This is the second blog related to events at the GLOBE Learning Expedition that took place in Cape Town, South Africa, from 22-27 June 2008. (You can find daily reports, a photo gallery, and student delegation blogs at the above link.)

Have you ever arrived at a school event, movie, or concert, shivering in a cold auditorium at first, but then feeling too warm by the time the auditorium was full? (For an earlier discussion, see the blog, Human Metabolism: What is That?, posted 23 February 2007).

The opening day of the GLOBE Learning Expedition offered a perfect opportunity to show the effect of people on the temperature of a large room, Jameson Hall at the University of Cape Town (Figure 1).

Figure 1. Jameson Hall; photo by Jan Heiderer. The GLE banners in front are slightly less than 9 meters high.

In order to measure the temperature, Jamie Larsen of GLOBE installed the temperature sensor on the speaker’s podium on the stage. This kept the sensor away from the doors to the outside, and put the sensor in full view of the audience. The sensor was supplied to us by Robyn Johnson of Vernier Software and Technology, one of the GLE sponsors. The sensor was installed while the auditorium was still empty, so that we would know the temperature of the room before many people came in. It was attached to a data logger, which was attached to a computer, so that the audience could see what happened to the temperature of the hall from the time it was empty, to when the approximately 500 people attending came in and sat down, and through several welcoming talks.

Thanks to Jamie and Robyn, my welcome talk could include a science question, “How much had the room warmed up during the time people came in?” Most of the people in the audience thought that the room was warmer. And the graph did in fact show that the temperature had warmed – about 3 degrees Celsius. Unfortunately, the data logger was turned off without storing the data (there were more talks and a performance before Jamie could get back to the logger), but the warming curve looked very much like the one in Figure 2, which is basically a sketch of the curve rather than actual data.

Based on our memories, the photograph in Figure 1, and some pictures of Jameson Hall on the Web, we estimated the size of the Jameson Hall Auditorium to be about 30 meters high on average, and about 40 m by 40 meters inside. So that there were about 48,000 cubic meters of air in the auditorium. The room started out empty, but by the time it was full, there were 500 people.

Each person was giving off about 100 Watts* (one Joule of energy each second). A Joule is a measure of energy. To get a feel for the rate of energy release, think of a 100-Watt light bulb.

Figure 2. Sketch of the observed warming of Jameson Hall before and during the GLOBE Learning Expedition Opening Ceremony at Jameson Hall, University of Cape Town.

The curve showed steady and rather cool temperatures before people came in, a rapid warming phase as the hall filled, and then the temperature was steady again as the air adjusted to the number of people in the hall. It was surprising that the temperature didn’t continue to warm – the people were still releasing heat, but they kept the doors open to keep the hall from getting too warm. This suggests a new “equilibrium” with the heat escaping to the outside the same as the heat given off by those of us in the hall. (There did not seem to be any heating or air conditioning operating at the time.) The actual curve was so “perfect” many found it hard to believe it was real data!

So does the temperature increase make sense?

From the earlier blog, the heating per unit time by the 500 people is given by:

500 people times 100 Watts per person = 50,000 Watts.

50,000 Watts is equal to the change in heat content in the air per unit time (here seconds), written

Heat content change per second =
specific heat
times volume
times density of air
times temperature change per second

The specific heat is around 1000 Joules per kilogram per degree Celsius. (Specific heat is a nearly-constant number that relates heating of a given mass to its change in temperature.)

Let’s use this relationship to figure out what the temperature change should be over the roughly one hour or 3600 seconds the temperature climbed.

Temperature change = total heat input, divided by (volume x air density x specific heat)

Total heat input is 50,000 Watt times about 3600 seconds, or 180,000,000 Joules

Specific heat times volume times air density = 1000 K per Joule per degree C times 48,000 cubic meters x 1 kg air per cubic meter = 48,000,000 Joules per degree C

Temperate change in degree C = 180,000,000 Joules divided by 48,000,000 Joules per degree C, or about 3.8 degrees Celsius!

This is amazingly close to the measured temperature change.

You could try this experiment in your school. All you need is a thermometer (or perhaps more than one) to take temperatures before and during an event. The results might not always look like Figure 2, since heating and air conditioning systems are designed to keep the temperature the same. What does it mean if the temperature stays the same? If you had thermometers in different parts of the auditorium, would they show the same temperature changes? (Note: since the temperature change is important rather than the actual temperature, it is o.k. if the thermometers aren’t starting out at the same temperature).

