Doppler spectral width studies from polar mesospheric summer echoes

2020 ◽  
Author(s):  
Nikoloz Gudadze ◽  
Gunter Stober ◽  
Hubert Luce ◽  
Jorge Luis Chau
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Spectral Width ◽  
Target Area ◽  
Fundamental Parameter ◽  
Dissipation Rates ◽  
Summer Echoes ◽  
Width Measurements ◽  
Fossil Turbulence

<p>Investigation of turbulence in the polar mesopause is essential for a better understanding of dynamical or mixing processes in the region. Polar Mesospheric Summer Echoes (PMSEs), occurring at mesopause altitudes during the summer season, are known to be a result of turbulence-induced fluctuations in the refractive index. The presence of ice particles controls and reduce the free-electron diffusivity in D region plasma, which in turn leads to complex, strong radar echoes at very high frequencies.</p><p>Often, Doppler spectral width of radar measurements are associated with the strength of turbulence in the target area and traditionally used to estimate turbulent kinetic energy dissipation rates, a fundamental parameter of the turbulence processes. Besides the cooling of summer mesopause region induced by GW drag, the turbulence produced by GW breaking contributes to the total energy budget due to release of turbulent kinetic energy to heat. We use PMSE spectral width measurements observed by Middle Atmosphere Alomar Radar System (MAARSY) during summer of 2016 to study their summer temporal mean profiles as well as temporal evolution and connection to the atmospheric turbulence at PMSE altitudes - 80 and 90 km. The current theoretical models suggest that the radar reflectivity should correlate to the strength of the turbulence; however, such a relation is mainly observed for the weaker PMSEs. The mean summer behaviour of estimated turbulent kinetic energy dissipation rates shows an increase from lower altitudes up to 90 km. It should be noticed that spectral width measurements contain additional broadening rather than turbulence, so derived energy dissipation rates are “upper values” than expected from pure turbulence. The results are still slightly lower than those known from climatology obtained from rocket soundings, mostly at altitudes close to the maximum occurrence of PMSE, 86-87 km.</p><p>We discuss a possible consequence of spectral width measurements under strong PMSEs. In such conditions, the strength of the echo does not correlate with the turbulence intensity, and the observed spectral width is weaker. However, the uniform distribution of spectral width values throughout the echo power is expected from the present theoretical understandings. Based on previous studies, strong PMSEs can also be observed during fossil turbulence. The interpretation of connection the spectral with measurements under fossil turbulence with the turbulence energy dissipation rates and the possibility of using PMSEs for the turbulence studies will be discussed.</p>

scholarly journals Diffusional and accretional growth of water drops in a rising adiabatic parcel: effects of the turbulent collision kernel

2009 ◽  
Vol 9 (7) ◽  
pp. 2335-2353 ◽  
Author(s):  
W. W. Grabowski ◽  
L.-P. Wang
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Collision Kernel ◽  
Small Scale ◽  
Large Set ◽  
Initiation Time ◽  
Cloud Droplets ◽  
Dissipation Rates ◽  
Speedup Factor

Abstract. A large set of rising adiabatic parcel simulations is executed to investigate the combined diffusional and accretional growth of cloud droplets in maritime and continental conditions, and to assess the impact of enhanced droplet collisions due to small-scale cloud turbulence. The microphysical model applies the droplet number density function to represent spectral evolution of cloud and rain/drizzle drops, and various numbers of bins in the numerical implementation, ranging from 40 to 320. Simulations are performed applying two traditional gravitational collection kernels and two kernels representing collisions of cloud droplets in the turbulent environment, with turbulent kinetic energy dissipation rates of 100 and 400 cm2 s−3. The overall result is that the rain initiation time significantly depends on the number of bins used, with earlier initiation of rain when the number of bins is low. This is explained as a combination of the increase of the width of activated droplet spectrum and enhanced numerical spreading of the spectrum during diffusional and collisional growth when the number of model bins is low. Simulations applying around 300 bins seem to produce rain at times which no longer depend on the number of bins, but the activation spectra are unrealistically narrow. These results call for an improved representation of droplet activation in numerical models of the type used in this study. Despite the numerical effects that impact the rain initiation time in different simulations, the turbulent speedup factor, the ratio of the rain initiation time for the turbulent collection kernel and the corresponding time for the gravitational kernel, is approximately independent of aerosol characteristics, parcel vertical velocity, and the number of bins used in the numerical model. The turbulent speedup factor is in the range 0.75–0.85 and 0.60–0.75 for the turbulent kinetic energy dissipation rates of 100 and 400 cm2 s−3, respectively.

