scholarly journals A Case Study of Radar Observations and WRF LES Simulations of the Impact of Ground-Based Glaciogenic Seeding on Orographic Clouds and Precipitation. Part II: AgI Dispersion and Seeding Signals Simulated by WRF

2016 ◽  
Vol 55 (2) ◽  
pp. 445-464 ◽  
Author(s):  
Lulin Xue ◽  
Xia Chu ◽  
Roy Rasmussen ◽  
Daniel Breed ◽  
Bart Geerts
Keyword(s):  
Nucleation Rate ◽  
Wrf Model ◽  
Grid Spacing ◽  
Medicine Bow Mountains ◽  
Eddy Simulation ◽  
Cloud Dynamics ◽  
Vertical Dispersion ◽  
Orographic Clouds ◽  
Glaciogenic Seeding ◽  
The Impact

AbstractSeveral Weather Research and Forecasting (WRF) Model simulations of natural and seeded clouds have been conducted in non-LES and LES (large-eddy simulation) modes to investigate the seeding impact on wintertime orographic clouds for an actual seeding case on 18 February 2009 in the Medicine Bow Mountains of Wyoming. Part I of this two-part series has shown the capability of WRF LES with 100-m grid spacing to capture the essential environmental conditions by comparing the model results with measurements from a variety of instruments. In this paper, the silver iodide (AgI) dispersion features, the AgI impacts on the turbulent kinetic energy (TKE), the microphysics, and the precipitation are examined in detail using the model data, which leads to five main results. 1) The vertical dispersion of AgI particles is more efficient in cloudy conditions than in clear conditions. 2) The wind shear and the buoyancy are both important TKE production mechanisms in the wintertime PBL over complex terrain in cloudy conditions. The buoyancy-induced eddies are more responsible for the AgI vertical dispersion than the shear-induced eddies are. 3) Seeding has insignificant effects on the cloud dynamics. 4) AgI particles released from the ground-based generators affect the cloud within the boundary layer below 1 km AGL through nucleating extra ice crystals, converting liquid water into ice, depleting more vapor, and generating more precipitation on the ground. The AgI nucleation rate is inversely related to the natural ice nucleation rate. 5) The seeding effects on the ground precipitation are confined within narrow areas. The relative seeding effect ranges between 5% and 20% for the simulations with different grid spacing.

The Dispersion of Silver Iodide Particles from Ground-Based Generators over Complex Terrain. Part II: WRF Large-Eddy Simulations versus Observations

2014 ◽  
Vol 53 (6) ◽  
pp. 1342-1361 ◽  
Author(s):  
Lulin Xue ◽  
Xia Chu ◽  
Roy Rasmussen ◽  
Daniel Breed ◽  
Bruce Boe ◽  
...  
Keyword(s):  
Complex Terrain ◽  
Silver Iodide ◽  
Wrf Model ◽  
Static Stability ◽  
Particle Dispersion ◽  
Grid Spacing ◽  
Medicine Bow Mountains ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Orographic Clouds

AbstractA numerical modeling study has been conducted to explore the ability of the Weather Research and Forecasting (WRF) model-based large-eddy simulation (LES) with 100-m grid spacing to reproduce silver iodide (AgI) particle dispersion by comparing the model results with measurements made on 16 February 2011 over the Medicine Bow Mountains in Wyoming. Xue et al.'s recently developed AgI cloud-seeding parameterization was applied in this study to simulate AgI release from ground-based generators. Qualitative and quantitative comparisons between the LES results and observed AgI concentrations were conducted. Analyses of turbulent kinetic energy (TKE) features within the planetary boundary layer (PBL) and comparisons between the 100-m LES and simulations with 500-m grid spacing were performed as well. The results showed the following: 1) Despite the moist bias close to the ground and above 4 km AGL, the LES with 100-m grid spacing captured the essential environmental conditions except for a slightly more stable PBL relative to the observed soundings. 2) Wind shear is the dominant TKE production mechanism in wintertime PBL over complex terrain and generates a PBL of about 1000-m depth. The terrain-induced turbulent eddies are primarily responsible for the vertical dispersion of AgI particles. 3) The LES-simulated AgI plumes were shallow and narrow, in agreement with observations. The LES overestimated AgI concentrations close to the ground, which is consistent with the higher static stability in the model than is observed. 4) Non-LES simulations using PBL schemes had difficulty in capturing the shear-dominant turbulent PBL structure over complex terrain in wintertime. Therefore, LES of wintertime orographic clouds with grid spacing close to 500 m or finer are recommended.

