scholarly journals Assimilation of Lightning Data Using a Nudging Method Involving Low-Level Warming

2014 ◽  
Vol 142 (12) ◽  
pp. 4850-4871 ◽  
Author(s):  
Max R. Marchand ◽  
Henry E. Fuelberg
Keyword(s):  
Numerical Models ◽  
Deep Convection ◽  
Computational Cost ◽  
Wrf Model ◽  
Stage Iv ◽  
Simulated Precipitation ◽  
Synoptic Forcing ◽  
Total Lightning ◽  
Mu Method ◽  
Short Time

Abstract This study presents a new method for assimilating lightning data into numerical models that is suitable at convection-permitting scales. The authors utilized data from the Earth Networks Total Lightning Network at 9-km grid spacing to mimic the resolution of the Geostationary Lightning Mapper (GLM) that will be on the Geostationary Operational Environmental Satellite-R (GOES-R). The assimilation procedure utilizes the numerical Weather Research and Forecasting (WRF) Model. The method (denoted MU) warms the most unstable low levels of the atmosphere at locations where lightning was observed but deep convection was not simulated based on the absence of graupel. Simulation results are compared with those from a control simulation and a simulation employing the lightning assimilation method developed by Fierro et al. (denoted FO) that increases water vapor according to a nudging function that depends on the observed flash rate and simulated graupel mixing ratio. Results are presented for three severe storm days during 2011 and compared with hourly NCEP stage-IV precipitation observations. Compared to control simulations, both the MU and FO assimilation methods produce improved simulated precipitation fields during the assimilation period and a short time afterward based on subjective comparisons and objective statistical scores (~0.1, or 50%, improvement of equitable threat scores). The MU generally performs better at simulating isolated thunderstorms and other weakly forced deep convection, while FO performs better for the case having strong synoptic forcing. Results show that the newly developed MU method is a viable alternative to the FO method, exhibiting utility in producing thunderstorms where observed, and providing improved analyses at low computational cost.

scholarly journals WRF Sensitivity for Seasonal Climate Simulations of Precipitation Fields on the CORDEX South America Domain

Atmosphere ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 107
Author(s):  
Helber Barros Gomes ◽  
Maria Cristina Lemos da Silva ◽  
Henrique de Melo Jorge Barbosa ◽  
Tércio Ambrizzi ◽  
Hakki Baltaci ◽  
...  
Keyword(s):  
South America ◽  
Numerical Models ◽  
Regional Climate ◽  
Wrf Model ◽  
Added Value ◽  
Climate Projections ◽  
South American ◽  
Climate Forecasting ◽  
Climate Simulations ◽  
Simulated Precipitation

Dynamic numerical models of the atmosphere are the main tools used for weather and climate forecasting as well as climate projections. Thus, this work evaluated the systematic errors and areas with large uncertainties in precipitation over the South American continent (SAC) based on regional climate simulations with the weather research and forecasting (WRF) model. Ten simulations using different convective, radiation, and microphysical schemes, and an ensemble mean among them, were performed with a resolution of 50 km, covering the CORDEX-South America domain. First, the seasonal precipitation variability and its differences were discussed. Then, its annual cycle was investigated through nine sub-domains on the SAC (AMZN, AMZS, NEBN, NEBS, SE, SURU, CHAC, PEQU, and TOTL). The Taylor Diagrams were used to assess the sensitivity of the model to different parameterizations and its ability to reproduce the simulated precipitation patterns. The results showed that the WRF simulations were better than the ERA-interim (ERAI) reanalysis when compared to the TRMM, showing the added value of dynamic downscaling. For all sub-domains the best result was obtained with the ensemble compared to the satellite TRMM. The largest errors were observed in the SURU and CHAC regions, and with the greatest dispersion of members during the rainy season. On the other hand, the best results were found in the AMZS, NEBS, and TOTL regions.

scholarly journals A modified lightning potential index for numerical models with parameterized deep convection

2021 ◽  
Author(s):  
Guido Schröder
Keyword(s):  
Central Europe ◽  
Vertical Velocity ◽  
Large Scale ◽  
Numerical Models ◽  
Deep Convection ◽  
Potential Temperature ◽  
Wrf Model ◽  
Lightning Flash ◽  
Potential Index ◽  
Forecasting System

