Geoscience Reference
In-Depth Information
4.2.2 Radar-derived wind and reflectivity fields
Figure 10 presents multiple-Doppler analysis of radar data produced every 6 hours from 12
UTC, Sept 6 to 00 UTC, Sept 8 at a height of 2.5 km (left panel) and 6 km (right panel). The
composite reflectivity patterns (right panel) show extensive frontal rainbands propagating
eastwards in good agreement with the surface analyses shown in Fig. 8. Starting from 18
UTC, 6 September (Fig. 10c), one can notice the presence of widespread convective cells over
southeastern France and northern Spain that seem to be triggered by the pronounced relief
of the Pyrenees. These cells, which develop in a southwesterly midlevel level flow, are
advected northeastwards towards the Massif Central Mountains before eventually
aggregating into a stationary mesoscale convective system (MCS) along the flank of the
mountains. The retrieved wind circulation at both 2.5 and 6 km altitude shows relatively
uniform southwesterly wind, except near the Massif Central where the mid-level flow
exhibits a more pronounced southerly component. This southerly flow, which tends to
advect warm and moist air masses from the Mediterranean Sea toward the coast, impinges
on the Massif Central Mountains and is responsible for the enhancement of convection over
Fig. 9. 24-h accumulated precipitation (mm) over France starting at 00 UTC, 7 Sept 2010