An Airborne Profiling Radar Study of the Impact of Glaciogenic Cloud Seeding on Snowfall from Winter Orographic Clouds

2010 ◽  
Vol 67 (10) ◽  
pp. 3286-3302 ◽  
Author(s):  
Bart Geerts ◽  
Qun Miao ◽  
Yang Yang ◽  
Roy Rasmussen ◽  
Daniel Breed
Keyword(s):  
Doppler Radar ◽  
Weather Conditions ◽  
Cold Season ◽  
Near Surface ◽  
Medicine Bow Mountains ◽  
Orographic Clouds ◽  
Surface Reflectivity ◽  
Glaciogenic Seeding ◽  
The Impact ◽  
Composite Data

Abstract Data from an airborne vertically pointing millimeter-wave Doppler radar are used to study the cloud microphysical effect of glaciogenic seeding of cold-season orographic clouds. Fixed flight tracks were flown downstream of ground-based silver iodide (AgI) generators in the Medicine Bow Mountains of Wyoming. Composite data from seven flights, each with a no-seeding period followed by a seeding period, indicate that radar reflectivity was higher near the ground during the seeding periods. Several physical considerations argue in favor of the hypothesis that the increase in near-surface reflectivity is attributed to AgI seeding. While the increase in near-surface reflectivity and thus snowfall rate are statistically significant, caution is warranted in view of the large natural variability of weather conditions and the small size of the dataset.

Dual-Polarization Radar Data Analysis of the Impact of Ground-Based Glaciogenic Seeding on Winter Orographic Clouds. Part I: Mostly Stratiform Clouds

2015 ◽  
Vol 54 (9) ◽  
pp. 1944-1969 ◽  
Author(s):  
Xiaoqin Jing ◽  
Bart Geerts ◽  
Katja Friedrich ◽  
Binod Pokharel
Keyword(s):  
Radar Data ◽  
Control Area ◽  
Target Area ◽  
Dual Polarization ◽  
Stratiform Clouds ◽  
Orographic Clouds ◽  
Close Range ◽  
Glaciogenic Seeding ◽  
Differential Reflectivity ◽  
The Impact

AbstractThe impact of ground-based glaciogenic seeding on wintertime orographic, mostly stratiform clouds is analyzed by means of data from an X-band dual-polarization radar, the Doppler-on-Wheels (DOW) radar, positioned on a mountain pass. This study focuses on six intensive observation periods (IOPs) during the 2012 AgI Seeding Cloud Impact Investigation (ASCII) project in Wyoming. In all six storms, the bulk upstream Froude number below mountaintop exceeded 1 (suggesting unblocked flow), the clouds were relatively shallow (with bases below freezing), some liquid water was present, and orographic flow conditions were mostly steady. To examine the silver iodide (AgI) seeding effect, three study areas are defined (a control area, a target area upwind of the crest, and a lee target area), and comparisons are made between measurements from a treated period and those from an untreated period. Changes in reflectivity and differential reflectivity observed by the DOW at low levels during seeding are consistent with enhanced snow growth, by vapor diffusion and/or aggregation, for a case study and for the composite analysis of all six IOPs, especially at close range upwind of the mountain crest. These low-level changes may have been affected by natural changes aloft, however, as evident from differences in the evolution of the echo-top height in the control and target areas. Even though precipitation in the target region is strongly correlated with that in the control region, the authors cannot definitively attribute the change to seeding because there is a lack of knowledge about natural variability, nor can the outcome be generalized, because the sample size is small.

scholarly journals Comparison of the Vertical Distributions of Cloud Properties from Idealized Extratropical Deep Convection Simulations Using Various Horizontal Resolutions

