The mesospheric metal layer topside: a possible connection to meteoroids

[摘要] In the past, many studies have been carried out to demonstrate the influenceof meteoroids on the atmospheric metal layer, observed roughly in thealtitude range 80–105 km. Even with the capability of present dayresonance lidars to measure metal densities within single meteor trails, ithas been difficult to prove any influence of meteors on the average metallayer. In contrast to approaches taken earlier, we discuss here the seasonalcharacteristics of potassium, calcium, calcium ion, iron and sodium above110 km altitude where the average nocturnal densities are so low that theexistence of a baseline level of metal atoms and ions is often overlooked.By comparing simultaneous and common-volume observations of different metallayers at one location, we demonstrate that despite their different seasonalcharacteristics at lower altitudes remarkably similar seasonalcharacteristics are observed at higher altitudes. In addition, a qualitativeagreement is also found for potassium at different latitudes. A comparisonof metal densities at 113 km altitude with known meteor showers indicates astrong influence of shower meteoroids on the topside of the metal layers.Simultaneous observations of K along with Ca, Fe and/or Na permit thecalculation of abundance ratios, which at 113 km altitude are quite similarto values measured in single meteor trails by ground based lidars.Furthermore, the increase in densities throughout summer is strong evidencefor the influence of sporadic meteoroids on the high metal layers. Thisincrease correlates well with the seasonal variation of sporadic micrometeorinput independent of meteor showers. Given these evidences, we contend thatthere is a direct influence of ablating meteoroids on the topside of themesospheric metal layer.

[学科分类] 大气科学