Why are the icicles so long on our house?

On a recent walk just a day or two after our first snow, my husband and I noticed that we had the longest icicles in the neighborhood. Some houses built the same time as our house had icicles, but they were shorter. One new house had almost no icicles.

But what was the most fun, was our own house. The picture below shows our “champion” icicles.

Figure 1. Sketch of icicles on the east side of our house. The windows to the right of the icicles are about 1 meter high. The part to the right is the front part of the house; the part to the left is the back part of the house.

Notice that the icicles only cover the middle third of the side of the house. To the right and to the left, there are no icicles. Were we to walk on the roof, we would probably find the snow melted in the middle third of the roof, but not on the sides.

Why? Our house was built in stages. The front two-thirds were built were built in 1950. There was little insulation in the roof. A few months before I made this sketch, we tore out the old ceiling in the room in the front of the house and found that the insulation from 1950 was in poor condition, just like the insulation in the middle of house. The new insulation was much better. The picture confirms that the new insulation was working. No icicles implies no water from melting snow. This means that little heat was escaping through the roof, so there was little or no snowmelt on the roof.

Similarly, the back part of the house was built in 1979. When that part of the house was built, we made sure we had good thick insulation in the roof. There are no icicles on the new part of the house. Again – the insulation must be working.

Using the data from our house, can we explain why our house had the longest icicles? I’m guessing that the new house in our neighborhood that had almost no icicles had good insulation – just like the newer parts of our house and the room we just insulated. We could that the snow on the roof of the new house was fairly deep – there was little melting.

What about the older houses with shorter icicles? Let’s imagine an older house with about the same insulation as the old parts of our house (Figure 2). If this is true, the snow would melt at about the same rate (I am assuming that the roof was exposed to the same amount of sunlight per unit area). Why then would the icicles be shorter on the other (imaginary) house?

If you believe my assumptions, the answer is that the area of the roof “draining” toward the eaves (where the icicles grow) was smaller. Say the distance from the top to the icicles on our imaginary house is 5 meters, and the distance on our house is 10 meters. As the melted snow moves down from the top of the roof to the eaves, twice as much water reaches a given length along the eaves for the 10-meter roof (ours) compared to the five-meter roof. It follows that the icicles on our house would contain twice as much water and be longer than on the other house. The icicles may be not twice as long, because the icicles we had might be wider as well as longer.

Figure 2. View of a one-meter slice of our house (top) and an imaginary neighborhood house (bottom). More water is available to flow over the eaves for our house. We are looking at the two houses from the north.

So the amount of water in the icicles is determined by the amount of snow upstream of (or straight up the roof from) the eaves.

21 December 2007

It is the last official day of the 2007 surface temperature field campaign. Although we will not know for several weeks the total number of schools that have participated and the total number of observations taken, it was a great success. It has been a lot of fun watching the observations come in and to post blogs a couple times a week. Of course, if you want to keep taking measurements into the new year, please do. I know of a couple schools that are going to do that.

Here is an update on the snow situation. In North America, the snow has been melting back a bit in the center and eastern parts of the United States (Figure 1). You will also notice that there is a little more snow coverage in Eastern Europe. That is a common occurrence in the winter for cold air to move back a forth from the Eastern to the Western Hemisphere. When the cold weather was affecting the United States, Eastern Europe was warm. Now, it has flipped a little.

Figure 1. Snow extent in the Northern Hemisphere from 20 December 2007.

In the Western Hemisphere, there has been a fundamental change in the atmospheric flow. When it was cold and there were several major snow storms in the United States, the flow was out of Canada which is a source of cold air in the winter (Figure 2). This type of flow is called meridional. The upper level flow is at around 5500 meters above sea level. It steers the weather systems. This week, the pattern has changed and the upper level flow is sending weather systems from the Pacific Ocean into the west coast of the United States. Then the systems track across the United States. This type of flow is called zonal. This is bringing in warmer and moister air and is one of the reasons that the temperatures across much of the central part of the United States have gone above freezing.

This shift in weather patterns is evident in the surface temperature observations that were recorded. On 17 December 2007, Rockhill Elementary School in Alliance, Ohio recorded a surface temperature 3.0° C where there was no snow in the parking lot to –5.4° C on their grassy field where there was 78 mm of snow. On 20 December 2007, the students at Rockhill Elementary School measured 4.5° C on the parking lot and 0.4° C on the snow covered field with 80 mm of snow. As you can see, the temperature of the snow pack warmed up to right around freezing.

It is the last official day of the 2007 surface temperature field campaign. Although we will not know for several weeks the total number of schools that have participated and the total number of observations taken, it was a great success. It has been a lot of fun watching the observations come in and to post blogs a couple times a week. Of course, if you want to keep taking measurements into the new year, please do. I know of a couple schools that are going to do that.

