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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.

The gravity wave drag parametrization of the Whole Atmosphere Community Climate Model (WACCM) has been modified to include the wave‐driven atmospheric vertical mixing caused by propagating, non‐breaking, gravity waves. The strength of this atmospheric mixing is represented in the model via the “effective wave diffusivity” coefficient (K_wave). UsingK_wave, a new total dynamical diffusivity (K_Dyn) is defined.K_Dynrepresents the vertical mixing of the atmosphere by both breaking (dissipating) and vertically propagating (non‐dissipating) gravity waves. Here we show that, when the new diffusivity is used, the downward fluxes of Fe and Na between 80 and 100 km largely increase. Larger meteoric ablation injection rates of these metals (within a factor 2 of measurements) can now be used in WACCM, which produce Na and Fe layers in good agreement with lidar observations. Mesospheric CO₂is also significantly impacted, with the largest CO₂concentration increase occurring between 80 and 90 km, where model‐observations agreement improves. However, in regions where the model overestimates CO₂concentration, the new parametrization exacerbates the model bias. The mesospheric cooling simulated by the new parametrization, while needed, is currently too strong almost everywhere. The summer mesopause in both hemispheres becomes too cold by about 30 K compared to observations, but it shifts upward, partially correcting the WACCM low summer mesopause. Our results highlight the far‐reaching implications and the necessity of representing vertically propagating non‐breaking gravity waves in climate models. This novel method of modeling gravity waves contributes to growing evidence that it is time to move away from dissipative‐only gravity wave parametrizations.

The Southwestern North American megadrought began in 2000 and is now believed to be the driest 22‐year period in the region since 800 CE. The precipitation deficit during the megadrought (8.3% during 2000–2021) has been accompanied by a significant decrease in gravity waves observed in the upper atmosphere. Prior to the drought (1990–2000), the mean wave‐driven temperature fluctuation variances, between 85 and 100 km at Albuquerque and Ft. Collins, were comparable (62.2 ± 5.3 K²and 60.5 ± 1.8 K², respectively), with the largest variances occurring during winter and summer storm seasons. During the first decade of the drought (2001–2010), wave activity above Ft. Collins decreased by 28 ± 3%, mostly above 94 km, and changed from primarily semiannual to primarily annual variations. These changes may be related to reduced wave generation by tropospheric storms during the megadrought and to an altered geographic distribution of precipitation events in the western and mid‐western United States.

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.

Utilizing 956 nights of Na lidar nocturnal mesopause region temperature profiles acquired at Fort Collins, CO (40.6°N, 105.1°W) over a 20‐year period (March 1990–2010), we deduce background nightly mean temperatureand the square of the buoyancy frequencyN²(z) at 2‐km resolution between 83 and 105 km. The temperature climatology reveals the two‐level mesopause structure with clarity and sharp mesopause transitions, resulting in 102 days of summer from Days 121 to 222 of the year. The same data set analyzed at 10‐min and 1‐km resolution gives the gravity wave (GW) temperature perturbationsT_i'(z) and the wave varianceVar(T′(z)) and GW potential energyE_pm(z) between 85 and 100 km. Seasonal averages of GWVar(T′(z)) andE_pm(z) between 90 and 100 km, show thatVar(T′) for spring and autumn are comparable and lower than for summer and winter. Due mainly to the higher background stability, or largerN²(z) in summer,E_pm(z) between 85 and 100 km is comparable in spring, summer, and autumn seasons, but ∼30%–45% smaller than the winter values at the same altitude. The uncertainties are about 4% for winter and about 5% for the other three seasons. The values forE_pmare (156.0, 176.2, 145.6, and 186.2 J/kg) at 85 km for (spring, summer, autumn, and winter) respectively, (125.4, 120.2, 115.2, and 168.7 J/kg) at 93 km, and (207.5, 180.5, 213.1, and 278.6 J/kg) at 100 km. Going up in altitude, all profiles first decrease and then increase, suggesting that climatologically, GWs break below 85 km.

We report the first lidar observations of vertical fluxes of sensible heat and meteoric Na from 78 to 110 km in late May 2020 at McMurdo, Antarctica. The measurements include contributions from the complete temporal spectrum of gravity waves and demonstrate that wave‐induced vertical transport associated with atmospheric mixing by non‐breaking gravity waves, Stokes drift imparted by the wave spectrum, and perturbed chemistry of reactive species, can make significant contributions to constituent and heat transport in the mesosphere and lower thermosphere (MLT). The measured sensible heat and Na fluxes exhibit downward peaks at 84 km (−3.0 Kms⁻¹and −5.5 × 10⁴ cm⁻²s⁻¹) that are ∼4 km lower than the flux peak altitudes observed at midlatitudes. This is likely caused by the strong downwelling over McMurdo in late May. The Na flux magnitude is double the maximum at midlatitudes, which we believe is related to strong persistent gravity waves in the MLT at McMurdo. To achieve good agreement between the measured Na flux and theory, it was necessary to infer that a large fraction of gravity wave energy was propagating downward, especially between 80 and 95 km where the Na flux and wave dissipation were largest. These downward propagating waves are likely secondary waves generated in‐situ by the dissipation of primary waves that originate from lower altitudes. The sensible heat flux transitions from downward below 90 km to upward from 97 to 106 km. The observations are explained with the fully compressible solutions for polarization relations of primary and secondary gravity waves withλ_z > 10 km.

We report the first simultaneous, common‐volume lidar observations of thermosphere‐ionosphere Fe (TIFe) and Na (TINa) layers in Antarctica. We also report the observational discovery of nearly one‐to‐one correspondence between TIFe and aurora activity, enhanced ionization layers, and converging electric fields. Distinctive TIFe layers have a peak density of ~384 cm⁻³and the TIFe mixing ratio peaks around 123 km, ~5 times the mesospheric layer maximum. All evidence shows that Fe⁺ion‐neutralization is the major formation mechanism of TIFe layers. The TINa mixing ratio often exhibits a broad peak at TIFe altitudes, providing evidence for in situ production via Na⁺neutralization. However, the tenuous TINa layers persist long beyond TIFe disappearance and reveal gravity wave perturbations, suggesting a dynamic background of neutral Na, but not Fe, above 110 km. The striking differences between distinct TIFe and diffuse TINa suggest differential transport between Fe and Na, possibly due to mass separation.