2007
HOUGHTON LECTURE
SERIES
ABSTRACTS:
Lec. 1 Snowballs, Glacial Sliding and the Quantum
Electrodynamics of Ice April 2
The slipperiness of snow and ice holds practical
interest, for skiers,
skaters and commuters alike, but its physical origin is of broad
scientific interest, from basic physics to a spate of problems
in the earth and planetary sciences.
Although the surface of ice near
its melting point is ostensibly the same as the surface of any other
material near its melting point, the unique properties of ice
and water provide us with a wonderful macroscopic
manifestation of a pillar
of quantum electrodynamics: the Casimir Effect.
Moreover, such
fundamental issues underlie the mechanism responsible for our ability
to make snowballs, the heaving up of freezing soils, the
uptake of atmospheric trace gases on ice crystals and
many other
phenomena. In this
talk I describe the basic issues and trace some of
the related geophysical tendrils, several of which will be developed
in more detail in a subsequent lecture.
___________________________
Lec.
2 Sea Ice, Weyprecht, Stefan, Boltzmann, and the Metallography
of the AArctic
Ocean April 3
On any given day, one of the polar oceans is
solidifying. To an
excellent approximation, we can view the oceans as a binary
alloy and, as such,
understand the growth and melting of sea ice in much the same manner
as does the metallurgist.
Indeed, the crystallographic structure
and morphology of sea ice bears a striking resemblance to that
of a metal casting.
Thus, while understanding the growth and dynamics
of sea ice is a cornerstone of polar science, it is also an ideal
transparent analogue for other systems.
Because this understanding
underpins the processes that drive buoyancy forcing in
the polar oceans, where the evaporation/precipitation
cycle is replaced by
freezing and melting, this talk will begin with the
history of sea ice thermodynamics and trace that to
present day quantitative
treatments, from theory to laboratory and field experimentation.
____________________________
Lec. 3 Halocline Catastrophes and Related
Matters April 5
Cooling in the shelf regions of lakes and polar
seas, or evaporation in
marginal seas, leads to the formation of dense water masses that form
cascading density currents. When a density current enters a
two-layer stratification, there are two possible outcomes: if
the impinging current
is lighter than the lower layer, then an intrusion forms
on the thermocline; otherwise, it will intrude at the very base of
the reservoir. We examine this in the context of the rejection
of brine from growing
sea-ice on the shelf
regions of the Arctic ocean.
In the present climate, these shelf waters intrude at a
depth of around 150m
in the Arctic halocline, and it is important to know how stable
this circulation pattern is to possible changes in either the buoyancy
forcing or the halocline strength.
An abrupt ventilation of the
halocline would have a serious effect on the sea ice cover.
A related
issue occurs on the surface of the ice cover, viz., ice- albedo
feedback. Here we
see how, using the ICCP AR4 GCM output,
without deliberate tuning of the albedo, GCM predictions
of the fate of the
Arctic sea ice cover are not credible.
_____________________________
Lec. 4 Snowstorms, Thunderstorms and Other
Post-holiday Trauma April 6
The first systematic laboratory studies of the
growth of snowflakes were
performed by Nakaya, who referred to these hydrometeors as
"letters from the sky."
His hope was that by systematically studying the
conditions of growth, one might be able to understand something
important about the atmosphere.
Although this ambitious effort provides
only a qualitative glimpse into the atmospheric conditions under
which ice crystals are born and evolve, his experiments provide some
of the most intriguing and compelling mysteries of atmospheric
science and crystal growth in general.
An extension of the processes revealed
by their quantitative study helps us understand crucial processes
at play in thunderstorm electrification.
The collisions between
ice particles are at the center of the process that gives
rise to charge separation in an active
thundercloud; these collisions are
detailed and their implications for the climatology of lightning are
developed.
