A combined rocket-borne and ground-based study of the sodium layer and charged dust in the upper mesosphere

• First co-located measurement of atomic Na and O in the upper mesosphere.
• Na layer and meteoric smoke modelled with the same meteoric input.
• Small metal silicate particles attach electrons very efficiently.
• Satisfactory modelling of ions, electrons and charge dust above 80 km.

The Hotel Payload 2 rocket was launched on January 31st 2008 at 20.14 LT from the Andøya Rocket Range in northern Norway (69.31° N, 16.01° E). Measurements in the 75–105 km region of atomic O, negatively-charged dust, positive ions and electrons with a suite of instruments on the payload were complemented by lidar measurements of atomic Na and temperature from the nearby ALOMAR observatory. The payload passed within 2.58 km of the lidar at an altitude of 90 km. A series of coupled models is used to explore the observations, leading to two significant conclusions. First, the atomic Na layer and the vertical profiles of negatively-charged dust (assumed to be meteoric smoke particles), electrons and positive ions, can be modelled using a self-consistent meteoric input flux. Second, electronic structure calculations and Rice–Ramsperger–Kassel–Markus theory are used to show that even small Fe–Mg–silicates are able to attach electrons rapidly and form stable negatively-charged particles, compared with electron attachment to O2 and O3. This explains the substantial electron depletion between 80 and 90 km, where the presence of atomic O at concentrations in excess of 1010 cm−3 prevents the formation of stable negative ions.