scholarly journals Eddy turbulence parameters inferred from radar observations at Jicamarca

2007 ◽  
Vol 25 (2) ◽  
pp. 475-481 ◽  
Author(s):  
M. N. Vlasov ◽  
M. C. Kelley ◽  
D. L. Hysell
Keyword(s):  
Nitric Oxide ◽  
Diffusion Coefficient ◽  
Electron Density ◽  
Lower Thermosphere ◽  
Eddy Diffusion ◽  
Thermal Balance ◽  
Plasma Dynamic ◽  
Eddy Diffusion Coefficient ◽  
E Region ◽  
Turbulence Parameters

Abstract. Significant electron density striations, neutral temperatures 27 K above nominal, and intense wind shear were observed in the E-region ionosphere over the Jicamarca Radio Observatory during an unusual event on 26 July 2005 (Hysell et al., 2007). In this paper, these results are used to estimate eddy turbulence parameters and their effects. Models for the thermal balance in the mesosphere/lower thermosphere and the charged particle density in the E region are developed here. The thermal balance model includes eddy conduction and viscous dissipation of turbulent energy as well as cooling by infrared radiation. The production and recombination of ions and electrons in the E region, together with the production and transport of nitric oxide, are included in the plasma density model. Good agreement between the model results and the experimental data is obtained for an eddy diffusion coefficient of about 1×103 m2/s at its peak, which occurs at an altitude of 107 km. This eddy turbulence results in a local maximum of the temperature in the upper mesosphere/lower thermosphere and could correspond either to an unusually high mesopause or to a double mesosphere. Although complicated by plasma dynamic effects and ongoing controversy, our interpretation of Farley-Buneman wave phase velocity (Hysell et al., 2007) is consistent with a low Brunt-Väisälä frequency in the region of interest. Nitric oxide transport due to eddy diffusion from the lower thermosphere to the mesosphere causes electron density changes in the E region whereas NO density modulation due to irregularities in the eddy diffusion coefficient creates variability in the electron density.

Variation of CO/CO2 profiles in the Marian mesosphere and lower thermosphere retrieved from TGO/NOMAD

2021 ◽  
Author(s):  
Nao Yoshida ◽  
Hiromu Nakagawa ◽  
Shohei Aoki ◽  
Justin Erwin ◽  
Ann Carine Vandaele ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Atmospheric Circulation ◽  
Dust Storm ◽  
Lower Thermosphere ◽  
Eddy Diffusion ◽  
Mixing Ratio ◽  
Solar Occultation ◽  
Eddy Diffusion Coefficient ◽  
Mesosphere And Lower Thermosphere ◽  
Mlt Region

<p>CO is produced by the photodissociation of CO<sub>2</sub> and recycled to CO<sub>2</sub> by the catalytic cycle involving HOx in the Martian atmosphere [e.g., McElroy & Donahue, 1972]. In the mesosphere and lower thermosphere (MLT) region of Mars, the number density of CO is determined by photodissociation, diffusion, and atmospheric circulation. The increase of the CO mixing ratio in the MLT region and further enhancement in the polar region due to the transport of CO-enriched air via meridional circulation are predicted in the 3D models [Daerden et al., 2018; Holmes et al., 2019]. On the other hand, the decrease in the CO mixing ratio in the MLT region during a global dust storm is detected by TGO/ACS, which suggests that the increase in the hygropause altitude leads to the increase in the vertical range over which OH becomes available to convert into CO<sub>2</sub> [Olsen et al., 2021]. Additionally, a substantial variation of the homopause altitude has been investigated [Slipski et al., 2018; Jakosky et al., 2017; Yoshida et al., 2020], which suggests that the order of magnitude changes in the eddy diffusion coefficient at the homopause [Slipski et al., 2018], and then variations in the profile of CO mixing ratio in the MLT region. However, the effects of change in the eddy diffusion coefficient on the profile of CO mixing ratio have not been investigated. The variability of the CO mixing ratio profiles can be a clue for understanding the dynamical coupling between the lower and the upper atmospheres.</p> <p>To clarify the contributions of photochemistry, diffusion, and atmospheric circulation to the CO/CO<sub>2</sub> profiles in the MLT region, we use the Nadir and Occultation for MArs Discovery (NOMAD) instrument aboard Trace Gas Orbiter (TGO). NOMAD solar occultation is designed as the combination of the Acousto Optical Turnable Filter and echelle grating [Neefs et al., 2015; Thomas et al., 2016]. NOMAD solar occultation operates in the wavelength range of 2.2 - 4.3 μm (2320 to 4350 cm<sup>-1</sup>) with a high spectral resolution (λ/dλ = 20000) [Vandaele et al., 2018]. It provides us CO and CO<sub>2</sub> spectra below 100 km and 180 km altitudes, respectively.</p> <p>In this study, we applied the equivalent width technique [Chamberlain and Hunten, 1987; Krasnopolsky, 1986] to derive a new set of CO and CO<sub>2</sub> column densities, respectively, with the observed atmospheric transmittance spectra by NOMAD solar occultation. The absorption lines centered at 4285.0, 4288.2, and 4291.5 cm<sup>-1</sup> for CO (2-0) band and 3358.7, 3364.9, and 3366.4 cm<sup>-1</sup> for CO<sub>2</sub> (21102-00001) band are carefully selected for retrievals due to the contribution of nearby and central orders [cf. Liuzzi et al., 2019]. It is noted that the line strengths of the selected CO<sub>2</sub> have high sensitivity to the background temperature. In this study, we applied the vertical profiles of temperature simulated in the GEM-Mars model [Neary et al., 2018; Daerden et al., 2019]. We retrieve the CO and CO<sub>2</sub> slant column densities between 60 and ~100 km altitudes because those slant opacities are saturated below 60 km altitude. The CO and CO<sub>2</sub> spectra observed from April 2018 to September 2020, corresponding to from MY 34 Ls ~ 150 to MY 35 Ls ~ 280, are investigated.</p> <p>We found that the retrieved CO/CO<sub>2</sub> ratio between 60 and ~100 km increases with altitude. A behavior of the decrease in the CO/CO<sub>2</sub> ratio during the global dust storm corresponds to the previous observations [Olsen et al., 2021]. However, the CO/CO<sub>2</sub> profiles also vary with season and latitude. For interpretation, the 1D photochemical model will be compared with newly obtained CO/CO<sub>2</sub> profiles, especially in order to discuss the contributions from the variations in eddy diffusion coefficient and photochemistry in the MLT region on Mars.</p>

