Below the paper titles are links to GNUzipped PostScript files which may be quite large. This is not a complete list of my Mars publications; nor are all the papers necessarily in the final form in which they appeared. The papers have been ordered with more recent ones higher on the list.
Lewis, S.R., Collins, M., Read, P.L., Forget, F., Fournier, R., Hourdin, C., Hourdin, F., Talagrand, O. and Huot, J.-P. (1998) ``A climate database for the martian atmosphere,'' a 16 A4 page (or 1 A0 page) colour poster which illustrates the Mars Climate Database. [GNUzipped PostScript of colour poster, 589Kb]
A database of statistics has been developed in order to describe the climate and surface environment of Mars. The database may be used as a tool for mission planning, and also provides a valuable resource for scientific studies of the Martian atmosphere. This poster presents examples of database output including comparisons with previous observations. The database is based directly on output from multi-annual integrations of two General Circulation Models (GCMs) which were developed jointly at Laboratoire de Météorologie Dynamique du CNRS, Paris, and the University of Oxford, with support from the European Space Agency. The models have been validated against the main features of the meteorology of Mars, as observed by past spacecraft missions. As well as the usual statistical measures used for mission design studies, the database also includes techniques for representing variability. Large-scale variability, captured by the GCMs, is modelled using empirical eigenfunctions derived from an analysis of the full simulations. It is also possible to incorporate some variability on scales smaller than the GCMs can represent explicitly by the use of parameterizations of processes such as gravity wave propagation. The database is continuously updated as new observations become available and the models are improved. A version may be obtained from http://www.lmd.jussieu.fr/mars.html.
Lewis, S.R., Collins, M., Read, P.L., Forget, F., Fournier, R., Hourdin, C., Hourdin, F., Talagrand, O. and Huot, J.-P. (1998) ``A climate database for the martian atmosphere,'' COSPAR 1998 . [Now superseeded by poster above]
Lewis, S.R., Collins, M., Read, P.L., Forget, F., Fournier, R., Hourdin, C., Hourdin, F., Talagrand, O. and Huot, J.-P. (1998) ``A climate database for the martian atmosphere,'' Annales Geophysicae 16, C 1000. [Now superseeded by poster above]
Collins, M., Lewis, S.R. and Read, P.L. (1997) ``Gravity wave drag in a global circulation model of the martian atmosphere: Parametrisation and validation,'' Advances in Space Research 19, 1245--1254. [GNUzipped PostScript, 330Kb]
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.
Lewis, S.R., Collins, M., and Read, P.L. (1997) ``Data assimilation with a martian atmospheric GCM: An example using thermal data,'' Advances in Space Research 19, 1267--1270. [GNUzipped PostScript, 83Kb]
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.
Read, P.L., Collins, M., Forget, F., Fournier, R., Hourdin, F., Lewis, S.R., Talagrand, O., Taylor, F.W. and Thomas, N.P.J. (1997) ``A GCM climate database for Mars: For mission planning and for scientific studies,'' Advances in Space Research 19, 1213--1222. [GNUzipped PostScript, 290Kb]
Abstract not available.
Collins, M., Lewis, S.R., Read, P.L. and Hourdin, F. (1996) ``Baroclinic wave transitions in the martian atmosphere,'' Icarus 120, 344--357. [GNUzipped PostScript, 333Kb]
Surface pressure data from the Viking Lander mission and from GCM simulations of the Martian atmosphere have been analysed using singular systems analysis. Very regular oscillations are found with frequencies that are are distributed bimodally with peaks corresponding to periods of approximately 2-4 days and 5-7 days respectively. Reconstructions of the amplitudes of the two oscillations are often negatively correlated, i.e. when the amplitude of one oscillation is large that of the other is small. The GCM simulations show that the negative correlation in the amplitudes of the two oscillations can be explained as a flipping between two different wavenumber modes. In the absence of diurnal forcing in the model, transition from an unrealistically regular high frequency mode to a similarly unrealistic regular low frequency mode occurs at most once during the northern winter season. The diurnal cycle in the model, however, acts in a non-linear sense to stimulate the transitions between the two wavenumbers and thus increases the frequency of mode flipping events. The corresponding simulations bear a closer resemblance to the observations.
Collins, M., Lewis, S.R., Read, P.L., Thomas, N.P.J., Talagrand, O., Forget, F., Fournier, R., Hourdin, F. and Huot, J.-P. (1996) ``A climate database for the martian atmosphere,'' in Environment Modelling for Space-Based Applications, European Space Agency SP--392, 323--327. [GNUzipped PostScript, 224Kb]
Abstract not available.
Lewis, S.R., Read, P.L., and Collins, M. (1996) ``Martian atmospheric data assimilation with a simplified general circulation model: Orbiter and lander networks,'' Planetary and Space Science 44, 1395--1409. [GNUzipped PostScript, 262Kb]
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 UK 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 Météorologie 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. In this paper, 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.
Collins, M., Lewis, S.R. and Read, P.L. (1995) ``Regular and irregular baroclinic waves in a martian general circulation model: A role for diurnal forcing?'' Advances in Space Research 16, (6)3--(6)7. [GNUzipped PostScript, 127Kb]
The development and evolution of baroclinic transient waves are simulated in a high resolution, general circulation model (GCM) of the Martian atmosphere, including simulations both with and without a representation of the diurnal cycle of solar heating. Simulations with diurnally-averaged insolation are found to develop highly regular baroclinic transients during northern hemisphere autumn, winter and spring seasons, characterised by zonal wavenumber 1 or 2 and periods of 2-6 sols (a sol being a Martian day). With a diurnal cycle, however, transients are found to be significantly more irregular throughout the winter season, sporadically changing their dominant wavenumber and frequency, and resemble more closely data from the Viking Lander time series. These results are discussed with reference to some simple conceptual models in nonlinear dynamics, in terms either of a periodically-perturbed, self-exciting oscillator, or of attractor-merging near a crisis in a periodically perturbed bistable system.
Lewis, S.R. and Read, P.L. (1995) ``An operational data assimilation scheme for the martian atmosphere,'' Advances in Space Research 16, (6)9--(6)13. [GNUzipped PostScript, 48Kb]
A meteorological data assimilation scheme has been developed for Mars, based on techniques used for the current operational scheme at the UK Meteorological Office (UKMO). The scheme has been designed to interface with a range of models of varying complexity, from a simple primitive equations model to a full martian general circulation model with detailed parameterizations of the most important physical processes. The scheme was originally intended to be used primarily for analysis of temperature profiles from the Pressure Modulator Infrared Radiometer (PMIRR) onboard the Mars Observer (MO) spacecraft. It is, however, capable of analysing any asynoptic, randomly-distributed dataset, which may include surface pressure, temperature, velocity or constituent data originating either from other past or future spacecraft missions or from models. It is proposed to use the scheme not only for interpretation of forthcoming data from future spacecraft but also for model inter-comparisons, for hind-casting earlier martian data for model validation and for data impact studies in the planning of new missions. Initial results have demonstrated successful assimilations of trial orbiter and lander data into models with different initial conditions and physics, although a large number of landers might be required if orbiter data were not available. An optimum approach would combine orbiter data with simultaneous measurements from a small number of landers.