scholarly journals Sixteen years (2002-2018) of SABER measurements and the MSIS model were used to study the average SAO (semiannual oscillation) and AO (annual oscillation) variations of k$_{zz}$ (eddy diffusion coefficient) in the mesosphere (80-96 km).

2021 ◽  
Author(s):  
Gary Swenson ◽  
Fabio Vargas ◽  
McArthur Jones Jr
Keyword(s):  
Diffusion Coefficient ◽  
Eddy Diffusion ◽  
Eddy Diffusion Coefficient ◽  
Semiannual Oscillation

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 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.

scholarly journals The urban canopy meteorological forcing and its impact on ozone and PM<sub>2.5</sub>: role of the vertical turbulent transport

2019 ◽  
Author(s):  
Peter Huszar ◽  
Jan Karlický ◽  
Jana Ďoubalová ◽  
Kateřina Šindelářová ◽  
Tereza Nováková ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Turbulent Transport ◽  
Urban Canopy ◽  
Eddy Diffusion ◽  
Meteorological Forcing ◽  
Eddy Diffusion Coefficient ◽  
The Impact ◽  
Vertical Eddy ◽  
Vertical Eddy Diffusion

Abstract. Urban surfaces due to specific geometry and physical properties bring modified transport of momentum, moisture and heat between them and the air above and perturb the radiative, thermal and mechanical balance resulting in changed meteorological condition (e.g. the UHI – urban heat island phenomenon). From an air quality perspective, many studies argue that one of the most important changes is the increased turbulence enhancing vertical mixing of pollutants above cities, although increased temperatures and wind stilling play an important role too. Using the regional climate model RegCM4 coupled to chemistry transport model CAMx over central Europe we study how urban surfaces affect the vertical turbulent transport of selected pollutants through modifications of the vertical eddy diffusion coefficient (Kv). For the period of 2007–2011 and over central Europe numerous experiments are carried out in order to evaluate the impact of six different methods for Kv calculation on the surface concentrations as well as vertical profiles of ozone and PM2.5 over selected cities (Prague and Berlin). Three cascading domains are set up at 27 km, 9 km and 3 km resolutions, which further enables to analyze the sensitivity to model grid resolution. Numerous experiments are performed where urban surfaces are considered or replaced by rural ones in order to isolate the urban canopy meteorological forcing. Apart from the well pronounced and expected impact on temperature (increases up to 2 °C) and wind (decreases up to −2 m s−1) there is strong impact on vertical eddy diffusion in all of the six Kv methods. The Kv enhancement ranges from a few 0.5 up to 30 m2 s−1 at the surface and from 1 to 100 m2 s−1 at higher levels depending on the methods, while the turbulent kinetic energy (TKE) based methods produce the largest impact. The range of impact on the vertical eddy diffusion coefficient propagates to a range of ozone (O3) increase of 0.4 to 4 ppbv near the surface in both summer and winter, while at higher levels, decreases occur from a few −0.4 ppbv to as much as −2 ppbv. In case of PM2.5, enhanced vertical eddy diffusion leads to decrease of near surface concentrations ranging from almost zero to −1 μg m−3 in summer and to decreases from −0.5 to −2 μg m−3 in winter. Comparing these results to the total-impact, i.e. to the impact of all considered urban meteorological changes, we can conclude that much of the overall urban meteorological forcing is explained by acting of the enhanced vertical eddy diffusion, which counterweights the opposing effects of other components of this forcing (temperature, humidity and wind impact). The results further show that this conclusion holds regardless of the resolution chosen and in both the warm and cold part of the year. Our study demonstrates the dominant role of turbulent transport of pollutants above urban areas and stresses the need for further investigation how variation of urban land-use influence the pollutant transport from the urban canopy.