2018 ◽  
Vol 146 (3) ◽  
pp. 833-851 ◽  
Author(s):  
Wei Huang ◽  
J.-W. Bao ◽  
Xu Zhang ◽  
Baode Chen
Keyword(s):  
Deep Convection ◽  
Wrf Model ◽  
Coarse Graining ◽  
Vertical Flux ◽  
Coarse Grained ◽  
Moist Static Energy ◽  
Grid Spacing ◽  
Eddy Simulation ◽  
Cloud Properties ◽  
Static Energy

ABSTRACT The authors coarse-grained and analyzed the output from a large-eddy simulation (LES) of an idealized extratropical supercell storm using the Weather Research and Forecasting (WRF) Model with various horizontal resolutions (200 m, 400 m, 1 km, and 3 km). The coarse-grained physical properties of the simulated convection were compared with explicit WRF simulations of the same storm at the same resolution of coarse-graining. The differences between the explicit simulations and the coarse-grained LES output increased as the horizontal grid spacing in the explicit simulation coarsened. The vertical transport of the moist static energy and total hydrometeor mixing ratio in the explicit simulations converged to the LES solution at the 200-m grid spacing. Based on the analysis of the coarse-grained subgrid vertical flux of the moist static energy, the authors confirmed that the nondimensional subgrid vertical flux of the moist static energy varied with the subgrid fractional cloudiness according to a function of fractional cloudiness, regardless of the box size. The subgrid mass flux could not account for most of the total subgrid vertical flux of the moist static energy because the eddy-transport component associated with the internal structural inhomogeneity of convective clouds was of a comparable magnitude. This study highlights the ongoing challenge in developing scale-aware parameterizations of subgrid convection.

A Case Study on the Impact of Ground-based Glaciogenic Seeding on Winter Orographic Clouds at Daegwallyeong

2015 ◽  
Vol 36 (4) ◽  
pp. 301-314 ◽  
Author(s):  
Ha-Young Yang ◽  
◽  
Sanghee Chae ◽  
Jin-Yim Jeong ◽  
Seong-Kyu Seo ◽  
...  
Keyword(s):  
Orographic Clouds ◽  
Glaciogenic Seeding ◽  
The Impact

Evaluation of the Impact of Horizontal Grid Spacing in Terra Incognita on Coupled Mesoscale–Microscale Simulations Using the WRF Framework

2019 ◽  
Vol 147 (3) ◽  
pp. 1007-1027 ◽  
Author(s):  
Raj K. Rai ◽  
Larry K. Berg ◽  
Branko Kosović ◽  
Sue Ellen Haupt ◽  
Jeffrey D. Mirocha ◽  
...  
Keyword(s):  
Spatial Scales ◽  
Wrf Model ◽  
Spectral Energy ◽  
Grid Spacing ◽  
Terra Incognita ◽  
Wide Range ◽  
Large Eddy ◽  
Microscale Simulations ◽  
The Impact ◽  
Horizontal Grid

Abstract Coupled mesoscale–microscale simulations are required to provide time-varying weather-dependent inflow and forcing for large-eddy simulations under general flow conditions. Such coupling necessarily spans a wide range of spatial scales (i.e., ~10 m to ~10 km). Herein, we use simulations that involve multiple nested domains with horizontal grid spacings in the terra incognita (i.e., km) that may affect simulated conditions in both the outer and inner domains. We examine the impact on simulated wind speed and turbulence associated with forcing provided by a terrain with grid spacing in the terra incognita. We perform a suite of simulations that use combinations of varying horizontal grid spacings and turbulence parameterization/modeling using the Weather Research and Forecasting (WRF) Model using a combination of planetary boundary layer (PBL) and large-eddy simulation subgrid-scale (LES-SGS) models. The results are analyzed in terms of spectral energy, turbulence kinetic energy, and proper orthogonal decomposition (POD) energy. The results show that the output from the microscale domain depends on the type of turbulence model (e.g., PBL or LES-SGS model) used for a given horizontal grid spacing but is independent of the horizontal grid spacing and turbulence modeling of the parent domain. Simulation using a single domain produced less POD energy in the first few modes compared to a coupled simulation (one-way nesting) for similar horizontal grid spacing, which highlights that coupled simulations are required to accurately pass the mesoscale features into the microscale domain.

