Role of moisture patterns in the backbuilding formation of HyMeX IOP13 heavy precipitation systems

Abstract

International audienceMediterranean regions are regularly affected by heavy convective precipitation. During the Hydrological Cycle in the Mediterranean Experiment Intensive Observation Period 13 (HyMeX-IOP13), the multi-platform observation strategy allowed analysing the backbuilding convective systems which developed on 14 October 2012 as well as the associated moisture structures in the environment upstream of convection.The numerical simulation at 2.5-km horizontal resolution succeeds in reproducing the location and time evolution of the observed heavy precipitation systems and the main characteristics of the marine air mass. Convection develops in Southeastern France over the foothills closest to the coast when a moist conditionally unstable marine boundary layer topped by particularly dry air masses is advected inland. Cold air formed by evaporative cooling under the precipitating cells flows down the valleys slowly shifting the location of the backbuilding convective cells from the mountainsides to the coast and over the sea. Surface observations confirm that these simulated backbuilding mechanisms describe realistically the processes involved in the maintenance of the heavy precipitation event.A lagrangian analysis shows that the moisture supply to the convective system is provided by the moist conditionally unstable marine boundary layer while the dry air masses above are involved in the cold pool formation. Four days before the event, both, the dry and the moist air masses, come from the Atlantic Ocean in the lower half of the troposphere. The dry air mass involved in the cold pool formation results from both the advection of mid-level air masses and the drying of low-level air masses lifted up over Spain. For the moist air mass feeding the backbuilding convective systems, most of the air parcels overpass France before travelling almost 48 hours in the lowest 1000m above the Mediterranean. About 50 % of the moisture supply to the precipitating system originates from the evaporation over the sea

High‐resolution air–sea coupling impact on two heavy precipitation events in the Western Mediterranean

“…Meteorol. Soc ., .) and described to a lesser extent in Barthlott and Davolio (2016) and Rainaud et al (2016).…”

Mechanisms for a Record‐Breaking Rainfall in the Coastal Metropolitan City of Guangzhou, China: Observation Analysis and Nested Very Large Eddy Simulation With the WRF Model

“…Schumacher and Johnson () examined the organization and environmental properties of extreme‐rain‐producing MCSs in the United States over a 3‐year period and showed that extreme local rainfall is often associated with back‐building/quasi‐stationary MCSs, which occur when new convective cells repeatedly form upstream of their predecessors and pass over a particular area. The continuous development of upstream convection requires triggering factors, for example, frontal lifting (Schumacher et al, ), outflow boundaries (Houston & Wilhelmson, ; Houze, ; Jeong et al, ; Schumacher, ; Schumacher & Peters, ; Wang et al, ), interaction between the low‐level jet and the midlevel circulation (mesoscale convective vortices; Schumacher, ; Schumacher & Johnson, , ), orographic lifting (Duffourg et al, ; Soderholm et al, ), and thermodynamic effects associated with latent heating/cooling (Wang et al, ). Schumacher and Johnson () also indicated that back‐building/quasi‐stationary MCSs are more dependent on mesoscale and storm‐scale processes, particularly lifting provided by cold outflows from previous convection, than on preexisting synoptic boundaries.…”

Contrasting stable water isotope signals from convective and large-scale precipitation phases of a heavy precipitation event in southern Italy during HyMeX IOP 13: a modelling perspective

“…Jaussaume et al, 1984;Sturm et al, 2005;Blossey et al, 2010). COSMOiso has already shown its capability to simulate the variations of stable water isotopes at the event timescale Aemisegger et al, 2015) as well as in a climatological context (Christner et al, 2018;Dütsch et al, 2018). It includes two additional parallel water cycles for each of the heavy isotopes (H 18 2 O, HD 16 O), which are applied only diagnostically and do not influence other components.…”

“…In this favourable large-scale situation, organized deep convection can occur and often produces highimpact events, with rainfall amounts larger than 100 mm in less than 6 h. The origin of the moisture feeding the convective systems is an important research topic that has been addressed using different techniques and tools, such as trajectory and numerical tracer analyses (e.g. Turato et al 2004;Winschall et al, 2012;Duffourg and Ducrocq, 2013;Winschall et al, 2014;Röhner et al, 2016;Duffourg et al, 2018;Lee et al, 2018). These studies found substantial contributions of subtropical and tropical moisture coming from various sources such as Africa (latitude ≥ 20 • N) and the extratropical remnants of Atlantic tropical cyclones, among others.…”

“…Thanks to a tremendous expansion in the number of datasets of water vapour isotopic composition and a substantially improved set of theories and models for interpreting them, the related studies have been expanded during the past several years (e.g. Pfahl et al, 2008;Bonne et al 2014;Aemisegger et al, 2015;Dütsch et al, 2018;Lacour et al, 2017;Christner et al, 2018).…”