Atomic oxygen (O) in the mesosphere and lower thermosphere (MLT) results from a balance between production via photo‐dissociation in the lower thermosphere and chemical loss by recombination in the upper mesosphere. The transport of O downward from the lower thermosphere into the mesosphere is preferentially driven by the eddy diffusion process that results from dissipating gravity waves and instabilities. The motivation here is to probe the intra‐annual variability of the eddy diffusion coefficient (k
This content will become publicly available on November 3, 2024
As a companion study of the Part 1 (J. C. Wang et al., 2022,
- NSF-PAR ID:
- 10476279
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 128
- Issue:
- 11
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract zz ) and eddy velocity in the MLT based on the climatology of the region, initially accomplished by Garcia and Solomon (1985,https://doi.org/10.1029/JD090iD02p03850 ). In the current study, the intra‐annual cycle was divided into 26 two‐week periods for each of three zones: the northern hemisphere (NH), southern hemisphere (SH), and equatorial (EQ). Both 16 years of SABER (2002–2018) and 10 years of SCIAMACHY (2002–2012) O density measurements, along with NRLMSIS®2.0 were used for calculation of atomic oxygen eddy diffusion velocities and fluxes. Our prominent findings include a dominant annual oscillation below 87 km in the NH and SH zones, with a factor of 3–4 variation between winter and summer at 83 km, and a dominant semiannual oscillation at all altitudes in the EQ zone. The measured global average kzz at 96 km lacks the intra‐annual variability of upper atmosphere density data deduced by Qian et al. (2009,https://doi.org/10.1029/2008JA013643 ). The very large seasonal (and hemispherical) variations in kzz and O densities are important to separate and isolate in satellite analysis and to incorporate in MLT models. -
more » « less
Abstract Wave‐induced adiabatic mixing in the winter midlatitudes is one of the key processes impacting stratospheric transport. Understanding its strength and structure is vital to understanding the distribution of trace gases and their modulation under a changing climate. Age‐of‐air is often used to understand stratospheric transport, and this study proposes refinements to the vertical age gradient theory of Linz et al. (2021),
https://doi.org/10.1029/2021JD035199 . The theory assumes exchange of air between a well‐mixed tropics and a well‐mixed extratropics, separated by a transport barrier, quantifying the adiabatic mixing flux across the interface using age‐based measures. These assumptions are re‐evaluated and a refined framework that includes the effects of meridional tracer gradients is established to quantify the mixing flux. This is achieved, in part, by computing a circulation streamfunction in age‐potential temperature coordinates to generate a complete distribution of parcel ages being mixed in the midlatitudes. The streamfunction quantifies the “true” age of parcels mixed between the tropics and the extratropics. Applying the revised theory to an idealized and a comprehensive climate model reveals that ignoring the meridional gradients in age leads to an underestimation of the wave‐driven mixing flux. Stronger, and qualitatively similar fluxes are obtained in both models, especially in the lower‐to‐middle stratosphere. While the meridional span of adiabatic mixing in the two models exhibits some differences, they show that the deep tropical pipe, that is, latitudes equatorward of 15° barely mix with older midlatitude air. The novel age‐potential temperature circulation can be used to quantify additional aspects of stratospheric transport. -
more » « less
Abstract A dramatic thermospheric temperature enhancement and inversion layer (TTEIL) was observed by the Fe Boltzmann lidar at McMurdo, Antarctica during a geomagnetic storm (Chu et al. 2011,
