Lateral Boundary Conditions Research Articles

Inter-comparison of two regional climate models (RegCM and WRF) in downscaling CFSv2 for the seasonal prediction of Indian summer monsoon

The efficacy of two latest versions of regional climate models (RegCM and WRF) for simulating the Indian summer monsoon (JJAS) is tested in this study. The CFSv2 hindcast outputs are downscaled over the Indian monsoon domain for 11 contrasting monsoon seasons using the regional models. The April start ensembles of the CFSv2 are averaged to generate the initial and lateral boundary conditions for driving the WRF and RegCM. The regional models perform better in simulating the Indian summer monsoon features better than the parent CFSv2 model. The rainfall pattern as well as the intensities are improved with the dynamical downscaling and the errors in the rainfall are minimized over the GCM hindcast. On comparing the two regional models, the RegCM overestimates the rainfall during the excess and normal monsoon seasons. The RCMs improve the skill of rainfall prediction as compared to the GCM and WRF shows better skill in particular. One peculiar finding of this study is that the daily rainfall biases averaged over all the years of simulation shows that the two RCMs show similar biases with RegCM showing stronger biases occasionally. It may be implied that the errors from GCM in the form of the ICBC might be influencing the simulation in the RCMs. The upper air and surface parameters analysis shows that the WRF performs better in representing the meridional overturning of the lower atmospheric circulation, monsoon trough and the heat low over north western India which are prominent features of the semi-permanent features of the Indian summer monsoon which may be helping in improving the rainfall over the RegCM. The wind pattern as well as the relative humidity along the vertical column of the atmosphere are captured better in the WRF model. Diagnostics of CAPE & vertically integrated moisture transport supports the finding of the rainfall being simulated better in the WRF model.

Mesoscale Simulation of Open Cellular Convection: Roles of Model Resolutions and Physics Parameterizations

The Open Cellular Convection (OCC) associated with cold air outbreaks is a common phenomenon over the North Sea where a large number of wind parks are presented. Thus, reliable numerical simulations of OCC events have great importance for offshore wind energy. We investigate the ability to simulate the OCC events using the Weather Research and Forecast (WRF) model with the ERA5 reanalysis data as initial and lateral boundary conditions and the OSITA data as the sea surface temperature. The domains were nested from 9 km as the outermost domain to 1 km as the innermost domain surrounding the Teesside wind farm located in the North Sea off the northeast coast of England. We simulated an OCC event in 2015 with three series of sensitivity numerical experiments of planetary boundary layer, microphysics, and radiation parameterizations. The model outputs were validated against the wind observation at the Teesside’s meteorological mast. The results suggest that the planetary boundary layer schemes are the most sensitive during the events compared to other parameterization schemes. Futher more, a convective-resolved resolution is necessary for simulating the OCC variation properly. The paper also discuss the verification methods for such short time-scale events like the OCC.

Dynamic Downscaling Simulation and Projection of Precipitation Extremes Over China Under a Shared Socioeconomic Pathway Scenario

AbstractIn this study, Weather Research and Forecasting (WRF) ‐based dynamic downscaling simulation was performed over China at a horizontal resolution of 25 km. To reduce the systematic large‐scale biases from lateral boundary conditions, a dynamic blending (DB) technique was introduced in downscaling, and its performance was compared with downscaling without DB (NO_DB) as well as the driving global climate model (GCM, i.e., HadGEM3). In the present‐day simulation for verification, added values were found in DB, relative to the GCM and NO_DB, in simulating the precipitation extremes, especially over southeastern China. Possible causes responsible for this improvement were further analyzed. In the GCM, excessive moisture and atmospheric heating in the upper troposphere in conjunction with abnormally strong deep convection resulted in excessive extreme precipitation over southeastern China, while in NO_DB, insufficient moisture and atmospheric heating in the whole troposphere in conjunction with abnormally weak convection suppressed extreme precipitation there. In comparison, DB showed a closer representation of observations in terms of vertical velocity and vertical profiles of atmospheric moisture and heating, accounting for the improved simulation of extreme precipitation. In the future projection under the SSP5‐8.5 scenario, both the GCM and DB predicted that extreme precipitation would increase in most parts of China; however, DB indicated a larger increase over southeastern China relative to the GCM. Stronger moisture flux convergence over southeastern China in DB accounted for this larger increase, and in addition, the thermodynamic effect associated with more precipitable water dominated the stronger moisture flux convergence.

