Plume material spreading

How far can plume material spread before it cools and becomes sluggish Initially, the plmne material is thick and spreads rapidly. Little cooling occurs away from the boundaries of the plume material and the centre of the ponded layer remains hot and fluid. Eventually, the plume material becomes thin enough that conduction becomes important. The time for a thickness of material to cool is... 

In addition to observations in Los Angeles, Blumenthal and White have reported measurements of a power-plant plume and an urban plume 35 and 46 km downwind from St. Louis, Nfissouri. Bgute 4-25 shows the evidence of extensive ozone buildup in the urban plume. Simultaneous measurements of scattering coefficient, 6>cat, trace the spread and dilution of suspended particulate material. It is interesting that in the urban plume, which spreads to 20 km in width, the ozone increases while the particulate matter decreases this suggests considerable photochemical production at an altitude of 750 m. Contrary to the statements of Davis and co-workers reported above, the power-plant plume causes a decrease, rather than an increase, in ozone. Nitric oxide in the plume reacts with the ozone as it mixes. This is clearly indicated by the distribution of particulate matter, which acts as a tracer. 

It can be seen from (A5) and (AlO) that the behaviour of an inviscid blob is qualitatively similar to that predicted by lubrication theory. The blob spreads quickly at first and slowly thereafter. The qualitative behaviour of a plume of plume material is understood from (A9). Initially, the vertical-to-horizontal aspect ratio of the blob is relatively large and the surrounding mantle resists flow. Eventually the blob becomes thin enough that lubrication theory applies. 

In this paper, we are mainly interested in the blob when it is about to pond that is, when it is thin and it has cooled somewhat so that its viscosity is higher than that of fresh plume material. These are the conditions for which lubrication theory applies. The blob is near this final state for much of its existence as the initial flow is fairly rapid. For somewhat cool plume material, which is a few tens of kilometres thick and has a spread over 1000 km, the criterion that II in (A9) is less than unity is likely to be satisfied and the scaling results in the text apply. 

As the viscosity of the normal mantle and that of plume material are unknown, we present scaling relationships for the spreading time of inviscid material. Truly inviscid material continues to spread forever. Here the plume material is fluid until conductive cooling increases its viscosity. Equating the cooling time in (12) to the spreading time from (A6) yields the ponding thickness for infinite radial flow ... 

Plumes disperse as they are transported downwind, which means that concentrations of released radionuclides would decrease with plume travel distance. Because dispersion causes plume materials (droplets, particles, gas molecules) to move away from the plume centerline by random steps, plume concentrations tend to assume normal (Gaussian) distributions in both the vertical and horizontal directions. The rate of spreading depends on atmospheric stability and is usually different in the vertical and horizontal directions. 

The information on the quantities of combusted materials, and on aerosol and elemental carbon production, which is collected in Tables II-V, has been combined in Table VI to derive the state of the atmosphere during the nuclear war. We assume that the war would last for only a few days the aerosol particles would also be given off to the atmosphere in such a short time. Most fire produced aerosol would initially be located between 30°N and 60 N, where most of the nuclear targets are located. If the nuclear explosions would occur over a period of three days, the fire plumes produced on the West and East coast of the US and over Europe (including the USSR) could cover most of the 30-60°N latitude belt, except the Pacific Ocean. This is based on an average westerly wind speed of 20 m/s in tbe middle and upper troposphere (Oort and Rasmussen, 1971). Spread in South-North direction within the latitude zone should... 

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