HR: 16:45h
AN: SA42B-04    [PDF]
TI: Interactions between polar mesospheric clouds and the meteoric metal layers
AU: Murray, B J
EM: b.murray@uea.ac.uk
AF: University of East Anglia, School of Environmental Sciences, Norwich, NR4 7TJ United Kingdom
AU: * Plane, J M
EM: j.plane@uea.ac.uk
AF: University of East Anglia, School of Environmental Sciences, Norwich, NR4 7TJ United Kingdom
AB: Polar mesospheric clouds overlap in altitude with the layers of metal atoms that are produced by the ablation of meteoroids entering the atmosphere. This paper will examine several of the probable interactions between PMCs and metals. The Fe layer exhibits "bite-outs" where essentially all of the Fe atoms in the vicinity of a strong PMC are removed. Na and K atoms disappear completely below 90 km in the high-latitude summer mesosphere, and the undersides of these layers exhibit extremely small scale-heights. These features indicate that the metals are removed rapidly from the gas phase by adsorption on the ice particles, at a rate that exceeds their replenishment by meteoric ablation and vertical transport. It has been speculated that the incorporation of these metals into the ice lowers the photoelectric work function sufficiently to explain the observation of positively-charged ice particles. Another very interesting possibility is that metal-containing molecules actually provide the condensation nuclei for forming ice particles at the mesopause. In this paper we will report new laboratory studies of the uptake of Fe, Na and K on low-temperature ice, and a measurement of the photo-electric work function of Na in ice. An atmospheric model incorporating the experimental results will be used to address the nucleation problem, and also to show that the metal depletions are indeed explained by heterogeneous uptake. An important conclusion is that there appears to be a permanent layer of small (less than 20 nm) particles above 85 km throughout mid-summer at high latitudes.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0340 Middle atmosphere--composition and chemistry
SC: SPA - Aeronomy [SA]
MN: 2003 Fall Meeting