Search

We explore the effects of lower thermospheric water vapor deposited by launch vehicle plumes on polar mesospheric cloud (PMC) frequencies at 80°N. We use July‐averaged PMC frequencies from 2007 to 2022 from the Cloud Imaging and Particle Size (CIPS) instrument on NASA's Aeronomy of Ice in the Mesosphere (AIM) satellite. Launch sites worldwide are typically located near northern mid‐latitudes. Using the orbital launch record for the same time period, we find that the number of launches correlates with PMC frequencies with a coefficient of r = 0.60, which increases to r = 0.75 when only selecting launches from 2.5 to 21.5 local time (LT), indicating a weak LT dependence on global‐scale transport to 80°N. To support our findings, we use meridional winds from the Michelson Interferometer for Global High‐resolution Imaging experiment on NASA's Ionospheric Connection Explorer satellite and winds from the Horizontal Wind Model climatology to interpret the northward motion of air parcels at 105 km. We find the launch LT window that maximizes the correlation coefficient to be consistent with the expected maximum northward motion from the diurnal variation of mid‐latitude meridional winds. Comparisons with Microwave Limb Sounder satellite observations of upper mesospheric temperature and water vapor reveal a strong dependence of cloud frequency on water vapor (r = 0.86) but not on temperature (r = −0.26), indicating that water vapor is the primary source of PMC variability for the bright PMCs at 80°N. We therefore find that launch vehicle plumes originating primarily from northern mid‐latitudes modulate PMC frequency at 80°N in July. Plain Language Summary: Formation of clouds in the mesosphere in the polar summer depends heavily on atmospheric water vapor. Main engine exhaust plumes from space shuttles and other launch vehicles contain many tons of water vapor which can be transported poleward at an altitude of ∼105 km. Over several days this water vapor descends to ∼80–85 km and aids in the formation of summertime polar mesospheric clouds (PMCs). This work shows how the number of launches per year correlates with the mean interannual PMC frequency averaged over July at 80°N latitude. The correlation maximizes for vehicles launched from 2.5 to 21.5 local time. To provide additional important evidence for the poleward transport of plumes launched at these local times, we use wind data to quantify the maximum northward motion of an exhaust plume over the diurnal cycle near 105 km altitude. We also use satellite temperature and water vapor data at PMC altitudes to show that bright PMCs vary more with the water vapor content than with the air temperature. We conclude that the total water vapor deposited by summertime space traffic worldwide modulates the PMC frequency at 80°N. Key Points: The correlation between orbital rocket launches and polar mesospheric clouds at 80°N in July from 2007 to 2022 is quantifiedMeridional wind, temperature, and water vapor data are used to support causal interpretation of the correlation coefficientsEvidence indicates that water vapor in space traffic exhaust plumes modulates frequencies of polar mesospheric clouds at 80°N [ABSTRACT FROM AUTHOR]

The cloud imaging and particle size (CIPS) instrument onboard the Aeronomy of Ice in the Mesosphere satellite provides images of gravity waves (GWs) near the stratopause and lowermost mesosphere (altitudes of 50–55 km). GW identification is based on Rayleigh Albedo Anomaly (RAA) variances, which are derived from GW‐induced fluctuations in Rayleigh scattering at 265 nm. Based on 3 years of CIPS RAA variance data from 2019 to 2022, we report for the first time the seasonal distribution of GWs entering the mesosphere with high (7.5 km) horizontal resolution on a near‐global scale. Seasonally averaged GW variances clearly show spatial and temporal patterns of GW activity, mainly due to the seasonal variation of primary GW sources such as convection, the polar vortices and flow over mountains. Measurements of stratospheric GWs derived from Atmospheric InfraRed Sounder (AIRS) observations of 4.3 μm brightness temperature perturbations within the same 3‐year time range are compared to the CIPS results. The comparisons show that locations of GW hotspots are similar in the CIPS and AIRS observations. Variability in GW variances and the monthly changes in background zonal wind suggest a strong GW‐wind correlation. This study demonstrates the utility of the CIPS GW variance data set for statistical investigations of GWs in the lowermost mesosphere, as well as provides a reference for location/time selection for GW case studies. Key Points: Aeronomy of Ice in the Mesosphere cloud imaging and particle size (CIPS) provides first near‐global images of gravity waves at 50–55 km with high horizontal resolutionCIPS observes gravity wave hotspots generated by convection, topography, and the polar vortexLocations of gravity wave hotspots near the stratopause/lowermost mesosphere are similar to those in the mid‐stratosphere near 35 km [ABSTRACT FROM AUTHOR]

The Andes account for the largest source of orographic gravity waves (GWs) in the middle atmosphere. This results from persistent, strong zonal winds at the surface encountering the north‐south mountain chain, producing strong orographic lift, and resulting GWs. Here, we consider GWs in the stratosphere and mesosphere above the Andes as observed by the Cloud Imaging and Particle Size instrument, the Solar Occultation for Ice Experiment on the AIM satellite, and the Sounding of the Atmosphere using Broadband Emission Radiometry instrument onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. GW variability is considered in the context of the location of the stratospheric wintertime westerly jet and planetary wave (PW) amplitude and phase. The occurrence of GWs in the middle and upper atmosphere depends not only on tropospheric sources, like the Andes, but also on the background winds through which they propagate. Results suggest that the propagation of GWs into the mesosphere is well correlated with winds throughout the middle and upper stratosphere. PWs cause the westerly jet to move over the Andes, resulting in an increase in GW amplitude throughout the middle and upper stratosphere. The evolution and variability of GWs are tied closely to the phase of the PW‐1 and are linked to PW‐2 when the PW amplitudes are sufficiently large. GW amplitude, as observed by all three data sets, increases in the upper stratosphere and lower mesosphere when the trough of the PW‐1 in the stratosphere is over the Andes. Plain Language Summary: In the Southern Hemisphere, strong wintertime winds continuously flow west to east at mid‐latitudes (40°–50°S). As these winds flow over surface features like the Andes Mountains, the air is forced upwards, creating waves in the atmosphere that propagate both horizontally and vertically. These gravity waves (GWs) transport energy from the surface to the upper atmosphere, where they break and deposit their momentum, causing either turbulent mixing, an acceleration of the winds, or the generation of additional waves. The energy deposited from GWs has a significant impact on the circulation in the upper atmosphere, so it is important to understand where they break and to characterize sources of variability. As GWs propagate vertically, they encounter horizontal wind shear associated with a band of strong winds in the middle atmosphere, causing them to turn toward the area of strong winds. The latitude where these strong winds occur can change significantly, driven by planetary‐scale waves. This work shows that the occurrence of GWs in the middle atmosphere, observed by several NASA instruments, strongly depends on the amplitude and orientation of the planetary scale waves and the resulting location of the middle atmospheric winds. Key Points: Gravity waves (GWs) at the stratopause show significant variability over the Andes associated with stratospheric winds and planetary wave (PW) phaseEnhanced GW activity follows the trough of the PW‐1 and strong stratospheric winds at mid‐southern latitudesGW activity is enhanced over the Andes when the PW trough and the polar night jet are over the Andes [ABSTRACT FROM AUTHOR]