AbstractWe 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.

Abstract 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.

This study explores the meteorological source and vertical propagation of gravity waves (GWs) that drive daytime traveling ionospheric disturbances (TIDs), using the specified dynamics version of the SD-WACCM-X (Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension) and the SAMI3 (Sami3 is Also a Model of the Ionosphere) simulations driven by SD-WACCM-X neutral wind and composition. A cold weather front moved over the northern-central USA (90–100°W, 35–45°N) during the daytime of 20 October 2020, with strong upward airflow. GWs with ~500–700 km horizontal wavelengths propagated southward and northward in the thermosphere over the north-central USA. Also, the perturbations were coherent from the surface to the thermosphere; therefore, the GWs were likely generated by vertical acceleration associated with the cold front over Minnesota and South Dakota. The convectively generated GWs had almost infinite vertical wavelength below ~100 km due to being evanescent. This implies that the GWs tunneled through their evanescent region in the middle atmosphere (where a squared vertical wavenumber is equal to or smaller than 0) and became freely propagating in the thermosphere and ionosphere. Medium-scale TIDs (MSTIDs) also propagated southward with the GWs, suggesting that the convectively generated GWs created MSTIDs.

Complex spatial structures in polar mesospheric cloud (PMC) images provide visual clues to the dynamics that occur in the summer mesosphere. In this study, we document one such structure, a PMC front, by analyzing PMC images in the northern hemisphere from the Cloud Imaging and Particle Size (CIPS) instrument onboard the aeronomy of ice in the mesosphere (AIM) satellite. A PMC front is defined as a sharp boundary that separates cloudy and mostly clear regions, and where the clouds at the front boundary are brighter than the clouds in the cloudy region. We explore the environment that supports the formation of PMC fronts using near-coincident temperature and water vapor observations from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument. A comparison of PMC front locations to near-coincident temperature profiles reveals the presence of inversion layers at PMC altitudes. The adiabatic and superadiabatic topside lapse rates of these temperature inversions indicate that some of the identified inversion layers may have been formed by gravity wave (GW) dissipation. The structure of the squared buoyancy frequency profiles indicates a stable layer or thermal duct that can be associated with large-amplitude mesospheric inversion layers (MILs) that extend large distances. These inversion layers may be conducive to horizontal wave propagation. We hypothesize that ducted GWs may be a formation mechanism of PMC fronts.

A new Cloud Imaging and Particle Size (CIPS) gravity wave (GW) variance data set is available that facilitates automated analysis of GWs entering the mesosphere. This work examines several years of CIPS GW variances from 50 to 55 km in the context of the Arctic and Antarctic polar vortices. CIPS observes highest GW activity in the vortex edge region where horizontal wind speeds are largest, consistent with previously published GW climatologies in the stratosphere and mesosphere. CIPS observes the well‐documented planetary wave (PW)‐1 patterns in GW activity in both hemispheres. In the Northern Hemisphere, maximum GW activity occurs over the North Atlantic and western Europe. In the Southern Hemisphere, maximum GW activity stretches from the Andes over the South Atlantic and Indian Oceans, as expected. In the NH, CIPS GW spatial patterns are highly correlated with horizontal wind speed. In the SH, CIPS GW patterns are less positively correlated with the winds due to increased zonal symmetry and orographic forcing. The Andes Mountains and Antarctic Peninsula, South Georgia Island, Kerguelen/Heard Islands, New Zealand, and Tasmania are persistent sources of orographic GWs. Atmospheric Infrared sounder observations of stratospheric GWs are analyzed alongside CIPS to explore vertical GW coherence and to infer GW propagation and sources. NH midlatitude GW activity is reduced during the January 2021 SSW, as expected. This reduction in GWs leads to a simultaneous reduction in traveling ionospheric disturbances (TIDs), providing more evidence that weak polar vortex events with weak GW activity leads to reduced daytime TID activity.

