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

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

10.5194/acp-2019-766 ◽

2019 ◽

Author(s):

César Sauvage ◽

Cindy Lebeaupin Brossier ◽

Marie-Noëlle Bouin ◽

Véronique Ducrocq

Keyword(s):

Weather Prediction ◽

Heavy Precipitation ◽

Mediterranean Area ◽

Turbulent Fluxes ◽

Western Mediterranean ◽

Precipitation Event ◽

Coupled Modes ◽

Heavy Precipitation Event ◽

Low Level ◽

The Waves

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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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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Strong Cross-Barrier Flow under Stable Conditions Producing Intense Winter Orographic Precipitation: A Case Study over the Subtropical Central Andes

Weather and Forecasting ◽

10.1175/2009waf2222168.1 ◽

2009 ◽

Vol 24 (4) ◽

pp. 1009-1031 ◽

Cited By ~ 22

Author(s):

Maximiliano Viale ◽

Federico A. Norte

Keyword(s):

Heavy Precipitation ◽

Stable Stratification ◽

Central Andes ◽

Precipitation Event ◽

Windward Side ◽

Orographic Precipitation ◽

Near Surface ◽

Low Level ◽

Precipitation Enhancement ◽

Subtropical Central Andes

Abstract The most intense orographic precipitation event over the subtropical central Andes (36°–30°S) during winter 2005 was examined using observational data and a regional model simulation. The Eta-Programa Regional de Meteorología (PRM) model forecast was evaluated and used to explore the airflow structure that generated this heavy precipitation event, with a focus on orographic influences. Even though the model did not realistically reproduce any near-surface variables, nor the precipitation shadow in the leeside lowlands, its reliable forecast of heavy precipitation over the windward side and the wind fields suggests that it can be used as a valuable forecasting tool for such events in the region. The synoptic flow of the 26–29 August 2005 storm responded to a well-defined dipole from low to upper levels with anomalous low (high) geopotential heights at midlatitudes (subtropical) latitudes located off the southeast Pacific coast, resulting in a large meridional geopotential height gradient that drove a strong anomalous cross-barrier flow. Precipitation enhancement in the Andes was observed during the entire event; however, the highest rates were in the prefrontal sector under the low-level stable stratification and cross-barrier winds exceeding 2.5 standard deviations (σ) from the climatological monthly mean. The combination of strong cross-mountain winds with the stable stratification in the air mass of a frontal system, impinging on the high Andes range, appears to be the major factor in determining the flow structure that produced the pattern of precipitation enhancement, with uplift maximized near mountaintops and low-level blocking upwindleading to the formation of a low-level along-barrier jet. Additionally, only the upstream wind anomalies for the 15 heaviest events over a 10-yr (1967–76) period were investigated. They exhibited strong anomalous northwesterly winds for 14 of the 15 events, whereas for the remaining event there were no available observations to evaluate. Thus, these anomalies may also be exploited for forecasting capabilities.

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The impact of GPS and high-resolution radiosonde nudging on the simulation of heavy precipitation during HyMeX IOP6

10.5194/wcd-2021-2 ◽

2021 ◽

Author(s):

Alberto Caldas-Alvarez ◽

Samiro Khodayar ◽

Peter Knippertz

Keyword(s):

