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1. Impact of Atmospheric Compressibility and Stokes Drift on the Vertical Transport of Heat and Constituents by Gravity Waves

   https://doi.org/10.1029/2023JD040436  

   Gardner, Chester_S (April 2024, Journal of Geophysical Research: Atmospheres)

   Abstract Vertical transport of heat and atmospheric constituents by gravity waves plays a crucial role in shaping the thermal and constituent structure of the middle atmosphere. We show that atmospheric mixing by non‐breaking waves can be described as a diffusion process where the potential temperature (K_H) and constituent (K_Wave) diffusivities depend on the compressibility of the wave fluctuations and the vertical Stokes drift imparted to the atmosphere by the wave spectrum. K_Hand K_Waveare typically much larger than the eddy diffusivity (K_zz), arising from the turbulence generated by breaking waves, and can exceed several hundred m²s⁻¹in regions of strong wave dissipation. We also show that the total diffusion of heat and constituents caused by waves, turbulence, and the thermal motion of molecules, is enhanced in the presence of non‐breaking waves by a factor that is proportional to the variance of the wave‐driven lapse rate fluctuations. Diffusion enhancements of both heat and constituents of 50% or more can be experienced in regions of low atmospheric stability, where the lapse rate fluctuations are large. These important transport effects are not currently included in most global chemistry‐climate models, which typically only consider the eddy diffusion that is induced when the unresolved, but parameterized waves, experience dissipation. We show that the theoretical results compare favorably with observations of the mesopause region at midlatitudes and describe how the theory may be used to more fully account for the unresolved wave transport in global models. 

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2. Seasonal Variations of Gravity Wave Induced Thermal and Constituent Diffusivities in the Mesopause Region Above Ft. Collins, CO (40.6°N, 105.1°W)

   https://doi.org/10.1029/2021JD036387  

   Gardner, Chester S.; She, Chiao‐Yao; Yan, Zhao‐Ai (June 2022, Journal of Geophysical Research: Atmospheres)

   Abstract Quasi‐random vertical displacement fluctuations, caused by the spectrum of non‐breaking gravity waves, mix the atmosphere, similar to turbulence, which induces significant vertical transport of heat and constituents in the upper atmosphere. Multi‐decade observations of temperature, made between 85 and 100 km with a Na lidar at Colorado State University (CSU, 40.6°N, 105.1°W), are used to derive the seasonal variations of the wave‐induced thermal (K_H) and constituent (K_Wave) diffusivities. Both show strong annual oscillations with maxima in winter, which increase with increasing altitude.K_HandK_Waveexhibit summer minima of ∼40 and ∼70 m²s⁻¹, respectively, that are approximately constant with altitude. In winter,K_Hvaries from ∼50 at 85 to ∼180 m²s⁻¹at 100 km, whileK_Wavevaries from ∼110 at 85 to ∼340 m²s⁻¹at 100 km. These values are much larger than the eddy diffusivity (K_zz∼ 35 m²s⁻¹) predicted for this site by the Whole Atmosphere Community Climate Model. The CSU diffusivities are comparable to similar measurements made at other mid‐latitude mountain sites in both hemispheres, and derived from global observations of atomic O. However, the seasonal variations differ from the O observations, which may reflect differences in wave sources at these sites and the different approaches employed to derive the wave diffusivities. Even so, the CSU results demonstrate that heat and constituent transport by unresolved, non‐breaking gravity waves are important processes that need to be incorporated in global chemistry models to properly characterize the thermal and constituent structure of the upper atmosphere. 

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3. Simulating diverse instabilities of dust in magnetized gas

   https://doi.org/10.1093/mnras/staa1046  

   Hopkins, Philip F; Squire, Jonathan; Seligman, Darryl (August 2020, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT Recently, Squire & Hopkins showed that charged dust grains moving through magnetized gas under the influence of a uniform external force (such as radiation pressure or gravity) are subject to a spectrum of instabilities. Qualitatively distinct instability families are associated with different Alfvén or magnetosonic waves and drift or gyro motion. We present a suite of simulations exploring these instabilities, for grains in a homogeneous medium subject to an external acceleration. We vary parameters such as the ratio of Lorentz-to-drag forces on dust, plasma β, size scale, and acceleration. All regimes studied drive turbulent motions and dust-to-gas fluctuations in the saturated state, rapidly amplify magnetic fields into equipartition with velocity fluctuations, and produce instabilities that persist indefinitely (despite random grain motions). Different parameters produce diverse morphologies and qualitatively different features in dust, but the saturated gas state can be broadly characterized as anisotropic magnetosonic or Alfvénic turbulence. Quasi-linear theory can qualitatively predict the gas turbulent properties. Turbulence grows from small to large scales, and larger scale modes usually drive more vigorous gas turbulence, but dust velocity and density fluctuations are more complicated. In many regimes, dust forms structures (clumps, filaments, sheets) that reach extreme overdensities (up to ≫109 times mean), and exhibit substantial substructure even in nearly incompressible gas. These can be even more prominent at lower dust-to-gas ratios. In other regimes, dust self-excites scattering via magnetic fluctuations that isotropize and amplify dust velocities, producing fast, diffusive dust motions. 

