Table Of ContentPlanetary
Atmospheres
F. W. Taylor
Planetary
Atmosp11eres
Original artwork by Taylor
OXFORD
D.J.
F.W. Taylor
Department of Physics
University of Oxford, UK
UNIVERSITY PRESS
Great Clarendon Street, Oxford 6DP
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Preface
The final year of the Physics undergraduate degree (M.Phys.) course at
Oxford University involves specialisation in two areas of Physics,
which the student chooses from a list of eleven options. One of these
The Physics of Atmospheres and Oceans,
options, called is further
subdivided into short courses on basic Atmospheric Physics and
Oceanography, Theory and Practice of Remote Sounding, Weather
Forecasting, Climate Change and Chaos, and Comparative Planet
ology. All of the students, whether they choose this option or not,
Climate Physics
took, in the previous year, the course called which
Atmospheres
provides a basis for the more advanced material in the
and Oceans Elem
option. A textbook for the Climate Physics course,
entary Climate Physics,
was published in 2005.
Comparative Planetology
This book is the text for the segment ofthe
Planetary Atmospheres
final year course. The title has been chosen to
avoid the confusion that might result when 'comparative planetology'
is no longer obviously meant to be in the context of a course about
atmospheres and oceans. The coverage is also extended somewhat
beyond the boundaries of the Oxford course in order to make it
compara
more useful to students elsewhere. The emphasis remains on
tive
aspects of planetary atmospheres, generally meaning comparison
with the Earth, including atmospheric composition, thermal structure,
cloud properties, dynamics, weather and climate, and aeronomy. The
goal is to look for common processes at work under different bound
ary conditions in order to reach a fundamental understanding of the
physics of atmospheres.
It is appropriate for a short module that forms part of a general
Physics course that it should choose to emphasise certain aspects that
are of broad topical interest. Here, those are (i) evolutionary processes,
setting the Earth in its context as a planet and a member of the Solar
System; (ii) the properties of atmospheres that affect the climate near
the surface of each planet; and (iii) measurement techniques and
models, where the same experimental and theoretical physics is applied
under different conditions to investigate and explain atmospheric be
haviour. These might be thought of as the astronomical, environmen
tal, and technical sides of the discipline, respectively.
The syllabus for the Oxford course is summarised in the student
handbook as:
Origins of planetary atmospheres and evolution;
Composition and photochemistry;
Radiative properties and energy balance;
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Preface
Clouds, dust, and aerosol;
Atmospheres in radiative equilibrium;
Climate and climate change;
and
Observation of planetary atmospheres.
The recommended textbooks used before the present book existed are
listed below; it had been a problem that a minimum of five books were
needed to support one short course, and that some of those are
somewhat out of date, requiring further subsidiary references to
cover the course adequately. This book was produced to cover the
basics in a single manuscript. Of course, some secondary reading is also
appropriate, and the other recommended books are still relevant. In
addition, specific references to important sources or seminal papers are
given at the ends of the chapters, along with key definitions and some
historical background in footnotes and in the Glossary at the end of
the book.
Elementary Climate Physics:
The approach is the same as in an
overview, followed by more detailed discussion of key topics, arranged
by physical phenomenon and not planet by planet as usually found in
this field. There is an emphasis on acquiring and interpreting measure
ments, including the basic physics of instruments and models. The
resulting knowledge about atmospheres is set in the context of simple
models that can be manipulated with no more computing power than
is available with a simple spreadsheet and which do not obscure the
basic physics. A clear, basic discussion sometimes requires a difficult
balance between repetition and cross-referencing. Where terms are
introduced in the text they appear in italics and are defined and
explained in the glossary at the end of the book. Values for important
parameters and useful constants are also collected in an appendix. A
handy set of simplified reference model atmospheres is also provided,
as are some sample questions, mostly from past examinations and
tutorials, for which the answers are to be found in the text.
Additional topics that fall outside the Oxford syllabus are covered
whenever that gives a more well-rounded treatment of the subject for
the benefit of readers who are not at Oxford and not taking this
particular course. In this way, it is horred that this book will be
found to be useful for a wide range of students everywhere, or anyone
interested in the fundamental science of planetary atmospheres.
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Acknovvledgements
Thanks are extended to the many colleagues past and present whose
work in one way or another contributed to the material presented here.
Particular acknowledgement and gratitude is due to Dr D.J. Taylor
who drew all of the original diagrams and created the cover image. Ms
Jo Barstow, Dr Colin Wilson and Professor Peter Read scrutinised
some or all of the manuscript and made very useful suggestions and
corrections.
Parts of the chapter on atmospheric dynamics are based on unpub
lished lecture notes produced by the present author with P.L. Read, R.
Hide, and P.J. Gierasch in the 1980s for a graduate course on the
subject, and on some current lectures given by Professor Read. Sec
tions 9.5 and 9.8 on the climates of Mars and Titan, respectively,
The Scientific Exploration of Mars,
follow the author's books: Cam
Titan: Exploring an Earthlike
bridge University Press, 2009, and
World,
(with A. Coustenis), World Scientific Publishing, 2008, where
more detailed coverage, illustrations and references may be found.