Evaluation of WRF-Chem-RTFDDA dust forecasts over the MENA region using in-situ and remote-sensing observations

We employed the combined WRF-Chem-RTFDDA model to forecast dust storms in the Middle East and North Africa (MENA). WRF-Chem simulates the emission, transport, mixing, and chemical transformation of trace gases and aerosols simultaneously with the meteorology. RTFDDA continuously assimilates both conventional and nonconventional meteorological observations and provides improved initial conditions for dust analyses and forecasts. WRF-Chem-RTFDDA was run at a horizontal resolution of 9 km using the dust only option without inclusion of anthropogenic aerosols and chemical reactions. The synoptic conditions of the dust events were characterized by a cold front at the low level and an upper-level low-pressure system over the Western Mediterranean. WRF-Chem-RTFDDA was run in continuous assimilation mode, assimilating meteorological observations only, and launching 48-h free forecasts (FF) every 6 h. Two cold starts (CSs) for data assimilation and dust emissions initiation were performed during the study period. NCEP/GFS global analyses and forecasts provided initial and lateral boundary conditions. No global dust model was used for initialization and no dust observations were assimilated. We analyzed the skill of the WRF-Chem-RTFDDA system in reproducing the horizontal and vertical distributions of dust by comparing the FF to Meteosat SEVIRI dust images, MODIS AOD retrievals, CALIPSO extinction coefficients and CAMS aerosols-reanalysis AOD calculations. The skill was analyzed as a function of FF lead time and of the period of time from the CSs. RMSE, bias and correlation between the modeled and CALIPSO measured extinction coefficients were also examined. WRF-Chem-RTFDDA reproduced the main features of the studied dust storms reasonably well. The time distance from the CSs played a more significant role in determining the dust-forecast skill than free-forecast lead time. Since no external dust information was provided to the model, dust emissions and dust spin-up by WRF-Chem played a critical role in dust forecasts. The vertical extent of the CALIPSO extinction coefficients were reasonably well reproduced once model emissions were spun-up. False alarms rates range from 0.03 to 0.26, with many below 0.15, indicating satisfactory performance as a warning system. This study shows the feasibility of dust forecasts using minimal input data over the MENA region.

Impact of transported dust aerosols on precipitation over the Nepal Himalayas using convection-permitting WRF-Chem simulation

In this study, we implemented a convection-permitting Weather Research and Forecasting model coupled with chemistry (WRF-Chem) to assess the impact of the long-range transported dust aerosols on the precipitation and convective processes over the Nepal Himalayas. A substantial amount of dust aerosol was transported to the Central Himalayan region during the dust storm event that occurred from 12 to 15 June, 2018 in the Thar desert, northwestern India. Two different sensitivity simulations, with and without transported dust aerosols, in a cloud-resolving scale of 3 km horizontal resolution was performed. We isolated the long-range transported dust aerosols by zeroing out dust aerosols from lateral boundary conditions and keeping all other locally emitted and remotely transported aerosols from anthropogenic, biogenic, and biomass burning sources. The simulation results show the noticeable impacts of transported dust aerosols on the cloud microphysical properties and regional precipitation over the southern slopes of the Nepal Himalayas. In comparison to the simulation without dust, precipitation is enhanced by 9.6% over the mountainous terrains (500–3000 m) in the presence of dust aerosols. An activation of dust aerosols as condensation nuclei significantly increased the droplet concentration resulting in enhanced convection and upward velocity with the release of latent heat of condensation. Though we simulated one event of long-range transported dust aerosols and some biases in simulation exist, this study highlights the discernible impact of remote dust aerosol on the convection and cloud microphysical properties, which can significantly influence the regional precipitation and Himalayan hydrology.

