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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. Plain Language Summary: A new satellite gravity wave (GW) variance data set is available that facilitates automated analysis of GWs entering the mesosphere. This work examines several years of GW variances from 50 to 55 km in the context of the Arctic and Antarctic polar vortices. Highest GW activity is observed in the vortex edge region where horizontal wind speeds are largest, consistent with previous work. Known planetary wave‐1 patterns are confirmed in the new data set. 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. In the Arctic winter, GW spatial patterns are highly correlated with horizontal wind speed. In the Antarctic winter, GW patterns are less positively correlated with the winds due to smaller variations around a latitude circle and larger orographic forcing. We show that Arctic 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. Key Points: This is the first work to present gravity waves (GWs) from 50 to 55 km observed by AIM CIPS with a focus on the winter polar vorticesDuring the 2020–2021 Arctic winter the longitude of maximum GW activity, maximum horizontal wind speed, and the polar vortex are co‐locatedReduced GW activity during the January 2021 SSW leads to simultaneous reductions in daytime traveling ionospheric disturbances [ABSTRACT FROM AUTHOR]

The atmospheric effects of precipitating electrons are not fully understood, and uncertainties are large for electrons with energies greater than ~30 keV. These electrons are underrepresented in modeling studies today, primarily because valid measurements of their precipitating spectral energy fluxes are lacking. This paper compares simulations from the Whole Atmosphere Community Climate Model (WACCM) that incorporated two different estimates of precipitating electron fluxes for electrons with energies greater than 30 keV. The estimates are both based on data from the Polar Orbiting Environmental Satellite Medium Energy Proton and Electron Detector (MEPED) instruments but differ in several significant ways. Most importantly, only one of the estimates includes both the 0° and 90° telescopes from the MEPED instrument. Comparisons are presented between the WACCM results and satellite observations poleward of 30°S during the austral winter of 2003, a period of significant energetic electron precipitation. Both of the model simulations forced with precipitating electrons with energies >30 keV match the observed descent of reactive odd nitrogen better than a baseline simulation that included auroral electrons, but no higher energy electrons. However, the simulation that included both telescopes shows substantially better agreement with observations, particularly at midlatitudes. The results indicate that including energies >30 keV and the full range of pitch angles to calculate precipitating electron fluxes is necessary for improving simulations of the atmospheric effects of energetic electron precipitation. Plain Language Summary: The study presented here investigates the effects from energetic electron precipitation (EEP) in the southern hemisphere winter of 2003. Electron precipitation is common during periods of enhanced geomagnetic activity and can create reactive nitrogen oxides and hydrogen oxides that can destroy ozone. Most global climate models currently do not include precipitating electrons with energies greater than 30 keV. To test whether this deficiency is important, this investigation compares observations with model simulations that included electrons with energies greater than 30 keV, as observed by the Medium Energy Proton and Electron Detector (MEPED) satellite instruments. In addition, one of the EEP data sets used in the simulations included data from just one of the telescopes on the MEPED instruments, whereas the other included data from both of the telescopes. We found that including both of the telescopes is important for capturing chemistry changes at polar and subpolar latitudes. The model simulation that only included only one of the telescopes showed significant improvement compared to a simulation with only low energy electrons. However, it did not perform as well as the model simulation that included both MEPED telescopes. This work is important because it shows that including energies >30 keV and the full range of precipitating electron pitch angles is necessary to show the impact electrons have on the atmosphere and provides an EEP data set for use in future model simulations. Key Points: Effects of energetic electron precipitation in southern hemisphere 2003 simulated with Whole Atmosphere Community Climate ModelSimulations of middle atmosphere chemistry improve significantly by including >30‐keV precipitating electronsIncluding the full range of pitch angles is necessary to capture precipitating electron impacts at subpolar latitudes [ABSTRACT FROM AUTHOR]

Abstract: This work investigates middle atmosphere effects of the September 2005 solar flares and solar proton events (SPEs). X‐17 and X‐6.2 flares occurred on 7 and 9 September, respectively, while two moderate SPEs occurred on 10 and 15 September. Flare ionization and dissociation were calculated in the Whole Atmosphere Community Climate Model (WACCM) using the Flare Irradiance Spectral Model. Proton measurements from the Geostationary Operational Environmental Satellite system were used to compute solar proton ionization. SPEs are shown to have a larger impact than solar flares on the polar stratosphere and mesosphere; however, flares have a larger influence on the sunlit and equatorial lower thermosphere. The two flares differed significantly with respect to photon spectrum. The larger, X‐17 flare was stronger during the impulsive phase, while the X‐6.2 flare was stronger during the gradual phase. This resulted in the X‐17 flare causing more initial ionization but for a shorter duration. The simulated flare impacts also differed because specific wavelengths of the flares influenced the atmosphere above the model top. Model‐measurement comparisons show that WACCM captures the overall timing and spatial distribution of the observed electron enhancements, indicating a reasonable simulation of flare and SPE‐induced ionization. Both the SPEs and flares caused odd nitrogen increases in the mesosphere. Odd hydrogen produced in the lower mesosphere by the SPEs led to short‐lived ozone decreases of nearly 100%. The flares caused small temperature increases in the lower thermosphere but had no effect on the stratosphere. [ABSTRACT FROM AUTHOR]

