to a restoration of pre-El Nino conditions have been more elusive. Graham, White and others propose that the cooling is the result of events that occur outside the equatorial waveguide: the region bounded by about three degrees north and south latitude. In the off-equatorial regions the warming of the eastern sea disturbs wind patterns over the central Pacific, leading to an oceanic upwelling in that region, which in turn gives rise to westward-moving Rossby waves. At this point in the cycle the Rossby waves are essentially regions in which the warm upper layer is thinner than usual (in other words, where the thermocline is elevated).
The Rossby waves travel more slowly than the Kelvin waves, but within a year or two they are thought to reach the western border of the Pacific, travel along the border back into the equatorial region and become shallow, fast-moving Kelvin waves. The arrival of these waves in the eastern Pacific raises the thermocline there, allows cold water to surface and enables the easterly winds to gain strength.
At first, surface cooling is further reinforced by the easterlies, which generate shallow, eastward-moving Kelvin waves in the central equatorial Pacific. Yet the cooling in the equatorial waveguide helps to trigger the next heating phase. It leads to wind patterns in the off-equatorial areas that produce downwelling and deep (rather than shallow) Rossby waves. These westward-moving Rossby waves eventually turn into deep Kelvin waves, which, when they reach the east, depress the thermocline, thus raising the sea-surface temperature once again.
By examining various indicators of the movement of Rossby waves-such as wind patterns and changes in sea level and water temperature-in the off-equatorial regions, Graham and White have determined that the Rossby waves appear to have been in the expected places when El Ninos have occurred in the past. They also note that models including calculations of Rossby-wave activity predicted the 1986-87 El Nino a year in advance of its onset. -Ricki Rusting
More Setbacks at SlAC
Aging technology adds to a linear collider's woes
This past spring physicists at the Stanford Linear Accelerator Center (SlAc) jubilantly announced
that the center's unconventional new
particle accelerator, known as the Stanford Linear Collider (SLC), was ready to roll. After months of delay and a slew of unforeseen technical problems, they had succeeded in bringing two tightly focused particle beams, one of electrons and one of positrons, into head-on collision-the most precise beam collision ever attempted. "That was the good news," said Kaye D. Lathrop, an associate director of SlAe. "A lot of people had said we wouldn't be able to make such small beams collide."
The bad news was that there were not enough collisions. The collisions are supposed to churn out Zo's ("Znaughts"), heavy particles whose properties elucidate certain fundamental aspects of matter. But by the end of July no Zo's had been seen. Indeed, the machine achieved useful collisions only 3 percent of the time that it was running. Alarmed by this setback, SlAC director Burton Richter assumed direct control of the project on August 1 and assigned teams to tackle the multitude of problems besetting the machine.
The SLC is trying to achieve collisions by an untried method: boosting electrons and positrons to high energies in a linear accelerator, or linac, and then aiming the beams at each other. Unlike conventional machines, in which beams collide repeatedly as they whirl in opposite directions along the same circular track, the SLC has only one shot at a time. To compensate, the beams have to be squeezed to unprecedented densities.
When Richter first proposed the idea in 1980, he decided to piggyback the new design onto the existing twomile-long Stanford Linear Accelerator, which was built in the early 1960's. The linac would accelerate both electron and positron beams and inject them into an oval track; they would go around the track in opposite directions and slam into each other on the other side. This decision, calculated to catapult the SLC ahead of a rival European machine of conventional design costing 10 times as much, has created problems of its own.
The old linac was designed to produce beams with energies of about 25 billion electron volts (GeV) and diameters of a few millimeters, but the SLC must produce two 50-GeV beams focused down to less than 10 micronsand aim them at each other. Among other things, it turned out that some of the older power supplies are too jittery to achieve such precision; it could take six months to replace them. To add to these troubles, during the
July heat wave some aging microelectronic parts overheated and failed in alarming numbers inside the unrefrigera ted shed housing the linac.
Longer-term obstacles arise from the untried design of the machine. The "kicker magnets," which extract particles from "damping rings" where they are squeezed down to the required densities, proved unequal to the task. Unexpectedly large effects induced by the electrical current of the beams prevented the damping rings from making adequately short bunches of the particles. The positron source, a metal target that emits positrons when it is bombarded by electrons, must be made more durable. There also are not enough instruments yet to adjust errors in the position and quality of the beams accurately.
Lathrop was philosophical about the setbacks: "To put the best face on it, we've learned what we have to do." For the next few months, weekdays will be spent studying and fine-tuning the SLC and weekends will be devoted to producing collisions. The plan is now to get the SLC up and running stably in February. -JK
Planetary Consomme Terrestrial experiments mimic alien atmospheres
From the makers of synthetic primordial soup come two new flavors: Titan and Uranus. Back in
195 3 investigators first simulated the earth's primordial atmosphere. They zapped a gas mixture with electricity, which yielded a soup of organic molecules. Now this technique has been modified by astronomers trying to simulate chemical processes in the present-day atmospheres of the planets and moons of the outer solar system. The simulations may help to explain the planets' color and atmospheric chemistry, and they may even provide insight into the origin of life in this solar system and others.