Here is an update on the snow situation. In North America, the snow has been melting back a bit in the center and eastern parts of the United States (Figure 1). You will also notice that there is a little more snow coverage in Eastern Europe. That is a common occurrence in the winter for cold air to move back a forth from the Eastern to the Western Hemisphere. When the cold weather was affecting the United States, Eastern Europe was warm. Now, it has flipped a little.

Figure 2. Upper level flow on 15 December 2007 (top) and 21 December 2007 (bottom).

In general, all of the measurements in the United States showed a warming from 17 December to 20 December. The warmest temperature for this past week was 12.4° C and was measured 20 December 2007 at Waynesboro High School in Waynesboro, Pennsylvania on their dry parking lot while the coldest temperature was measured at Eastwood Middle School, Pemberville, Ohio of –11.0° C where there was 83 mm of snow. If the students at Moosewood Farm Home School in Fairbanks, Alaska had reported this week, they would have reported the coldest temperature by far. The air temperature hovered between –35° C and –40° C. But, they did not report any temperatures. It was probably too cold for the students to go outside.

Below is a pair of figures that was recently published about the Arctic ice cover on the NASA Earth Observatory website along with an article (Figure 3). The 1978-2002 median value is shown as the yellow line (Median is the middle value of a bunch of numbers. For example, if you are one of five children, of ages 1, 3, 7, 11, and 13, the median age of the children in your family is 7 years). You can see that the ice melted in the Arctic Ocean to record low levels in September this year and recovered quite a bit by November. But, the ice extent is still far below the 1978-2002 median level.

Figure 3. Ice extent compared to the 1979-2002 median extent for November (top) and September (bottom) 2007. Maps of ice extent from NASA Earth Observatory.

Schools involved in the surface temperature field campaign to date:

Dr. C

17 December 2007

The storm that moved through the center of the United States lived up to its billing. There was heavy snow, strong winds, heavy rain, tornadoes, freezing rain and sleet. In Toledo, Ohio we had about 5 cm of snow and then freezing rain and sleet on top of that. One of my friends could not get into his car because the ice froze over the car. I broke two ice scrapers trying to get the ice off of my car. After the ice, I think we had about 20 cm (8 inches) of snow at my house but then the wind blew the snow into drifts so it was hard to tell how deep the snow is. I was driving home from the store last night when I saw a car slide off the road into the deep snow in the ditch. I carry a shovel with me in my car in the winter so I was able to help him. A couple of young men, maybe seniors in high school, stopped and helped me push the car out. It felt good to help someone.

Figure 1 shows the snow and ice cover extent in the Northern Hemisphere. Compare that to the mean December snow water equivalent in Figure 2. The snow water equivalent is the depth of water that the snow will melt down to. For the storm over the weekend, the ratio of snow to water was probably on the order of 10:1 or 8:1. That means that for every 10 cm of snow it will melt to 1 cm of water. So, for the 20 cm of snow that we received in Toledo, Ohio there should be about 2 cm of water when the snow melts. Although the snow water equivalent and the snow extent are two different observations, the area of snow water equivalent can be used as an indication of snow extent. When you compare Figure 1 with Figure 2, how does the extent of snow cover today compare to the snow extent as indicated by the mean December snow water equivalent map in Figure 2?

Current Northern Hemisphere Snow Extent

Figure 1. Current (17 Dec. 2007) snow extent in the Northern Hemisphere.

Figure 2. Mean snow water equivalent (SWE) for December. Source: National Snow and Ice Data Center.

How are the maps of snow extent created? One of the sources of data is from satellite imagery. Figure 3 is a satellite image from a geostationary satellite called GOES. Snow covers most of the image including the states of Iowa, Illinois, Wisconsin, Missouri and Indiana. How can you tell where the snow is in this image? Do you see clouds in this image as well?

Figure 3. GOES (Geostationary) satellite image from 17 December 2007, 18:15 Universal Time.

As of this morning, we are up to 556 observations from 32 schools. I was able to add the observations from the University of Toledo.

Take care,

Dr. C

13 December 2007

I’ll have to say that I haven’t posted a message on the blog lately partly because I was busy with finals at the University of Toledo and my trip to San Francisco for the American Geophysical Union meeting. But, I also have had bloggers block. I didn’t know what to write about. Well, now I have a lot of things that I want to write about. Some of it will have to wait until next week.

All of the snow has melted in Toledo, Ohio. The temperatures over the last couple of days have gotten above freezing. You are all probably aware of the ice storm that hit the center of the country. That system caused a little bit of snow yesterday in Toledo but the forecast of 5-10 cm (2-4 inches) of snow did not pan out. But, the system caused a good amount of snow in southern New York state, Pennsylvania and even 25 cm (10 inches) in Boston, Massachusetts. Among the schools that have entered data for the surface temperature field campaign, White Cloud School in White Cloud, Michigan has reported 27 cm (11 inches) of snow on the ground.

