10:45
Geophysical and Astrophysical Turbulence 2
10:45
15 mins
#192
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WAVING PERTURBATION OF OUTLYING SHEETS AND CORE OF MOLECULAR CLOUDS IN HEAD-ON COLLISION
Valery Goryachev, Boris Rybakin
Abstract: High energy and cold plasma streams and gas/dust flows in the interstellar medium (ISM) form the net spatio-temporal structure of the Universe. Cloud-cloud collisions (CCC) between molecular clouds (MCs) and interplay of the last with strong shock wave of remnants after supernova explosion are proposed as a key mechanisms for triggering protostars originated in highly compression zones of new formations. The paper is devoted to consequences of supersonic turbulization of MCs matter in numerical simulation based on different scenarios of shock interplay and key instabilities influence onto emergent dense clumps and filamentous structures originated here. To simulate a fine structure of shock colliding flows authorized Eulerian code with parallelization on high resolution mesh with more two billions nodes was performed. Numerical experience of such modelling since pioneering work [1] was used.
Numerical simulations of initially spherical clouds embedded in a hot ISM and colliding in head-on motion revealed a few details of energy reinforcement and density conformation in zones of energy change between MCs and ISM matter. In situations with insufficiently smoothness of pressure/energy fields in high gradient zones a spatial intermittency of outer layers of clouds and their lens-like clump (core) deformation leads to coherrent wave perturbation here and outside. Process is accompanied by Kelvin-Helmholtz (KH) instability and disturbance of gas density over perturbed superficial layers of clouds. Oscillations initiated by extremely strong contractions of clouds core become clearly observable in time pulsations of density contrast that accompanies process of penetration bullet cloud into target one. Very likely this process is generated by means of energy interchange in high-gradient outer layers and clumpy membrane wave deformation. Nonlinear Thin Shell Instability (NTSI) in gas phase can play a crucial role of triggering this process. KH instability and conceivably NTSI lead to formation of bubble-like structure and deformation of MCs at distortion phase of their shaping. Observed effects of CCC and generated turbulence heterogeneity are considered in presented report.
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11:00
15 mins
#51
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BRIDGING THE TURBULENT VORTEX DYNAMO THEORY AND TROPICAL CYCLONE INVESTIGATIONS
Galina Levina
Abstract: A fundamental theoretical hypothesis on the turbulent vortex dynamo advanced and substantiated by the scientists of Space Research Institute (USSR, 1983), is based on the special properties of small-scale helical turbulence characterized by the broken mirror symmetry. The helical turbulence is known as that allowing the existence of inverse energy cascade. From the outset, the hypothesis’ authors envisioned it as a possibility to explain the generation of large-scale intense vortex structures in the atmosphere due to the inverse energy transfer from smaller scale motions, for example, in a case of tropical cyclones formation in the Earth's atmosphere. A discussion of the proposed mathematical model and its further development, as well as related works carried out up to 1999, can be found in review [1].
Bridging the turbulent vortex dynamo theory and tropical cyclone investigations was not possible, based on the knowledge of the 20th century, and it was awaiting "its time". This required the breakthrough of American scientists in tropical meteorology and cloud-resolving numerical modeling of atmospheric processes that happened in the 2000s. The decisive opportunity for such a compound became the discovery of rotating cloud convection in the tropics and immediately followed it, a new scenario of tropical cyclogenesis based on self-organization of moist atmospheric convection - USA, 2004-2006. On the background of these findings, the ideas of vortex dynamo acquired a completely new sound meaning.
The first discovery of the undertaken collaborative Russian-American efforts (see, review [2]), based on cloud-resolving atmospheric modeling, was the break of the mirror symmetry of atmospheric turbulence – non-zero helicity generation – during tropical cyclone formation that gave us the impetus to further search for the large-scale helical-vortex instability. In this presentation, we are going to discuss our recent results on the applicability of the vortex dynamo theory to the study of tropical cyclones. They allowed answering the key question on tropical cyclogenesis – “When does the nascent large-scale hurricane vortex become energy self-sustaining and intensifying?” – and diagnosing the time moment of emergence of large-scale vortex instability. An analogy was traced between the role of interaction “moist convection – vertical wind shear” in creating the vortex dynamo in the atmosphere and the role of the mean electromotive force providing the MHD dynamo in an electrically conducting medium.
