Abstract
The first global atmospheric model (WACCM-Al) of meteor-ablated aluminum
was constructed from three components: the Whole Atmospheric Community
Climate Model (WACCM6); a meteoric input function for Al derived by
coupling an astronomical model of dust sources in the solar system with
a chemical meteoric ablation model; and a comprehensive set of neutral,
ion-molecule and photochemical reactions relevant to the chemistry of Al
in the upper atmosphere. The reaction kinetics of two important
reactions that control the rate at which Al+ ions are
neutralized were first studied using a fast flow tube with pulsed laser
ablation of an Al target, yielding k(AlO+ + CO)
= (3.7 ± 1.1) × 10-10 and
k(AlO+ + O) = (1.7 ± 0.7) ×
10-10 cm3
molecule-1 s-1 at 294 K. The first
attempt to observe AlO by lidar was made by probing the bandhead of the
B2Σ+(v’ = 0) ←
X2Σ+(v” = 0) transition at
λair = 484.23 nm. An upper limit for AlO of 57
cm-3 was determined, which is consistent with a
night-time concentration of ~5 cm-3
estimated from the decay of AlO following rocket-borne grenade releases.
WACCM-Al predicts the following: AlO, AlOH and Al+ are
the three major species above 80 km; the AlO layer at mid-latitudes
peaks at 89 km with a half-width of ~5 km, and a peak
density which increases from a night-time minimum of ~10
cm-3 to a daytime maximum of ~60
cm‑3; and that the best opportunity for observing AlO
is at high latitudes during equinoctial twilight.