scholarly journals A Case Study of Cloud Radar Observations and Large-Eddy Simulations of a Shallow Stratiform Orographic Cloud, and the Impact of Glaciogenic Seeding

2017 ◽  
Vol 56 (5) ◽  
pp. 1285-1304 ◽  
Author(s):  
Xia Chu ◽  
Bart Geerts ◽  
Lulin Xue ◽  
Binod Pokharel
Keyword(s):  
Liquid Water ◽  
Supercooled Liquid ◽  
Cold Season ◽  
Cloud Base ◽  
Target Area ◽  
Blowing Snow ◽  
Large Eddy ◽  
Orographic Clouds ◽  
Glaciogenic Seeding ◽  
The Impact

AbstractThe impact of glaciogenic seeding on precipitation remains uncertain, mainly because of the noisy nature of precipitation. Operational seeding programs often target cold-season orographic clouds because of their abundance of supercooled liquid water. Such clouds are complicated because of common natural seeding from above (seeder–feeder effect) or from below (blowing snow). Here, observations, mainly from a profiling airborne Doppler radar, and numerical simulations are used to examine the impact of glaciogenic seeding on a very shallow (<1 km), largely blocked cloud that is not naturally seeded from aloft or from below. This cloud has limited but persistent supercooled liquid water, a cloud-base (top) temperature of −12°C (−16°C), and produces only very light snowfall naturally. A Weather Research and Forecasting Model large-eddy simulation at 100-m resolution captures the observed upstream stability and wind profiles and reproduces the essential characteristics of the orographic flow, cloud, and precipitation. Both observations and simulations indicate that seeding locally increases radar (or computed) reflectivity in the target area, even after removal of the natural trend between these two periods in a nearby control region. A model sensitivity run suggests that seeding effectively glaciates the mostly liquid cloud and substantially increases snowfall within the seeding plume. This is due to a dramatic increase in the number of ice particles and not to their size. The increased ice particle concentration facilitates snow growth by vapor deposition in a cloud the temperature range of which is conducive to the Bergeron process.

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 Large-Eddy Simulations of the Impact of Ground-Based Glaciogenic Seeding on Shallow Orographic Convection: A Case Study

2017 ◽  
Vol 56 (1) ◽  
pp. 69-84 ◽  
Author(s):  
Xia Chu ◽  
Bart Geerts ◽  
Lulin Xue ◽  
Roy Rasmussen
Keyword(s):  
Liquid Water ◽  
Supercooled Liquid ◽  
Liquid Water Content ◽  
Diffusional Growth ◽  
Large Eddy Simulation Model ◽  
Surface Precipitation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Glaciogenic Seeding ◽  
The Impact

AbstractThis study uses the WRF large-eddy simulation model at 100-m resolution to examine the impact of ground-based glaciogenic seeding on shallow (~2 km deep), cold-based convection producing light snow showers over the Sierra Madre in southern Wyoming on 13 February 2012, as part of the AgI Seeding Cloud Impact Investigation (ASCII). Detailed observations confirm that simulation faithfully captures the orographic flow, convection, and natural snow production, especially on the upwind side. A comparison between treated and control simulations indicates that glaciogenic seeding effectively converts cloud water in convective updrafts to ice and snow in this case, resulting in increased surface precipitation. This comparison further shows that seeding enhances liquid water depletion by vapor deposition, and enhances buoyancy, updraft strength, and cloud-top height. This suggests that the dynamic seeding concept applies, notwithstanding the clouds’ low natural supercooled liquid water content. But the simulated cloud-top-height changes are benign (typically <100 m). This, combined with the fact that most natural and enhanced snow growth occurs in a temperature range in which the Bergeron diffusional growth process is effective, suggests that the modeled snowfall enhancement is largely due to static (microphysical) processes rather than dynamic ones.

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.

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.

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.

Potential for ground-based glaciogenic cloud seeding over mountains in the interior western United States, and anticipated changes in a warmer climate

2021 ◽  
Author(s):  
Thomas O. Mazzetti ◽  
Bart Geerts ◽  
Lulin Xue ◽  
Sarah Tessendorf ◽  
Courtney Weeks ◽  
...  
Keyword(s):  
United States ◽  
Liquid Water ◽  
Climate Model ◽  
Microwave Radiometer ◽  
Supercooled Liquid ◽  
Cold Season ◽  
Horizontal Resolution ◽  
Western United States ◽  
Cloud Seeding ◽  
Orographic Clouds

AbstractGlaciogenic cloud seeding has long been practiced as a way to increase water availability in arid regions, such as the interior western United States. Many seeding programs in this region target cold–season orographic clouds with ground–based silver iodide generators. Here, the “seedability” (defined as the fraction of time conditions are suitable for ground–based seeding) is evaluated in this region, based on 10 years of hourly output from a regional climate model with a horizontal resolution of 4 km. Seedability criteria are based on temperature, presence of supercooled liquid water, and Froude number, which is computed here as a continuous field relative to the local terrain. The model’s supercooled liquid water compares reasonably well against microwave radiometer observations.Seedability peaks at 20–30% for many mountain ranges in the cold season, with the best locations just upwind of crests, over the highest terrain in Colorado and Wyoming, as well as over ranges in the Northwest Interior. Mountains further south are less frequently seedable, due to warmer conditions, but when they are, cloud supercooled liquid water content tends to be relatively high.This analysis is extended into a future climate, anticipated for later this century, with a mean temperature 2.0 K warmer than the historical climate. Seedability generally will be lower in this future warmer climate, especially in the most seedable areas, but when seedable, clouds tend to contain slightly more supercooled liquid water.