Evidently, our most important finding, contributing to both the fundamental science and practical issues of the earlier warning of the population about the hurricane danger, is connected to the fact that the onset of cyclogenesis is now getting the precise interpretation - it coincides with the beginning of new found instability. Moreover, our results show that this instability starts earlier (from a few hours up to a few tens of hours) than the formation of a tropical depression vortex takes place - the event, for which the regional storm tracking services usually declare a tropical cyclone emergency.
To illustrate, both the diagnosis of tropical cyclogenesis based on idealized simulations and the diagnosis for an observed formation of atmospheric vortex will be shown and discussed.
References
[1] G. V. Levina, S. S. Moiseev, and P. B. Rutkevich. Hydrodynamic alpha-effect in a convective system. Advances in Fluid Mechanics 25: 111–162, 2000.
[2] G. Levina. On the path from the turbulent vortex dynamo theory to diagnosis of tropical cyclogenesis. Open Journal of Fluid Dynamics 8: 86–114, 2018.
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11:15
15 mins
#511
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Statistics of extreme convective penetration in stellar interiors
Dimitar Vlaykov, Isabelle Baraffe, Jane Pratt
Abstract: please see attached file
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11:30
15 mins
#289
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ROCKET-BORNE TURBULENCE MEASUREMENTS IN MESOSPHERE/LOWER THERMOSPHERE REGION
Boris Strelnikov, Franz-Josef Lübken, Victor Avsarkisov
Abstract: We present and discuss spectra measured in the Earth's mesosphere in different flow regimes which includes atmospheric waves, 3D "Kolmogorov" turbulence, strongly stratified turbulence, and their combinations.
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11:45
15 mins
#452
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Development of turbulence and clouds under strong wind jet in atmospheric boundary layers; large-eddy simulations
Metodija Meto Shapkalijevski, Vera Schemann, Daisuke Sakurai, Nikki Vercauteren
Abstract: In this study, generation of shear-driven turbulent mixing by the strong nocturnal boundary-layer (NBL) wind jets, leading to local cloud formation is examined and explained. For that purpose, realistic case studies over the Jülich observatory site in Germany are developed and represented.
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12:00
15 mins
#590
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POTENTIAL VORTICITY, HELICITY, AND VORTEX STRUCTURES IN THE ATMOSPHERIC BOUNDARY LAYER
Otto Chkhetiani, Boris Koprov, Victor Koprov, Michael Kurgansky, Egor Shishov, Valery Kramar
Abstract: The results of the experiments of 2012-2018 for the studies of helicity, potential vorticity and vortex structures in the atmospheric boundary layer, carried out in summer convective conditions on an untouched plain steppe area on the territory of the Tsimlyansk scientific station, are presented. The potential vorticity and helicity were measured by simultaneous measurement of the components of velocity and temperature by four acoustic anemometers placed at the vertices of a rectangular tetrahedron.
In 2012, the lower measuring plane was located at a height of 5.5 m, and the upper anemometer at a height of 10.5 [1]. From the velocities and temperatures measured at the vertices of the tetrahedron, the components of the vortex, helicity, and potential vorticity were calculated by a difference method.In 2014, a new attempt of joint measurements of the helicity and potential vortex using a tetrahedron of considerably smaller size (0.7 m) placed on top of a mast of variable altitude was undertaken. This allowed us to measure the parameters at altitudes of 3.5, 5, 13.5, and 25 m [2].
The spectra, structural functions, as well as data on helicity and potential vorticity flows, depending on the parameters of atmospheric stability, were obtained. The measurements confirm the correlation of the pair correlation of the vertical component of the vorticity with temperature pulsations and the combination of correlations of the vertical velocity with the potential vorticity, which follows from the analysis of the generation of turbulent helicity based on a simple relaxation model [3].
Simultaneously, multipoint measurements of wind speed directions were carried out at a height of 2 m using a spatially separated network of sensors with a step from 2 m to 5 m [4, 5], which made it possible to identify episodes of vortex structures and compare them with the dynamics of turbulent helicity and potential vorticity. Additional information about the vortex structures, their statistics and large-scale turbulence was obtained using a new high resolution sodar, which allows determining the vertical-temporal structure of the wind speed field at altitudes of 2-50 meters with a spatial resolution of 1 m and a time step of 1s. The spatial horizontal scales of large vortex structures are in the range of 300-500 m with a time of 5-7 minutes.