<p>A modified lightning potential index (MLPI) for numerical models with parameterized deep convection is presented. It is based on the LPI formula of Lynn and Yair (2010). Following the idea of Lopez (2016), the quantities (e.g. vertical velocity) needed in the LPI formula are derived from the updraft of the Bechtold-Tiedtke parameterization scheme (Bechtold et al., 2014). The formula is further improved by taking into account the vertical equivalent potential temperature gradient.</p><p>The LPI and MLPI are tested in ICON with 20km resolution (ICON-20) over central Europe. A key component in the LPI is the vertical velocity. To assess its quality, the vertical velocity of the updraft in the convection scheme in ICON-20 is compared to updrafts in the convection-resolving COSMO model with 2.2 km resolution (COSMO-D2). It is shown that in ICON-20 the extension of the vertical velocity is generally broader with the maximum located in higher altitudes. In the charge separation area where the vertical velocity is relevant, the ICON-20 vertical velocity is less than in COSMO-D2. Consequently, the LPI values in ICON-20 are lower by a factor of 2 compared to COSMO-D2.</p><p>The MLPI is verified against LINET lightning data (Betz et al. 2009) over central Europe for summer 2020 and compared to LPI in COSMO-D2. The MLPI is also compared to the LPI and the lightning flash density (LFD,  Lopez, 2016), all computed in ICON-20. For the test period the MLPI outperforms the LPI and LFD. However, the quality of the LPI in COSMO-D2 cannot quite be reached.</p><p> </p><p>Bechtold et al. 2014: Representing Equilibrium and Nonequilibrium Convection in Large-Scale Models. J. Atmos. Sci. 71, 734-753.</p><p>Betz et al., 2009:  LINET - An international lightning detection network in Europe. Atmos.  Res. 91 564–573.</p><p>Lopez, 2016: A Lightning Parameterization for the ECMWF Integrated Forecasting System. Mon. Wea. Rev., 144, 3057-2075.</p><p>Lynn and Yair, 2010: Prediction of lightning flash density with the WRF model  Adv. Geosci., 23, 11–16.</p>

A Study of the Behaviour of a Single-Bladed Waste-Water Pump

2006 ◽  
Vol 220 (2) ◽  
pp. 79-87 ◽  
Author(s):  
J Keays ◽  
C Meskell
Keyword(s):  
Waste Water ◽  
Power Consumption ◽  
Turbulence Model ◽  
Numerical Models ◽  
Sewage Treatment ◽  
Computational Cost ◽  
Primary Source ◽  
Pressure Head ◽  
Primary Objective ◽  
Pump Efficiency

A single-vaned centrifugal pump, typical of the kind employed in waste-water applications (e.g. sewage treatment), has been investigated numerically. The primary objective was to identify a modelling approach that was accurate, but at an acceptable computational cost. A test program has been executed to provide data to validate the numerical models. The global performance of the pump was assessed in terms of the pressure head, the mass flowrate, the power consumption, and the pump efficiency. In addition, time-resolved surface-pressure measurements were made at the volute wall. Five combinations of three modelling approximations (two or 3D; k-ε or Reynolds stress model turbulence model; unsteady or quasi-steady) were investigated and compared with the experimental results. It was found that the choice of turbulence model did not have a significant effect on the predictions. In all cases, the head-discharge curve was well predicted. However, it was found that only the quasi-steady models could capture the trend of the power consumption curve, and hence that of the efficiency. Discrepancies in the magnitude of the power consumption can be accounted for by the lack of losses such as leakage in the numerical models. Qualitative analysis of the numerical results identifies the trailing edge of the impeller as the primary source of power loss, with the flow in the region of the cut water also contributing significantly to the poor overall efficiency of the design.

scholarly journals Nondissipative and Dissipative Momentum Deposition by Mountain Wave Events in Sheared Environments