Whole-Lake Model for the Distribution of Sediment-Derived Chemical Species

1980 ◽  
Vol 37 (3) ◽  
pp. 552-558 ◽  
Author(s):  
R. H. Hesslein
Keyword(s):  
Diffusion Coefficient ◽  
Dissolved Inorganic Carbon ◽  
Chemical Species ◽  
Eddy Diffusion ◽  
Sole Source ◽  
Experimental Lakes Area ◽  
Lake Model ◽  
Eddy Diffusion Coefficient ◽  
Vertical Eddy ◽  
Vertical Eddy Diffusion

The distribution of CH4, ΣCO2, and NH3-N below the thermocline of Lake 227 can be reproduced using a simple numerical model. The model uses a constant vertical eddy diffusion coefficient and assumes the sediments to be the sole source of the chemical species. Analogs dependent on oxygen concentration can effectively represent conditions at the interface of the modeled region and the shallower depths in the lake. The best tit value for the vertical eddy diffusion coefficient is 3.1 × 10−3 cm2∙s−1. This is in good agreement with other independent measurements of this phenomena. The best fit fluxes of CH4, dissolved inorganic carbon and NH3-N are respectively: 13 × 10−3 mol∙m−2∙d−1, 7.5 × 10−3 mol∙m−2∙d−1, and 1.65 × 10−3 mol∙m−2∙d−1. The flux of methane is similar to that found in other small productive northern lakes and the ratio of CH4:ΣCO2 production of 1.73 falls in the range of values established for fermentation of mixed organic materials and sediments. The flux of ΣCO2 is 50–75% of the bicarbonate flux (10–15 × 10−3 mol∙m−2∙d−1) found previously in Linsley Pond, Connecticut.Key words: sediment–water interactions, methane, CO2, and ammonia fluxes, diffusion from sediments, Experimental Lakes Area

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

&lt;p&gt;CO is produced by the photodissociation of CO&lt;sub&gt;2&lt;/sub&gt; and recycled to CO&lt;sub&gt;2&lt;/sub&gt; by the catalytic cycle involving HOx in the Martian atmosphere [e.g., McElroy &amp; 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&lt;sub&gt;2&lt;/sub&gt; [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.&lt;/p&gt; &lt;p&gt;To clarify the contributions of photochemistry, diffusion, and atmospheric circulation to the CO/CO&lt;sub&gt;2&lt;/sub&gt; 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 &amp;#956;m (2320 to 4350 cm&lt;sup&gt;-1&lt;/sup&gt;) with a high spectral resolution (&amp;#955;/d&amp;#955; = 20000) [Vandaele et al., 2018]. It provides us CO and CO&lt;sub&gt;2&lt;/sub&gt; spectra below 100 km and 180 km altitudes, respectively.&lt;/p&gt; &lt;p&gt;In this study, we applied the equivalent width technique [Chamberlain and Hunten, 1987; Krasnopolsky, 1986] to derive a new set of CO and CO&lt;sub&gt;2&lt;/sub&gt; 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&lt;sup&gt;-1&lt;/sup&gt; for CO (2-0) band and 3358.7, 3364.9, and 3366.4 cm&lt;sup&gt;-1&lt;/sup&gt; for CO&lt;sub&gt;2&lt;/sub&gt; (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&lt;sub&gt;2&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt; slant column densities between 60 and ~100 km altitudes because those slant opacities are saturated below 60 km altitude. The CO and CO&lt;sub&gt;2&lt;/sub&gt; spectra observed from April 2018 to September 2020, corresponding to from MY 34 Ls ~ 150 to MY 35 Ls ~ 280, are investigated.&lt;/p&gt; &lt;p&gt;We found that the retrieved CO/CO&lt;sub&gt;2&lt;/sub&gt; ratio between 60 and ~100 km increases with altitude. A behavior of the decrease in the CO/CO&lt;sub&gt;2&lt;/sub&gt; ratio during the global dust storm corresponds to the previous observations [Olsen et al., 2021]. However, the CO/CO&lt;sub&gt;2&lt;/sub&gt; profiles also vary with season and latitude. For interpretation, the 1D photochemical model will be compared with newly obtained CO/CO&lt;sub&gt;2&lt;/sub&gt; profiles, especially in order to discuss the contributions from the variations in eddy diffusion coefficient and photochemistry in the MLT region on Mars.&lt;/p&gt;

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