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1. Preliminary Dual-Satellite Observations of Atmospheric Gravity Waves in Airglow

   https://doi.org/10.3390/atmos10110650  

   Yue, Jia ; Perwitasari, Septi ; Xu, Shuang ; Hozumi, Yuta ; Nakamura, Takuji ; Sakanoi, Takeshi ; Saito, Akinori ; Miller, Steven D. ; Straka, William ; Rong, Pingping ( November 2019 , Atmosphere)

   Atmospheric gravity waves (AGWs) are among the important energy and momentum transfer mechanisms from the troposphere to the middle and upper atmosphere. Despite their understood importance in governing the structure and dynamics of these regions, mesospheric AGWs remain poorly measured globally, and largely unconstrained in numerical models. Since late 2011, the Suomi National Polar-orbiting Partnership (NPP) Visible/Infrared Imaging Radiometer Suite (VIIRS) day–night band (DNB) has observed global AGWs near the mesopause by virtue of its sensitivity to weak emissions of the OH* Meinel bands. The wave features, detectable at 0.75 km spatial resolution across its 3000 km imagery swath, are often confused by the upwelling emission of city lights and clouds reflecting downwelling nightglow. The Ionosphere, Mesosphere, upper Atmosphere and Plasmasphere (IMAP)/ Visible and near-Infrared Spectral Imager (VISI) O2 band, an independent measure of the AGW structures in nightglow based on the International Space Station (ISS) during 2012–2015, contains much less noise from the lower atmosphere. However, VISI offers much coarser resolution of 14–16 km and a narrower swath width of 600 km. Here, we present preliminary results of comparisons between VIIRS/DNB and VISI observations of AGWs, focusing on several concentric AGW events excited by the thunderstorms over Eastern Asia in August 2013. The comparisons point toward suggested improvements for future spaceborne airglow sensor designs targeting AGWs. 

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2. Thermospheric Density Perturbations Produced by Traveling Atmospheric Disturbances During August 2005 Storm

   https://doi.org/10.1029/2021JA030071  

   Pham, K. H. ; Zhang, B. ; Sorathia, K. ; Dang, T. ; Wang, W. ; Merkin, V. ; Liu, H. ; Lin, D. ; Wiltberger, M. ; Lei, J. ; et al ( February 2022 , Journal of Geophysical Research: Space Physics)

   Thermospheric mass density perturbations are commonly observed during geomagnetic storms and fundamental to upper atmosphere dynamics, but the sources of these perturbations are not well understood. Large neutral density perturbations during storms greatly affect the drag experienced by low Earth orbit. We investigated the thermospheric density perturbations at all latitudes observed along the CHAMP and GRACE satellite trajectories during the August 24–25, 2005 geomagnetic storm. Observations show that large neutral density enhancements occurred not only at high latitudes, but also globally. Large density perturbations were seen in the equatorial regions away from the high‐latitude, magnetospheric energy sources. We used the high‐resolution Multiscale Atmosphere Geospace Environment (MAGE) model to simulate consecutive neutral density changes observed by satellites during the storm. The MAGE simulation, which resolved mesoscale high‐latitude convection electric fields and field‐aligned currents, and included physics‐based specification of auroral precipitation, was contrasted with a standalone ionosphere‐thermosphere simulation driven by a high‐latitude electrodynamics empirical model. The comparison demonstrates that first‐principles representations of highly dynamic and localized Joule heating events in a fully coupled whole geospace model is critical to accurately capture both generation and propagation of traveling atmospheric disturbances (TADs) that produce neutral density perturbations globally. The MAGE simulation shows that larger density peaks in the equatorial region observed by CHAMP and GRACE are the result of TADs generated at high‐latitudes in both hemispheres, and intersect at low‐latitudes. This study reveals the importance of investigating thermospheric density variations at all latitudes in a fully coupled geospace model with sufficiently high resolving power.

    

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3. The impacts of warming on rapidly retreating high-altitude, low-latitude glaciers and ice core-derived climate records

   Thompson, L. G. ; Davis, M. E. ; Mosley-Thompson, E. ; Porter, S. E. ; Corrales, G. V. ; Shuman, C. A. ; Tucker, C. J. ( January 2021 , Global and planetary change)

   null (Ed.)

   Alpine glaciers in the low- and mid-latitudes respond more quickly than large polar ice sheets to changes in temperature, precipitation, cloudiness, humidity, and radiation. Many high-altitude glaciers are monitored by ground observations, aerial photography, and satellite-borne sensors. Regardless of latitude and elevation, nearly all nonpolar glaciers and ice caps are undergoing mass loss, which compromises the records of past climate preserved within them. Almost without exception, the retreat of these ice fields is persistent, and a very important driver is the recent warming of the tropical troposphere and oceans. Here we present data on the decrease in the surface area of four glaciers from low- to mid-latitude mountainous regions: the Andes of Peru and northern Bolivia, equatorial east Africa, equatorial Papua, Indonesia, and the western Tibetan Plateau. Climate records based on oxygen isotopic ratios (δ18O) measured in ice cores drilled from several glaciers in these regions reveal that the records from elevations below ~6000 m above sea level have been substantially modified by seasonal melting and the movement of meltwater through porous upper firn layers. Fortunately, δ18O records recovered from higher altitude sites still contain well-preserved seasonal variations to the surface; however, the projected increase in the rate of atmospheric warming implies that climate records from higher elevation glaciers will eventually also be degraded. A long-term ice core collection program on the Quelccaya ice cap in Peru, Earth’s largest tropical ice cap, illustrates that the deterioration of its climate record is concomitant with the increase in mid-troposphere temperatures. The melting ice and resulting growth of proglacial lakes presents an imminent hazard to nearby communities. The accelerating melting of glaciers, if sustained, ensures the eventual loss of unique and irreplaceable climate histories, as well as profound economic, agricultural, and cultural impacts on local communities. 

