Characterization of the air-sea exchanges mechanisms during a Mediterranean heavy precipitation event using realistic sea state modelling

Abstract. This study investigates the mechanisms acting at the air-sea interface during the heavy precipitation event that occurred between the 12–14 October 2016 over the north-western Mediterranean area, and that led to large amounts of rainfall (up to 300 mm in 24 h) over the Hérault region (South of France). The study case was characterized by a very strong easterly to southeasterly wind at low level (> 20 m/s) generating a very rough sea (significant wave height up to 6 m) along the French Riviera and the Gulf of Lion. In order to investigate the role of the waves on those air-sea exchanges during such extreme events a set of numerical experiments was designed using the Météo-France kilometer-scale AROME-France Numerical Weather Prediction model – including the WASP sea surface turbulent fluxes parametrization – and the wave model WaveWatchIII. Results from those sensitivity experiments in the forced or coupled modes showed that taking the waves generated by the model into account increases the surface roughness. Thus the easterly low-level atmospheric flow was slowed-down and the turbulent fluxes upstream of the precipitating system were significantly modified. This modified the forecast of the heaviest precipitation, notably in term of location.

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Characterization of the air–sea exchange mechanisms during a Mediterranean heavy precipitation event using realistic sea state modelling

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-1675-2020 ◽

2020 ◽

Vol 20 (3) ◽

pp. 1675-1699 ◽

Cited By ~ 1

Author(s):

César Sauvage ◽

Cindy Lebeaupin Brossier ◽

Marie-Noëlle Bouin ◽

Véronique Ducrocq

Keyword(s):

Weather Prediction ◽

Heavy Precipitation ◽

Precipitation Event ◽

Turbulent Heat ◽

Coupled Modes ◽

Sea State ◽

Heavy Precipitation Event ◽

Easterly Wind ◽

Low Level ◽

The Waves

Abstract. This study investigates the mechanisms acting at the air–sea interface during a heavy precipitation event that occurred between 12 and 14 October 2016 over the north-western Mediterranean area and led to large amounts of rainfall (up to 300 mm in 24 h) over the Hérault region (southern France). The study case was characterized by a very strong (>20 m s−1) easterly to south-easterly wind at low level that generated very rough seas (significant wave height of up to 6 m) along the French Riviera and the Gulf of Lion. In order to investigate the role of the waves on air–sea exchanges during such extreme events, a set of numerical experiments was designed using the Météo-France kilometre-scale AROME-France numerical weather prediction model – including the WASP (Wave-Age-dependant Stress Parametrization) sea surface turbulent flux parametrization – and the WaveWatch III wave model. Results from these sensitivity experiments in the forced or coupled modes showed that taking the waves generated by the model into account increases the surface roughness. Thus, the increase in the momentum flux induces a slowdown of the easterly low-level atmospheric flow and a displacement of the convergence line at sea. Despite strong winds and a young sea below the easterly flow, the turbulent heat fluxes upstream of the precipitating system are not significantly modified. The forecast of the heaviest precipitation is finally modified when the sea state is taken into account; notably, in terms of location, this modification is slightly larger in the forced mode than in the coupled mode, as the coupling interactively balances the wind sea, the stress and the wind.

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Towards kilometer-scale ocean–atmosphere–wave coupled forecast: a case study on a Mediterranean heavy precipitation event

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-11857-2021 ◽

2021 ◽

Vol 21 (15) ◽

pp. 11857-11887

Author(s):

César Sauvage ◽

Cindy Lebeaupin Brossier ◽

Marie-Noëlle Bouin

Keyword(s):

