The mesospheric metal layer topside: a possible connection to meteoroids J. Höffner1 and J. S. Friedman2 1Leibniz-Institute of Atmospheric Physics, Kühlungsborn, Germany 2National Astronomy and Ionosphere Center, Arecibo Observatory, Arecibo, Puerto Rico
Abstract. In the past, many studies have been carried out to demonstrate the influence
of meteoroids on the atmospheric metal layer, observed roughly in the
altitude range 80–105 km. Even with the capability of present day
resonance lidars to measure metal densities within single meteor trails, it
has been difficult to prove any influence of meteors on the average metal
layer. In contrast to approaches taken earlier, we discuss here the seasonal
characteristics of potassium, calcium, calcium ion, iron and sodium above
110 km altitude where the average nocturnal densities are so low that the
existence of a baseline level of metal atoms and ions is often overlooked.
By comparing simultaneous and common-volume observations of different metal
layers at one location, we demonstrate that despite their different seasonal
characteristics at lower altitudes remarkably similar seasonal
characteristics are observed at higher altitudes. In addition, a qualitative
agreement is also found for potassium at different latitudes. A comparison
of metal densities at 113 km altitude with known meteor showers indicates a
strong influence of shower meteoroids on the topside of the metal layers.
Simultaneous observations of K along with Ca, Fe and/or Na permit the
calculation of abundance ratios, which at 113 km altitude are quite similar
to values measured in single meteor trails by ground based lidars.
Furthermore, the increase in densities throughout summer is strong evidence
for the influence of sporadic meteoroids on the high metal layers. This
increase correlates well with the seasonal variation of sporadic micrometeor
input independent of meteor showers. Given these evidences, we contend that
there is a direct influence of ablating meteoroids on the topside of the
mesospheric metal layer.
Citation: Höffner, J. and Friedman, J. S.: The mesospheric metal layer topside: a possible connection to meteoroids, Atmos. Chem. Phys., 4, 801-808, doi:10.5194/acp-4-801-2004, 2004.