A Doppler Radar Emulator with an Application to the Detectability of Tornadic Signatures

Abstract

A Doppler radar emulator was developed to simulate the expected mean returns from scanning radar, including pulse-to-pulse variability associated with changes in viewing angle and atmospheric structure. Based on the user's configuration, the emulator samples the numerical simulation output to produce simulated returned power, equivalent radar reflectivity, Doppler velocity, and Doppler spectrum width. The emulator is used to evaluate the impact of azimuthal over-and undersampling, gate spacing, velocity and range aliasing, antenna beamwidth and sidelobes, nonstandard (anomalous) pulse propagation, and wavelength-dependent Rayleigh attenuation on features of interest.As an example, the emulator is used to evaluate the detection of the circulation associated with a tornado simulated within a supercell thunderstorm by the Advanced Regional Prediction System (ARPS). Several metrics for tornado intensity are examined, including peak Doppler velocity and axisymmetric vorticity, to determine the degradation of the tornadic signature as a function of range and azimuthal sampling intervals. For the case of a 2°half-power beamwidth radar, like those deployed in the first integrated project of the Center for Collaborative Adaptive Sensing of the Atmosphere (CASA), the detection of the cyclonic shear associated with this simulated tornado will be difficult beyond the 10-km range, if standard metrics such as azimuthal gate-to-gate shear from a single radar are used for detection.

A Diabatic Lagrangian Technique for the Analysis of Convective Storms. Part II: Application to a Radar-Observed Storm

“…Unfortunately, independent measurements of the true 3D wind field with which to quantify the impact of coarse radial velocity sampling at low elevation angles on multiple-radar estimates of the low-level airflow do not exist. An alternative method for providing high-resolution wind information to test radar analysis techniques is the ''radar emulator'' approach, according to which high-resolution simulated storm output fields are sampled using appropriate weighting functions to create proxy radar fields (e.g., May et al 2007;Wood and Brown 1997) from which the wind field may be approximated using conventional Doppler wind synthesis methods (e.g., Majcen et al 2008). The following simplified error analysis considers only the impact of radar beam averaging and downward extrapolation below the lowest data-bearing level while neglecting other effects of the spatial interpolation and wind synthesis algorithms.…”

Impact of a Vertical Vorticity Constraint in Variational Dual-Doppler Wind Analysis: Tests with Real and Simulated Supercell Data

“…The impact of the vorticity constraint was tested using a very high-resolution ARPS simulation of a supercell (also used by Xue et al 2007;Liu et al 2007;May et al 2007;Potvin et al 2009). This facilitated verification of analyses (because the true u, y, and w fields are known) while providing a more realistic test of the technique than the analytical wind fields used in SPG09.…”

A Time Series Sodar Simulator Based on Large-Eddy Simulation

“…Radar simulators, which can scan the output from high-resolution atmospheric models and largeeddy simulations, have been developed for weather radars (e.g., May et al 2007;Cheong et al 2008), millimeter-wavelength cloud radars (Clothiaux et al 1996), boundary layer wind profiling radars (e.g., Muschinski et al 1999;Scipi on et al 2009), threedimensional imaging radars (e.g., Yu and Palmer 2001;Cheong et al 2004), and radars with dual-polarimetric scanning capabilities (e.g., Capsoni et al 2001;Jung et al 2008). Radar simulators, which can scan the output from high-resolution atmospheric models and largeeddy simulations, have been developed for weather radars (e.g., May et al 2007;Cheong et al 2008), millimeter-wavelength cloud radars (Clothiaux et al 1996), boundary layer wind profiling radars (e.g., Muschinski et al 1999;Scipi on et al 2009), threedimensional imaging radars (e.g., Yu and Palmer 2001;Cheong et al 2004), and radars with dual-polarimetric scanning capabilities (e.g., Capsoni et al 2001;Jung et al 2008).…”