2018 ◽  
Vol 75 (8) ◽  
pp. 2721-2740 ◽  
Author(s):  
Christopher G. Kruse ◽  
Ronald B. Smith
Keyword(s):  
Broad Spectrum ◽  
Numerical Models ◽  
Wrf Model ◽  
Vertical Wind Shear ◽  
Mountain Wave ◽  
Subsequent Evolution ◽  
Event Duration ◽  
Mountain Waves ◽  
Vertical Dispersion ◽  
Nonlinear Transient

AbstractMountain waves (MWs) are generated during episodic cross-barrier flow over broad-spectrum terrain. However, most MW drag parameterizations neglect transient, broad-spectrum dynamics. Here, the influences of these dynamics on both nondissipative and dissipative momentum deposition by MW events are quantified in a 2D, horizontally periodic idealized framework. The influences of the MW spectrum, vertical wind shear, and forcing duration are investigated. MW events are studied using three numerical models—the nonlinear, transient WRF Model; a linear, quasi-transient Fourier-ray model; and an optimally tuned Lindzen-type saturation parameterization—allowing quantification of total, nondissipative, and dissipative MW-induced decelerations, respectively. Additionally, a pseudomomentum diagnostic is used to estimate nondissipative decelerations within the WRF solutions. For broad-spectrum MWs, vertical dispersion controls spectrum evolution aloft. Short MWs propagate upward quickly and break first at the highest altitudes. Subsequently, the arrival of additional longer MWs allows breaking at lower altitudes because of their greater contribution to u variance. As a result, minimum breaking levels descend with time and event duration. In zero- and positive-shear environments, this descent is not smooth but proceeds downward in steps as a result of vertically recurring steepening levels. Nondissipative decelerations are nonnegligible and influence an MW’s approach to breaking, but breaking and dissipative decelerations quickly develop and dominate the subsequent evolution. Comparison of the three model solutions suggests that the conventional instant propagation and monochromatic parameterization assumptions lead to too much MW drag at too low an altitude.

scholarly journals Effects of Dynamic Crop Growth on the Simulated Precipitation Response to Irrigation*

2015 ◽  
Vol 19 (14) ◽  
pp. 1-31 ◽  
Author(s):  
Keith J. Harding ◽  
Tracy E. Twine ◽  
Yaqiong Lu
Keyword(s):  
Environmental Variability ◽  
Wrf Model ◽  
Crop Growth ◽  
Climate Impacts ◽  
Rapid Expansion ◽  
Area Index ◽  
Community Land Model ◽  
Precipitation Response ◽  
Simulated Precipitation ◽  
Dynamic Crop Growth

Abstract The rapid expansion of irrigation since the 1950s has significantly depleted the Ogallala Aquifer. This study examines the warm-season climate impacts of irrigation over the Ogallala using high-resolution (6.33 km) simulations of a version of the Weather Research and Forecasting (WRF) Model that has been coupled to the Community Land Model with dynamic crop growth (WRF-CLM4crop). To examine how dynamic crops influence the simulated impact of irrigation, the authors compare simulations with dynamic crops to simulations with a fixed annual cycle of crop leaf area index (static crops). For each crop scheme, simulations were completed with and without irrigation for 9 years that represent the range of observed precipitation. Reduced temperature and precipitation biases occur with dynamic versus static crops. Fundamental differences in the precipitation response to irrigation occur with dynamic crops, as enhanced surface roughness weakens low-level winds, enabling more water from irrigation to remain over the region. Greater simulated rainfall increases (12.42 mm) occur with dynamic crops compared to static crops (9.08 mm), with the greatest differences during drought years (+20.1 vs +5.9 mm). Water use for irrigation significantly impacts precipitation with dynamic crops (R2 = 0.29), but no relationship exists with static crops. Dynamic crop growth has the largest effect on the simulated impact of irrigation on precipitation during drought years, with little impact during nondrought years, highlighting the need to simulate the dynamic response of crops to environmental variability within Earth system models to improve prediction of the agroecosystem response to variations in climate.

scholarly journals rpe v5: An emulator for reduced floating-point precision in large numerical simulations

2016 ◽  
Author(s):  
Andrew Dawson ◽  
Peter Düben
Keyword(s):  
Numerical Simulations ◽  
Climate Models ◽  
Numerical Models ◽  
Computational Cost ◽  
Floating Point ◽  
Climate Modelling ◽  
Acceptable Quality ◽  
Weather And Climate ◽  
Code Changes ◽  
Numerical Precision