Whereas the primordial-soup experiment was based on conjecture about the earth's ancient atmosphere, the new simulations rely on information collected by the Voyager 2 spacecraft during its flybys of Saturn and Uranus. Carl Sagan, W. Reid Thompson and Bishun N. Khare of Cornell University duplicated in their laboratory the conditions found in the upper atmospheres of Titan (Saturn's largest moon) and Uranus. Hydrogen, helium, nitrogen and methane were mixed at pressures and concentrations typical
SCIENTIFIC AMERICAN October 1 988 25
© 1988 SCIENTIFIC AMERICAN, INC
QU ESTAR ' . . . t h e pr ice less te l esco pe
QUt��TAR. THt WORI O'S tlNF.�T. MOST H .RSATIU Q U E S TA R TU.ES( OPt. IS OES( RIBU) I N OUR BOOKl.ET. SF N O S 3 T O ( OV t.R M A i l ('OSTS ON THIS ( ONTI N t N T . B\ AIR TO S. AMERI( A . $4; HIROPt. & N . A t R I ( A . S5.00; ���;:tH�:!;'1 �:. INQlJlRt AROler OlIR txn .... mJ) no, 59. Dept . 2 1 ') . 'l'" 1I0pe . I' A 1 119311
I'hone ( 2 1 5 ) 1162-5277
26 SCIENTIFIC AMERICAN October 1 988
of those atmospheres. The gases were pumped continuously through glass tubing, and a coil of wire was wrapped around a section of the tubing. A highvoltage current flowing through the wire created an intense magnetic field in the gas, The field energized the gas molecules and stripped electrons from them, forming a state of matter known as a plasma. The laboratory plasma mimics the aurora, in which atmospheric gases are bombarded by charged particles accelerated by a planet's magnetic field. Chemical reactions are known to abound in planetary auroras.
The laboratory plasma was Similarly fecund, creating many different organic molecules, including hydrocarbon chains up to seven carbon atoms long. As these chemicals and others flowed farther through the glass tubing, they were separated for analysis. Some gases condensed at room temperature. Others solidified in places where the tubing was cooled in baths of dry ice and liquid nitrogen. After the simulation had run for a few days, enough material was produced to be detected and analyzed.
The astronomers were thereby able to study the chemistry of Titan and Uranus at a level of detail not possible for the Voyager spacecraft or telescopes. The Titan experiments produced a brownish organic solid whose optical properties agreed well with Voyager and ground-based measurements of the omnipresent Titan haze. Over the lifetime of Titan this material may have accumulated on the moon's surface in a layer hundreds of meters thick.
The investigators also report that the nitrogen-rich atmosphere of Titan produced a great variety of pre biotic chemicals called nitriles. Nitriles are precursors of amino acids, the basic building blocks of proteins. "Something similar may have happened on the early earth, but on Titan the prebiological chemistry is probably stillborn: the temperatures are far below the freezing point of water," Sagan observes.
The Uranus experiment, reported in Journal of Geophysical Research, simulated a hydrocarbon smog that is created by the aurora in the planet's hydrogen-and-methane atmosphere. In the reaction chamber of the simulation, the astronomers collected solid hydrocarbons on glass slides. They measured optical properties of the hydrocarbons and found they account for the subtle hues of yellow, red, brown and black that tinge the bluegreen globe of Uranus. The Cornell
© 1988 SCIENTIFIC AMERICAN, INC
workers hypothesize that such hydrocarbons, created in the same way, contribute to the colors of other planets as well. -Russell Ruthen
BIOLOGICAL SCIENCES
Postprandial Warmth Certain fish rise to the surface in order to digest better
Does a warm bath make you hungry? For certain fish the answer apparently is yes. Ac
cording to a report in Nature, these fish, juvenile Bear Lake sculpins, feed on the chilly bottom of Bear Lake (in Utah and Idaho) during the day and rise to the warmer surface waters at night to digest. The warm water speeds their metabolism, accelerating the rate at which they absorb their food and making it possible for them to eat a larger meal the next day.
Daily vertical migrations are not uncommon among fish species, but they usually occur for other reasons. For example, a fish might come up to the surface to feed on plankton during the night and then return to the depths during the day in order to hide from predators or to conserve energy by slowing its metabolism in cold water. Indeed, the authors of the report, Wayne A Wurtsbaugh and Darcy Neverman of Utah State University, thought they were dealing with one of these migration patterns, until they discovered that the sculpins' stomachs were fullest at dusk, just before the fish rose to the surface. Inside the stomachs were the remains of organisms that live only on or near the bottom. The fish could not have been rising to the surface to eat; perhaps they were rising to digest.
To test their hypothesis that warm surface water acts as an aid to digestion, the investigators fed a collection of sculpins a full meal and kept them in separate tanks, some at five degrees Celsius (the temperature of the bottom waters) and some at 15 degrees (the temperature of water near the surface at night). The fish kept at 15 degrees digested their stomach contents at a rate of 23 percent per hour and had evacuated 80 percent of their meal within 7.5 hours. The fish kept at five degrees, on the other hand, digested only 3.2 percent of their stomach contents per hour; at that rate it would have taken them 50 hours to evacuate 80 percent of the meal.
How much real good does such an
trek s to
gre�t River Ganga ...
High up in an ice cave, from the waters of the melting Gangotri Glacier, the Ganga River begins.
The view is breattitaking, as mag"-�"'1711'."''' peaks rise 20,000 feet to meet
sJ<.r-NQithern India is a land of brilliant
COfltniSts. Valleys yield ing st.Mlc:lenly to peaks. Deep silences giv
thunderous rush of
trf'!kklnO enthusiast, " .",aTa.." which
all of :ItoI'them lnelta,
offer some of the world's �t rugged
and rewarding
o Yes! I'd like to plan an exciting visit to India. Please send me information.
Name
Address
City State Zip
Mail to: Government of India Tourist Office Dept. MH, 30 Rockefeller Plaza North Mezzanine, New York, NY 10 1 12
New York 212-586-4901 Chicago 312-236-6899 Los Angeles 213-380-8855 SA10S
SCIENTIFIC AMERICAN October 1 988 27
© 1988 SCIENTIFIC AMERICAN, INC
Top Related