scholarly journals Estimates of eddy turbulence consistent with seasonal variations of atomic oxygen and its possible role in the seasonal cycle of mesopause temperature

2010 ◽  
Vol 28 (11) ◽  
pp. 2103-2110 ◽  
Author(s):  
M. N. Vlasov ◽  
M. C. Kelley
Keyword(s):  
Diffusion Coefficient ◽  
Gravity Waves ◽  
Seasonal Variations ◽  
Atomic Oxygen ◽  
Lower Thermosphere ◽  
Eddy Diffusion ◽  
Downward Motion ◽  
Adiabatic Cooling ◽  
Eddy Diffusion Coefficient ◽  
The Impact

Abstract. According to current understanding, adiabatic cooling and heating induced by the meridional circulation driven by gravity waves is the major process for the cold summer and warm winter polar upper mesosphere. However, our calculations show that the upward/downward motion needed for adiabatic cooling/heating of the summer/winter polar mesopause simultaneously induces a seasonal variation in both the O maximum density and the altitude of the [O] peak that is opposite to the observed variables generalized by the MSISE-90 model. It is usually accepted that eddy turbulence can produce the [O] seasonal variations. Using this approach, we can infer the eddy diffusion coefficient for the different seasons. Taking these results and experimental data on the eddy diffusion coefficient, we consider in detail and estimate the heating and cooling caused by eddy turbulence in the summer and winter polar upper mesosphere. The seasonal variations of these processes are similar to the seasonal variations of the temperature and mesopause. These results lead to the conclusion that heating/cooling by eddy turbulence is an important component in the energy budget and that adiabatic cooling/heating induced by upward/downward motion cannot dominate in the mesopause region. Our study shows that the impact of the dynamic process, induced by gravity waves, on [O] distributions must be included in models of thermal balance in the upper mesosphere and lower thermosphere (MLT) for a consistent description because (a) the [O] distribution is very sensitive to dynamic processes, and (b) atomic oxygen plays a very important role in chemical heating and infrared cooling in the MLT. To our knowledge, this is the first attempt to consider this aspect of the problem.

Observations of O2(¹Δg) in the atmosphere and allowable values of the eddy diffusion coefficient

1970 ◽  
Vol 75 (31) ◽  
pp. 6398-6401 ◽  
Author(s):  
L. R. Megill ◽  
J. C. Haslett ◽  
H. I. Schiff ◽  
G. W. Adams
Keyword(s):  
Diffusion Coefficient ◽  
Eddy Diffusion ◽  
Eddy Diffusion Coefficient

scholarly journals Specific features of eddy turbulence in the turbopause region

2014 ◽  
Vol 32 (4) ◽  
pp. 431-442 ◽  
Author(s):  
M. N. Vlasov ◽  
M. C. Kelley
Keyword(s):  
Diffusion Coefficient ◽  
Heat Transport ◽  
Diffusion Coefficients ◽  
Transport Coefficient ◽  
Molecular Diffusion ◽  
Eddy Diffusion ◽  
Cooling Rates ◽  
Eddy Diffusion Coefficient ◽  
Eddy Heat Transport ◽  
The Mean

