Mesoscale numerical analysis of the historical November 1982 heavy precipitation event over Andorra (Eastern Pyrenees)

Abstract. From 6 to 8 November 1982 one of the most catastrophic flash-flood events was recorded in the Eastern Pyrenees affecting Andorra and also France and Spain with rainfall accumulations exceeding 400 mm in 24 h, 44 fatalities and widespread damage. This paper aims to exhaustively document this heavy precipitation event and examines mesoscale simulations performed by the French Meso-NH non-hydrostatic atmospheric model. Large-scale simulations show the slow-evolving synoptic environment favourable for the development of a deep Atlantic cyclone which induced a strong southerly flow over the Eastern Pyrenees. From the evolution of the synoptic pattern four distinct phases have been identified during the event. The mesoscale analysis presents the second and the third phase as the most intense in terms of rainfall accumulations and highlights the interaction of the moist and conditionally unstable flows with the mountains. The presence of a SW low level jet (30 m s−1) around 1500 m also had a crucial role on focusing the precipitation over the exposed south slopes of the Eastern Pyrenees. Backward trajectories based on Eulerian on-line passive tracers indicate that the orographic uplift was the main forcing mechanism which triggered and maintained the precipitating systems more than 30 h over the Pyrenees. The moisture of the feeding flow mainly came from the Atlantic Ocean (7–9 g kg−1) and the role of the Mediterranean as a local moisture source was very limited (2–3 g kg−1) due to the high initial water vapour content of the parcels and the rapid passage over the basin along the Spanish Mediterranean coast (less than 12 h).

Download Full-text

Mesoscale numerical analysis of the historical November 1982 heavy precipitation event over Andorra (Eastern Pyrenees)

Natural Hazards and Earth System Sciences Discussions ◽

10.5194/nhessd-1-2495-2013 ◽

2013 ◽

Vol 1 (3) ◽

pp. 2495-2545 ◽

Cited By ~ 1

Author(s):

L. Trapero ◽

J. Bech ◽

F. Duffourg ◽

P. Esteban ◽

J. Lorente

Keyword(s):

Large Scale ◽

Flash Flood ◽

Heavy Precipitation ◽

Atmospheric Model ◽

Mediterranean Coast ◽

Precipitation Event ◽

Heavy Precipitation Event ◽

Water Vapour Content ◽

Initial Water ◽

Eastern Pyrenees

Abstract. From 6 to 8 November 1982 was recorded one of the most catastrophic flash-flood events in the Eastern Pyrenees affecting Andorra and also France and Spain with rainfall accumulations exceeding 400 mm in 24 h, 44 fatal victims and widespread damage. This paper aims to document exhaustively this heavy precipitation event and examines mesoscale simulations performed by the French Meso-NH non-hydrostatic atmospheric model. Large scale simulations show the slow-evolving synoptic environment favourable for the development of a deep Atlantic cyclone which induced a strong southerly flow over the Eastern Pyrenees. From the evolution of the synoptic pattern four distinct phases have been identified during the event. The mesoscale analysis presents the second and the third phase as the most intense in terms of rainfall accumulations and highlights the interaction of the moist and conditionally unstable flows with the mountains. The presence of a SW low level jet (30 m s−1) around 1500 m also had a crucial role on focusing the precipitation over the exposed south slopes of the Eastern Pyrenees. Backward trajectories based on Eulerian on-line passive tracers indicate that the orographic uplift was the main forcing mechanism which triggered and maintained the precipitating systems more than 30 h over the Pyrenees. The moisture of the feeding flow mainly came from the Atlantic Ocean (7–9 g kg−1) and the role of the Mediterranean as a local moisture source was very limited (2–3 g kg−1) due to the high initial water vapour content of the parcels and the rapid passage over the basin along the Spanish Mediterranean coast (less than 12 h).

Download Full-text

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-7487-2019 ◽

2019 ◽

Vol 19 (11) ◽

pp. 7487-7506

Author(s):

Keun-Ok Lee ◽

Franziska Aemisegger ◽

Stephan Pfahl ◽

Cyrille Flamant ◽

Jean-Lionel Lacour ◽

...