It looks like another major winter storm is going to move out of the mountains over the weekend, across the country, to the east coast of the U.S. (see Figure 1 below). The map shows the low pressure system will be over Tennessee Saturday evening and will be spreading snow from Oklahoma to Pennsylvania. It looks like the drought stricken parts of United States will be getting some much needed rain. This storm should be a good one with strong winds. The forecast for Toledo, Ohio is 10-15 cm (4-6 inches) of snow. Locations in the southern part of Ohio should get more snow as should the eastern United States. I bet all of the students will be wishing the storm had hit during the week….

It looks like the snow will stick around as well. After the storm goes by, much colder conditions are expected. The temperature should remain below freezing for several days at the minimum. I hope I can get out my cross country skis. Also, I’ll try to go sledding with my kids.

Figure 1. Forecast map for 0Z Sunday, 16 Dec. 2007 (which is Saturday night in North America).

Surface Temperature Satellite Data

Timothy Ault, a Research Scientist at the University of Toledo, helped me by plotting up the students’ surface temperature observations. He took the student observations from the GLOBE Web site and plotted them in a Geographic Information System (GIS) to map the values overlaid on MODIS data from the Aqua satellite image. In the image below, you will see how much of Michigan, central Pennsylvania, and western New York are covered with clouds. [I apologize to the schools from Alaska, Iowa, Illinois, Estonia and Poland that are not on this map. I wanted to show what could be done with the data so I picked an area that covered the most schools possible.] The MODIS image was acquired from the rapid response Web site.

As you can see from the student measurements, the surface temperatures in Michigan under the cloud cover are much cooler than the surface temperatures in northeast Ohio and southwest Pennsylvania. The areas without cloud cover tend to have much warmer temperatures. When I was at AGU, Dr. Dorothy Hall from NASA Goddard Space Flight Center mentioned that scientists do not know the surface temperature under clouds because the clouds block the signal that the satellite can observe. This is a good example of how student observations are adding to our scientific knowledge. The students can measure something that the satellites can’t.

The students’ observations of cloud cover are denoted by the numbers to the left or above the circle. These are the nominal cloud cover percentages associated with the categories of the GLOBE observations. Clear – 5%, Isolated – 17.5%, Scattered – 37.5%, Broken – 70% and Overcast – 95%. You might be able to see that the student cloud cover observations do not seem to match the MODIS cloud observations especially in northern Ohio and southwest Pennsylvania. Why do you think that is? If you notice, Tim did not put the time the satellite went over and the time of the student observations on the map. Would the time of observation of clouds be important? And could that be the reason that there are differences?

In the MODIS image, you can see the urban heat island effect. I have an arrow pointing out Columbus, Ohio which shows up clearly as warmer than the rural areas surrounding it. Dayton, Ohio and Pittsburgh, Pennsylvania also show up warmer as well.

Figure 2. Student observations of surface temperature mapped onto a surface temperature MODIS image for 27 November 2007. The surface temperature measured by the students is in the circles and color coded according to the legend on the left. The number above or to the left of the circle is the nominal cloud cover percentage.

As of this morning, we are up to 556 observations from 32 schools. I was able to add the observations from the University of Toledo last night. It is nice to see so many observations coming in. Not that this is a competition, but the students from some schools are putting a lot of effort into the field campaign. I’m very impressed. I put the number of observations next to the schools with more than 20 observations.

Take care,

Dr. C

11 December 2007

Today I am in San Francisco, California at the Annual American Geophysical Union (AGU) conference. I heard today that there are over 15,000 scientists here. I bet you did not know that scientists are always learning. As you can see in Figure 1, the areas that I flew over were snow covered for the most part, that is if there were no clouds which was very common.

Figure 1. My flight path over the United States from Detroit, Michigan to San Francisco, California.

I took a bunch of pictures as I was flying from Detroit, Michigan to San Francisco, California.

Figure 2. Picture I took from my airplane of a snow covered mountainous area.

The view was great. Isn’t it amazing the quality of pictures that can be taken from an airplane with a regular digital camera? I really enjoy having a window seat when I fly.

A conference like this one is a way for scientists to share information. There are two ways that we present our work to other scientists. One is through an oral presentation, i.e. giving a talk. This is similar to what your teacher might do presenting information to you in class. The other way is through poster presentations. See figure 3 below. In this picture, there are hundreds of posters being presented at the same time. Poster presentations are very similar to science fair projects that students do.

Figure 3. Poster session at the AGU meeting December 11, 2007.

Attending the AGU meeting is also a chance for me to see my scientist friends again.

I learned some interesting things about remote sensing of snow today. Scientists at NASA Marshall Space Flight Center are using a satellite sensor called AMSR-E (Advanced Microwave Scanning Radiometer EOS). It is a sensor that uses microwave wavelengths to estimate the amount of water, called snow water equivalent, in the snow at specific locations. Interestingly, one scientist said that the ability to accurately retrieve snow water equivalent from AMSR-E is dependent on the surface temperature. This may be a type of project that could use student observations from the surface temperature field campaign.

Thirty schools and counting have participated thus far in the surface temperature field campaign. Thank you for all of your hard work.

Take care,

Dr. C