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

Geophysical Research Letters

2017

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Turbulence is ubiquitous in the mesopause region, where the atmospheric stability is low and wave breaking is frequent. Measuring turbulence is challenging in this region and is traditionally done by rocket soundings and radars. In this work, we show for the first time that the modern Na wind/temperature lidar located at Andes Lidar Observatory in Cerro Pachón, Chile, is able to directly measure the turbulence perturbations in temperature and vertical wind between 85 and 100 km. Using 150 h of lidar observations, we derived the frequency (ω) and vertical wave number (m) spectra for both gravity wave and turbulence, which follow the power law with slopes consistent with theoretical models. The eddy heat flux generally decreases with altitude from about −0.5 Km s−1 at 85 km to −0.1 Km s−1 at 100 km, with a local maximum of −0.6 Km s−1 at 93 km. The derived mean turbulence thermal diffusivity and energy dissipation rate are 43 m2 s−1 and 37 mW kg−1, respectively. The mean net cooling resulted from the heat transport and energy dissipation is −4.9 ± 1.5 K d−1, comparable to that due to gravity wave transport at −7.9 ± 1.9 K d−1. Turbulence key parameters show consistency with turbulence theories.

“…With the assumption of k H ≈ k z z , ϵ can be related to k H according to Weinstock [] as

k_{H} \approx \frac{π^{1 / 2}}{4 C_{0}} \frac{ϵ}{N^{2}} .

The variance of relative temperature perturbation

\overset{T^{' 2}}{false}

is also related to ϵ according to Gardner and Liu []

\frac{\overset{T^{' 2}}{false}}{{\overset{T}{true}}^{2}} \approx \frac{4 N}{g^{2}} ϵ .

Using these equations, we can then derive ϵ from equation and compare the measured

\overset{w^{' 2}}{false}

and

\overset{T^{' 2}}{false}

with those predicted by equations and .…”

Section: Key Parameters Of Turbulencementioning

confidence: 99%

First Na lidar measurements of turbulence heat flux, thermal diffusivity, and energy dissipation rate in the mesopause region

Guo

Liu

Geophysical Research Letters

2017

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“…This is true for Rothera, Davis, and South Pole, but may not be for McMurdo where Fe + could also be important (see section 4). The primary chemical loss of Fe is through the formation of the FeOH dimer [ Plane et al ., ; Gardner and Liu , ] and photoionization. The net production and loss of Fe (excluding PMC absorption) is given by

\begin{matrix} left \\ {\overset{P}{true}}_{F e} - {\overset{L}{true}}_{F e} = - (k_{13} {([], FeOH)}^{2} + k_{18} [{NO}^{+}] [F e] + k_{19} [O_{2}^{+}] [F e] + J_{33} [F e]) = - k_{13} {([], FeOH)}^{2} - J_{33} [F e] \\ where \\ {normalk}_{13} = 9 \times 10^{- 10} {normalcm}^{3} {molecule}^{- 1} {normals}^{- 1} \\ k_{18} = 9.2 \times 10^{- 10} {normalcm}^{3} {molecule}^{- 1} {normals}^{- 1} \\ k_{19} = 1.1 \times 10^{- 9} {normalcm}^{3} {molecule}^{- 1} {normals}^{- 1} \\ J_{33} = 5 \times 10^{- 7} {normals}^{- 1} . \end{matrix}

…”

Section: Fe Chemistry Transport and Continuitymentioning

confidence: 99%

“…Conversely, the vertical flux in winter is larger than even the value measured at Table Mountain, CO, because of the large Fe influx caused by meridional transport. Vertical transport, which is related to wave activity [ Gardner and Liu , , ], is comparable at Rothera and South Pole in summer and winter. The chemical loss increases appreciably below 86 km as the densities of H, H 2 O, and O 2 increase, and the densities of O 3 and O decrease.…”

Section: Fe Chemistry Transport and Continuitymentioning

confidence: 99%

“…This is about 14 times smaller than the value employed here (10 5 cm −2 s −1 ), which is based upon lidar measurements and the Zodiacal Cloud particle model [e.g., Huang et al ., ]. It is believed that this large discrepancy arises because of the way that vertical transport by waves and turbulence is calculated in WACCM [ Gardner and Liu , ]. Although they disagree with WACCM‐Fe, our estimates of the vertical Fe fluxes are in sensible agreement with the net impact of Fe chemistry, horizontal transport, and meteoric influx.…”

Section: Fe Chemistry Transport and Continuitymentioning

confidence: 99%

“…Eddy transport by turbulent mixing may be slower at McMurdo, than at Rothera, but it is even slower at the pole. However, turbulent mixing is not the only wave‐induced transport mechanism [ Gardner and Liu , , ] and the vigorous wave activity, observed at McMurdo and South Pole, has been well documented [ Collins et al ., ; Pfenninger et al ., ; Chu et al ., ; Lu et al ., ]. Furthermore, it is difficult to understand why wave‐induced fluctuations of the neutral winds and temperature in the polar cap would reach a local minimum at McMurdo.…”

Section: Impact Of Fe+ Transportmentioning

confidence: 99%

See 2 more Smart Citations

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

Huang

2016

JGR Atmospheres

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We analyze year‐round Fe lidar observations made in Antarctica at Rothera (67.7°S), South Pole (90°S), and McMurdo (77.8°S). During midsummer, when the mesopause region is continuously sunlit, the Fe density between 84 and 88 km is independent of temperature, because photolysis of FeOH is so fast that virtually all of the FeOH is converted to Fe via this path, rather than via the temperature‐dependent FeOH + H reaction. The extremely low summertime densities at Rothera and South Pole are caused primarily by meridional transport northward out of the polar cap and, to a lesser extent, by uptake of Fe species on polar mesospheric cloud (PMC) ice particles. In midwinter, both meridional transport and temperature dominate Fe variations. The temperature sensitivity of Fe during winter is 2.2%/K at Rothera and 3.0%/K at South Pole. The annual mean Fe abundance at McMurdo is more than 50% larger than that observed at any other lidar site in both the Northern and Southern Hemispheres. McMurdo is located at the magnetic poleward edge of the auroral oval, just north of the deep polar cap. We hypothesize that southward transport of Fe+ out of the auroral oval in winter and northward transport of Fe+ out of the deep polar cap and auroral zone in summer, to McMurdo where it is neutralized, could be the source of the enhanced Fe. Theoretical calculations show that Fe+ densities of ~13,000 cm−3 in midwinter and ~1600 cm−3 in midsummer, between 84 and 88 km, are required to account for the high Fe densities at McMurdo.

OH* imager response to turbulence‐induced temperature fluctuations

Vargas

2016

JGR Atmospheres

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The layer of the excited state hydroxyl radical (OH*) is formed in the mesopause region by the reaction of ozone (O3) and atomic hydrogen (H). We derive the theoretical expressions for the OH* brightness and rotational temperature (T*) responses to high‐frequency atmospheric temperature perturbations. The theory is used to calculate the 1‐D and 2‐D horizontal wave number spectra of the OH* and T* image fluctuations induced by atmospheric turbulence. By applying the theory to images of a breaking gravity wave packet, acquired by the Utah State University Advanced Mesospheric Temperature Mapper, we show that existing infrared OH* imager technology can observe the evolution of gravity wave breakdown and characterize the resulting turbulent eddies in the source region and in the inertial subrange of the turbulence spectrum. For the example presented here, the RMS OH* brightness fluctuations induced by the gravity wave packet was 2.90% and by the associated turbulence was 1.07%. Unfortunately, the T* fluctuations induced by turbulence are usually too small to be observed in the OH* rotational temperature maps.