Examination of surfaces exposed to a noctilucent cloud, August 1, 1968

Abstract

A successful flight of a recoverable payload designed to collect particles from a noctilucent cloud was made on August 1, 1968, at 0410 local daylight time (0910 UT), from Fort Churchill, Canada. Photographs obtained by project observers at Thompson, Canada, 400 km southwest of Churchill, showed that the noctilucent cloud was over the launch site at the time of flight. Electron microscope examinations of collecting surfaces exposed above 60 km showed about 6000 particles/cm • of a certain type on surfaces facing the flight direction. Few of these particles were found on nonflight control surfaces. Most of the particles range in size from 0.1-0.2 • and do not exhibit features suggesting that any liquid was associated with them. The shape of these particles is generally equant, often rod-like, subrounded to rounded; the particles are moderately dense to electrons, show internal structure, and have occasional protuberances. Considerable variation of particle concentration was observed from one flight surface to the next. Flight surfaces show some damage from aerodynamic heating. Thus, caution is necessary in applying these findings pending confirmatory sounding rocket flights through noctilucent clouds. Evidence from this flight, from previous rocket and satellite flights, and theoretical studies suggests that the noctilucent cloud particles are uplifted from lower altitudes and could have a terrestrial as well as cosmic origin. Intensive investigations of noctilucent clouds have been made since their first recorded discovery as an unusual phenomenon by Backhouse [1885]. These tenuous clouds form at an altitude of 80 km during the summer seasons above latitudes of 60 ø in both hemispheres. Fogle and Haurwitz [1966] have summarized the historical and observational data that they and numerous other investigators have obtained. Despite extensive study, the origin and composition of noctilucent clouds remain in doubt. Helmholtz [1889] and later StSrmer [1933] observed and confirmed that the clouds were composed of particles made visible by scattered sunlight. Visual observations by Vestine [1934], Astapovich [1939], Ludlam [1957], and Witt [1957] led these investigators to predict a particle size less than i /•. Spectra obtained by Grishin [1956] were later interpreted by Deirmendjian and Vestine [1959], who concluded that dielectric spheres smaller than 0.8 /• could cause the observed scattering. Polarization measurements were interpreted by Witt [1960a, b] and Villmann [1962] using Mie scattering

An aerosol chamber investigation of the heterogeneous ice nucleating potential of refractory nanoparticles

“…A series of rocket-borne sampling devices launched in the 1960's did Published by Copernicus Publications on behalf of the European Geosciences Union. R. W. Saunders et al: Ice nucleation by refractory nanoparticles recover a variety of particulate samples from the upper atmosphere (Hemenway et al, 1963;Farlow et al, 1970) which showed a range of sizes, morphologies and compositions, although whether any of these samples could be classed as meteoric smoke remains unanswered. However, two groups of collected particles, labelled "type 2" and "type 5" in the paper of Farlow et al (1970), did show an aggregated nature and extended morphology, possibly indicative of meteoric smoke.…”

“…R. W. Saunders et al: Ice nucleation by refractory nanoparticles recover a variety of particulate samples from the upper atmosphere (Hemenway et al, 1963;Farlow et al, 1970) which showed a range of sizes, morphologies and compositions, although whether any of these samples could be classed as meteoric smoke remains unanswered. However, two groups of collected particles, labelled "type 2" and "type 5" in the paper of Farlow et al (1970), did show an aggregated nature and extended morphology, possibly indicative of meteoric smoke. More recently, in situ measurements of positively charged particles at 80-90 km (Rapp et al, 2005) and satellite solar occultation measurements (Hervig et al, 2009) have lent further support to the presence of nano-sized meteoric smoke in the upper atmosphere, whilst line features observed in radar spectra have been shown to be consistent with the effect of charged particles present in the upper atmosphere (Strelnikova et al, 2007).…”

The Tromsø programme of in situ and sample return studies of mesospheric nanoparticles

“…A number of early attempts to sample and return NLC/PMSE particles were made (e. g. Hemenway et al, 1964Hemenway et al, , 1972Witt, 1969;Farlow et al, 1970;Ferry and Farlow, 1972;Rauser andFechtig, 1973, Havnes et al, 1996), but no such particles were firmly identified. The existence of impacting particles with halo radii ranging from 100 nm to 600 nm and solid nuclei having radii between 50 and 200 nm was claimed (Hemenway et al, 1964;Ferry and Farlow, 1972).…”

Technical Note: A novel rocket-based in situ collection technique for mesospheric and stratospheric aerosol particles

“…On the other hand, the microphysical properties of meteoric-smoke particles are still poorly understood. This lack of knowledge is due to the complications involved with in situ measurements at mesospheric altitudes that can only be reached by sounding rockets (Farlow et al, 1970;Havnes et al, 1996;Goldberg et al, 2001;Smiley et al, 2002;Rapp et al, 2005;Lynch et al, 2005;Hedin et al, 2007b). Furthermore, the detection of nanometre-sized particles is constrained by the shock wave in front of the rocket, which may prevent small particles from reaching the detector (Hedin et al, 2007a) and by contamination from the rocket itself.…”