Northern Mid-Latitude Mesospheric Cloud Frequencies Observes by AIM/CIPS: Interannual Variability Driven by Space Traffic

Recent advances in data processing from the Cloud Imaging and Particle Size (CIPS) instrument on the NASA Aeronomy of Ice in the Mesosphere satellite allow observation of bright mesospheric clouds at mid-latitudes (<60 degrees). When adjusted for the evolving local time (LT) of the CIPS observations during its mission we find that the frequencies of these bright clouds in the northern hemisphere show no trend from 2007 to 2021 and no dependence on the solar cycle, although the interannual variability is extreme. Rather we investigate the possible link with propellant exhaust from orbital vehicles, typically launched at lower latitudes. By filtering the launch record equatorward of 60 degrees N using only those launches between 23 and 10 LT, we find a strong correlation with the observed mid-latitude mesospheric cloud frequency variability between 56 degrees and 60 degrees N. Meridional winds at 92 km from a meteorological analysis system reveal that these morning launches occurred at the time of maximum northward transport. Based upon this combination of high correlation between the cloud frequency and the launch record plus favorable transport conditions, it is likely that space traffic has a strong influence on the interannual variability of these bright mesospheric clouds.

Automated summary

Recent advances in data processing from the NASA Aeronomy of Ice in the Mesosphere satellite's Cloud Imaging and Particle Size (CIPS) instrument allow the observation of bright mesospheric clouds at mid-latitudes. The frequency of these clouds in the northern hemisphere shows no trend from 2007 to 2021 and no dependence on the solar cycle, but extreme interannual variability. This study investigates the possible link between these clouds and the propellant exhaust from orbital vehicles launched at lower latitudes. The analysis suggests that space traffic has a strong influence on the interannual variability of these bright mesospheric clouds.