Numerical Simulation of Squall line in idealized SINGV and WRF Models

2020 ◽  
Author(s):  
Ragi Rajagopalan ◽  
Anurag Dipankar ◽  
Xiang-Yu Huang
Keyword(s):  
Weather Prediction ◽  
Numerical Weather Prediction Model ◽  
Squall Line ◽  
Cross Sectional ◽  
Spatial And Temporal Scales ◽  
Weather Forecasts ◽  
Convective Systems ◽  
Squall Lines ◽  
Rain Events ◽  
Onset Location

<p>Squall lines are the prominent feature over Singapore region creating strongly localized rain events due to vigorous localized convective activity. These convective systems have relatively small spatial and temporal scales compared to other atmospheric features like monsoons, thus the prediction of these features lack accuracy. The SINGV numerical weather prediction model is able to provide improved weather forecasts over Singapore region, however, challenges still exist in predicting the thunderstorm/squall line events in onset, location, intensity and lead time. A few real-time case studies of squall lines indicate that SINGV could not capture these features appropriately, while WRF did a better forecasting. To understand the issues with SINGV model, idealized simulations replicating the Weismann & Klemp ‘82 case are conducted keeping similar physics in both the models. Preliminary results indicate that both models behave differently: WRF displays organized convection whereas in SINGV the storm splits at the early stages. Cross-sectional details along the propagating squall line suggest that the updrafts and downdrafts, at the storm development stages, are moderately higher in SINGV compared to WRF. It is speculated that these stronger updrafts in SINGV carry anomalously large amount of liquid water to the upper troposphere where these are converted into rain, which in turn result in stronger downdrafts facilitating the splitting of initial storm. Further analysis is required to conclude our speculation.</p>

scholarly journals Evaluation of the WRF Model to Simulate a High-Intensity Rainfall Event over Kampala, Uganda

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 873
Author(s):  
Yakob Umer ◽  
Janneke Ettema ◽  
Victor Jetten ◽  
Gert-Jan Steeneveld ◽  
Reinder Ronda
Keyword(s):  
High Intensity ◽  
Flood Hazard ◽  
Weather Prediction ◽  
Wrf Model ◽  
Numerical Weather Prediction Model ◽  
Rainfall Event ◽  
Weather Research And Forecasting ◽  
Event Triggering ◽  
Rain Events

Simulating high-intensity rainfall events that trigger local floods using a Numerical Weather Prediction model is challenging as rain-bearing systems are highly complex and localized. In this study, we analyze the performance of the Weather Research and Forecasting (WRF) model’s capability in simulating a high-intensity rainfall event using a variety of parameterization combinations over the Kampala catchment, Uganda. The study uses the high-intensity rainfall event that caused the local flood hazard on 25 June 2012 as a case study. The model capability to simulate the high-intensity rainfall event is performed for 24 simulations with a different combination of eight microphysics (MP), four cumulus (CP), and three planetary boundary layer (PBL) schemes. The model results are evaluated in terms of the total 24-h rainfall amount and its temporal and spatial distributions over the Kampala catchment using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) analysis. Rainfall observations from two gauging stations and the CHIRPS satellite product served as benchmark. Based on the TOPSIS analysis, we find that the most successful combination consists of complex microphysics such as the Morrison 2-moment scheme combined with Grell-Freitas (GF) and ACM2 PBL with a good TOPSIS score. However, the WRF performance to simulate a high-intensity rainfall event that has triggered the local flood in parts of the catchment seems weak (i.e., 0.5, where the ideal score is 1). Although there is high spatial variability of the event with the high-intensity rainfall event triggering the localized floods simulated only in a few pockets of the catchment, it is remarkable to see that WRF is capable of producing this kind of event in the neighborhood of Kampala. This study confirms that the capability of the WRF model in producing high-intensity tropical rain events depends on the proper choice of parametrization combinations.

The Response of Simulated Nocturnal Convective Systems to a Developing Low-Level Jet

2010 ◽  
Vol 67 (10) ◽  
pp. 3384-3408 ◽  
Author(s):  
Adam J. French ◽  
Matthew D. Parker
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Wind Shear ◽  
Squall Line ◽  
Stable Boundary ◽  
Low Level ◽  
Convective Systems ◽  
Squall Lines ◽  
Central United States ◽  
Low Level Jet

