scholarly journals Precipitation formation from orographic cloud seeding

2018 ◽  
Vol 115 (6) ◽  
pp. 1168-1173 ◽  
Author(s):  
Jeffrey R. French ◽  
Katja Friedrich ◽  
Sarah A. Tessendorf ◽  
Robert M. Rauber ◽  
Bart Geerts ◽  
...  
Keyword(s):  
Scientific Evidence ◽  
Supply And Demand ◽  
Particle Growth ◽  
Supercooled Liquid ◽  
Ice Crystals ◽  
Cloud Seeding ◽  
Critical Set ◽  
Mountainous Regions ◽  
Orographic Clouds ◽  
Glaciogenic Seeding

Throughout the western United States and other semiarid mountainous regions across the globe, water supplies are fed primarily through the melting of snowpack. Growing populations place higher demands on water, while warmer winters and earlier springs reduce its supply. Water managers are tantalized by the prospect of cloud seeding as a way to increase winter snowfall, thereby shifting the balance between water supply and demand. Little direct scientific evidence exists that confirms even the basic physical hypothesis upon which cloud seeding relies. The intent of glaciogenic seeding of orographic clouds is to introduce aerosol into a cloud to alter the natural development of cloud particles and enhance wintertime precipitation in a targeted region. The hypothesized chain of events begins with the introduction of silver iodide aerosol into cloud regions containing supercooled liquid water, leading to the nucleation of ice crystals, followed by ice particle growth to sizes sufficiently large such that snow falls to the ground. Despite numerous experiments spanning several decades, no direct observations of this process exist. Here, measurements from radars and aircraft-mounted cloud physics probes are presented that together show the initiation, growth, and fallout to the mountain surface of ice crystals resulting from glaciogenic seeding. These data, by themselves, do not address the question of cloud seeding efficacy, but rather form a critical set of observations necessary for such investigations. These observations are unambiguous and provide details of the physical chain of events following the introduction of glaciogenic cloud seeding aerosol into supercooled liquid orographic clouds.

A Transformational Approach to Winter Orographic Weather Modification Research: The SNOWIE Project

2019 ◽  
Vol 100 (1) ◽  
pp. 71-92 ◽  
Author(s):  
Sarah A. Tessendorf ◽  
Jeffrey R. French ◽  
Katja Friedrich ◽  
Bart Geerts ◽  
Robert M. Rauber ◽  
...  
Keyword(s):  
Silver Iodide ◽  
Supercooled Liquid ◽  
Cloud Seeding ◽  
Remotely Sensed Data ◽  
Weather Modification ◽  
Before And After ◽  
Orographic Clouds ◽  
Seeding Material ◽  
Airborne Sensors

AbstractThe Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment (SNOWIE) project aims to study the impacts of cloud seeding on winter orographic clouds. The field campaign took place in Idaho between 7 January and 17 March 2017 and employed a comprehensive suite of instrumentation, including ground-based radars and airborne sensors, to collect in situ and remotely sensed data in and around clouds containing supercooled liquid water before and after seeding with silver iodide aerosol particles. The seeding material was released primarily by an aircraft. It was hypothesized that the dispersal of the seeding material from aircraft would produce zigzag lines of silver iodide as it dispersed downwind. In several cases, unambiguous zigzag lines of reflectivity were detected by radar, and in situ measurements within these lines have been examined to determine the microphysical response of the cloud to seeding. The measurements from SNOWIE aim to address long-standing questions about the efficacy of cloud seeding, starting with documenting the physical chain of events following seeding. The data will also be used to evaluate and improve computer modeling parameterizations, including a new cloud-seeding parameterization designed to further evaluate and quantify the impacts of cloud seeding.

scholarly journals Observing ice particle growth along fall streaks in mixed-phase clouds using spectral polarimetric radar data

2018 ◽  
Author(s):  
Lukas Pfitzenmaier ◽  
Christine M. H. Unal ◽  
Yann Dufournet ◽  
Herman J. W. Russchenberg
Keyword(s):  
Particle Growth ◽  
Supercooled Liquid ◽  
Radar Data ◽  
Detection Algorithm ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Liquid Droplets ◽  
Growth Processes ◽  
Retrieval Technique ◽  
Mixed Phase Clouds

