Publications
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
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.
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
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
Evidence for control of Atlantic subtropical humidity by large scale advection
GEOPHYSICAL RESEARCH LETTERS 25 (1998) 4537-4540
Investigation of Saturn's atmosphere by Cassini
PLANET SPACE SCI 46 (1998) 1315-1324
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.
On the scattering greenhouse effect of CO2 ice clouds
JOURNAL OF THE ATMOSPHERIC SCIENCES 55 (1998) 1897-1903
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
Lateral mixing as a source of subtropical water vapor
GEOPHYSICAL RESEARCH LETTERS 25 (1998) 151-154
Wave interactions and baroclinic chaos: A paradigm for long timescale variability in planetary atmospheres
CHAOS SOLITON FRACT 9 (1998) 231-249
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
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.
Warming early Mars with carbon dioxide clouds that scatter infrared radiation.
Science (New York, N.Y.) 278 (1997) 1273-1276
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.
Mode selection, wave breaking and parametric sensitivity in the quasi-biennial oscillation
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY 123 (1997) 2041-2068
Lower-tropospheric heat transport in the Pacific storm track
JOURNAL OF THE ATMOSPHERIC SCIENCES 54 (1997) 1533-1543
A laboratory study of baroclinic waves and turbulence in an internally heated rotating fluid annulus with sloping endwalls
JOURNAL OF FLUID MECHANICS 339 (1997) 173-198
Laboratory and numerical studies of baroclinic waves in an internally heated rotating fluid annulus: A case of wave/vortex duality?
JOURNAL OF FLUID MECHANICS 337 (1997) 155-191
Wave interactions and the transition to chaos of baroclinic waves in a thermally driven rotating annulus
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 355 (1997) 101-153
Data assimilation with a Martian atmospheric GCM: An example using thermal data
ADV SPACE RES 19 (1997) 1267-1270
Data assimilation is a technique for the analysis of atmospheric observations which combines current information with prior knowledge from previous observations, summarized and forecast in time via the use of a numerical model. A sequential data assimilation scheme has been implemented with a full general circulation model (GCM) of the martian atmosphere for the first time, and has been adapted for the types of atmospheric data which might be expected in the near future, e.g. remote-sensed temperature profiles from a polar orbiter mission such as Mars Surveyor '96 and '98. Tests demonstrate the performance of the scheme using artificial data generated from independent model experiments. (C) 1997 COSPAR. Published by Elsevier Science Ltd.
A GCM climate database for Mars: For mission planning and for scientific studies
ADV SPACE RES 19 (1997) 1213-1222
The construction of a new database of statistics on the climate and environment of the Martian atmosphere is currently under way, with the support of the European Space Agency. The primary objectives of this database are to provide information for mission design specialists on the mean state and variability of the Martian environment in unprecedented detail, through the execution of a set of carefully validated simulations of the Martian atmospheric circulation using comprehensive numerical general circulation models. The formulation of the models used are outlined herein, noting especially new improvements in various schemes to parametrize important physical processes, and the scope of the database to be constructed is described. A novel approach towards the representation of large-scale variability in the output of the database using empirical eigenfunctions derived from statistical analyses of the numerical simulations, is also discussed. It is hoped that the resulting database will be of value for both scientific and engineering studies of Mars' atmosphere and near-surface environment. (C) 1997 COSPAR. Published by Elsevier Science Ltd.
Gravity wave drag in a global circulation model of the Martian atmosphere: Parameterisation and validation
ADV SPACE RES 19 (1997) 1245-1254
The effect of orographically generated breaking gravity waves is parametrised in a global circulation model of the Martian atmosphere using schemes adapted from terrestrial models. The schemes are 'tuned' by comparing model integrations with and without gravity wave drag with temperatures derived from the Mariner 9 IRIS instrument. Without gravity wave drag the global circulation model temperature field has excessively cold upper level polar regions. Gravity wave drag can correct for such cold temperatures by warming the atmosphere adiabatically via a dynamically induced circulation. The model climatology is significantly improved in the polar regions with the introduction of the parametrisation. (C) 1997 COSPAR. Published by Elsevier Science Ltd.
Martian atmospheric data assimilation with a simplified general circulation model: Orbiter and lander networks
PLANET SPACE SCI 44 (1996) 1395-1409
A meteorological data assimilation scheme for the martian atmosphere has been implemented and tested, based on techniques used in the current operational scheme for weather forecasting at the U.K. Meteorological Office. The scheme has been interfaced with a range of simple models and with the martian GCM currently under simultaneous development at Laboratoire de Meteorologie Dynamique du CNRS in Paris and at Oxford. As well as the interpretation of data from any future spacecraft, the assimilation scheme may be used for comparisons between different models, for model validation using earlier martian data, and for data impact studies to assist in planning new missions. Despite proposed new missions to Mars, observations of the atmosphere of Mars in the near future are still likely to be very sparse compared to those of the Earth (perhaps comprising a single orbiter and a few surface stations at any one time) and the scheme has been adapted with this in mind. Twin model experiments are conducted in which simulated observations are generated from a second model started from different initial conditions. Such experiments reveal the importance of surface pressure measurements (in combination with an accurate topographic map, such as will be available from laser altimetry) in the determination of the amplitude of large-scale atmospheric waves. It is shown that atmospheric temperature profiles from a remote-sensing instrument on a polar orbiting satellite combined with simultaneous surface pressure observations at a limited number of sites, as planned for the InterMarsNet mission, is a useful scenario for data assimilation. Copyright (C) 1996 Elsevier Science Ltd
