Radiatively driven dynamics of the plume from 1991 Kuwait oil fires

Abstract

Optical properties of the aerosol from the 1991 Kuwait oil fires are calculated using measured aerosol size distributions and a spectral refractive index based on the measured chemical composition of the particulate matter. At a wavelength of 538 nm the calculated light-scattering coefficient agrees well with measurements, but the calculated single-scattering albedo is systematically higher by about 18% than the measured value. Radiative transfer calculations indicate maximum net daytime heating rates of 94 and 56 K d -• for smoke 1 and 3 hours downwind of the fires, respectively. In the upper regions of the plume, where the calculated heating rates decrease with height, a radiative-convective mixed layer developed. There was no significant temperature inversion at the top of this layer, which allowed rapid entrainment of air into the top of the plume, causing it to thicken at an observed rate of ~ 0.1 rn s -•. In addition, radiative heating of the plume as a whole caused it to lift as a unit at a measured rate of ~ 0.1 rn s -• during the first few hours of plume evolution. A theory, based on mixed layer modeling and a scale analysis of the equations of motion, is presented that successfully reproduces the two rates of vertical transport. This model of the dynamics of a radiatively heated plume can be used to predict the evolution and lofting of large composite smoke plumes, such as those from forest fires; it also has implications for the transport, lifetime, and climatic importance of smoke generated on continental scales. 18,80918,810 HERRING AND HOBBS' PLUME DYNAMICS OF KUWAIT OIL FIRES Section 4 contains a brief description of the radiative transfer model that we used to calculate heating rates of the smoke. Vertical profiles of the heating rate are calculated for several different hypothetical smoke distributions to examine how the location and magnitude of the heating was affected by changes in smoke concentration. Heating rates are also calculated for two vertical cross sections of the smoke plume from the Kuwait oil fires and are compared to measurements reported by Pilewsla'e and Valero [ 1992].Solar heating of the smoke from the Kuwait fires played a major role in the dynamical evolution of the smoke plume. In section 5 we examine various theories for the interactions between radiative heating and plume dynamics. Lilly's [1988] analysis of the dynamics of upper tropospheric cirrus clouds heated by terrestrial radiation is found to provide a useful model of the Kuwait smoke plume.One of the most valuable flight patterns conducted with the Convair C-131A was designed to track the smoke plume in a Lagrangian fashion. In section 6 we describe the results from one of these flights in some detail. Not only does this flight provide important insights into the dynamics of the plume but it is also the source of much important data on the chemical evolution of the gas phase and aerosol constituents of the plume. Using our calculated heating rates, we estimate the self-lofting and entrainment rates of the Kuwai...

A case study of pyro-convection using transport model and remote sensing data

“…Similar processes have been observed to be effective in tropical pyroconvection (Andreae et al, 2004). Furthermore, the radiation absorption by black carbon particles emitted by the fires and the associated heating of the atmosphere above the cloud tops could lead to further lifting after the initial convective injection into the UT/LS region (Westphal and Toon, 1991;Herring and Hobbs, 1994;Trentmann et al, 2002). While the relative importance of these different mechanisms is not clear, several recent papers have presented dedicated case studies of pyro-convection events (Fromm and Servranckx, 2003;Fromm et al, 2005), or cases that can likely be explained by pyro-convection although the authors did not explicitly suggest pyro-convection to be the transport mechanism (Livesey et al, 2004;Jost et al, 2004).…”

Characterisation of episodic aerosol types over the Australian continent

“…4.3 above. A comparably low single scattering albedo of 0.66 at 538 nm was found by Herring and Hobbs (1994) for the plume arising from the Kuwait oil fires following the 1991 Gulf War. In addition, Omar et al (2005) identified a cluster labelled "dirty pollution" with a single scattering albedo of 0.72 at 673 nm.…”

Dependence of solar radiative forcing of forest fire aerosol on ageing and state of mixture

“…Herring and Hobbs (1994) use airborne measurements of the microphysical and optical particle properties inside the plume to calculate an instantaneous net heating rate of up to 3.9 K/h at 1 h and 2.3 K/h at 3 h plume age for a solar zenith angle of 6 • . The observed lapse rate was stable at the bottom of the plume and almost neutral at the top while the whole plume ascended with a rate of ≈0.1 m/s.…”

“…To obtain an estimate of the applicability of the theory used by Herring and Hobbs (1994), the radiative transfer model of Wendisch et al (2002) was employed to calculate the net instantaneous heating rate within the LACE 98 plume assuming scenario 2, a plume age of 3 days, an external mixture of absorbing and non-absorbing components and the same soot volume fraction as inferred over Lindenberg. This choice of parameters results in a maximum likelihood estimate for the heating rate at this plume age since this scenario reproduces the aerosol observed in the lower sub-layer.…”