Figure 1. Schematic of the rectangular tetrahedron ABCD used for helicity measurements in 2012. Horizontal (x, y) axes are directed northward and westward, respectively. Three anemometers are positioned at the vertices of a rectangular isosceles triangle ABC with the length of AB and AC equal to 5 m, and the fourth anemometer at point D is located 5 m higher, exactly above the vertex of right angle BAC
This work was supported by Russian Foundation for Basic Research (project № 17-05-01116).
References
[1] B. Koprov, V. Koprov, M. Kurgansky , and O. Chkhetiani. Helicity and potential vorticity in surface turbulence. Izvestiya, Atmospheric and Oceanic Physics 51(6): 565-575, 2015.
[2] B. Koprov, V. Koprov, O. Solenaya, O. Chkhetiani, and E. Shishov. Technique and results of measurements of turbulent helicity in a stratified surface layer. Izvestiya, Atmospheric and Oceanic Physics 54(5): 446-455, 2018.
[3] O. Chkhetiani, M. Kurgansky, and N. Vazaeva Turbulent Helicity in the Atmospheric Boundary Layer. Boundary-Layer Meteorology 168(3): 361–385, 2018
[4] E. Shishov, B. Koprov, and V. Koprov. Statistical parameters of the spatiotemporal variability of the wind direction in the surface layer. Izvestiya, Atmospheric and Oceanic Physics 53(1): 19-23, 2017.
[5] E. Shishov, O. Solyonaya, B. Koprov, and V Koprov. Investigation into Variations of Wind Directions Near the Surface. Izvestiya, Atmospheric and Oceanic Physics 54(6): 515-523, 2018.
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12:15
15 mins
#284
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TURBULENCE IN MARINE BOUNDARY LAYER CLOUDS: A META-ANALYSIS OF AIRBORNE MEASUREMENTS
Szymon Malinowski, Marta Waclawczyk, Yong-Feng Ma, Moein Mohammadi, Jesper Pedersen
Abstract: A comprehensive information on turbulence properties in marine convective clouds using measurement data from 5 airborne research campaigns in various locations around the world is provided and discussed. Novel methods of turbulence kinetic energy dissipation rate retrievals from under resolving measurements are applied in the course of data analysis.
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12:30
15 mins
#484
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Turbulence transport modelling in core-collapsed supernovae explosion
Nobumitsu Yokoi, Tomoya Takiwaki, Youhei Masada
Abstract: \begin{document}
\title{Turbulence transport modelling in core-collapsed supernovae explosion}
\authors{\underline{Nobumitsu Yokoi}$^1$, Tomoya Takiwaki$^2$ \& Yohei Masada$^3$}
\affiliations{$^1$Institute of Industrial Science, University of Tokyo, Tokyo, Japan\\
$^2$National Astronomical Observatory of Japan (NAOJ), Japan\\
$^3$Aichi University of Education, Japan}
\maketitle
The life end of massive stars, supernovae explosion, is one of the most spectacular phenomena in the universe. Its physical process contains several complicated processes from the collapsing due to self-gravitation, balancing by the degeneracy pressure, neutrino cooling and heating, shocks, standing-accretion shock instability (SASI), convection, etc. It has been recognised that the turbulence plays a key role in effective transport such as the Reynolds and turbulent Maxwell stresses, the turbulent electromotive force, the turbulent mass flux, turbulent heat flux, etc. In the turbulent supernovae studies, it has been pointed out that a simple gradient-diffusion approximation model does not represent well the momentum transport due to turbulence. In order to properly reproduce the turbulence profile and the evolution of the core-collapsed supernovae explosion, a model deviating from the usual gradient-diffusion approximation, including a global plume entrainment model, is needed \cite{bib:murphy2011,bib:mabanta2018}.