Abstract. The growth of ice crystals in presence of super-cooled liquid droplets represents the most important process for precipitation formation in the mid-latitudes. Such mixed-phase interaction processes remain however pretty much unknown, as capturing the complexity in cloud dynamics and microphysical variabilities turns to be a real observational challenge. Ground-based radar systems equipped with fully polarimetric and Doppler capabilities in high temporal and spatial resolutions 5 such as the S-band Transportable Atmospheric Radar (TARA) are best suited to observe mixed-phase growth processes. In this paper, measurements are taken with the TARA radar during the ACCEPT campaign (Analysis of the Composition of Clouds with Extended Polarization Techniques). Besides the common radar observables, the 3D wind field is also retrieved due to TARA unique three beam configuration. The novelty of this paper is to combine all these observations with a particle evolution detection algorithm based on a new fall streak retrieval technique in order to study ice particle growth within complex 10 precipitating mixed-phased cloud systems. In the presented cases, three different growth processes of ice crystals, plate-like crystals, and needles, are detected and related to the presence of supercooled liquid water. Moreover, TARA observed signatures are assessed with co-located measurements obtained from a cloud radar and radiosondes. This paper shows that it is possible to observe ice particle growth processes within complex systems taking advantage of adequate technology and state of the art retrieval algorithms. A significant improvement is made towards a conclusive interpretation of ice particle growth processes 15 and their contribution to rain production using fall streak rearranged radar data.

Microphysical characteristics and evolution of seeded orographic clouds

2021 ◽  
Author(s):  
Katja Friedrich ◽  
Jeffrey R. French ◽  
Sarah A. Tessendorf ◽  
Melinda Hatt ◽  
Courtney Weeks ◽  
...  
Keyword(s):  
Silver Iodide ◽  
Particle Growth ◽  
Liquid Water Content ◽  
Atmospheric Conditions ◽  
Cloud Seeding ◽  
Spatiotemporal Evolution ◽  
Widespread Occurrence ◽  
Orographic Clouds ◽  
Microphysical Processes

AbstractThe spatial distribution and magnitude of snowfall resulting from cloud seeding with silver iodide (AgI) is closely linked to atmospheric conditions, seeding operations, and dynamical, thermodynamical, and microphysical processes. Here, microphysical processes leading to ice and snow production are analyzed in orographic clouds for three cloud seeding events, each with light or no natural precipitation and well-defined, traceable seeding lines. Airborne and ground-based radar observations are linked to in-situ cloud and precipitation measurements to determine the spatiotemporal evolution of ice initiation, particle growth, and snow fallout in seeded clouds. These processes and surface snow amounts are explored as particle plumes evolve from varying amounts of AgI released, and within changing environmental conditions, including changes in liquid water content (LWC) along and downwind of the seeding track, wind speed, and shear. More AgI did not necessarily produce more liquid equivalent snowfall (LESnow). The greatest amount of LESnow, largest area covered by snowfall, and highest peak snowfall produced through seeding occurred on the day with the largest and most widespread occurrence of supercooled drizzle, highest wind shear, and greater LWC along and downwind of the seeding track. The day with the least supercooled drizzle and the lowest LWC downwind of the seeding track produced the smallest amount of LESnow through seeding. The stronger the wind, the farther away the snowfall occurred from the seeding track.

Mobile Microwave Radiometer Observations: Spatial Characteristics of Supercooled Cloud Water and Cloud Seeding Implications

1995 ◽  
Vol 34 (2) ◽  
pp. 432-446 ◽  
Author(s):  
Arlen W. Huggins
Keyword(s):  
Liquid Water ◽  
Microwave Radiometer ◽  
Particle Growth ◽  
Supercooled Liquid ◽  
Winter Storms ◽  
Stable Conditions ◽  
Research Aircraft ◽  
Orographic Clouds ◽  
Liquid Depth ◽  
Windward Slope

Abstract Previous studies of the spatial distribution of supercooled liquid water in winter storms over mountainous terrain were performed primarily with instrumented aircraft and to a lesser extent with scans from a stationary microwave radiometer. The present work describes a new technique of mobile radiometer operation that was successfully used during numerous winter storms that occurred over the Wasatch Plateau of central Utah to determine the integrated depth of cloud liquid water relative to horizontal position on the mountain barrier. The technique had the advantage of being able to measure total liquid from the terrain upward, without the usual terrain avoidance problems that research aircraft face in cloudy conditions. The radiometer also collected data during several storms in which a research aircraft could not be operated because of severe turbulence and icing conditions. Repeated radiometer transects of specific regions of the plateau showed significant variability in liquid water depth over 30–60-min time periods, but also revealed that the profile of orographically generated cloud liquid was consistent, regardless of the absolute quantities. Radiometer liquid depth generally increased across the windward slope of the plateau to a peak near the western edge of the plateau top and then decreased across the relatively flat top of the plateau. These observations were consistent with regions where maximum and minimum vertical velocities were expected, and with depiction of cloud liquid by accretional ice particle growth across the mountain barrier. A comparison of data from the mobile radiometer and a stationary radiometer verified the general decrease in liquid depth from the windward slope to the top of the plateau and also showed that many liquid water regions were transient mesoscale features that moved across the plateau. Implications of the results, relative to the seeding of orographic clouds, were that seeding aerosols released from valley-based generators could at times be inhibited by stable conditions from reaching appropriate super-cooled liquid water regions and, as found by others, the region of cloud most likely to be encountered by an AgI seeding agent released from the ground was also relatively warm compared to the ice-forming capability of the particular agent used in these experiments. Also, one convective case study that exhibited relatively warm temperatures in the cloud layer indicated that, even in conditions that permit vertical transport to supercooled liquid zones, sufficient time for ice particle growth and fallout from seeded plumes on this plateau may be lacking.

