Category: Natural World

Heat and Hurricanes

What could possibly go wrong?

— Kai Ryssdal (2011) in Freakonomics: Preventing a hurricane on Marketplace by American Public Radio.

In what one can only hope is an extremely tongue-in-cheek article, Marketplace discusses how we might geoengineer a solution to stop hurricanes forming.

Hurricanes get their energy from the warm surface waters in the tropics. The warm water evaporates, transferring heat from the oceans to the atmosphere as latent heat in the form of water vapor. As the air rises, the water vapor condenses to form water droplets (clouds) releasing the stored heat into the air, causing the air to rise faster, sucking up more moisture, and setting up a positive feedback loop that turns storms and hurricanes.

But they need a constant supply of warm water.

Between 100 and 200 m below the ocean's surface, the temperature drops rapidly. This is called the thermocline. You will notice that the deepest, coldest water is at 4 °C, the temperature at which water is most dense. (Image adapted from the Woods Hole Oceanographic Institute, via Wikipedia).

Unfortunately for the storms, the warm water in the tropics is only a thin layer, a couple of hundred meters deep, that sits above about 3,000 meters of colder deep-water. As the storms suck up the heat and moisture, they stir the oceans, cooling down the surface water, and leaving cooler water in their wakes. The cooler water means that subsequent storms have access to less energy.

The energy in the atmosphere and oceans “wants” to distribute itself evenly over the surface of the Earth. Hurricanes are just one violent means of moving heat from the tropics to the poles, and from the surface to the depths of the oceans.

Cool water from the deep Atlantic is stirred up to the surface by hurricanes. This image shows the cool wake of Hurricane Igor. (Image from

NOAA’s National Hurricane Center monitors sea-surface temperatures closely: it’s one of the key factors that go into their predictions of how bad the hurricane season is going to be, and what path a storm might take.

A Salter Sink for mixing the warm shallow water with the deeper cold water. Image from Intellectual Venture via NewScientist.

The suggestion in the Marketplace article is that we could build about 10,000 long tubes (called Salter Sinks) to connect the warm shallow surface water to the colder water below the thermocline. Wave energy at the surface would drive the warm water downward, causing mixing that would reduce the temperature of the surface water the storms feed off.

The devices might cost tens of millions of dollars per year, but that would be a lot less than the cost in property damage alone of a large storm like Irene, not to mention the loss of life it would prevent.

Apart from the “benign” environmental impact (according to Stephen Dubner) the only real question left is:

What could possibly go wrong?

— Kai Ryssdal (2011)

Infrared Cloak

Image adapted from Wired.

In an interesting application of thermodynamics, BAE Systems has developed panels that can be placed on a tank to mask what it looks like to infra-red goggles, or help it fade into the background.

The panels measure the temperature around them and then warm up or cool so they’re the same temperature and therefore emitting the same wavelength of infrared light. So someone looking at the tank with infra-red goggles would have a harder time distinguishing the tank from the background.

The panels are thermoelectric, which means they use electricity to raise or lower their temperatures, probably using a Peltier device.

Peltier devices, also known as thermoelectric (TE) modules, are small solid-state devices that function as heat pumps. A “typical” unit is a few millimeters thick by a few millimeters to a few centimeters square. It is a sandwich formed by two ceramic plates with an array of small Bismuth Telluride cubes (“couples”) in between. When a DC current is applied heat is moved from one side of the device to the other – where it must be removed with a heatsink. The “cold” side is commonly used to cool an electronic device such as a microprocessor or a photodetector. If the current is reversed the device makes an excellent heater.

— Peltier-info.com: Peltier Device Information Directory

A Peltier element - it cools on one side and heats on the other. Image via Wikipedia.

Supernova Viewing this Week

The green arrow points to the exploding star. (Image via LBL).

During the next week or so, you should be able to see this supernova in the Pinwheel Galaxy with a good pair of binoculars, or a small telescope, as it waxes to its maximum brightness on September 9th.

The supernova was discovered just hours after the explosion. Astronomers are pointing every telescope they can manage at it, so this is going to be very well studied over the next decade, something high-schoolers interested in astronomy might consider.

It’s worth reiterating that since the supernova is occurring 21 million light years away, this star exploded 21 million years ago.

The video below explains where to look to find it in the night sky.

Algebra and Programming with VPython

Computer programming is the place where algebra comes to life. Students seem to get really excited when they write even the simplest instructions and see the output on the screen. I’m not sure exactly why this is the case, but I suspect it has something to do with being able to see the transition from abstract programming instructions to “concrete” results.

So I’ve decided to supplement my Algebra classes with an introduction to programming. I’m using the Python programming language, or, more specifically, the VPython variant of the language.

Why VPython? Because it’s free, it’s an easy-to-use high-level language, and it’s designed for 3d output, which seems to be somewhat popular these days. The oohs and aahs of seeing the computer print the result of a+b turn into wows when they create their first box. I’ve used the language quite a bit myself, and there are a lot of other interesting applications available if you search the web.