Recently with the aid of the multiple-scale direct-interaction approximation, we developed theory and modelling of the transport fluxes in strongly compressible magnetohydrodynamic (MHD) turbulence \cite{bib:yokoi2018a,bib:yokoi2018b}. For example, the turbulent internal-energy flux $\langle {e' {\textbf{u}}'} \rangle$ ($e'$: internal-energy fluctuation, ${\textbf{u}}'$: velocity fluctuation) are expressed in terms of the mean internal energy $E$, mean density $\overline{\rho}$, and the mean magnetic field ${\textbf{B}}$ as
\begin{equation}
\langle {e' {\textbf{u}}'} \rangle
= - \eta_E \nabla E
- \eta_{\overline{\rho}} \nabla \overline{\rho}
- \eta_B {\textbf{B}},
\label{eq:turb_internal-en_flux}%(1)
\end{equation}
where $\eta_E$, $\eta_{\overline{\rho}}$, and $\eta_B$ are the transport coefficients. In addition to the usual gradient diffusion $- \eta_E \nabla E$, whose transport coefficient $\eta_E$ is determined by the solenoidal and dilatational kinetic energy, there are two other terms that arise from the strong compressibility. The transport coefficients $\eta_{\overline{\rho}}$ and $\eta_B$ are determined by the density variance $\langle {\rho'{}^2} \rangle$ and the dilatational cross helicity $\langle {{\textbf{u}}' \cdot {\textbf{b}}'} \rangle_{\textrm{c}}$, respectively ($\rho'$: density fluctuation, ${\textbf{b}}'$: magnetic-field fluctuation). These two terms suggest possibilities of deviation from the gradient diffusion in strongly compressible magnetohydrodynamic turbulence.
With the aid of the direct numerical simulations in a global spherical geometry (global simulation) and a local boxed geometry (local simulation), we examine several turbulence correlations such as $\langle {{\textbf{u}}'{\textbf{u}}'} \rangle$, $\langle {\rho' {\textbf{u}}'} \rangle$, $\langle {e' {\textbf{u}}'} \rangle$, etc., and compare them with the turbulence model expressions including (\ref{eq:turb_internal-en_flux}) and the plume entrainment assumption. We attempt to develop a simple and plausible turbulence model for the core-collapsed supernovae explosion. For this purpose, we perform a 3D full global simulation with the 20-27 solar mass progenitors model, with the 3D entropy profile with the neutrino heating and a local cooling as well as the nuclear equation of state being included (Figure~\ref{fig:fig1}). At the same time, we perform a series of local simulations, where the initial conditions of the field quantities are adopted from the counterparts in the global simulations (Figures~\ref{fig:fig2} and \ref{fig:fig3}). In these local simulations, we can compare the turbulence model results with the DNS results in a much concise manner, and can examine the validity of the turbulence models.
\vspace{0pt}
\begin{figure}[h]
\setlength{\unitlength}{1cm}
\begin{minipage}[t]{2.1in}
\begin{center}
\includegraphics[width=2.2cm]{yokoi_etc17_fig01}
\end{center}
\caption{Three dimensional entropy profile of a 20-solar-mass progenitor}
\label{fig:fig1}
\end{minipage}
\begin{minipage}[t]{2.1in}
\begin{center}
\includegraphics[width=5.2cm]{yokoi_etc17_fig02}
\end{center}
\caption{Contours of the vertical velocity at shallow (radius of 128\ {\textrm{km}}) and mid radius (94\ {\textrm{km}}) regions in local simulations}
\label{fig:fig2}
\end{minipage}
\begin{minipage}[t]{2.1in}
\begin{center}
\includegraphics[width=4.0cm]{yokoi_etc17_fig03}
\end{center}
\caption{Space-time diagram that shows the strength of the Reynolds stress $R_{rr}$}
\label{fig:fig3}
\end{minipage}
\end{figure}
\vspace{-0pt}
%%%%%%%%%%%
\bibliographystyle{plainbv}
\bibliography{biblio}
% Alternatively use this for the bibliography :
%
\begin{thebibliography}{1}
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\bibitem{bib:murphy2011}
J. W. Murphy and C. Meakin. A global turbulence model for neutrino-driven convection in core-collapse supernovae. \textit{Astrophysical Journal} \textbf{742}: 74-1--21, 2011.
%
\bibitem{bib:mabanta2018}
Q. A. Mabanta and J. W. Murphy. How turbulence enables core-collapse supernova explosions. \textit{Astrophysical Journal} \textbf{856}: 22-1--14, 2018.
%
\bibitem{bib:yokoi2018a}
N. Yokoi. Electromotive force in strongly compressible magnetohydrodynamic turbulence. \textit{Journal of Plasma Physics}, \textbf{84}: 735840501-1--26, 2018.
\bibitem{bib:yokoi2018b}
N. Yokoi. Mass and internal-energy transports in strongly compressible magnetohydrodynamic turbulence. \textit{Journal of Plasma Physics}, \textbf{84}: 775840603-1--30, 2018.
\end{thebibliography}
\end{document}
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