The quasi 5‐day wave (Q5DW) with zonal wavenumber 1 is a dominant planetary wave (PW) oscillation in the polar summer mesospheric temperature and polar mesospheric cloud (PMC) fields. In this paper, the Q5DW signal derived from 16 years (2007–2022) of Microwave Limb Sounder temperature observations is used to investigate the role of this PW mode on the onset of PMC seasons in the northern hemisphere (NH). PMC data from the Cloud Imaging and Particle Size (CIPS) instrument during this time indicates that NH PMC season onsets ranged from 15 to 28 May, with earliest onsets in 2013, 2015, 2019, 2020, 2021, and 2022. Except 2013 and 2022, the other four earlier onsets were also characterized by enhanced Q5DW activity. The wave amplification appears to be driven by baroclinic instability arising from the negative meridional gradient of potential vorticity in the high‐latitude summer mesosphere. CIPS data show that when the Q5DW was present at the beginning of the season, clouds formed preferentially in the cold troughs of the wave. We thus propose that the much colder troughs due to enhanced Q5DW activity in mid‐May of 2015, 2019, 2020, and 2021 influenced the timing of PMC onset in these years. While the 11‐year solar cycle, inter‐ and intra‐hemispheric coupling due to gravity wave and PW activity have been shown to contribute to earlier onset of PMC seasons in the NH, our analysis suggests that enhanced Q5DW activity also plays a major role.

We present evidence that, during the winter season, hotspots in stratospheric and mesospheric gravity waves (GWs) seen over Europe are strongly correlated with daytime Medium Scale Traveling Ionospheric Disturbances (MSTIDs) above the US. The roles of the stratospheric and mesospheric polar vortex, the average zonal wind component and total wind vectors in the propagation of these GWs are also examined. Travelling Ionospheric disturbances (TIDs) are perturbations in the background plasma density and are ubiquitous in many types of ionospheric data during both geomagnetically disturbed and geomagnetically quiet times. They are highly variable in space and time, and are a source of uncertainty in high frequency radio systems and Global Navigation Satellite Systems (GNSS). Medium scale TIDs, or MSTIDs can significantly affect HF communication, and cause disruptions to GNSS signals that can make geolocation difficult. Therefore, understanding them and being able to predict their occurrence is important not only from a scientific but also from a technological perspective. We use data from the Atmospheric Infrared Sounder (AIRS) on board the Aqua satellite and Cloud Imaging and Particle Size (CIPS) instrument on board the AIM satellite to locate stratospheric and mesospheric GW hotspots over Europe (at an altitude of ? 35 km and 50 - 55 km respectively) during Arctic winters of 2019 - 2020 and 2020 - 2021. We show that these GW hotspots are strongly correlated with TIDs over a wide range of latitudes (25 - 60? N) over the central US. The state of the polar vortex is shown to play a major role in the propagation of GWs. A strong polar vortex dominates throughout the entire winter of 2019 - 2020, whereas a weak vortex develops during the winter of 2020 - 2021 due to a Sudden Stratospheric Warming (SSW). We show that the effect of GW hotspots over Europe on MSTIDs over the mid-latitude US is significant only when the polar vortex is strong for a period longer than that observed during years with a Sudden Stratospheric Warming (SSW). From our observations, this implies a strong vortex lasting longer than a period of 30 days. In addition, the mesospheric wind system is shown to correlate highly with the amplitude of MSTIDs over mid-latitude North America and is theorized to modulate the propagation of GWs to higher altitudes.

The satellite‐based Cloud Imaging and Particle Size (CIPS) instrument and Atmospheric Infrared Sounder (AIRS) observed concentric gravity waves (GWs) generated by Typhoon Yutu in late October 2018. This work compares CIPS and AIRS nadir viewing observations of GWs at altitudes of 50–55 and 30–40 km, respectively, to simulations from the high‐resolution European Centre for Medium‐Range Weather Forecasting Integrated Forecasting System (ECMWF‐IFS) and ECMWF reanalysis v5 (ERA5). Both ECMWF‐IFS with 9 km and ERA5 with 31 km horizontal resolution show concentric GWs at similar locations and timing as the AIRS and CIPS observations. The GW wavelengths are ∼225–236 km in ECMWF‐IFS simulations, which compares well with the wavelength inferred from the observations. After validation of ECMWF GWs, five category five typhoon events during 2018 are analyzed using ECMWF to obtain characteristics of concentric GWs in the Western Pacific regions. The amplitudes of GWs in the stratosphere are not strongly correlated with the strength of typhoons, but are controlled by background wind conditions. Our results confirm that amplitudes and shapes of concentric GWs observed in the stratosphere and lowermost mesosphere are heavily influenced by the background wind conditions.