scholarly journals Diffusional and accretional growth of water drops in a rising adiabatic parcel: effects of the turbulent collision kernel

2008 ◽  
Vol 8 (4) ◽  
pp. 14717-14763 ◽  
Author(s):  
W. W. Grabowski ◽  
L.-P. Wang
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Collision Kernel ◽  
Small Scale ◽  
Large Set ◽  
Initiation Time ◽  
Cloud Droplets ◽  
Dissipation Rates ◽  
Speedup Factor

Abstract. A large set of rising adiabatic parcel simulations is executed to investigate the combined diffusional and accretional growth of cloud droplets in maritime and continental conditions, and to assess the impact of enhanced droplet collisions due to small-scale cloud turbulence. The microphysical model applies the droplet number density function to represent spectral evolution of cloud and rain/drizzle drops, and various numbers of bins in the numerical implementation, ranging from 40 to 320. Simulations are performed applying two traditional gravitational collection kernels and two kernels representing collisions of cloud droplets in the turbulent environment, with turbulent kinetic energy dissipation rates of 100 and 400 cm2 s−3. The overall result is that the rain initiation time significantly depends on the number of bins used, with earlier initiation of rain when the number of bins is low. This is explained as a combination of the increase of the width of activated droplet spectrum and enhanced numerical spreading of the spectrum during diffusional and collisional growth when the number of model bins is low. Simulations applying around 300 bins seem to produce rain at times which no longer depend on the number of bins, but the activation spectra are unrealistically narrow. These results call for an improved representation of droplet activation in numerical models of the type used in this study. Despite the numerical effects that impact the rain initiation time in different simulations, the turbulent speedup factor, the ratio of the rain initiation time for the turbulent collection kernel and the corresponding time for the gravitational kernel, is approximately independent of aerosol characteristics, parcel vertical velocity, and the number of bins used in the numerical model. The turbulent speedup factor is in the range 0.75–0.85 and 0.60–0.75 for the turbulent kinetic energy dissipation rates of 100 and 400 cm2 s−3, respectively.

scholarly journals Observations of turbulent kinetic energy dissipation at the Labrador Sea surface layer

2017 ◽  
Vol 8 (3) ◽  
pp. 161-172
Author(s):  
Silvia Gremes-Cordero
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Phytoplankton Bloom ◽  
Global Climate ◽  
Energy Dissipation Rate ◽  
Labrador Sea ◽  
Wave Phase ◽  
Dissipation Rates ◽  
First Time

We present an analysis of turbulent kinetic energy dissipation rates in the upper ocean using in situ measurements collected by a coherent Doppler sonar in the Labrador Sea during summer 2004. The sonar recorded horizontal velocity fluctuations of the upper 2 m with an uncommonly small spatial resolution of 0.8 cm, allowing direct calculations of wavenumber spectra and the application of Kolmogorov theory to obtain turbulent kinetic energy dissipation rates for the first time in this area. The project presented a unique opportunity for the study of air–sea exchange during a phytoplankton bloom, being the first time a specialized air–sea interaction spar buoy was deployed during such particular event. An additional uniqueness of this experiment resulted from being the first turbulent kinetic energy dissipation rate observations obtained at higher latitudes, coincidentally in a well-known region of dense water formation, with a fundamental role in both global circulation and forecasting studies of global climate change. Focusing on the relationship between turbulent kinetic energy dissipation rates and wave phase in the upper 2 m, we estimated O[Formula: see text] turbulent kinetic energy dissipation rates, consistent with previous estimates obtained through similar devices and methods. A T-test between dissipation rates calculated at the crest and at the trough of waves showed no dependency of turbulent kinetic energy dissipation rates on the wave phase at 2 m depth, coinciding with many of the earlier findings available. a comparison with previous research showing conflicting results with our values is also discussed here linking them to the relative roles of experimental design variations, diverse dynamical frames, and particular environmental conditions.

