Sensitivity of quantitative precipitation forecasts to boundary layer parameterization: a flash flood case study in the Western Mediterranean

Abstract. The "Montserrat-2000" severe flash flood event which occurred over Catalonia on 9 and 10 June 2000 is analyzed. Strong precipitation was generated by a mesoscale convective system associated with the development of a cyclone. The location of heavy precipitation depends on the position of the cyclone, which, in turn, is found to be very sensitive to various model characteristics and initial conditions. Numerical simulations of this case study using the hydrostatic BOLAM and the non-hydrostatic MOLOCH models are performed in order to test the effects of different formulations of the boundary layer parameterization: a modified version of the Louis (order 1) model and a custom version of the E-ℓ (order 1.5) model. Both of them require a diagnostic formulation of the mixing length, but the use of the turbulent kinetic energy equation in the E-ℓ model allows to represent turbulence history and non-locality effects and to formulate a more physically based mixing length. The impact of the two schemes is different in the two models. The hydrostatic model, run at 1/5 degree resolution, is less sensitive, but the quantitative precipitation forecast is in any case unsatisfactory in terms of localization and amount. Conversely, the non-hydrostatic model, run at 1/50 degree resolution, is capable of realistically simulate timing, position and amount of precipitation, with the apparently superior results obtained with the E-ℓ parameterization model.

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High resolution numerical study of the Algiers 2001 flash flood: sensitivity to the upper-level potential vorticity anomaly

Advances in Geosciences ◽

10.5194/adgeo-7-251-2006 ◽

2006 ◽

Vol 7 ◽

pp. 251-257 ◽

Cited By ~ 13

Author(s):

S. Argence ◽

D. Lambert ◽

E. Richard ◽

N. Söhne ◽

J.-P. Chaboureau ◽

...

Keyword(s):

Potential Vorticity ◽

Flash Flood ◽

Numerical Study ◽

Western Mediterranean ◽

Precipitation Forecast ◽

Inversion Method ◽

Strong Impact ◽

Upper Level ◽

Vorticity Anomaly ◽

The Impact

Abstract. From 9 to 11 November 2001, intense cyclogenesis affected the northern coasts of Africa and more particularly the densely populated city of Algiers. During the morning of 10 November, more than 130 mm of precipitation was recorded at Bouzareah and resulted in mudslides which devastated the Bab-el-Oued district. This disaster caused more than 700 casualties and catastrophic damage. Like many other heavy rainstorms in the western Mediterranean, this event was associated with the presence of an upper-level trough materialized by a deep stratospheric intrusion and characterized by high potential vorticity values. In this study, the impact of this synoptic structure on the localization and intensity of the precipitation which affected Algiers is investigated using a potential vorticity (PV) inversion method coupled for the first time with the French non-hydrostatic MESO-NH model. A set of perturbed synoptic environments was designed by slightly modifying the extent and the intensity of the coherent potential vorticity structures in the operational ARPEGE analysis. It is shown that such modifications may have a strong impact on the fine-scale precipitation forecast in the Algiers region, thereby demonstrating the fundamental role played by the potential vorticity anomaly during this exceptional meteorological event.

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Cloud-scale modelling of the impact of deep convection on the fate of oceanic bromoform in the troposphere: a case study over the west coast of Borneo

10.5194/acp-2020-655 ◽

2020 ◽

Author(s):

Paul D. Hamer ◽

Virginie Marécal ◽

Ryan Hossaini ◽

Michel Pirre ◽

Gisèle Krysztofiak ◽

...

Keyword(s):