Weather Prediction ◽

Heavy Precipitation ◽

Western Mediterranean ◽

Precipitation Event ◽

Coupled Modeling ◽

Low Level ◽

First Case ◽

Short Period ◽

Ocean Atmosphere

Abstract. The western Mediterranean Sea area is frequently affected in autumn by heavy precipitation events (HPEs). These severe meteorological episodes, characterized by strong offshore low-level winds and heavy rain in a short period of time, can lead to severe flooding and wave-submersion events. This study aims to progress towards an integrated short-range forecast system via coupled modeling for a better representation of the processes at the air–sea interface. In order to identify and quantify the coupling impacts, coupled ocean–atmosphere–wave simulations were performed for a HPE that occurred between 12 and 14 October 2016 in the south of France. The experiment using the coupled AROME-NEMO-WaveWatchIII system was notably compared to atmosphere-only, coupled atmosphere–wave and ocean–atmosphere simulations. The results showed that the HPE fine-scale forecast is sensitive to both couplings: the interactive coupling with the ocean leads to significant changes in the heat and moisture supply of the HPE that intensify the convective systems, while coupling with a wave model mainly leads to changes in the low-level dynamics, affecting the location of the convergence that triggers convection over the sea. Result analysis of this first case study with the AROME-NEMO-WaveWatchIII system does not clearly show major changes in the forecasts with coupling and highlights some attention points to follow (ocean initialization notably). Nonetheless, it illustrates the higher realism and potential benefits of kilometer-scale coupled numerical weather prediction systems, in particular in the case of severe weather events over the sea and/or in coastal areas, and shows their affordability to confidently progress towards operational coupled forecasts.

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Towards kilometer-scale ocean-atmosphere-wave coupled forecast: a case study on a Mediterranean heavy precipitation event

10.5194/acp-2021-239 ◽

2021 ◽

Author(s):

César Sauvage ◽

Cindy Lebeaupin Brossier ◽

Marie-Noëlle Bouin

Keyword(s):

Weather Prediction ◽

Heavy Precipitation ◽

Western Mediterranean ◽

Precipitation Event ◽

Coupled Modelling ◽

Low Level ◽

First Case ◽

Short Period ◽

Ocean Atmosphere

Abstract. The Western Mediterranean Sea area is frequently affected in autumn by heavy precipitation events (HPEs). These severe meteorological episodes, characterized by strong offshore low-level winds and heavy rain in a short period of time, can lead to severe flooding and wave-submersion events. This study aims to progress towards integrated short-range forecast system via coupled modelling for a better representation of the processes at the air–sea interface. In order to identify and quantify the coupling impacts, coupled ocean–atmosphere–wave simulations were performed for a HPE that occurred between October 12 and 14, 2016 in the South of France, using the coupled AROME-NEMO-WaveWatchIII system and notably compared to atmosphere only, coupled atmosphere–wave and ocean–atmosphere simulations. The results showed that the HPE fine-scale forecast is sensitive to both couplings: The interactive coupling with the ocean leads to significant changes in the heat and moisture supply of the HPE that intensify the convective systems, while coupling with a wave model mainly leads to changes in the low-level dynamics, affecting the location of the convergence that triggers convection over sea. Even if this first case study with the AROME-NEMO-WaveWatchIII system does not clearly show major changes in the forecasts with coupling and highlights some attention points to follow (ocean initialisation notably), it illustrates the higher realism and potential benefits of kilometer-scale coupled numerical weather prediction systems, in particular in case of severe weather events over sea and/or in coastal areas, and shows their affordability to confidently progress towards operational coupled forecasts.

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Comment on ``The heavy precipitation event of 14–15 October 2018 in the Aude catchment: A meteorological study based on operational numerical weather prediction systems and standard and personal observations´´

10.5194/nhess-2020-310-rc1 ◽

2020 ◽

Author(s):

Anonymous

Keyword(s):

Numerical Weather Prediction ◽

Weather Prediction ◽

Heavy Precipitation ◽

Precipitation Event ◽

Heavy Precipitation Event ◽

Numerical Weather ◽

Prediction Systems

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The heavy precipitation event of 14–15 October 2018 in the Aude catchment: a meteorological study based on operational numerical weather prediction systems and standard and personal observations

Natural Hazards and Earth System Science ◽

10.5194/nhess-21-1135-2021 ◽

2021 ◽

Vol 21 (3) ◽

pp. 1135-1157

Author(s):

Olivier Caumont ◽

Marc Mandement ◽

François Bouttier ◽

Judith Eeckman ◽

Cindy Lebeaupin Brossier ◽

...

