The potential for sea ice-albedo feedback to give rise to nonlinear climate change in the Arctic Ocean – defined as a nonlinear relationship between polar and global temperature change or, equivalently, a time-varying polar amplification – is explored in IPCC AR4 climate models. Five models supplying SRES A1B ensembles for the 21 st century are examined and very linear relationships are found between polar and global temperatures (indicating linear Arctic Ocean climate change), and between polar temperature and albedo (the potential source of nonlinearity). Two of the climate models have Arctic Ocean simulations that become annually sea ice-free under the stronger CO 2 increase to quadrupling forcing. Both of these runs show increases in polar amplification at polar temperatures above-5 o C and one exhibits heat budget changes that are consistent with the small ice cap instability of simple energy balance models. Both models show linear warming up to a polar temperature of-5 o C, well above the disappearance of their September ice covers at about-9 o C. Below-5 o C, surface albedo decreases smoothly as reductions move, progressively, to earlier parts of the sunlit period. Atmospheric heat transport exerts a strong cooling effect during the transition to annually ice-free conditions. Specialized experiments with atmosphere and coupled models show that the main damping mechanism for sea ice region surface temperature is reduced upward heat flux through the adjacent ice-free oceans resulting in reduced atmospheric heat transport into the region.

Geophysical fluid dynamics.

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Stability And Transition In Shear Flows

This review highlights the profound and unexpected ways in which viscosity varying in space and time can affect flow. The most striking manifestations are through alterations of flow stability, as established in model shear flows and industrial applications. Future studies are needed to address the important effect of viscosity stratification in such diverse environments as Earth's core, the Sun, blood vessels, and the re-entry of spacecraft.

Instabilities in Viscosity-Stratified Flow

Fiber-shaped stretchable strain sensors with small testing areas can be directly woven into textiles. This paves the way for the design of integrated wearable devices capable of obtaining real-time mechanical feedback for various applications. However, for a simple fiber that undergoes uniform strain distribution during deformation, it is still a big challenge to obtain high sensitivity. Herein, a new strategy, surface strain redistribution, is reported to significantly enhance the sensitivity of fiber-shaped stretchable strain sensors. A new method of transient thermal curing is used to achieve the large-scale fabrication of modified elastic microfibers with intrinsic microbeads. The proposed strategy is independent of the active materials utilized and can be universally applied for various active materials. The strategy used here will shift the vision of the sensitivity enhancement method from the active materials design to the mechanical design of the elastic substrate, and the proposed strategy can also be applied to nonfiber-shaped stretchable strain sensors.

Surface Strain Redistribution on Structured Microfibers to Enhance Sensitivity of Fiber-Shaped Stretchable Strain Sensors.

A novel fractal solution for permeability and Kozeny-Carman constant of fibrous porous media made up of solid particles and porous fibers

Dynamics of quasi-2D dissipative granular gas is studied in micro-gravity condition (of the order of 10 − 4 g) in the limit of Knudsen regime The gas, made of 4 spheres, is confined in a square cell enforced to follow linear sinusoidal vibration in ten different vibration modes The trajectory of one of the particles is followed for 2 hours, and is reconstructed from video data by particle tracking From statistical analysis, we find that (i) loss due to wall friction is small, (ii) trajectory looks ergodic in space, and (iii) distribution ρ(ν) of speed follows an exponential distribution, ie, $\rho (v) \approx \exp \left[ {{-\nu } \mathord{\left/ {\vphantom {{-\nu } {\left( {\nu _{x_0 ,y_0 } } \right)}}} \right \kern-\nulldelimiterspace} {\left( {\nu _{x_0 ,y_0 } } \right)}} \right]$
 , with $\nu _{x_0 ,y_0 } $
 being a characteristic velocity along a direction parallel (y) or perpendicular (x) to vibration direction This law deviates strongly from the Boltzmann distribution of speed in molecular gas Comparisons of this result with previous measurements in earth environment, and what was found in 3D cell (Falcon et al, Europhys Lett 74:830, 2006) performed in environment of about ±5 ×10 − 2 g are given

/pdf/velocity-distribution-of-vibration-driven-granular-gas-in-22499tw7tj.pdf

Velocity Distribution of Vibration-driven Granular Gas in Knudsen Regime in Microgravity

The problem of a film flowing down an inclined porous layer is considered The fully developed basic flow is driven by gravitation A careful linear instability analysis is carried out We use Darcy's law to describe the porous layer and solve the coupling equations of the fluid and the porous medium rather than the decoupled equations of the one-sided model used in previous works The eigenvalue problem is solved by means of a Chebyshev collocation method We compare the instability of the two-sided model with the results of the one-sided model The result reveals a porous mode instability which is completely neglected in previous works For a falling film on an inclined porous plane there are three instability modes, ie, the surface mode, the shear mode, and the porous mode We also study the influences of the depth ratio d, the Darcy number delta, and the Beavers-Joseph coefficient alpha(BJ) on the instability of the system

/pdf/instabilities-of-a-liquid-film-flowing-down-an-inclined-2uuzszsht1.pdf

Instabilities of a liquid film flowing down an inclined porous plane

The instability of Poiseuille flow in a fluid-porous system is investigated. The system consists of a fluid layer overlying porous media and is subjected to a horizontal plane Poiseuille flow. We use Brinkman's model instead of Darcy's law to describe the porous layer. The eigenvalue problem is solved by means of a Chebyshev collocation method. We study the influence of the depth ratio (d) over cap and the Darcy number delta on the instability of the system. We compare systematically the instability of Brinkman's model with the results of Darcy's model. Our results show that no satisfactory agreement between Brinkman's model and Darcy's model is obtained for the instability of a fluid-porous system. We also examine the instability of Darcy's model. A particular comparison with early work is made. We find that a multivalued region may present in the (k, Re) plane, which was neglected in previous work. Here k is the dimensionless wavenumber and Re is the Reynolds number. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3000643]

Instability of plane Poiseuille flow in a fluid-porous system

Dynamics of thin liquid films flowing down the uniformly heated/cooled cylinder with wall slippage

In this paper, we study the linear stability of a plane Couette flow of a power-law fluid. The influence of shear-thinning effect on the stability is investigated using the classical eigenvalue analysis, the energy method and the non-modal stability theory. For the plane Couette flow, there is no stratification of viscosity. Thus, for the stability problem the stress tensor is anisotropic aligned with the strain rate perturbation. The results of the eigenvalue analysis and the energy method show that the shear-thinning effect is destabilizing. We focus on the effect of non-Newtonian viscosity on the transition from laminar flow towards turbulence in the framework of non-modal stability theory. Response to external excitations and initial conditions has been studied by examining the epsilon-pseudospectrum and the transient energy growth. For both Newtonian and non-Newtonian fluids, it is found that there can be a rather large transient growth even though the linear operator of the Couette flow has no unstable eigenvalue. The results show that shear-thinning significantly increases the amplitude of response to external excitations and initial conditions.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S002211201100036X

Rong Liu

Papers

Velocity Distribution of Vibration-driven Granular Gas in Knudsen Regime in Microgravity

Instabilities of a liquid film flowing down an inclined porous plane

Instability of plane Poiseuille flow in a fluid-porous system

Dynamics of thin liquid films flowing down the uniformly heated/cooled cylinder with wall slippage

Non-modal instability in plane Couette flow of a power-law fluid