Idea Transcript
Studies of the Martian Upper Atmosphere with the UCL Mars Thermosphere and Ionosphere General Circulation Model William Peter Nicholson
Submitted for the degree of Doctor of Philosophy
Atmospheric Physics Laboratory Department of Physics and Astronomy University College London October 2010
I, William Peter Nicholson, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis.
Abstract Simulations of the Martian upper atmosphere have been conducted with ‘MarTIM’, University College London’s Martian thermosphere and ionosphere general circulation model (GCM). MarTIM, a finite difference model, solves the coupled non-linear Navier-Stokes equations of continuity and momentum as well as an energy equation with calculations conducted on a fixed co-rotating grid of variable size in the pressure coordinate system. From its lower boundary of 0.883 Pa (∼60 km) to its upper boundary of 9.9×10−8 Pa (∼200−350 km), it evaluates the main sources of solar forcing (EUV/UV and IR absorption) while self-consistently determining the composition of four of the major gas species, CO2 , N2 , CO and O. These four major gases are mutually diffused throughout the model in a typical run. Development of MarTIM includes a consideration of the importance of neutral species diffusion and advection on the thermodynamics of the modelled Martian atmosphere. The influence on the modelled atmosphere of including additional neutral species is investigated. Next, a new infrared heating parameterization has been introduced from background research of detailed non-LTE modelling. This has allowed MarTIM to study thermospheric polar warming features as found in Mars Odyssey accelerometer data. MarTIM’s lower boundary is coupled to the Mars Climate Database (MCD v4.3) developed by the University of Oxford, the Open University and Laboratoire de M´et´eorologie Dynamique. This database of GCM results provides MarTIM a physically self-consistent lower boundary derived from multiple runs of the aforementioned circulation models. Consequently the effects of dust storms, non-migrating tides and the influence of Martian topography are studied by prescription of MarTIM’s lower boundary. MarTIM is also compared against density and temperature measurements derived from SPICAM stellar occultation profiles. Lastly, a new ionospheric code has been developed through collaboration with Laboratoire de Plan´etologie de Grenoble. This has provided a more sophisticated ionosphere model that solves a one-dimensional kinetic Boltzmann transport equation for the suprathermal population of electrons present in the Martian ionosphere. MarTIM can now self-consistently describe an ionosphere produced by both primary (photoionisation) and secondary ionisation (suprathermal electron propagation). This new ionospheric model has been used to study the variation in secondary ionization efficiency (ratio of secondary to primary ion production) through a large range of seasonal and solar conditions.
Acknowledgements My PhD simply would not have been completed had it not been for the kind and generous help of so many people. Too many to mention, but here are the most important! • Atmospheric Physics Laboratory staff - in particular my primary supervisor Professor Alan D. Aylward and secondary supervisor Dr Anasuya Aruliah. • Dr Chris Smith, formerly of the Atmospheric Physics Laboratory - for patiently and very helpfully answering my many, many questions as well as offering invaluable advice and support. • Dr John Deacon, Astrophysics Computer Manager, UCL Physics and Astronomy, Astrophysics Group - many thanks for keeping my eMac in working order! • Dr Jean Lilensten and Dr Guillaume Gronoff, Laboratoire de Plan´etologie de Grenoble and Dr Cyril Simon, Belgian Institute for Space Aeronomy - it was a pleasure working with you all! I am particularly proud to have published my first paper with you. Hopefully we can work together again one day soon! • Dr Paul Withers, Center for Space Physics, Boston University - for kindly providing me the dataset of Mars Odyssey aerobraking measurements. • Dr Fran¸cois Forget, Laboratoire de M´et´eorologie Dynamique, Paris - for kindly providing me the dataset of Mars Express UV spectrometer density measurements. And finally, many thanks to the two examiners, Professor Andrew J. Coates, Mullard Space Science Laboratory and Professor Peter L. Read, Oxford University, for taking the time to consider the work described in this thesis.