https://doi.org/10.1029/2011GL050016 ). The Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) driven by empirical auroral precipitation and background electric fields cannot adequately reproduce the TTEIL. We incorporate the Defense Meteorological Satellite Program (DMSP)/Special Sensor Ultraviolet Spectrographic Imager (SSUSI) auroral precipitation maps, which capture the regional‐scale features into TIEGCM and add subgrid electric field variability in the regions with strong auroral activity. These modifications enable the simulation of neutral temperatures closer to lidar observations and neutral densities closer to GRACE satellite observations (~475 km). The regional scale auroral precipitation and electric field variabilities are both needed to generate strong Joule heating that peaks around 120 km. The resulting temperature increase leads to the change of pressure gradients, thus inducing a horizontal divergence of air flow and large upward winds that increase with altitude. Associated with the upwelling wind is the adiabatic cooling gradually increasing with altitude and peaking at ~200 km. The intense Joule heating around 120 km and strong cooling above result in differential heating that produces a sharp TTEIL. However, vertical heat advection broadens the TTEIL and raises the temperature peak from ~120 to ~150 km, causing simulations deviating from observations. Strong local Joule heating also excites traveling atmospheric disturbances that carry the TTEIL signatures to other regions. Our study suggests the importance of including fine‐structure auroral precipitation and subgrid electric field variability in the modeling of storm‐time ionosphere‐thermosphere responses. -
more » « less
Abstract We present modeling results of tube and knot (T&K) dynamics accompanying thermospheric Kelvin Helmholtz Instabilities (KHI) in an event captured by the 2018 Super Soaker campaign (R. L. Mesquita et al., 2020,
https://doi.org/10.1029/2020JA027972 ). Chemical tracers released by a rocketsonde on 26 January 2018 showed coherent KHI in the lower thermosphere that rapidly deteriorated within 45–90 s. Using wind and temperature data from the event, we conducted high resolution direct numerical simulations (DNS) employing both wide and narrow spanwise domains to facilitate (wide domain case) and prohibit (narrow domain case) the axial deformation of KH billows that allows tubes and knots to form. KHI T&K dynamics are shown to produce accelerated instability evolution consistent with the observations, achieving peak dissipation rates nearly two times larger and 1.8 buoyancy periods faster than axially uniform KHI generated by the same initial conditions. Rapidly evolving twist waves are revealed to drive the transition to turbulence; their evolution precludes the formation of secondary convective instabilities and secondary KHI seen to dominate the turbulence evolution in artificially constrained laboratory and simulation environments. T&K dynamics extract more kinetic energy from the background environment and yield greater irreversible energy exchange and entropy production, yet they do so with weaker mixing efficiency due to greater energy dissipation. The results suggest that enhanced mixing from thermospheric KHI T&K events could account for the discrepancy between modeled and observed mixing in the lower thermosphere (Garcia et al., 2014,https://doi.org/10.1002/2013JD021208 ; Liu, 2021,https://doi.org/10.1029/2020GL091474 ) and merits further study. -
more » « less
Abstract Analysis of an established geocoronal H
α data set indicates a seasonal trend in observed dusk‐to‐dawn intensity variation, consistent with a diurnal variation in the underlying thermospheric hydrogen density. Observations were obtained at Pine Bluff Observatory, WI, from 2000 to 2001 using a high spectral resolution (R ∼80,000) Fabry‐Perot annular summing spectrometer. This dusk‐to‐dawn asymmetry in intensity is highest in winter months with a difference of ∼2.7 Rayleighs and smallest in summer months with a difference of ∼0.5 Rayleighs; observations near equinox show a dusk‐to‐dawn difference in intensity close to ∼1.3 Rayleighs. Comparisons between modeled and observed dusk‐to‐dawn intensity variation show good agreement near the equinoxes. The modeled intensity was generated using the lyao_rt radiative transport code of Bishop (1999,https://doi.org/10.1016/S0022-4073(98)00031-4 ), employing NRLMSISE‐00 thermospheric hydrogen profiles extended into the exosphere via the evaporative case of the Bishop analytic exosphere. Near the equinoxes and summer solstice, the model tends to agree with observations. Near the winter solstice, the model underestimates the dusk‐to‐dawn asymmetry by 1.5–2 Rayleighs. Overall, modeled Hα intensity generated with NRLMSISE‐00 as the thermospheric input is shown to be consistently lower than observed intensity by a factor of ∼2.
