Monthly Archives: August 2011

Raising the water table the natural way

Today’s Wall Street Journal ran a story about using beavers to raise the water table and rehabilitate natural areas.  Beavers?  How can beavers do this?

Photo by Walter Siegmund
Beaver dam of Hat Lake and Hat Creek in foreground.  Bridge over Hat Creek on highway 89, Lassen Volcanic National Park.

Beavers are rodents that live in and along streams and rivers.  They gnaw down trees and build dams, which back up the rivers and streams.  The standing water behind the dam can percolate into the ground, recharging the groundwater and raising the water table.  The dams minimize flooding during the wet season and keep water from drying up during the dry season.

It’s especially important to recharge the groundwater in areas that don’t have precipitation throughout the year.  As we draw water out of the ground for our own uses, the water table falls, so much so that natural watering holes dry up.  One solution is for us to simply use less water during the dry seasons.  Another solution for humans to build dams.  Using less water is a good start (for as much as that is possible during the dry season), but we can also turn to natural sources–such as beavers–to recharge the water supply AND restore natural habitats.

“We can spend $200,000 putting wood into a stream, cabling down logs. Sometimes it works and sometimes it doesn’t.  Put in a colony of beavers and it always works.”

-Celeste Coulter, stewardship director at the North Coast Land Conservancy, a Seaside, Oregon, group that urges developers to set aside land for beavers

Learn about the science behind groundwater recharge and the water table in the High-Adventure Science investigation, “Will there be enough fresh water?”.

What makes scientists more certain?

For the past five days, Hurricane Irene affected the weather for residents on the East Coast.  For the Northeastern United States, the forecasts of the storm’s intensity turned out to be wrong; the storm weakened more than meteorologists had expected.
At the same time, the prediction of where the storm would go was very good.  Why was there such a difference between the two forecasts?
“People see that and assume we can predict everything,” National Hurricane Center senior forecaster Richard Pasch said.

“It’s frustrating when people take our forecasts verbatim and say, ‘This is where it’s going to be at this time and this is how strong it’s going to be,'” Pasch said. “Because even though the track is good it’s not certain.”
What will improve the forecasts?  More data.
The computer models that did so well as predicting the path that Irene would take use large-scale data.  “The keys to intensity changes are usually too small for big computer models,” said Georgia Tech meteorology professor Judith Curry.
Retired hurricane center director Max Mayfield says what’s needed is better real-time, small-scale information, like Doppler radar. NOAA used old propeller planes to take Doppler radar data inside Irene, but the information will be used to design better intensity forecasts in the future, he said.

With more data, meteorologists are able to make better models, which will more accurately predict the intensity of future storms.  This is applicable across all fields of science: more data leads to better models, leading to more accurate predictions of the future.

Learn about how scientists use new data to make better models of Earth’s future climate and fresh water availability with High-Adventure Science investigations.

Causality: How to Interpret Graphs

Graphs are often used to show data; they provide a very powerful way to show numerical trends.  But graphs can also be done poorly and be misinterpreted.


In the comic, the man in the hat has made a graph that shows the incidence of cancer in the United States with the number of cell phone users.  The incidence of cancer has been fairly steady over the past 30 years while the number of cell phone users has increased.

This means that cancer causes cell phones, right?  The graph shows that there are increases in cell phone users just as the cancer incidences start to plateau, so that conclusion makes sense, or does it?

Is there another–better–way to interpret this graph?  What does that graph really show?

Explore how good scientists draw conclusions from data in our High-Adventure Science investigations in climate, space, and water.

The Physics Teacher Magazine features IR article

The Physics Teacher Magazine published by the American Association of Physics Teachers (AAPT) selected our article "Infrared Imaging for Inquiry-Based Learning" as a featured article on the September 2011 issue. A featured article is made free to the public. Each issue chooses three featured articles.

In this paper, we described a series of IR experiments that can be readily used to teach the basic concepts of heat transfer and their applications to engineering.

A Red “Snow White”

Astronomers at the California Institute of Technology have discovered that “Snow White,” a dwarf planet officially named 2007 OR10, is actually red.  Time to come up with another name!  But why was it called Snow White to begin with?

It was originally called Snow White because Mike Brown, a professor of planetary astronomy at Caltech, had guessed that it was an icy body formed by a breakup of another dwarf planet.  Since he thought the planet would be icy and water ice appears to be white, the name fit.

Dr. Brown and his team have discovered that the little planet known as Snow White is actually red.  And it is covered with water ice, which is usually white.  So what makes this little planet red?

The explanation is probably in Snow White’s disappearing atmosphere.  In 2002, Dr. Brown helped to discover a similar dwarf planet, Quaoar.