Abstract Some recent numerical experiments have examined the dynamics of initially surface-based squall lines that encounter an increasingly stable boundary layer, akin to what occurs with the onset of nocturnal cooling. The present study builds on that work by investigating the added effect of a developing nocturnal low-level jet (LLJ) on the convective-scale dynamics of a simulated squall line. The characteristics of the simulated LLJ atop a simulated stable boundary layer are based on past climatological studies of the LLJ in the central United States. A variety of jet orientations are tested, and sensitivities to jet height and the presence of low-level cooling are explored. The primary impacts of adding the LLJ are that it alters the wind shear in the layers just above and below the jet and that it alters the magnitude of the storm-relative inflow in the jet layer. The changes to wind shear have an attendant impact on low-level lifting, in keeping with current theories for gust front lifting in squall lines. The changes to the system-relative inflow, in turn, impact total upward mass flux and precipitation output. Both are sensitive to the squall line–relative orientation of the LLJ. The variations in updraft intensity and system-relative inflow are modulated by the progression of the low-level cooling, which mimics the development of a nocturnal boundary layer. While the system remains surface-based, the below-jet shear has the largest impact on lifting, whereas the above-jet shear begins to play a larger role as the system becomes elevated. Similarly, as the system becomes elevated, larger changes to system-relative inflow are observed because of the layer of potentially buoyant inflowing parcels becoming confined to the layer of the LLJ.

Diagnosis of an Intense Atmospheric River Impacting the Pacific Northwest: Storm Summary and Offshore Vertical Structure Observed with COSMIC Satellite Retrievals

2008 ◽  
Vol 136 (11) ◽  
pp. 4398-4420 ◽  
Author(s):  
Paul J. Neiman ◽  
F. Martin Ralph ◽  
Gary A. Wick ◽  
Ying-Hwa Kuo ◽  
Tae-Kwon Wee ◽  
...  
Keyword(s):  
Pacific Northwest ◽  
Numerical Weather Prediction ◽  
Weather Prediction ◽  
Numerical Weather Prediction Model ◽  
Cross Sectional ◽  
Vapor Flux ◽  
Numerical Weather ◽  
Atmospheric River ◽  
The Pacific ◽  
Flooding Events

Abstract This study uses the new satellite-based Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission to retrieve tropospheric profiles of temperature and moisture over the data-sparse eastern Pacific Ocean. The COSMIC retrievals, which employ a global positioning system radio occultation technique combined with “first-guess” information from numerical weather prediction model analyses, are evaluated through the diagnosis of an intense atmospheric river (AR; i.e., a narrow plume of strong water vapor flux) that devastated the Pacific Northwest with flooding rains in early November 2006. A detailed analysis of this AR is presented first using conventional datasets and highlights the fact that ARs are critical contributors to West Coast extreme precipitation and flooding events. Then, the COSMIC evaluation is provided. Offshore composite COSMIC soundings north of, within, and south of this AR exhibited vertical structures that are meteorologically consistent with satellite imagery and global reanalysis fields of this case and with earlier composite dropsonde results from other landfalling ARs. Also, a curtain of 12 offshore COSMIC soundings through the AR yielded cross-sectional thermodynamic and moisture structures that were similarly consistent, including details comparable to earlier aircraft-based dropsonde analyses. The results show that the new COSMIC retrievals, which are global (currently yielding ∼2000 soundings per day), provide high-resolution vertical-profile information beyond that found in the numerical model first-guess fields and can help monitor key lower-tropospheric mesoscale phenomena in data-sparse regions. Hence, COSMIC will likely support a wide array of applications, from physical process studies to data assimilation, numerical weather prediction, and climate research.

Impact of Environmental Variations on Simulated Squall Lines Interacting with Terrain

2011 ◽  
Vol 139 (10) ◽  
pp. 3163-3183 ◽  
Author(s):  
Casey E. Letkewicz ◽  
Matthew D. Parker
Keyword(s):  
Wind Profile ◽  
Windward Side ◽  
Squall Line ◽  
Cold Pool ◽  
Convective System ◽  
Low Level ◽  
Convective Systems ◽  
Squall Lines ◽  
Strong Convection ◽  
The Mean

