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.     

Heterogeneous reaction probabilities, solubilities, and the physical state of cold volcanic aerosols

On 19 January 1992, heterogeneous loss of HNO(3), ClNO(3), and HCl was observed in part of the Mount Pinatubo volcanic cloud that had cooled as a result of forced ascent. Portions of the volcanic cloud froze near 191 kelvin. The reaction probability of ClNO(3) and the solubility of HNO(3) were close to laboratory measurements on liquid sulfuric acid. The magnitude of the observed loss of HCl suggests that it underwent a heterogeneous reaction. Such reactions could lead to substantial loss of HCl on background sulfuric acid particles and so be important for polar ozone loss.     

Automatic detection of lameness in dairy cattle—Vision-based trackway analysis in cow's locomotion

The occurrence of lameness in dairy cattle is of increasing importance in herd health management and herd productivity. Current practice, involves visual observation by human experts to score cow's locomotion in order to estimate the lameness in the herd. The trackway defined as “hind hoof compared to fore hoof position” is one of the main components to score the locomotion. However, because of the time-consuming observation method, lame cows are undiagnosed until the problem has become severe. Up till now there is no automatic (visual) method for detecting lameness in dairy cattle. The objective of our study was to make an automatic system for continuous on-farm detection and prediction of lameness in the farm by using vision techniques. The current focus was on demonstrating the possibility of capturing cow's hoof locations by vision and strong correlation between automatically calculated hoof trackway and visual locomotion scores. Fifteen selected lactating cows were scored visually by four trained observers at the Gent University Research Farm. Scoring varied from 1 (normal walking) to 5 (extremely lame). Side-view images with resolution of 1024 × 768 pixels were recorded when cows passed an experimental set-up freely. Recorded videos were split into sequences of bitmap images. After background subtraction, binary image operations, calibration and hoof separation, the trackway information containing hoof location in the real world and its related time in the video was calculated. The accuracy of automatically captured results was checked by comparing with the output from manually labeled hoof locations. The mean correlation coefficient of all measurements was 94.8%. Hence, the results suggest that the automatic method by vision analysis is feasible to present the cows’ real locomotion situations. The first result showed a positive linear relationship between cows’ trackways overlap and locomotion scores by human visualization. This research proved that vision techniques have great potential to be used for continuous quantification of lameness in cows.     

Ozone and aerosol changes during the 1991-1992 airborne arctic stratospheric expedition

Stratospheric ozone and aerosol distributions were measured across the wintertime Arctic vortex from January to March 1992 with an airborne lidar system as part of the 1992 Airborne Arctic Stratospheric Expedition (AASE II). Aerosols from the Mount Pinatubo eruption were found outside and inside the vortex with distinctly different distributions that clearly identified the dynamics of the vortex. Changes in aerosols inside the vortex indicated advection of air from outside to inside the vortex below 16 kilometers. No polar stratospheric clouds were observed and no evidence was found for frozen volcanic aerosols inside the vortex. Between January and March, ozone depletion was observed inside the vortex from 14 to 20 kilometers with a maximum average loss of about 23 percent near 18 kilometers.     

Environmental effects of an impact-generated dust cloud: implications for the cretaceous-tertiary extinctions

A model of the evolution and radiative effects of a debris cloud from a hypothesized impact event at the Cretaceous-Tertiary boundary suggests that the cloud could have reduced the amount of light at the earth's surface below that required for photosynthesis for several months and, for a somewhat shorter interval, even below that needed for many animals to see. For 6 months to 1 year, the surface would cool; the oceans would cool only a few degrees Celsius at most, but the continents might cool a maximum of 40 Kelvin. Extinctions in the ocean may have been caused primarily by the temporary cessation of photosynthesis, but those on land may have been primarily induced by a combination of lowered temperatures and reduced light.     

Climatic change on Mars

The equatorial sinuous channels on Mars detected by Mariner 9 point to a past epoch of higher pressures and abundant liquid water. Advective instability of the martian atmosphere permits two stable climates-one close to present conditions, the other at a pressure of the order of 1 bar depending on the quantity of buried volatiles. Variations in the obliquity of Mars, the luminosity of the sun, and the albedo of the polar caps each appear capable of driving the instability between a current ice age and more clement conditions. Obliquity driving alone implies that epochs of much higher and of much lower pressure must have characterized martian history. Climatic change on Mars may have important meteorological, geological, and biological implications.     

Influence of solar heating and precipitation scavenging on the simulated lifetime of post--nuclear war smoke

The behavior of smoke injected into the atmosphere by massive fires that might follow a nuclear war was simulated. Studies with a three-dimensional global atmospheric circulation model showed that heating of the smoke by sunlight would be important and might produce several effects that would decrease the efficiency with which precipitation removes smoke from the atmosphere. The heating gives rise to vertical motions that carry smoke well above the original injection height. Heating of the smoke also causes the tropopause, which is initially above the smoke, to reform below the heated smoke layer. Smoke above the tropopause is physically isolated from precipitation below. Consequently, the atmospheric residence time of the remaining smoke is greatly increased over the prescribed residence times used in previous models of nuclear winter.