scholarly journals Development of a forecast-oriented km-resolution ocean-atmosphere coupled system for Western Europe and evaluation for a severe weather situation

2021 ◽  
Author(s):  
Joris Pianezze ◽  
Jonathan Beuvier ◽  
Cindy Lebeaupin Brossier ◽  
Guillaume Samson ◽  
Ghislain Faure ◽  
...  
Keyword(s):  
High Resolution ◽  
Western Europe ◽  
Heavy Precipitation ◽  
Sea Surface ◽  
Extreme Weather Events ◽  
Precipitation Event ◽  
Surface Cooling ◽  
Area Of Interest ◽  
Weather Situation ◽  
Ocean Atmosphere

Abstract. To improve high-resolution numerical environmental prediction, it is essential to represent ocean-atmosphere interactions properly, which is not the case in current operational regional forecasting systems used in Western Europe. The objective of this paper is to present a new forecast-oriented coupled ocean-atmosphere system and its evaluation. This system uses the state-of-the-art numerical models AROME (cy43t2) and NEMO (v3.6) with a horizontal resolution of 2.5 km. The OASIS coupler (OASIS3MCT-4.0), implemented in the SurfEX surface scheme and in NEMO, is used to perform the communications between models. The evaluation of this system is carried out using 7-day simulations from 12 to 19 October 2018, characterised by extreme weather events (storms and heavy precipitation event) in the area of interest. Comparisons with in-situ and L3 satellite observations show that the fully coupled simulation reproduces quantitatively well the spatial and temporal evolution of the sea surface temperature and 10 m wind speed. Sensitivity analysis to OA coupling show that the use of an interactive and high resolution SST, in contrast to actual NWP where SST is persistent and at low resolution, modifies the atmospheric circulation and the location of heavy precipitation. When compared to the operational-like ocean forecast, simulated oceanic fields show a large sensitivity to coupling. Forced ocean simulations highlight that this sensitivity is mainly controlled by the change in the atmospheric model used to drive NEMO (AROME vs. ECMWF IFS operational forecast). The oceanic boundary layer depths can vary by more than 40%. This impact is amplified by the interactive coupling and is attributed to positive feedback between sea surface cooling and evaporation.

Trois phénomènes météorologiques exceptionnels durant l'automne 2020

2021 ◽  
pp. 115
Author(s):  
Michaël Kreitz
Keyword(s):  
Heavy Precipitation ◽  
Extreme Weather ◽  
Extreme Weather Events ◽  
Precipitation Event ◽  
Heavy Precipitation Event ◽  
Weather Events

Durant cet automne 2020, la France est concernée par trois phénomènes météorologiques exceptionnels. Tout d'abord, le 19 septembre, un épisode cévenol intense apporte 700 mm en 12 heures sur la région de Valleraugue. Puis, le 1er octobre, la tempête Alex traverse le nord-ouest de la France, où les rafales atteignent 186 km/h à Belle-Île-en-Mer en raison de la présence d'un sting jet. Le lendemain, un nouvel épisode fortement précipitant déverse localement 500 mm de pluie sur les Alpes-Maritimes. Ces trois phénomènes ont tous relevé d'une vigilance rouge. During fall 2020, France is concerned by three extreme weather events. First, on september 19th , an intense cévenol event brings 700 mm in 12 hours over Valleraugue area. Then, on October the 1 st , Alex windstorm crosses northwestern France where gusts reach 186 km/h over Belle-Île-en-Mer because of the occurrence of a sting jet. The day after, a new heavy precipitation event spills a 500 mm rainfall locally over Alpes-Maritimes. All those three events received a red warning.

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

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.

A deep learning based approach for inferring the distribution of potential extreme events from coarse resolution climate model output

2020 ◽  
Author(s):  
Leroy Bird ◽  
Greg Bodeker ◽  
Jordis Tradowsky
Keyword(s):  
Deep Learning ◽  
High Resolution ◽  
Computational Cost ◽  
Extreme Weather Events ◽  
Precipitation Event ◽  
Model Output ◽  
Coarse Resolution ◽  
Extreme Precipitation Events ◽  
Resolution Model ◽  
High Resolution Model

