Publications


Subtropical water vapor as a mediator of rapid global climate change

in Mechanisms of Global Climate Change at Millennial Time Scales, American Geophysical Union (1999) 22
Part of a series from Geophysical Monograph Series

RT Pierrehumbert


POD analysis of baroclinic wave flows in the thermally-driven, rotating annulus experiment

Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere 24 (1999) 449-453

AV Stephen, IM Moroz, PL Read

The Proper Orthogonal Decomposition (POD) is a procedure to compute an orthogonal basis from a time series of spatial fields. This basis is optimal among all linear decompositions, in the sense that for a given number of modes, the projection of the original signal onto the subspace will contain the most variance on average. This algorithm is applied to streamfunction fields derived from measurements of the flow in the thermally forced rotating annulus experiment. Results of this analysis are presented, and a method to derive low-dimensional models of the flow by projecting the equations of motion onto these empirical eigenfunctions is discussed.


A climate database for Mars

JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 104 (1999) 24177-24194

SR Lewis, M Collins, PL Read, F Forget, F Hourdin, R Fournier, C Hourdin, O Talagrand, JP Huot


Mixing of an advected-diffused tracer in the lower stratosphere: probability distribution functions of tracer gradients and differences

12TH CONFERENCE ON ATMOSPHERIC AND OCEANIC FLUID DYNAMICS (1999) 303-306

YY Hu, RT Pierrehumbert, AMS, AMS


The effect of sloping boundaries on baroclinic instability in two related internally heated, rotating fluid systems

PHYSICS AND CHEMISTRY OF THE EARTH PART B-HYDROLOGY OCEANS AND ATMOSPHERE 24 (1999) 481-486

ME Bastin, PL Read


Spatially inhomogeneous random advection

12TH CONFERENCE ON ATMOSPHERIC AND OCEANIC FLUID DYNAMICS (1999) 307-311

K Ngan, RT Pierrehumbert, AMS, AMS


Huascaran delta O-18 as an indicator of tropical climate during the Last Glacial Maximum

GEOPHYSICAL RESEARCH LETTERS 26 (1999) 1345-1348

RT Pierrehumbert


Dynamics of a passive tracer in a velocity field of four identical point vortices

JOURNAL OF FLUID MECHANICS 394 (1999) 137-174

S Boatto, RT Pierrehumbert


Subtropical water vapor as a mediator of rapid global climate change

in Geophysical Monograph Series, 112 (1999) 339-361

RT Pierrehumbert

© 1999 by the American Geophysical Union. This article surveys the essential features of atmospheric water vapor dynamics needed to address current issues regarding the possible role of water vapor changes in mediating climate fluctuations on the millennial to Milankovic time scales. The focus is on the subtropics, which afford the most interesting possibilities for significant feedbacks. The observed distribution of water vapor, the amount by which water vapor must change in order to cause a significant temperature change, and the physical factors that determine the water vapor content of the subtropical atmosphere are discussed. It is shown that halving the subtropical relative humidity would lead to a 2.5K cooling of the tropics, while doubling it would lead to a 3K warming. The humidity content of the subtropics could be reduced by enhancing subsidence, reducing transient eddy activity, or contracting the convective region. Further work is needed to determine which, if any, of these changes occur in concert with the observed millennial and longer scale climate fluctions.


Generation of inertia-gravity waves by a time-dependent baroclinic wave in the laboratory

PHYSICS AND CHEMISTRY OF THE EARTH PART B-HYDROLOGY OCEANS AND ATMOSPHERE 24 (1999) 455-460

AF Lovegrove, PL Read, CJ Richards


Experiments on a barotropic rotating shear layer. Part 1. Instability and steady vortices

JOURNAL OF FLUID MECHANICS 383 (1999) 143-173

WG Fruh, PL Read


Flow-field and point velocity measurements in a barotropically unstable shear layer

PHYSICS AND CHEMISTRY OF THE EARTH PART B-HYDROLOGY OCEANS AND ATMOSPHERE 24 (1999) 461-466

WG Fruh, PL Read


Experiments on the structure of baroclinic waves and zonal jets in an internally heated, rotating, cylinder of fluid

