HR: 08:30h
AN: SA21B-03 INVITED     [Abstracts]
TI: Imaging and Analysis of Meteoritic Smoke Particles Collected in the Mesosphere
AU: * Stroud, R M
EM: stroud@nrl.navy.mil
AF: Materials Science and Technology Division, Naval Research Laboratory, 4555 Overlook Avenue, Washington, DC 20375 United States
AU: Giovane, F
EM: frank.giovane@nrl.navy.mil
AF: Space Sciences Division, Naval Research Laboratory, 4555 Overlook Avenue, Washington, DC 20375 United States
AU: Waldemarsson, T
EM: twaldemarsson@yahoo.com
AF: Department of Meteorology, Stockholm University, Svante Arrhenius v„g 12, Stockholm, 10691 Sweden
AB: Most of the 10 to 100 tons of meteoritic material incident daily on the Earth's atmosphere is predicted to vaporize and recondense as nanoparticles in the mesosphere. Although the presence of the recondensed meteoritic smoke particles has long been suspected, they have not been directly observed. Here we discuss the successful collection of nanometer sized smoke particles on transmission electron microscopy sample grids as part of the rocket-based MAGIC experiment. Analysis of the grids using high-angle annular dark-field imaging (HAADF) revealed abundant particles in the 1 to 3-nm-diameter size range on collection grids exposed at altitudes between 70 and 97 km. In order to understand the formation and evolution of the smoke particles and their effect on atmospheric processes, detailed information about the particle sizes, morphologies and compositions is required. We are using transmission electron microscopy, including high-resolution imaging, HAADF imaging and energy dispersive x-ray spectroscopy to obtain these data as a function of collection altitude. The preliminary results show that many of the 1 to 3-nm particles are clustered in fluffy agglomerates, 10's to 1,000's of nm's across, and that these are primarily composed of Si and O. Other particle morphologies are present, including: isolated 5 to 10 nm particles, incompletely ablated 50 to 250 nm monolithic particles, holes left by particles that breached the collection film, and rings of particles indicating evaporation of liquid droplets. Witness grids that were flown but not exposed, show no particles other than a few isolated micrometer-sized particles (< 10 per collection grid) that we attribute to terrestrial dust. The diverse morphologies of the collected material must result from diverse origins and atmospheric processes. That the most abundant observed particles are in the 1 to 3-nm size range is generally consistent with the predictions of the standard Community Aerosol and Radiation Model for Atmospheres (CARMA), which predicts an exponentially decreasing particle abundance with increasing size. However, the absolute abundance observed (>10⁶ cm^-3) is greater than predicted by several orders of magnitude.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 3332 Mesospheric dynamics
SC: SPA-Aeronomy [SA]
MN: Fall Meeting 2005