scholarly journals Impact of Model Resolution and Initial/Boundary Conditions in Forecasting Flood-Causing Precipitations

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 592
Author(s):  
Francesco Ferrari ◽  
Federico Cassola ◽  
Peter Enos Tuju ◽  
Alessandro Stocchino ◽  
Paolo Brotto ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Mesoscale Model ◽  
Flash Flood ◽  
Late Summer ◽  
Initial Boundary ◽  
Small Scale ◽  
Topographic Effects ◽  
Model Resolution ◽  
Convective Systems ◽  
The Impact

In late summer and autumn Mediterranean coastal regions are quite regularly affected by small-scale, flood-producing convective systems. The complexity of mesoscale triggering mechanisms, related to low-level temperature gradients, moisture convergence, and topographic effects contributes to limit the predictability of such phenomena. In the present work, a severe convection episode associated to a flash flood occurred in Cannes (southern France) in October 2015, is investigated by means of numerical simulations with a state-of-the-art nonhydrostatic mesoscale model. In the modelling configuration operational at the University of Genoa precipitation maxima were underestimated and misplaced. The impact of model resolution as well as initial and boundary conditions on the quantitative precipitation forecasts is analyzed and discussed. In particular, the effect of ingesting a high-resolution satellite-derived sea surface temperature field is proven to be beneficial in terms of precipitation intensity and localization, especially when also associated with the most accurate lateral boundary conditions.

scholarly journals A numerical study of cell merger over Cuba – Part I: implementation of the ARPS/MM5 models

2006 ◽  
Vol 24 (11) ◽  
pp. 2781-2792 ◽  
Author(s):  
D. Pozo ◽  
I. Borrajero ◽  
J. C. Marín ◽  
G. B. Raga
Keyword(s):  
Mesoscale Model ◽  
Numerical Study ◽  
Initial Boundary ◽  
Radar Data ◽  
Horizontal Resolution ◽  
Convective Systems ◽  
Maximum Reflectivity ◽  
Radar Echoes ◽  
Good Agreement ◽  
Made In

Abstract. On 21 July 2001 a number of severe storms developed over the region of Camaguey, Cuba, which were observed by radar. A numerical simulation was performed in order to realistically reproduce the development of the storms observed that day. The mesoscale model MM5 was used to determine the initial, boundary and update conditions for the storm-scale simulation with the model ARPS. Changes to the source code of ARPS were made in order to assimilate the output from the MM5 as input data and a new land-use file with a 1-km horizontal resolution for the Cuban territory was created. A case representing the merger between cells at different stages of development was correctly reproduced by the simulation and is in good agreement with radar observations. The state of development of each cell, the time when the merger occurred, starting from the formation of clouds, the propagation motion of the cells and the increase in precipitation, due to the growth of the area after the merger, were correctly reproduced. Simulated clouds matched the main characteristics of the observed radar echoes, though in some cases, reflectivity tops and horizontal areas were overestimated. Maximum reflectivity values and the heights where these maximum values were located were in good agreement with radar data, particularly when the model reflectivity was calculated without including the snow. The MM5/ARPS configuration introduced in this study, improved sensibly the ability to simulate convective systems, thereby enhancing the local forecasting of convection in the region.

scholarly journals Small-Scale Spatial Gradients in Climatological Precipitation on the Olympic Peninsula

2007 ◽  
Vol 8 (5) ◽  
pp. 1068-1081 ◽  
Author(s):  
Alison M. Anders ◽  
Gerard H. Roe ◽  
Dale R. Durran ◽  
Justin R. Minder
Keyword(s):  
Simple Model ◽  
Mesoscale Model ◽  
Windward Side ◽  
Small Scale ◽  
Precipitation Pattern ◽  
State University ◽  
Spatial Gradients ◽  
The Individual ◽  
High Topography ◽  
The Impact