Keyword(s):

Large Scale ◽

Cold Front ◽

Heavy Precipitation ◽

Convective Precipitation ◽

Water Isotopes ◽

Precipitation Event ◽

Stable Water Isotopes ◽

Heavy Precipitation Event ◽

The North ◽

Upper Level

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.

Download Full-text

Contrasting stable water isotope signals from convective and large-scale precipitation phases of a heavy precipitation event in Southern Italy during HyMeX IOP 13 by Keun-Ok Lee et al.

10.5194/acp-2018-1134-rc2 ◽

2019 ◽

Author(s):

Anonymous

Keyword(s):

Large Scale ◽

Southern Italy ◽

Heavy Precipitation ◽

Precipitation Event ◽

Heavy Precipitation Event ◽

Water Isotope

Download Full-text

Review of "Contrasting stable water isotope signals from convective and large-scale precipitation phases of a heavy precipitation event in Southern Italy during HyMeX IOP 13" by Lee et al.

10.5194/acp-2018-1134-rc1 ◽

2019 ◽

Author(s):

Anonymous

Keyword(s):

Large Scale ◽

Southern Italy ◽

Heavy Precipitation ◽

Precipitation Event ◽

Heavy Precipitation Event ◽

Water Isotope

Download Full-text

Mesoscale GPS Zenith Delay assimilation during a Mediterranean heavy precipitation event

Advances in Geosciences ◽

10.5194/adgeo-17-71-2008 ◽

2008 ◽

Vol 17 ◽

pp. 71-77 ◽

Cited By ~ 7

Author(s):

X. Yan ◽

V. Ducrocq ◽

P. Poli ◽

G. Jaubert ◽

A. Walpersdorf

Keyword(s):

Initial Conditions ◽

Heavy Precipitation ◽

Horizontal Resolution ◽

Precipitation Forecast ◽

Precipitation Event ◽

Total Delay ◽

Heavy Precipitation Event ◽

Water Vapour Content ◽

Single Observation ◽

The Impact

Abstract. The impact of assimilating Zenith Total delay (ZTD) observations from a mesoscale ground-based GPS network over Western Europe is evaluated for the heavy precipitation event of 5–9 September 2005 over Southern France. The ZTD assimilation is performed using a three dimensional variational data assimilation system at the 9.5-km horizontal resolution. Then using as initial conditions the 3DVAR analyses with and without assimilation of ZTD, we perform 2.4-km non-hydrostatic MESO-NH simulations. The results of the fine-scale simulations indicate that assimilation of ZTD help to improve the forecast of the tropospheric water vapour content and the quantitative precipitation forecast. We have also assessed through single observation experiments the influence of the formulation of the observation operator which is used to compute the model equivalent ZTD.

Download Full-text

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

10.5194/acp-2018-1134 ◽

2018 ◽

Author(s):

Keun-Ok Lee ◽

Franziska Aemisegger ◽

Stephan Pfahl ◽

Cyrille Flamant ◽

Jean-Lionel Lacour ◽

...

Keyword(s):

Large Scale ◽

Southern Italy ◽

Cold Front ◽

Heavy Precipitation ◽

Precipitation Event ◽

Heavy Precipitation Event ◽

Air Masses ◽

Surface Evaporation ◽

The North ◽

Upper Level

Abstract. The dynamical context and moisture transport pathways associated with a heavy precipitation event (HPE) in Southern Italy (SI) are investigated with the help of stable water isotopes (SWIs). 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. SI experienced intense rainfall of 62.4 mm over 27 hr with two precipitation phases during this event. The first one (P1) was induced by convective precipitation linked to a frontal feature, 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. 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 &leq; −25 ‰, water vapour mixing ratio q &leq; 2 g kg−1) close to the surface, which induces strong surface evaporation. These air parcels are rapidly enriched in SWI (δ18O &geq; −14 ‰) and moistened (q &geq; 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 precipitation of convective nature in SI. Most of the moist processes (i.e. evaporation, convective mixing) related to the HPE take place during the 18 hours preceding the occurrence of P1 over SI. Four hours 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 moist and SWI-enriched African plume towards SI, and leads to large-scale uplift of the warm African air mass along the cold front. This brings moist and SWI-enriched air masses (median δ18O &geq; −18 ‰, median q &geq; 6 g kg−1) to higher altitudes 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 hours preceding P2 in SI. This work sheds light on the variety of thermodynamic mechanisms occurring at the meso- and synoptic scales and leading to two distinct precipitation phases of a HPE over the densely populated SI region.