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Contents 1 Introduction and Background Theory
16
1.1
Introduction to the Martian Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.2
Basic Atmospheric Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.3
1.4
1.5
1.6
1.2.1
The Equation of State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.2.2
Hydrostatic Equilibrium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.2.3
The Variation of Pressure and Density with Altitude . . . . . . . . . . . . . . . . . 21
1.2.4
The Adiabatic Lapse Rate and Atmospheric Stability . . . . . . . . . . . . . . . . 23
1.2.5
The Gravitational Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
The Navier-Stokes Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 1.3.1
The Momentum Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.3.2
Conservation of Energy and the Energy Equation . . . . . . . . . . . . . . . . . . . 29
1.3.3
The Continuity Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
1.3.4
Reference Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Structure of the Martian Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 1.4.1
The Martian Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
1.4.2
The Troposphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
1.4.3
The Mesosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
1.4.4
The Thermosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
1.4.5
The Exosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.4.6
The Ionosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.4.7
Turbulence and Diffusive Separation . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Modelling Carbon Dioxide Radiative Transfer . . . . . . . . . . . . . . . . . . . . . . . . . 41 1.5.1
Atmospheric Radiative Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
1.5.2
Local Thermodynamic Equilibrium . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
1.5.3
Non-local Thermodynamic Equilibrium . . . . . . . . . . . . . . . . . . . . . . . . 44
Structure and Aims of this Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
6
2 MarTIM: Mars Thermosphere and Ionosphere Model 2.1
2.2
2.3
46
The Model: An Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 2.1.1
Model History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.1.2
Present Day Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Basic Model Structure and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 2.2.1
Fundamental Assumptions and Approximations . . . . . . . . . . . . . . . . . . . . 48
2.2.2
Pressure Coordinate System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
2.2.3
Coordinate Reference Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
The Primitive Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 2.3.1
Momentum Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.3.2
Energy Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.3.3
Continuity Equation and the Vertical Wind . . . . . . . . . . . . . . . . . . . . . . 57
2.4
Neutral Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
2.5
EUV and UV Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.6
Modelling Carbon Dioxide Radiative Transfer . . . . . . . . . . . . . . . . . . . . . . . . . 62 2.6.1
The Carbon Dioxide Molecule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
2.6.2
The Two-Level Modelling Approach . . . . . . . . . . . . . . . . . . . . . . . . . . 64
2.6.3
Modelling Difficulties and Complexity . . . . . . . . . . . . . . . . . . . . . . . . . 65
2.6.4
The IR Heating Parameterisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
2.6.5
The IR Cooling Parameterisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
2.7
Stationary State Ionosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
2.8
Numerical Modelling Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
2.9
2.8.1
Initial Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
2.8.2
Finite Difference Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
2.8.3
Model Boundary Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
2.8.4
Smoothing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Closing Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3 Improvements to the Standard MarTIM
79
3.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.2
Initial MarTIM Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3.3
3.2.1
New Solar Flux Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3.2.2
New Neutral Photoabsorption Cross-Sections . . . . . . . . . . . . . . . . . . . . . 82
3.2.3
MarTIM Total Solar Heating Rate: A Brief Comparison . . . . . . . . . . . . . . . 84
3.2.4
Atomic Oxygen Content and the V-TCO2 −O Coefficient . . . . . . . . . . . . . . . 86
The Standard MarTIM Model Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 3.3.1
The Initial Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3.3.2
The MarTIM Base Run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 7