Abstract Persistent, 10-km-scale gradients in climatological precipitation tied to topography are documented with a finescale rain and snow gauge network in the Matheny Ridge area of the Olympic Mountains of Washington State. Precipitation totals are 50% higher on top of an ∼800-m-high ridge relative to valleys on either side, 10 km distant. Operational fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) runs on a 4-km grid produce similar precipitation patterns with enhanced precipitation over high topography for 6 water years. The performance of the MM5 is compared to the gauge data for 3 wet seasons and for 10 large precipitation events. The cumulative MM5 precipitation forecasts for all seasons and for the sum of all 10 large events compare well with the precipitation measured by the gauges, although some of the individual events are significantly over- or underforecast. This suggests that the MM5 is reproducing the precipitation climatology in the vicinity of the gauges, but that errors for individual events may arise due to inaccurate specification of the incident flow. A computationally simple model of orographic precipitation is shown to reproduce the major features of the event precipitation pattern on the windward side of the range. This simple model can be coupled to landscape evolution models to examine the impact of long-term spatial variability in precipitation on the evolution of topography over thousands to millions of years.

scholarly journals Polar Lows over the Nordic Seas: Improved Representation in ERA-Interim Compared to ERA-40 and the Impact on Downscaled Simulations

2014 ◽  
Vol 142 (6) ◽  
pp. 2271-2289 ◽  
Author(s):  
Thibaut Laffineur ◽  
Chantal Claud ◽  
Jean-Pierre Chaboureau ◽  
Gunnar Noer
Keyword(s):  
Barents Sea ◽  
Mesoscale Model ◽  
Cold Season ◽  
Small Scale ◽  
Polar Lows ◽  
Wind Speeds ◽  
Short Life Span ◽  
Synoptic Conditions ◽  
Polar Low ◽  
The Impact

Abstract Polar lows are intense high-latitude mesocyclones that form during the cold season over open sea. Their relatively small-scale and short life span lead to a rather poor representation in model outputs and meteorological reanalyses. In this paper, the ability of the Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) to represent polar lows over the Norwegian and Barents Sea is assessed, and a comparison with the 40-yr ECMWF Re-Analysis (ERA-40) is provided for three cold seasons (1999–2000 until 2001–02). A better representation in ERA-Interim is found, with 13 systems captured out of the 29 observed, against 6 in the case of ERA-40. Reasons for the lack of representation are identified. Unexpectedly, the representation of different polar low sizes does not appear to be linked to the resolution. Rather, it is the representation of synoptic conditions that appears to be essential. In a second part, a downscaling is conducted using the mesoscale model Méso-NH. For each observed polar low, a pair of simulations is performed: one initialized by ERA-Interim and the other one by ERA-40. An improvement is noted with 22 polar lows represented when ERA-Interim is used. Through a model-to-satellite approach, it is shown that even if polar lows are simulated, convective processes remain insufficiently represented. Wind speeds, which were underestimated in reanalyses, are nevertheless more realistic in the Méso-NH simulations. These results are supported by a spectral analysis of reanalyses and Méso-NH fields.

scholarly journals Dark Matter Halos: The Dynamical Basis of Effective Empirical Models

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Andrea Lapi ◽  
Alfonso Cavaliere
Keyword(s):  
Dark Matter ◽  
Boundary Conditions ◽  
Empirical Models ◽  
Small Scale ◽  
Dark Matter Halos ◽  
Close Approximation ◽  
Dynamical Models ◽  
Dynamical Equilibrium ◽  
The Impact ◽  
Physical Boundary

We investigate the dynamical basis of the classic empirical models (specifically, Sérsic-Einasto and generalized NFW) that are widely used to describe the distributions of collisionless matter in galaxies. We submit that such a basis is provided by ourα-profiles, shown to constitute solutions of the Jeans dynamical equilibrium with physical boundary conditions. We show how to set the parameters of the empirical in terms of the dynamical models; we find the empirical models, and specifically Sérsic-Einasto, to constitute a simple and close approximation to the dynamical models. Finally, we discuss how these provide a useful baseline for assessing the impact of the small-scale dynamics that may modulate the density slope in the central galaxy regions.

scholarly journals Air-Sea interaction over the Gulf Stream in an ensemble of HighResMIP present climate simulations

2021 ◽  
Author(s):  
Alessio Bellucci ◽  
P. J. Athanasiadis ◽  
E. Scoccimarro ◽  
P. Ruggieri ◽  
S. Gualdi ◽  
...  
Keyword(s):  
Gulf Stream ◽  
Ocean Surface ◽  
Ocean Dynamics ◽  
Small Scale ◽  
Present Climate ◽  
Model Resolution ◽  
Coupled Models ◽  
Climate Simulations ◽  
Cross Covariance ◽  
The Impact

