Speaker
Description
The ablation of meteoroids entering a planetary atmosphere is the critical process which produces layers of metal atoms and ions, as well as the meteoric smoke particles which act as condensation nuclei for middle atmospheric clouds. Ablation has been modelled in the past by coupling the classical equations of meteor physics to a thermodynamic model of a high temperature silicate melt, and assuming Langmuir evaporation of the constituent elements into a vacuum. A current example of such a model is the Chemical Ablation Model (CABMOD), developed at the University of Leeds. CABMOD successfully predicts the differential ablation which is inferred from the relative abundances of the layers of Na, Fe and Ca atoms in the terrestrial mesosphere, and the time-resolved variation of radar head echoes. The underlying assumptions of CABMOD have been tested using the Meteoric Ablation Simulator (MASI) developed at Leeds. In this apparatus, meteoritic analogues of cosmic dust are flash heated to over 2800 K in a few seconds, simulating the particle heating profile that would be experienced by a meteoroid of specified mass, entry angle and velocity would experience. The evaporation of metals is measured in real time by time-resolved laser induced fluorescence spectroscopy. In this presentation I will describe the development of the CABMOD model, and how it might be developed to treat the ablation of particles larger than a few hundred microns in size.
I will then discuss the requirements for global modelling of the evolution, transport and chemical impacts of space debris ablation products. In the past we have used a 3-D chemistry-climate model to simulate the transport and deposition of plutonium-238 oxide nanoparticles formed after the ablation of a power unit in the upper stratosphere (~11°S) in 1964. The model reproduces both the observed hemispheric asymmetry and time scale of Pu-238 deposition. More recently we have used the Whole Atmosphere Community Climate Model (WACCM), coupled with a sectional aerosol model, to study the transport of meteoric smoke particles from the upper mesosphere to the surface, including the processing of these particles in the stratosphere. Models of this type can be used to assess the likely atmospheric impacts of increased space debris re-entry over the next few decades.