PHYSICS OF FLUIDS 10 (1998) 374-389

ME Bastin, PL Read


On the scattering greenhouse effect of CO2 ice clouds

JOURNAL OF THE ATMOSPHERIC SCIENCES 55 (1998) 1897-1903

RT Pierrehumbert, C Erlick


Evidence for control of Atlantic subtropical humidity by large scale advection

GEOPHYSICAL RESEARCH LETTERS 25 (1998) 4537-4540

RT Pierrehumbert, R Roca


Lateral mixing as a source of subtropical water vapor

GEOPHYSICAL RESEARCH LETTERS 25 (1998) 151-154

RT Pierrehumbert


Wave interactions and baroclinic chaos: A paradigm for long timescale variability in planetary atmospheres

CHAOS SOLITON FRACT 9 (1998) 231-249

PL Read, M Collins, WG Fruh, SR Lewis, AF Lovegrove

Baroclinic instability is the principal mode of non-axisymmetric flow in the large-scale atmospheric circulation at mid-latitudes, and is responsible for oganising the structure and behaviour of major weather systems. This instability can also be fruitfully studied in the laboratory under controlled conditions. In this paper, we review recent work carried out by the authors and collaborators on various routes to chaotic behaviour in rotating, stratified flows. Results include the discovery of new multi-mode regimes in which small ensembles of baroclinic waves interact in a nonlinear mode competition with the thermally-driven axisymmetric component of the Bow, generating chaotic oscillatory variability on very long timescales. We discuss various attempts to capture this type of behaviour in simple models, and consider the significance of the phenomenon as a paradigm for understanding the nature of long timescale variability in the climates of the Earth and Mars. (C) 1998 Elsevier Science Ltd. All rights reserved.


A comparison of empirical orthogonal decomposition methods in baroclinic flows

Dynamics of Atmospheres and Oceans 27 (1998) 649-660

AV Stephen, IM Moroz, PL Read, WG Früh

The relative merits of three contrasting empirical orthogonal decomposition methods in common use (namely, Proper Orthogonal Decomposition, Biorthogonal Decomposition and Multivariate Singular Systems Analysis) are considered as applied to baroclinic flow data. The regimes analysed are a steady, drifting wave, a modulated amplitude vacillating wave flow and a neighbouring multi-mode state which exhibits intermittency. The results are used to make a qualitative comparison of the methods in terms of convergence properties, variance capture and eigenfunction structure. The feasibility of using the resulting empirical orthogonal functions to transform partial differential equations to ordinary differential equations by Galerkin projection is mentioned. © 1997 Elsevier Science B.V.


Investigation of Saturn's atmosphere by Cassini

PLANET SPACE SCI 46 (1998) 1315-1324

FW Taylor, SB Calcutt, PGJ Irwin, CA Nixon, PL Read, PJC Smith, TJ Vellacott

This paper considers the rationale for the exploration of Saturn's atmosphere by the Cassini mission, taking account of the key scientific questions posed by the earlier investigation by Voyager, and the capabilities of the instrumentation making up the Cassini payload. While by no means all objectives can be addressed by this particular configuration, in particular without a Saturn entry probe, if everything goes according to plan important progress should be possible on a number of key objectives. (C) 1998 Elsevier Science Ltd. All rights reserved.


Warming early Mars with carbon dioxide clouds that scatter infrared radiation.

Science (New York, N.Y.) 278 (1997) 1273-1276

F Forget, RT Pierrehumbert

Geomorphic evidence that Mars was warm enough to support flowing water about 3.8 billion years ago presents a continuing enigma that cannot be explained by conventional greenhouse warming mechanisms. Model calculations show that the surface of early Mars could have been warmed through a scattering variant of the greenhouse effect, resulting from the ability of the carbon dioxide ice clouds to reflect the outgoing thermal radiation back to the surface. This process could also explain how Earth avoided an early irreversible glaciation and could extend the size of the habitable zone on extrasolar planets around stars.

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