 |
| Titel |
A time-resolved model of the mesospheric Na layer: constraints on the meteor input function |
| VerfasserIn |
J. M. C. Plane |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 4, no. 3 ; Nr. 4, no. 3 (2004-04-16), S.627-638 |
| Datensatznummer |
250001703
|
| Publikation (Nr.) |
 copernicus.org/acp-4-627-2004.pdf |
|
|
|
|
|
| Zusammenfassung |
| A time-resolved model of the Na layer in the mesosphere/lower thermosphere region is
described, where the continuity equations for the major sodium species Na, Na+ and NaHCO3
are solved explicity, and the other short-lived species are treated in steady-state. It is shown
that the diurnal variation of the Na layer can only be modelled satisfactorily if sodium species
are permanently removed below about 85 km, both through the dimerization of NaHCO3 and
the uptake of sodium species on meteoric smoke particles that are assumed to have formed
from the recondensation of vaporized meteoroids. When the sensitivity of the Na layer to the
meteoroid input function is considered, an inconsistent picture emerges. The ratio of the
column abundance of Na+ to Na is shown to increase strongly with the average meteoroid
velocity, because the Na is injected at higher altitudes. Comparison with a limited set of Na+
measurements indicates that the average meteoroid velocity is probably less than about
25 km s-1, in agreement with velocity estimates from conventional meteor radars, and considerably
slower than recent observations made by wide aperture incoherent scatter radars. The Na
column abundance is shown to be very sensitive to the meteoroid mass input rate, and to the
rate of vertical transport by eddy diffusion. Although the magnitude of the eddy diffusion
coefficient in the 80–90 km region is uncertain, there is a consensus between recent models
using parameterisations of gravity wave momentum deposition that the average value is less
than 3×105 cm2 s-1. This requires that the global meteoric mass input rate is less than about
20 td-1, which is closest to estimates from incoherent scatter radar observations. Finally, the
diurnal variation in the meteoroid input rate only slight perturbs the Na layer, because the
residence time of Na in the layer is several days, and diurnal effects are effectively averaged
out. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|