Boundary Layer ◽

West Coast ◽

Deep Convection ◽

Convective System ◽

The West ◽

Upper Troposphere ◽

Convective Systems ◽

Mixing Ratios ◽

The Impact

Abstract. Coastal oceans emit bromoform (CHBr3) that can be transported rapidly to the upper troposphere by deep convection. In the troposphere, the spatial and vertical distribution of CHBr3 and its product gases (PGs) depend on emissions, chemical processing, transport by large scale flow, convection, and associated washout. This paper presents a modelling study on the fate of CHBr3 and its PGs in the troposphere. A case study at cloud scale was conducted along the west coast of Borneo, when several deep convective systems triggered in the afternoon and early evening of November 19th 2011. These systems were sampled by the Falcon aircraft during the field campaign of the SHIVA project. We analyse these systems using a simulation with the cloud-resolving meteorological model C-CATT-BRAMS at 2 × 2 km resolution that describes transport, photochemistry, and washout of CHBr3. We find that simulated CHBr3 mixing ratios and the observed values in the boundary layer and the outflow of the convective systems agree. However, the model underestimates the background CHBr3 mixing ratios in the upper troposphere, which suggests a missing source. An analysis of the simulated chemical speciation of bromine within and around each simulated convective system during the mature convective stage reveals that > 85 % of the bromine derived from CHBr3 and its PGs is transported vertically to the point of convective detrainment in the form of CHBr3 and that the remaining small fraction is in the form of organic PGs, principally insoluble brominated carbonyls produced from the photo-oxidation of CHBr3. The model simulates that within the boundary layer and free troposphere, the inorganic PGs are only present in soluble forms, i.e., HBr, HOBr, and BrONO2, and consequently, within the convective clouds, the inorganic PGs are almost entirely removed by wet scavenging. For the conditions of the simulated case study Br2 plays no significant role in the vertical transport of bromine. This likely results from the small simulated quantities of inorganic bromine involved, the presence of HBr in large excess compared to HOBr and the less soluble BrO, and the relatively quick removal of soluble compounds within the convective column. This prevalence of HBr is a result of the wider simulated regional atmospheric composition whereby background tropospheric ozone levels are exceptionally low.

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Investigating 3D and 4D Variational Rapid-Update-Cycling Assimilation of Weather Radar Reflectivity for a Flash Flood Event in Central Italy

10.5194/nhess-2020-406 ◽

2021 ◽

Author(s):

Vincenzo Mazzarella ◽

Rossella Ferretti ◽

Errico Picciotti ◽

Frank S. Marzano

Keyword(s):

Data Assimilation ◽

Roc Curve ◽

Initial Conditions ◽

Flash Flood ◽

Central Italy ◽

Wrf Model ◽

Radar Reflectivity ◽

Precipitation Forecast ◽

Precipitation Pattern ◽

The Impact

Abstract. The precipitation forecast over the Mediterranean basin is still a challenge because of the complex orographic region which amplifies the need for local observation to correctly initialize the forecast. In this context the data assimilation techniques play a key role in improving the initial conditions and consequently the timing and position of precipitation pattern. For the first time, the ability of a cycling 4D-Var to reproduce a severe weather event in central Italy, as well as to provide a comparison with the largely used cycling 3D-Var, is evaluated in this study. The radar reflectivity measured by the Italian ground radar network is assimilated in the WRF model to simulate an event occurred on May 3, 2018 in central Italy. In order to evaluate the impact of data assimilation, several simulations are objectively compared by means of a Fraction Skill Score (FSS), which is calculated for several threshold values, and a Receiver Operating Characteristic (ROC) curve. The results suggest that both assimilation methods in cycling mode improve the 1, 3 and 6-hourly quantitative precipitation estimation. More specifically, the cycling 4D-Var with a warm start initialization shows the highest FSS values in the first hours of simulation both with light and heavy precipitation. Finally, the ROC curve confirms the benefit of 4D-Var: the area under the curve is 0.91 compared to the 0.88 of control experiment without data assimilation.

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Cloud-scale modelling of the impact of deep convection on the fate of oceanic bromoform in the troposphere: a case study over the west coast of Borneo

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-16955-2021 ◽

2021 ◽

Vol 21 (22) ◽

pp. 16955-16984

Author(s):

Paul D. Hamer ◽

Virginie Marécal ◽

Ryan Hossaini ◽

Michel Pirre ◽

Gisèle Krysztofiak ◽

...

Keyword(s):

