Publications


Synchronization in a coupled two-layer quasigeostrophic model of baroclinic instability-Part 1: Master-slave configuration

Nonlinear Processes in Geophysics 16 (2009) 543-556

AA Castrejón-Pita, PL Read

Synchronization is studied using a pair of diffusively-coupled, two-layer quasi-geostrophic systems each comprising a single baroclinic wave and a zonal flow. In particular, the coupling between the systems is in the well-known master-slave or one-way configuration. Nonlinear time series analysis, phase dynamics, and bifurcation diagrams are used to study the dynamics of the coupled system. Phase synchronization, imperfect synchronization (phase slips), or complete synchronization are found, depending upon the strength of coupling, when the systems are either in a periodic or a chaotic regime. The results of investigations when the dynamics of each system are in different regimes are also presented. These results also show evidence of phase synchronization and signs of chaos control.


Sensitivity of stable water isotopic values to convective parameterization schemes

GEOPHYSICAL RESEARCH LETTERS 36 (2009) ARTN L23801

J-E Lee, R Pierrehumbert, A Swann, BR Lintner


Gyrokinetic simulations of spherical tokamaks

Plasma Physics and Controlled Fusion 51 (2009)

CM Roach, IG Abel, RJ Akers, W Arter, M Barnes, Y Camenen, FJ Casson, G Colyer, JW Connor, SC Cowley, D Dickinson, W Dorland, AR Field, W Guttenfelder, GW Hammett, RJ Hastie, E Highcock, NF Loureiro, AG Peeters, M Reshko, S Saarelma, AA Schekochihin, M Valovic, HR Wilson

This paper reviews transport and confinement in spherical tokamaks (STs) and our current physics understanding of this that is partly based on gyrokinetic simulations. Equilibrium flow shear plays an important role, and we show how this is consistently included in the gyrokinetic framework for flows that greatly exceed the diamagnetic velocity. The key geometry factors that influence the effectiveness of turbulence suppression by flow shear are discussed, and we show that toroidal equilibrium flow shear can sometimes entirely suppress ion scale turbulence in today's STs. Advanced nonlinear simulations of electron temperature gradient (ETG) driven turbulence, including kinetic ion physics, collisions and equilibrium flow shear, support the model that ETG turbulence can explain electron heat transport in many ST discharges. © 2009 IOP Publishing Ltd.


Saturn atmospheric structure and dynamics

in Saturn from Cassini-Huygens, Springer Verlag (2009) 113-159

AD Del Genio, RK Achterberg, KH Baines, FM Flasar, PL Read, A Sanchez-Lavega, AP Showman

Saturn inhabits a dynamical regime of rapidly rotating, internally heated atmospheres similar to Jupiter. Zonal winds have remained fairly steady since the time of Voyager except in the equatorial zone and slightly stronger winds occur at deeper levels. Eddies supply energy to the jets at a rate somewhat less than on Jupiter and mix potential vorticity near westward jets. Convective clouds exist preferentially in cyclonic shear regions as on Jupiter but also near jets, including major outbreaks near 35°S associated with Saturn electrostatic discharges, and in sporadic giant equatorial storms perhaps generated from frequent events at depth. The implied meridional circulation at and below the visible cloud tops consists of upwelling (downwelling) at cyclonic (anti-cyclonic) shear latitudes. Thermal winds decay upward above the clouds, implying a reversal of the circulation there. Warm-core vortices with associated cyclonic circulations exist at both poles, including surrounding thick high clouds at the south pole. Disequilibrium gas concentrations in the tropical upper troposphere imply rising motion there. The radiative-convective boundary and tropopause occur at higher pressure in the southern (summer) hemisphere due to greater penetration of solar heating there. A temperature "knee" of warm air below the tropopause, perhaps due to haze heating, is stronger in the summer hemisphere as well. Saturn's south polar stratosphere is warmer than predicted by radiative models and enhanced in ethane, suggesting subsidence-driven adiabatic warming there. Recent modeling advances suggest that shallow weather layer theories of jet pumping may be viable if water condensation is the source of energy input driving the flow, and that deep convective cylinder models with a sufficiently large tangent cylinder radius can reproduce observed flow features as well.


