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.

Synchronization and chaos control in a periodically forced quasi-geostrophic two-layer model of baroclinic instability


FJR Eccles, PL Read, TWN Haine

Anisotropic turbulence and zonal jets in rotating flows with a beta-effect


B Galperin, S Sukoriansky, N Dikovskaya, PL Read, YH Yamazaki, R Wordsworth

A GEOCLIM simulation of climatic and biogeochemical consequences of Pangea breakup


Y Donnadieu, Y Godderis, R Pierrehumbert, G Dromart, F Fluteau, R Jacob

Validation of martian meteorological data assimilation for MGS/TES using radio occultation measurements

ICARUS 185 (2006) 113-132

L Montabone, SR Lewis, PL Read, DP Hinson

Reconstructing the weather on Mars at the time of the MERs and Beagle 2 landings


L Montabone, SR Lewis, PL Read, P Withers

Direct numerical simulations of bifurcations in an air-filled rotating baroclinic annulus


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

Instabilities of a barotropic shear layer in a rotating fluid: Asymmetries with respect to sgn(Ro)

Meteorologische Zeitschrift 15 (2006) 417-422

A Aguiar, P Read

The aim of the work reported in this article is to provide new insights into the dynamics and instabilities of a barotropic shear layer in a rotating fluid. Above a critical value of horizontal stress, the flow within a bounded system in rotation is driven to an unstable limit, beyond which it develops chains of vortices. The number of these vortices depends not only upon the value of the stress imposed but also on the sense of the shear in some cases, highlighting discrepancies between earlier experiments. Quasi-geostrophic theory, however, predicts that there should be no qualitative differences with respect to the sign of the stress. We present laboratory experiments in cylindrical geometry, where a detached shear layer occurs tangential to the differentially rotating sections at the top and bottom of the tank. For stepped end walls, we found that the spatial organization of the flow patterns is a function of the sign of Rossby number. Furthermore, we observe a weak dependence of the azimuthal wavenumber on the sign of Rossby number. © by Gebrüder Borntraeger 2006.

Modelling the primary control of paleogeography on Cretaceous climate


Y Donnadieu, R Pierrehumbert, R Jacob, F Fluteau

Using microwave observations to assess large-scale control of free tropospheric water vapor in the mid-latitudes


H Brogniez, RT Pierrehumbert

Mapping potential-vorticity dynamics on Jupiter. II: The Great Red Spot from Voyager 1 and 2 data

Quarterly Journal of the Royal Meteorological Society 132 (2006) 1605-1625

PL Read, PJ Gierasch, BJ Conrath

Maps of Ertel potential vorticity on isentropic surfaces (IPV) and quasi-geostrophic potential vorticity (QGPV) on isobaric surfaces in the vicinity of Jupiter's Great Red Spot (GRS) are derived by making use of a combination of velocity measurements, derived from the tracking of cloud features in Voyager 1 and 2 images, and thermal measurements from the Voyager 1 IRIS instrument. The thermal data were obtained during Voyager 1's closest approach to Jupiter. IPV and QGPV in the vicinity of the GRS show a clearly isolated anticyclonic patch in the troposphere, with a suggestion of some spiral structure. The relationship of IPV and QGPV q with the corresponding isentropic or isobaric stream function Ψ near the GRS is not compatible with marginal stability with respect to Arnol'd's second stability theorem, and does not indicate a relaxed, maximum entropy structure except perhaps close to the tropopause. q(Ψ) in the upper troposphere and lower stratosphere for both Ertel and QGPV is reasonably well defined within the GRS and on a different branch to the ambient zonal flow, though is less well defined close to the cloud tops where local thermodynamic forcing may be significant. The profile in the upper troposphere is consistent with an isolated 'free mode' structure for which the air inside the GRS has a different dynamical origin to the atmosphere outside. © Royal Meteorological Society, 2006.

Mapping potential vorticity dynamics on Jupiter: 1. zonal mean circulation from Cassini and Voyager 1 data

Quarterly Journal of the Royal Meteorological Society 132 (2006) 1577-1603

PL Read, P J Gierasch, B J Conrath, A Simon-Miller

Mapping potential-vorticity dynamics on Jupiter. II: the Great Red Spot from Voyager 1 and 2 data


PL Read, PJ Gierasch, BJ Conrath

Two scenarios on the driving mechanism of the Jovian equatorial jet with secondary hydrodynamic instabilities