scholarly journals Seedability of Winter Orographic Clouds

1986 ◽  
Vol 43 ◽  
pp. 127-138 ◽  
Author(s):  
Geoffrey E. Hill
Keyword(s):  
Wind Speed ◽  
Liquid Water ◽  
Supercooled Liquid ◽  
Direct Measurements ◽  
Orographic Clouds ◽  
The Subject ◽  
Relationship Of ◽  
Increasing Precipitation ◽  
Cloud Top Temperature ◽  
Limiting Value

Abstract This article is a review of work on the subject of seedability of winter orographic clouds for increasing precipitation. Various aspects of seedability are examined in the review, including definitions, distribution of supercooled liquid water, related meteorological factors, relationship of supercooled liquid water to storm stage, factors governing seedability, and the use of seeding criteria. Of particular interest is the conclusion that seedability is greatest when supercooled liquid water concentrations are large and at the same time precipitation rates are small. Such a combination of conditions is favored if the cloud-top temperature is warmer than a limiting value and as the cross-barrier wind speed at mountaintop levels increases. It is also suggested that cloud seeding is best initiated in accordance with direct measurements of supercooled liquid water, precipitation, and cross-barrier wind speed. However, in forecasting these conditions or in continuation of seeding previously initiated, the cloud-top temperature and cross-barrier wind speed are the most useful quantities.

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

scholarly journals Assessing the impact of different liquid water permittivity models on the fit between model and observations

2018 ◽  
Author(s):  
Katrin Lonitz ◽  
Alan J. Geer
Keyword(s):  
Liquid Water ◽  
Laboratory Experiments ◽  
Supercooled Liquid ◽  
Intertropical Convergence Zone ◽  
Forecast System ◽  
Microwave Frequencies ◽  
Brightness Temperatures ◽  
Model Configuration ◽  
The Impact ◽  
Permittivity Model

Abstract. Permittivity models for microwave frequencies of liquid water below 0 °C (supercooled liquid water) are poorly constrained due to limited laboratory experiments and observations, especially for high microwave frequencies. This uncertainty translates directly into errors in retrieved liquid water paths of up to 80 %. This study investigates the effect of different liquid water permittivity models on simulated brightness temperatures by using the all-sky assimilation framework of the Integrated Forecast System. Here, a model configuration with an improved representation of supercooled liquid water has been used. The comparison of five different permittivity models with the current one shows a small mean reduction in simulated brightness temperatures of at most 0.15 K at 92 GHz on a global monthly scale. During austral winter differences occur more prominently in the storm tracks of the southern hemisphere and in the Intertropical Convergence Zone with values of around 0.5 K to 1.5 K. For most permittivity models the fit to observations is slightly improved compared to the default one. The permittivity model by Rosenkranz (2015) is recommended to be used inside the observation operator RTTOV-SCATT for frequencies below 183 GHz.

scholarly journals Evaluation of Orographic Cloud Seeding Using a Bin Microphysics Scheme: Three-Dimensional Simulation of Real Cases

2020 ◽  
Vol 59 (9) ◽  
pp. 1537-1555
Author(s):  
István Geresdi ◽  
Lulin Xue ◽  
Noémi Sarkadi ◽  
Roy Rasmussen
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Cloud Condensation Nuclei ◽  
Three Dimensional ◽  
Liquid Water Content ◽  
Weather Modification ◽  
Diffusional Growth ◽  
Surface Precipitation ◽  
Orographic Clouds ◽  
The Impact

AbstractThe University of Pécs and NCAR Bin (UPNB) microphysical scheme was implemented into the mesoscale Weather Research and Forecast (WRF) Model that was used to study the impact of silver iodide (AgI) seeding on precipitation formation in winter orographic clouds. Four different experimental units were chosen from the Wyoming Weather Modification Pilot Project to simulate the seeding effect. The results of the numerical experiments show the following: (i) Comparisons with the soundings, snow gauges, and microwave radiometer data indicate that the three-dimensional simulations with detailed microphysics reasonably represent both the dynamics and the microphysics of real clouds. (ii) The dispersion of the AgI particles from the simulated ground-based seeding was effective because of turbulent mixing. (iii) In the investigated cases (surface temperature is less than 0°C), surface precipitation and precipitation efficiency show low susceptibility to the concentrations of cloud condensation nuclei and natural ice nucleating particles. (iv) If the available liquid water content promotes the enhancement of the number of snowflakes by diffusional growth, the surface precipitation can be increased by more than 5%. A novel parameter relevant to orographic clouds, horizontally integrated liquid water path (LWP), was evaluated to find the relation between seeding efficiency and liquid water content. The impact of seeding is negligible if the horizontal LWP is less than 0.1 mm and is apparent if the horizontal LWP is larger than 1 mm, as based on the cases investigated in this study.

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