3.4
3.5
The Impact of Neutral Diffusion and Advection on the Martian Thermosphere . . . . . . 99 3.4.1
Influence of the New Diffusion and Advection Subroutine . . . . . . . . . . . . . . 99
3.4.2
The Impact of Multiple Species Diffusion and Advection . . . . . . . . . . . . . . . 118
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
4 The new Near-IR Heating Parameterisation
122
4.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
4.2
The New Infrared Heating Parameteristion . . . . . . . . . . . . . . . . . . . . . . . . . . 122
4.3
4.2.1
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
4.2.2
Effect of new IR heating parameterisation . . . . . . . . . . . . . . . . . . . . . . . 124
Thermospheric Winter Polar Warming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 4.3.1
Background Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
4.3.2
MarTIM Simulations of Polar Warming Features . . . . . . . . . . . . . . . . . . . 138
4.4
Global Modelling Parameters: A Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 148
4.5
Solar Cycle Variation of Mars Dayside Exospheric Temperatures . . . . . . . . . . . . . . 152
4.6
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
5 Coupling MarTIM to the Mars Climate Database
158
5.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
5.2
Regarding a Physically Consistent Lower Boundary . . . . . . . . . . . . . . . . . . . . . . 158
5.3
The Mars Climate Database Version 4.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
5.4
5.5
5.6
5.7
5.3.1
What is the MCD? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
5.3.2
Coupling MarTIM to the Mars Climate Database: The New Lower Boundary . . . 164
Studies with the Coupled MarTIM-MCD General Circulation Model . . . . . . . . . . . . 167 5.4.1
General Lower Boundary Influence: Lower Atmosphere . . . . . . . . . . . . . . . 167
5.4.2
General Lower Boundary Influence: Mesosphere
5.4.3
General Lower Boundary Influence: Thermosphere . . . . . . . . . . . . . . . . . . 188
5.4.4
Coupled MarTIM-MCD results versus MCD alone: A Discussion . . . . . . . . . . 194
. . . . . . . . . . . . . . . . . . . 174
Thermospheric Winter Polar Warming with the Coupled MarTIM-MCD Model . . . . . . 204 5.5.1
Northern Winter Polar Regions During Perihelion Conditions . . . . . . . . . . . . 204
5.5.2
Southern Winter Polar Regions During Aphelion Conditions . . . . . . . . . . . . . 212
Nightside Results: Comparison to Mars Express SPICAM Temperatures . . . . . . . . . . 214 5.6.1
Vertical Temperature Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
5.6.2
Subfreezing Mesopause Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . 222
5.6.3
Seasonal Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
5.6.4
SPICAM Measurements versus Coupled Model Results: A Discussion . . . . . . . 231
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
8
6 MarTIM and TransMars: The New Ionosphere
235
6.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
6.2
The Martian Ionosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
6.3
Production Computation
6.4
6.5
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
6.3.1
The Kinetic Electron Transport Model . . . . . . . . . . . . . . . . . . . . . . . . . 238
6.3.2
The Background Neutral Atmosphere Model . . . . . . . . . . . . . . . . . . . . . 244
6.3.3
Coupling the Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
6.3.4
The Problem to Solve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 6.4.1
Polynomial Fit to the Production Efficiency . . . . . . . . . . . . . . . . . . . . . . 248
6.4.2
Production Efficiency General Trends . . . . . . . . . . . . . . . . . . . . . . . . . 249
6.4.3
The Effect of Variation in Solar Zenith Angle on Efficiency . . . . . . . . . . . . . 255
6.4.4
The Effect of Variation of Solar Longitude on Efficiency . . . . . . . . . . . . . . . 257
6.4.5
The Effect of Variation of the Solar Cycle on Efficiency . . . . . . . . . . . . . . . 259
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
7 Conclusions and Future Work
261
7.1
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
7.2
Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 7.2.1
Introduce photochemistry, neutral-neutral and neutral-ion chemistry . . . . . . . . 267
7.2.2
Expand MarTIM to higher pressures (lower altitudes) . . . . . . . . . . . . . . . . 268
7.2.3
Expand MarTIM to lower pressures (higher altitudes) . . . . . . . . . . . . . . . . 271
7.2.4
Develop the General MarTIM Solution . . . . . . . . . . . . . . . . . . . . . . . . . 272
A References of Photo-absorption Cross Sections
274
A.1 Carbon Dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 A.2 Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 A.3 Carbon Monoxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 A.4 Atomic Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 A.5 Molecular Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 A.6 Nitric Oxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 A.7 Argon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 B Polynomial Coefficients for use in Equations 6.11 and 6.12 of Chapter 6
