Meteor Ablated Aluminum in the Mesosphere Lower Thermosphere

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<SUP>+</SUP> ions are neutralized were first studied using a fast flow tube with pulsed laser ablation of an Al target, yielding k(AlO<SUP>+</SUP> + CO) = (3.7 ± 1.1) × 10<SUP>-10</SUP> and k(AlO<SUP>+</SUP> + O) = (1.7 ± 0.7) × 10<SUP>-10</SUP> cm<SUP>3</SUP> molecule<SUP>-1</SUP> s<SUP>-1</SUP> at 294 K. The first attempt to observe AlO by lidar was made by probing the bandhead of the B<SUP>2</SUP>Σ<SUP>+</SUP>(v′ = 0) ← X<SUP>2</SUP>Σ<SUP>+</SUP>(v″ = 0) transition at λ<SUB>air</SUB> = 484.23 nm. An upper limit for AlO of 60 cm<SUP>-3</SUP> was determined, which is consistent with a night time concentration of ∼5 cm<SUP>-3</SUP> estimated from the decay of AlO following rocket borne grenade releases. WACCM Al predicts the following: AlO, AlOH and Al<SUP>+</SUP> 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<SUP>-3</SUP> to a daytime maximum of ∼60 cm<SUP>-3</SUP>; and that the best opportunity for observing AlO is at high latitudes during equinoctial twilight.