High Resolution ◽

Temporal Resolution ◽

Hydrological Cycle ◽

Weather Prediction ◽

Heavy Precipitation ◽

Convective Precipitation ◽

Small Scale ◽

High Temporal Resolution ◽

The Impact

Abstract. Heavy precipitation is one of the most devastating weather extremes in the western Mediterranean region. Our capacity to prevent negative impacts from such extreme events requires advancements in numerical weather prediction, data assimilation and new observation techniques. In this paper we investigate the impact of two state-of-the-art data sets with very high resolution, Global Positioning System-Zenith Total Delays (GPS-ZTD) with a 10 min temporal resolution and radiosondes with ~700 levels, on the representation of convective precipitation in nudging experiments. Specifically, we investigate whether the high temporal resolution, quality, and coverage of GPS-ZTDs can outweigh their lack of vertical information or if radiosonde profiles are more valuable despite their scarce coverage and low temporal resolution (24 h to 6 h). The study focuses on the Intensive Observation Period 6 (IOP6) of the Hydrological Cycle in the Mediterranean eXperiment (HyMeX; 24 September 2012). This event is selected due to its severity (100 mm/12 h), the availability of observations for nudging and validation, and the large observation impact found in preliminary sensitivity experiments. We systematically compare simulations performed with the COnsortium for Small scale MOdelling (COSMO) model assimilating GPS, high- and low vertical resolution radiosoundings in model resolutions of 7 km, 2.8 km and 500 m. The results show that the additional GPS and radiosonde observations cannot compensate errors in the model dynamics and physics. In this regard the reference COSMO runs have an atmospheric moisture wet bias prior to precipitation onset but a negative bias in rainfall, indicative of deficiencies in the numerics and physics, unable to convert the moisture excess into sufficient precipitation. Nudging GPS and high-resolution soundings corrects atmospheric humidity, but even further reduces total precipitation. This case study also demonstrates the potential impact of individual observations in highly unstable environments. We show that assimilating a low-resolution sounding from Nimes (southern France) while precipitation is taking place induces a 40 % increase in precipitation during the subsequent three hours. This precipitation increase is brought about by the moistening of the 700 hPa level (7.5 g kg−1) upstream of the main precipitating systems, reducing the entrainment of dry air above the boundary layer. The moist layer was missed by GPS observations and high-resolution soundings alike, pointing to the importance of profile information and timing. However, assimilating GPS was beneficial for simulating the temporal evolution of precipitation. Finally, regarding the scale dependency, no resolution is particularly sensitive to a specific observation type, however the 2.8 km run has overall better scores, possibly as this is the optimally tuned operational version of COSMO. In follow-up experiments the Icosahedral Nonhydrostatic Model (ICON) will be investigated for this case study to assert whether its numerical and physics updates, compared to its predecessor COSMO, are able to improve the quality of the simulations.

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A case study carried out with two different NWP systems

Natural Hazards and Earth System Science ◽

10.5194/nhess-6-755-2006 ◽

2006 ◽

Vol 6 (5) ◽

pp. 755-760

Author(s):

P. Kållberg ◽

A. Montani

Keyword(s):

Weather Prediction ◽

Heavy Precipitation ◽

Northern Italy ◽

Limited Area ◽

Model Intercomparison ◽

Atmospheric Models ◽

Screen Level ◽

Prediction Systems ◽

Surface Fields

Abstract. A model intercomparison between two atmospheric models, the non–hydrostatic Lokal Modell (LM) and the hydrostatic HIgh Resolution Limited Area Model (HIRLAM) is carried out for a one-week period, including a case of cyclogeneis leading to heavy precipitation over Northern Italy. The two models, very different in terms of data-assimilation and numerics, provide different results in terms of forecasts of surface fields. Opposite diurnal biases for the two models are found in terms of screen level temperatures. HIRLAM wind speed forecasts are too strong, while LM precipitation forecasts have larger extremes. The intercomparison exercise identifies some systematic differences in the weather products generated by the two systems and sheds some light on the biases of the two numerical weather prediction systems.

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Evaluation of GEOS Precipitation Flagging for SMAP Soil Moisture Retrieval Accuracy

Journal of Hydrometeorology ◽

10.1175/jhm-d-20-0038.1 ◽

2021 ◽

Author(s):

Maheshwari Neelam ◽

Rajat Bindlish ◽

Peggy O’Neill ◽

George J. Huffman ◽

Rolf Reichle ◽

...

Keyword(s):

Soil Moisture ◽

Weather Prediction ◽

Heavy Precipitation ◽

Precipitation Event ◽

Retrieval Accuracy ◽

Accuracy Requirement ◽

Earth Observing System ◽

Precipitation Estimates ◽

Global Precipitation Mission ◽

Global Precipitation

The precipitation flag in the Soil Moisture Active Passive (SMAP) Level 2 passive soil moisture (L2SMP) retrieval product indicates the presence or absence of heavy precipitation at the time of the SMAP overpass. The flag is based on precipitation estimates from the Goddard Earth Observing System (GEOS) Forward Processing numerical weather prediction system. An error in flagging during an active or recent precipitation event can either (1) produce an overestimation of soil moisture due to short-term surface wetting of vegetation and/or surface ponding (if soil moisture retrieval was attempted in the presence of rain), or (2) produce an unnecessary non-retrieval of soil moisture and loss of data (if retrieval is flagged due to an erroneous indication of rain). Satellite precipitation estimates from the Integrated Multi-satellite Retrievals for GPM (IMERG) Version 06 Early Run (latency of ~4 hrs) precipitationCal product are used here to evaluate the GEOS-based precipitation flag in the L2SMP product for both the 6 PM ascending and 6 AM descending SMAP overpasses over the first five years of the mission (2015-2020). Consisting of blended precipitation measurements from the GPM (Global Precipitation Mission) satellite constellation, IMERG is treated as the “truth” when comparing to the GEOS model forecasts of precipitation used by SMAP. Key results include: i) IMERG measurements generally show higher spatial variability than the GEOS forecast precipitation, ii) the IMERG product has a higher frequency of light precipitation amounts, and iii) the effect of incorporating IMERG rainfall measurements in lieu of GEOS precipitation forecasts are minimal on the L2SMP retrieval accuracy (determined vs. in situ soil moisture measurements at core validation sites). Our results indicate that L2SMP retrievals continue to meet the mission’s accuracy requirement (standard deviation of the ubRMSE less than 0.04 m3/m3).