*A nice discussion of the amount of heat release by an individual can be found in Energy, Environment, and Climate, by Richard Wolfson. (published 2008, by W.W. Norton and Company)

In the last blog, I looked down – at a puddle. But most of the time, I look up: to see what birds are overhead, and to watch clouds.

Figure 1. Picture of fair-weather cumulus clouds east of Beloit, Wisconsin, USA.

Have you ever wondered how big a cloud is? Or how much it weighs? Or how long it lasts?

I’ve often thought about these questions, and it is actually fairly simple to get some “typical” answers.

How big is a cloud? What is its height? Width? Volume?

There are a several ways to get an idea how “big” clouds are.

You can look at clouds in a satellite image of your area, and “scale” the clouds to the size of the state or country you live in. This works best for larger clouds like thunderstorm clouds, or sheets of stratocumulus or altocumulus that stretch across the sky. Some sites for accessing satellite pictures are:

• For the United States: RAP Real-Time Weather Data.
• For Australia: Bureau of Meteorology Satellite Images.
• The British Met Office has images for much of the world, for example:
  • For Europe
  • For Asia
  • For Africa
  • For South America
  • For North America

When you are in an airplane or on a mountainside or tall building, you can look at the shads of the clouds on the ground. In the Midwestern United States, the land is divided into one-mile (1.6-kilometer) sections; with roads often marking the sides of the section, so that the land looks like graph paper. By comparing the size of the shadow to the mile-square sections, you can see how big the cloud is.

When you are in airplane (or a car, bus, or train), you can time how long it takes to pass through a cloud or its shadow. For the airplane, you need to know how fast it is traveling with respect to the air.

• For a jet airplane at cruising altitude, 550 miles per hour or 250 meters per second is a good first guess. So, if it takes 10 seconds to pass through a cloud, the cloud is 2.5 kilometers wide.
• For a car, you need to assume that the cloud isn’t traveling very fast, since clouds can travel as fast as cars. If you are traveling at 70 miles per hour (about 35 meters per second) beneath a cloud that is not moving, and it takes 10 seconds to go through the its shadow, the cloud is 350 meters across. If the cloud is traveling with the car, you might overestimate the cloud’s width. (If the cloud travels as fast as you are traveling in the same direction as the car, you will stay in shadow as long as the cloud exists). Things get more complicated if the cloud moves across your path. Also, late in the afternoon, cloud shadow size increases with the depth as well as the width of the cloud. But remember, we’re only trying to get a rough idea of cloud size.

How much does a cloud weigh?

I include only the water in the cloud – not the air. Think about a “typical” cumulus cloud, about a kilometer on a side.

The volume of this cumulus cloud is:

1000 meters times 1000 meters .times 1000 meters, or 1,000,000,000 cubic meters

Measurements from aircraft flying through cumulus clouds suggest a cubic meter contains about 0.5 grams of water – that’s the equivalent of a drop about 0.5 cm in diameter – about the size of small marble. Thus our “typical” cloud weighs

0.5 gram per cubic meter times 1,000,000,000 cubic meter = 500,000,000 grams or 500,000 kilograms, 1,100,000 pounds, or 550 tons.

Why doesn’t a cloud fall out of the sky, if it’s so heavy?

If the cloud were a 550-ton weight, the cloud would fall out of the sky. But a cloud is made up of tiny droplets, which fall very, very slowly. (You can check this out by dropping tiny pieces of paper and watch how slowly they fall). A cloud droplet is tiny – it’s about 100th the diameter of a typical rain drop – or one-millionth of the volume!

Cloud droplets do fall, only slowly. But something else is often happening. The air in many clouds is rising. For example, in our typical cumulus cloud, the air can be rising at a rate of several meters a second – enough not only to keep the smallest cloud droplets from falling, but even smaller raindrops might never reach the ground.

Why is the air rising? In the case of our cumulus cloud, the air is rising because it is less dense than the surrounding air. This is mostly because the air in the cloud is warmer than the surrounding air. The air, being buoyant, will rise until it encounters air warmer than it is.

Figure 2. The air in this cumulonimbus cloud was rising, but slowed down and spread out when it was no longer buoyant.

In some clouds, though, the particles are falling. In the cloud in the photograph below, ice particles are falling.

