2007 Workshop:CEDAR Prize Lecture
The CEDAR Prize Lecture is nominated and presented each year at the CEDAR workshop.
For 2007, our Prize Lecturer is John Plane
Abstract: About 50 tonnes of interplanetary dust enters the earth’s atmosphere every day at speeds ranging from 11 to 72 km s-1. Impact with the atmosphere causes most of the dust to vaporize completely. This lecture will follow the fate of these dust particles (meteoroids) from the parent comet to the eventual deposition of their constituent elements in the polar ice caps. Along the way, the metals which ablate from meteoroids are involved in a very diverse range of atmospheric phenomena.
The lecture will start with a new kinetic and thermodynamic model of the process of meteoric ablation. Ablation is the source of the layers of metal atoms such as Na and Fe that occur in the upper mesosphere and lower thermosphere (MLT). These layers are observed with impressive vertical resolution by resonance lidars; complementary satellite measurements of metal atom resonance fluorescence in the earth’s dayglow can now be used to retrieve the layers globally. The metallic compounds and silica produced by ablation polymerise together and then agglomerate into meteoric “smoke” particles (MSPs). Laboratory studies of MSP mimics show that fractal-like particles grow very rapidly, driven by magnetic dipole attraction because of the high Fe content in the particles. MSPs are hypothesized to act as condensation nuclei for polar mesospheric (noctilucent) ice clouds in the upper mesosphere. Whether this is the case or not, what is known is that ice clouds efficiently remove metal atoms below 85 km during the summer at high latitudes, and this may also affect the charged state of the ice particles through efficient photo-electric emission. The only direct evidence so far for MSPs in the mesosphere is the measurement of heavy charged particles from rockets, although the quantitative interpretation of these measurements is challenging.
MSPs are also thought to nucleate sulphuric acid droplets in the stratosphere below 30 km, and meteoritic material is found at significant concentrations in Junge layer sulphate particles, especially in the winter polar vortex. The presence of MSPs has also been detected in polar ice cores from measurements of iridium and platinum, demonstrating that they provide a potentially useful tracer of transport from the MLT to the troposphere. The lecture will end by examining the theory that the paleo-proterozoic and neo-proterozoic “snowball Earth” glaciations were caused by the solar system moving through dusty interstellar clouds.
Chairs and Presenters
Monday, 8:30 - 9:15
Images, power point, pdf