First Simultaneous Rocket and Radar Detections of Rare Low Summer Mesospheric Clouds

• Published in: Geophysical research letters Vol. 45; no. 11; pp. 5727 - 5734
• Main Authors: Havnes, O., Latteck, R., Hartquist, T. W., Antonsen, T.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.06.2018; American Geophysical Union (AGU)
• Subjects: Atmosphere; Atmospheric particulates; Berg‑ og petroleumsfag: 510; Charge density; Clouds; Density; Dust; Dust particles; dust size sorting; Dust storms; Earth; Gases; in situ dust measurements; Low clouds; Measuring instruments; mesospheric clouds; meteoric smoke; Meteorites; Middle atmosphere; Photoelectric effect; Photoelectric properties; Photoelectricity; positive dust charges; Probability theory; Radar; Radar observation; Rock and petroleum disciplines: 510; rocket and radar; Rockets; Smoke; Smoke particles; Summer; Technology: 500; Teknologi: 500; Thin films; VDP; Velocity
• ISSN: 0094-8276; 1944-8007; 1944-8007
• DOI: 10.1029/2018GL078218

On 30 June 2016 a layer of dust, possibly meteoric smoke particles (MSPs), was observed with a rocket borne probe at 69.29°N, 16.02°E and altitudes of ~74 km where patchy thin cloud layers, detected with the Middle Atmosphere Alomar Radar System, were present. The rocket traversed a layer with a net positive dust charge density of ~107 unit charges per cubic meters and a number density of neutral dust particles with sizes ≥4 nm of ~108 m−3. The positive charge density may require that elements that lower the photoelectric work function coat MSPs. The presence of this relatively large dust is consistent with smaller MSPs being swept out of the low mesospheric cloud region during the summer, while larger MSPs remain where their fall velocities equals the circulation updraught velocities. Large MSPs initially embedded in icy particles that subsequently sublimate may also fall until their fall velocities match the updraught velocities. Plain Language Summary A rocket and radar campaign was conducted in the summer of 2016 to investigate the clouds in the Earth's polar middle atmosphere and the role of meteoric smoke particles. They are produced by meteorites entering the atmosphere at high velocities, where they are heated by friction and ablate. We lack knowledge of the cloud transition phases from winter to summer conditions in late May and back in late August. Recent radar observations show that contrary to the belief a few years back, weak and low clouds are not totally absent in the summer season. One of the rockets flew through a very weak and low cloud, which also was observed by radar. The probability for this to happen is very low. Analysis shows that the cloud consists of 4‐ to 5‐nm‐sized meteoric smoke particles of number density a few times 108 particles m−3 with a low positive dust charge density of ~107 m−3. Our findings are consistent with size sorting being active and important in the low cloud region especially during the transition phases. The positive charge density apparently requires that the photoelectric properties of the smoke particles are affected by coating with or absorption of gases. Key Points The first simultaneous radar and rocket observations of weak, low, and rare polar mesospheric summer clouds were obtained The majority of the dust particles appear to be neutral but with a net positive dust charge density Size sorting of dust must take place