Detection of meteoric smoke particles in the mesosphere by a rocket-borne mass spectrometer

highlights
• An aerosol mass spectrometer was flown on 2 sounding rockets (day and night, 2011).
• Charged meteoric smoke particles (MSPs)were detected at altitudes of 63–94 km.
• The detected MSPs have radii less than 1.2 nm (8000 amu).
• MSPs above ~80 km are all negatively charged; both charge states occur below 80 km.
• MSP charge densities are lower during the daytime than nighttime.

In October 2011, two CHAMPS (Charge And Mass of meteoric smoke ParticleS) sounding rockets were launched into the polar mesosphere, each carrying an electrostatic multichannel mass analyzer for charged meteoric smoke particles (MSPs) that operated from 60 to 100 km and returned data on the number density of the charged MSPs in several ranges of mass. The payloads also carried Faraday rotation antennas and an array of plasma probes for determining electron and ion densities and the payload charging potential, thus providing a comprehensive picture of the distribution of charges over a wide range of altitudes that can be compared with models for the vertical distribution of MSPs and for the distribution of charge. The launches were from the Andøya Rocket Range, Norway, following the end of the noctilucent cloud season to avoid detection of ice. A night launch (11 October 21:50 UT) and a day launch (13 October 13:50 UT) helped to elucidate the role of solar ultraviolet in determining the charge state of the particles. The night data show a distinct change in the charge state of MSPs at the D-region ledge (~78 km) below which the density of free electrons is greatly reduced. Above the ledge, negative MSPs are detected at up to 92 km, have number densities reaching ~200 cm−3, and positive MSPs are absent. Below the ledge, positive and negative MSPs are about equally abundant, each with densities of ~2000 cm−3 at 70 km and with slightly lower densities at 60 km. The MSPs are seen predominantly in mass bins spanning 500–2000 amu and 2000–8000 amu, with more massive particles (radii above ~1.2 nm assuming a smoke particle density of 2 g/cm3) having number densities below the detection threshold (10 cm−3) and less massive particles being indistinguishable from ions. The daytime launch data show positive MSPs present only below the ledge and their number density is reduced to below 300 cm−3. The daytime data show negative MSPs both above and below the D-region ledge and their number density is also reduced, perhaps as a consequence of photodetachment. Modeling of the charge state of the MSPs shows that the total number density of MSPs, charged and uncharged, is approximately 20,000 cm−3 below the ledge and the model reproduces the absence of positive MSPs above the ledge.