Study of storm-induced changes in circulation and temperature over the northern South China Sea during Typhoon Linfa

Hydrodynamic responses of the northern South China Sea (nSCS) to Typhoon Linfa in 2009 are examined using observations and model results. A shelf circulation model based on the Regional Ocean Modelling System (ROMS-nSCS) is used in quantifying the important physical processes affecting the storm-induced changes in circulation and hydrography in the upper ocean during Linfa. The ROMS-nSCS is forced by atmospheric forcing taken from the Climate Forecast System Reanalysis (CFSR). A parametric vortex is inserted into the CFSR atmospheric forcing to improve winds and sea-level air pressures associated with Linfa. The lateral open boundary condition of ROMS-nSCS is specified based on the global ocean circulation reanalysis produced by the Hybrid Coordinate Ocean Model (HYCOM). The simulated upper ocean circulation produced by ROMS-nSCS is characterized by strong wind-driven currents over the area affected directly by Linfa and intense near-inertial oscillations (NIOs) in the wake of Linfa. The simulated cooling in the wake of the storm is biased to the right of the storm track and agrees well with satellite-derived analysis data. The simulated NIOs also have significant rightward biases. The rotary spectral analysis of model currents demonstrates that the peak frequency fp of NIOs is about 9% greater than the local inertial frequency, which can be explained mostly by the vorticity of the background circulation. Analysis of model results also reveal that different dynamics are responsible for storm-induced cooling at different stages of Linfa. In the early development stage of Linfa, the cooling in the wake of the storm is affected mostly by the storm-induced advection in the vertical. In the mature stage of Linfa, the cooling in the wake of the storm is dominated by the joint effect of the storm-induced mixing and advection. Storm-induced warming occurs outside the wake of Linfa, due to downwelling generated by the storm.

Comparison of Flame Describing Functions Measured in Single and Multiple Injector Configurations

Abstract Recent investigations of combustion instabilities in annular systems indicate that considerable insights may be gained by using information gathered in single-sector experiments. Such experiments are, for example, employed to measure flame describing functions (FDFs), which represent the flame response to incident perturbations. These data may be used in combination with low-order models to interpret instabilities in multiple injector annular systems. It is known, however, that the structure and dynamical behavior of an isolated flame do not necessarily coincide with those of a flame placed in an annular environment with neighboring side flames. It is then worth analyzing effects that may be induced by the difference in lateral boundary conditions and specifically examining the extent to which the FDF data from single-sector experiments portrays the dynamical response of the flame in the annular environment. These issues are investigated with a new setup named TICCA-Spray, which comprises a linear arrangement of three injectors. The central flame is surrounded by two identical side flames in a rectangular geometry with key dimensions, sidewall separation, and spacing between injectors identical to those of the annular system MICCA-Spray. The describing function of the central flame is determined with techniques recently developed in single-sector experiments (SICCA-Spray). The FDFs obtained in the two configurations are compared for two swirler types having different swirl numbers and pressure drops. The effect of the swirl direction of the neighboring injectors is also explored by operating with co- and counter-swirl combinations. Differences between FDFs determined in the two test facilities, sometimes modest and in other cases less negligible, are found to depend on the flames' spatial extension and interactions. The general inference is that the FDFs measured in a single-injector combustor are better suited if the flame-wall interaction is weak, and provided that the area is equivalent to that of a single sector of an annular combustor. Nonetheless, using a multi-injector system would be more appropriate for a more precise FDF determination.