AbstractA dominant paradigm for mid-latitude air-sea interaction identifies the synoptic-scale atmospheric “noise” as the main driver for the observed ocean surface variability. While this conceptual model successfully holds over most of the mid-latitude ocean surface, its soundness over frontal zones (including western boundary currents; WBC) characterized by intense mesoscale activity, has been questioned in a number of studies suggesting a driving role for the small scale ocean dynamics (mesoscale oceanic eddies) in the modulation of air-sea interaction. In this context, climate models provide a powerful experimental device to inspect the emerging scale-dependent nature of mid-latitude air-sea interaction. This study assesses the impact of model resolution on the representation of air-sea interaction over the Gulf Stream region, in a multi-model ensemble of present-climate simulations performed using a common experimental design. Lead-lag correlation and covariance patterns between sea surface temperature (SST) and turbulent heat flux (THF) are diagnosed to identify the leading regimes of air-sea interaction in a region encompassing both the Gulf Stream system and the North Atlantic subtropical basin. Based on these statistical metrics it is found that coupled models based on “laminar” (eddy-parameterised) and eddy-permitting oceans are able to discriminate between an ocean-driven regime, dominating the region controlled by the Gulf Stream dynamics, and an atmosphere-driven regime, typical of the open ocean regions. However, the increase of model resolution leads to a better representation of SST and THF cross-covariance patterns and functional forms, and the major improvements can be largely ascribed to a refinement of the oceanic model component.

Defining a cold pool-resolving scale for numerical simulations of convective self-organisation

2021 ◽  
Author(s):  
Romain Fiévet ◽  
Bettina Meyer ◽  
Jan Olaf Haerter
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Field Studies ◽  
Cold Pool ◽  
Small Scale ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Gust Fronts ◽  
Self Organisation ◽  
The Impact

<p>Spontaneous aggregation of clouds is a puzzling phenomenon observed in field studies [Holloway et al. (2017)] and idealized simulations alike [Held et al. (1993), Bretherton et al. (2005)]. With its relevance to climate sensitivity and extreme events, aggregation continues to be heavily studied, [Wing et al., 2017 for a review], with radiative-convective feedbacks emerging as main drivers of simulated convective self-aggregation (CSA) [Mueller & Bony (2015)].</p><p>In state-of-the art cloud-resolving models, CSA finds itself consistently hampered by finer horizontal resolutions [Muller & Held (2012), Yanase et al. (2020)]. This feature was ascribed to the effect of cold pool (CP) gust fronts in opposing the positive moisture feedback underlying CSA [Jeevanjee & Romps (2013)]. In contrast, recent numerical experiments [Haerter et al. (2020)] with diurnally oscillating surface temperature highlights an orthogonal effect: stronger CPs, driven by small-scale density gradients, promote cloud field self-organization into mesoscale convective systems (MCS). Interestingly, this upscale growth, which we here term diurnal self-organisation (DSO), differs from classical CSA as it is driven by CPs rather than large-scale radiative imbalances. In stark contrast to CSA, strengthening CPs promotes this organization effect.</p><p>Hence, numerical simulations of CSA and DSO should go beyond the typical cloud-resolving paradigm and achieve cold pool-resolving capabilities. The current study systematically examines the impact of model resolution on CP effects. First, numerical convergence is probed in a 12km x 20km laterally periodic domain where a single CP propagates and self-collides at the domain's edges. As the spatial resolution is stepwise increased from 250 to 25m, it is shown that the initially coarsely resolved density current dissipates and collision and updraft effects are weak. As finer resolution is approached, we identify a cold pool resolving resolution D, which is deemed satisfactory for propagation and collision properties. Second, convergence for a (250km)2 domain under a diurnal radiative cycle is assessed at various spatial resolutions, including the scale D. This mesoscale configuration allows us to quantify the impact of resolution of cold pool dynamics on DSO.</p><p>Together, this work systematically lays out the numerical requirements to study mesoscale clustering by means of explicit numerical simulations.</p>

scholarly journals On the Impact of NWP Model Background on Very High–Resolution Analyses in Complex Terrain

2015 ◽  
Vol 30 (4) ◽  
pp. 1077-1089 ◽  
Author(s):  
Alexander Kann ◽  
Christoph Wittmann ◽  
Benedikt Bica ◽  
Clemens Wastl
Keyword(s):  
High Resolution ◽  
Complex Terrain ◽  
Weather Prediction ◽  
Background Information ◽  
Small Scale ◽  
Topographic Effects ◽  
Mountainous Regions ◽  
Nwp Model ◽  
The Impact ◽  
Very High