Keyword(s):

Numerical Weather Prediction ◽

Weather Prediction ◽

Heavy Precipitation ◽

Convective Precipitation ◽

Precipitation Event ◽

Synoptic Situation ◽

Heavy Precipitation Event ◽

Cold Air ◽

Numerical Weather ◽

Prediction Systems

Abstract. The case of the heavy precipitation event on 14 and 15 October 2018 which has led to severe flash flooding in the Aude watershed in south-western France is studied from a meteorological point of view using deterministic and probabilistic numerical weather prediction systems, as well as a unique combination of observations from both standard and personal weather stations. This case features typical characteristics of Mediterranean heavy precipitation events such as its classic synoptic situation and its quasi-stationary convective precipitation that regenerates continuously, as well as some peculiarities such as the presence of a former hurricane and a pre-existing cold air mass close to the ground. Mediterranean Sea surface temperature and soil moisture anomalies are briefly reviewed, as they are known to play a role in this type of hydrometeorological events. A study of rainfall forecasts shows that the event had limited predictability, in particular given the small size of the watersheds involved. It is shown that the stationarity of precipitation, whose estimation benefits from data from personal stations, is linked to the presence near the ground of a trough and a strong potential virtual temperature gradient, the stationarity of both of which is highlighted by a combination of observations from standard and personal stations. The forecast that comes closest to the rainfall observations contains the warmest, wettest, and fastest low-level jet and also simulates near the ground a trough and a marked boundary between cold air in the west and warm air in the east, both of which are stationary.

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The heavy precipitation event of 14–15 October 2018 in the Aude catchment: A meteorological study based on operational numerical weather prediction systems and standard and personal observations

10.5194/nhess-2020-310 ◽

2020 ◽

Author(s):

Olivier Caumont ◽

Marc Mandement ◽

François Bouttier ◽

Judith Eeckman ◽

Cindy Lebeaupin Brossier ◽

...

Keyword(s):

Numerical Weather Prediction ◽

Weather Prediction ◽

Heavy Precipitation ◽

Convective Precipitation ◽

Precipitation Event ◽

Synoptic Situation ◽

Heavy Precipitation Event ◽

Cold Air ◽

Numerical Weather ◽

Prediction Systems

Abstract. The case of the heavy precipitation event on 14 and 15 October 2018 which has led to severe flash flooding in the Aude watershed in south-western France is studied from a meteorological point of view using deterministic and probabilistic numerical weather prediction systems, as well as a unique combination of observations from both standard and personal weather stations. This case is typical of Mediterranean heavy precipitation events due to its classic synoptic situation and its quasi-stationary convective precipitation that regenerates continuously, but with some peculiarities such as the presence of a former hurricane and a pre-existing cold air mass close to the ground. It is shown that the positive Mediterranean sea surface temperature anomaly may have played an aggravating role in the amount of precipitation that poured into the Aude basin. On the other hand, soil moisture does not seem to have played a significant role. A study of rainfall forecasts shows that the event had limited predictability, in particular given the small size of the watersheds involved. It is shown that the stationarity of precipitation, whose estimation benefits from data from personal stations, is linked to the presence near the ground of a trough and a strong potential virtual temperature gradient, the stationarity of both of which is highlighted by a combination of observations from standard and personal stations. The forecast that comes closest to the rainfall observations contains the warmest, wettest and fastest low-level jet and also simulates near the ground a trough and a marked boundary between cold air in the west and warm air in the east, both of which are stationary.

