Vertical and horizontal transport of mesospheric Na: Implications for the mass influx of cosmic dust

doi:10.1016/j.jastp.2016.07.013

Journal of Atmospheric and Solar-Terrestrial Physics

Volume 162, September 2017, Pages 192-202

https://doi.org/10.1016/j.jastp.2016.07.013 Get rights and content

Highlights

•
Vertical fluxes of mesospheric metals are derived theoretically.
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Fluxes are related to meteoric influx, chemical loss and large-scale transport.
•
Vertical metal fluxes are insensitive to wave activity.
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Theory applied to Na lidar measurements and used to determine meteoric influx.
•
Global influx of Na vapor is 389±18 kg/d.
•
Influx of cosmic dust is 176±38 t/d if Na composition is equal to CI chondrites.
•
Influx of cosmic dust is 107±22 t/d if composition is equal to ordinary chondrites.

Abstract

The mesospheric metal layers are formed by the vaporization of high-speed cosmic dust particles as they enter the Earth's upper atmosphere. We show that the downward fluxes of these metal atoms, induced locally by waves and turbulence, are related in a straightforward way to the meteoric influxes of the metals, their chemical losses and their advective transport by the large-scale vertical and horizontal motions associated with the meridional circulation system. Above the peak of the metal layers where chemical losses and large-scale vertical motions are small, the wave-induced flux is insensitive to changes in local wave activity. If the downward transport velocity increases, because wave activity increases, then in response, the metal densities will decrease to maintain a constant vertical flux. By fitting the theoretical Na flux profile to the annual mean vertical flux profile measured during the night at the Starfire Optical Range, NM, we derive improved estimates for the global influxes of both Na and cosmic dust. The mean Na influx is 22,500±1050 atoms/cm²/s, which equals 389±18 kg/d for the global input of Na vapor. If the Na composition of the dust particles is identical to CI chondritic meteorites (4990 ppm by mass), then the global influx of cosmic dust is 176±38 t/d. If the composition is identical to ordinary chondrites (7680 ppm), the global dust influx is 107±22 t/d.

Introduction

Fe, Mg and Na are the most abundant gas-phase metal species in the mesosphere and lower thermosphere (MLT). During the last two decades our understanding of the chemistry and physics of these metal layers has improved significantly, in large part because of extensive lidar and satellite observations, chemical modeling and laboratory studies of key reactions (e.g. McNeil et al., 1995, McNeil et al., 2002; Plane, 2003; Marsh et al., 2013; Plane et al., 2015). The metal layers are formed by meteoric ablation between about 70 and 120 km. Various dynamical processes transport the vaporized atoms and ions downward to chemical sinks below 90 km, where they form stable compounds, which then polymerize to form meteoric smoke particles. This meteoric debris is advected to the winter pole by the prevailing winds where it eventually settles onto the surface. Although the ablation and sputtering processes and the metal chemistry in the upper atmosphere, are reasonably well understood, there is still considerable uncertainty in the absolute influx of the metals and their transport downward and poleward (Vondrak et al., 2008, Plane, 2012, Plane et al., 2015, Carrillo-Sánchez et al., 2015, Gardner and Liu, 2016).

Between 80 and 100 km, the chemical loss rates of Fe, Mg and Na, due to their reactions with O₃, are significant. However, this reaction produces the metal oxide, which reacts with O, to quickly recycle the metals back to their atomic forms. Because of this recycling, these metals behave much like inert species above 90 km, where the meteoric influx is balanced by downward transport to maintain the steady state layer profiles. Below 90 km, where the O density decreases rapidly with decreasing altitude, while the atmospheric density and the densities of CO₂, H₂O and H₂ increase, this recycling is inhibited as the metals are tied up in the more stable compounds FeOH, Mg(OH)₂ and NaHCO₃. When these compounds form dimers or polymermize with other meteoric constituent molecules, the metals are permanently removed from the gas phase. Above about 95 km, reactions of all three metals with O₂⁺ and NO⁺ create metals ions. Of course, during the day, photo-ionization is an additional loss process for these metals. In this way, Fe, Mg and Na are slowly depleted between 80 and 100 km as they are transported downward and converted, at least temporarily, to Fe⁺, Mg⁺, Na⁺, FeOH, Mg(OH)₂, and NaHCO₃. These losses influence both the metal atom densities and their vertical fluxes.

In this paper we focus on the vertical and horizontal transport of mesospheric Na. By assuming that Na is in chemical and dynamical equilibrium (i.e. the steady state Na density is constant), we show how the vertical flux of atomic Na, induced by waves and turbulence, is related in a straightforward way, to the meteoric influx of Na, its chemical loss and the effects of large-scale vertical and horizontal motions. The results are used to infer the global meteoric influx of Na vapor from the extensive lidar measurements of Na flux and other key atmospheric parameters made at the Starfire Optical Range (SOR), NM (35.0°N, 106.5°W) (Gardner and Liu, 2007 and 2010).