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4. The impacts of warming on rapidly retreating high-altitude, low-latitude glaciers and ice core-derived climate records

   https://doi.org/https://doi.org/10.1016/j.gloplacha.2021.103538  

   Thompson, L. G. ; Davis, M. E. ; Mosley-Thompson, E. ; Porter, S. E. ; Corrales, G. V. ; Shuman, C. A. ; Tucker, C. J. ( January 2021 , Global and planetary change)

   null (Ed.)

   Alpine glaciers in the low- and mid-latitudes respond more quickly than large polar ice sheets to changes in temperature, precipitation, cloudiness, humidity, and radiation. Many high-altitude glaciers are monitored by ground observations, aerial photography, and satellite-borne sensors. Regardless of latitude and elevation, nearly all nonpolar glaciers and ice caps are undergoing mass loss, which compromises the records of past climate preserved within them. Almost without exception, the retreat of these ice fields is persistent, and a very important driver is the recent warming of the tropical troposphere and oceans. Here we present data on the decrease in the surface area of four glaciers from low- to mid-latitude mountainous regions: the Andes of Peru and northern Bolivia, equatorial east Africa, equatorial Papua, Indonesia, and the western Tibetan Plateau. Climate records based on oxygen isotopic ratios (δ18O) measured in ice cores drilled from several glaciers in these regions reveal that the records from elevations below ~6000 m above sea level have been substantially modified by seasonal melting and the movement of meltwater through porous upper firn layers. Fortunately, δ18O records recovered from higher altitude sites still contain well-preserved seasonal variations to the surface; however, the projected increase in the rate of atmospheric warming implies that climate records from higher elevation glaciers will eventually also be degraded. A long-term ice core collection program on the Quelccaya ice cap in Peru, Earth’s largest tropical ice cap, illustrates that the deterioration of its climate record is concomitant with the increase in mid-troposphere temperatures. The melting ice and resulting growth of proglacial lakes presents an imminent hazard to nearby communities. The accelerating melting of glaciers, if sustained, ensures the eventual loss of unique and irreplaceable climate histories, as well as profound economic, agricultural, and cultural impacts on local communities. 

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5. pH-dependent production of molecular chlorine, bromine, and iodine from frozen saline surfaces

   https://doi.org/10.5194/acp-19-4917-2019  

   Halfacre, John W. ; Shepson, Paul B. ; Pratt, Kerri A. ( January 2019 , Atmospheric Chemistry and Physics)

   null (Ed.)

   Abstract. The mechanisms of molecular halogen production from frozen saline surfacesremain incompletely understood, limiting our ability to predict atmosphericoxidation and composition in polar regions. In this laboratory study,condensed-phase hydroxyl radicals (OH) were photochemically generated infrozen saltwater solutions that mimicked the ionic composition of oceanwater. These hydroxyl radicals were found to oxidize Cl−, Br−, andI−, leading to the release of Cl2, Br2, I2, and IBr. Atmoderately acidic pH (buffered between 4.5 and 4.8), irradiation of icecontaining OH precursors (either of hydrogen peroxide or nitrite ion)produced elevated amounts of I2. Subsequent addition of O3produced additional I2, as well as small amounts of Br2. At lowerpH (1.7–2.2) and in the presence of an OH precursor, rapid dark conversionof I− to I2 occurred from reactions with hydrogen peroxide ornitrite, followed by substantial photochemical production of Br2 uponirradiation. Exposure to O3 under these low pH conditions alsoincreased production of Br2 and I2; this likely results fromdirect O3 reactions with halides, as well as the production ofgas-phase HOBr and HOI that subsequently diffuse to frozen solution to reactwith Br− and I−. Photochemical production of Cl2 was onlyobserved when the irradiated sample was composed of high-purity NaCl andhydrogen peroxide (acting as the OH precursor) at pH = 1.8. Thoughcondensed-phase OH was shown to produce Cl2 in this study, kineticscalculations suggest that heterogeneous recycling chemistry may be equallyor more important for Cl2 production in the Arctic atmosphere. Thecondensed-phase OH-mediated halogen production mechanisms demonstrated hereare consistent with those proposed from recent Arctic field observations ofmolecular halogen production from snowpacks. These reactions, even if slow,may be important for providing seed halogens to the Arctic atmosphere. Ourresults suggest the observed molecular halogen products are dependent on therelative concentrations of halides at the ice surface, as we only observewhat diffuses to the air–surface interface. 

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