9
276
List of Figures 1.1
Diagram representing the balance of forces in a column of atmosphere. . . . . . . . . . . . 20
1.2
Schematic representing a vector modified from inertial to rotating frame. . . . . . . . . . . 27
1.3
Temperature structure of the Martian atmosphere. . . . . . . . . . . . . . . . . . . . . . . 32
1.4
Global topographic map of Mars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.5
Atmospheric temperature profile from entry phase of Mars Pathfinder and Viking 1. . . . 34
1.6
Illustration of non-migrating wave generation. . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.1
MarTIM’s Eulerian coordinate reference frame. . . . . . . . . . . . . . . . . . . . . . . . . 52
2.2
Vertical profile of solar EUV/UV absorption. . . . . . . . . . . . . . . . . . . . . . . . . . 62
2.3
Fundamental vibrations of the CO2 molecule. . . . . . . . . . . . . . . . . . . . . . . . . . 63
2.4
CO2 IR heating photoabsorption coefficients. . . . . . . . . . . . . . . . . . . . . . . . . . 67
2.5
Schematic of CO2 levels and transitions in a simplified model. . . . . . . . . . . . . . . . . 70
2.6
MarTIM CO2 cooling parameterisation: escape functions. . . . . . . . . . . . . . . . . . . 71
3.1
MarTIM’s new SOLAR2000 solar irradiance input. . . . . . . . . . . . . . . . . . . . . . . 81
3.2
MarTIM’s new CO2 photoabsorption cross section versus wavelength at various temperatures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
3.3
Heating rate profiles for MarTIM’s various neutral species and for different solar conditions. 85
3.4
Experimental estimates of CO2 -O relaxation rate. . . . . . . . . . . . . . . . . . . . . . . . 89
3.5
Base run MarTIM initial 1D neutral density and temperature profiles . . . . . . . . . . . 91
3.6
Base run MarTIM steady state result: major (globally averaged) energy inputs. . . . . . . 93
3.7
Base run MarTIM steady state result: equatorial EUV/UV/IR energy balance and O to CO2 ratio. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
3.8
Base run MarTIM steady state result: temperature, vertical wind and adiabatic heating output fields at PL 14 and 30 (1.33×10−3 and 4.45×10−7 Pa). . . . . . . . . . . . . . . . 97
3.9
Comparison of basic MarTIM temperatures at PL 25 (5.43×10−6 Pa) and 10 (9.81×10−3 Pa) versus those with additional tracer species added. . . . . . . . . . . . . . . . . . . . . 102
3.10 Tracer species (4 amu) number density fields for days 1 to 5 and day 10. . . . . . . . . . . 104 3.11 Tracer species (4 amu) number density fields for days 15, 20, 25, 50, 100 and 200. . . . . . 105
10
3.12 Tracer species (4 amu), day 200 temperatures, geopotential heights and meridional geopotential & Coriolis terms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 3.13 Comparison of basic MarTIM O mixing ratio versus with additional tracer species added. 107 3.14 Comparison of basic MarTIM CO2 mixing ratio versus with additional tracer species added.108 3.15 Tracer species (4 amu) number density fields (at day 200) versus longitude. . . . . . . . . 109 3.16 Tracer species (40 amu) number density fields for days 10, 25, 50 and 200. . . . . . . . . . 110 3.17 Tracer species (60 amu) number density fields for days 10, 25, 50 and 200. . . . . . . . . . 111 3.18 Tracer species (40 & 60 amu) number density fields (at day 200) versus longitude. . . . . 112 3.19 Tracer species (60, 40 & 4 amu) number density fields for day 200. . . . . . . . . . . . . . 114 3.20 Tracer species (60, 40 & 4 amu), day 200 geopotential heights and temperatures. . . . . . 115 3.21 Background atmosphere neutral species number densities at PL 10 (9.81×10−3 Pa). . . . . 116 3.22 Tracer species number density profiles with pressure level at day 200 . . . . . . . . . . . . 117 3.23 MarTIM steady state result with various neutral species included: upper atmosphere temperatures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 3.24 MarTIM steady state result with various neutral species included: global average temperatures and energy balance terms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 4.1
The new infrared heating parameterisation. . . . . . . . . . . . . . . . . . . . . . . . . . . 123
4.2
Effect of the new IR heating parameterisation: Equatorial slice of IR radiative balance, temperature and log10 O to CO2 ratio. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
4.3
Effect of the new IR heating parameterisation: Pressure level 30 (4.45×10−7 Pa) zonal and meridional winds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
4.4
Effect of the new IR heating parameterisation: Zonal average zonal and meridional winds. 129
4.5
Tidal influence of the new IR heating parameterisation: Temperature amplitudes at PL 10 (9.81×10−3 Pa). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