Figure 3. Ice crystal fall streaks forming cirrus clouds.

This discussion is from:
LeMone, M.A., 2008: The Stories Clouds Tell. Published by the University Corporation for Atmospheric Research. Available from the NCAR Science Store. This booklet was originally written for the American Meteorological Society for use by teachers participating in Project ATMOSPHERE.

For more about clouds, GLOBE has the following resources:

• Cloud protocol
• Cloud quiz
• Elementary GLOBE Do you know that clouds have names?

Also, you can find more at Windows to the Universe:

• Cloud types
• Cloud Image Gallery

Go to bottom of page and you will see a link to clouds in art.

Finally, there are time-lapse cloud pictures at:

• Time-lapse movies of clouds from Olympus Cove

As the last (I promise!) blog on the Missouri puddle, I describe the informal puddle investigation in terms of the GLOBE Inquiry Model.

The GLOBE Inquiry Model is a simple way to describe how scientists investigate questions. It’s easier to deal with the inquiry process in the classroom if the steps are described. In reality, the way scientists “do” inquiry is much messier, and different scientists have different ways of doing their research. But, in the end, they have to do all the same things that will be described here. Often, scientists return to each step a number of times while they are learning about the question they are investigating. This was illustrated a little bit in the puddle blog.

To summarize, here are the steps

1. Observe natural phenomenon
2. Explore, extend, and refine observations
3. Develop investigation plan
4. Conduct investigation
5. Analyze data
6. Summarize findings and conclusions
7. Share findings and conclusions
8. Identify new research questions

This is but one summary. There are many other ways of summarizing the inquiry process. For example, “Form a hypothesis” is often a listed step (in fact, is an option under “Explore, extend, and refine observations.”) Also, “Conduct Investigation” includes making observations, but they are now more systematic.

Note that not all scientific investigations start with a hypothesis. In some investigations, a question is narrowed down until an answer seems possible given the time and resources available for the investigation. For example, it is quite legitimate to ask “Has snowfall decreased in my hometown in the last 50 years?” Sometimes scientists start investigations with a question and develop a hypothesis in the course of the study. Other times, scientists alter their hypotheses as they discover new things.

Okay, let’s get started.

1. Observe the natural phenomenon
The way I work is that I look for surprises – something I can’t easily explain. Maybe if I don’t understand it, other people don’t either.
In this case, I saw a puddle that remained large (and possibly even grew) even though it had not rained or snowed for several days. Also, the puddle remained liquid, which seemed surprising given subfreezing temperatures for several days. This didn’t make sense to me. So I started to watch the puddle.

2. Explore, extend, and refine questions
In February, I walked to the puddle several times in a few days, to see what was happening to it. The fact that it was still there intrigued me. Also, I discovered a line of fire hydrants on the same side of the road as the puddle, which meant that there was an underwater pipe. (Was the pipe broken?) Finally, I noticed salt crystals on the road one morning; with newly fallen snow melting around the salt crystals. (Could the salt be keeping the water from freezing?)

3. Develop investigation plan
Given the observations I had made – no rain, possible broken underground pipe, very cold weather, I had two hypotheses regarding the origin of the puddle, namely:

1. The puddle was the result of a break in the pipe connecting the fire hydrants.
2. The puddle was fed by water running downhill beneath the surface (it was frozen at the surface).

I also had two hypotheses why the puddle was liquid.

1. The puddle was supplied by underground water that was warm enough to be liquid
2. The puddle didn’t freeze because of the salt on the road.

To see whether a leaky pipe caused the puddle:

1. In February, I decided to interview people who knew about the road.
2. In March, I decided to check to see if the puddle was there after several warm and dry days. If there was a leaky pipe, I would have expected to see a puddle.

To see whether the puddle came from water below the frozen ground:

1. In February, I decided to look for data showing it was possible for the soil (and water) below the surface to be warmer than freezing during short (week-long) periods with air below freezing. (It would have been ideal to take measurements near the puddle, but I did not have the proper equipment).
2. In February, I also decided it was important to check to see whether there was water on the surface, even thought it was quite cold.
3. In March, I decided to check to find how underground water could flow onto the street.

Notice that this was not all done at once. I went back and refined my investigation plan, when I found out I had the opportunity to check further.

