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1. Michigan Tech Physicists Make a Splash with Rain Discovery |
by Jennifer Donovan, public relations director
It's conventional wisdom in atmospheric science circles: large raindrops fall faster than smaller drops because they're bigger and heavier. And no raindrop can fall faster than its "terminal speed"--its speed when the downward force of gravity is exactly the same as the upward air resistance.
Now two physicists from Michigan Tech and colleagues at the Universidad Nacional Autónoma de México (National University of Mexico) have discovered that it ain't necessarily so.
Some smaller raindrops can fall faster than bigger ones. In fact, they can fall faster than their terminal speed. In other words, they can fall faster than drops of that size and weight are supposed to be able to fall.
And that could mean that the weatherman has been overestimating how much it rains.
The findings of Michigan Tech physics professors Alexander Kostinski and Raymond Shaw--coauthors with Guillermo Montero-Martinez and Fernando Garcia-Garcia on a paper published in the latest issue of the American Geophysical Union's journal, Geophysical Research Letters--could improve the accuracy of weather measurement and prediction.
The researchers gathered data during natural rainfalls at the Mexico City campus of the National University of Mexico. They studied approximately 64,000 raindrops over three years, using optical array spectrometer probes and a particle analysis and collecting system. They also modified an algorithm, or computational formula, to analyze the raindrop sizes.
They found clusters of raindrops falling faster than their terminal speed, and as the rainfall became heavier, they saw more and more of these unexpectedly speedy drops. They think that the "super-terminal" drops come from the breakup of larger drops, which produces smaller fragments, all moving at the same speed as their parent raindrop and faster than the terminal speed predicted by their size.
"In the past, people have seen indications of faster-than-terminal drops, but they always attributed it to splashing on the instruments," Shaw explains. He and his colleagues took special precautions to prevent such interference, including collecting data only during extremely calm conditions.
Their findings could significantly alter the understanding of the physics of rain.
"Existing rain models are based on the assumption that all drops fall at their terminal speed, but our data suggest that this is not the case," Shaw and Kostinski say. If rainfall is measured based on that assumption, large raindrops that are not really there will be recorded.
"If we want to forecast weather or rain, we need to understand the rain formation processes and be able to accurately measure the amount of rain," Shaw pointed out.
Taking super-terminal raindrops into account could be of real economic benefit, even if it leads only to incremental improvements in precipitation measurement and forecasting. Approximately one-third of the economy--including agriculture, construction and aviation--is directly influenced by the ability to predict precipitation accurately. "And one-third of the economy is a very large sum of money, even during a recession," Shaw remarks.
The physicists' research was supported in part by the National Science Foundation. |
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2. Noontime Pilates Class Offered June 10-Aug. 12 |
Community Programs is offering a noontime pilates class in the ROTC Gym. The class will meet from noon to 12:45 p.m. on Wednesdays from June 10 to Aug. 12. Cost is $40 for non-students and $25 for students. Participants are asked to bring their own mats.
To register, go to www.aux.mtu.edu/rec/community/community.html or visit the SDC Central Ticket Office. For more information, call Sports and Recreation at 487-2975. |
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3. On the Road |
Joe Burns (Michigan Tech Research Institute) presented a poster
coauthored with Edward Domino, Judith Fetterolf, Deborah Ruzicka and Ronald Chervin (University of Michigan), "Sigma Band Interhemispheric Coherence Distinguishes Children With and Without Obstructive Sleep Apnea," at SLEEP 2009, the 23rd Annual Meeting of the Associated Professional Sleep Societies, held June 6-11 in Seattle. |
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4. Job Posting |
Staff job descriptions are available in Human Resources or at http://www.admin.mtu.edu/hro/postings . For more information regarding staff positions, call 487-2280 or email jobs@mtu.edu .
Faculty job descriptions can be found at www.admin.mtu.edu/hro/facpers/facvac.htm . For more information regarding faculty positions, contact the academic department in which the position is posted.
Staff Job Posting
06/11/2009
Research Engineer/Scientist I
Michigan Technological Research Institute--Ann Arbor, Mich.
Michigan Technological University is an equal opportunity educational institution/equal opportunity employer. |
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5. In the News |
Alex Mayer, director of Michigan Tech's Center for Water and Society and a professor of geological and mining engineering and sciences, was quoted in an article in the Christian Science Monitor on water resource management.
Click here to read what Mayer has to say about tracking your "water footprint." |
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6. Settee Available for Free |
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Public Safety has an orange, four-seater upholstered settee with arms (lounge couch), in very good condition, available for free. If you are interested, contact Al Hoffman in Public Safety at afhoffma@mtu.edu or 487-2216. |
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