Publications


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.


Global warming, convective threshold and false thermostats

GEOPHYSICAL RESEARCH LETTERS 36 (2009) ARTN L21805

IN Williams, RT Pierrehumbert, M Huber


Low-order dynamical behavior in the martian atmosphere: Diagnosis of general circulation model results

Icarus 204 (2009) 48-62

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

The hypothesis of a low dimensional martian climate attractor is investigated by the application of the proper orthogonal decomposition (POD) to a simulation of martian atmospheric circulation using the UK Mars general circulation model (UK-MGCM). In this article we focus on a time series of the interval between autumn and winter in the northern hemisphere, when baroclinic activity is intense. The POD is a statistical technique that allows the attribution of total energy (TE) to particular structures embedded in the UK-MGCM time-evolving circulation. These structures are called empirical orthogonal functions (EOFs). Ordering the EOFs according to their associated energy content, we were able to determine the necessary number to account for a chosen amount of atmospheric TE. We show that for Mars a large fraction of TE is explained by just a few EOFs (with 90% TE in 23 EOFs), which apparently support the initial hypothesis. We also show that the resulting EOFs represent classical types of atmospheric motion, such as thermal tides and transient waves. Thus, POD is shown to be an efficient method for the identification of different classes of atmospheric modes. It also provides insight into the non-linear interaction of these modes. © 2009 Elsevier Inc. All rights reserved.


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.


Radiative transfer in CO2-rich paleoatmospheres

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 114 (2009) ARTN D18112

I Halevy, RT Pierrehumbert, DP Schrag


The impact of methane thermodynamics on seasonal convection and circulation in a model Titan atmosphere

ICARUS 203 (2009) 250-264

JL Mitchell, RT Pierrehumbert, DMW Frierson, R Caballero


Saturn's rotation period from its atmospheric planetary-wave configuration

NATURE 460 (2009) 608-610

PL Read, TE Dowling, G Schubert


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.


Modeling Jupiter's cloud bands and decks. 2. Distribution and motion of condensates

Icarus 200 (2009) 563-573

LC Zuchowski, YH Yamazaki, PL Read

A simple jovian cloud scheme has been developed for the Oxford Planetary Unified model System (OPUS). NH3-ice, NH4SH-solid, H2O-ice and H2O-liquid clouds have been modeled in Southern hemisphere limited area simulations of Jupiter. We found that either three or four of the condensates existed in the model. For a deep atmospheric water abundance close to solar composition, an NH3-ice deck above 0.7 bar, an NH4SH-solid deck above 2.5 bar and a H2O-liquid deck with a base at about 7.5 bar and frozen cloud tops formed. If a depleted deep water abundance is assumed, however, a very compact cloud structure develops, where an H2O-ice cloud forms by direct sublimation above 3 bar. The condensates constitute good tracers of atmospheric motion, and we have confirmed that zonal velocities determined from manual feature tracking in the modeled cloud layers agree reasonably well with the modeled zonal velocities. Dense and elevated clouds form over latitudes with strong atmospheric upwelling and depleted clouds exist over areas with strong downwelling. In the NH3-ice deck this leads to elevated cloud bands over the zones in the domain and thin clouds over the belts, which is consistent with the observationally deduced distribution. Due to changes in the vertical velocity pattern in the deeper atmosphere, the NH4SH-solid and water cloud decks are more uniform. This modeled cloud structure thus includes the possibility of more frequent water cloud observations in belts, as this deeper deck could be more easily detected under areas with thin NH3-ice clouds. Large scale vortices appeared spontaneously in the model and were characterized by elevated NH3-ice clouds, as expected from observations. These eddies leave the most discernible imprint on the lighter condensate particles of the uppermost layer. © 2008 Elsevier Inc. All rights reserved.


Erratum to Kronos: Exploring the depths of Saturn with probes and remote sensing through an international mission

Experimental Astronomy 23 (2009) 977-980

B Marty, T Guillot, A Coustenis, N Achilleos, Y Alibert, S Asmar, D Atkinson, S Atreya, G Babasides, K Baines, T Balint, D Banfield, S Barber, B Bézard, GL Bjoraker, M Blanc, S Bolton, N Chanover, S Charnoz, E Chassefière, JE Colwell, E Deangelis, M Dougherty, P Drossart, FM Flasar, T Fouchet, R Frampton, I Franchi, D Gautier, L Gurvits, R Hueso, B Kazeminejad, T Krimigis, A Jambon, G Jones, Y Langevin, M Leese, E Lellouch, J Lunine, A Milillo, P Mahaffy, B Mauk, A Morse, M Moreira, X Moussas, C Murray, I Mueller-Wodarg, TC Owen, S Pogrebenko, R Prangé, P Read, A Sanchez-Lavega, P Sarda, D Stam, G Tinetti, P Zarka, J Zarnecki, J Schmidt, H Salo