Abstract. This paper describes the rpe library which has the capability to emulate the use of arbitrary reduced floating-point precision within large numerical models written in Fortran. The rpe software allows model developers to test how reduced floating-point precision affects the result of their simulations without having to make extensive code changes or port the model onto specialised hardware. The software can be used to identify parts of a program that are problematic for numerical precision and to guide changes to the program to allow a stronger reduction in precision. The development of rpe was motivated by the strong demand for more computing power. If numerical precision can be reduced for an application under consideration while still achieving results of acceptable quality, computational cost can be reduced, since a reduction in numerical precision may allow an increase in performance or a reduction in power consumption. For simulations with weather and climate models, savings due to a reduction in precision could be reinvested to allow model simulations at higher spatial resolution or complexity, or to increase the number of ensemble members to improve predictions. rpe was developed with particular focus on the community of weather and climate modelling, but the software could be used with numerical simulations from other domains.

scholarly journals Wave Propagation in Thin-Walled Aortic Analogues

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
C. G. Giannopapa ◽  
J. M. B. Kroot ◽  
A. S. Tijsseling ◽  
M. C. M. Rutten ◽  
F. N. van de Vosse
Keyword(s):  
Experimental Data ◽  
Wave Propagation ◽  
Frequency Domain ◽  
Analytical Model ◽  
Viscoelastic Properties ◽  
Numerical Models ◽  
Computational Cost ◽  
One Dimensional ◽  
Arterial Blood

Research on wave propagation in liquid filled vessels is often motivated by the need to understand arterial blood flows. Theoretical and experimental investigation of the propagation of waves in flexible tubes has been studied by many researchers. The analytical one-dimensional frequency domain wave theory has a great advantage of providing accurate results without the additional computational cost related to the modern time domain simulation models. For assessing the validity of analytical and numerical models, well defined in vitro experiments are of great importance. The objective of this paper is to present a frequency domain analytical model based on the one-dimensional wave propagation theory and validate it against experimental data obtained for aortic analogs. The elastic and viscoelastic properties of the wall are included in the analytical model. The pressure, volumetric flow rate, and wall distention obtained from the analytical model are compared with experimental data in two straight tubes with aortic relevance. The analytical results and the experimental measurements were found to be in good agreement when the viscoelastic properties of the wall are taken into account.

scholarly journals Relationships between Deep Convection Updraft Characteristics and Satellite-Based Super Rapid Scan Mesoscale Atmospheric Motion Vector–Derived Flow

2018 ◽  
Vol 146 (10) ◽  
pp. 3461-3480 ◽  
Author(s):  
Jason M. Apke ◽  
John R. Mecikalski ◽  
Kristopher Bedka ◽  
Eugene W. McCaul ◽  
Cameron R. Homeyer ◽  
...  
Keyword(s):  
Doppler Radar ◽  
Deep Convection ◽  
Motion Vector ◽  
Three Dimensional ◽  
Radar Data ◽  
Severe Weather ◽  
Lightning Flash ◽  
Rapid Scan ◽  
Total Lightning ◽  
The Relationship

Abstract Rapid acceleration of cloud-top outflow near vigorous storm updrafts can be readily observed in Geostationary Operational Environmental Satellite-14 (GOES-14) super rapid scan (SRS; 60 s) mode data. Conventional wisdom implies that this outflow is related to the intensity of updrafts and the formation of severe weather. However, from an SRS satellite perspective, the pairing of observed expansion and updraft intensity has not been objectively derived and documented. The goal of this study is to relate GOES-14 SRS-derived cloud-top horizontal divergence (CTD) over deep convection to internal updraft characteristics, and document evolution for severe and nonsevere thunderstorms. A new SRS flow derivation system is presented here to estimate storm-scale (<20 km) CTD. This CTD field is coupled with other proxies for storm updraft location and intensity such as overshooting tops (OTs), total lightning flash rates, and three-dimensional flow fields derived from dual-Doppler radar data. Objectively identified OTs with (without) matching CTD maxima were more (less) likely to be associated with radar-observed deep convection and severe weather reports at the ground, suggesting that some OTs were incorrectly identified. The correlation between CTD magnitude, maximum updraft speed, and total lightning was strongly positive for a nonsupercell pulse storm, and weakly positive for a supercell with multiple updraft pulses present. The relationship for the supercell was nonlinear, though larger flash rates are found during periods of larger CTD. Analysis here suggests that combining CTD with OTs and total lightning could have severe weather nowcasting value.

