Causal or casual link between the rise of nannoplankton calcification and a tectonically-driven massive decrease in Late Triassic atmospheric CO2?


Y Godderis, Y Donnadieu, C de Vargas, RT Pierrehumbert, G Dromart, B van de Schootbrugge

Axisymmetric, nearly inviscid circulations in non-condensing radiative-convective atmospheres


R Caballero, RT Pierrehumbert, JL Mitchell

Breeding and predictability in the baroclinic rotating annulus using a perfect model

Nonlin. Proc. Geophys. Copernicus Publications 15 (2008) 469-487

RMB Young, PL Read

We present results from a computational study of predictability in fully-developed baroclinically unstable laboratory flows. This behaviour is studied in the Met Office/Oxford Rotating Annulus Laboratory Simulation a model of the classic rotating annulus laboratory experiment with differentially heated cylindrical sidewalls, which is firmly established as an insightful laboratory analogue for certain kinds of atmospheric dynamical behaviour. This work is the first study of 'predictability of the first kind' in the annulus experiment. We devise an ensemble prediction scheme using the breeding method to study the predictability of the annulus in the perfect model scenario. This scenario allows one simulation to be defined as the true state, against which all forecasts are measured. We present results from forecasts over a range of quasi-periodic and chaotic annulus flow regimes. A number of statistical and meteorological techniques are used to compare the predictability of these flows: bred vector growth rate and dimension, error variance, ''spaghetti plots", probability forecasts, Brier score, and the Kolmogorov-Smirnov test. These techniques gauge both the predictability of the flow and the performance of the ensemble relative to a forecast using a climatological distribution. It is found that in the perfect model scenario, the two quasi-periodic regimes examined may be indefinitely predictable. The two chaotic regimes (structural vacillation and period doubled amplitude vacillation) show a loss of predictability on a timescale of hundreds to thousands of seconds (65-280 annulus rotation periods, or 1-3 Lyapunov times).

Data discrepancies in solar-climate link.

Science (New York, N.Y.) 320 (2008) 746-

RT Pierrehumbert

Causal or casual link between the rise of nannoplankton calcification and an abrupt tectonically-driven atmospheric CO2 decline in the Late Triassic?


Y Godderis, Y Donnadieu, C De Vargas, RT Pierrehumbert, G Dromart, BV De Schootbrugge

Synchronization in baroclinic systems


AA Castrejon-Pita, PL Read

Flow transitions resembling bifurcations of the logistic map in simulations of the baroclinic rotating annulus

Physica D Elsevier 237 (2008) 2251-2262

RMB Young, PL Read

We present evidence for a sequence of bifurcations in simulations of the differentially heated baroclinic rotating annulus, similar to bifurcations of the logistic map. The Met. Office / Oxford Rotating Annulus Laboratory Simulation (MORALS) code is used to construct a detailed numerical regime diagram for the annulus, and the distribution of regimes in parameter space is discussed. The bifurcations are observed in a sequence of runs at high temperature forcing, identified by Poincare sections of the dominant temperature mode amplitude time series. Higher order return maps and predictions using quadratic fits to the data are used to verify this result, and Lyapunov exponents are calculated to identify and quantify the chaotic parts of the sequence. (c) 2008 Elsevier B.V. All rights reserved.

Dynamics of convectively driven banded jets in the laboratory (vol 64, pg 4031, 2007)


PL Read, YH Yamazaki, SR Lewis, PD Williams, R Wordsworth, K Miki-Yamazaki, J Sommeria, H Didelle, AM Fincham

Erratum: "Dynamics of convectively driven banded jets in the laboratory" (Journal of the Atmospheric Sciences (2007))

Journal of the Atmospheric Sciences 65 (2008) 287-

PL Read, YH Yamazaki, SR Lewis, PD Williams, R Wordsworth, K Miki-Yamazaki, J Sommeria, H Didelle, AM Fincham

Direct numerical simulation of transitions towards structural vacillation in an air-filled, rotating, baroclinic annulus

PHYSICS OF FLUIDS 20 (2008) ARTN 044107

PL Read, P Maubert, A Randriamampianina, W-G Fruh

Tubulence, waves, and jets in a differentially heated rotating annulus experiment

Physics of Fluids 20 (2008)

RD Wordsworth, PL Read, YH Yamazaki

We report an analog laboratory study of planetary-scale turbulence and jet formation. A rotating annulus was cooled and heated at its inner and outer walls, respectively, causing baroclinic instability to develop in the fluid inside. At high rotation rates and low temperature differences, the flow became chaotic and ultimately fully turbulent. The inclusion of sloping top and bottom boundaries caused turbulent eddies to behave like planetary waves at large scales, and eddy interaction with the zonal flow then led to the formation of several alternating jets at mid-depth. The jets did not scale with the Rhines length, and spectral analysis of the flow indicated a distinct separation between jets and eddies in wavenumber space, with direct energy transfer occurring nonlocally between them. Our results suggest that the traditional "turbulent cascade" picture of zonal jet formation may be an inappropriate one in the geophysically important case of large-scale flows forced by differential solar heating.