Grid refinement in ICON v2.6.4

Abstract. This article describes the implementation of grid refinement in the ICOsahedral Nonhydrostatic (ICON) modeling system. It basically follows the classical two-way nesting approach known from widely used mesoscale models like MM5 or WRF, but it differs in the way feedback from fine grids to coarser grids is applied. Moreover, the ICON implementation supports vertical nesting in the sense that the upper boundary of a nested domain may be lower than that of its parent domain. Compared to the well-established implementations on quadrilateral grids, new methods had to be developed for interpolating the lateral boundary conditions from the parent domain to the child domain(s). These are based on radial basis functions (RBFs) and partly apply direct reconstruction of the prognostic variables at the required grid points, whereas gradient-based extrapolation from parent to child grid points is used in other cases. The runtime flow control is written such that limited-area domains can be processed identically to nested domains except for the lateral boundary data supply. To demonstrate the functionality and quality of the grid nesting in ICON, idealized tests based on the Jablonowski–Williamson test case (Jablonowski and Williamson, 2006) and the Schär mountain wave test case (Schär et al., 2002) are presented. The results show that the numerical disturbances induced at the nest boundaries are small enough to be negligible for real applications. This is confirmed by experiments closely following the configuration used for operational numerical weather prediction at DWD, which demonstrate that a regional refinement over Europe has a significant positive impact on the forecast quality in the Northern Hemisphere.

Sensitivity analysis of mesoscale simulations to physics parameterizations over the Belgian North Sea using Weather Research and Forecasting – Advanced Research WRF (WRF-ARW)

Abstract. The Weather Research and Forecasting (WRF) model offers a multitude of physics parameterizations to study and analyze the different atmospheric processes and dynamics that are observed in the Earth's atmosphere. However, the suitability of a WRF model setup is known to be highly sensitive to the type of weather phenomena and the type and combination of physics parameterizations. A multi-event sensitivity analysis is conducted to identify general trends and suitable WRF physics setups for three extreme weather events identified to be potentially harmful for the operation and maintenance of wind farms located in the Belgian offshore concession zone. The events considered are Storm Ciara on 10 February 2020, a low-pressure system on 24 December 2020, and a trough passage on 27 June 2020. A total of 12 WRF simulations per event are performed to study the effect of the update interval of lateral boundary conditions and different combinations of physics parameterizations (planetary boundary layer, PBL; cumulus; and microphysics). Specifically, the update interval of ERA5 lateral boundary conditions is varied between hourly and 3-hourly. Physics parameterizations are varied between three PBL schemes (Mellor–Yamada–Nakanishi–Niino, MYNN; scale-aware Shin-Hong; and scale-aware Zhang), four cumulus schemes (Kain–Fritsch, Grell–Dévényi, scale-aware Grell–Freitas, and multi-scale Kain–Fritsch), and three microphysics schemes (WRF Single-Moment five-class scheme, WSM5; Thompson; and Morrison). The simulated wind direction and wind speed are compared qualitatively and quantitatively to operational supervisory control and data acquisition (SCADA) data. Overall, a definitive best-case setup common to all three events is not identified in this study. For wind direction and wind speed, the best-case setups are identified to employ scale-aware PBL schemes. These are most often driven by hourly update intervals of lateral boundary conditions as opposed to 3-hourly update intervals, although it is only in the case of Storm Ciara that significant differences are observed. Scale-aware cumulus schemes are identified to produce better results when combined with scale-aware PBL schemes, specifically for Storm Ciara and the trough passage cases. However, for the low-pressure-system case this trend is not observed. No clear trend in utilizing higher-order microphysics parameterization considering the combinations of WRF setups in this study is found in all cases. Overall, the combination of PBL, cumulus, and microphysics schemes is found to be highly sensitive to the type of extreme weather event. Qualitatively, precipitation fields are found to be highly sensitive to model setup and the type of weather phenomena.

Assessment of the data assimilation framework for the Rapid Refresh Forecast System v0.1 and impacts on forecasts of a convective storm case study