ADV SPACE RES 38 (2006) 2639-2644

YH Yamazaki, PL Read

We test the feasibility of two scenarios that may drive the broad, prograde, equatorial jets in the Jovian atmosphere within the shallow "weather layer". The first idea attempts to explain the flat-headed jet as a consequence of a hydrodynamic instability along an equatorially trapped primarily jet. The strong primary jet is induced by a 300 in s(-1) Kelvin wave. The second idea is a bridging of a pair of off-equatorial jets due to horizontal eddy diffusion (the so-called Gierasch mechanism). The primary jets can be induced by a Hadley circulation, and might then be interconnected by subsequent hydrodynamic instabilities between them. We test the two scenarios using a general circulation model, but have so far been unable to obtain an equatorial jet that resembles observations. It appears, therefore, that the previously proposed model of combining Kelvin and Hadley forcing, is more plausible under the shallow hypothesis. (c) 2006 COSPAR. Published by Elsevier Ltd. All rights reserved.

Climate Change: A Catastrophe in Slow Motion

Chicago Journal of International Law 6 (2006) 6

RT Pierrehumbert

Atmospheric temperature sounding on Mars, and the climate sounder on the 2005 reconnaissance orbiter

ADV SPACE RES 38 (2006) 713-717

FW Taylor, SB Calcutt, PL Read, SR Lewis, DJ McCleese, JT Schofield, RW Zurek

Detailed measurements of the vertical profiles of atmospheric temperature, water vapour, dust and condensates in the Martian atmosphere are needed to characterize the present-day Martian climate and to understand the intricately related processes upon which it depends. Among the most important of these are accurate and extensive temperature measurements. Progress to date, key problems still to be addressed and upcoming new approaches to the measurement task are briefly reviewed, and expectations for the Mars Climate Sounder experiment on the 2005 Mars Reconnaissance Orbiter are described. Some even more advanced methods for temperature, humidity and condensate sounding in the decade beyond MCS/MRO, and promising approaches to achieving these are also considered. (c) 2006 Published by Elsevier Ltd on behalf of COSPAR.

A simplified model of the Martian atmosphere - Part 2: A POD-Galerkin analysis

Nonlinear Processes in Geophysics 12 (2005) 625-642

SG Whitehouse, SR Lewis, IM Moroz, PL Read

In Part I of this study Whitehouse et al. (2005) performed a diagnostic analysis of a simplied model of the Martian atmosphere, in which topography was absent and in which heating was modelled as Newtonian relaxation towards a zonally symmetric equilibrium temperature field. There we derived a reduced-order approximation to the vertical and the horizonal structure of the baroclinically unstable Martian atmosphere, retaining only the barotropic mode and the leading order baroclinic modes. Our objectives in Part II of the study are to incorporate these approximations into a Proper Orthogonal Decomposition-Galerkin expansion of the spherical quasi-geostrophic model in order to derive hierarchies of nonlinear ordinary differential equations for the time-varying coefficients of the spatial structures. Two different vertical truncations are considered, as well as three different norms and 3 different Galerkin truncations. We investigate each in turn, using tools from bifurcation theory, to determine which of the systems most closely resembles the data for which the original diagnostics were performed. © 2005 Author(s). This work is licensed under a Creative Commons License.

A simplified model of the Martian atmosphere - Part 1: A diagnostic analysis

Nonlinear Processes in Geophysics 12 (2005) 603-623

SG Whitehouse, SR Lewis, IM Moroz, PL Read

In this paper we derive a reduced-order approximation to the vertical and horizontal structure of a simplified model of the baroclinically unstable Martian atmosphere. The original model uses the full hydrostatic primitive equations on a sphere, but has only highly simplified schemes to represent the detailed physics of the Martian atmosphere, e.g. forcing towards a plausible zonal mean temperature state using Newtonian cooling. Three different norms are used to monitor energy conversion processes in the model and are then compared. When four vertical modes (the barotropic and first three baroclinic modes) are retained in the reduced-order approximation, the correlation norm captures approximately 90% of the variance, while the kinetic energy and total energy norms capture approximately 83% and 78% of the kinetic and total energy respectively. We show that the leading order Proper Orthogonal Decomposition (POD) modes represent the dominant travelling waves in the baroclinically-unstable, winter hemisphere. In part 2 of our study we will develop a hierarchy of truncated POD-Galerkin expansions of the model equations using up to four vertical modes. © 2005 Author(s). This work is licensed under a Creative Commons License.

The effects of the martian regolith on GCM water cycle simulations

ICARUS 177 (2005) 174-189

HM Bottger, SR Lewis, PL Read, F Forget

Titan's Atmospheric Temperatures, Winds, and Composition.

Science 308 (2005) 975-978

FW Taylor, Flasar F.M., Achterberg, R.K., Conrath, B.J.