Cloud Formation From a Localized Water Release in the Upper Mesosphere: Indication of Rapid Cooling

Abstract

Polar mesospheric clouds (PMCs) occur in the summer near 82 ‐85km altitude due to seasonal changes of temperature and humidity. However, water vapor and associated PMCs have also been observed associated with rocket exhaust. The effects of this rocket exhaust on the temperature of the upper mesosphere are not well understood. To investigate these effects, 220 kg of pure water was explosively released at 85 km as part of the Super Soaker sounding rocket experiment on the night of January 25–26, 2018 at Poker Flat Research Range (65°N, 147°W). A cloud formed within 18 s and was measured by a ground‐based Rayleigh lidar. The peak altitude of the cloud appeared to descend from 92 to 78 km over 3 min. Temperatures leading up to the release were between 197 and 232 K, about 50 K above the summertime water frost point when PMCs typically occur. The apparent motion of the cloud is interpreted in terms of the expansion of the explosive release. Analysis using a water vapor radiative cooling code coupled to a microphysical model indicates that the cloud formed due to the combined effects of rapid radiative cooling (∼25 K) by meter‐scale filaments of nearly pure water vapor (∼1 ppv) and an increase in the frost point temperature (from 150 to 200 K) due to the high concentration of water vapor. These results indicate that water exhaust not only acts as a reservoir for mesospheric cloud production but also actively cools the mesosphere to induce cloud formation.

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

“…The monthly average cloud frequencies presented here are also quite low (<1%, see Figure 4), so they can be more affected by water‐rich exhaust plumes from lower latitudes. Furthermore, recent work has shown that the plume water vapor itself with its extremely high concentrations can locally cool the upper mesosphere to enable cloud formation, even in the polar winter (Collins et al., 2021).…”

“…Figure 8 does not consider size of launch vehicle (e.g., Stevens et al., 2012), launch site latitude (Table 2), ascent trajectory, or the water vapor yield of the propellant combination which requires additional study that is beyond the scope of this work. On the other hand it should be emphasized that water vapor mixing ratios from a single plume can be near unity (e.g., Collins et al., 2021 and references therein) and are many orders of magnitude larger than ambient mixing ratios, which are typically reported in parts per million at these altitudes. Figures 8a and 8b provide evidence that the migrating tides (i.e., those that follow the sun) contribute importantly to the northward transport of space traffic exhaust during the summer.…”

Solar Cycle and Long‐Term Trends in the Observed Peak of the Meteor Altitude Distributions by Meteor Radars

“…(2007), DeLand and Thomas (2019), and Shettle et al. (2009) reported an increase in the occurrence, frequency, and brightness of polar mesospheric clouds (PMCs), themselves a sensitive indicator of climate change as they occur under specific conditions of both temperature and water vapor content (Collins et al., 2021). The predicted temperature changes in the middle atmosphere (up to 2–3 K dec −1 cooling) are much larger than the warming at the surface (∼0.5 K dec −1 during the last 50 years (IPCC, 2021)), indicating that the middle and upper atmosphere are very sensitive and could act as an early warning signal for future climate change.…”

Lower Thermospheric Material Transport via Lagrangian Coherent Structures

“…Transport over the Atlantic resulted in observed increases in water vapor in the sub‐Arctic and in PMC brightness in the Arctic (Stevens et al., 2012 ). More recently, an experiment depositing water vapor in the mesosphere showed the vapor locally cooled and increased the frost point, leading to the rapid formation of PMCs (Collins et al., 2021 ).…”