Joe M. Straus

Large amplitude convection in porous media

The properties of convective flow driven by an adverse temperature gradient in a fluid-filled porous medium are investigated. The Galerkin technique is used to treat the steady-state two-dimensional problem for Rayleigh numbers as large as ten times the critical value. The flow is found to look very much like ordinary Benard convection, but the Nusselt number depends much more strongly on the Rayleigh number than in Benard convection. The stability of the finite amplitude two-dimensional solutions is treated. At a given value of the Rayleigh number, stable two-dimensional flow is possible for a finite band of horizontal wavenumbers as long as the Rayleigh number is small enough. For Rayleigh numbers larger than about 380, however, no two-dimensional solutions are stable. Comparisons with previous theoretical and experimental work are given.

A dynamical-chemical model of wave-driven fluctuations in the OH nightglow

A theory is presented to explain tidally induced oscillations in the emission intensity I and rotational temperature T of the OH nightglow. The theory includes photochemical reactions among H, O, O3, OH, and HO2 and the complete dynamics of tides in an isothermal, uniformly rotating atmosphere. The ratio refers to a perturbation quantity and the overbar signifies an average) depends on basic state atmospheric structure, minor constituent scale heights, especially that of O, and altitude of OH emission. For both semidiurnal and diurnal migrating modes, η has an amplitude in the approximate range 1–2.5 and a phase between about 10° and 30°.

Route to chaos in porous-medium thermal convection

A pseudo-spectral numerical scheme is used to study two-dimensional, single-cell, time-dependent convection in a square cross-section of fluid saturated porous material heated from below. With increasing Rayleigh number R convection evolves from steady S to chaotic NP through the sequence of bifurcations S→P (1) →QP 2 →P (2) →NP, where P (1) and P (2) are simply periodic regimes and QP 2 is a quasi-periodic state with two basic frequencies. The transitions (from onset of convection to chaos) occur at Rayleigh numbers of 4π 2 , 380–400, 500–520, 560–570, and 850–1000. In the first simply periodic regime the fundamental frequency f 1 varies as

Infinite Prandtl number thermal convection in a spherical shell

R^{\frac{7}{8}}

Effects of heating at high latitudes on global thermospheric dynamics

and the average Nusselt number

Instabilities of Steady, Periodic, and Quasi-Periodic Modes of Convection in Porous Media

\overline{Nu}

Modes of finite-amplitude three-dimensional convection in rectangular boxes of fluid-saturated porous material

is proportional to

On the existence of three-dimensional convection in a rectangular box containing fluid-saturated porous material

R^{\frac{2}{3}}

Time-dependent convection in a fluid-saturated porous cube heated from below

; in P (2) , f 1 varies as

On the upper bounding approach to thermal convection at moderate Rayleigh numbers, II. Rigid boundaries

R^{\frac{3}{2}}