Quaoar was covered with volcanoes that spewed an icy slush.  Quaoar was too small to hold on to its atmosphere, so it has slowly drifted away into space. What was left behind was some methane, the heaviest gas thought to have been in its atmosphere.  The methane, after being exposed to space radiation, combined into long hydrocarbon chains.  The hydrocarbon chains rest on the icy surface, giving Quaoar a rosy hue.

The spectrum of “Snow White” looks similar to the spectrum of Quaoar, an indication that the planets’ atmospheric compositions may be the same.

“That combination — red and water — says to me, ‘methane,'” Brown explains. “We’re basically looking at the last gasp of Snow White. For four and a half billion years, Snow White has been sitting out there, slowly losing its atmosphere, and now there’s just a little bit left.”

Mike Brown doesn’t yet know that Snow White has methane; there’s no evidence, other than the comparison with Quaoar.  It will take more investigation, with a larger telescope, to determine that for sure.

And now that the astronomy community has determined that Snow White is an interesting object to study, it needs a real name.

Before the discovery of water ice and the possibility of methane, “2007 OR10” might have sufficed for the astronomy community, since it didn’t seem noteworthy enough to warrant an official name. “We didn’t know Snow White was interesting,” Brown says. “Now we know it’s worth studying.”

That’s science–there’s always more to discover, even when it seems like all of the interesting discoveries have already been made.

Stay tuned to see what they re-name “Snow White.”

Explore how spectroscopy is used to determine the atmospheric composition of distant planets in our space investigation.

Students enjoyed Energy3D in Engineering Energy Efficiency Summer School 2011

Click to enlarge
This week 11 students of different ages (10-17) participated in our three-day summer school for the Engineering Energy Efficiency project. They were charged with using Energy3D to design their own model houses on a computer first and then construct them using inexpensive materials.

Although Energy3D is still in its alpha phase, it seemed to work remarkably well for these students who used the Mac computers we provided (thanks to Dr. Saeid Nourian, the lead developer of the software). Despite of some glitches, the students easily designed their own computer models. Creating the roof, the hardest part using other programs such as SketchUp, has been greatly simplified in Energy3D.

Interestingly, of the five groups, none used the template houses we provided to help them get started, indicating the fact that the students actually preferred designing their very own houses from scratch.

Strange thermal conductivity of leaves?

One way to tell if a plant is a plastic fake or not is to touch a leaf. If it feels cool, the plant is a real one. Have you ever wondered why a leaf feels cool? (A leaf of an indoor plant always rests at about the room temperature, plastic or real. It is not really cooler before you touch it. You can confirm this by measuring its temperature using a sensitive temperature sensor.)

We know metals feel cold because they conduct heat fast. Within a given amount of time, our fingers lose more thermal energy to a piece of metal than to a piece of wood.

Do leaves also conduct heat fast? On the contrary.

Let's put a fresh leaf on top of a piece of dry paper. The first set of IR images in this post shows what happened after I used two fingers to touch the leaf (on the left) and the paper to warm them up. The result tells that the leaf actually conducted heat more slowly than the paper, which has much lower thermal conductivity than metals.

Source: Wikipedia.
Now, we have a problem. We know leaves feel cooler than paper. But leaves conduct heat more slowly than paper! Our sense of touch honestly tells us that our fingers lose more thermal energy to leaves than to paper. So where does the thermal energy go on a leaf, if it doesn't diffuse to other parts?

My theory is that the thermal energy goes to heat up the water in the spongy layer of the leaf. The spongy layer lies beneath the palisade layer--the waxy surface layer of the leaf. Its cells are irregular in shape and loosely packed--hence the name "the spongy layer." During transpiration, the spongy layer is full of water in the spaces before they exit stoma. The specific heat of water is considerably high--4.18 J/(g*K) and the spongy layer is filled with water.

My theory is backed by the fact that a dry leaf conducts heat as fast as paper (IR images not shown here). This should not surprise you as paper is made of dehydrated wood fibers.

Now, the question is why the water in the spongy layer doesn't dissipate thermal energy quickly as water in a cup does (I confirmed the energy dissipation in water by IR imaging, which is not shown here). The thermal conductivity of liquid water is about 0.58 W/(m*K), compared with 0.024 W/(m*K) for air, 0.016 W/(m*K) for water vapor, and 0.05 W/(m*K) for paper. Somehow, the water trapped in the spongy layer cannot conduct heat like free water does.

Let's get get a wet (20% of full water absorption capacity) sponge (left) and a dry one (right) and look at their thermal conductivities under an IR camera. Again, I used my fingers to leave a heat mark on each. The second set of IR images shows a surprising result: the wet sponge appeared to conduct heat more slowly than the dry one!

Does this thermal conductivity protect plants' leaves? Have you wondered why some plants are anti-freezing and some are not? Leaves may have very complicated thermal regulation that we don't quite understand.