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

Abstract

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 100km 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 (~78km) below which the density of free electrons is greatly reduced. Above the ledge, negative MSPs are detected at up to 92km, have number densities reaching ~200cm−3, and positive MSPs are absent. Below the ledge, positive and negative MSPs are about equally abundant, each with densities of ~2000cm−3 at 70km and with slightly lower densities at 60km. The MSPs are seen predominantly in mass bins spanning 500–2000amu and 2000–8000amu, with more massive particles (radii above ~1.2nm assuming a smoke particle density of 2g/cm3) having number densities below the detection threshold (10cm−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 300cm−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 20,000cm−3 below the ledge and the model reproduces the absence of positive MSPs above the ledge.