Abstract The capability to accurately analyze the spatial distribution of temperature and wind at very high spatial (2.5–1 km) and temporal (60–5 min) resolutions is of interest in many modern techniques (e.g., nowcasting and statistical downscaling). In addition to observational data, the generation of such analyses requires background information to adequately resolve nonstatic, small-scale phenomena. Numerical weather prediction (NWP) models are of continuously increasing skill and are more capable of providing valuable information on convection-resolving scales. The present paper discusses the impact of two operational NWP models on hourly 2-m temperature and 10-m wind analyses as created by the Integrated Nowcasting through Comprehensive Analysis (INCA) system, which includes a topographic downscaling procedure. The NWP models used for this study are a revised version of ARPEGE–ALADIN (ALARO; 4.8-km resolution) and the Applications of Research to Operations at Mesoscale (AROME; 2.5-km resolution). Based on a case study and a longer-term validation, it is shown that, generally, the finer the grid spacing of the background model and the higher the resolution of the target grid in the downscaling procedure, the slightly more accurate is the analysis. This is especially true for wind analyses in mountainous regions, where a realistic simulation of topographic effects is crucial. In the case of 2-m temperature, the impact is less pronounced, but the topographic downscaling at very high resolution at least adds detail in complex terrain. However, in the vicinity of station observations, the analysis algorithm is capable of spatially adjusting the larger biases found in the ALARO model while having a lesser effect on the downscaled AROME model.

scholarly journals MM5 simulation of the 1999 Orissa Super Cyclone : Impact of bogus vortex on track and intensity prediction

MAUSAM ◽  
2021 ◽  
Vol 57 (1) ◽  
pp. 129-134
Author(s):  
R. G. ASHRIT ◽  
M. DAS GUPTA ◽  
A. K. BOHRA
Keyword(s):  
Boundary Conditions ◽  
Mesoscale Model ◽  
Intensity Prediction ◽  
Super Cyclone ◽  
Initial And Boundary Conditions ◽  
Orissa Coast ◽  
The Impact

lkj & bl v/;;u esa 29 vDrwcj] 1999 dks mM+hlk ds rV ij vk, egkpØokr ds izfr:i.k ds fy, ,u- lh- ,- vkj@ih- ,l- ;w-  ,e- ,e- 5 eslksLdsy fun’kZ ¼xzsy bR;kfn 1995½ dk mi;ksx fd;k x;k gsA bl fun’kZ esa pØokr dh izkjafHkd voLFkk vkSj mldh ifjlhekvksa dh voLFkkvksa ds :i  esa jk"Vªh; e/;&vof/k ekSle iwokZuqeku dsUnz Vh- 80 ds izpkyukRed fo’ys"k.kksa dk iz;ksx fd;k x;k gS vkSj rwQku dh vof/k esa 3 fnu rd dk iwokZuqeku rS;kj djus ds fy, bl fun’kZ dks 72 ?kaVs dh vof/k ds fy, lekdfyr fd;k x;k gSA bl v/;;u dk mn~ns’; pØokr ds ekxZ ij dfYir Hkzfey ds izHkko dk ewY;kadu djuk vkSj pØokr dh rhozrk dk iwokZuqeku yxkuk gSA In this study NCAR/PSU MM5 mesoscale model (Grell et al. 1995) is used to simulate the super cyclone that struck the Orissa coast on 29th October 1999. The model makes use of the operational NCMRWF T 80 analysis as initial and boundary conditions and is integrated up to 72 hr for producing 3-day forecast of the storm. The aim of this study is to assess the impact of bogus vortex on track and intensity prediction. 

scholarly journals Sensitivities of a Flash Flood Event over Catalonia: A Numerical Analysis

2007 ◽  
Vol 135 (2) ◽  
pp. 651-669 ◽  
Author(s):  
A. Martín ◽  
R. Romero ◽  
A. De Luque ◽  
S. Alonso ◽  
T. Rigo ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Mesoscale Model ◽  
Flash Flood ◽  
Temporal Distribution ◽  
High Sensitivity ◽  
Active Role ◽  
Test Bed ◽  
Convective Systems ◽  
The Mediterranean ◽  
Upper Level