VPython was created to help with undergraduate physics classes, but since it was made to be usable by non-science majors, it’s really easy for middle and high school students to pick up. In fact, NCSU also has a distance education course for high school physics teachers. They also have some instructional videos available on YouTube that provide a basic introduction.

Image from a game created by middle school student Ryan W.

I use VPython models for demonstrations in my science classes, I’ve had middle school students use it for science projects, and I’ve just started my middle school algebra/pre-algebra students learning it as a programming language and they’re doing very well so far.

What I hope to document here is the series of lessons I’m putting together to tie, primarily, into my middle school algebra class, but should be useful as a general introduction to programming using VPython.

Getting VPython

You’ll need to install Python and VPython on your system. They can be directly downloaded from the VPython website’s download page for Windows, Macintosh or LINUX.

Running a Python program.

Once they’re installed, you’ll have the IDLE (or VIDLE) program somewhere on your system; a short-cut is usually put on the desktop of your Windows system. Run (double-click) this program and the VPython programming editor will pop up any you’re ready to go. You can test it by typing in something simple like:

a = 1
b = 2
c = a + b
print c

Then you run the program by going through the Run–>Run Module in the menu bar.

Which should cause a new window to pop up with: 

Python 2.7.1 (r271:86882M, Nov 30 2010, 09:39:13) 
[GCC 4.0.1 (Apple Inc. build 5494)] on darwin
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
3
>>>

Even better might be to test the 3d rendering, which you can do with the following program:

from visual import *

box()

which creates the following exciting image:

A box created with VPython. It looks much more interesting if you rotate it to see it in perspective.

To rotate the view, hold down and drag the right mouse button. To zoom in or out, hold down the right and left buttons together and drag in and out.

A rotated, zoomed-out view of a box.

Lessons

Lesson 1: Variables, Basic Operations, Real and Integer Numbers and the First Box.

Lesson 2: Creating a graphical calculator: Coordinates, lists, loops and arrays: A Study in Linear Equations

Global Warming Art

Global temperatures (averaged from 1961-1990). Image created for Global Warming Art by Robert A. Rohde.

Talk about evoking conflicting emotions. The image is astoundingly beautiful – I particularly like the rich, intense colors – but the subject, global warming, always leaves me with sense of apprehension since it seems so unlikely that enough will be done to ameliorate it.

The source of the image, Global Warming Art has a number of excellent images, diagrams and figures. The National Oceanic and Atmospheric Administration also has lots of beautiful, weather-related diagrams. I particularly like the seasonal temperature change animation I made from their data.

How to Write Lab Reports

If I have seen further it is only by standing on the shoulders of giants
— Isaac Newton (1676) via Wikiquotes.

Science advances when scientists share their results. If someone tests an hypothesis and finds that it’s wrong, if they share their results, others won’t have to waste time by repeating the same experiments. If someone makes a breakthrough and publishes what they found, then scientists all around the world can use that information to develop new experiments and new applications of that newly discovered principle. Sharing is essential, so it’s important for students to learn how to share well.

Scientists usually communicate their results by giving presentations to other scientists at conferences and publishing articles in scientific journals. Often these presentations are full of the specialized language different types of scientists use with each other, so sometimes science journalists will translate that into regular English news articles that everyone can read and understand. The New York Times and the BBC have good science sections, but what they present comes first from scientists’ formal presentations and articles.

As a result, good presentations and good lab reports are a great way to start learning how to communicate like a scientist.

Lab Reports

A good way to figure out what should go into a lab report is to look at a published article. We have a bunch of copies of Science, which has research articles toward the middle and the back. Articles in Science tend to be brief and fairly dense because it’s one of the premiere journals, so the outlines are not as explicit as you’d find in other places; an Open Access Journal might provide better examples, especially if you’re looking them up online.

Based on our observations, we decided on the following parts for a good lab report:

  • Title: Be short, but unique to give a good idea of what your project is about. Since my classes seldom all do the same experiment, this is very useful. Answer the questions: What did you do? Why did you do it? and What did you find?
  • Authors: Who gets the credit for the work. Usually authors are listed by who did the most work first, but since everyone’s expected to work equally on their group projects you can choose some random or arbitrary order.
  • Abstract: A brief summary of the work, include: what is the problem you’re trying to solve; what you did to solve the problem; and what results you came up with. The abstract should contain all the spoilers.
  • Introduction: Go into some more detail about what the problem is you’re working on, and why it’s important. State your hypothesis and how you’re going to test it. Overview previous work your project is based on.
  • Procedure/Methods: Describe, in detail, what you did, what apparatus you used. Both words and diagrams are useful here.
  • Results: Tell us what you found. Graphs, charts and tables will be very useful here.
    • Figure 1. An example of a diagram. In this case labels have been placed on a photograph of the apparatus. Notice also the caption, which you are reading at this very moment, that goes with the figure.
  • Note on Figures: You should have figures, charts, diagrams and tables in your Procedure and Results sections, but you can have them anywhere they’re appropriate. Each figure needs to have a caption explaining the figure. A useful approach to figures and captions is to try to write them so that someone could understand the entire article by only looking at the figures and reading their captions. One of my students says that popular magazines, like People, are written that way (or at least that’s how they’re read).
  • Analysis and Discussion: To paraphrase a student, “Explain why you think you got those results.” Even if the results are unexpected, or especially if they’re unexpected, you need to explain them. This is also your chance to explain why all of your critics are wrong and you were right all along. If you do that though, it should be written in scientific, passive-aggressive language.
  • Conclusions: Summarize. In the abstract you’re telling them what you’re going to tell them. In the Introduction, Procedure, Results and Discussion sections you’re telling them. In the Conclusion, you’re telling them what you told them. Hopefully by that time they’ll have had enough chances to figure out what you were trying to tell them.
    • Figure 2. An example of a citation for a website.
  • References: Be sure to include a list of the references you used to do your work. This is how you give credit to the people who’s work you are building on. The Yale Library has an excellent page on citing sources. There are a different citation styles you can use but remember the purpose: to give credit where it’s due, and to allow others to be able to find those references easily. All citations should have the author, the date published (or when you accessed it if it is a website), the title, and a way to track down the work.

Note that scientific magazines, like Science and Nature, are very different from a popular magazine like People, for one thing, as was pointed out to me today, the pages don’t smell like perfume (instead they smell like science).

Updates

This paper, on how to bend a soccer ball, is a good example of a student research paper.

The Thermal Difference Between Land and Water

The change in temperatures over the course of the year. Click image to enlarge. Images from 1987 via NOAA's GLOBE Earth System Poster.

The continents heat up faster than the oceans, and they cool down faster too. You can see this quite clearly in the animation above: notice how cold North America gets in the winter compared to the North Atlantic. It’s why London has an average January low temperature of 2˚C while Winnepeg’s is closer to -20˚C, even though they’re at almost the same latitude. There are a few reasons for the land-ocean cooling differences, and they all have to do with how heat is absorbed and transported.

(1) Specific Heat Capacity. Water has a higher heat capacity than land. So it takes more heat to raise the temperature of one gram of water by one degree than it does to raise the temperature of land. 1 calorie of solar energy (any type of energy really) will warm one gram of water by 1 degree Celcius, while the same calorie would raise the temperature of a gram of granite by more than 5 degrees C. The Engineering Toolbox has specific heat capacities of common materials.

(2) Transparency. The heat absorbed by the ocean is spread out over a greater volume because the oceans are transparent (to some degree). Since light can penetrate the surface of the water the heat from the sun is dispersed over a greater depth.

(3) Evaporation. The oceans loose a lot of heat from evaporation. In the evaporative heat loss experiment, While there is some evaporation from wet soils and transpiration by plants, the land does not have anywhere near as much available moisture to cool it down.

(4) Currents. Not only do the oceans absorb heat over a greater depth, but they can also move that energy around with their currents. The solar energy absorbed at the equator gets transported towards the poles, while the colder polar water gets transported the other way. Currents help average out ocean temperatures.

The Freezing Core Keeps the Earth Warm

The internal structure of the Earth.

The inner core of the Earth is made of solid metal, mostly iron. The outer core is also made of metal, but it’s liquid. Since it formed from the solar nebula, our planet has been cooling down, and the outer core has been freezing onto the inner core. Somewhat counter-intuitively, the freezing process is a phase change that releases energy – after all, if you think about it, it takes energy to melt ice.

The energy released from the freezing core is transported upward through the Earth’s mantle by convection currents, much like the way water (or jam) circulates in a boiling pot. These circulating currents are powerful enough to move the tectonic plates that make up the crust of the earth, making them responsible for the shape and locations of the mountain ranges and ocean basins on the Earth’s surface, as well as the earthquakes and volcanics that occur at plate boundaries.

Conceptual drawing of assumed convection cells in the mantle. (via The Dynamic Earth from the USGS).

Eventually, the entire inside of the earth will solidify, the latent heat of fusion will stop being released, and tectonics at the surface will slow to a stop.

The topic came up when we were talking about the what heats the Earth. Although most of the energy at the surface comes from solar radiation, students often think first of the heat from volcanoes.

Note: An interesting study recently published showed that although the core outer core is mostly melting, in some places it’s freezing at the same time. Unsurprising given the convective circulation in the mantle.

Model of convection in the Earth's mantle. Notice that some areas on the mantle are hotter, creating hot plumes, and some are cooler (image from Wikipedia).

Note 2: Convection in the liquid outer core is what’s responsible for the Earth’s magnetic field, and explains why the magnetic polarity (north-south) switches occasionally. We’ll revisit this when we talk about electricity and dynamos.