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 Observing ice particle growth along fall streaks in mixed-phase clouds using spectral polarimetric radar data

2018 ◽  
Vol 18 (11) ◽  
pp. 7843-7862 ◽  
Author(s):  
Lukas Pfitzenmaier ◽  
Christine M. H. Unal ◽  
Yann Dufournet ◽  
Herman W. J. Russchenberg
Keyword(s):  
Particle Growth ◽  
Supercooled Liquid ◽  
Radar Data ◽  
Detection Algorithm ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Liquid Droplets ◽  
Growth Processes ◽  
Retrieval Technique ◽  
Mixed Phase Clouds

Abstract. The growth of ice crystals in presence of supercooled liquid droplets represents the most important process for precipitation formation in the mid-latitudes. However, such mixed-phase interaction processes remain relatively unknown, as capturing the complexity in cloud dynamics and microphysical variabilities turns to be a real observational challenge. Ground-based radar systems equipped with fully polarimetric and Doppler capabilities in high temporal and spatial resolutions such as the S-band transportable atmospheric radar (TARA) are best suited to observe mixed-phase growth processes. In this paper, measurements are taken with the TARA radar during the ACCEPT campaign (analysis of the composition of clouds with extended polarization techniques). Besides the common radar observables, the 3-D wind field is also retrieved due to TARA unique three beam configuration. The novelty of this paper is to combine all these observations with a particle evolution detection algorithm based on a new fall streak retrieval technique in order to study ice particle growth within complex precipitating mixed-phased cloud systems. In the presented cases, three different growth processes of ice crystals, plate-like crystals, and needles are detected and related to the presence of supercooled liquid water. Moreover, TARA observed signatures are assessed with co-located measurements obtained from a cloud radar and radiosondes. This paper shows that it is possible to observe ice particle growth processes within complex systems taking advantage of adequate technology and state of the art retrieval algorithms. A significant improvement is made towards a conclusive interpretation of ice particle growth processes and their contribution to rain production using fall streak rearranged radar data.

scholarly journals Estimating the Fraction of Winter Orographic Precipitation Produced under Conditions Meeting the Seeding Criteria for the Wyoming Weather Modification Pilot Project

2015 ◽  
Vol 54 (6) ◽  
pp. 1202-1215 ◽  
Author(s):  
Jaclyn M. Ritzman ◽  
Terry Deshler ◽  
Kyoko Ikeda ◽  
Roy Rasmussen
Keyword(s):  
Climate Model ◽  
Dynamical Downscaling ◽  
Winter Precipitation ◽  
State Legislature ◽  
Atmospheric Conditions ◽  
Cloud Seeding ◽  
Weather Modification ◽  
Orographic Clouds ◽  
Glaciogenic Seeding ◽  
The Impact

AbstractAnnual precipitation increases of 10% or more are often quoted for the impact of winter orographic cloud seeding; however, establishing the basis for such values is problematic for two reasons. First, the impact of glaciogenic seeding of candidate orographic storms has not been firmly established. Second, not all winter precipitation is produced by candidate “seedable” storms. Addressing the first question motivated the Wyoming state legislature to fund a multiyear, crossover, randomized cloud-seeding experiment in southeastern Wyoming to quantify the impact of glaciogenic seeding of wintertime orographic clouds. The crossover design requires two barriers, one randomly selected for seeding, for comparisons of seeded and nonseeded precipitation under relatively homogeneous atmospheric conditions. Addressing the second question motivated the work here. The seeding criteria—700-hPa temperatures ≤−8°C, 700-hPa winds between 210° and 315°, and the presence of supercooled liquid water—were applied to eight winters to determine the percent of winter precipitation that may fall under the seeding criteria. Since no observational datasets provide precipitation and all of the atmospheric variables required for this study, a regional climate model dynamical downscaling of historical data over 8 years was used. The accuracy of the model was tested against several measurements, and the small model biases were removed. On average, ~26% of the time between 15 November and 15 April atmospheric conditions were seedable over the barriers in southeastern Wyoming. These seedable conditions were accompanied by precipitation ~12%–14% of the time, indicating that ~27%–30% of the winter precipitation resulted from seedable clouds.

