Nonlinear Processes in Geophysics 8 (2001) 191-192

PL Read

The advection-diffusion problem for stratospheric flow. Part I: Concentration probability distribution function


Y Hu, RT Pierrehumbert

Impact of ocean dynamics on the simulation of the Neoproterozoic "snowball Earth"


CJ Poulsen, RT Pierrehumbert, RL Jacob

A new approach to stable isotope-based paleoaltimetry: implications for paleoaltimetry and paleohypsometry of the High Himalaya since the Late Miocene


DB Rowley, RT Pierrehumbert, BS Currie

Physical Climate Processes and Feedbacks

in Climate Change 2001: The Scientific Basis Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press (2001) 7

T Stocker, RT Pierrehumbert, G Clarke, TN Palmer, K Trenberth, R Lindzen

Climate Change 2001: The Scientific Basis is the most comprehensive and up-to-date scientific assessment of past, present and future climate change.

Transition to geostrophic turbulence in the laboratory, and as a paradigm in atmospheres and oceans

SURVEYS IN GEOPHYSICS 22 (2001) 265-317

PL Read

Bifurcations and instabilities in rotating two-layer fluids: I. f-plane

Nonlinear Processes in Geophysics 8 (2001) 21-36

AF Lovegrove, IM Moroz, PL Read

In this paper, we show that the behaviour of weakly nonlinear waves in a 2-layer model of baroclinic instability on an f-plane with varying viscosity is determined by a single, degenerate codimension three bifurcation. In the process, we show how previous studies, using the method of multiple scales to derive evolution equations for the slowly varying amplitude of the growing wave, arise as special limits of the general evolution description. A companion study will extend the results to a β-plane.

Achievements and directions in nonlinear geophysics - Editorial


PL Read

An evaluation of Eulerian and Semi-Lagrangian advection schemes in simulations of rotating, stratified flows in the laboratory. Part I: Axisymmetric flow

Monthly Weather Review 128 (2000) 2835-2852

PL Read, NPJ Thomas, SH Risch

A series of numerical simulations of steady, thermally stratified flow of a Boussinesq, incompressible fluid in a rotating, cylindrical fluid annulus were carried out over ranges of spatial resolution, grid stretch, and rotation rate. A range of different numerical advection schemes were used for the representation of heat transport, including a conventional conservative second-order Eulerian scheme and three different variants of a semi-Lagrangian scheme used either for temperature advection alone, or for both thermal and momentum advection. The resulting simulations were compared both with each other, and with high precision measurements of velocity, temperature, and total heat transport in the laboratory. The performance of the semi-Lagrangian scheme was found to be quite strongly sensitive to the spatial interpolation algorithm. A basic tensor cubic scheme generally produced good simulations of steady 2D and 3D flows, although the somewhat more accurate tensor quintic scheme (which is, however, also significantly more expensive) appeared to offer some detectable improvements in accuracy and performance in some cases. A split cubic scheme (which is computationally cheaper but formally less accurate) gave generally poor results in practice and is not recommended. In all cases considered, both the fully Eulerian and most forms of the semi-Lagrangian schemes gave good quantitative agreement with the laboratory measurements when extrapolated to very high resolution. Some significant systematic errors in the simulated heat transport and zonal momentum were found with all schemes, however, when run at moderate (though by no means very low) resolution. The semi-Lagrangian schemes had a tendency to overestimate heat transport relative to the laboratory measurements compared with the Eulerian schemes, but the latter tended to overestimate zonal momentum relative to the laboratory flows compared with the fully semi-Lagrangian simulations.

A mechanistic model of the quasi-quadrennial oscillation in Jupiter's stratosphere