The snowball Earth aftermath: Exploring the limits of continental weathering processes

EARTH AND PLANETARY SCIENCE LETTERS 277 (2009) 453-463

G Le Hir, Y Donnadieu, Y Godderis, RT Pierrehumbert, GR Halverson, M Macouin, A Nedelec, G Ramstein


Transient teleconnection event at the onset of a planet-encircling dust storm on Mars

ANNALES GEOPHYSICAE 27 (2009) 3663-3676

O Martinez-Alvarado, L Montabone, SR Lewis, IM Moroz, PL Read


Modeling Jupiter's cloud bands and decks. 1. Jet scale meridional circulations

Icarus 200 (2009) 548-562

LC Zuchowski, YH Yamazaki, PL Read

We have investigated the formation of jet scale meridional circulation cells on Jupiter in response to radiative and zonal momentum forcing. In the framework of semi-geostrophic theory, the meridional streamfunction is described by an elliptic equation with a source term dependent on the sum of the latitudinal derivative of the radiative forcing and the vertical derivative of the zonal momentum forcing. Using this equation with analytic terms similar to the assumed forcing on Jupiter, we obtained two set of atmospheric circulations cells, a stratospheric and a tropospheric one. A possible shift in the overturning circulation of the high and deep atmosphere can be induced by breaking the latitudinal alignment of radiative heating with the enforced belt and zones. A series of numerical simulations was conducted with the Jovian GCM OPUS, which was initiated with observational data obtained from the Cassini CIRS temperature cross-section and a corresponding geostrophic zonal wind field. Newtonian forcing of potential temperature as well as zonal momentum was applied respectively towards latitudinally and vertically uniform equilibrium fields. In accordance with the analytic illustrations two rows of jet scale circulation cells were created. The stratospheric circulation showed the distribution of upwelling over zones and downwelling over belts, consistent with cloud observations. The tropospheric cells featured a partial reversal of the downward vertical velocity over the belts and a considerable reduction of the upward movement over the zones in the domain, consistent with recent detections of high water clouds and lightning in belts. We also used the modeled new forcing fields as source terms for the semi-geostrophic Poisson equation to attribute the origin of the modeled secondary circulation. In this analysis, the stratospheric circulation cells observed in the model are primarily generated in response to radiative forcing, while momentum forcing induces the shifted configurations in the deep atmosphere. © 2008 Elsevier Inc. All rights reserved.


Saturn's exploration beyond cassini-huygens

in Saturn from Cassini-Huygens, (2009) 745-761

T Guillot, S Atreya, S Charnoz, MK Dougherty, P Read

For its beautiful rings, active atmosphere and mysterious magnetic field, Saturn is a fascinating planet. It also holds some of the keys to understanding the formation of our Solar System and the evolution of giant planets in general. While the exploration by the Cassini-Huygens mission has led to great advances in our understanding of the planet and its moons, it has left us with puzzling questions: What is the bulk composition of the planet? Does it have a helium core? Is it enriched in noble gases like Jupiter? What powers and controls its gigantic storms? We have learned that we can measure an outer magnetic field that is filtered from its non-axisymmetric components, but what is Saturn's inner magnetic field? What are the rings made of and when were they formed? These questions are crucial in several ways: a detailed comparison of the compositions of Jupiter and Saturn is necessary to understand processes at work during the formation of these two planets and of the Solar System: was the pro-tosolar disk progressively photoevaporated of its hydrogen and helium while forming its planets? Did Jupiter and Saturn form at the same time from cores of similar masses? Saturn is also a unique laboratory for studying the meteorology of a planet in which, in contrast to the Earth, the vapor of any condensing species (in particular water) is heavier than the surrounding air. A precise measurement of its magnetic field is needed to constrain dynamo theories and apply it to other contexts, from our Earth to extrasolar planets. Finally, the theory behind the existence of its rings is still to be confirmed, and has consequences for a variety of subjects from theories of accretion of grains to the study of physical mechanisms at work in protoplanetary systems. All in all, this calls for the continued exploration of the second largest planet in our Solar System, with a variety of means including remote observations and space missions. Measurements of gravity and magnetic fields very close to the planet's cloud tops would be extremely valuable. Very high spatial resolution images of the rings would provide details on their structure and the material that form them. Last but not least, one or several probes sent into the atmosphere of the planet would provide the critical measurements that would allow a detailed comparison with the same measurements at Jupiter. © 2009 Springer Science+Business Media B.V.


A heat engine based moist convection parametrization for Jupiter

Planetary and Space Science 57 (2009) 1525-1537

LC Zuchowski, PL Read, YH Yamazaki, NO Renno

We have developed a parametrization of Jovian moist convection based on a heat engine model of moist convection. In comparison to other moist convection schemes, this framework allows the computation of the total available convective energy TCAPE and the corresponding mass flux M as dynamic variables from the mean atmospheric state. The effects of this parametrization have been investigated both analytically and numerically. In agreement with previous numerical experiments and observations, the inclusion of moist convection leads to heat and water vapor transport from the water condensation level into higher altitudes. The time development of the modeled convective events was found to be strongly influenced by a rapid reduction of kinetic energy and a subsequent lowering of the cumulus tower's top in response to convective heating. We have tested the sensitivity of the scheme to different variations in the fractional cloud coverage and under the inclusion of external radiative forcing towards a stable/unstable temperature profile. While the time development of convective events differs in response to these variations, the general moist convective heating and moistening of the upper troposphere was a robust feature observed in all experiments. © 2009 Elsevier Ltd.