4.6
Tidal influence of the new IR heating parameterisation: Temperature amplitudes at PL 20 (6.61×10−5 Pa). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
4.7
Tidal influence of the new IR heating parameterisation: Temperature amplitudes at PL 30 (4.45×10−7 Pa). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
4.8
Tidal influence of the new IR heating parameterisation: Equatorial slice of temperature amplitudes expressed as a percentage of the zonal means. . . . . . . . . . . . . . . . . . . 134
4.9
MarTIM perihelion simulations of northern polar warming features at 120 km over a range of local times. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
4.10 MarTIM perihelion temperatures at constant altitude of 120 km. . . . . . . . . . . . . . . 140 4.11 Northern hemisphere perihelion temperature differences to 30◦ N with the old and new IR heating parameterisations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 4.12 Latitudinal slice of MarTIM zonal average total angular momentum. . . . . . . . . . . . . 144
11
4.13 MarTIM simulations of polar warming features at 100 km (night time average) at aphelion season. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 4.14 MarTIM aphelion temperatures at constant altitude of 100 km. . . . . . . . . . . . . . . . 146 4.15 Comparison of different global modelling parameters: Simulation of polar warming features at 120 km. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 4.16 Comparison of different global modelling parameters: MarTIM perihelion temperatures at constant altitude of 120 km. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 4.17 MarTIM temperatures at PL 30 (4.45×10−7 Pa) for different global modelling parameter setups. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 4.18 MarTIM exospheric temperatures versus Mars Global Surveyor Precise Orbit Determination results (a). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 4.19 MarTIM exospheric temperatures versus Mars Global Surveyor Precise Orbit Determination results (b). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 5.1
Coupled MarTIM-MCD temperatures at constant pressure level 2 (5.36×10−1 Pa), SMIN, low dust.
5.2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
Coupled MarTIM-MCD temperatures at constant pressure level 2 (5.36×10−1 Pa), SMIN, average dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
5.3
Coupled MarTIM-MCD temperatures at constant pressure level 2 (5.36×10−1 Pa), SMIN, global dust storm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
5.4
Coupled MarTIM-MCD temperatures at constant pressure level 2 (5.36×10−1 Pa), SMAX, high dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
5.5
Coupled MarTIM-MCD zonal winds at constant pressure level 2 (5.36×10−1 Pa) for low and average dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
5.6
Coupled MarTIM-MCD temperatures at constant pressure level 5 (1.20×10−1 Pa), SMIN, average dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
5.7
Coupled MarTIM-MCD temperatures at constant pressure level 10 (9.81×10−3 Pa), SMIN, average dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
5.8
Coupled MarTIM-MCD and MCD DVD zonal winds at constant pressure level 10 (9.81×10−3 Pa) for average dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
5.9
Values used to calculate geopotential height gradients of the coupled MarTIM-MCD simulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
5.10 Latitudinal slice of coupled MarTIM-MCD and MCD alone zonal average zonal winds. . . 181 5.11 Latitudinal slice of coupled MarTIM-MCD zonal average IR balance. . . . . . . . . . . . . 182 5.12 Tidal influence of the coupled MarTIM-MCD model versus the MCD alone: PL 2 (5.36×10−1 Pa). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 5.13 Tidal influence of the coupled MarTIM-MCD model versus the MCD alone: PL 5 (1.20×10−1 Pa). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 12
5.14 Tidal influence of the coupled MarTIM-MCD model versus the MCD alone: PL 10 (9.81×10−3 Pa). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 5.15 Latitude versus pressure level structure of (1, 1) tidal influence for the coupled MarTIMMCD model versus the MCD alone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 5.16 Coupled MarTIM-MCD temperatures at constant pressure level 15 (8.05×10−4 Pa), SMIN, average dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 5.17 Coupled MarTIM-MCD temperatures at constant pressure level 20 (6.61×10−5 Pa), SMIN, average dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 5.18 Coupled MarTIM-MCD temperatures at constant pressure level 30 (4.45×10−7 Pa), SMIN, average dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 5.19 Latitude by pressure level structure of IR radiative balance, CO2 cooling rate and temperatures with different mixing ratios in 15-µm cooling routine. . . . . . . . . . . . . . . . 