Other major sources and references that will be of value to the
student are listed at the end of each chapter or, where needed to bolster
a specific point or measurement, in a footnote. Background notes are
also provided in footnotes.
Recommended books
The present book assumes knowledge of the material covered in:
Elementary Climate Physics,
F.W. Taylor, Oxford University Press,
2005, which relates to a course taken by Physics undergraduates in the
Planetary Atmospheres
Third Year at Oxford, i.e., one year before the
course. For very important material or derivations a summary is given
in this book, with a reference back to the longer discussion in the
introductory text for those who find the material unfamiliar.
For further reading, the following general texts are recommended:
An Introduction to the Solar System,
N. McBride and I. Gilmour, eds.,
Cambridge University Press, 2004.
The Physics and Chemistry of the Solar System,
J.S. Lewis, Academic
Press, 1995.
Theory of Planetary Atmospheres,
J.W. Chamberlain and D.M. Hunten,
Academic Press, 2nd edition, 1987.
Remote Sounding of
J.T. Houghton, F.W. Taylor, and C.D. Rodgers,
Atmospheres,
Cambridge University Press, 1986, republished 2009.
Planetary Sciences,
I. de Pater and J.J. Lissauer, Cambridge University
Press, 2001.
Contents
1 The Solar System, the planets and their
atmospheres 1
1.1 The Solar System 1
1.2 The inner planets 4
1.2.1 V olatiles on Mercury 5
1.2.2 The atmosphere and climate of Venus 8
1.2.3 The atmosphere and climate of Earth 13
1.2.4 The atmosphere and climate of Mars 15
1.3 The outer planets 16
1.3.1 The atmosphere of Jupiter 17
1.3.2 The atmosphere of Saturn 18
1.3.3 Uranus and Neptune 20
1.4 Titan: a satellite with an atmosphere and a climate 23
1.5 Comparative climatology 25
1.6 References and further reading 29
2 Origin and evolution of planetary atmospheres 30
2.1 The origin of the Solar System 30
2.2 Planetary system formation theories 31
2.2.1 The Kant-Laplace nebular hypothesis 32
2.2.2 Encounter theories 32
2.2.3 The protoplanet theory 32
2.3 Models of planet formation 35
2.3.1 Collapse criteria for the protosolar nebula 35
2.3.2 Formation of planets 36
2.3.3 The shape of the solar nebula 36
2.3.4 Compositional variations between planets 38
2.3.5 The T-Tauri phase of the Sun 39
2.4 Formation of atmospheres 40
2.5 Atmospheric stability and escape mechanisms 41
2.5.1 Thermal escape: Jeans' formula 42
2.5.2 Hydrodynamic escape 44
2.5.3 Solar wind erosion 44
2.5.4 Impact escape 45
2.6 References and further reading 46
2.7 Questions 46
Contents
3 Observations of planetary atmospheres 48
3.1 Planetary missions 48
3.2 Venus exploration 48
Mariner Venera
3.2.1 (1962) and the
series (1961-1984) 48
Pioneer Venus
3.2.2 (1979) 49
Venus Express
3.2.3 (2006) 49
3.2.4 Future observations 49
3.3 Mars exploration 51
Mariner
3.3.1 (1971) 51
Viking
3.3.2 (1976) 51
Mars Express
3.3.3 (2003) 51
Mars Reconnaissance Orbiter
3.3.4 (2006) 51
3.4 Outer planets: Jupiter and Saturn exploration 52
Voyager
3.4.1 and (1979) 52
Galileo
3.4.2 (1996) 52
3.5 Titan 52
3.6 Infrared remote sounding instruments 53
3.7 Radiometric performance 54
3.7.1 The radiative transfer equation 55
3.7.2 Signal-to-noise ratio and errors 56
3.7.3 Retrievals 58
3.8 Venus experiments 58
Mariner
3.8.1 microwave radiometer 58
Pioneer Venus
3.8.2 orbiter Radiometric
Temperature-Sounding Experiment
(VORTEX) 60
Venus Express
3.8.3 VIRT IS 63
3.9 Mars experiments 63
Mariner
3.9.1 radio occultation 63
Mariner
3.9.2 Infrared Interferometer
Spectrometer (IRIS) 64
3.9.3 Mars Express Fourier Spectrometer (PFS) 64
3.9.4 Mars Climate Sounder 64
3.10 Jupiter experiments 66
Pioneer
3.10.1 and Infrared Radiometer
(IRR) 66
Voyager
3.10.2 Infrared Interferometer
Spectrometer (IRIS) 67
Galileo
3.10.3 Near Infrared Mapping
Spectrometer (NIMS) 68
3.11 Titan experiments 70
Cassini
3.11.1 Composite Infrared Spectrometer
(CIRS) 70
3.12 References and f2u rther reading 72
3.13 Questions 73
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