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Abstract 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 withλz > 10 km.
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Effect of Temperature and Vertical Drift on Helium Ion Concentration Over Arecibo During Solar Maximum
Abstract We present an analysis of helium ion (He+) fraction in an altitude range from about 400 km to around 700 km and its relationship to the ion temperature (Ti) and the vertical ion drift under solar maximum conditions. The data were obtained from the Arecibo incoherent scatter radar during 27 September to 1 October 2014 and 16–20 December 2014. The large He+fraction (>10%) lasts 15 hr per day during the winter solstice, which is 3 times larger than during fall equinox. This difference is caused by the more persistent downward ion drift in the winter. The incremental He+fraction and incrementalTiare well anticorrelated, and the anticorrelation is more prominent during the daytime. These characteristics are associated with whether O+and He+are in diffusive equilibrium. During nighttime, we show that the vertical ion flow is downward causing the He+layer peak altitude to move to an altitude of 500 km from above 650 km. According to our analysis, He+fraction has to be larger than two thirds for diffusive equilibrium to occur above the He+peak height. Therefore, above the He+peak altitude, O+and He+cannot be in diffusive equilibrium with He+being the minor species. The vertical ion flow plays an important role in determining the diurnal variation and seasonal difference of He+distribution and whether He+is in a diffusive equilibrium with O+.
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- Award ID(s):
- 1744033
- PAR ID:
- 10450745
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 124
- Issue:
- 11
- ISSN:
- 2169-9380
- Page Range / eLocation ID:
- p. 9194-9202
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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