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AROME-WMED, a real-time mesoscale model designed for the HyMeX Special Observation Periods

Geoscientific Model Development Discussions ◽

10.5194/gmdd-8-1801-2015 ◽

2015 ◽

Vol 8 (2) ◽

pp. 1801-1856 ◽

Cited By ~ 12

Author(s):

N. Fourrié ◽

&Eacute;. Bresson ◽

M. Nuret ◽

C. Jany ◽

P. Brousseau ◽

...

Keyword(s):

Real Time ◽

Hydrological Cycle ◽

Mesoscale Model ◽

Weather Prediction ◽

Heavy Precipitation ◽

Western Mediterranean ◽

Western Mediterranean Basin ◽

Convective Scale ◽

Observation Instruments ◽

High Precipitation Events

Abstract. During autumn 2012 and winter 2013, two Special Observation Periods (SOPs) of the Hydrological cycle in the Mediterranean Experiment (HyMeX) took place. For the preparatory studies and to support the instrument deployment during the field campaign, a dedicated version of the operational convective-scale AROME-France model was developed: the AROME-WMED model. It covers the western Mediterranean basin with a 48 h forecast range. It provided real time analyses and forecasts which were sent daily to the HyMeX operational centre to forecast high precipitation events and to help decision makers on the deployment of observation instruments. This paper presents the main features of this numerical weather prediction system in terms of data assimilation and forecast. Some specific data of the HyMeX SOP were assimilated in real time. The forecast skill of the AROME-WMED is then assessed with objective scores and compared to the operational AROME-France model, for both autumn 2012 (5 September to 6 November 2012) and winter 2013 (1 February to 15 March 2013) SOPs. The overall performance of AROME-WMED is good and similar to those of AROME-France for the 0 to 30 h common forecast range. The 24 to 48 h forecast range is of course less accurate but remains useful for scheduling observation deployment. The characteristics of parameters such as precipitation, temperature or humidity, are illustrated by one heavy precipitation case study that occurred over the south of Spain.

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Impact analysis of dynamical downscaling on the treatment of convection in a regional NWP model – COSMO: a case study during the passage of a very severe cyclonic storm OCKHI

10.5194/nhess-2018-288 ◽

2018 ◽

Cited By ~ 2

Author(s):

S. Roshny ◽

D. Bala Subrahamanyam ◽

T. J. Anurose ◽

Radhika Ramachandran

Keyword(s):

Impact Analysis ◽

Dynamical Downscaling ◽

Weather Prediction ◽

Heavy Precipitation ◽

Small Scale ◽

Cyclonic Storm ◽

Tropical Regions ◽

Rainfall Prediction ◽

Convection Parameterization

Abstract. A significant source of uncertainty in Numerical Weather Prediction (NWP) models arises from the parameterization of sub-grid scale convection, whose inherent nature of complexity is amplified while applied to tropical regions where weather systems are controlled by many intricate factors. However, as the model resolution becomes finer, it is possible to switch off the convection parameterization, although it is still unclear at what resolution this can be achieved. Ambiguity arises due to the inter-linking of various parameterization schemes within a model, and efficiency of one scheme depends on the output of another. In order to explore these issues, an intense convective episode with very heavy precipitation over the coastal Arabian Sea associated with the passage of OCKHI, one of the very severe cyclonic storms, is chosen as a case study. A set of distinct numerical simulations are carried out using Consortium for Small-scale Modelling (COSMO) to assess the direct and indirect impacts of dynamical downscaling on the treatment of convection. Results obtained from the present investigation indicate dynamical downscaling together with switching off the convection parameterization could simulate the magnitudes of CAPE, one of the proxies for characterizing the occurrence of tropical convection, more realistically. But the downscaling did not improve the rainfall prediction, which were seen to deteriorate in the absence of convection parameterization.

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