Temperature and composition of Saturn's polar hot spots and hexagon.

Science 319 (2008) 79-81

LN Fletcher, PGJ Irwin, GS Orton, NA Teanby, RK Achterberg, GL Bjoraker, PL Read, AA Simon-Miller, C Howett, R de Kok, N Bowles, SB Calcutt, B Hesman, FM Flasar

Saturn's poles exhibit an unexpected symmetry in hot, cyclonic polar vortices, despite huge seasonal differences in solar flux. The cores of both vortices are depleted in phosphine gas, probably resulting from subsidence of air into the troposphere. The warm cores are present throughout the upper troposphere and stratosphere at both poles. The thermal structure associated with the marked hexagonal polar jet at 77 degrees N has been observed for the first time. Both the warm cyclonic belt at 79 degrees N and the cold anticyclonic zone at 75 degrees N exhibit the hexagonal structure.

Recurrence analysis of quasiperiodicity in experimental fluid data


Y Zou, M Thiel, MC Romano, PL Read, J Kurths

Mars Climate Sounder: An investigation of thermal and water vapor structure, dust and condensate distributions in the atmosphere, and energy balance of the polar regions


DJ McCleese, JT Schofield, FW Taylor, SB Calcutt, MC Foote, DM Kass, CB Leovy, DA Paige, PL Read, RW Zurek

DNS of Structural Vacillation in the transition to geostrophic turbulence

Advances in Turbulence XI - Proceedings of the 11th EUROMECH European Turbulence Conference (2007) 432-434

WG Früh, P Maubert, PL Read, A Randriamampianina

The onset of small-scale fluctuations around a steady convection pattern in a rotating baroclinic annulus filled with air is investigated using Direct Numerical Simulations (DNS). In previous laboratory experiments of baroclinic waves, such fluctuations have been associated with Structural Vacillation which is regarded as the first step in the transition to fully-developed geostrophic turbulence. Here we present an analysis which focusses on the small-scale features.

Dynamics of convectively driven banded jets in the laboratory

Journal of the Atmospheric Sciences 64 (2007) 4031-4052

PL Read, YH Yamazaki, SR Lewis, PD Williams, R Wordsworth, K Miki-Yamazaki, J Sommeria, H Didelle

The banded organization of clouds and zonal winds in the atmospheres of the outer planets has long fascinated observers. Several recent studies in the theory and idealized modeling of geostrophic turbulence have suggested possible explanations for the emergence of such organized patterns, typically involving highly anisotropic exchanges of kinetic energy and vorticity within the dissipationless inertial ranges of turbulent flows dominated (at least at large scales) by ensembles of propagating Rossby waves. The results from an attempt to reproduce such conditions in the laboratory are presented here. Achievement of a distinct inertial range turns out to require an experiment on the largest feasible scale. Deep, rotating convection on small horizontal scales was induced by gently and continuously spraying dense, salty water onto the free surface of the 13-m-diameter cylindrical tank on the Coriolis platform in Grenoble, France. A "planetary vorticity gradient" or "β effect" was obtained by use of a conically sloping bottom and the whole tank rotated at angular speeds up to 0.15 rad s-1. Over a period of several hours, a highly barotropic, zonally banded large-scale flow pattern was seen to emerge with up to 5-6 narrow, alternating, zonally aligned jets across the tank, indicating the development of an anisotropic field of geostrophic turbulence. Using particle image velocimetry (PIV) techniques, zonal jets are shown to have arisen from nonlinear interactions between barotropic eddies on a scale comparable to either a Rhines or "frictional" wavelength, which scales roughly as (β/Urms) -1/2. This resulted in an anisotropic kinetic energy spectrum with a significantly steeper slope with wavenumber k for the zonal flow than for the nonzonal eddies, which largely follows the classical Kolmogorov k-5/3 inertial range. Potential vorticity fields show evidence of Rossby wave breaking and the presence of a "hyperstaircase" with radius, indicating instantaneous flows that are supercritical with respect to the Rayleigh-Kuo instability criterion and in a state of "barotropic adjustment." The implications of these results are discussed in light of zonal jets observed in planetary atmospheres and, most recently, in the terrestrial oceans. © 2007 American Meteorological Society.

Intercomparison of tropical tropospheric humidity in GCMs with AMSU-B water vapor data


H Brogniez, RT Pierrehumbert

An ocean of air: A natural history of the atmosphere

NATURE 447 (2007) 911-911

RT Pierrehumbert

Assimilation of thermal emission spectrometer atmospheric data during the Mars Global Surveyor aerobraking period

ICARUS 192 (2007) 327-347

SR Lewis, PL Read, BJ Conrath, JC Pearl, MD Smith

Dynamics of convectively driven banded jets in the laboratory


PL Read, YH Yamazaki, SR Lewis, PD Williams, R Wordsworth, K Miki-Yamazaki