Boundary Layer ◽

West Coast ◽

Deep Convection ◽

Regional Scale ◽

Convective System ◽

The West ◽

Convective Systems ◽

Mixing Ratios ◽

The Impact

Abstract. This paper presents a modelling study on the fate of CHBr3 and its product gases in the troposphere within the context of tropical deep convection. A cloud-scale case study was conducted along the west coast of Borneo, where several deep convective systems were triggered on the afternoon and early evening of 19 November 2011. These systems were sampled by the Falcon aircraft during the field campaign of the SHIVA project and analysed using a simulation with the cloud-resolving meteorological model C-CATT-BRAMS at 2×2 km resolution that represents the emissions, transport by large-scale flow, convection, photochemistry, and washout of CHBr3 and its product gases (PGs). We find that simulated CHBr3 mixing ratios and the observed values in the boundary layer and the outflow of the convective systems agree. However, the model underestimates the background CHBr3 mixing ratios in the upper troposphere, which suggests a missing source at the regional scale. An analysis of the simulated chemical speciation of bromine within and around each simulated convective system during the mature convective stage reveals that >85 % of the bromine derived from CHBr3 and its PGs is transported vertically to the point of convective detrainment in the form of CHBr3 and that the remaining small fraction is in the form of organic PGs, principally insoluble brominated carbonyls produced from the photo-oxidation of CHBr3. The model simulates that within the boundary layer and free troposphere, the inorganic PGs are only present in soluble forms, i.e. HBr, HOBr, and BrONO2, and, consequently, within the convective clouds, the inorganic PGs are almost entirely removed by wet scavenging. We find that HBr is the most abundant PG in background lower-tropospheric air and that this prevalence of HBr is a result of the relatively low background tropospheric ozone levels at the regional scale. Contrary to a previous study in a different environment, for the conditions in the simulation, the insoluble Br2 species is hardly formed within the convective systems and therefore plays no significant role in the vertical transport of bromine. This likely results from the relatively small quantities of simulated inorganic bromine involved, the presence of HBr in large excess compared to HOBr and BrO, and the relatively efficient removal of soluble compounds within the convective column.

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The impact of a foehn wind on PM10 concentrations and the urban boundary layer in complex terrain: a case study from Kraków, Poland

Tellus B ◽

10.1080/16000889.2021.1933780 ◽

2021 ◽

Vol 73 (1) ◽

pp. 1-26

Author(s):

Piotr Sekuła ◽

Anita Bokwa ◽

Zbigniew Ustrnul ◽

Mirosław Zimnoch ◽

Bogdan Bochenek

Keyword(s):

Boundary Layer ◽

Complex Terrain ◽

Urban Boundary Layer ◽

The Impact

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Numerical simulations of June 7, 2020 convective precipitation over Slovakia using deterministic, probabilistic, and convection-permitting approaches

Időjárás ◽

10.28974/idojaras.2021.4.3 ◽

2021 ◽

Vol 125 (4) ◽

pp. 571-607

Author(s):

André Simon ◽

Martin Belluš ◽

Katarína Čatlošová ◽

Mária Derková ◽

Martin Dian ◽

...

Keyword(s):

Satellite Imagery ◽

Weather Prediction ◽

Severe Weather ◽

Precipitation Forecast ◽

Convective Precipitation ◽

Small Scale ◽

Limited Area ◽

Systematic Effect ◽

The Impact

The paper presented is dedicated to the evaluation of the influence of various improvements to the numerical weather prediction (NWP) systems exploited at the Slovak Hydrometeorological Institute (SHMÚ). The impact was illustrated in a case study with multicell thunderstorms and the results were confronted with the reference analyses from the INCA nowcasting system, regional radar reflectivity data, and METEOSAT satellite imagery. The convective cells evolution was diagnosed in non-hydrostatic dynamics experiments to study weak mesoscale vortices and updrafts. The growth of simulated clouds and evolution of the temperature at their top were compared with the brightness temperature analyzed from satellite imagery. The results obtained indicated the potential for modeling and diagnostics of small-scale structures within the convective cloudiness, which could be related to severe weather. Furthermore, the non-hydrostatic dynamics experiments related to the stability and performance improvement of the time scheme led to the formulation of a new approach to linear operator definition for semi-implicit scheme (in text referred as NHHY). We demonstrate that the execution efficiency has improved by more than 20%. The exploitation of several high resolution measurement types in data assimilation contributed to more precise position of predicted patterns and precipitation representation in the case study. The non-hydrostatic dynamics provided more detailed structures. On the other hand, the potential of a single deterministic forecast of prefrontal heavy precipitation was not as high as provided by the ensemble system. The prediction of a regional ensemble system A-LAEF (ALARO Limited Area Ensemble Forecast) enhanced the localization of precipitation patterns. Though, this was rather due to the simulation of uncertainty in the initial conditions and also because of the stochastic perturbation of physics tendencies. The various physical parameterization setups of A-LAEF members did not exhibit a systematic effect on precipitation forecast in the evaluated case. Moreover, the ensemble system allowed an estimation of uncertainty in a rapidly developing severe weather case, which was high even at very short range.

