DISCUSSION OF CIRRUS CRYSTALS:
These crystals were collected during the FIRE
2 project sponsored by NASA
in 1991. The acronym FIRE is actually an embedded acronym: First ISCCP (International Satellite Cloud Climatology
Project) Regional Experiment. The project was centered in Coffeyville, Kansas,
and the purpose was to measure properties of mid-latitude jet stream cirrus.
Have you ever wondered about the high wispy clouds you see in the atmosphere
called cirrus clouds? The Atmospheric
Sciences Center at the Desert Research Institute (DI)
in Reno Nevada, operates several instruments that are used to get close-up
images of the particles in clouds. One instrument is called the replicator
(like the machine on Star Trek that makes food). The replicator uses 16
mm film coated with a liquid varnish called formvar that is exposed to the
air as the airplane flies along. Particles impact on the formvar and leave
behind an impression that, once the liquid has dried, can be viewed at our
leisure back in the laboratory with a digital image analysis system.
To understand how clouds work, we need to know about the particles in them.
We all have seen satellite images
of clouds. These images are made possible by sunlight reflecting from
clouds or by the infrared energy projected by and through them. Cloud particles
determine the appearance of clouds from satellites, they determine the amount
and type of precipitation falling on the earth, and finally, on a larger
scale, they strongly affect the rate of heating and cooling of the climate
system.
Incidently, the DRI replicator was flown on the University of North Dakota
Cessna Citation aircraft, Mike Poellot copilot and coinvestigator on the
project. Many forms of ice crystals have been seen in the replicator
images observed from these flights, from snowflake like shapes to simple
plates and columns, as well as polycrystals.
The basic structure of ice is formed around hexagonal symmetry. Think
of a hexagon (six-sided figure). Ice crystals frequently have 6-fold symmetry,
though some only have 3-fold symmetry. [Remember for a moment that 360 degrees
are rotated in going around a circle. The terminology "an object with
6-fold symmetry, or simply 6-fold symmetry" pertains to the fact that
you can rotate the object 360/6 degrees = 60 degrees and the object will
appear the same.]
Not all of the above ice crystals have 3 or 6-fold symmetry. Some only have
mirror symmetry, and some are distorted. We always like to say that the
lack of symmetry is due to defects or impurities in the crystal lattice,
though without further detailed analysis to pin-point the precise reason,
this is like saying the sky is blue because sunlight hits it.
Crystal form, or habit as it is known to meteorologists, is a major difficulty for people trying to figure out how sunlight and infrared "heat" rays interact with ice particles. The complex crystal geometry makes it difficult to know where sunlight is sent after interaction with these crystals. Do you see many crystals that are the same?
As you continue along the tour, you will be provided with links to return to this page if so desired.
(Here is another example of mixed habits, with column polycrystals along with high aspect ratio columns taken from the same 1 km of cloud.)
(Here is an example of plate polycrystals along with very high aspect ratio columns, probably better referred to as needles, again from the same 1 km of cloud.)
(Here is an example of almost dendritic, needle like habits from the same 1 km of cloud.)
(Here is another example of needle like habits in a cloud along with a strange single crystal plate and polycrystals plates.)
(Polycrystals, needles, single crystals, they are all here)
For a spectacular view of some of nature's art work check out our art gallery.
RETURN to replicator data selection