4. Conduct Investigation

To investigate whether the puddle was supplied by underground water:

1. I continued to observe the puddle to see whether it was changing in size (February).
2. I obtained wintertime data from Smileyberg, Kansas, and Bondville, Illinois, to see how soil temperature behaved during ~week-long periods when temperatures were much colder than normal (and also below freezing). I plotted the air temperature and soil temperature during the cold periods, to confirm that the soil temperature could be above freezing (February).
3. I looked for openings in the street and curb for underground water to flow through to supply the puddle.

To investigate the broken-pipe hypothesis:

1. I asked my nephew about whether the pipe could be broken. He thought it unlikely because the pipes were very new.
2. I checked the puddle location a month later, when warm weather dried the ground. There was no puddle, which made me think that the pipe was probably o.k.
3. Also, I knew from my family and the appearance of the ground that the pipe had not been repaired.

To investigate the salt hypothesis:

1. I looked for evidence of salt on the road (salt crystals, melting around the crystals, and white stain on the road where salty water had dried up).
2. I interviewed a colleague who had been involved in studying arctic ice.

5. Analysis of the data

1. I compared the puddle sizes (from memory and photographs).
2. I plotted the air temperature and soil temperature at several levels to confirm that the soil could remain above freezing even when the air got quite cold.
3. I compiled evidence of salt (the crystals, the stain the road where the puddle had been, Even the slushy appearance of the water was associated with it being cold and salty).
4. I compiled evidence that the pipes were not leaking (the pipes were new, the contractor had a good reputation, there was no puddle after a dry spell, and it was obvious no one had repaired the pipe between my visits to the site).

6 and 7. Summarizing findings and conclusion and sharing findings

By doing my blog, I was working on this part even before I had finished the investigation. Were I to write this as a report, I would summarize the hypothesis, methods, and results as if they were done in an orderly manner. The timing of a result – be it before or after I was working on hypotheses, doesn’t really matter in the final report.

Were I not doing a blog, I would have recorded similar information in my laboratory notebook, so that I could be reminded of the details when I wrote the final report. (Here is a sample final report.)

8. Identify new research questions

It is rare that someone finishes up a research project without thinking of more questions. I was thinking of them the entire time. I was so excited about the possibility of underground water causing a liquid puddle when the air temperature was well below freezing, I didn’t think of the effects of salt. That is, until the next day when I saw the snow melting around the salt crystals. Now, I’m wondering if the cars disturbing the puddle kept it from freezing as well. And tomorrow I might think of other ideas.

It is not easy to decide when to finish a study. If you are a student, you have a due date that forces you to stop. If you are scientist, and are being paid to finish a project by a deadline, you also have to stop – at least until you can find someone to pay you to answer your next question.

In fact, scientists I know usually find that their investigations often lead to more questions than answers.

In the same way, thinking about the evidence kept giving me new ideas for what to look for. So, instead of a few tasks done one by one, I was sometimes doing several at once.

(If you are interested in the Pole to Pole videoconference, just scroll down – it’s just below this one. I’m finishing up the puddles blog so that I can write a blog or two on inquiry, using the puddles as my example).

As I was proofreading the puddles blog upon returning to Colorado, I started wondering if the puddle simply had been left behind from the previous week’s rains, and that salt may have kept the puddle from freezing.

I had the opportunity to check this last week, on a second trip to Missouri. Again, there had been rain a few days before I arrived. And again, there was a puddle in the same place. But this time I could see clearly that water was flowing into the puddle (and other places along the road) from gaps in the curb as well as some in the street. You can see this in Figures 11 and 12.

Figure 11. A new puddle (photographed 19 March) at the same location of the one photographed in February, in Columbia, Missouri. Note that water is leaking through a gap in the curb as well as part of the crack.

I also discovered that the puddle was not in a dip in the road, as I had suspected earlier, but it was located in a place the road was nearly horizontal (okay, maybe a very shallow drip): There was actually some flow downhill toward the lowest spot, where water drained into a sewer. Finally, I discovered that the puddle is only about 2 meters (6.6 feet) above the lake.

Figure 12. Closeup of the puddle.

There were other puddles along the road, formed from drainage through gaps in the curb and sometimes gaps in the pavement of the road (most of the cracks in the roadbed are sealed with tar).

After a few days with temperatures rising to around 15 degrees Celsius (59 degrees Fahrenheit, the puddle finally disappeared. Where the water was, a white stain on the road revealed that salt had collected there; and there was drier soil carried along with the water feeding the puddle.

