In-situ detection of noctilucent cloud particles by the Colorado Dust Detectors onboard the PHOCUS sounding rocket

摘要

The Particles, Hydrogen and Oxygen Chemistry in the Upper Summer mesosphere (PHOCUS) sounding rocket campaign is a payload that carried multiple in-situ instruments for the detection of charged icy particles of noctilucent clouds (NLCs). The PHOCUS payload was launched on July 21st, 2011 and carried 18 scientific instruments. Three of these instruments were dedicated to the detection of the charged aerosol particles. All three instruments detected a narrow ice layer at around 81.5 km altitude. The Colorado Dust Detectors (CDDs) collected the net charge from the impact of aerosol particles on two graphite surfaces mounted flush with the payload skin. A combination of a small bias potential and permanent magnets were used to suppress the collection of plasma particles. The efficiency of the magnetic shielding improves with increasing altitude where there are fewer scattering collisions with neutrals. The data analysis shows that the net collected current can be decomposed into contributions from photoelectron emission, plasma electrons and ions, and the aerosol particles. The results show that the current corresponding to the collection of aerosol particles is positive, which is due to secondary charging effects.