Kronos: exploring the depths of Saturn with probes and remote sensing through an international mission

EXPERIMENTAL ASTRONOMY 23 (2009) 947-976

B Marty, T Guillot, A Coustenis, N Achilleos, Y Alibert, S Asmar, D Atkinson, S Atreya, G Babasides, K Baines, T Balint, D Banfield, S Barber, B Bezard, GL Bjoraker, M Blanc, S Bolton, N Chanover, S Charnoz, E Chassefiere, JE Colwell, E Deangelis, M Dougherty, P Drossart, FM Flasar, T Fouchet, R Frampton, I Franchi, D Gautier, L Gurvits, R Hueso, B Kazeminejad, T Krimigis, A Jambon, G Jones, Y Langevin, M Leese, E Lellouch, J Lunine, A Milillo, P Mahaffy, B Mauk, A Morse, M Moreira, X Moussas, C Murray, I Mueller-Wodarg, TC Owen, S Pogrebenko, R Prange, P Read, A Sanchez-Lavega, P Sarda, D Stam, G Tinetti, P Zarka, J Zarnecki, K Consortium


Mars environment and magnetic orbiter model payload

EXPERIMENTAL ASTRONOMY 23 (2009) 761-783

B Langlais, F Leblanc, T Fouchet, S Barabash, D Breuer, E Chassefiere, A Coates, V Dehant, F Forget, H Lammer, S Lewis, M Lopez-Valverde, M Mandea, M Menvielle, A Pais, M Paetzold, P Read, C Sotin, P Tarits, S Vennerstrom, G Branduardi-Raymont, G Cremonese, JGM Merayo, T Ott, H Reme, JG Trotignon, JE Walhund


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


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


Synchronization of modulated traveling baroclinic waves in a periodically forced, rotating fluid annulus.

Phys Rev E Stat Nonlin Soft Matter Phys 79 (2009) 015202-

FJR Eccles, PL Read, AA Castrejón-Pita, TWN Haine

Frequency entrainment and nonlinear synchronization are commonly observed between simple oscillatory systems, but their occurrence and behavior in continuum fluid systems are much less well understood. Motivated by possible applications to geophysical fluid systems, such as in atmospheric circulation and climate dynamics, we have carried out an experimental study of the interaction of fully developed baroclinic instability in a differentially heated, rotating fluid annulus with an externally imposed periodic modulation of the thermal boundary conditions. In quasiperiodic and chaotic amplitude-modulated traveling wave regimes, the results demonstrate a strong interaction between the natural periodic modulation of the wave amplitude and the externally imposed forcing. This leads to partial or complete phase synchronization. Synchronization effects were observed even with very weak amplitudes of forcing, and were found with both 1:1 and 1:2 frequency ratios between forcing and natural oscillations.


FLUID DYNAMICS Rotating convection on the edge

NATURE 457 (2009) 270-271

PL Read


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.


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


Mars environment and magnetic orbiter scientific and measurement objectives.

Astrobiology 9 (2009) 71-89

F Leblanc, B Langlais, T Fouchet, S Barabash, D Breuer, E Chassefière, A Coates, V Dehant, F Forget, H Lammer, S Lewis, M Lopez-Valverde, M Mandea, M Menvielle, A Pais, M Paetzold, P Read, C Sotin, P Tarits, S Vennerstrom

In this paper, we summarize our present understanding of Mars' atmosphere, magnetic field, and surface and address past evolution of these features. Key scientific questions concerning Mars' surface, atmosphere, and magnetic field, along with the planet's interaction with solar wind, are discussed. We also define what key parameters and measurements should be performed and the main characteristics of a martian mission that would help to provide answers to these questions. Such a mission--Mars Environment and Magnetic Orbiter (MEMO)--was proposed as an answer to the Cosmic Vision Call of Opportunity as an M-class mission (corresponding to a total European Space Agency cost of less than 300 Meuro). MEMO was designed to study the strong interconnection between the planetary interior, atmosphere, and solar conditions, which is essential to our understanding of planetary evolution, the appearance of life, and its sustainability. The MEMO main platform combined remote sensing and in situ measurements of the atmosphere and the magnetic field during regular incursions into the martian upper atmosphere. The micro-satellite was designed to perform simultaneous in situ solar wind measurements. MEMO was defined to conduct: * Four-dimensional mapping of the martian atmosphere from the surface up to 120 km by measuring wind, temperature, water, and composition, all of which would provide a complete view of the martian climate and photochemical system; Mapping of the low-altitude magnetic field with unprecedented geographical, altitude, local time, and seasonal resolutions; A characterization of the simultaneous responses of the atmosphere, magnetic field, and near-Mars space to solar variability by means of in situ atmospheric and solar wind measurements.

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