Abstract The complex evolution of convective systems crossing (or attempting to cross) mountainous terrain represents a substantial forecasting challenge. This study examines the processes associated with environments of “crossing” squall lines (which were able to redevelop strong convection in the lee of a mountain barrier) and “noncrossing” squall lines (which were not able to redevelop strong convection downstream of the barrier). In particular, numerical simulations of mature convective systems crossing idealized terrain roughly approximating the Appalachian Mountains were used to test the first-order impact of variations in the vertical wind profile upon system maintenance. By itself, the wind profile showed no ability to uniquely discriminate between simulated crossing and noncrossing squall lines; each test revealed a similar pattern of orographic enhancement, suppression, and lee reinvigoration in which a hydraulic jump deepened the system’s cold pool and renewed the low-level lifting. Increasing the mean wind led to greater enhancement of vertical velocities on the windward side of the barrier and greater suppression on the lee side. Variations in the low-level shear influenced the temperature and depth of the outflow, which in turn altered the lifting along the system’s gust front. However, in all of the wind profile tests, convection redeveloped in the lee. Additional simulations explored more marginal environments in which idealized low-level cooling or drying stabilized the downstream environment. In most such tests, the systems weakened but the presence of CAPE aloft still enabled the systems to survive in the lee. However, the combination of a stronger mean wind with diminished CAPE and increased convective inhibition (CIN) was ultimately found to eliminate downstream redevelopment and produce a noncrossing mesoscale convective system (MCS). Within these experiments, the ability of a squall line to cross a barrier similar to the Appalachians is primarily tied to the characteristics of the downstream thermodynamic environment; however, as the lee thermodynamic environment becomes less favorable, the mean wind exerts a greater influence on system intensity and redevelopment.

scholarly journals Characteristics of Sundowner Winds near Santa Barbara, California, from a Dynamically Downscaled Climatology: Environment and Effects near the Surface

2018 ◽  
Vol 57 (3) ◽  
pp. 589-606 ◽  
Author(s):  
Craig M. Smith ◽  
Benjamin J. Hatchett ◽  
Michael L. Kaplan
Keyword(s):  
Fire Suppression ◽  
Weather Prediction ◽  
Internal Gravity Wave ◽  
Numerical Weather Prediction Model ◽  
Wind Component ◽  
Pressure Gradients ◽  
Santa Barbara ◽  
Weather Forecasts ◽  
Downslope Wind ◽  
Support Resource

AbstractSundowners are downslope windstorms that occur over the southern slopes of the east–west-trending Santa Ynez range in Santa Barbara County, California. In the past, many extreme fires in the area, including the Painted Cave, Montecito Tea, Jesusita, and Sherpa fires, have occurred during sundowner events. A high-resolution 11-yr dynamically downscaled climatology was produced using a numerical weather prediction model in order to elucidate the general dynamical characteristics of sundowners. The downscaled climatology is validated with observations during the 2016 Sherpa fire. A sundowner index (SI) is computed from the climatology that quantifies the magnitude of adiabatic warming and northerly (downslope) wind component during sundowner events. The SI allows for the classification of historical events into categories of various strengths. The primary characteristics of strong sundowners from this classification include 1) internal gravity wave breaking over the Santa Ynez range, 2) initiation in the western Santa Ynez range with eastward progression over the course of a day, 3) a maximum likelihood of occurrence in April and May near 2000 Pacific standard time, and 4) a limited downstream extent for most events, such that the long-term historical weather station, Santa Barbara airport, often does not experience moderate events. Analysis of an operational forecast rubric composed of the surface pressure difference from Bakersfield to Santa Barbara indicates that this rubric is not skillful. However, offshore pressure gradients are skillful and are related to the strong northwesterly alongshore jet. The findings presented herein can be used to provide guidance for fire weather forecasts and support resource allocation during fire suppression efforts.

Analysis of Gust Characteristics and Forecast Correction for the 2022 Olympic and Paralympic Winter Games in Zhangjiakou

2020 ◽  
Author(s):  
Jiarui Li ◽  
Quan Dong ◽  
Rong Li
Keyword(s):  
Wind Speed ◽  
Weather Prediction ◽  
Numerical Weather Prediction Model ◽  
Original Model ◽  
Observation Data ◽  
Systematic Bias ◽  
High Demand ◽  
Scaling Method ◽  
Weather Forecasts ◽  
The Relationship

<p>In order to meet the high demand for advanced weather forecasts in the 2022 Olympic and Paralympic Winter Games, hourly wind observation data of some venues in Zhangjiakou City  is analyzed. Based on the specific gust characteristics in these venues, deviation of numerical weather prediction model is initially calculated to demonstrate the systematic bias of instantaneous wind speed forecasts derived from ECMWF. Additionally, a statistical down scaling method is further used by establishing the relationship between model forecasts and observation. Then independent samples are imported to the established equations to generate revised outputs. Tests show that the established equations have a better effect on forecasting the instantaneous wind speed than original model outputs and the corrected outputs have significantly better accuracy in predicting the instantaneous wind speed in the studied area.</p>

scholarly journals Use of a Rain Gauge Network to Infer the Influence of Environmental Factors on the Propagation of Quasi-Linear Convective Systems in West Africa