<p>Frequency based climate change attribution of extreme weather events requires thousands of years worth of model output in order to obtain a statistically sound result. Additionally, extreme precipitation events in particular require a high resolution model as they can occur over a relatively small area. Unfortunately due storage and computational restrictions it is not feasible to run traditional models at a sufficiently high spatial resolution for the complete duration of these simulations. Instead, we suggest that deep learning could be used to emulate a proportion of a high resolution model, at a fraction of the computational cost. More specifically, we use a U-Net, a type of convolutional neural network. The U-Net takes as input, several fields from coarse resolution model output and is trained to predict corresponding high resolution precipitation fields. Because there are many potential precipitation fields associated with the coarse resolution model output, stochasticity is added to the U-Net and a generative adversarial network is employed in order to help create a realistic distribution of events. By sampling the U-Net many times, an estimate of the probability of a heavy precipitation event occurring on the sub-grid scale can be derived.</p>

scholarly journals Simulation of a flash-flood event over the Adriatic Sea with a high-resolution atmosphere–ocean–wave coupled system

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Antonio Ricchi ◽  
Davide Bonaldo ◽  
Guido Cioni ◽  
Sandro Carniel ◽  
Mario Marcello Miglietta
Keyword(s):  
High Resolution ◽  
Marine Boundary Layer ◽  
Adriatic Sea ◽  
Flash Flood ◽  
Coupled System ◽  
Heavy Precipitation ◽  
Numerical Approach ◽  
Venice Lagoon ◽  
Precipitation Event ◽  
Consistent Treatment

AbstractOn the morning of September 26, 2007, a heavy precipitation event (HPE) affected the Venice lagoon and the neighbouring coastal zone of the Adriatic Sea, with 6-h accumulated rainfall summing up to about 360 mm in the area between the Venetian mainland, Padua and Chioggia. The event was triggered and maintained by the uplift over a convergence line between northeasterly flow from the Alps and southeasterly winds from the Adriatic Sea. Hindcast modelling experiments, using standalone atmospheric models, failed to capture the spatial distribution, maximum intensity and timing of the HPE. Here we analyze the event by means of an atmosphere-wave-ocean coupled numerical approach. The combined use of convection permitting models with grid spacing of 1 km, high-resolution sea surface temperature (SST) fields, and the consistent treatment of marine boundary layer fluxes in all the numerical model components are crucial to provide a realistic simulation of the event. Inaccurate representations of the SST affect the wind magnitude and, through this, the intensity, location and time evolution of the convergence zone, thus affecting the HPE prediction.

scholarly journals Surface processes in the 7 November 2014 medicane from air–sea coupled high-resolution numerical modelling

2020 ◽  
Vol 20 (11) ◽  
pp. 6861-6881 ◽  
Author(s):  
Marie-Noëlle Bouin ◽  
Cindy Lebeaupin Brossier
Keyword(s):  
Tropical Cyclones ◽  
Sea Surface ◽  
Convective Precipitation ◽  
Surface Cooling ◽  
Air Masses ◽  
Coupled Modelling ◽  
Low Level ◽  
Cold Pools ◽  
Ocean Atmosphere ◽  
The Impact

Abstract. A medicane, or Mediterranean cyclone with characteristics similar to tropical cyclones, is simulated using a kilometre-scale ocean–atmosphere coupled modelling platform. A first phase leads to strong convective precipitation, with high potential vorticity anomalies aloft due to an upper-level trough. Then, the deepening and tropical transition of the cyclone result from a synergy of baroclinic and diabatic processes. Heavy precipitation results from uplift of conditionally unstable air masses due to low-level convergence at sea. This convergence is enhanced by cold pools, generated either by rain evaporation or by advection of continental air masses from northern Africa. Back trajectories show that air–sea heat exchanges moisten the low-level inflow towards the cyclone centre. However, the impact of ocean–atmosphere coupling on the cyclone track, intensity and life cycle is very weak. This is due to a sea-surface cooling 1 order of magnitude weaker than for tropical cyclones, even in the area of strong enthalpy fluxes. Surface currents have no impact. Analysing the surface enthalpy fluxes shows that evaporation is controlled mainly by the sea-surface temperature and wind. Humidity and temperature at the first level play a role during the development phase only. In contrast, the sensible heat transfer depends mainly on the temperature at the first level throughout the medicane lifetime. This study shows that the tropical transition, in this case, is dependent on processes widespread in the Mediterranean Basin, like advection of continental air, rain evaporation and formation of cold pools, and dry-air intrusion.

scholarly journals Probabilistic high-resolution forecast of heavy precipitation over Central Europe

2004 ◽  
Vol 4 (2) ◽  
pp. 315-322 ◽  
Author(s):  
C. Marsigli ◽  
A. Montani ◽  
F. Nerozzi ◽  
T. Paccagnella
Keyword(s):  
High Resolution ◽  
Central Europe ◽  
Heavy Precipitation ◽  
Precipitation Event ◽  
Ensemble Prediction ◽  
Limited Area ◽  
Ensemble Forecasts ◽  
Ensemble Prediction System ◽  
Precipitation Structure ◽  
High Precipitation

