Initiation and development of a mesoscale convective system in the Ebro River Valley and related heavy precipitation over northeastern Spain during HyMeX IOP 15a

Keun-Ok Lee 1, * Cyrille Flamant 1 Véronique Ducrocq 2 Fanny Duffourg 2 Nadia Fourrié 2 Julien Delanoë 3 Joan Bech 4
* Corresponding author
1 TROPO - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
3 SPACE - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : During Intensive Observation Period 15a (20 October 2012) of the first Special Observation Period of the Hydrological cycle in the Mediterranean Experiment, north-eastern Spain experienced heavy precipitation (130 mm in 24 h) associated with a retrograde regeneration mesoscale convective system (MCS) developing in the exit region of the Ebro River Valley (ERV). The life cycle of the MCS that brought intense hourly rainfall (34 mm) from the foothill of Iberian Plateau to the central Pyrenees, as well as the detailed structure of moist marine flow upstream, were analysed using a combination of ground-based, airborne and space-borne observations as well as model analyses. Over the Balearic Sea, the south-westerlies along the north-eastern flank of a surface low converged with south-easterlies from north Africa, creating a near surface moisture tongue in the region of the Balearic Islands, and a southeast-northwest oriented convergence line within a cloud cluster advecting from northern Africa. Airborne lidar measurements, acquired upstream of the ERV, evidenced water vapour mixing ratios in excess of 15 g kg−1 in the marine atmospheric boundary layer. In the mid-level (700 hPa), the presence of an elevated moisture plume from tropical Africa contributed for about one third to the large moisture content present over the western Mediterranean Sea. In this moist environment, the MCS was initiated over the orography of the north-eastern tip of the Iberian plateau, due to the combined influence of the approaching convergence line ahead of the surface low and the convergence resulting from weak north-westerlies channeled in the ERV and the easterlies impinging on the coastal range. After the initiation phase, the MCS further developed over the foothill of Iberian Plateau and moved into the ERV and along the southern flank of the Pyrenees, thanks to the penetration of the warm and moist maritime south-easterly flow through the narrow gap between the north-eastern part of the Iberian Plateau and the Catalan coastal range.
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Keun-Ok Lee, Cyrille Flamant, Véronique Ducrocq, Fanny Duffourg, Nadia Fourrié, et al.. Initiation and development of a mesoscale convective system in the Ebro River Valley and related heavy precipitation over northeastern Spain during HyMeX IOP 15a. Quarterly Journal of the Royal Meteorological Society, Wiley, 2017, 143 (703), pp.942-956. ⟨10.1002/qj.2978⟩. ⟨insu-01413157⟩

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