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reflectivity fields at a horizontal resolution of 2.5 km within a domain of approximately 1000
x 1000 x 12 km 3 . This achievement, through the size of the retrieval domain, the number of
Doppler radars (24) involved in the analysis, and the fact that retrieved three-dimensional
winds rely exclusively on an operational infrastructure, represents an unprecedented
breakthrough in operational applications of the Doppler information, which are so far
generally limited to clutter filtering and Velocity Azimuth Display analysis (VAD, Browning
and Wexler 1968).
The present study aims at examining the technical requirements needed to achieve real-time
operational multiple-Doppler analysis in an operational framework, as well as to evaluate
the performance and usefulness of three-dimensional wind composite retrieved from
operational radar systems. After a recall of the principle of dual-Doppler wind retrieval and
a description of the French radar network characteristics winds retrieved in this operational
framework are evaluated using outputs produced during various high impact weather
events that recently occurred over mainland France. This includes the extratropical storm
Klaus, already referred to as the storm of the decade by many European forecasters, which
stroke France with hurricane strength winds on 24 January 2009, as well as a heavy
orographic precipitation event that occurred over the Massif Central Mountains in
September 2010. The potential value of these unique datasets for both operational and a
research application is also discussed with emphasis on the upcoming HyMeX program.
2. Wind retrieval
2.1 Principle of dual-Doppler wind retrieval
All current dual-Doppler analysis techniques originate from the seminal work of Armijo
(1969) who demonstrates that it was possible to retrieve the three components of the wind
field in precipitating area using i) the precipitation radial velocity data collected by 2
Doppler radars, ii) the anelastic air mass continuity equation and iii) empirical
relationships between radar reflectivity and precipitation fallspeed (Z-R relationships).
Among the numerous methods based on Armijo's methodology, three groups can be
identified: i) analytical approaches (e.g. Scialom and Lemaitre 1990), which aim at
retrieving the wind field under its analytical form, ii) coplane techniques (Lhermitte and
Miller 1970, Chong and Testud 1996), which allow resolving the wind field in a cylindrical
space and, iii) Cartesian methods, which aim to resolve the wind field in a Cartesian space
by the mean of an iterative process between the radial velocity equations and the
continuity equation (Heymsfield 1978). Among those 3 families, the latter is the most
computationally efficient and the easiest to implement, making it by far the most popular
method with researchers.
Despite its relative simplicity, the Cartesian method has nevertheless been an inexhaustible
source of inspiration for radar scientists and led to more than 50 peer-reviewed publications
over the last 30 years. Although highlighting a particular method among all available
Cartesian techniques is difficult, one could mention the approaches proposed by Gamache
(1995) - detailed information about this technique can be found in the appendix of Reasor et
al. (2009) - Bousquet and Chong (1998) and Gao et al. (1999). All three techniques
significantly improved the Cartesian approach by suppressing the iterative process
traditionally associated with Cartesian retrieval algorithm (see below).
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