Abstract. The Rapid Refresh Forecast System (RRFS) is currently under development and aims to replace the National Centers for Environmental Prediction (NCEP) operational suite of regional- and convective-scale modeling systems in the next upgrade. In order to achieve skillful forecasts comparable to the current operational suite, each component of the RRFS needs to be configured through exhaustive testing and evaluation. The current data assimilation component uses the hybrid three-dimensional ensemble–variational data assimilation (3DEnVar) algorithm in the Gridpoint Statistical Interpolation (GSI) system. In this study, various data assimilation algorithms and configurations in GSI are assessed for their impacts on RRFS analyses and forecasts of a squall line over Oklahoma on 4 May 2020. A domain of 3 km horizontal grid spacing is configured, and hourly update cycles are performed using initial and lateral boundary conditions from the 3 km grid High-Resolution Rapid Refresh (HRRR). Results show that a baseline RRFS run is able to represent the observed convection, although with stronger cells and large location errors. With data assimilation, these errors are reduced, especially in the 4 and 6 h forecasts using 75 % of the ensemble background error covariance (BEC) and 25 % of the static BEC with the supersaturation removal function activated in GSI. Decreasing the vertical ensemble localization radius from 3 layers to 1 layer in the first 10 layers of the hybrid analysis results in overall less skillful forecasts. Convection is greatly improved when using planetary boundary layer pseudo-observations, especially at 4 h forecast, and the bias of the 2 h forecast of temperature is reduced below 800 hPa. Lighter hourly accumulated precipitation is predicted better when using 100 % ensemble BEC in the first 4 h forecast, but heavier hourly accumulated precipitation is better predicted with 75 % ensemble BEC. Our results provide insight into the current capabilities of the RRFS data assimilation system and identify configurations that should be considered as candidates for the first version of RRFS.

Towards a convection‐permitting regional reanalysis over the Italian domain

AbstractA new convection‐permitting regional reanalysis, SPHERA (High Resolution REAnalysis over Italy), has been developed over Italy and the surrounding seas using the COSMO model at 2.2 km horizontal resolution. The reanalysis system is nested in the global reanalysis ERA5; upper‐air and surface observations are assimilated at the convection‐permitting scale by the COSMO nudging scheme. Before the complete production of the hourly three‐dimensional fields and surface/soil parameters over the period 1995–2020, general issues regarding the reanalysis set‐up needed to be addressed over a shorter test period. These include the identification of the best approach to downscale the lateral boundary conditions from the global driver, and the definition of the bottom boundary condition related to deep soil temperature. With respect to the downscaling methodology, the results show a clear benefit in using lateral boundary conditions directly from the global ERA5, despite the large resolution difference between the two modes (1:15), instead of providing them from an intermediate resolution COSMO‐based reanalysis. Moreover, the soil bottom boundary condition for temperature is reconstructed from the shallower ERA5 soil, using a site‐dependent method based on a delayed running mean of the ERA5 temperature at the deepest soil level. Finally, an evaluation of SPHERA has been performed with respect to the skill in simulating daily precipitation over 2 years. Compared with ERA5, SPHERA shows a higher ability in simulating moderate and intense events, markedly during summer, in terms of skill scores, frequency of occurrence and bias.

Impacts of Horizontal Resolution of the Lateral Boundary Conditions and Downscaling Method on the Performance of RegCM4.6 in Simulating the Surface Climate Over Central‐Eastern China

AbstractThis study investigated the impacts of horizontal resolution of lateral boundary condition (LBC) and downscaling method on the performance of RegCM4.6 in simulating the 2 m air temperature and precipitation over central eastern China. Two groups of experiments (direct downscaling experiments using LBC derived from the same reanalysis data but with different horizontal resolutions [0.75°, 1.5°, and 2.5°] and double‐nested downscaling experiment) with the model horizontal resolution of 20 km over central eastern China have been carried out. Results show that the direct downscaling experiments consistently outperform the double‐nested experiment to simulate the 2 m air temperature and precipitation over central eastern China, suggesting that adopting the direct downscaling method is appropriate to simulate the surface climate over central eastern China. Meanwhile, the direct downscaling experiments driven by the LBC derived from the reanalysis data with the horizontal resolution ranging from 0.75° to 2.5° display very comparable performance with a little better performance by adopting the LBC derived from the reanalysis data of much finer resolution. Further mechanism analysis indicates that much larger errors of LBC produced by the double‐nested downscaling method lead to the positive pressure biases and negative biases of water vapor convergence flux over Jianghuai Valley, which contribute to the much larger biases of precipitation and 2 m air temperature in the double‐nested downscaling experiment compared to the direct downscaling experiments. This study emphasizes that the direct downscaling method is superior to the double‐nested downscaling method for the simulations of 2 m air temperature and precipitation over central eastern China.