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4. Temperature Fluctuations of Different Vertical Scales in Raw and Processed U.S. High Vertical-Resolution Radiosonde Data

   https://doi.org/10.1175/JTECH-D-24-0012.1  

   Wang, Ling; Geller, Marvin A (March 2025, Journal of Atmospheric and Oceanic Technology)

   Abstract One-second U.S. high vertical-resolution radiosonde data (HVRRD) contain two different sets of temperature data—the raw data and the processed data. The processed data have been subject to radiation corrections, which have been well documented, and smoothing, the details of which are proprietary to the radiosonde manufacturers. We have tried to characterize this smoothing by computing the root-mean-square (rms) of normalized temperature perturbations derived from removing a second-degree polynomial fit for altitude segments (Δz) from 100 m to 5 km. We find that for Δz= 100 m, rms values are larger at higher altitudes, are larger in the raw data than in the processed data, and are larger during daytime than during nighttime, for both the raw and processed data. The rms values and their daytime to nighttime differences are larger in the raw data than in the processed data. As Δzincreases toward 5 km, the geographical patterns of rms over the contiguous United States from both the raw and processed data start resembling previously published gravity wave total energy patterns obtained from the older 6-s U.S. radiosonde data. An example is shown of a discontinuity in the small-scale rms values when radiosonde instrumentation is changed, so it is concluded that small-scale temperature fluctuations will be different for different radiosonde instruments. Examples are shown of enhanced small-scale rms temperature values indicative of turbulence resulting from gravity wave critical levels and from enhanced gravity waves due to seasonal maxima in convection. Significance StatementWe have characterized the variability of the raw and processed temperature profiles of the U.S. high vertical resolution radiosonde data for various vertical scales. We have argued that sources of small-scale fluctuations in the processed data include turbulence and the radiation effects which have not been accounted for in the current derivation of the processed data. Temperature fluctuations of larger scales correspond to those from gravity waves. We have shown an example of a discontinuity in small-scale fluctuations at a radiosonde station when the instrumentation was changed. These results suggest that temperature fluctuations resulting from varying amounts of solar radiation falling on the temperature sensor as the radiosonde instrumentation swings and rotates should be evaluated for each radiosonde system. 

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5. Lidar Observations of Instability and Estimates of Vertical Eddy Diffusivity Induced by Gravity Wave Breaking in the Arctic Mesosphere

   https://doi.org/10.1029/2020JD033450  

   Li, Jintai; Collins, Richard; Lu, Xian; Williams, Bifford (February 2021, Journal of Geophysical Research: Atmospheres)

   Abstract On the night of 18–19 October 2018, sodium resonance lidar measurements show the presence of overturning in the mesospheric sodium layer. Two independent tracers, sodium mixing ratio and potential temperature, derived from resonance and Rayleigh lidar measurements, reveal that vertical spreading of the sodium mixing ratio contours and a layer of convective instability coincide with this overturning. Analysis of lidar measurements also reveals the presence of gravity waves that propagate upward, are saturated, and dissipate at the height of the convective instability. The vertical spreading is analyzed in terms of turbulent diffusive transport using a model based on material continuity of sodium. Estimates of the turbulent eddy diffusion coefficient, K, and energy dissipation rate,εare derived from the transport model. The energy dissipated by the gravity waves is also calculated and found to be sufficient to generate the turbulence. We consider three other examples of overturning, instability and spreading on the nights of: 17–18 February 2009, 25–26 January 2015, and 8–9 October 2018. For all four events we find that the values of K (∼1,000 m²/s) are larger and the values ofε(∼10–100 mW/kg) are of similar magnitude to those values typically reported by ionization gauge measurements. These examples also reveal that higher levels of turbulent mixing are consistently found in regions of lower stability. 

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