Trace metals in atmospheric deposition: A review and assessment

Precipitation over Antarctica is an important climatic variable whose study has been limited by the frequent inability to discriminate between actual snow precipitation and drifting snow. Recent advances in point precipitation measurements promise to circumvent this problem. In addition, indirect estimates based upon the atmospheric water balance equation provide seasonal precipitation amounts for areas larger than 1×106 km². For broad-scale studies in the continental interior net snow accumulation closely approximates precipitation. Annual precipitation is relatively high over the marginal ice slopes in relation to amounts in the interior. This meridional distribution is due to the orographic lifting of moist air by the ice sheet. Zonal precipitation variations are related to the quasi-stationary cyclones in the circumpolar low-pressure trough. Most precipitation falls in winter, when the average moisture content of the air is low. The intensity of cyclonic activity is the key factor governing the amount of precipitation and its variations. Precipitation generation in coastal regions is strongly influenced by the fact that poleward moving, moist maritime air masses are deflected by the steep marginal ice slopes to blow parallel to the terrain contours. Direct orographic lifting with accompanying adiabatic cooling is the dominant precipitation formation mechanism inland of the 1-km elevation contour; intrusions of moist air far into the continent are accompanied by southerly winds through a deep tropospheric layer. Above 3000 m elevation where terrain slopes are gentle, radiative cooling is the primary mechanism by which saturation is maintained within moist air, and thus by which precipitation is formed. Most precipitation at these elevations falls from clear skies. This phenomenon does not differ from precipitation originating in clouds but is a direct result of the low moisture content of the air, and hence ice layers are optically too thin to be visible as clouds.

/pdf/snowfall-in-high-southern-latitudes-4aqsdkpwoc.pdf

Snowfall in high southern latitudes

A study of an outstanding Saharan dust event at the high-alpine site Jungfraujoch, Switzerland

[1] A field campaign designed to investigate the second indirect aerosol effect (reduction of precipitation by anthropogenic aerosols which produce more numerous and smaller cloud droplets) was conducted during winter in the northern Rocky Mountains of Colorado Combining remote sensing and in-situ mountain-top measurements it was possible to show higher concentrations of anthropogenic aerosols (∼1 μg m−3) altered the microphysics of the lower orographic feeder cloud to the extent that the snow particle rime growth process was inhibited, or completely shut off, resulting in lower snow water equivalent precipitation rates

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002GL016855

Mountaintop and radar measurements of anthropogenic aerosol effects on snow growth and snowfall rate

Chemistry of rainwater in the Massif Central (France): a strontium isotope and major element study

Last fall the National Research Council of the National Academy of Sciences published a report entitled, “Critical Issues in Weather Modification Research”. One of their conclusions was that “there is still no convincing scientific proof of the efficacy of international weather modification efforts. In some instances there are strong indications of induced changes, but this evidence has not been subject to tests of significance and reproducibility.” The report was very disappointing, with little support for operational cloud seeding. It showed little support for hail suppression and it was extremely short on its review of winter orographic cloud seeding. At the WMA semi-annual executive board meeting held in Reno, Nevada on October 17, 2003, there was a lively discussion about the report but little detail was known. It was concluded that the WMA needed to respond to the report and its conclusions. The board voted to charge Rick Stone, its president, with forming an ad-hoc committee to review the report and develop a statement reflecting the WMA position on the report. This was done in early November, with Bruce Boe, George Bomar, William Cotton, Byron Marler, Harold Orville and Joe Warburton being appointed as members. The committee solicited input from all members of the WMA before its meeting in early December in Fort Collins. The first draft was distributed to all members and further input invited. The committee received numerous comments and many additions and changes were made. The final report was completed in early February. A press release was issued in March. This WMA report is intended to provide an informed review to the membership and to the public and is now published on the WMA web page (www.weathermodification.org) as well as being published in this current WMA Journal. In addition the report has been sent to various political leaders, policy makers, and scientists in the U.S. and abroad.

https://arizonaskywatch.com/article/articles/Weather_Mod_Assn_Report_2004.pdf

The Weather Modification Association’s Response to the National Research Council’s Report Titled, “Critical Issues in Weather Modification Research”

Trace chemical analysis techniques have been used in a series of cloud-seeding experiments in the central Sierra Nevada with the ultimate purpose of distinguishing whether the submicron-sized aerosol particles used for seeding are removed by nucleation or by scavenging in snowfall. The research programs used submicron-sized seeding aerosols with different nucleating characteristics. When winter storms were seeded with silver iodide in the Lake Tahoe and Lake Almanor watersheds, positive correlations were observed between silver concentrations and precipitation amounts in both catchment areas.This is considered to be evidence that the AgI aerosols are not being removed in the snowfall entirely by scavenging processes. When two separate aerosols of silver iodide and indium sesquioxide were released simultaneously from the same ground locations during winter snowstorms in the Lake Almanor watershed, it was found that considerably more of the ice-nucleating aerosol particles (AgI) were removed by the...

Assessment of Seeding Effects in Snowpack Augmentation Programs: Ice Nucleation and Scavenging of Seeding Aerosols

Oxygen isotopic composition of Central Sierra Nevada precipitation, I. Identification of ice-phase water capture regions in winter storms

Results of lidar measurements of atmospheric ice crystal layers during 36 clear-sky precipitation events at South Pole (2850 m MSL) during the winter over the period March-November 1975 are presented and correlated with ice crystal replicator, radiosonde and visual data. Low-lying “precipitation” and higher “formation” layers were frequently discerned in the lidar returns. In 25% of the events a single surface layer was observed with intermittent or no higher layers present. It was determined from the backscatter profiles that the crystals were growing in the precipitation layer in more than 50% of the events. The average altitudes of the precipitation layer tops during austral night and day were 420 ± 130 m and 650 ± 170 m, respectively, while the average altitudes of the temperature inversion tops for the same two periods were 580 ± 200 m and 500 ± 150 m, respectively. The lidar returns for a few days before and a few days after sunrise (21 September) were unique; high, geometrically thick laye...

Lidar Determinations of Atmospheric Ice Crystal Layers at South Pole during Clear-Sky Precipitation

Trace chemical measurements of the silver content of snow have been used to investigate the transport and dispersion of silver iodide cloud seeding aerosols into and around two large target areas in the central Sierra Nevada between 1978 and 1992. The background concentration of silver in snow samples in this region is extremely low [BAg = 2.0 parts per trillion (ppt); standard deviation, σ = 1.0 ppt], and the silver from the seeding activities is readily detectable. The studies, in winter snowstorm conditions, show that targeting of the seeding aerosols was modest to poor with large variability both spatially and temporally. Analysis of several thousand snow samples over a period of several years has demonstrated that only 20% (average) of the precipitation that fell within the intended target area during seeding activities contained silver from the silver iodide seeding aerosol above the assigned “threshold” concentration of BAg + 2σ = 4.0 ppt. Targeting of one of the catchment areas under sout...

Joseph A. Warburton

Papers

The Weather Modification Association’s Response to the National Research Council’s Report Titled, “Critical Issues in Weather Modification Research”

Assessment of Seeding Effects in Snowpack Augmentation Programs: Ice Nucleation and Scavenging of Seeding Aerosols

Oxygen isotopic composition of Central Sierra Nevada precipitation, I. Identification of ice-phase water capture regions in winter storms

Lidar Determinations of Atmospheric Ice Crystal Layers at South Pole during Clear-Sky Precipitation

How the Transport and Dispersion of AgI Aerosols May Affect Detectability of Seeding Effects by Statistical Methods