Abstract. The turbopause region is characterized by transition from the mean molecular mass (constant with altitude) to the mean mass (dependent on altitude). The former is provided by eddy turbulence, and the latter is induced by molecular diffusion. Competition between these processes provides the transition from the homosphere to the heterosphere. The turbopause altitude can be defined by equalizing the eddy and molecular diffusion coefficients and can be located in the upper mesosphere or the lower thermosphere. The height distributions of chemical inert gases very clearly demonstrate the transition from turbulent mixing to the diffusive separation of these gases. Using the height distributions of the chemical inert constituents He, Ar, and N2 given by the MSIS-E-90 model and the continuity equations, the height distribution of the eddy diffusion coefficient in the turbopause region can be inferred. The eddy diffusion coefficient always strongly reduces in the turbopause region. According to our results, eddy turbulence above its peak always cools the atmosphere. However, the cooling rates calculated with the eddy heat transport coefficient equaled to the eddy diffusion coefficient were found to be much larger than the cooling rates corresponding to the neutral temperatures given by the MSIS-E-90 model. The same results were obtained for the eddy diffusion coefficients inferred from different experimental data. The main cause of this large cooling is the very steep negative gradient of the eddy heat transport coefficient, which is equal to the eddy diffusion coefficient if uniform turbulence takes place in the turbopause region. Analysis of wind shear shows that localized turbulence can develop in the turbopause region. In this case, eddy heat transport is not so effective and the strong discrepancy between cooling induced by eddy turbulence and cooling corresponding to the temperature given by the MSIS-E-90 model can be removed.

scholarly journals Simulations of large winds and wind shears induced by gravity wave breaking in the mesosphere and lower thermosphere (MLT) region

2014 ◽  
Vol 32 (5) ◽  
pp. 543-552 ◽  
Author(s):  
X. Liu ◽  
J. Xu ◽  
H.-L. Liu ◽  
J. Yue ◽  
W. Yuan
Keyword(s):  
Numerical Model ◽  
Phase Velocity ◽  
Lower Thermosphere ◽  
Eddy Diffusion ◽  
Vertical Wavelength ◽  
Eddy Diffusion Coefficient ◽  
Background Temperature ◽  
Mesosphere And Lower Thermosphere ◽  
Wind Shears ◽  
Mlt Region

Abstract. Using a fully nonlinear two-dimensional (2-D) numerical model, we simulated gravity waves (GWs) breaking and their contributions to the formation of large winds and wind shears in the mesosphere and lower thermosphere (MLT). An eddy diffusion coefficient is used in the 2-D numerical model to parameterize realistic turbulent mixing. Our study shows that the momentum deposited by breaking GWs accelerates the mean wind. The resultant large background wind increases the GW's apparent horizontal phase velocity and decreases the GW's intrinsic frequency and vertical wavelength. Both the accelerated mean wind and the decreased GW vertical wavelength contribute to the enhancement of wind shears. This, in turn, creates a background condition that favors the occurrence of GW instability, breaking, and momentum deposition, as well as mean wind acceleration, which further enhances the wind shears. We find that GWs with longer vertical wavelengths and faster horizontal phase velocity can induce larger winds, but they may not necessarily induce larger wind shears. In addition, the background temperature can affect the time and height of GW breaking, thus causing accelerated mean winds and wind shears.

scholarly journals Estimates of vertical eddy diffusivity in the upper mesosphere in the presence of a mesospheric inversion layer

2011 ◽  
Vol 29 (11) ◽  
pp. 2019-2029 ◽  
Author(s):  
R. L. Collins ◽  
G. A. Lehmacher ◽  
M. F. Larsen ◽  
K. Mizutani
Keyword(s):  
Diffusion Coefficient ◽  
Inversion Layer ◽  
Eddy Diffusion ◽  
Lapse Rate ◽  
The Arctic ◽  
Maximum Temperature ◽  
Lower Edge ◽  
Sodium Layer ◽  
Eddy Diffusion Coefficient ◽  
Lidar Observations

Abstract. Rayleigh and resonance lidar observations were made during the Turbopause experiment at Poker Flat Research Range, Chatanika Alaska (65° N, 147° W) over a 10 h period on the night of 17–18 February 2009. The lidar observations revealed the presence of a strong mesospheric inversion layer (MIL) at 74 km that formed during the observations and was present for over 6 h. The MIL had a maximum temperature of 251 K, amplitude of 27 ± 7 K, a depth of 3.0 km, and overlying lapse rate of 9.4 ± 0.3 K km−1. The MIL was located at the lower edge of the mesospheric sodium layer. During this coincidence the lower edge of the sodium layer was lowered by 2 km to 74 km and the bottomside scale height of the sodium increased from 1 km to 15 km. The structure of the MIL and sodium are analyzed in terms of vertical diffusive transport. The analysis yields a lower bound for the eddy diffusion coefficient of 430 m2 s−1 and the energy dissipation rate of 2.2 mW kg−1 at 76–77 km. This value of the eddy diffusion coefficient, determined from naturally occurring variations in mesospheric temperatures and the sodium layer, is significantly larger than those reported for mean winter values in the Arctic but similar to individual values reported in regions of convective instability by other techniques.

Sign in / Sign up

Export Citation Format

Share Document