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Ensemble cloud-resolving modelling of a historic back-building mesoscale convective system over Liguria: the San Fruttuoso case of 1915

Climate of the Past ◽

10.5194/cp-13-455-2017 ◽

2017 ◽

Vol 13 (5) ◽

pp. 455-472 ◽

Cited By ~ 10

Author(s):

Antonio Parodi ◽

Luca Ferraris ◽

William Gallus ◽

Maurizio Maugeri ◽

Luca Molini ◽

...

Keyword(s):

Extreme Event ◽

Flash Flood ◽

Western Mediterranean ◽

Mesoscale Convective Systems ◽

Convective System ◽

Water Vapour Content ◽

Ligurian Sea ◽

Convective Systems ◽

Position Errors ◽

Mesoscale Convective

Abstract. Highly localized and persistent back-building mesoscale convective systems represent one of the most dangerous flash-flood-producing storms in the north-western Mediterranean area. Substantial warming of the Mediterranean Sea in recent decades raises concerns over possible increases in frequency or intensity of these types of events as increased atmospheric temperatures generally support increases in water vapour content. However, analyses of the historical record do not provide a univocal answer, but these are likely affected by a lack of detailed observations for older events. In the present study, 20th Century Reanalysis Project initial and boundary condition data in ensemble mode are used to address the feasibility of performing cloud-resolving simulations with 1 km horizontal grid spacing of a historic extreme event that occurred over Liguria: the San Fruttuoso case of 1915. The proposed approach focuses on the ensemble Weather Research and Forecasting (WRF) model runs that show strong convergence over the Ligurian Sea (17 out of 56 members) as these runs are the ones most likely to best simulate the event. It is found that these WRF runs generally do show wind and precipitation fields that are consistent with the occurrence of highly localized and persistent back-building mesoscale convective systems, although precipitation peak amounts are underestimated. Systematic small north-westward position errors with regard to the heaviest rain and strongest convergence areas imply that the reanalysis members may not be adequately representing the amount of cool air over the Po Plain outflowing into the Ligurian Sea through the Apennines gap. Regarding the role of historical data sources, this study shows that in addition to reanalysis products, unconventional data, such as historical meteorological bulletins, newspapers, and even photographs, can be very valuable sources of knowledge in the reconstruction of past extreme events.

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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.

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Impact of Radiance Data Assimilation on the Prediction of Heavy Rainfall in RMAPS: A Case Study

Remote Sensing ◽

10.3390/rs10091380 ◽

2018 ◽

Vol 10 (9) ◽

pp. 1380 ◽

Cited By ~ 4

Author(s):

Yanhui Xie ◽

Jiancheng Shi ◽

Shuiyong Fan ◽

Min Chen ◽

Youjun Dou ◽

...

Keyword(s):

Data Assimilation ◽

Heavy Rainfall ◽

Precipitation Forecast ◽

Observation Data ◽

Rainfall Events ◽

Satellite Radiance Data ◽

Radiance Data ◽

The Impact ◽

Heavy Rainfall Events

Herein, a case study on the impact of assimilating satellite radiance observation data into the rapid-refresh multi-scale analysis and prediction system (RMAPS) is presented. This case study targeted the 48 h period from 19–20 July 2016, which was characterized by the passage of a low pressure system that produced heavy rainfall over North China. Two experiments were performed and 24 h forecasts were produced every 3 h. The results indicated that the forecast prior to the satellite radiance data assimilation could not accurately predict heavy rainfall events over Beijing and the surrounding area. The assimilation of satellite radiance data from the advanced microwave sounding unit-A (AMSU-A) and microwave humidity sounding (MHS) improved the skills of the quantitative precipitation forecast to a certain extent. In comparison with the control experiment that only assimilated conventional observations, the experiment with the integrated satellite radiance data improved the rainfall forecast accuracy for 6 h accumulated precipitation after about 6 h, especially for rainfall amounts that were greater than 25 mm. The average rainfall score was improved by 14.2% for the 25 mm threshold and by 35.8% for 50 mm of rainfall. The results also indicated a positive impact of assimilating satellite radiances, which was primarily reflected by the improved performance of quantitative precipitation forecasting and higher spatial correlation in the forecast range of 6–12 h. Satellite radiance observations provided certain valuable information that was related to the temperature profile, which increased the scope of the prediction of heavy rainfall and led to an improvement in the rainfall scoring in the RMAPS. The inclusion of satellite radiance observations was found to have a small but beneficial impact on the prediction of heavy rainfall events as it relates to our case study conditions. These findings suggest that the assimilation of satellite radiance data in the RMAPS can provide an overall improvement in heavy rainfall forecasting.

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