scholarly journals Dual-Polarization Radar Data Analysis of the Impact of Ground-Based Glaciogenic Seeding on Winter Orographic Clouds. Part II: Convective Clouds

2015 ◽  
Vol 54 (10) ◽  
pp. 2099-2117 ◽  
Author(s):  
Xiaoqin Jing ◽  
Bart Geerts
Keyword(s):  
Cloud Base ◽  
Base Temperature ◽  
Target Area ◽  
Dual Polarization ◽  
Low Level ◽  
Convective Clouds ◽  
Orographic Clouds ◽  
Orographic Convection ◽  
Glaciogenic Seeding ◽  
The Impact

AbstractThis second paper of a two-part series aims to explore the ground-based glaciogenic seeding impact on wintertime orographic clouds using an X-band dual-polarization radar. It focuses on three cases with shallow to moderately deep orographic convection that were observed in January–February of 2012 as part of the AgI Seeding Cloud Impact Investigation (ASCII) project over the Sierra Madre in Wyoming. In each of the storms the bulk upstream Froude number exceeded 1, suggesting unblocked flow. Low-level potential instability was present, explaining orographic convection. The clouds contained little supercooled liquid water on account of the low cloud-base temperature. Ice-crystal photography shows that snow mainly grew by diffusion and aggregation. To examine the seeding effect of silver iodide (AgI), five study areas are defined: two target areas and three control areas. Comparisons are made between the control and target areas as well as between a treated, or seeded, period and an untreated period. Low-level reflectivity tends to increase in the target areas relative to the control. This increase is larger in the lee target area than in the upwind target area, suggesting that precipitation enhancement is delayed in the presence of convection. The echo tops of the convective cells are not higher during seeding, relative to simultaneous changes in the control regions. This result suggests that the dynamic-seeding mechanism does not apply for the cold-base convective clouds that are studied here. An analysis of differential reflectivity and snow photography suggests that static seeding is the more likely snow-enhancement mechanism in these clouds.

scholarly journals Influences of Horizontal Grid Spacing and Microphysics on WRF Forecasts of Convective Morphology Evolution for Nocturnal MCSs in Weakly Forced Environments

2019 ◽  
Vol 34 (5) ◽  
pp. 1495-1517 ◽  
Author(s):  
Jonathan E. Thielen ◽  
William A. Gallus
Keyword(s):  
Wrf Model ◽  
Forecast Accuracy ◽  
Warm Season ◽  
Grid Spacing ◽  
Convective Systems ◽  
Model Configuration ◽  
Mesoscale Convective ◽  
Microphysical Parameterization ◽  
The Impact ◽  
Horizontal Grid

Abstract Nocturnal mesoscale convective systems (MCSs) are important phenomena because of their contributions to warm-season precipitation and association with severe hazards. Past studies have shown that their morphology remains poorly forecast in current convection-allowing models operating at 3–4-km horizontal grid spacing. A total of 10 MCS cases occurring in weakly forced environments were simulated using the Weather Research and Forecasting (WRF) Model at 3- and 1-km horizontal grid spacings to investigate the impact of increased resolution on forecasts of convective morphology and its evolution. These simulations were conducted using four microphysics schemes to account for additional sensitivities to the microphysical parameterization. The observed and corresponding simulated systems were manually classified into detailed cellular and linear modes, and the overall morphology depiction and the forecast accuracy of each model configuration were evaluated. In agreement with past studies, WRF was found to underpredict the occurrence of linear modes and overpredict cellular modes at 3-km horizontal grid spacing with all microphysics schemes tested. When grid spacing was reduced to 1 km, the proportion of linear systems increased. However, the increase was insufficient to match observations throughout the evolution of the systems, and the accuracy scores showed no statistically significant improvement. This suggests that the additional linear modes may have occurred in the wrong subtypes, wrong systems, and/or at the wrong times. Accuracy scores were also shown to decrease with forecast length, with the primary decrease in score generally occurring during upscale growth in the early nocturnal period.