Assessing the contribution of dynamical downscaling to austral autumn Northeast Brazil seasonal precipitation prediction performance

This study aims to assess the contribution to prediction performance of dynamically downscaling seasonal precipitation for the Brazilian Northeast region (NEB) produced in February with a global climate model for the austral autumn (March-April-May). This season includes the peak precipitation period of a large portion of this region. To achieve this aim, 32 years of hindcasts for the period 1979–2010 were produced with a regional model known as the Brazilian developments on the Regional Atmospheric Modeling System (BRAMS) run at 30 km spatial resolution, which was unidirectional nested to a global model run at approximately 200 km spatial resolution. The used global model was the Atmospheric General Circulation Models of the Brazilian Center for Weather Forecast and Climate Studies (CPTEC/AGCM), which provided initial and lateral boundary conditions for BRAMS. Hindcast ensembles of 10 members were produced with both the global and the regional models, simulating an operational prediction environment using persisted sea surface temperature (SST) anomalies observed in the previous January of each of the 32 hindcast years as oceanic boundary conditions. A comparative deterministic and probabilistic performance assessment of the two models was conducted. The deterministic assessment included the investigation of the mean error (bias) of the produced seasonal precipitation hindcasts, the degree of linear association between the observed and predicted precipitation anomalies measuring phase error through the correlation of the ensemble means with the corresponding observations, and amplitude error investigated through the ratio between the hindcast ensemble mean and observed variances. The probabilistic assessment was performed investigation the reliability, resolution, and discrimination characteristics of tercile probability predictions for the above normal and below normal categories, and also for probabilistic predictions for the occurrence of the symmetric event positive (or negative) precipitation anomaly. The two investigated modeling approaches showed similar performance, with an indication for dynamically downscaled predictions to have reduced amplitude error and slightly improved reliability and resolution compared to the predictions produced with the global model.

On the representation of atmospheric circulation modes in regional climate models over Western Europe

AbstractAtmospheric circulation is a key driver of climate variability, and the representation of atmospheric circulation modes in regional climate models (RCMs) can enhance the credibility of regional climate projections. This study examines the representation of large‐scale atmospheric circulation modes in Coupled Model Inter‐comparison Project phase 5 RCMs once driven by ERA‐Interim, and by two general circulation models (GCMs). The study region is Western Europe and the circulation modes are classified using the Promax rotated T‐mode principal component analysis. The results indicate that the RCMs can replicate the classified atmospheric modes as obtained from ERA5 reanalysis, though with biases dependent on the data providing the lateral boundary condition and the choice of RCM. When the boundary condition is provided by ERA‐Interim that is more consistent with observations, the simulated map types and the associating time series match well with their counterparts from ERA5. Further, on average, the multi‐model ensemble mean of the analysed RCMs, driven by ERA‐Interim, indicated a slight improvement in the representation of the modes obtained from ERA5. Conversely, when the RCMs are driven by the GCMs that are models without assimilation of observational data, the representation of the atmospheric modes, as obtained from ERA5, is relatively less accurate compared to when the RCMs are driven by ERA‐Interim. This suggests that the biases stem from the GCMs. On average, the representation of the modes was not improved in the multi‐model ensemble mean of the five analysed RCMs driven by either of the GCMs. However, when the best‐performed RCMs were selected on average the ensemble mean indicated a slight improvement. Moreover, the presence of the North Atlantic Oscillation (NAO) in the simulated modes depends also on the lateral boundary conditions. The relationship between the modes and the NAO was replicated only when the RCMs were driven by reanalysis. The results indicate that the forcing model is the main factor in reproducing the atmospheric circulation.