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. In the Southern Hemisphere, strong wintertime winds continuously flow west to east at mid-latitudes (40 degrees-50 degrees 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. 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

It is well-known that equatorial plasma bubbles (EPBs) are highly correlated to the post-sunset rise of the ionosphere on a climatological basis. However, when proceeding to the daily EPB development, what controls the day-to-day/longitudinal variability of EPBs remains a puzzle. In this study, we investigate the underlying physics responsible for the day-to-day/longitudinal variability of EPBs using the Sami3 is A Model of the Ionosphere (SAMI3) and the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X). Simulation results on October 20, 22, and 24, 2020 were presented. SAMI3/WACCM-X self-consistently generated midnight EPBs on October 20 and 24, displaying irregular and regular spatial distributions, respectively. However, EPBs are absent on October 22. We investigate the role of gravity waves on upwelling growth and EPB development and discuss how gravity waves contribute to the distributions of EPBs. Of particular significance is that we found the westward wind associated with solar terminator waves and gravity waves causes midnight vertical drift enhancement and collisional shear instability, which provides conditions favorable for upwelling growth and EPB development. The converging and diverging winds associated with solar terminator waves and midnight temperature maximum also affect the longitudinal distribution of EPBs. The absence of EPBs on October 22 is related to the weak upward drift induced by weak westward wind associated with solar terminator waves.

The drivers and atmospheric impacts of energetic electron precipitation are not yet well understood. Further, electron precipitation is often poorly represented in atmospheric modeling. Additional investigations of the drivers and impacts of electron precipitation are needed to improve models and space weather forecasting requirements. To accurately represent the troposphere through the ionosphere in model simulations, it is vital to account for the chemistry accurately. Electron precipitation is a frequent, yet often ignored middle to high latitude forcing that can have dramatic effects on the middle and upper atmosphere. Over the past decade, several electron precipitation data sets have been developed, however, validation has been difficult due to the lack of independent observations of electron fluxes. Additionally, the limited number of satellites making measurements of global magnetospheric wave activity in concert with the resulting electron precipitation restricts our ability to accurately capture the drivers simultaneously with the precipitation. Accurate characterization of the drivers is needed for physics-based magnetosphere modeling. Likewise, accurate precipitating electron fluxes and relative energies are needed to improve our atmospheric modeling studies. Finally, in order to properly validate and improve our current modeling efforts, observations of atmospheric composition are necessary.

Precipitation losses of Earth's ring current and radiation belt particles represent a major loss process that ultimately helps balance the intensity levels of the radiation environment in near-Earth space.Energetic particle precipitation (EPP) involves particles that are quasi-trapped along magnetic field lines venturing to very high magnetic latitudes, where their mirror points in the dipole-like magnetic trap start to move to altitudes ≤ ~100 km, where collisions with atmospheric neutrals and ionospheric particles becomes significant.Such collisions result in radiation belt particles depositing their energy into the ionosphere and atmosphere and being lost from the system, but the altitude at which a precipitating energetic particle deposits the majority of its energy is highly dependent on the particle's energy and pitch angle.The highest energy, several MeV electrons from Earth's outer radiation belt deposit most of their energy at altitudes < 40 km, within the stratosphere.Many outstanding questions remain concerning the nature of radiation belt precipitation losses into the atmosphere and the impacts of such energy input on atmospheric heating and chemistry and the bottom-side ionosphere.Implications of these unknowns are broad ranging and cross-divisional, spanning Earth and Atmospheric Sciences, such as sudden stratospheric warming events and terrestrial climate, to Heliophysics, such as ionospheric energy budgets, radiation belt physics, and space weather.We encourage the Decadal Survey Committee to consider the following science objectives to be of high priority for dedicated missions and research over the next decade: Prioritize new missions to be developed that adequately instrument and populate a constellation of satellites at various altitudes in LEO with energetic particle instrumentation plus ionospheric and atmospheric remote sensing capabilities.Such a constellation should explore and establish the consequences of and causal role between energetic particle precipitation (i.e., ring current, radiation belt, and solar energetic particles) and: i) transient events of mesospheric NOx and HOx production, ozone depletion, and stratospheric and tropospheric warming and ii) localized, transient structures and sporadic intensification of the D-and E-region ionospheres.