PLANET SPACE SCI 48 (2000) 637-669

X Li, PL Read

An analytical model, previously developed for investigating the propagation of equatorially-trapped waves on an equatorial beta-plane in a uniform zonal flow in the presence of Rayleigh friction and Newtonian cooling in the Earth's stratosphere, is applied to Jupiter's upper troposphere and lower stratosphere. By analogy with the Earth, a 'spectral window' is identified for each of the main classes of equatorial wave mode, suggesting a mode-selection criterion for the dominant modes observed in association with strong wave-zonal flow interactions in the stratosphere. The modes favoured by this approach are compared with recent observations of wave activity and the quasi-quadrennial oscillation (QQO) in Jupiter's tropical atmosphere. Two modes with zonal wavenumber k similar to 8-11 are identified which may correspond to: (i) an equatorial Rossby mode moving eastward at around 100 m s(-1): and (ii) a mixed Rossby-gravity mode which is similar to stationary in System III, apparently excited by a wave source moving with the zonal wind in the deep troposphere. A Kelvin mode is also predicted to be present, but observational evidence for this mode is lacking to date. A numerical model, capable of solving for wave structures and wave-zonal flow interactions in arbitrary zonal flows using a Hermite spectral method, is adapted to conditions in Jupiter's stratosphere. The latter numerical model is shown to successfully simulate a plausible QQO with a period around four Earth years, given a single pair of forced Kelvin and MRG modes with tropospheric amplitudes consistent with observations. This model demonstrates that the QQO may indeed result, at least in principle, from interactions of a small number of equatorially-trapped wave modes with the zonal flow in the stratosphere. The selection of wave modes taking part in this process is not unique, however, and the precise identification of the relevant modes from observations remains elusive. (C) 2000 Elsevier Science Ltd. All rights reserved.

'Equability' in an unequal world: The early Eocene revisited

GFF 122 (2000) 101-102

PJ Markwick, PJ Valdes, BW Sellwood, RT Pierrehumbert

Lattice models of advection-diffusion.

Chaos (Woodbury, N.Y.) 10 (2000) 61-74

RT Pierrehumbert

We present a synthesis of theoretical results concerning the probability distribution of the concentration of a passive tracer subject to both diffusion and to advection by a spatially smooth time-dependent flow. The freely decaying case is contrasted with the equilibrium case. A computationally efficient model of advection-diffusion on a lattice is introduced, and used to test and probe the limits of the theoretical ideas. It is shown that the probability distribution for the freely decaying case has fat tails, which have slower than exponential decay. The additively forced case has a Gaussian core and exponential tails, in full conformance with prior theoretical expectations. An analysis of the magnitude and implications of temporal fluctuations of the conditional diffusion and dissipation is presented, showing the importance of these fluctuations in governing the shape of the tails. Some results concerning the probability distribution of dissipation, and concerning the spatial scaling properties of concentration fluctuation, are also presented. Though the lattice model is applied only to smooth flow in the present work, it is readily applicable to problems involving rough flow, and to chemically reacting tracers. (c) 2000 American Institute of Physics.

Spatially correlated and inhomogeneous random advection

PHYSICS OF FLUIDS 12 (2000) 822-834

K Ngan, RT Pierrehumbert

Atmospheric pCO(2) sensitivity to the biological pump in the ocean


DE Archer, G Eshel, A Winguth, W Broecker, R Pierrehumbert, M Tobis, R Jacob

Generation of inertia-gravity waves in a baroclinically unstable fluid


AF Lovegrove, PL Read, CJ Richards

Climate change and the tropical Pacific: the sleeping dragon wakes.

Proceedings of the National Academy of Sciences of the United States of America 97 (2000) 1355-1358

RT Pierrehumbert

An evaluation of Eulerian and semi-Lagrangian advection schemes in simulations of rotating, stratified flows in the laboratory. Part I: Axisymmetric flow

MONTHLY WEATHER REVIEW 128 (2000) 2835-2852

PL Read, NPJ Thomas, SH Risch

A climate database for Mars


SR Lewis, M Collins, PL Read, F Forget, F Hourdin, R Fournier, C Hourdin, O Talagrand, JP Huot

Improved general circulation models of the Martian atmosphere from the surface to above 80 km


F Forget, F Hourdin, R Fournier, C Hourdin, O Talagrand, M Collins, SR Lewis, PL Read, JP Huot

Vortices in a rotating shear layer

Proceedings of the 1999 3rd ASME/JSME Joint Fluids Engineering Conference, FEDSM'99, San Francisco, California, USA, 18-23 July 1999 (CD-ROM) (1999) 1-

WG Fruh, PL Read

Results from an experimental study of vortices in a rotating shear layer will be presented. Through the rotation of circular sections in the base and lid of a circular tank, a vertical shear layer is created in the fluid interior. In supercritical conditions, the flow is in the form of a regular string of two-dimensional, vertically uniform, vortices along the now wavy shear layer. Once established, the vortices are very stable flow structures that persist as long as the shear is maintained. Under most conditions the vortices were steady, but quasi-periodic and chaotic flows were also observed. The data from the experiments are in the form of maps of the instantaneous horizontal velocity field obtained by a particle tracking technique similar to Particle Image Velocimetry (PIV). The data would be useful validate both the spatial and temporal behaviour of numerical models.