Section snippets

Na chemistry, transport and continuity

The rate of change of Na density is governed by the continuity equation. We assume that Na is in chemical and dynamical equilibrium so that in the steady state, the mean Na density is constant with respect to time, in which case the continuity equation is given by $\nabla • (\bar{\underset{̲}{V} [N a]}) = {\bar{μ}}_{N a} + ({\bar{P}}_{N a} - {\bar{L}}_{N a}) w h e r e [N a] = N a density {(cm}^{- 3}) \underset{̲}{V} = wind velocity vector (cm / s) \underset{̲}{V} [N a] = total Na flux {(cm}^{- 2} s^{- 1}) μ_{N a} = meteoric influx rate of Na {(cm}^{- 3} s^{- 1}) P_{N a} = chemical production rate of Na {(cm}^{- 3} s^{- 1}) L_{N a} = chemical loss rate of Na {(cm}^{- 3} s^{- 1}),$ where the overbar

Comparison with observations

Observations of Na, temperature, horizontal and vertical winds and the momentum, heat and Na fluxes were made during the night throughout the year at SOR in 1998–2000 with a Doppler lidar system (Gardner and Liu, 2007 and 2010). We estimate the meteoric influx μ_Na by fitting the theoretical flux profile predicted by the right-hand-side of Eq. (12) to the annual mean Na flux profile measured at SOR. The Na flux at 100 km, the large-scale vertical motions and the vertical gradient of [Na] are

Implications for the mass influx of cosmic dust

The meteoric influx inferred by fitting the theoretical Na flux profile to the measured profile is the annual mean nighttime value of μ_Na corresponding to the location of SOR. The Nesvorny et al. (2010 and 2011) zodiacal cloud model and the Fenzke and Jaunches (2008) meteor radar model show that the meteoric influx exhibits some seasonal variability, which increases towards the poles where it is about ±30% (e.g. see Fig. 1, Marsh et al., 2013). However, the annual mean influx, which we computed

Discussion and conclusions

We have used the continuity equation to show that the vertical flux of mesospheric Na, induced by waves and turbulence, is related in a straightforward way to the meteoric influx of Na atoms, their chemical loss and their transport by large-scale atmospheric motions. By fitting the theoretical vertical flux profile to the Na flux profile measured at the Starfire Optical Range, we derived an accurate estimate for the meteoric Na influx. While it's possible to also derive the total mass influx of

Acknowledgments

The data and programs used in this research are available upon request. This research was supported in part by National Science Foundation grants AGS 11-15725 and PLR 12-4631. The authors thank Juan Carrillo-Sánchez of the University of Leeds for providing the Na meteoric influx profiles calculated using CABMOD for the different cosmic dust models, including the fractions of Na injected between 84–100 km. We also thank Wuhu Feng of the University of Leeds for providing the H₂ and H₂O profiles

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View full text

Vertical and horizontal transport of mesospheric Na: Implications for the mass influx of cosmic dust

Highlights

Abstract

Introduction

Section snippets

Na chemistry, transport and continuity

Comparison with observations

Implications for the mass influx of cosmic dust

Discussion and conclusions

Acknowledgments

Planet. Space Sci.

Adv. Space Res.

First multi-year occultation observations of CO2 in the MLT by ACE satellite: observations and analysis using extended CMAM

J. Atmos. Chem. Phys.

On the size and velocity distribution of cosmic dust particles entering the atmosphere

Geophys. Res. Letts

An ion-molecule mechanism for the formation of neutral sporadic Na layers

J. Geophys. Res.

A semi-empirical model of the contribution from sporadic meteoroid sources on the meteor input function in the MLT observed at Arecibo

J. Geophys. Res.

Constraints on the formation environment of two chondrule-like igneous particles from comet 81P/Wild 2

Meteorit. Planet. Sci.

The effects of breaking gravity waves on the dynamics and chemical composition of the mesosphere and lower thermosphere

J. Geophys. Res.

Simulation of secular trends in the middle atmosphere, 1950-2003

J. Geophys. Res.

Seasonal variations of the vertical fluxes of heat and horizontal momentum in the mesopause region at Starfire Optical Range, New Mexico

J. Geophys. Res.

Wave-induced transport of atmospheric constituents and its effect on the mesospheric Na layer

J. Geophys. Res.

Chemical transport of neutral atmospheric constituents by waves and turbulence: Theory and observations

J. Geophys. Res. Atmos.

Inferring the global cosmic dust influx to the Earth's atmosphere from lidar observations of the vertical flux of mesospheric Na

J. Geophys. Res. Space Phys.

Impact of horizontal transport, temperature and PMC uptake on mesospheric Fe at high latitudes

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Reaction kinetics of meteoric sodium reservoirs in the upper atmosphere

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Measurements of the vertical fluxes of Atomic Fe and Na at the mesopause: Implications for the velocity of cosmic dust entering the atmosphere

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