At around 04:14 UTC on the 15th January 2022, a major volcanic eruption began beneath the Tongan islands of Hunga Tonga and Hunga Ha’apai (175.4W, 20.5S). Located under only a shallow depth of water, the volcano rapidly launched a plume of super-heated ash and vapourised water upwards into the atmosphere. Over the next few hours, satellite observations reveal unprecedented large-scale concentric waves in the mid-stratosphere (near 40km altitude) radiating away from the eruption across the entire Pacific Ocean. In this presentation, we show brightness temperature perturbations in the 4.3 micron bands of the AIRS/Aqua, CrIS/Suomi-NPP and CrIS/JPSS-1 instruments that reveal three groups of atmospheric waves of special interest. First, an initial concentric wave is found travelling near the stratospheric speed of sound, likely to be an acoustic compression wave. There then follows a gap, which corresponds to phase speeds not permitted by theory, then a second group of waves likely to be gravity waves. These gravity waves are shown to be travelling near the maximum phase speed permitted, and there is a suggestion that some may travel the whole way around the globe in the tropics. Third, we observe small-scale gravity waves that pervade many thousands of kilometres across almost the entire Pacific Ocean, suggesting an extremely consistent heating source. All three of these wave observations are unprecedented in more than 20 years of stratospheric satellite observations, and this eruption may potentially have produced the first observations of an acoustic wave in the mid-stratosphere that can be measured from space. Now that we have space-borne instruments to observe it, this volcanic eruption provides a unique test of theoretical predictions of atmospheric wave phase speeds on some of the largest scales possible.

Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Space Physics. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Travelling Ionospheric Disturbances Detected by the Scintillation Observations and Response of The Ionosphere to Electrodynamics (SORTIE) CubeSat at 420 km AltitudeAuthorsIrfanAzeemiDGeoffCrowelyiDWanliWuCora ERandallV. LynnHarveyiDSharon L.SharonM. JoanAlexanderiDKarthikVenkatarmaniRussell AlanStonebackMichaelPerdueMatthewDepewErikStrombergiDChadFishAdamReynoldsAnthonySwensonTedTashiDSee all authors Irfan AzeemiDCorresponding Author• Submitting AuthorASTRA LLC.iDhttps://orcid.org/0000-0002-8928-9837view email addressThe email was not providedcopy email addressGeoff CrowelyiDASTRAiDhttps://orcid.org/0000-0002-2058-7254view email addressThe email was not providedcopy email addressWanli WuASTRA LLCview email addressThe email was not providedcopy email addressCora E RandallUniversity of Colorado Boulderview email addressThe email was not providedcopy email addressV. Lynn HarveyiDUniversity of Colorado BoulderiDhttps://orcid.org/0000-0002-7928-0804view email addressThe email was not providedcopy email addressSharon L. SharonNorthWest Research Associatesview email addressThe email was not providedcopy email addressM. Joan AlexanderiDNorthWest Research Associates, CoRA OfficeiDhttps://orcid.org/0000-0003-2495-3597view email addressThe email was not providedcopy email addressKarthik VenkatarmaniASTRA LLCview email addressThe email was not providedcopy email addressRussell Alan StonebackStoneris LLCview email addressThe email was not providedcopy email addressMichael PerdueUniversity of Texas at Dallasview email addressThe email was not providedcopy email addressMatthew DepewUniversity of Texas at Dallasview email addressThe email was not providedcopy email addressErik StrombergiDASTRA LLC.iDhttps://orcid.org/0000-0001-5187-2261view email addressThe email was not providedcopy email addressChad FishASTRA LLCview email addressThe email was not providedcopy email addressAdam ReynoldsASTRAview email addressThe email was not providedcopy email addressAnthony SwensonASTRA LLCview email addressThe email was not providedcopy email addressTed TashiDASTRA LLCiDhttps://orcid.org/0000-0002-3603-4478view email addressThe email was not providedcopy email address

