Questions 31-40 are based on the following passage.NATURAL SCIENCE: This passage is adapted from the article "When Research Is a Snow Job" by Sarah Boyle (©2002 by National Wildlife).
The figure is beyond comprehension: Every year,
1,000,000,000,000,000,000,000,000 (1 septillion)
snowflakes fall worldwide. As the crystals fall, they
encounter different atmospheric conditions that produce
5 flakes with unique attributes. The more complex those
conditions are, the more elaborate the crystals.
Kenneth Libbrecht is a physicist at the California
Institute of Technology. Along with the work of scien-
tists at the U,S. Department of Agriculture's Agricul-
10 tural Research Service (ARS), his research is
uncovering new information about the magical world of
snow crystals-information that has practical applica-
tions in such diverse areas as agriculture and the pro-
duction of electricity.
15 Snow crystals are indi.vidual crystals-usually in a
hexagonal form--,-while snowflakes are collections of
two or more snow crystals. Beginning as condensed
water vapor, a crysti:il typically grows around a nucleus
of dust. Its shape depends on how the six side facets-
20 or faces-grow in relation to the top and bottom facets.
If they grow relatively tall, the crystal appears column-
like; if the side facets are short compared to the length
of the bottom and top facets, the crystal looks platelike.
Currently Libbrecht is trying to crack the problem
25 of why the crystal facets' growth varies with tempera-
ture. He believes this may have something to do with
the ice surface's "quasi-liquid" layer, which affects how
water molecules stick to the surface.
By manipulating the temperature and humidity
30 within an incubation chamber (and by adding an elec-
tric current or various gases at times), Libbrecht creates
"designer" snowflakes in his lab. Such experiments are
helping him determine how crystals form.
William Wergin, a retired ARS research biologist,
35 and a colleague, Eric Erbe, were using scanning elec-
tron microscopy to look at biological problems relating
to agriculture. To avoid the laborious procedure that
using such equipment usually entails, the two scientists
decided to freeze the tissue they were working with and
40 look at it in the frozen state
"One day it happened to be snowing," says
Wergin, "and we were looking for a specimen. We
imaged some snowflakes and were very surprised to see
what we did." It was the first time anyone had
45 attempted to image snow crystals with scanning elec-
tron microscopy, which provides precise detail about
the crystals' shape, structural features and metamor-
phosed conditions (crystals often change once on the
ground depending on the surrounding environment).
50 Wergin called another ARS colleague, hydrologist
Albert Rango, to see if the snow crystal magnifications
had any applications for his research. Rango now uses
Wergin's electron microscopy data, along with
microwave satellite data, in the Snowmelt Runoff
55 Model to predict the amount of water available in a
winter. snowpack. For western states such as Colorado,
Montana, Utah and Wyoming, about 75 percent of the
annual water supply comes from snowmelt. Snowmelt
water is critical to crop irrigation and hydroelectric
60 power, as .well as recreation and domestic water sup-
plies, fisheries management and flood control.
Before employing the scanning electron micros-
copy results, the forecasted amounts of snowpack water
were inaccurate whenever the size and shape of the
65 snow crystals varied much from the norm. "The more
we know about crystals," notes Rango, "the easier it
will be to use microwave satellite data for predictions
of the snow water equivalent."
Currently, forecasts using the model are about
70 90. percent accurate. A 1980 study estimated that
improving the prediction by 1 percent would save
$38 million in irrigation and hydropower in the western
Rango is also looking ahead at climate change pre-
75 dictions. "Following the estimates that have been made
about what will happen by 2100, things are definitely
warming up," he says. Temperature increases will
likely result in a reduction in stream flow as overall
snow accumulation decreases, winter precipitation runs
80 off as rain, and water evaporates at a quicker rate. The
gap between water supply and demand will magnify
even more, greatly increasing water's economic value,
Not only does the crystal research help gauge
85 snowmelt, it is also useful in predicting avalanches,
designing artificial snow, and, perhaps in the near
future, examining air pollution. "You can put snow in a
scanning electron microscope and tell which elements
are present, such as sulfur and nitrogen," says Wergin.
90 "You can then see what kind of pollution is in the area
and possibly track the source."