On the relative humidity of the atmosphere

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

RT Pierrehumbert

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


C Lee, SR Lewis, PL Read

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


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.


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

PL Read, I Roulstone

GCM representation of turbulence on Jupiter

SPRINGER PROC PHYS 117 (2007) 582-584

LC Zuchowski, YH Yamazaki, PL Read

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.

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


L Montabone, SR Lewis, PL Read, P Withers

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.

Modelling the primary control of paleogeography on Cretaceous climate


Y Donnadieu, R Pierrehumbert, R Jacob, F Fluteau

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

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


H Brogniez, RT Pierrehumbert

Climate Change: A Catastrophe in Slow Motion

Chicago Journal of International Law 6 (2006) 6

RT Pierrehumbert

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


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

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

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.

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


FJR Eccles, PL Read, TWN Haine

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


PL Read, PJ Gierasch, BJ Conrath