Turbulent kinetic energy dissipation rates and eddy diffusivities in the tropical mesosphere using Jicamarca radar data

2007 ◽  
Vol 40 (6) ◽  
pp. 744-750 ◽  
Author(s):  
L. Guo ◽  
G.A. Lehmacher ◽  
E. Kudeki ◽  
A. Akgiray ◽  
R. Sheth ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Radar Data ◽  
Eddy Diffusivities ◽  
Dissipation Rates

scholarly journals Evaluating stream CO<sub>2</sub> outgassing via drifting and anchored flux chambers in a controlled flume experiment

2021 ◽  
Vol 18 (3) ◽  
pp. 1223-1240
Author(s):  
Filippo Vingiani ◽  
Nicola Durighetto ◽  
Marcus Klaus ◽  
Jakob Schelker ◽  
Thierry Labasque ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Gas Exchange ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
High Energy ◽  
Running Waters ◽  
Flume Experiment ◽  
Co2 Fluxes ◽  
Dissipation Rates ◽  
Generalized Likelihood Uncertainty Estimation

Abstract. Carbon dioxide (CO2) emissions from running waters represent a key component of the global carbon cycle. However, quantifying CO2 fluxes across air–water boundaries remains challenging due to practical difficulties in the estimation of reach-scale standardized gas exchange velocities (k600) and water equilibrium concentrations. Whereas craft-made floating chambers supplied by internal CO2 sensors represent a promising technique to estimate CO2 fluxes from rivers, the existing literature lacks rigorous comparisons among differently designed chambers and deployment techniques. Moreover, as of now the uncertainty of k600 estimates from chamber data has not been evaluated. Here, these issues were addressed by analysing the results of a flume experiment carried out in the Summer of 2019 in the Lunzer:::Rinnen – Experimental Facility (Austria). During the experiment, 100 runs were performed using two different chamber designs (namely, a standard chamber and a flexible foil chamber with an external floating system and a flexible sealing) and two different deployment modes (drifting and anchored). The runs were performed using various combinations of discharge and channel slope, leading to variable turbulent kinetic energy dissipation rates (1.5×10-3<ε<1×10-1 m2 s−3). Estimates of gas exchange velocities were in line with the existing literature (4<k600<32 m2 s−3), with a general increase in k600 for larger turbulent kinetic energy dissipation rates. The flexible foil chamber gave consistent k600 patterns in response to changes in the slope and/or the flow rate. Moreover, acoustic Doppler velocimeter measurements indicated a limited increase in the turbulence induced by the flexible foil chamber on the flow field (22 % increase in ε, leading to a theoretical 5 % increase in k600). The uncertainty in the estimate of gas exchange velocities was then estimated using a generalized likelihood uncertainty estimation (GLUE) procedure. Overall, uncertainty in k600 was moderate to high, with enhanced uncertainty in high-energy set-ups. For the anchored mode, the standard deviations of k600 were between 1.6 and 8.2 m d−1, whereas significantly higher values were obtained in drifting mode. Interestingly, for the standard chamber the uncertainty was larger (+ 20 %) as compared to the flexible foil chamber. Our study suggests that a flexible foil design and the anchored deployment might be useful techniques to enhance the robustness and the accuracy of CO2 measurements in low-order streams. Furthermore, the study demonstrates the value of analytical and numerical tools in the identification of accurate estimations for gas exchange velocities. These findings have important implications for improving estimates of greenhouse gas emissions and reaeration rates in running waters.

scholarly journals Evaluating stream CO2 outgassing via Drifting and Anchored flux chambers in a controlled flume experiment