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.

The Mystery of Ice Crystal Multiplication in a Laboratory Experiment

2013 ◽  
Vol 71 (1) ◽  
pp. 89-97 ◽  
Author(s):  
Gianni Santachiara ◽  
Franco Belosi ◽  
Franco Prodi
Keyword(s):  
Laboratory Experiment ◽  
Supercooled Liquid ◽  
Ice Crystals ◽  
Formation Processes ◽  
Ice Crystal ◽  
Droplet Vaporization ◽  
Ice Nuclei ◽  
Cold Room ◽  
The Mean ◽  
Ice Multiplication

Abstract This paper addresses the problem of the large discrepancies between ice crystal concentrations in clouds and the number of ice nuclei in nearby clear air reported in published papers. Such discrepancies cannot always be explained, even by taking into account both primary and secondary ice formation processes. A laboratory experiment was performed in a cylindrical column placed in a cold room at atmospheric pressure and temperature in the −12° to −14°C range. Supercooled droplets were nucleated in the column, in the absence of aerosol ice nuclei, by injecting ice crystals generated outside in a small syringe. A rapid increase in the ice crystal concentration was observed in the absence of any known ice multiplication. The ratio between the mean number of ice crystals in the column, after complete droplet vaporization, and the number of ice crystals introduced in the column was about 10:1. The presence of small ice crystals (introduced at the top of the column) in the unstable system (supercooled droplets) appears to trigger the transformation in the whole supercooled liquid cloud. A possible explanation could be that the rapidly evaporating droplets cool sufficiently to determine a homogeneous nucleation.

scholarly journals How frequent is natural cloud seeding from ice cloud layers ( < −35 °C) over Switzerland?

2021 ◽  
Vol 21 (6) ◽  
pp. 5195-5216
Author(s):  
Ulrike Proske ◽  
Verena Bessenbacher ◽  
Zane Dedekind ◽  
Ulrike Lohmann ◽  
David Neubauer
Keyword(s):  
Prediction Models ◽  
Water Cycle ◽  
Weather Prediction ◽  
Ice Crystals ◽  
Occurrence Frequency ◽  
Climate Projections ◽  
Cirrus Cloud ◽  
Cloud Seeding ◽  
Cloud Properties ◽  
Layer Cloud

Abstract. Clouds and cloud feedbacks represent one of the largest uncertainties in climate projections. As the ice phase influences many key cloud properties and their lifetime, its formation needs to be better understood in order to improve climate and weather prediction models. Ice crystals sedimenting out of a cloud do not sublimate immediately but can survive certain distances and eventually fall into a cloud below. This natural cloud seeding can trigger glaciation and has been shown to enhance precipitation formation. However, to date, an estimate of its occurrence frequency is lacking. In this study, we estimate the occurrence frequency of natural cloud seeding over Switzerland from satellite data and sublimation calculations. We use the DARDAR (radar lidar) satellite product between April 2006 and October 2017 to estimate the occurrence frequency of multi-layer cloud situations, where a cirrus cloud at T < −35 ∘C can provide seeds to a lower-lying feeder cloud. These situations are found to occur in 31 % of the observations. Of these, 42 % have a cirrus cloud above another cloud, separated, while in 58 % the cirrus is part of a thicker cloud, with a potential for in-cloud seeding. Vertical distances between the cirrus and the lower-lying cloud are distributed uniformly between 100 m and 10 km. They are found to not vary with topography. Seasonally, winter nights have the most multi-layer cloud occurrences, in 38 % of the measurements. Additionally, in situ and liquid origin cirrus cloud size modes can be identified according to the ice crystal mean effective radius in the DARDAR data. Using sublimation calculations, we show that in a significant number of cases the seeding ice crystals do not sublimate before reaching the lower-lying feeder cloud. Depending on whether bullet rosette, plate-like or spherical crystals were assumed, 10 %, 11 % or 20 % of the crystals, respectively, could provide seeds after sedimenting 2 km. The high occurrence frequency of seeding situations and the survival of the ice crystals indicate that the seeder–feeder process and natural cloud seeding are widespread phenomena over Switzerland. This hints at a large potential for natural cloud seeding to influence cloud properties and thereby the Earth's radiative budget and water cycle, which should be studied globally. Further investigations of the magnitude of the seeding ice crystals' effect on lower-lying clouds are necessary to estimate the contribution of natural cloud seeding to precipitation.

Sign in / Sign up

Export Citation Format

Share Document