Dynamical downscaling of temperature extremes over China using the WRF model driven by different lateral boundary conditions

Extreme temperature events have considerable impact on society and natural ecosystems, which receive less attention. This study examined the impact of lateral boundary conditions (LBCs) on the downscaling simulations of the Weather Research and Forecasting (WRF) model for temperature extremes over China for the period 1981–2010. The driving data comprised two reanalysis datasets from two different institutes, ERA-interim and NECP-R2. Twelve extreme temperature indices were calculated from the WRF simulations and compared with both reanalysis products and observations. The comparison includes their climate mean and interannual variation. Results indicated that WRF can skillfully reproduce the spatial distributions of extreme temperature indices, despite some biases in certain regions. The large biases in the warmest and coldest days, warm spell duration and cool days over eastern China from reanalysis data were reduced significantly. The simulation driven by ERA-interim outperforms NECP-R2. In terms of interannual variation, the WRF model was able to capture the observational trends except the number of days with warm spell and days with moderate warm. Furthermore, the accuracy of WRF in simulating interannual variation was consistent with that of the driving data. The WRF simulation driven by ERA-interim appeared best in terms of bias frequency distributions for most indices. Overall, the results revealed that WRF dynamical downscaling of temperature extremes is sensitive to selection of LBCs, and that performance could be improved by adopting driving data such as ERA-interim.

Modelling CO2 plume spreading in highly heterogeneous rocks with anisotropic, rate-dependent saturation functions: A field-data based numeric simulation study of Otway

In this field-data-based simulation study, we apply novel rate-dependent, anisotropic saturation functions curve-fitted to match the flow behaviour of laminated sand- and siltstones from the CO2CRC's Otway International Test Centre (Australia), in well-spot simulations of plume spreading at the site. Scenario analysis is conducted by performing simulations on various stochastic model realisations under different conditions, investigating what controls plume migration. Results indicate that high-permeability streaks and intraformational baffles determine plume spreading in flat-lying stratigraphy. Displacement of CO2 is unstable and focussed by high-permeability streaks, leading to multi-layer plumes. In inclined stratigraphy, buoyancy forces control plume migration channelling it up dip. However, high-permeability streaks still influence plume shape. Comparisons for different injection rates show that heterogeneity-induced fingering dominates at high injection rates, whereas gravity override and vertical movement of the plume are prominent at low injection rates. Continuous build-up of fluid pressure in the storage horizon influences the properties of CO2 when no-flow (closed) lateral boundary conditions are applied. By contrast, a marked pressure drop occurs in the near-well region for hydrostatic (open) lateral boundary conditions. These also foster uneven heterogeneity-fingering of the plume. Since flow velocity in the highly heterogeneous Paaratte formation varies over many orders of magnitude, force balances range between the capillary and the viscous limit even at some distance to the injector. A comparison with simulations based on standard Brooks-Corey saturation functions shows that taking flow-rate dependence and anisotropy into account leads to significant differences in the shape of the evolving CO2 plume and the saturation within.

Hydrodynamic and TS Structure Dataset of the São Francisco and Parnaiba Brazilian Rivers

Running a numerical simulation with the ROMS model in the regions of the mouths and plumes of the São Francisco and Parnaiba rivers, this dataset was obtained. It is the result of two scenarios, one of them taking into account the tides and the other not. It consists of 50 files (in NetCDF format) divided into 25 for each of the mentioned scenarios. Among the 25 files, 1 corresponds to the spatial discretization parameters of the input; 12 corresponds to the numer-ical simulation in the Parnaiba River and the remaining 12 to the São Francisco River. These files contain the daily average of all input and output parameters of the simulations. The ROM-STOOLS scripting package was used to prepare the input data. The ROMS model input was the surface forcings from the COADS dataset; the WOA09 and SODA datasets were used as initial and lateral boundary conditions, respectively. The bathymetry was taken from ETOPO2 and the tide was acquired from the TPXO7 satellite product. The hydrodynamics and TS structure data contained in this dataset are useful for physical oceanographers to study the thermodynamics of the waters and other physical processes occurring in the mouth and plume region of the São Francisco and Parnaiba Rivers. It is also useful for chemical and biological oceanographers to study the behavior of nutrients, chlorophyll and primary productivity.