Abstract. The limited-area ensemble prediction system COSMO-LEPS has been running operationally at ECMWF since November 2002. Five runs of the non-hydrostatic limited-area model Lokal Modell (LM) are available every day, nested on five selected members of three consecutive 12-h lagged ECMWF global ensembles. The limited-area ensemble forecasts range up to 120h and LM-based probabilistic products are disseminated to several national weather services. COSMO-LEPS has been constructed in order to have a probabilistic system with high resolution, focussing the attention on extreme events in regions with complex orography. In this paper, the performance of COSMO-LEPS for a heavy precipitation event that affected Central Europe in August 2002 has been examined. At the 4-day forecast range, the probability maps indicate the possibility of the overcoming of high precipitation thresholds (up to 150mm/24h) over the region actually affected by the flood. Furthermore, one out of the five ensemble members predicts 4 days ahead a precipitation structure very similar to the observed one.

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

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.

scholarly journals On the sensitivity of oceanic precipitation to sea surface temperature

2019 ◽  
Author(s):  
Jörg Burdanowitz ◽  
Stefan A. Buehler ◽  
Stephan Bakan ◽  
Christian Klepp
Keyword(s):  
High Resolution ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Vertical Velocity ◽  
Climate Models ◽  
Sea Surface ◽  
Precipitation Event ◽  
Temporal Sampling ◽  
Precipitation Measurement ◽  
Oceanic Precipitation

Abstract. Our study forms the oceanic counterpart to numerous observational studies over land considering the sensitivity of extreme precipitation to a change in air temperature. We explore the sensitivity of oceanic precipitation to changing sea surface temperature (SST) by exploiting two novel datasets at high resolution. First, we use the Ocean Rainfall And Ice-phase precipitation measurement Network (OceanRAIN) as an observational along-track shipboard dataset at 1-minute resolution. Second, we exploit the most recent European Re-Analysis version 5 (ERA5) at hourly resolution on 31 km grid. Matched with each other, ERA5 vertical velocity allows to constrain OceanRAIN precipitation. Despite the inhomogeneous sampling along ship tracks, OceanRAIN agrees with ERA5 on the average latitudinal distribution of precipitation with fairly good seasonal sampling. However, the 99th percentile of OceanRAIN precipitation follows a super-Clausius-Clapeyron scaling with SST that exceeds 8.5 % K−1 while ERA5 precipitation scales with 4.5 % K−1. The sensitivity decreases towards lower precipitation percentiles while OceanRAIN keeps an almost constant offset to ERA5 due to higher spatial resolution and temporal sampling. Unlike over land, we find no evidence for decreasing precipitation event duration with SST. ERA5 precipitation reaches a local minimum at about 26 °C that vanishes when constraining vertical velocity to strongly rising motion and excluding areas of weak correlation between precipitation and vertical velocity. This indicates that instead of moisture limitations as over land, circulation dynamics rather limit precipitation formation over the ocean. For strongest rising motion, precipitation scaling converges to a constant value at all precipitation percentiles. Overall, high resolution in observations as well as climate models is key to understand and predict the sensitivity of oceanic precipitation extremes to a change in SST.

scholarly journals Matchup Characteristics of Sea Surface Salinity Using a High-Resolution Ocean Model

2021 ◽  
Vol 13 (15) ◽  
pp. 2995
Author(s):  
Frederick M. Bingham ◽  
Severine Fournier ◽  
Susannah Brodnitz ◽  
Karly Ulfsax ◽  
Hong Zhang
Keyword(s):  
High Resolution ◽  
Time Window ◽  
Single Point ◽  
Ocean Model ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Argo Floats ◽  
Statistical Measures ◽  
Salinity Difference

Sea surface salinity (SSS) satellite measurements are validated using in situ observations usually made by surfacing Argo floats. Validation statistics are computed using matched values of SSS from satellites and floats. This study explores how the matchup process is done using a high-resolution numerical ocean model, the MITgcm. One year of model output is sampled as if the Aquarius and Soil Moisture Active Passive (SMAP) satellites flew over it and Argo floats popped up into it. Statistical measures of mismatch between satellite and float are computed, RMS difference (RMSD) and bias. The bias is small, less than 0.002 in absolute value, but negative with float values being greater than satellites. RMSD is computed using an “all salinity difference” method that averages level 2 satellite observations within a given time and space window for comparison with Argo floats. RMSD values range from 0.08 to 0.18 depending on the space–time window and the satellite. This range gives an estimate of the representation error inherent in comparing single point Argo floats to area-average satellite values. The study has implications for future SSS satellite missions and the need to specify how errors are computed to gauge the total accuracy of retrieved SSS values.

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