192 5.20 Equatorial slice of log10 O to CO2 ratio for coupled MarTIM-MCD and MCD DVD. . . . 193 5.21 Coupled MarTIM-MCD temperatures at constant pressure level 5 (1.20×10−1 Pa), SMIN, average dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 5.22 Coupled MarTIM-MCD temperatures at constant pressure level 10 (9.81×10−3 Pa), SMIN, average dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199 5.23 Coupled MarTIM-MCD temperatures at constant pressure level 30 (4.45×10−7 Pa), SMIN, average dust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 5.24 Latitudinal slice of coupled MarTIM-MCD (5◦ ×8◦ grid) and MCD alone (5◦ ×5◦ grid) zonal average zonal winds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 5.25 Latitudinal slice of coupled MarTIM-MCD (5◦ ×5◦ grid) zonal average zonal winds. . . . . 203 5.26 Coupled MarTIM-MCD simulations of polar warming features at 120 km for a range of dust conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 5.27 Latitudinal slice of coupled MarTIM-MCD and MarTIM alone zonal mean zonal winds during perihelion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 5.28 Latitudinal slice of MCD zonal mean zonal winds during perihelion. . . . . . . . . . . . . 208 5.29 Latitudinal versus pressure level structure of (1, −1) tidal influence of the coupled MarTIMMCD model versus the MCD alone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 5.30 Coupled MarTIM-MCD simulations of polar warming features at 120 km versus the MCD alone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 5.31 Coupled MarTIM-MCD simulations of polar warming features at 100 km versus the MCD alone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212 5.32 Latitudinal distribution of the 616 SPICAM solar occultations. . . . . . . . . . . . . . . . 214 5.33 Average SPICAM temperature profiles versus coupled MarTIM-MCD results (Ls 75◦ to 120◦ ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
13
5.34 Average SPICAM temperature profiles versus coupled MarTIM-MCD results (Ls 105◦ to 195◦ ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 5.35 Average SPICAM temperature profiles versus coupled MarTIM-MCD results (Ls 240◦ to 285◦ ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 5.36 Average SPICAM temperature profiles versus coupled MarTIM-MCD results (Ls 255◦ to 285◦ ). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 5.37 Average SPICAM density profiles versus coupled MarTIM-MCD results (Ls 90◦ to 120◦ ). 221 5.38 Coupled MarTIM-MCD energy balance terms for nightside Ls 90◦ to 120◦ . . . . . . . . . 221 5.39 Coupled MarTIM-MCD results versus the six “coldest” SPICAM temperatures profiles (A).223 5.40 Coupled MarTIM-MCD results versus the six “coldest” SPICAM temperatures profiles (B).223 5.41 Coupled MarTIM-MCD temperature profiles versus Pathfinder entry measurements. . . . 225 5.42 Seasonal variation in temperature and density for SPICAM and coupled MarTIM-MCD results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 5.43 Seasonal variation in net energy balance terms for coupled MarTIM-MCD results at 100 and 130 km. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 6.1
Electron density and electron temperature profiles used within the ionospheric kinetic code.242
6.2
MarTIM background neutral density and temperature profiles used in the ionospheric kinetic code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
6.3
Steady state downward electron flux comparison between various ionosphere models. . . . 247
6.4
+ Total, primary and secondary production rates for N+ , N++ 2 , N2 and electrons. . . . . . . 249
6.5
+ Production efficiency and polynomial fit transition altitude for N+ , N++ 2 , N2 and electrons.250
6.6
+ Total, primary and secondary production rates for C+ , O+ , CO++ 2 , CO . . . . . . . . . . 251
6.7
+ Production efficiency and polynomial fit transition altitude for C+ , O+ , CO++ 2 , CO . . . 252
6.8
+ ++ Total, primary and secondary production rates for O++ , CO+ 2 , O2 , O2 . . . . . . . . . . 253
6.9
+ ++ Production efficiency and polynomial fit transition altitude for for O++ , CO+ 2 , O2 , O2 . 254
6.10 CO+ 2 production efficiency versus altitude at various solar zenith angles and the altitude of maximum CO+ 2 production efficiency versus solar zenith angle. . . . . . . . . . . . . . . 256 6.11 CO+ 2 production efficiency versus altitude for various solar longitudes. . . . . . . . . . . . 258 6.12 CO+ 2 production efficiency versus altitude for various solar cycle conditions. . . . . . . . . 259
14
List of Tables 1.1
Composition and selected parameters of the Martian atmosphere. . . . . . . . . . . . . . . 17
1.2
Selected spacecraft observations of the Martian upper atmosphere. . . . . . . . . . . . . . 36
2.1
CO2 Radiative and collisional processes and their rate coefficients. . . . . . . . . . . . . . 71
