Publications


Synchronization in baroclinic systems

15TH INTERNATIONAL COUETTE-TAYLOR WORKSHOP 137 (2008) ARTN 012016

AA Castrejon-Pita, PL Read


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).


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


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.


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


GCM representation of turbulence on Jupiter

SPRINGER PROC PHYS 117 (2007) 582-584

LC Zuchowski, YH Yamazaki, PL Read


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.


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


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

GEOPHYSICAL RESEARCH LETTERS 34 (2007) ARTN L17812

H Brogniez, RT Pierrehumbert


An ocean of air: A natural history of the atmosphere

NATURE 447 (2007) 911-911

RT Pierrehumbert


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

JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 112 (2007) ARTN E05S06

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


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

Journal of Geophysical Research E: Planets 112 (2007)

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

Against a backdrop of intensive exploration of the Martian surface environment, intehded to lead to human exploration, some aspects of the modern climate and the meteorology of Mars remain relatively unexplored. In particular, there is a need for detailed measurements of the vertical profiles of atmospheric temperature, water vapor, dust, and condensates to understand the intricately related processes upon which the surface conditions, and those encountered during descent by landers, depend. The most important of these missing data are accurate and extensive temperature measurements with high vertical resolution. The Mars Climate Sounder experiment on the 2005 Mars Reconnaissance Orbiter, described here, is the latest attempt to characterize the Martian atmosphere with the sort of coverage and precision achieved by terrestrial weather satellites. If successful, it is expected to lead to corresponding improvements in our understanding of meteorological phenomena and to enable improved general circulation models of the Martian atmosphere for climate studies on a range of timescales. Copyright 2007 by the American Geophysical Union.


Superrotation in a Venus general circulation model

Journal of Geophysical Research E: Planets 112 (2007)

C Lee, SR Lewis, PL Read

A superrotating atmosphere with equatorial winds of ∼35 m s-1 is simulated using a simplified Venus general circulation model (GCM). The equatorial superrotation in the model atmosphere is maintained by barotropic instabilities in the midlatitude jets which transport angular momentum toward the equator. The midlatitude jets are maintained by the mean meridional circulation, and the momentum transporting waves are qualitatively similar to observed midlatitude waves; an equatorial Kelvin wave is also present in the atmosphere. The GCM is forced by linearized cooling and friction parameterizations, with hyperdiffusion and a polar Fourier filter to maintain numerical stability. Atmospheric superrotation is a robust feature of the model and is spontaneously produced without specific tuning. A strong meridional circulation develops in the form of a single Hadley cell, extending from the equator to the pole in both hemispheres, and from the surface to 50 km altitude. The zonal jets produced by this circulation reach 45 m s-1 at 60 km, with peak winds of 35 m s-1 at the equator. A warm pole and cold collar are also found in the GCM, caused by adiabatic warming in the mean meridional circulation. Wave frequencies and zonal wind speeds are smaller than in observations by cloud tracking but are consistent with a Doppler shifting by wind speeds in the generating region of each wave. Magnitudes of polar temperature anomalies are smaller than the observed features, suggesting dynamical processes alone may not be sufficient to maintain the large observed temperature contrasts at the magnitudes and periods found in this GCM. Copyright 2007 by the American Geophysical Union.


Superrotation in a Venus general circulation model

JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 112 (2007) ARTN E04S11

C Lee, SR Lewis, PL Read


Investigating plausible mechanisms to trigger a deglaciation from a hard snowball Earth

COMPTES RENDUS GEOSCIENCE 339 (2007) 274-287

G Le Hir, G Ramstein, Y Donnadieu, RT Pierrehumbert


Baroclinic waves in an air-filled thermally driven rotating annulus.

Phys Rev E Stat Nonlin Soft Matter Phys 75 (2007) 026301-

AA Castrejón-Pita, PL Read

In this study an experimental investigation of baroclinic waves in air in a differentially heated rotating annulus is presented. Air has a Prandtl number of 0.707, which falls within a previously unexplored region of parameter space for baroclinic instability. The flow regimes encountered include steady waves, periodic amplitude vacillations, modulated amplitude vacillations, and either monochromatic or mixed wave number weak waves, the latter being characterized by having amplitudes less than 5% of the applied temperature contrast. The distribution of these flow regimes in parameter space are presented in a regime diagram. It was found that the progression of transitions between different regimes is, as predicted by recent numerical modeling results, in the opposite sense to that usually found in experiments with high Prandtl number liquids. No hysteresis in the flow type, with respect to variations in the rotation rate, was found in this investigation.


On the relative humidity of the atmosphere

in The Global Circulation of the Atmosphere, Princeton University Press (2007) 6

RT Pierrehumbert


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.


Editorial

Quarterly Journal of the Royal Meteorological Society 133 (2007) 1-

PL Read, I Roulstone


The dynamics behind Titan's methane clouds.

Proceedings of the National Academy of Sciences of the United States of America 103 (2006) 18421-18426

JL Mitchell, RT Pierrehumbert, DMW Frierson, R Caballero

We present results of an axisymmetric global circulation model of Titan with a simplified suite of atmospheric physics forced by seasonally varying insolation. The recent discovery of midlatitude tropospheric clouds on Titan has caused much excitement about the roles of surface sources of methane and the global circulation in forming clouds. Although localized surface sources, such as methane geysers or "cryovolcanoes," have been invoked to explain these clouds, we find in this work that clouds appear in regions of convergence by the mean meridional circulation and over the poles during solstices, where the solar forcing reaches its seasonal maximum. Other regions are inhibited from forming clouds because of dynamical transports of methane and strong subsidence. We find that for a variety of moist regimes, i.e., with the effect of methane thermodynamics included, the observed cloud features can be explained by the large-scale dynamics of the atmosphere. Clouds at the solsticial pole are found to be a robust feature of Titan's dynamics, whereas isolated midlatitude clouds are present exclusively in a variety of moist dynamical regimes. In all cases, even without including methane thermodynamics, our model ceases to produce polar clouds approximately 4-6 terrestrial years after solstices.

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