scholarly journals Dependence of the critical Richardson number on the temperature gradient in the mesosphere

2018 ◽  
Author(s):  
Michael N. Vlasov ◽  
Michael C. Kelley
Keyword(s):  
Temperature Gradient ◽  
Atmospheric Turbulence ◽  
Gravity Waves ◽  
Wind Shear ◽  
Richardson Number ◽  
Buoyancy Force ◽  
Dynamic Instability ◽  
Critical Richardson Number ◽  
Vertical Accelerations ◽  
First Time

Abstract. Maximum upper atmospheric turbulence results in the mesosphere from convective and/or dynamic instabilities induced by gravity waves. For the first time, by comparing the vertical accelerations induced by wind shear and the buoyancy force, it is shown that the critical Richardson number Ric can be estimated. Dynamic instability is developed for Ri 

Waves in parallel or swirling stratified shear flows

1979 ◽  
Vol 93 (3) ◽  
pp. 401-412 ◽  
Author(s):  
S. Leibovich
Keyword(s):  
Dispersion Relation ◽  
Gravity Waves ◽  
Wave Energy ◽  
Richardson Number ◽  
Phase Speed ◽  
Internal Gravity Waves ◽  
Maximum Speed ◽  
Meridian Plane ◽  
Finite Rate ◽  
Critical Richardson Number

The dispersion relations for infinitesimal internal gravity waves (A) and axisymmetric waves in swirling streams (B) are considered. In both cases the mainstream may be sheared and density stratified in the transverse (vertical in case A, radial in case B) direction. The following results are proved for either case: If the maximum speed Wmax (or minimum speed Wmin) (in a meridian plane in case B) of the mainstream occurs at an interior point in the fluid, then the phase speed of any mode takes all values from the Wmax (or Wmin) to +∞ ( —∞) as the overall Richardson number λ2 varies from 0 to ∞. If Wmax(Wmin) is attained at a boundary point with finite rate of strain, there is a positive non-zero critical Richardson number below which one or both branches of the dispersion relation terminate. These results employ variational methods and correct erroneous results concerning problem B stated in Chandrasekhar's treatise on hydrodynamic stability. Furthermore, bounds are given on the group velocity for both branches of the dispersion relation. From these bounds it is shown that in the absence of reversals of the mainstream (Wmin > 0) upstream propagation of wave energy is impossible whenever upstream propagation of constant phase surfaces is impossible.

scholarly journals Rolls of the internal gravity waves in the Earth's atmosphere

2014 ◽  
Vol 32 (2) ◽  
pp. 181-186 ◽  
Author(s):  
O. Onishchenko ◽  
O. Pokhotelov ◽  
W. Horton ◽  
A. Smolyakov ◽  
T. Kaladze ◽  
...  
Keyword(s):  
Nonlinear Dynamics ◽  
Gravity Waves ◽  
Closed System ◽  
Wind Shear ◽  
Internal Gravity Waves ◽  
Temperature Gradients ◽  
System Of Equations ◽  
Vertical Temperature ◽  
Earth’S Atmosphere ◽  
Earth's Atmosphere

Abstract. The effect of the wind shear on the roll structures of nonlinear internal gravity waves (IGWs) in the Earth's atmosphere with the finite vertical temperature gradients is investigated. A closed system of equations is derived for the nonlinear dynamics of the IGWs in the presence of temperature gradients and sheared wind. The solution in the form of rolls has been obtained. The new condition for the existence of such structures was found by taking into account the roll spatial scale, the horizontal speed and wind shear parameters. We have shown that the roll structures can exist in a dynamically unstable atmosphere.

Novel Perturbation Analysis for a Widely Applicable Curvature Law of the Wall

1999 ◽  
Author(s):  
Namhyo Kim ◽  
David L. Rhode
Keyword(s):  
Perturbation Analysis ◽  
Richardson Number ◽  
Perturbation Technique ◽  
Solution Approach ◽  
Law Of The Wall ◽  
Streamline Curvature ◽  
Curvature Effects ◽  
Gradient Richardson Number ◽  
Closed Form Analytical Solution ◽  
First Time

Abstract A streamline curvature law of the wall is analytically derived to include very strong curved-channel wall curvature effects through a novel perturbation analysis. The new law allows improved analysis of such flows, and it provides the basis for improved wall function boundary conditions for their computation (CFD) over a wider range of y+, even for very strong curvature cases. The unique derivation is based on the Boussinesq eddy viscosity and curvature-corrected mixing length concepts, which is a linear function of the gradient Richardson number. For the first time, to include more complete curved flow physics, local streamline curvature effects in the gradient Richardson number are kept. To overcome the mathematical difficulty of keeping all of these local streamline curvature terms, a novel perturbation solution approach is successfully developed. This novel perturbation technique allows a closed-form analytical solution to many similar non-linear problems which previously required more complicated techniques. Qualitative and quantitative comparisons with measurements and previous curvature laws of the wall obtained by different approaches reveal that the new law shows improved representation of the wall curvature effects for all of the four test cases.