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Inondations de l'Aude du 15 octobre 2018 : analyse météorologique, conséquences hydrologiques et prévisibilité

La Météorologie ◽

10.37053/lameteorologie-2020-0067 ◽

2020 ◽

pp. 046

Author(s):

Michaël Kreitz ◽

Christophe Calas ◽

Sébastien Baille

Keyword(s):

Weather Prediction ◽

Heavy Precipitation ◽

Great Variability ◽

Precipitation Event ◽

Limited Area ◽

Synoptic Scale ◽

Heavy Precipitation Event ◽

River Catchment ◽

Convergence Line ◽

Low Level Jet

Dans la nuit du 14 au 15 octobre 2018, un épisode méditerranéen se déclenche sur le département de l'Aude, déversant jusqu'à 300 mm en un peu moins de 10 heures dans la région de Carcassonne, générant des crues meurtrières sur le bassin moyen de l'Aude et de ses affluents. Les ingrédients météorologiques typiques d'un tel événement sont bien présents : entrée droite d'un jet de sud en altitude, jet de basses couches méditerranéen chaud et humide alimentant une ligne de convergence. Le paroxysme de l'épisode s'étant produit à l'est immédiat de Carcassonne, région habituellement située à la périphérie des épisodes les plus intenses, les durées de retour des précipitations sur 6 heures sont au final d'ordre centennal. Même si la prévisibilité d'un épisode méditerranéen est relativement bonne à grande échelle, les modèles déterministes et leurs ensembles, qu'ils soient globaux ou à aire limitée, montrent une grande variabilité d'un réseau à l'autre, rendant très difficile la localisation précise du paroxysme pluvieux. During the night of 14th October 2018 a Mediterranean Heavy Precipitation Event occurred over the Aude département in Southern France, bringing up to 300 mm of rain in about 10 hours over the Carcassonne area, and generating deadly floods in the Aude River catchment. Typical meteorological ingredients were involved: an upper-jet right-entrance region, and a warm and wet low-level jet feeding a convergence line. As the peak of the event occurs around Carcassonne which is less familiar to such events, the return period for 6-hour rainfall was close to one-hundred years. The predictability of such events is rather good on a synoptic scale. However, when it comes to precise localisation and intensities, numerical weather prediction (NWP) models (be they deterministic or ensembles, global or limited-area ones) show a great variability between consecutive runs, making the exercise very challenging for forecasters.

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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.

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Evaluation of Two Cloud-Resolving Models Using Bin or Bulk Microphysics Representation for the HyMeX-IOP7a Heavy Precipitation Event

Atmosphere ◽

10.3390/atmos11111177 ◽

2020 ◽

Vol 11 (11) ◽

pp. 1177

Author(s):

Diana Arteaga ◽

Céline Planche ◽

Christina Kagkara ◽

Wolfram Wobrock ◽

Sandra Banson ◽

...

Keyword(s):

Hydrological Cycle ◽

Wrf Model ◽

Heavy Precipitation ◽

Sensitivity Study ◽

Precipitation Event ◽

Convective System ◽

Wind Fields ◽

Massif Central ◽

Surface Precipitation ◽

Low Level

The Mediterranean region is frequently affected in autumn by heavy precipitation that causes flash-floods or landslides leading to important material damage and casualties. Within the framework of the international HyMeX program (HYdrological cycle in Mediterranean EXperiment), this study aims to evaluate the capabilities of two models, WRF (Weather Research and Forecasting) and DESCAM (DEtailed SCAvenging Model), which use two different representations of the microphysics to reproduce the observed atmospheric properties (thermodynamics, wind fields, radar reflectivities and precipitation features) of the HyMeX-IOP7a intense precipitating event (26 September 2012). The DESCAM model, which uses a bin resolved representation of the microphysics, shows results comparable to the observations for the precipitation field at the surface. On the contrary, the simulations made with the WRF model using a bulk representation of the microphysics (either the Thompson scheme or the Morrison scheme), commonly employed in NWP models, reproduce neither the intensity nor the distribution of the observed precipitation—the rain amount is overestimated and the most intense cell is shifted to the East. The different simulation results show that the divergence in the surface precipitation features seems to be due to different mechanisms involved in the onset of the precipitating system: the convective system is triggered by the topography of the Cévennes mountains (i.e., south-eastern part of the Massif Central) in DESCAM and by a low-level flux convergence in WRF. A sensitivity study indicates that the microphysics properties have impacted the thermodynamics and dynamics fields inducing the low-level wind convergence simulated with WRF for this HyMeX event.

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