2.2
MarTIM ionosphere reactions and their rate coefficients. . . . . . . . . . . . . . . . . . . . 74
3.1
New diffusion and advection subroutine experiments. . . . . . . . . . . . . . . . . . . . . . 100
3.2
Comparison of background atmosphere temperatures and wind speeds. . . . . . . . . . . . 101
3.3
Experiments regarding the impact of multiple species diffusion and advection. . . . . . . . 118
4.1
Comparison of different global modelling parameters. . . . . . . . . . . . . . . . . . . . . . 149
5.1
Temperatures and geopotential heights introduced by MCD at 0.883 Pa. . . . . . . . . . . 167
5.2
Coupled MarTIM-MCD and MCD alone zonal wind speeds at pressure level 2 (5.36×10−1 Pa). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
B.1 Polynomial coefficients for use in equations 6.11 and 6.12 of Chapter 6. . . . . . . . . . . . 277
15
Chapter 1
Introduction and Background Theory 1.1
Introduction to the Martian Environment
Mars, fourth planet from the Sun, ranking third in brightness as seen from Earth, continues to intrigue space scientists and astronomers around the globe. Its dramatic environment, dynamic and highly variable atmosphere has been the focus of no less than sixteen space agency missions since the Viking landers touched down in the mid-1970’s. At the time of writing (early 2010) there are two unmanned exploration ‘rovers’ and one lander craft carrying out scientific experiments on the surface of Mars as well as three orbiters observing, taking measurements or otherwise studying its atmosphere. Furthermore with both European and American space agencies placing Mars exploration as major parts of their respective space science strategies, often with a manned mission as the ultimate goal, one can well imagine the exploration of Mars with such focus continuing through the next few decades. In prehistoric times Mars intrigued humanity because of its blood-red colour, which was associated with warfare by the Babylonian, Greek and Roman civilisations. Indeed the planet is named Mars after the Roman god of war. With the advent of the telescope astronomers were able to observe and study Mars’ many varied features. For example, from his observations of the Syrtis Major feature Christiaan Huygens concluded in 1659 that the rotation period of Mars was about 24 hours (Lang and Whitney, 1991). We now know the exact Martian day to be 24 hours, 37 minutes 22.6 seconds, remarkably similar to Earth. Further comparisons can be drawn between Earth and Mars with the rotational axes of both planets being tilted to almost the same degree (obliquity 23.45◦ and 25.19◦ respectively) such that both planets experience seasons (although Mars does take longer to complete an orbit of the Sun; 686 days to Earth’s 365). Later observations established the presence of an atmosphere on Mars by virtue of (a) the northern and southern polar caps that wax and wane with the seasons as gaseous material is condensed from and sublimed to the atmosphere (James et al., 1992), (b) the formation of yellow dust clouds that
16
occasionally grow and coalesce to envelope the entire planet (Kahn et al., 1992) and (c) the repeated appearance of white clouds over the Martian surface (Lang and Whitney, 1991). The fundamental attributes of the Martian atmosphere remained only vaguely known for many centuries until the dawn of space-age exploration. The Viking landers of the mid-1970’s established the principal chemical components as they descended to the surface. Carbon dioxide, nitrogen and argon are the major species with trace amounts of molecular oxygen and carbon monoxide (Lang and Whitney (1991), see Table 1.1(a)). The Martian atmosphere is very thin with a surface pressure only 1/160th that of the Earth’s and since CO2 is such an active coolant it is also a cold atmosphere with an average temperature at the Viking 1 lander site of −63◦ C. This combination makes Mars’ atmosphere capable of holding only a very little water, it is in fact saturated with water vapour, always on the verge of snowing. As the surface temperature drops with the approach of winter carbon dioxide begins to condense onto the surface at high latitudes. Whether the CO2 deposits are the result of direct vapor condensation at the ground (frost) or of atmospheric condensation and precipitation (snow) is still unknown (Giuranna et al., 2008) but certainly at the poles broad white polar caps of frozen carbon dioxide form, growing to occupy up to 30% of the winter hemisphere. Over the course of a year then, as the seasons pass, the average surface pressure varies some 20% as the northern and southern poles exchange and recycle one-fourth of the atmospheric carbon dioxide between their polar caps. This large scale atmospheric flow - the condensation flow - is one of several circulation features discussed during the course of this thesis. Table 1.1: (a) Composition of the present day Martian lower atmosphere (