2021 ◽  
Author(s):  
Filippo Vingiani ◽  
Nicola Durighetto ◽  
Marcus Klaus ◽  
Jakob Schelker ◽  
Thierry Labasque ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Gas Exchange ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
High Energy ◽  
Running Waters ◽  
Flume Experiment ◽  
Dissipation Rates ◽  
Floating System ◽  
Generalized Likelihood Uncertainty Estimation

&lt;p&gt;Carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) emissions from running waters represent a key component of the global carbon cycle. However, quantifying CO&lt;sub&gt;2&lt;/sub&gt; fluxes across air-water boundaries remains challenging due to practical difficulties in the estimation of reach-scale standardized gas exchange velocities (k&lt;sub&gt;600&lt;/sub&gt;) and water equilibrium concentrations. Whereas craft-made floating chambers supplied by internal CO&lt;sub&gt;2&lt;/sub&gt; sensors represent a promising technique to estimate CO&lt;sub&gt;2&lt;/sub&gt; fluxes from rivers, the existing literature lacks of &amp;#160;rigorous &amp;#160;comparisons &amp;#160;among &amp;#160;differently &amp;#160;designed chambers and deployment techniques. Moreover, as of now the uncertainty of k&lt;sub&gt;600&lt;/sub&gt; estimates from chamber data has not been evaluated. &amp;#160;Here, these issues were addressed analyzing the results of a flume experiment carried out in the Summer of 2019 in the Lunzer:::Rinnen - Experimental Facility (Austria). During the experiment, 100 runs were performed &amp;#160;using two different chamber designs (namely, a Standard Chamber and a Flexible Foil chamber with an external floating system and a flexible sealing) and two different deployment modes (drifting and anchored). The runs were performed using various combinations of discharge and channel slope, leading to variable turbulent kinetic energy dissipation rates (1.5 10&lt;sup&gt;-3&lt;/sup&gt;&lt; &amp;#949; &lt; 1 10&lt;sup&gt;-1&lt;/sup&gt; m&lt;sup&gt;2&lt;/sup&gt; s&lt;sup&gt;-3&lt;/sup&gt;). Estimates of gas exchange velocities were in line with the existing literature (4 &lt; k&lt;sub&gt;600&lt;/sub&gt; &lt; 32 m d&lt;sup&gt;-1&lt;/sup&gt;), with a general increase of k&lt;sub&gt;600&lt;/sub&gt; for larger turbulent kinetic energy dissipation rates. The Flexible Foil chamber gave consistent k&lt;sub&gt;600&lt;/sub&gt; patterns in response to changes in the slope and/or the flow rate. Moreover, Acoustic Doppler Velocimeter measurements indicated a limited increase of the turbulence induced by the Flexible Foil chamber on the flow field (22 % increase in &amp;#949;, leading to a theoretical 5 % increase in k&lt;sub&gt;600&lt;/sub&gt;).&lt;br&gt;The &amp;#160;uncertainty &amp;#160;in &amp;#160;the &amp;#160;estimate &amp;#160;of &amp;#160;gas &amp;#160;exchange &amp;#160;velocities &amp;#160;was &amp;#160;then estimated &amp;#160;using &amp;#160;a &amp;#160;Generalized Likelihood Uncertainty Estimation (GLUE) procedure. Overall, uncertainty in k&lt;sub&gt;600&lt;/sub&gt; was moderate to high, with enhanced uncertainty in high-energy setups. For the anchored mode, the standard deviations of k&lt;sub&gt;600&lt;/sub&gt; were between 1.6 and 8.2 m d&lt;sup&gt;-1&lt;/sup&gt;, whereas significantly higher values were obtained in drifting mode. Interestingly, for the Standard Chamber the uncertainty was larger (+ 20 %) as compared to the Flexible Foil chamber. &amp;#160;Our study suggests that a Flexible Foil design and the anchored deployment might be useful techniques to enhance the robustness and the accuracy of CO&lt;sub&gt;2&lt;/sub&gt; measurements in low-order streams. Furthermore, the study demonstrates the value of analytical and numerical tools in the identification of accurate estimations for gas exchange velocities.&lt;br&gt;These findings have important implications for improving estimates of greenhouse gas emissions and reaeration rates in running waters.&lt;/p&gt;

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