index scheme for quantitative uncertainty characterization of radar‐based precipitation

“…Hardware sources of errors are related to stability of electronics, antenna accuracy and signal processing accuracy (Gekat et al , 2004). Other non‐meteorological errors are results of electromagnetic interference with the Sun and other microwave emitters, attenuation due to a wet or snow (ice) covered radome, ground clutter (Germann and Joss, 2004), anomalous propagation of radar beam due to specific atmosphere temperature or moisture gradient (Bebbington et al , 2007), shielding due to topography (Bech et al , 2007) or by nearby objects such as trees and buildings, and other non‐precipitation echoes from birds and insects.…”