scholarly journals Turbulent dynamos beyond the heuristic modeling: Helicities and density variance

2018 ◽  
Author(s):  
Nobumitsu Yokoi
Keyword(s):  
Density Variance

scholarly journals Surface kinetic energy transfer in surface quasi-geostrophic flows

2008 ◽  
Vol 604 ◽  
pp. 165-174 ◽  
Author(s):  
XAVIER CAPET ◽  
PATRICE KLEIN ◽  
BACH LIEN HUA ◽  
GUILLAUME LAPEYRE ◽  
JAMES C. MCWILLIAMS
Keyword(s):  
Kinetic Energy ◽  
Surface Velocity ◽  
Small Scale ◽  
Surface Dynamics ◽  
Spectral Flux ◽  
Advection Term ◽  
Wide Range ◽  
Geostrophic Flows ◽  
Scale Range ◽  
Density Variance

The relevance of surface quasi-geostrophic dynamics (SQG) to the upper ocean and the atmospheric tropopause has been recently demonstrated in a wide range of conditions. Within this context, the properties of SQG in terms of kinetic energy (KE) transfers at the surface are revisited and further explored. Two well-known and important properties of SQG characterize the surface dynamics: (i) the identity between surface velocity and density spectra (when appropriately scaled) and (ii) the existence of a forward cascade for surface density variance. Here we show numerically and analytically that (i) and (ii) do not imply a forward cascade of surface KE (through the advection term in the KE budget). On the contrary, advection by the geostrophic flow primarily induces an inverse cascade of surface KE on a large range of scales. This spectral flux is locally compensated by a KE source that is related to surface frontogenesis. The subsequent spectral budget resembles those exhibited by more complex systems (primitive equations or Boussinesq models) and observations, which strengthens the relevance of SQG for the description of ocean/atmosphere dynamics near vertical boundaries. The main weakness of SQG however is in the small-scale range (scales smaller than 20–30 km in the ocean) where it poorly represents the forward KE cascade observed in non-QG numerical simulations.

scholarly journals The density variance-Mach number relation in supersonic turbulence - I. Isothermal, magnetized gas

2012 ◽  
Vol 423 (3) ◽  
pp. 2680-2689 ◽  
Author(s):  
F. Z. Molina ◽  
S. C. O. Glover ◽  
C. Federrath ◽  
R. S. Klessen
Keyword(s):  
Mach Number ◽  
Number Relation ◽  
Density Variance

Possible reason of ionospheric anomaly post the April 20, 2013, Mw = 6.6 China' Lushan earthquake: Applying two-dimensional principal component analysis (2DPCA) to two-dimensional total electron content (TEC)

2014 ◽  
Vol 80 (3) ◽  
pp. 437-446
Author(s):  
Jyh-Woei Lin
Keyword(s):  
Principal Component Analysis ◽  
Total Electron Content ◽  
Principal Component ◽  
Component Analysis ◽  
Lushan Earthquake ◽  
Electron Content ◽  
Two Dimensional ◽  
Total Electron ◽  
Acoustic Shock Wave ◽  
Density Variance

In this study, two-dimensional principal component analysis (2DPCA) was used to determine the reason for the ionospheric two-dimensional total electron content (TEC) anomaly after China's Lushan earthquake at 00:02:47 UT on April 20, 2013 (Mw = 6.6). TEC data from 00:00 to 00:15 (UT) on April 20, 2013 were examined. The TEC anomaly was very intense 00:05 to 00:10 (UT) after the earthquake. One potential cause of the TEC anomaly, which might have been a density variance, is a rising acoustic shock wave, with speed of at least 1127.82, ms−1, resulting from the mainshock. The duration of the TEC anomaly was at least 5 min.

Electromotive force in strongly compressible magnetohydrodynamic turbulence

2018 ◽  
Vol 84 (5) ◽  
Author(s):  
Nobumitsu Yokoi
Keyword(s):  
Shock Front ◽  
Density Gradient ◽  
Electromotive Force ◽  
Direct Interaction ◽  
Multiple Scale ◽  
Compressible Turbulence ◽  
Mhd Turbulence ◽  
Mean Velocity ◽  
The Mean ◽  
Density Variance

Fully compressible magnetohydrodynamic (MHD) turbulence is investigated in the framework of the multiple-scale direct-interaction approximation. With the aid of the propagators (correlation and Green’s functions), fluctuating fields are solved, and turbulent correlations are estimated in highly compressible turbulence. We focus on the expression of the turbulent electromotive force (EMF). Obliqueness between the mean magnetic field and the mean-density gradient, the mean internal density gradient and the non-equilibrium mean velocity contributes to the EMF in the presence of the density variance, which is ubiquitous in turbulence in strongly variable density flows such as the shock-front region. This density-variance effect is expected to locally enhance the turbulence intensity across the shock front, leading to a fast reconnection.

scholarly journals The link between solenoidal turbulence and slow star formation in G0.253+0.016

2016 ◽  
Vol 11 (S322) ◽  
pp. 123-128 ◽  
Author(s):  
C. Federrath ◽  
J. M. Rathborne ◽  
S. N. Longmore ◽  
J. M. D. Kruijssen ◽  
J. Bally ◽  
...  
Keyword(s):  
Star Formation ◽  
Mach Number ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Dust Emission ◽  
Volume Density ◽  
Galactic Centre ◽  
Galactic Disc ◽  
Density Variance

AbstractStar formation in the Galactic disc is primarily controlled by gravity, turbulence, and magnetic fields. It is not clear that this also applies to star formation near the Galactic Centre. Here we determine the turbulence and star formation in the CMZ cloud G0.253+0.016. Using maps of 3 mm dust emission and HNCO intensity-weighted velocity obtained with ALMA, we measure the volume-density variance σρ /ρ 0=1.3±0.5 and turbulent Mach number $\mathcal{M}$ = 11±3. Combining these with turbulence simulations to constrain the plasma β = 0.34±0.35, we reconstruct the turbulence driving parameter b=0.22±0.12 in G0.253+0.016. This low value of b indicates solenoidal (divergence-free) driving of the turbulence in G0.253+0.016. By contrast, typical clouds in the Milky Way disc and spiral arms have a significant compressive (curl-free) driving component (b > 0.4). We speculate that shear causes the solenoidal driving in G0.253+0.016 and show that this may reduce the star formation rate by a factor of 7 compared to nearby clouds.

scholarly journals THE DENSITY VARIANCE–MACH NUMBER RELATION IN SUPERSONIC, ISOTHERMAL TURBULENCE

2010 ◽  
Vol 727 (1) ◽  
pp. L21 ◽  
Author(s):  
Daniel J. Price ◽  
Christoph Federrath ◽  
Christopher M. Brunt
Keyword(s):  
Mach Number ◽  
Number Relation ◽  
Density Variance
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