The Impact of Ground-Based Glaciogenic Seeding on Orographic Clouds and Precipitation: A Multisensor Case Study

2014 ◽  
Vol 53 (4) ◽  
pp. 890-909 ◽  
Author(s):  
Binod Pokharel ◽  
Bart Geerts ◽  
Xiaoqin Jing
Keyword(s):  
Band 3 ◽  
Cloud Base ◽  
Near Surface ◽  
Target Region ◽  
Orographic Clouds ◽  
Snow Crystals ◽  
Corroborative Evidence ◽  
Glaciogenic Seeding ◽  
The Impact

AbstractA case study is presented from the 2012 AgI Seeding Cloud Impact Investigation, an experiment conducted over the Sierra Madre in southern Wyoming to study the impact of ground-based glaciogenic seeding on precipitation. In this case, on 21 February, the temperature in the turbulent boundary layer above cloud base in the target region was just below −8°C, the target orographic clouds contained liquid water, and the storm was rather steady during the measurement period, consisting of an untreated period, followed by a treated period. Eight silver iodide (AgI) generators were used, located on the windward mountain slope. This study is unprecedented in its diversity of radar systems, which included the W-band (3 mm) profiling Wyoming Cloud Radar (WCR), a pair of Ka-band (1 cm) profiling Micro Rain Radars (MRRs), and an X-band (3 cm) scanning Doppler-on-Wheels (DOW) radar. The WCR was on board a research aircraft flying geographically fixed tracks, the DOW was located on the main mountain pass in the target region, one MRR was at this pass, and the other was upstream of the generators. Composite data from the three radars indicate that near-surface reflectivity was higher during seeding, a change that could not be accounted for by storm intensification upstream of the generators. Data from a Parsivel disdrometer at the pass indicate that the concentration of snow crystals of all sizes was larger during seeding, although this change was somewhat delayed. This study highlights the challenge of an observational study to unambiguously identify a seeding signal, as well as the value of cumulative corroborative evidence from independent sources.

scholarly journals Evaluation of Lagrangian Particle Dispersion Models with Measurements from Controlled Tracer Releases

2013 ◽  
Vol 52 (12) ◽  
pp. 2623-2637 ◽  
Author(s):  
Jennifer Hegarty ◽  
Roland R. Draxler ◽  
Ariel F. Stein ◽  
Jerome Brioude ◽  
Marikate Mountain ◽  
...  
Keyword(s):  
Wrf Model ◽  
Particle Dispersion ◽  
Tracer Experiment ◽  
Grid Spacing ◽  
Dispersion Models ◽  
Lagrangian Particle ◽  
Statistical Parameters ◽  
The North ◽  
The Impact ◽  
Horizontal Grid

AbstractThree widely used Lagrangian particle dispersion models (LPDMs)—the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT), Stochastic Time-Inverted Lagrangian Transport (STILT), and Flexible Particle (FLEXPART) models—are evaluated with measurements from the controlled tracer-release experiments Cross-Appalachian Tracer Experiment (CAPTEX) and Across North America Tracer Experiment (ANATEX). The LPDMs are run forward in time driven by identical meteorological inputs from the North American Regional Reanalysis (NARR) and several configurations of the Weather Research and Forecasting (WRF) model, and the simulations of tracer concentrations are evaluated against the measurements with a ranking procedure derived from the combination of four statistical parameters. The statistical evaluation reveals that all three LPDMs have comparable skill in simulating the tracer plumes when driven by the same meteorological inputs, indicating that the differences in their formulations play a secondary role. Simulations with HYSPLIT and STILT demonstrate the benefit of using customized hourly WRF fields with 10-km horizontal grid spacing over the use of 3-hourly NARR fields with 32-km horizontal grid spacing. All three LPDMs perform better when the WRF wind fields in the planetary boundary layer are nudged to NARR, with FLEXPART benefitting the most. Case studies indicate that the nudging corrects an overestimate in plume transport speed possibly caused by a positive bias in WRF wind speeds near the surface. All three LPDMs also benefit from the use of time-averaged velocity and convective mass flux fields generated by WRF, but the impact on HYSPLIT and STILT is much greater than on FLEXPART. STILT backward runs perform as well as their forward counterparts, demonstrating this model’s reversibility and its suitability for application to inverse flux estimates.

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