Wednesday, July 11, 2007

Here comes the sun

I am spending some time in Northern Germany this July.
It's one of those "summers" when you hardly ever see the
sun in these overcast skies. Maybe I missed some major
world events, but, as I mentioned once already, this kind
of weather for a prolonged period of time in the summer
season, over an extensive territory, used to be classified
as "moderate to medium nuclear winter" at the time when some
careful studies of the climate effects of a major nuclear
conflict were carried out. All right, I assume we did not
have any major nuclear conflict to make summers look consistently
like cold and gloomy winters, and I am reassured by the thought
that this is just a local weather specialty.

Speaking of "nuclear winter",
there are two excellent books
on the subject produced during
the Cold War, at the time
when people finally realized
that the consequences of a
major nuclear (or "nucular" as the
current US president would
have it) exchange between superpowers would not be "merely"
a counting of megadeaths but a global change of world climate
with lasting consequences for life on earth. One of the two
references is a Soviet production, the other is American.

On the American side, I am talking about the Sagan-Turco volume "A path where no man thought: nuclear winter and the end of the arms race", published by Random House in 1980. On the Soviet side, there is "The night after", a collection of essays by various scientists on the effect of nuclear war.

The Sagan-Turco is a substantial volume, some 500 pages long, structured as a collection of essays trying to present to the general public the current (at the time recently developed) scientific knowledge about the nuclear winter effect. In essence, the idea is that the combined burning of cities and other likely targets such as oil fields and refineries, which would
inevitably result from a nuclear exchange involving even a small fraction of the combined nuclear arsenal in possession of the then Soviet Union and the US, would obscure the sun with sooth, dust and smoke for long enough to create a macroscopic change of climate over a large part of the globe for long enough to have devastating effects (the complete failure of crops and agriculture over most of the arable surface of the earth among them).
Depending on targets and levels of attack, nuclear winters are classified in six categories ranging from nominal to extreme (in the latter category, for months on end there is pitch darkness at noon over most of the earth surface).

This is a book that any informed citizen living in the nuclear age should read. The journalistic style of the writing is perhaps not ideal - I much prefer the more informative and less
verbose prose of technical scientific writings - but one can see that the point is more to inform the general public than to make a technical report.

Its Soviet counterpart, "The night after" is a smaller booklet,
just about 150 pages long, published in the international English
language version by the good old Mir Publisher (what would have
science students done all over the world had it not been for
Mir Publisher...?) in the year 1985, edited by the "Soviet
Scientists Committee for the Defense of Peace Against
Nuclear Threat" and by the Soviet Academy of Science. This book
is more structured in the style of a technical report, with
contributed papers from various scientists participating in
the meeting. After an introductory survey, the first part of
the volume, "Long-term worldwide consequences of a nuclear war"
collects papers concentrating on the changes produced to the
atmosphere, on climatic consequences simulated in hydrodynamic
climate models, on how our knowledge of natural phenomena
(from Krakatoa and Mt St Helen to dust storms on Mars) can
be applied to modeling effects of possible nuclear catastrophes,
one medical consequences and on effects of a nuclear war in Europe
on the "non-aligned" third-world countries. (Many of these same
themes are discussed in the Sagan-Turco volume as well, though
I find these short technical reports, with precise formulae and
equations, details of models and data, much clearer and concise.)
The second part of the volume simply collects abstracts of
talks given at the conference (Moscow, May 1983) from which the
volume resulted.

Most people may think that these Cold War preoccupations are
over, but just because we do not have a Soviet Union anymore,
it does not mean that the danger of nuclear war is over. On the
contrary, some may argue that the much more unstable world that
emerged from the end of the Cold War might have, if anything,
made it more likely. The US and Russia have recently effectively
marked the return of the arms race, and there is no lack of
tensions that can ignite new conflicts. It is important not to
lose the knowledge of the dangers of nuclear war that scientists
have accumulated during the Cold War years: closing our eyes to
the past leaves us blind to the future.

Coming back to more mundane matters, I do wonder more and more
often why is it that I end up spending most of my summers
locked up in this pit hole of stress and darkness, instead
of being on a sunny beach somewhere like many other wiser
people do. Sure enough, there is an excellent and world
famous research facility here, but how much can I take advantage
of being here when I am overloaded with unfinished work and
duties? Anyway, I end up thinking of the sun a whole lot in these
circumstances, wishing it would make at least a brief guest
appearance amidst the clouds.

So I dug out another book, one I bought some three years ago in a second hand bookstore in Toronto, called "An Introduction to Stellar Winds" authored by Henny and Lamers and produced by Cambridge University Press. Stellar winds refer to the particles (as opposed to radiation) emitted by stars, the mass loss rate, the terminal velocity (at far distances), which varies between 10 km/s for cool stars to 3000 km/s for hot stars. Various models predict the velocity law by which the emitted gas accelerates from the stars photosphere to far distances. These parameters are closely related to the evolution and life cycle of stars. After an overview on the development of the subject, the book dedicates a chapter to the observation of stellar winds, and the structure of spectral lines in the winds.
The analysis of molecular emission lines for cool stars and information on dust from radio and millimeter range, etc lead to mass loss and terminal velocity estimations for
the two different scenarios of cool and hot stars. Chapter 3 deals with the equations governing stellar winds, under idealized conditions of an isothermal wind subject to an outward force given by gas pressure (with variants that consider additional forces). Solutions of these equations yield complete information (in these simplified models) on velocity and density functions. The following chapters extend the models beyond the isothermal case. Polytropic winds, coronal winds with heat conduction (with a nice model of the solar corona), dust driven winds, and sound wave driven winds, with or without dissipation. There's a lot more in terms of specific models (radiative acceleration due to spectral lines and line driven winds, multiple scattering, equatorial winds, magnetic rotators, varying transverse B-fields, rotating stars with outflowing disks, wind compression, hydrodynamical results). The final chapters deal with the interaction of stellar winds with the interstellar medium, planetary nebulae, wind bubbles, and with the effects of the structure of stellar winds on the course of stellar evolution. All in all, there is a wealth of nice equations and realistic models in this book that makes for a very nice reading for anyone who is curious about one very intriguing features of our and other stars.

More about our Sun. I happened to watch recently in a Swedish movie theater the newly released "Sunshine", a Sci-Fi thriller by Danny Boyle, the British director of the famous "Trainspotting". The idea behind this movie is simple and elegant. Something is wrong with the Sun, which is slowly "switching off" and a space mission of earth scientists flies towards it carrying the most powerful bomb ever created, aimed at jump-starting the dying star and reigniting its cycle of fusion reaction. (Suspension of belief is called upon here as for most "scientific" premises of science fiction movies.) The most appealing point of the movie is the interest it takes in the psychological effects on the human mind of a close proximity with the Sun, which stirs up all of the deeply ingrained archetypal forces that exist in the human psyche since the dawn of our species, that associate the Sun with a sacred and godlike entity. It is the contrast between the modern mind of space flight and high energy
physics colliding with the primitive mind of sun-worship and superstition that caused, one finds out during the development of the story, the failure of a previous identical mission and threatens to jeopardize the one whose story is being related. Nice idea, perhaps a bit too colored with the current demands of the movie industry for special effects and action plots, but
nonetheless a different and more interesting sort of movie.