Geoscience Reference
In-Depth Information
Fig. 2. (a) Radar overlapping within mainland France as a function of height and detailed
overlapping map at (b) 2.5 and (c) 5 km AMSL.
3.3 Data processing
Reflectivity and radial velocity observations collected by all (24) ARAMIS radars are
concentrated at the national center, in Toulouse, and automatically processed every 15'. Data
consist in Cartesian, 512 km x 512 km, 1 km² in resolution, sweeps of radar observations, which
are already exploited for current operational applications such as VAD analysis, quantitative
precipitation estimates (Tabary et al. 2011) or data assimilation (Montmerle and Faccani 2009).
Spurious reflectivity echoes are removed by the mean of a threshold on the pulse-to-pulse
fluctuation of the reflectivity based on the work of Sugier et al. (2002). A 5x5 km² median filter
is then applied to radial velocity measurements to discard potential spurious velocities
resulting from dealiasing failures (Tabary et al. 2006). Finally, data are synchronized with
respect to the ending time of the 15' sampling period to account for the non-simultaneity of the
measurements following the approach of Tuttle and Foote (1990). Once pre-processed, data are
ingested in the MUSCAT analysis described in Section 2.
4. Examples of retrieved wind fields
A qualitative evaluation of the multiple-Doppler winds reconstructed in this framework is
provided through the analysis of radar data collected during various rain events that
occurred over mainland France between 2008 and 2010. This includes the extratropical
cyclone Klaus, which stroke France on 24 January 2009 with hurricane force gusts, and a
number of orographic convective precipitation events that produced large amount of rain
over the Massif Central Mountains.
4.1 Extratropical cyclone “Klaus”
4.1.1 Overview
On 24 January 2009, an extratropical cyclone called “Klaus” made landfall over
southwestern Europe with hurricane force gusts, causing widespread damage and many
fatalities, especially across France and Spain. This event is considered the most intense
storm affecting Western Europe since the infamous extratropical cyclones “Lothar”
