CARPE DIEM University of Essex Anthony Holt David

CARPE DIEM University of Essex Anthony Holt David Bebbington Martin Fleury Stephan Siemen + …………. . Carpe Diem Kickoff 1

Work packages WP 2 - Doppler Windfields - 3 -D wind field synthesis from dual Doppler data. WP 6 - Anomalous Propagation - implementation of hybrid PEM integrated with LAM Polarization Review - review of dual polarization techniques in operational weaher radar contexts Carpe Diem Kickoff 2

WP 2 - Doppler Windfields Dual Doppler Synthesis 3 -D windfields may be retrieved using near simultaneously scanned Doppler from two radars in overlap away from baseline. co-plane u r 1 r 2 Divergence condition enables 3 -D field to be recovered by integration given boundary conditions Carpe Diem Kickoff baseline 3

Dual Doppler in PADRE Project SMR San Pietro Capofiume 80 km Carpe Diem Kickoff CSIM Teolo (PD) 4

Dual Doppler Synthesis Dual Doppler windfield slice at 1. 5 km using NCAR CEDRIC (R. J. Watson Thesis 1996) Carpe Diem Kickoff 5

WP 6 - Anomalous Propagation Anomalous propagation can create radar returns from terrain due to partial or total beam bending when strong negative refractive gradients occur. Apparent elevation z Actual trajectory q PRECIP or ANAPROP? M(z) Carpe Diem Kickoff Strong surface ’reflectivity’ 6

ANAPROP event from DARTH Project 100 km Raytrace from HIRLAM model fields predicts RRI and position of ANAPROP Carpe Diem Kickoff 7

Parabolic equation methods: PEM ‘Split-step’ parabolic equation methods allow efficient numerical solution of radar wave field in atmosphere with stratified RRI M(T, q) = 106 (m-1) Solutions advanced between adjacent coordinate planes. O(100 m) Wavefront sampling must be dense to avoid aliasing: Equation becomes 1 st order ODE in Fourier z p domain: < /2 per sample z Carpe Diem Kickoff O(1 m) 8

Hybrid method: Ray/PEM It can be shown that the methodology for the PEM applies Huyghens’ principle with stationary phase integration. The constructed field closely fulfills Green’s Theorem applied to the Helmholtz equation. It is not necessary to select coordinate planes: any series of surfaces for which stationary phase points can be determined will do. Approximate wavefront The hybrid method generates surfaces orthogonal to local ray trajectories - surfaces that are very nearly parallel to the wave front. Phase aliasing is avoided, resulting in order of magnitude reduction in wavefront sampling Carpe Diem Kickoff 9