2007 ◽  
Vol 22 (5) ◽  
pp. 1016-1030 ◽  
Author(s):  
Jon M. Schrage ◽  
Andreas H. Fink
Keyword(s):  
Environmental Factors ◽  
Propagation Rate ◽  
Rain Gauge ◽  
West African ◽  
Squall Line ◽  
Propagation Characteristics ◽  
Convective Systems ◽  
Squall Lines ◽  
Radiosonde Station ◽  
The Impact

Abstract The West African squall line is a key quasi-linear storm system that brings much of the precipitation observed in the data-poor Sudanian climate zone. Squall lines propagate at a wide range of speeds and headings, but the lack of operational radar stations in the region makes quantifying the propagation of the squall lines difficult. A new method of estimating the propagation rate and heading for squall lines is proposed. Based on measurements of the time of onset of precipitation (OOP) at a network of rain gauge stations, an estimate of the propagation characteristics of the squall line can be inferred. By combining estimates of propagation rate with upper-air observations gathered at a nearby radiosonde station, the impact of various environmental factors on the propagation characteristics of West African squall lines is inferred. Results suggest that the propagation speed for West African squall lines is related to the conditions at midtropospheric levels, where dry air and an enhanced easterly flow favor faster propagation. Northerly anomalies at these levels are also associated with faster propagation. When applied to West African squall lines, the correlations between these environmental factors and the speed of propagation are significantly higher than those of methods developed for mesoscale convective systems in other parts of the world.

scholarly journals On Contrasting Ensemble Simulations of Two Great Plains Bow Echoes

2016 ◽  
Vol 31 (3) ◽  
pp. 787-810 ◽  
Author(s):  
John Lawson ◽  
William A. Gallus
Keyword(s):  
Great Plains ◽  
Initial Conditions ◽  
Weather Prediction ◽  
Model Error ◽  
Numerical Weather Prediction Model ◽  
Radius Of Curvature ◽  
Convective Systems ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Microphysical Parameterization

Abstract Bow echo structures, a subset of mesoscale convective systems (MCSs), are often poorly forecast within deterministic numerical weather prediction model simulations. Among other things, this may be due to the inherent low predictability associated with bow echoes, deficient initial conditions (ICs), and inadequate parameterization schemes. Four different ensemble configurations assessed the sensitivity of the MCSs’ simulated reflectivity and radius of curvature to the following: perturbations in initial and lateral boundary conditions using a global dataset, different microphysical schemes, a stochastic kinetic energy backscatter (SKEB) scheme, and a mix of the previous two. One case is poorly simulated no matter which IC dataset or microphysical parameterization is used. In the other case, almost all simulations reproduce a bow echo. When the IC dataset and microphysical parameterization is fixed within a SKEB ensemble, ensemble uncertainty is smaller. However, while differences in the location and timing of the MCS are reduced, variations in convective mode remain substantial. Results suggest the MCS’s positioning is influenced primarily by ICs, but its mode is most sensitive to the model error uncertainty. Hence, correct estimation of model error uncertainty on the storm scale is crucial for adequate spread and the probabilistic forecast of convective events.

scholarly journals Thunderstorms Do Not Get Butterflies

2016 ◽  
Vol 97 (2) ◽  
pp. 237-243 ◽  
Author(s):  
Dale R. Durran ◽  
Jonathan A. Weyn
Keyword(s):  
Large Scale ◽  
Squall Line ◽  
Small Scale ◽  
Lead Times ◽  
Initial State ◽  
Weather Forecasts ◽  
Kinetic Energy Spectrum ◽  
Initial Errors ◽  
Squall Lines ◽  
Homogeneous Environment

Abstract One important limitation on the accuracy of weather forecasts is imposed by unavoidable errors in the specification of the atmosphere’s initial state. Much theoretical concern has been focused on the limits to predictability imposed by small-scale errors, potentially even those on the scale of a butterfly. Very modest errors at much larger scales may nevertheless pose a more important practical limitation. We demonstrate the importance of large-scale uncertainty by analyzing ensembles of idealized squall-line simulations. Our results imply that minimizing initial errors on scales around 100 km is more likely to extend the accuracy of forecasts at lead times longer than 3–4 h than efforts to minimize initial errors on much smaller scales. These simulations also demonstrate that squall lines, triggered in a horizontally homogeneous environment with no initial background circulations, can generate a background mesoscale kinetic energy spectrum roughly similar to that observed in the atmosphere.

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