Dissipation of marine stratiform clouds and collapse of the marine boundary layer due to the depletion of cloud condensation nuclei by clouds.

When the production of cloud condensation nuclei in the stratocumulus-topped marine boundary layer is low enough, droplet collisions can reduce concentrations of cloud droplet numbers to extremely low values. At low droplet concentrations a cloud layer can become so optically thin that cloud-top radiative cooling cannot drive vertical mixing. Under these conditions, model simulations indicate that the stratocumulus-topped marine boundary layer collapses to a shallow fog layer. Through this mechanism, marine stratiform clouds may limit their own lifetimes.

Kuwait oil fires: correction.

In our article "Airborne studies of the smoke from the Kuwait oil fires" (15 May, p. 987) (1), we stated that the depletions of sulfur dioxide (SO(2)) and nitrogen oxides (NO(x)) in the smoke plume from the Kuwait oil fires were 50 and 60% per hour, respectively. These values were derived from measurements made aboard a Convair C-131 aircraft, and measurements of CO(2) were used as a conserved tracer. Subsequent comparisons of these measurements of CO(2) (which were obtained from a continuous analyzer) with independent measurements of CO(2) (obtained from "grab" samples) revealed that the continuous CO(2) measurements were occasionally contaminated by cabin air. Recalculation of the depletion rates of SO(2) and NO(x), with the use of uncontaminated measurements of CO(2) from the "grab" sampler aboard the aircraft yielded values of 6 and 22%, respectively (2). Our conclusions with regard to the climatic effects of the Kuwait oil fires are unchanged.

Airborne studies of the smoke from the kuwait oil fires.

Airborne studies of smoke from the Kuwait oil fires were carried out in the spring of 1991 when approximately 4.6 million barrels of oil were burning per day. Emissions of sulfur dioxide were approximately 57% of that from electric utilities in the United States; emissions of carbon dioxide were approximately 2% of global emissions; emissions of soot were approximately 3400 metric tons per day. The smoke absorbed approximately 75 to 80% of the sun's radiation in regions of the Persian Gulf. However, the smoke probably had insignificant global effects because (i) particle emissions were less than expected, (ii) the smoke was not as black as expected, (iii) the smoke was not carried high in the atmosphere, and (iv) the smoke had a short atmospheric residence time.

Radar detection of cloud-seeding effects.

The effects on precipitation of artificially seeding clouds with Dry Ice have been monitored from cloud to ground with a radar that has a wavelength of 8.6 millimeters.

Airborne studies of the emissions from the volcanic eruptions of mount st. Helens.

The concentrations of particles less than 10 micrometers in diameter in the ash emissions from Mount St. Helens have been more than 1000 times greater than those in the ambient air. Mass loadings of particles less than 2 micrometers in diameter were generally several hundred micrograms per cubic meter. In the ash clouds, produced by the large eruption on 18 May 1980, the concentrations of several trace gases generally were low. In other emissions, significant, but variable, concentrations of sulfur gases were measured. The 18 May eruption produced nuées ardentes, lightning flashes, and volcanic hail.

Eruptions of the st. Augustine volcano: airborne measurements and observations.

Airborne measurements of the effluents from the St. Augustine volcano obtained during a 10-day period of activity showed that aerosol was ejected at the rate of about 10(5) kilograms per second during brief eruptions (3 to 8 minutes). Steadier emissions contained much more water vapor and gaseous sulfur but less aerosol mass. A nuée ardente (glowing avalanche) produced by one eruption reached a maximum average speed of about 50 meters per second.

Cloud condensation nuclei on the atlantic seaboard of the United States.

Concentrations of cloud condensation nuclei measured along the East Coast from Virginia to Long Island ranged from 1000 to 3500 per cubic centimeter as compared to 100 per cubic centimeter in clean maritime air and 300 per cubic centimeter in continental air. The global anthropogenic production rate of cloud condensation nuclei may be comparable to the natural production rate; in some industrial areas cloud condensation nuclei are dominated by anthropogenic sources.

Atmospheric Effects of Pollutan: Pollutants which affect clouds are most likely to produce modifications in weather and climate.

We have argued that aerosols are probably the principal agents by which pollutants may affect weather and climate. They are most likely to act by influencing the structure and distribution of clouds. On the local scale, the effects of pollutants on some aspects of weather are unmistakable. The effects of man-made pollutants on global climate are a matter of debate, but they may already be significant.

Redistribution of Snowfall across a Mountain Range by Artificial Seeding: A Case Study.

Clouds over the western slopes of the Cascade Mountains were artificially seeded to reduce the riming and fall speeds of snow crystals and to divert snowfall across the crest. Aircraft observations showed that the clouds were glaciated by the seeding. The crystal habits and the degrees of riming of snow crystals reaching the target area were modified. Snowfall rates decreased at the crest and simultaneously increased 20 kilometers east of the crest.

Subsurface phenomena and the splashing of drops on shallow liquids.

High-speed movies have been taken of the formation of the sub-surface cavity and of the Rayleigh jet formed during the splash of a drop on a shallow liquid. They show that the initial increase and subsequent decrease in the rate of rise of the jet and the maximum jet height with decreasing depth of liquid are the result of the interaction of the subsurface cavity with the solid boundary beneath the liquid. This interaction modifies considerably the pressure gradients in the liquid during the formation and collapse of the cavity.

Cloud condensation nuclei from a simulated forest fire.

Measurements made downwind of a simulated forest fire showed that the concentration of cloud condensation nuclei active at a supersaturation of 1 percent was increased by a factor of about 2.5. Smaller increases were observed at lower supersaturations.

Splashing of drops on shallow liquids.

The events that follow the splashing of a drop on a liquid depend on the depth of the liquid. When the depth is less than about 5 millimeters the crown that is ejected is more unstable than that from a splash on a deep liquid. As the depth is decreased from 25 to 7 millimeters, there is an increase in the maximum height to which the Rayleigh jet rises, and in the number of drops that break away from the jet. With depths less than 7 millimeters these two quantities fall off sharply, and no jet drops are produced for depths less than about 3 millimeters.

Splashing of a water drop.

Measurements have been made of the number of spray droplets produced by the impact of a water drop on water, and of the charge to mass ratio for these droplets. For a drop 3 millimeters in diameter, the number of spray droplets increases linearly with the fall-distance of the drop over the range 10 to 200 centimeters. When the drop falls 100 centimeters, about 25 spray droplets are produced. The majority of the droplets carry a negative charge, and the ratio of the charge to the mass varies from 4 to 28 electrostatic units per gram.