Abstract On 9 and 10 June 2000, the northeastern part of the Iberian Peninsula was affected by heavy rains that produced severe floods over densely populated areas. The zones most affected were the provinces of Tarragona and Barcelona, located in the region of Catalonia. Five people were killed, 500 were evacuated, and the property losses were estimated to exceed 65 million euros. The episode was characterized by the entrance of an Atlantic low-level cold front and an upper-level trough that contributed to the generation of a mesoscale cyclone in the Mediterranean Sea east of mainland Spain. The circulation associated with this mesoscale cyclone advected warm and moist air toward Catalonia from the Mediterranean Sea. The convergence zone between the easterly flow and the Atlantic front, as well as the complex orography of the region, are shown to be involved in the triggering and organization of the convective systems. Radar shows the development of two long-lived mesoscale convective systems that merged and remained quasi-stationary nearby the city of Barcelona for nearly 2 h. The fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) short-range numerical simulations of the episode succeed reasonably well in capturing the accumulated rainfall patterns and important mesoscale aspects of the event. The role of the orography and latent heat release in generating and sustaining the quasi-stationary precipitating systems is assessed through numerical sensitivity analysis. A piecewise potential vorticity inversion technique, assisted by sensitivity fields derived from an adjoint model, provides a test bed to investigate the predictability of the damaging rains given uncertainties in the initial fields. The adjoint results highlight the importance of the details associated with the upper-level precursor trough. Therefore, the effects of small perturbations to the trough intensity and location are also investigated. Interestingly, despite the orography’s active role in the generation of the Mediterranean mesoscale cyclone and, hence, on the location of the precipitation maxima, the predictability of the spatial and temporal distribution and amounts of precipitation is shorter than might be expected. This reduced predictability of the rainfall field is attributed to the high sensitivity of the location and depth of the mesoscale cyclone identified in the Mediterranean Sea east of Catalonia to perturbations; that is, to the location and intensity of the precursor upper-level trough, compatible with realistic analysis errors.

scholarly journals Flash-flood forecasting in two Spanish Mediterranean catchments: a comparison of distinct hydrometeorological ensemble prediction strategies

2017 ◽  
Author(s):  
Béatrice Vincendon ◽  
Arnau Amengual
Keyword(s):  
Flash Flood ◽  
Forecast Error ◽  
Wrf Model ◽  
Heavy Precipitation ◽  
Flood Forecasting ◽  
Optimal Number ◽  
Ensemble Prediction ◽  
Small Scale ◽  
Convective Systems ◽  
Flash Flood Forecasting

Abstract. Hydrological Ensemble Prediction Systems (HEPSs) are becoming more and more popular methods to deal with the meteorological and hydrological uncertainties that affect discharge forecasts. These uncertainties are particularly difficult to handle when dealing with Mediterranean flash-flood forecasting as many hydrological and meteorological factors take place and precipitation comes from small scale convective systems. In this work, the performances of distinct HEPS are compared for two heavy precipitation events that affected two different semi-arid Spanish Mediterranean catchments: the cases of the 03 November 2011 on the Llobregat River in Catalonia, and the 28 September 2012 on the Guadalentín River near in Murcia. The latter case corresponds to the eighth Intense Observing Period (IOP8) of HYMEX field campaign. The uncertainty on quantitative precipitation forecasting is sampled by using two different convection-permitting meteorological ensemble generation strategies. The first EPS strategy consists in dynamically downscaling the ECMWF-EPS directly by means of the WRF model, whereas the second is based on the AROME-WMED model. Its deterministic QPFs are perturbed based on a previous rainfall forecast error climatology and by using the probability density functions of the errors, in term of total amounts and location of the heaviest rainfalls. The population of both ensembles is of 50 members, which are used to drive the semi-distributed and conceptual HEC-HMS and the fully distributed and physically-based ISBA-TOP hydrological models. For each HEPS, the performance is assessed in term of the quantitative discharge forecasts. The results point out the benefits of using (i) a hydrological model when evaluating highly-variable and convective-driven precipitation fields and (ii) an EPS to better encompass these uncertainties arising from the different elements of the HEPS. Issues about the optimal number of ensemble members and impact of the ensemble forecasting lead time are addressed for optimal flash-flood forecasting purposes as well.

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