Solar eruptions sometimes produce protons, which impact the Earth's atmosphere. These solar proton events (SPEs) generally last a few days and produce high energy particles that precipitate into the Earth's atmosphere. The protons cause ionization and dissociation processes that ultimately lead to an enhancement of odd-hydrogen and odd-nitrogen in the polar cap regions (>60° geomagnetic latitude). We have used the Whole Atmosphere Community Climate Model (WACCM3) to study the atmospheric impact of SPEs over the period 1963-2005. The very largest SPEs were found to be the most important and caused atmospheric effects that lasted several months after the events. We present the short- and medium-term (days to a few months) atmospheric influence of the four largest SPEs in the past 45 years (August 1972; October 1989; July 2000; and October-November 2003) as computed by WACCM3 and observed by satellite instruments. Polar mesospheric NOx (NO+NO2) increased by over 50 ppbv and mesospheric ozone decreased by over 30% during these very large SPEs. Changes in HNO3, N2O5, ClONO2, HOCl, and ClO were indirectly caused by the very large SPEs in October-November 2003, were simulated by WACCM3, and previously measured by Envisat Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). WACCM3 output was also represented by sampling with the MIPAS averaging kernel for a more valid comparison. Although qualitatively similar, there are discrepancies between the model and measurement with WACCM3 predicted HNO3 and ClONO2 enhancements being smaller than measured and N2O5 enhancements being larger than measured. The HOCl enhancements were fairly similar in amounts and temporal variation in WACCM3 and MIPAS. WACCM3 simulated ClO decreases below 50 km, whereas MIPAS mainly observed increases, a very perplexing difference. Upper stratospheric and lower mesospheric NOx increased by over 10 ppbv and was transported during polar night down to the middle stratosphere in several weeks past the SPE. The WACCM3 simulations confirmed the SH HALOE observations of enhanced NOx in September 2000 as a result of the July 2000 SPE and the NH SAGE II observations of enhanced NO2 in March 1990 as a result of the October 1989 SPEs. [ABSTRACT FROM AUTHOR]

This study focuses on the effects of polar mesospheric cloud (PMC) formation on the chemical environment of the mesosphere and lower thermosphere. Of specific interest is how the dehydration due to mesospheric ice particle formation leads to significant seasonal decreases in the atomic hydrogen near the mesopause at middle to high latitudes. Using a three‐dimensional whole atmosphere coupled chemistry/dynamics model, we simulate the effects of this dehydration, and via comparisons with three data sets taken from two NASA satellites, we quantify the perturbations to atomic hydrogen and water vapor. We also identify a local ozone maximum that results from the PMC‐induced decrease in atomic hydrogen. Further, the large interannual variability in the onset of the Southern Hemisphere PMC season correlates well with the interannual variability of early summer atomic hydrogen at 95 km. Since the PMC onset is known to be controlled by interannual variations in the Southern Hemisphere stratospheric polar vortex, this correlation indicates a coupling between the stratosphere and the chemistry of the mesosphere and lower thermosphere. Finally, our model results suggest that the seasonal biteout in atomic hydrogen propagates up into the thermosphere and to lower latitudes. This raises the intriguing possibility that PMC formation might play a role in modulating the escape of hydrogen from the atmosphere. Plain Language Summary: Polar mesospheric clouds (PMCs) are Earth's highest clouds (82 km altitude). They consist of nanometer‐sized ice crystals nucleated onto meteoric smoke particles. When these clouds are formed, they dehydrate the surrounding atmosphere and when these clouds sublimate, they release the water vapor back into the surrounding environment. These patterns of condensation and sublimation are observed from NASA satellites and we model these data with a general circulation model. We quantify the effects that they have on the chemistry of the atmosphere at the edge of space. Our results show that it is possible that PMC condensation could affect the flow of hydrogen upward into the upper atmosphere. Key Points: Model of polar mesospheric cloud (PMC) effects on mesospheric chemistrySeasonal depletion of hydrogen at 95 km due to PMC condensation and associated dehydrationEffects seen at latitudes away from the PMC region, at higher altitudes up into the thermosphere as well as in a localized ozone enhancement [ABSTRACT FROM AUTHOR]