Evaluating the conservation of energy variables in simulations of deep moist convection

2021 ◽  
Author(s):  
John M. Peters ◽  
Daniel R. Chavas
Keyword(s):  
Heat Capacity ◽  
Numerical Models ◽  
Deep Convection ◽  
Squall Line ◽  
Moist Convection ◽  
Conservation Of Energy ◽  
Deep Moist Convection ◽  
Static Energy ◽  
Hydrostatic Balance ◽  
Latent Heats

AbstractIt is often assumed in parcel theory calculations, numerical models, and cumulus parameterizations that moist static energy (MSE) is adiabatically conserved. However, the adiabatic conservation of MSE is only approximate because of the assumption of hydrostatic balance. Two alternative variables are evaluated here: MSE −IB and MSE +KE, wherein IB is the path integral of buoyancy (B) and KE is kinetic energy. Both of these variables relax the hydrostatic assumption and are more precisely conserved than MSE. This article quantifies the errors that result from assuming that the aforementioned variables are conserved in large eddy simulations (LES) of both disorganized and organized deep convection. Results show that both MSE −IB and MSE +KE better predict quantities along trajectories than MSE alone. MSE −IB is better conserved in isolated deep convection, whereas MSE −IB and MSE +KE perform comparably in squall line simulations. These results are explained by differences between the pressure perturbation behavior of squall lines and isolated convection. Errors in updraft B diagnoses are universally minimized when MSE−IB is assumed to be adiabatically conserved, but only when moisture dependencies of heat capacity and temperature dependency of latent heating are accounted for. When less accurate latent heat and heat capacity formulae were used, MSE−IB yielded poorer B predictions than MSE due to compensating errors. Our results suggest that various applications would benefit from using either MSE −IB or MSE +KE instead of MSE with properly formulated heat capacities and latent heats.

Fog forecasting for Schiphol airport at sub-kilometre scale.  

2021 ◽  
Author(s):  
Gert-Jan Steeneveld ◽  
Roosmarijn Knol
Keyword(s):  
Spatial Resolution ◽  
Numerical Models ◽  
Wrf Model ◽  
Horizontal Resolution ◽  
Physical Processes ◽  
Radiation Fog ◽  
Fog Forecasting ◽  
Elevation Data ◽  
The Individual ◽  
The Impact

<p>Fog is a critical weather phenomenon for safety and operations in aviation. Unfortunately, the forecasting of radiation fog remains challenging due to the numerous physical processes that play a role and their complex interactions, in addition to the vertical and horizontal resolution of the numerical models. In this study we evaluate the performance of the Weather Research and Forecasting (WRF) model for a radiation fog event at Schiphol Amsterdam Airport (The Netherlands) and further develop the model towards a 100 m grid spacing. Hence we introduce high resolution land use and land elevation data. In addition we study the role of gravitational droplet settling, advection of TKE, top-down diffusion caused by strong radiative cooling at the fog top. Finally the impact of heat released by the terminal areas on the fog formation is studied. The model outcomes are evaluated against 1-min weather observations near multiple runways at the airport.</p><p>Overall we find the WRF model shows an reasonable timing of the fog onset and is well able to reproduce the visibility and meteorological conditions as observed during the case study. The model appears to be relatively insensitive to the activation of the individual physical processes. An increased spatial resolution to 100 m generally results in a better timing of the fog onset differences up to three hours, though not for all runways. The effect of the refined landuse dominates over the effect of refined elevation data. The modelled fog dissipation systematically occurs 3-4 h hours too early, regardless of physical processes or spatial resolution. Finally, the introduction of heat from terminal buildings delays the fog onset with a maximum of two hours, an overestimated visibility of 100-200 m and a decrease of the LWC with 0.10-0.15 g/kg compared to the reference.</p>

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