Variable hydrograph inputs for a numerical debris-flow runout model

Debris flows affect people and infrastructure around the world, and as a result, many numerical models and modelling approaches have been developed to simulate their impacts. Observations from instrumented debris-flow channels show that variability in inflow depth, velocity and discharge in real debris flows is much higher than what is typically used in numerical simulations. However, the effect of this natural variability on numerical model outputs is not well known. In this study, we examine the effects of using complex inflow time series within a single-phase runout model utilizing a Voellmy flow-resistance model. The interactions between model topography and flow-resistance were studied first using a simple triangular hydrograph, which showed simulated discharges change because of local slopes and Voellmy parameters. Next, more complex inflows were tested using time series based on 24 real debris-flow hydrographs initiated from three locations. We described a simple method to scale inflow hydrographs by defining a target event volume and maximum allowable peak discharge. The results showed a large variation in simulated flow depths and velocities arising from the variable inflow. The effects of variable inflow conditions were demonstrated in simulations of two case histories of real debris flows, where the variation in inflow leads to significant variations in the simulation outputs. The real debris-flow hydrographs were used to provide an indication of the range of impacts that may result from the natural variability in inflow conditions. These results demonstrate variation in inflow conditions can lead to reasonable estimates of the potential variation in impacts.

Lessons learned after two years of operational high-resolution (1,5 km) WRF simulations in Catalonia and a plan to increase their skill

<p>The WRF-ARW has been the flagship mesoscale model in the Meteorological Service of Catalonia (SMC) since 2012. Several operational runs are performed daily (initialised at 00 and 12 UTC), using both the GFS and the IFS model for initial and boundary conditions, to account for uncertainties in the synoptic evolution. To provide more accurate forecasts to end-users, a convection-allowing simulation with a grid spacing of 1,5 km was added to the operational chain, starting in the summer of 2019. </p><p>However, the verification results show that the improvement over its mother domain (a 3 km simulation with parameterised convection) is irregular because it does not happen for all the variables. For instance, the 2 m temperature forecasts are more reliable for the highest resolution domain but the wind speed at 10 m has a comparable skill. Regarding the precipitation, there is a very slight improvement only for high daily precipitation rates (50 or 80 mm) during some seasons; nevertheless, the results are worse in forecasting the occurrence of precipitation (that is, when considering low daily precipitation quantities). The comparison of the verification results among different model configurations (with various resolutions and initial conditions) can be easily performed by using a skill score table. This table and its design will also be presented in this session. </p><p>Certainly, these results help to conceive strategies to enhance the skill of the 1,5 km simulations for some of the variables that arise as more inaccurate. For instance, it is evaluated to what extent using alternative static fields (changing the model topography or the land category) improves the forecasts of temperature, humidity or wind near the surface. Furthermore, the sensitivity of precipitation forecasts to several physics schemes is tested, seeking an enhancement of their skill. </p>

Mobilisation of friction in unstationary flows down a model topography

The frictional behaviour of a series of numerical 2D granular mass flows down a model topography is analysed. Effective friction coefficients estimated from final deposits are compared with data from documented natural geophysical flows, and show a consistent behaviour as far as run-out distances are concerned. The latter is used to estimate effective friction coefficients which capture well the frictional behaviour derived from the computation of micro-mechanical stress tensors near the gravity centre. Distinguishing between the different parts of the mass while spreading, we show that the downstream part of the flow exhibits a much larger friction than the core and the tail. A dependence between friction and flow volume is however observed in each region.

ESTUDO AVALIATIVO DA PREVISÃO NUMÉRICA DO TEMPO DE CURTO PRAZO PARA O MUNICÍPIO DE MACEIÓ/AL, UTILIZANDO O MODELO WRF

Sendo as diferentes atividades econômicas fortemente influenciadas pela condição do tempo, faz-se necessário antever com dias de antecedência a situação meteorológica favorável ou não para o cotidiano da sociedade. E os modelos atmosféricos são ferramentas amplamente utilizados para avaliar o estado futuro da atmosfera, neste contexto, avaliar a precisão das previsões realizadas por estas ferramentas, tem sido cada fez mais recorrente. Neste trabalho foi utilizado o modelo atmosférico WRF (Weather Research and Forecasting) para realizar previsões diárias com duração de 72h, durante o período de 10 a 19 de julho de 2017 para a cidade de Maceió/AL. Para validar as previsões foram utilizados os dados observados da estação meteorológica automática do INMET (Instituto Nacional de Meteorologia). Para este estudo também foi proposto a atualização da topografia e uso do solo da área de estudo em questão, que gerou melhorias nas comparações realizadas para todas as variáveis analisadas, em destaque a previsão da variável pressão atmosférica, quando atualizada a topografia houve sensíveis melhorias nos indicadores estatísticos em comparação aos demais testes que não contaram com mesma atualização. Além disso, as análises estatísticas e os gráficos apresentados comprovam que o modelo previu melhor para 24h do que para 48h e nesta sequência melhor que 72h, ou seja, existiu a depreciação das previsões com o aumento da duração das previsões. Study of the Efficiency of the Short-Term Numerical Forecast for the City of Maceió / Al, Using the WRF ModelA B S T R A C TThe different economic activities are strongly influenced by the condition of the weather, it is necessary to forecast with days in advance the meteorological situation favorable or not for the daily life of the society. The atmospheric models are tools widely used to assess the future state of the atmosphere, in this context, assess the accuracy of the forecasts made by these tools, has been each made more recurrent. In this work the atmospheric model WRF (Weather Research and Forecasting) was used to make daily forecasts with a duration of 72h during the period from July 10 to 19, 2017 for the city of Maceió / AL, to validate the forecasts were used the observed data of the INMET (National Meteorological Institute) automatic weather station. For this study it was also proposed to update the topography and land user of the study area, which generated improvements in the comparisons made for all variables analyzed, in particular the prediction of the variable atmospheric pressure, when updated the topography there were sensible improvements in statistical indicators compared to the other tests that did not have the same update. In addition, the statistical analyzes and the graphs presented show that the model predicted better for 24h than for 48h and in this sequence better than 72h, that is, there was depreciation of the forecasts with the increase of the forecast duration.Keywords: Weather Forecast, Atmospheric Model, Topography, Land User.