The January 2022 Hunga Tonga–Hunga Ha’apai eruption was one of the most explosive volcanic events of the modern era 1 , 2 , producing a vertical plume that peaked more than 50 km above the Earth 3 . The initial explosion and subsequent plume triggered atmospheric waves that propagated around the world multiple times 4 . A global-scale wave response of this magnitude from a single source has not previously been observed. Here we show the details of this response, using a comprehensive set of satellite and ground-based observations to quantify it from surface to ionosphere. A broad spectrum of waves was triggered by the initial explosion, including Lamb waves 5 , 6 propagating at phase speeds of 318.2 ± 6 m s −1 at surface level and between 308 ± 5 to 319 ± 4 m s −1 in the stratosphere, and gravity waves 7 propagating at 238 ± 3 to 269 ± 3 m s −1 in the stratosphere. Gravity waves at sub-ionospheric heights have not previously been observed propagating at this speed or over the whole Earth from a single source 8 , 9 . Latent heat release from the plume remained the most significant individual gravity wave source worldwide for more than 12 h, producing circular wavefronts visible across the Pacific basin in satellite observations. A single source dominating such a large region is also unique in the observational record. The Hunga Tonga eruption represents a key natural experiment in how the atmosphere responds to a sudden point-source-driven state change, which will be of use for improving weather and climate models.

Precipitating auroral and radiation belt electrons are considered an important part of the natural forcing of the climate system. Recent studies suggest that this forcing is underestimated in current chemistry‐climate models. The High Energy Particle Precipitation in the Atmosphere III intercomparison experiment is a collective effort to address this point. Here, eight different estimates of medium energy electron (MEE) (>30keV) $(> 30\hspace*{.5em}keV)$ ionization rates are assessed during a geomagnetic active period in April 2010. The objective is to understand the potential uncertainty related to the MEE energy input. The ionization rates are all based on the Medium Energy Proton and Electron Detector (MEPED) on board the NOAA/POES and EUMETSAT/MetOp spacecraft series. However, different data handling, ionization rate calculations, and background atmospheres result in a wide range of mesospheric electron ionization rates. Although the eight data sets agree well in terms of the temporal variability, they differ by about an order of magnitude in ionization rate strength both during geomagnetic quiet and disturbed periods. The largest spread is found in the aftermath of enhanced geomagnetic activity. Furthermore, governed by different energy limits, the atmospheric penetration depth varies, and some differences related to latitudinal coverage are also evident. The mesospheric NO densities simulated with the Whole Atmospheric Community Climate Model driven by highest and lowest ionization rates differ by more than a factor of eight. In a follow‐up study, the atmospheric responses are simulated in four chemistry‐climate models (CCM) and compared to satellite observations, considering both the CCM structure and the ionization forcing.

An altitude profile of Nitric Oxide (NO) in the 80–110 km altitude range was measured in the polar night from a sounding rocket on 27 January 2020. The observations were made using the technique of stellar occultation with a UV spectrograph observing the γ (1,0) band of NO near 215 nm. The tangent point for the altitude profile was at 74° latitude, a location that had been in darkness for 80 days. The retrieved slant column density profile is interpreted using an assumed four‐parameter analytic profile shape. Retrievals of the fitting parameters yield a profile with a peak NO concentration of 2.2 ± 0.7 × 10 8 cm −3 at 93.5 ± 4.1 km. The observations were made during a time of minimum solar and geomagnetic activity. The NO maximum retrieved from the rocket profile is significantly larger in abundance and lower in altitude than other observations on the same day at nearby latitudes just outside the polar night. These rocket‐borne results are consistent with NO that is created over the course over the polar winter and is confined to high latitudes in the polar night by the mesospheric polar vortex. During the course of that confinement the abundance increases due to the lack of photodissociation, allowing the NO to descend. We show that the observed descent can be explained by eddy diffusion‐driven transport, though vertical advection cannot be ruled out.