The Martian Climate Revisited

Transcription

1 Peter L. Read and Stephen R. Lewis The Martian Climate Revisited Atmosphere and Environment of a Desert Planet Springer Published in association with Praxis Publishing Chichester, UK

2 Contents Preface Abbreviations xi xv List of figures xvii List of tables '..." xxi List of plates xxiii 1 An introduction to Mars Comparative atmospheric science Planetary features Atmospheric properties Past and present climates Observations of the Martian climate and meteorology Beginnings of the space age Martian exploration renewed: the present campaign Plan of the book 13 2 Mars climate models Modelling the Martian atmosphere Mars GCM background Mesoscale modelling Upper atmosphere modelling GCMs ' 20

3 vi Contents Fluid dynamics Physical processes and environmental factors Data assimilation for Mars 39 3 Mars' global-scale atmospheric structure Some basics: the role of buoyancy forces Stable and unstable stratification Horizontal and vertical density contrasts Stratification in a compressible atmosphere Mars' zonal mean atmospheric structure Annual mean thermal structure and net heating Vertical structure and the atmospheric energy budget Annual and zonal mean atmospheric circulation The Held-Hou model CO2 sublimation and the seasonal cycle CO2 sublimation and the atmospheric circulation Seasonal variations in Mars' zonal mean circulation TES observations GCM simulations of the seasonal zonal mean circulation An osymmetric Held-Hou model Summary 71 4 Topographical influences on the atmospheric circulation The topography of Mars from MGS/MOLA Mapping Mars from space Large-scale areography of Mars Stationary planetary waves Simple models of wave excitation and propagation More realistic models Evidence for stationary planetary wave activity Low-level jets and western boundary currents (WBCs) WBCs on Earth A simple model of an equator-crossing WBC WBCs - more realistic models Observations of WBCs Small-scale gravity waves A simple model for internal gravity waves generated by mountains More realistic models of mountain lee waves Observations of mountain waves on Mars Large-scale gravity-wave drag Diurnal phenomena The diurnal cycle on Mars 113

4 Contents vii Mars Pathfinder (MPF) Planetary thermal tides Migrating tides Interaction with topography Planetary free modes Tides in a Mars GCM Morning clouds, fogs, and frosts Nocturnal jets Slope and thermal contrast winds Transient weather systems Variable weather on Earth Origins as instabilities Observations of Martian 'weather' systems Cloud features and weather systems Viking Lander (VL) time series Travelling thermal waves Basic theory of baroclinic and barotropic weather systems 'Classical'models of baroclinic and barotropic instability More realistic linearized models Mixed baroclinic-barotropic instability Transient weather systems in GCM simulations Seasonal variations in baroclinic transients Wave structures and frequencies Topography and 'storm zones' Transient eddy heat and momentum transports Predictability and chaos A GCM 'thought experiment': turning night into day Intransitivity and hysteresis A laboratory analogue - storms in a teacup? Weather regimes in simplified Mars GCMs Tidal perturbations and chaos: shaking the table? Overview : Dust storms, devils, and transport A desert planet., The nature of Mars' sand and suspended dust Martian soil and sand Suspended dust in the atrrtosphere How does dust enter and leave the atmosphere? Near-surface wind stress : Convection and 'dust devils' Dust deposition and removal processes Dust Storms Local and regional storms 199

5 viii Contents Planet-encircling storms Processes influencing dust storm initiation, evolution, and decay Meteorological organization of dust lifting Radiative-dynamical feedbacks Dust storms in GCMs Dust transport, climate, and interannual variability Transport, erosion, and deposition Interannual variability of dust storms and climate Water, climate, and the Martian environment Water and Mars Water and the formation of the ancient Martian landscape Valley networks Outflow channels and flood plains Oceanus Borealis? Glacial activity and permafrost Warm and wet or cold and dry? Evidence for water in Mars' present climate Residual ice caps Atmospheric water vapour Water ice clouds Fog and frost The regolith Modelling the atmospheric water cycle Diffusive models Water cycles in simple GCMs Comprehensive GCMs Outstanding questions Cyclic climate change Cyclic climate change and the polar layered terrains (PLTs) Quasiperiodic and chaotic astronomical cycles Spin orbit cycles on Mars Spin-orbit cycles and the Earth's climate Obliquity cycles and insolation Correlating PLTs with the obliquity cycle Modelling the response to the obliquity cycle Qualitative overview Quantitative models: energy balance models Quantitative models: GCMs Scenarios for Mars' response to obliquity variations Low obliquity conditions High obliquity conditions Obliquity cycles and the 'gullies'? Mars' variable climate 273

6 Contents ix 10 Future climates: the human factor? Human exploration of Mars in the short term Long-term exploration and colonization? Basic requirements for terraforming Mars Feedbacks and the 'runaway greenhouse'? Energy requirements and timescales Practical methods of achieving global warming Polar reflectors Polar albedo Artificially-enhanced greenhouse warming How long would it last? We can - but should we? 287 Appendix A A climate database for Mars 291 Afterword 301 References 303 Index 321