Download Full-text

Assimilating X- and S-Band Radar Data for a Heavy Precipitation Event in Italy

Water ◽

10.3390/w13131727 ◽

2021 ◽

Vol 13 (13) ◽

pp. 1727

Author(s):

Valerio Capecchi ◽

Andrea Antonini ◽

Riccardo Benedetti ◽

Luca Fibbi ◽

Samantha Melani ◽

...

Keyword(s):

Extreme Event ◽

Wrf Model ◽

Heavy Precipitation ◽

Radar Data ◽

Flash Floods ◽

Precipitation Event ◽

Weather Research And Forecasting ◽

Limited Area ◽

Heavy Precipitation Event ◽

The Town

During the night between 9 and 10 September 2017, multiple flash floods associated with a heavy-precipitation event affected the town of Livorno, located in Tuscany, Italy. Accumulated precipitation exceeding 200 mm in two hours was recorded. This rainfall intensity is associated with a return period of higher than 200 years. As a consequence, all the largest streams of the Livorno municipality flooded several areas of the town. We used the limited-area weather research and forecasting (WRF) model, in a convection-permitting setup, to reconstruct the extreme event leading to the flash floods. We evaluated possible forecasting improvements emerging from the assimilation of local ground stations and X- and S-band radar data into the WRF, using the configuration operational at the meteorological center of Tuscany region (LaMMA) at the time of the event. Simulations were verified against weather station observations, through an innovative method aimed at disentangling the positioning and intensity errors of precipitation forecasts. A more accurate description of the low-level flows and a better assessment of the atmospheric water vapor field showed how the assimilation of radar data can improve quantitative precipitation forecasts.

Download Full-text

Impact of multiple radar reflectivity data assimilation on the numerical simulation of a flash flood event during the HyMeX campaign

Hydrology and Earth System Sciences ◽

10.5194/hess-21-5459-2017 ◽

2017 ◽

Vol 21 (11) ◽

pp. 5459-5476 ◽

Cited By ~ 4

Author(s):

Ida Maiello ◽

Sabrina Gentile ◽

Rossella Ferretti ◽

Luca Baldini ◽

Nicoletta Roberto ◽

...

Keyword(s):

Hydrological Cycle ◽

Initial Conditions ◽

Flash Flood ◽

Central Italy ◽

Heavy Precipitation ◽

Radar Reflectivity ◽

Precipitation Event ◽

Italian Regions ◽

Reflectivity Data ◽

The Impact

Abstract. An analysis to evaluate the impact of multiple radar reflectivity data with a three-dimensional variational (3-D-Var) assimilation system on a heavy precipitation event is presented. The main goal is to build a regionally tuned numerical prediction model and a decision-support system for environmental civil protection services and demonstrate it in the central Italian regions, distinguishing which type of observations, conventional and not (or a combination of them), is more effective in improving the accuracy of the forecasted rainfall. In that respect, during the first special observation period (SOP1) of HyMeX (Hydrological cycle in the Mediterranean Experiment) campaign several intensive observing periods (IOPs) were launched and nine of which occurred in Italy. Among them, IOP4 is chosen for this study because of its low predictability regarding the exact location and amount of precipitation. This event hit central Italy on 14 September 2012 producing heavy precipitation and causing several cases of damage to buildings, infrastructure, and roads. Reflectivity data taken from three C-band Doppler radars running operationally during the event are assimilated using the 3-D-Var technique to improve high-resolution initial conditions. In order to evaluate the impact of the assimilation procedure at different horizontal resolutions and to assess the impact of assimilating reflectivity data from multiple radars, several experiments using the Weather Research and Forecasting (WRF) model are performed. Finally, traditional verification scores such as accuracy, equitable threat score, false alarm ratio, and frequency bias – interpreted by analysing their uncertainty through bootstrap confidence intervals (CIs) – are used to objectively compare the experiments, using rain gauge data as a benchmark.

Download Full-text