Flow Regimes over a Basin Induced by Upstream Katabatic Flows—An Idealized Modeling Study

Idealized two-dimensional model simulations are performed to study the frequent nocturnal occurrence of downslope-windstorm-type flows in Arizona’s Meteor Crater. The model topography is a simplified representation of the Meteor Crater and its surroundings, with an approximately 1° mesoscale slope upstream and downstream of the crater basin. A strong surface-based inversion and a katabatic flow develop above the mesoscale slope as a result of radiational cooling. The temperature and flow profiles are evaluated against observations over low-angle slopes from two field campaigns, showing that the model’s turbulence parameterization has a strong impact on the near-surface conditions. The interaction of the katabatic flow with the basin topography leads to the formation of waves and hydraulic jumps over the basin. The simplified two-dimensional simulations show good qualitative agreement with observations of downslope-windstorm-type flows from the Meteor Crater. The sensitivity of the flow solution over the basin to basin depth, basin width, and background wind speed is investigated. The resulting flow regimes include a sweeping of the basin atmosphere, a wake over the upstream crater sidewall, waves over the basin with one or two wave crests, and a hydraulic jump. The regimes are discussed in the context of stratified flow over mountains.

NCAR_Topo (v1.0): NCAR global model topography generation software for unstructured grids

It is the purpose of this paper to document the NCAR global model topography generation software for unstructured grids (NCAR_Topo (v1.0)). Given a model grid, the software computes the fraction of the grid box covered by land, the grid-box mean elevation (deviation from a geoid that defines nominal sea level surface), and associated sub-grid-scale variances commonly used for gravity wave and turbulent mountain stress parameterizations. The software supports regular latitude–longitude grids as well as unstructured grids, e.g., icosahedral, Voronoi, cubed-sphere and variable-resolution grids.

NCAR global model topography generation software for unstructured grids

It is the purpose of this paper to document the NCAR global model topography generation software for unstructured grids. Given a model grid, the software computes the fraction of the grid box covered by land, the gridbox mean elevation, and associated sub-grid scale variances commonly used for gravity wave and turbulent mountain stress parameterizations. The software supports regular latitude-longitude grids as well as unstructured grids; e.g. icosahedral, Voronoi, cubed-sphere and variable resolution grids. As an example application and in the spirit of documenting model development, exploratory simulations illustrating the impacts of topographic smoothing with the NCAR-DOE CESM (Community Earth System Model) CAM5.2-SE (Community Atmosphere Model version 5.2 – Spectral Elements dynamical core) are shown.

Tracking and Mean Structure of Easterly Waves over the Intra-Americas Sea

Easterly waves (EWs) are prominent features of the intertropical convergence zone (ITCZ), found in both the Atlantic and Pacific during the Northern Hemisphere summer and fall, where they commonly serve as precursors to hurricanes over both basins. A large proportion of Atlantic EWs are known to form over Africa, but the origin of EWs over the Caribbean and east Pacific in particular has not been established in detail. In this study reanalyses are used to examine the coherence of the large-scale wave signatures and to obtain track statistics and energy conversion terms for EWs across this region. Regression analysis demonstrates that some EW kinematic structures readily propagate between the Atlantic and east Pacific, with the highest correlations observed across Costa Rica and Panama. Track statistics are consistent with this analysis and suggest that some individual waves are maintained as they pass from the Atlantic into the east Pacific, whereas others are generated locally in the Caribbean and east Pacific. Vortex anomalies associated with the waves are observed on the leeward side of the Sierra Madre, propagating northwestward along the coast, consistent with previous modeling studies of the interactions between zonal flow and EWs with model topography similar to the Sierra Madre. An energetics analysis additionally indicates that the Caribbean low-level jet and its extension into the east Pacific—known as the Papagayo jet—are a source of energy for EWs in the region. Two case studies support these statistics, as well as demonstrate the modulation of EW track and storm development location by the MJO.