Another day with no puddles convinced me that the pipe connecting the fire hydrants (see earlier parts of this blog) was not leaking.

So, with a little extra data I was able to confirm the hypothesis that the puddle was being fed by subsurface water flowing at least through a gap in the curb (which is ~15 centimeters or 6 inches high) and possibly the crack in the road. Salt clearly also played a role in keeping the water from freezing.

I also found out something else. My brother and sister-in-law’s house was heated and cooled by pumping groundwater up to the house. Remember, the temperature 30 meters (100 feet) down – or even 10 meters (30 feet) down – is close to the average temperature for the whole year (in Columbia, about 13 degrees Celsius or 55 degrees Fahrenheit). So the water pumped up to the surface in the summer will be much cooler than the air temperature, and thus can be used to cool the house. In the winter, the ground water is almost always warmer than the house, so it can be pumped up to warm the house.

But remember – the temperature of the ground water – and the average temperature – is about 13 degrees Celsius (55 degrees Fahrenheit). That’s not warm enough to heat the house in winter, so another method is needed to bring the temperature up from 13 degrees to a more comfortable 20 degrees Celsius (68 degrees Fahrenheit) or so.

Next time: how the investigation of this puddle illustrates the inquiry process – or the “scientific method.”

During the summer, abundant sunshine during the long days heats up the ground near the surface. I’ve seen surface temperatures on dry ground up to 50°C in the south-central Great Plains of the United States. If you’ve dug a hole in the ground, have you noticed how cool the soil is? Last fall, when I was digging a hole for a dinosaur dig, I sat in the hole to cool off! (Figure 8).

Figure 8. Me enjoying the relatively cool temperatures in a hole. The shade helped, too! Photo by Lorrie McWhinny.

Figure 9 shows how the temperature varied beneath a winter wheat field in south-central Kansas during the late spring-early summer of 2002. The temperature 7.5 centimeters below the surface (blue curve) reaches a maximum in the early afternoon, with the peaks slightly later as you go to lower levels. Note that the daytime temperature at 7.5 centimeters below the surface is warmer than that at 15 centimeters, and so on, with the coolest temperatures at 80 centimeters below the surface.

Figure 9. Soil temperature as a function of day of year for a winter-wheat site in south-central Kansas. The distances in cm (centimeters) indicate how far below the ground surface the measurement is being taken. Day 138 is 18 May, Day 150 is 30 May, Day 180 is 29 June. All data for 2002. Date collected and processed by Professor Richard Cuenca, Oregon State University. The maxima in the blue curve occur in the early afternoon.

These data, which are fairly typical, are consistent with our impression that the soil is usually cooler than the surface for most of the day during summertime. (The cooler surface temperatures on some days appear to be related to rainfall.)

The surface temperature for the same site appears in figure 10. Notice how the surface temperature peaks during the day about five degrees higher than at 7.5 centimeters during the first part of the data record, and then 10-15 degrees higher than the temperature at 7.5 centimeters late in the record. The change is related to cooling of the winter wheat (the sensor is measuring the temperature of the winter wheat) due to evapotranspiration during the first part of the record. Once the winter wheat stops growing and becomes golden, transpiration is no longer happening and the dry wheat and then the wheat stubble and ground surface are strongly heated by the sun.

Figure 10. For same site as Figure 4, except for surface temperature. Note that the wheat becomes golden (senescent, stops growing, is almost ready to harvest) around Day 150 (30 May).

The same happens to the bare ground at other sites – the surface is much warmer than the temperature 7.5 cm below the surface.
Have you been in a cave in the summertime? Caves, being farther from the surface, are even cooler. At the Devil’s Icebox, a cave not far from where I am writing this blog in Columbia, Missouri, the temperature stays at about 56°F (13°C) all year, even though the average summertime high temperature in Columbia is in the upper eighties (around 30° Celsius) and the average wintertime low temperature here is in the mid-teens (around -8° C).

So in the summer, the ground gets cooler as you dig down, — at least through the upper few meters. In the winter, the ground gets warmer farther down. And in caves, the temperature doesn’t change much at all. In fact, I once read that a cave temperature is a good first guess of the average above-ground air temperature at the cave’s location.

Similarly, people in many countries take advantage of the cool below-ground temperatures too store food during the hot summer. Also, some people take advantage of the temperature several feet below the surface to heat their homes in the winter and cool their homes in the summer.