scholarly journals Structural Transitions at Microtubule Ends Correlate with Their Dynamic Properties in Xenopus Egg Extracts

2000 ◽  
Vol 149 (4) ◽  
pp. 767-774 ◽  
Author(s):  
Isabelle Arnal ◽  
Eric Karsenti ◽  
Anthony A. Hyman
Keyword(s):  
Dynamic Instability ◽  
Dynamic Properties ◽  
Microtubule Assembly ◽  
Two Dimensional ◽  
Egg Extracts ◽  
Xenopus Egg ◽  
Xenopus Egg Extracts ◽  
First Time ◽  
The Relationship ◽  
Dynamic Populations

Microtubules are dynamically unstable polymers that interconvert stochastically between growing and shrinking states by the addition and loss of subunits from their ends. However, there is little experimental data on the relationship between microtubule end structure and the regulation of dynamic instability. To investigate this relationship, we have modulated dynamic instability in Xenopus egg extracts by adding a catastrophe-promoting factor, Op18/stathmin. Using electron cryomicroscopy, we find that microtubules in cytoplasmic extracts grow by the extension of a two- dimensional sheet of protofilaments, which later closes into a tube. Increasing the catastrophe frequency by the addition of Op18/stathmin decreases both the length and frequency of the occurrence of sheets and increases the number of frayed ends. Interestingly, we also find that more dynamic populations contain more blunt ends, suggesting that these are a metastable intermediate between shrinking and growing microtubules. Our results demonstrate for the first time that microtubule assembly in physiological conditions is a two-dimensional process, and they suggest that the two-dimensional sheets stabilize microtubules against catastrophes. We present a model in which the frequency of catastrophes is directly correlated with the structural state of microtubule ends.

scholarly journals Thermodynamic properties of single crystals based on lithium tungstate by reaction and DSC calorimetry

2021 ◽  
Vol 2119 (1) ◽  
pp. 012140
Author(s):  
N I Matskevich ◽  
V N Shlegel ◽  
D A Samoshkin ◽  
S V Stankus ◽  
A N Semerikova ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Temperature Gradient ◽  
Single Crystals ◽  
Czochralski Technique ◽  
Formation Enthalpies ◽  
Stabilization Energies ◽  
Mo Content ◽  
First Time ◽  
Lithium Tungstate ◽  
Dsc Calorimetry

Abstract For the first time, single crystals of undoped lithium tungstate and lithium tungstate doped by 1.25% molybdenum were grown by the low-temperature-gradient Czochralski technique. The standard formation enthalpies, lattices enthalpies, stabilization energies, and the heat capacity were determined in the temperature range of 320-997 K. The lattice enthalpy dependence on Mo content was constructed.

scholarly journals Modulation of Small-Scale Turbulence by Ducted Gravity Waves in the Nocturnal Boundary Layer

2008 ◽  
Vol 65 (4) ◽  
pp. 1414-1427 ◽  
Author(s):  
Y. P. Meillier ◽  
R. G. Frehlich ◽  
R. M. Jones ◽  
B. B. Balsley
Keyword(s):  
Boundary Layer ◽  
Gravity Waves ◽  
Richardson Number ◽  
Potential Temperature ◽  
Nocturnal Boundary Layer ◽  
Small Scale ◽  
Temperature Structure ◽  
Turbulence Measurements ◽  
Gradient Richardson Number ◽  
Scale Turbulence

Abstract Constant altitude measurements of temperature and velocity in the residual layer of the nocturnal boundary layer, collected by the Cooperative Institute for Research in Environmental Sciences (CIRES) Tethered Lifting System (TLS), exhibit fluctuations identified by previous work (Fritts et al.) as the signature of ducted gravity waves. The concurrent high-resolution TLS turbulence measurements (temperature structure constant C2T and turbulent kinetic energy dissipation rate ɛ) reveal the presence of patches of enhanced turbulence activity that are roughly synchronized with the troughs of the temperature and velocity fluctuations. To investigate the potentially dominant role ducted gravity waves might play on the modulation of atmospheric stability and therefore, on turbulence, time series of the wave-modulated gradient Richardson number (Ri) and of the vertical gradient of potential temperature ∂θ/∂z(t) are computed numerically and compared to the TLS small-scale turbulence measurements. The results of this study agree with the predictions of previous theoretical studies (i.e., wave-generated fluctuations of temperature and velocity modulate the gradient Richardson number), resulting in periodic enhancements of turbulence at Ri minima. The patches of turbulence observed in the TLS dataset are subsequently identified as convective instabilities generated locally within the unstable phase of the wave.

Sign in / Sign up

Export Citation Format

Share Document