Pathways to Better Prediction of the MJO: 2. Impacts of Atmosphere-Ocean Coupling on the Upper Ocean and MJO Propagation.

This study investigates effects of atmosphere‐ocean coupling on MJO precipitation and eastward propagation, and upper ocean conditions during and after MJO passage. To explore pathways for improving MJO prediction, three model experiments are conducted using the Unified Wave Interface‐Coupled Model at convection‐permitting (4 km) resolution: (a) uncoupled atmosphere‐only, (b) coupled atmosphere‐ocean, and (c) coupled atmosphere‐ocean with improved air‐sea flux algorithm simulations. The model simulations are compared with observations from the DYNAMO field campaign in 2011. Both coupled atmosphere‐ocean simulations produced eastward propagation of the MJO where the uncoupled, atmosphere‐only simulation did not. The uncoupled model overestimates both precipitation and surface winds associated with the MJO, while coupled model simulations substantially reduce model bias. Improved air‐sea fluxes lead to systematic improvements in precipitation, winds, sea surface temperature, and the ocean mixed layer when compared to the original coupled simulation. This leads to further improvement of the MJO's eastward propagation speed compared with observations. Despite these improvements, the regional coupled simulations still have difficulty representing the extent of convectively suppressed conditions in the Indian Ocean after MJO passage, which indicates the importance of the large‐scale environment from lateral boundary conditions. Coupled model simulations also reveal some issues in the representation of upper ocean stratification in the ocean model, especially errors in salinity, which result in overestimation of the mixed layer depth after MJO passage.

Short-Term Prediction of a Nocturnal Significant Tornado Outbreak Using a Convection-Allowing Ensemble

Abstract A multiscale analysis of the significant nocturnal tornado outbreak in Tennessee on 2–3 March 2020 is presented. This outbreak included several significant tornadoes and resulted in the second most fatalities (25) and most injuries (309) of all nocturnal tornado events in Tennessee in 1950–2020. The two deadliest tornadoes struck Nashville (EF3 intensity) and Cookeville (EF4) resulting in 5 and 19 fatalities, respectively. The supercell responsible for the tornado outbreak initiated at 0330 UTC 3 March within a region of warm frontogenesis in western Tennessee. Throughout its life cycle, the supercell was located in a region of convective available potential energy near 1000 J kg−1 and 0–1-km storm-relative helicity over 350 m2 s−2. Retrospective 3-h forecasts from the experimental Warn-on-Forecast System (WoFS) convection-allowing ensemble initialized after the parent supercell initiated indicated a high probability, high severity scenario for tornadoes across Tennessee and into Nashville through 0700 UTC. Earlier WoFS forecasts indicated a low probability, high severity scenario owing to uncertainty in the initiation of supercells. The presence of these supercells was sensitive to the upstream thermodynamic conditions and warm frontogenesis regions that were inherited from the lateral boundary conditions. In all, this study highlights the potential of the WoFS ensemble to contribute useful probabilistic severe weather information to the short-term forecast process during a nocturnal significant tornado outbreak.

Two New Models for Dynamic Linear Elastic Beams and Simplifications for Double Symmetric Cross-Sections

We present two new models for dynamic beams deduced from three dimensional theory of linear elasticity. The first model is deduced from virtual work considered for small beam sections. For the second model, we suppose a Taylor-Young expansion of the displacement field up to the fourth order in transverse dimensions of the beam. We consider the Fourier series expansion for considering Neumann lateral boundary conditions together with dynamical equations, we obtain a system of fifteen vector equations with the fifteen coefficients vector unknown of the displacement field. For beams with two fold symmetric cross sections commonly used (for example circular, square, rectangular, elliptical…), a unique decomposition of any three-dimensional loads is proposed and the symmetries of these loads is introduced. For these two theories, we show that the initial problem decouples into four subproblems. For an orthotropic material, these four subproblems are completely independent. For a monoclinic material, two subproblems are coupled and independent of the two other coupled subproblems. For the first model, we also give the detailed expression of these four subproblems when we consider the approximation of the displacement field used in the second model.