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

Lee, Keun-Ok; Flamant, Cyrille; Ducrocq, Véronique; Duffourg, Fanny; Fourrié, Nadia; Delanoë, Julien; Bech, Joan

doi:10.1002/qj.2978

Cited by 24 publications

(31 citation statements)

References 46 publications

(69 reference statements)

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“…The moisture content simulated with AW2.5 along the backward trajectories (about 10 g kg −1 below 800 m ASL) and along the ATR flight legs (not shown) agrees well with the LEANDRE2 observations. However, the simulated well‐mixed layer seems to be about 200 m too deep (mainly in the cross‐flow leg) and the vertical gradient is less sharp in the simulation, as also observed in AROME‐WMED analyses over the Balearic Sea during IOP 15a by Lee et al ().…”

Section: Environment and Lifting Mechanismssupporting

confidence: 66%

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

Duffourg

Lee

Ducrocq

et al. 2018

Quart J Royal Meteoro Soc

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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

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Section: Environment and Lifting Mechanismssupporting

confidence: 66%

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

Duffourg

Lee

Ducrocq

et al. 2018

Quart J Royal Meteoro Soc

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“…A few studies focused on the assessment of small-scale integrated water vapour (IWV) variability (<10 km/<1 day) and/or on the relationship between water vapour and precipitation systems on a larger scale (>1,000 km/>1 day; e.g. Van Baelen et al, 2011;Winschall et al, 2012;Chazette et al, 2016a;Lee et al, 2016;2017).…”

mentioning

confidence: 99%

Multi‐scale observations of atmospheric moisture variability in relation to heavy precipitating systems in the northwestern Mediterranean during HyMeX IOP12

Khodayar

Czajka

Caldas-Álvarez

et al. 2018

Quart J Royal Meteoro Soc

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The deployment of special instrumentation for the Hydrological Cycle in the Mediterranean Experiment (HyMeX) provides a valuable opportunity to investigate the spatio‐temporal variability of atmospheric water vapour across scales in relationship with the occurrence of Heavy Precipitation Systems (HPSs) in the north Western Mediterranean (WMed) during the Intensive Observation Period (IOP12), which is the focus of this investigation. High‐resolution convection‐permitting COSMO simulations complement the observational network and allow the calculation of on‐line trajectories. In addition to the presence of a favourable large‐scale situation and low‐level convergence, atmospheric moisture changes resulting in conditionally unstable air are identified as responsible for convective initiation (CI). All HPSs within the north‐WMed form in periods/areas of maximum integrated water vapour (IWV; 35–45 kg/m2) after an increase of about 10–20 kg/m2. The most intense events receive moisture from different sources simultaneously and show a sudden increase of about 10 kg/m2 between 6 and 12 h prior to the event, whereas in the less intense events the increase is larger, about 20 kg/m2, over a period of at least 24–36 h. Changes in the lower (∼900 hPa) and mid‐troposphere (∼700 hPa) control the evolution of the atmospheric moisture and the instability increase prior to CI. Spatial inhomogeneities in the lower boundary layer determine the timing and location of deep convection, whereas enhanced moisture in the mid‐troposphere favours intensification. Moister and deeper boundary layers, with updraughts reaching up to 2 km are identified in those pre‐convective environments leading to HPS, whereas dry, shallow boundary layers are found everywhere else. The build‐up time and vertical distribution of the moisture changes are found to be crucial for the evolution and severity of the HPSs rather than the amount of total column atmospheric moisture.

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“…14b) induces the advection of the African moisture plume towards SI and leads to large-scale uplift of the warm and moist air mass along the cold front. The existence of an African moisture plume is often associated with the presence of a deepening, north-south-oriented upper-level trough over the western Mediterranean (Chazette et al, 2015;Lee et al, 2016Lee et al, , 2017. It brings moisture and leads to gradual rain out of the air parcels over Italy.…”

Section: Resultsmentioning

confidence: 99%

“…More recent studies (e.g. Lee et al, 2016Lee et al, , 2017 pointed out a significant moisture contribution, one-quarter of the total integrated water vapour, from north Africa in the middle troposphere (3-5 km above sea level, a.s.l.) feeding the deep convective systems together with the local water vapour sources over the Mediterranean in the lower troposphere (below 2 km a.s.l.).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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Abstract. The dynamical context and moisture transport pathways embedded in large-scale flow and associated with a heavy precipitation event (HPE) in southern Italy (SI) are investigated with the help of stable water isotopes (SWIs) based on a purely numerical framework. The event occurred during the Intensive Observation Period (IOP) 13 of the field campaign of the Hydrological Cycle in the Mediterranean Experiment (HyMeX) on 15 and 16 October 2012, and SI experienced intense rainfall of 62.4 mm over 27 h with two precipitation phases during this event. The first one (P1) was induced by convective precipitation ahead of a cold front, while the second one (P2) was mainly associated with precipitation induced by large-scale uplift. The moisture transport and processes responsible for the HPE are analysed using a simulation with the isotope-enabled regional numerical model COSMOiso. The simulation at a horizontal grid spacing of about 7 km over a large domain (about 4300 km ×3500 km) allows the isotopes signal to be distinguished due to local processes or large-scale advection. Backward trajectory analyses based on this simulation show that the air parcels arriving in SI during P1 originate from the North Atlantic and descend within an upper-level trough over the north-western Mediterranean. The descending air parcels reach elevations below 1 km over the sea and bring dry and isotopically depleted air (median δ18O ≤-25 ‰, water vapour mixing ratio q≤2 g kg−1) close to the surface, which induces strong surface evaporation. These air parcels are rapidly enriched in SWIs (δ18O ≥-14 ‰) and moistened (q≥8 g kg−1) over the Tyrrhenian Sea by taking up moisture from surface evaporation and potentially from evaporation of frontal precipitation. Thereafter, the SWI-enriched low-level air masses arriving upstream of SI are convectively pumped to higher altitudes, and the SWI-depleted moisture from higher levels is transported towards the surface within the downdrafts ahead of the cold front over SI, producing a large amount of convective precipitation in SI. Most of the moisture processes (i.e. evaporation, convective mixing) related to the HPE take place during the 18 h before P1 over SI. A period of 4 h later, during the second precipitation phase P2, the air parcels arriving over SI mainly originate from north Africa. The strong cyclonic flow around the eastward-moving upper-level trough induces the advection of a SWI-enriched African moisture plume towards SI and leads to large-scale uplift of the warm air mass along the cold front. This lifts moist and SWI-enriched air (median δ18O ≥-16 ‰, median q≥6 g kg−1) and leads to gradual rain out of the air parcels over Italy. Large-scale ascent in the warm sector ahead of the cold front takes place during the 72 h preceding P2 in SI. This work demonstrates how stable water isotopes can yield additional insights into the variety of thermodynamic mechanisms occurring at the mesoscale and synoptic scale during the formation of a HPE.

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

Cited by 24 publications

References 46 publications

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

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

Multi‐scale observations of atmospheric moisture variability in relation to heavy precipitating systems in the northwestern Mediterranean during HyMeX IOP12

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

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