QUAGMIRE v1.3: a quasi-geostrophic model for investigating rotating fluids experiments

GEOSCIENTIFIC MODEL DEVELOPMENT 2 (2009) 13-32

PD Williams, TWN Haine, PL Read, SR Lewis, YH Yamazaki


Transient teleconnection event at the onset of a planet-encircling dust storm on Mars

Annales Geophysicae 27 (2009) 3663-3676

O Martínez-Alvarado, L Montabone, SR Lewis, IM Moroz, PL Read

We use proper orthogonal decomposition (POD) to study a transient teleconnection event at the onset of the 2001 planet-encircling dust storm on Mars, in terms of empirical orthogonal functions (EOFs). There are several differences between this and previous studies of atmospheric events using EOFs. First, instead of using a single variable such as surface pressure or geopotential height on a given pressure surface, we use a dataset describing the evolution in time of global and fully three-dimensional atmospheric fields such as horizontal velocity and temperature. These fields are produced by assimilating Thermal Emission Spectrometer observations from NASA's Mars Global Surveyor spacecraft into a Mars general circulation model. We use total atmospheric energy (TE) as a physically meaningful quantity which weights the state variables. Second, instead of adopting the EOFs to define teleconnection patterns as planetary-scale correlations that explain a large portion of long time-scale variability, we use EOFs to understand transient processes due to localised heating perturbations that have implications for the atmospheric circulation over distant regions. The localised perturbation is given by anomalous heating due to the enhanced presence of dust around the northern edge of the Hellas Planitia basin on Mars. We show that the localised disturbance is seemingly restricted to a small number (a few tens) of EOFs. These can be classified as low-order, transitional, or high-order EOFs according to the TE amount they explain throughout the event. Despite the global character of the EOFs, they show the capability of accounting for the localised effects of the perturbation via the presence of specific centres of action. We finally discuss possible applications for the study of terrestrial phenomena with similar characteristics.


Testing the Trapped Gyro-Landau Fluid Transport Model with Data from Tokamaks and Spherical Tori

Proc. 22nd IAEA FEC (2008)

GM Staebler, G Colyer, S Kaye, JE Kinsey, RE Waltz


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

EARTH AND PLANETARY SCIENCE LETTERS 267 (2008) 247-255

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


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

GEOCHIMICA ET COSMOCHIMICA ACTA 72 (2008) A315-A315

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


Intense polar temperature inversion in the middle atmosphere on Mars

Nature Geoscience 1 (2008) 745-749

DJ McCleese, JT Schofield, FW Taylor, WA Abdou, O Aharonson, D Banfield, SB Calcutt, NG Heavens, PGJ Irwin, DM Kass, A Kleinböhl, WG Lawson, CB Leovy, SR Lewis, DA Paige, PL Read, MI Richardson, N Teanby, RW Zurek

Current understanding of weather, climate and global atmospheric circulation on Mars is incomplete, in particular at altitudes above about 30 km. General circulation models for Mars are similar to those developed for weather and climate forecasting on Earth and require more martian observations to allow testing and model improvements. However, the available measurements of martian atmospheric temperatures, winds, water vapour and airborne dust are generally restricted to the region close to the surface and lack the vertical resolution and global coverage that is necessary to shed light on the dynamics of Mars middle atmosphere at altitudes between 30 and 80 km (ref.7). Here we report high-resolution observations from the Mars Climate Sounder instrument on the Mars Reconnaissance Orbiter. These observations show an intense warming of the middle atmosphere over the south polar region in winter that is at least 10-20 K warmer than predicted by current model simulations. To explain this finding, we suggest that the atmospheric downwelling circulation over the pole, which is part of the equator-to-pole Hadley circulation, may be as much as 50 more vigorous than expected, with consequences for the cycles of water, dust and CO"2 that regulate the present-day climate on Mars. © 2008 Macmillan Publishers Limited.


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.


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.


Inertia-Gravity Waves Emitted from Balanced Flow: Observations, Properties, and Consequences

JOURNAL OF THE ATMOSPHERIC SCIENCES 65 (2008) 3543-3556

PD Williams, TWN Haine, PL Read

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