Geography 110H - Fall 1998
Third assignment - for Thursday, Sept. 24

In order to understand the behavior of the atmosphere and oceans and the global pattern of climates, we need first to have some basic understanding of the earth's radiation balance. The components of the radiation balance are discussed in chapter 4 of the textbook. Also discussed are the various processes that may transport energy from one part of the system to another. The global radiation balance not only controls the spatial pattern and annual cycle of temperatures; it also drives the motions of the atmosphere and ocean currents and plays a critical role in the distribution of moisture and precipitation and of storm activity. This week we will take a closer look at aspects of the radiation balance and at patterns of global temperature.

I recommend doing at least the first part of the assignment on Tuesday in class, so that you can discuss what you see and make notes based on that discussion.

It will help you to have read chapters 4 and 5 in Christopherson before proceeding.

1.    In order to understand the relationship among the components of the daily radiation balance, consult the web site of the SURFRAD (surface radiation) network, which provides detailed field measurements of each component at five locations from different climatic regions of the U.S. Start by reading the "General information" pages, a set of four pages that explains where the information comes from. Next read the "Site information" pages in order to see the actual locations. After that, go to the "Data Display" page and do the following:

• select a location and a date (if you don't enter a date, you will get data for the most recent day)
• select "direct solar" and "diffuse solar" and plot them together for each location you decide to examine. Note the daily cycle. The sum of these two should be equal to the total downwelling solar, but if you add this as a third curve you will notice that sometimes the direct solar actually plots as being higher than total downwelling solar, particularly at the sites that are drier and have more direct sunlight.These three components are actually measured by different instruments, and therefore the discrepancy may be due to instrument error; I'm not really sure.
• now go back to "data display" and select "downwelling solar" and "upwelling solar" (upwelling solar presumably is reflected shortwave radiation). If you plot these together with "net solar" you wil note that "net solar" is the difference between what comes down from the sky and what is reflected from the surface. At least it should be.
• again go back to "data display" and select "downwelling infrared", "upwelling infrared", and "net infrared"; when you plot these together, you should see that net IR = downwelling-upwelling.
• now plot "solar net radiation", "infrared net radiation", and "total net radiation"; since the infrared net radiation is generally upward and therefore negative, total net radiation is the sum of solar net radiation and infrared net radiation.
• take a short break and review pages 101-105 in the textbook in order to see how "net radiation" is defined there and how the energy represented by net radiation is allocated or expended. Note also the patterns in figures 4-18 through 4-20.
• finally, go back to "data display" and plot air temperature for the same location and date where you were working before. Look at the daily cycle of air temperature and try to relate it to the daily cycle of net radiation, focusing particularly on the timing of maximum and minimum temperature. (Because temperature and radiation have different units, you can't plot them on the same graph, so you may want to print copies of this plot and the previous plot in order to look at them together.) How would you expect these two curves to be related?  Try making this comparison for 6/26/98 at Desert Rock, Nevada. After looking at the discussion on p.102 and figures 4-18 through 4-20, would you expect the relationship between the pattern of net radiation and the pattern of daily temperature to be the same in a humid area as it is in a desert? Why or why not?
  
  Write a paragraph summarizing your answers to the questions above. To the extent that your conclusions benefit from discussion in class, so much the better.
  
  [One caveat: the graphs shown at this site all have the same time base; rather than local time, it uses UTC, equivalent to Greenwich Mean Time. The major drawback is that you are not seeing a complete daily cycle. Instead the graph begins with the tail end of the previous day, then shows the nighttime portion of the cycle, and then the daytime portion of the current day, but only up through late afternoon. If you want to see the rest you have to look at the next day's graph. However for days with relatively stable conditions and sunny weather, this will make less of a difference.] 

2.  Call up the "Wxwise ERBE" Web site. This is a site at the University of Wisconsin at Madison that contains an article discussing the earth's radiation balance. Read the article and look at the images showing global distributions of monthly mean net radiation.  View the animated loop showing the annual cycle. (If you can't get the loop to show up as an animation, then look at several individual months spaced over the year.) How is the pattern you see related to the exercise you did last week on seasonal patterns of length of daylight at different latitudes? Also note the comparison between continents and oceans; can you explain the major differences shown?

Next go to the "SSEC Sea Surface Temperatures" Web site and go to "Latest SST".  This is a beautiful color image showing the global distribution of sea-surface temperature. It is updated daily. There is an archive containing daily images for the last two weeks, but unfortunately this site doesn't retain images for long enough to compare patterns showing seasonal changes. Another site sponsored by NOAA does contain monthly SST images for the period between 1984 and 1996. Look here in order to see whether you can pick up any significant changes between images taken a few months apart.  How do they relate to the patterns you observed in the annual cycle of the net radiation balance? (This is a slow site; if the images take too long to load, don't worry about it.) Another, faster site with monthly SST images based on long-term average conditions is NOAA's "Live access to climate data."  Note in particular that although temperature varies mostly with latitude, there are significant anomalies that clearly are affected by factors other than latitude. Identify one or two such anomalies. What do you think might explain them?

You can also try another NOAA site with an animation showing the seasonal cycle of sea-surface temperatures. Or you might also try looking at the animated view of sea-surface temperatures for the North Atlantic. This will show you the seasonal cycle of changing temperatures over a span of about 1.5 years. You can get a fascinating view of how temperatures reflect not only seasonal cycles of the global radiation balance, but also the dynamics of the ocean surface itself. An even better view of the same phenomenon is available in the Ocean Surface Temperature Movie from NASA. Does this help in answering the question at the end of the preceding paragraph?

3. Next we are going to focus on changing patterns of temperature over time and space by looking at records from individual stations. Before visiting the next Web site, do the following:

Pick a latitude for comparative study. Locate at least one continental and one maritime location at or close to the same latitude. If you're ambitious you might choose one west-coast location and one east-coast location as well as a continental interior location. This does not have to be limited to sites in the U.S.; there are both U.S. and global data sets available.

You may also choose a pair of stations at different latitudes but comparable maritime or continental interior locations, if you so desire.

Visit the Web site entitled "NCDC Climate Visualization". Under the heading CLIMVIS Graphics Choices, you will see options for both National Weather Service Summary of the Day and Global Summary of the Day. Pick whichever one is appropriate. You have the choice of plotting a time series or a contour map. Start with a time series option. Select the option that allows you to plot one parameter for a month from two separate stations in the same region or in separate regions. Pick your stations and plot both stations together on the same graph for a summer month and a winter month. (For the summer month pick either mean or maximum daily temperature; for the winter month pick either mean or minimum daily temperature.) Comment on any patterns that strike you as interesting or noteworthy. (For example, I tried doing this with Anchorage and Fairbanks, both in Alaska, using the minimum temperature for February 1997. The results are shown below. I also tried comparing Asahikawa, Japan with Zamin Ude, Mongolia. Those results are not shown here; you can look them up for yourself if you wish.)

Afterwards, go back and try a different graph type: "display the period of record for one parameter at one station" (only works for U.S. stations) or "display one parameter for a specified time frame" (up to one year; works for U.S. and global data sets). You can use this to plot temporal variations in maximum, mean, or minimum temperatures to show seasonal cycles. In the case of the U.S. data set you can also see multiple years laid out in sequence and get a real feel for year-to-year variation in temperature patterns. Do this for at least two stations, preferably the ones you have already been looking at.  (Here's an example: I compared maximum daily temperature at Phoenix and Flagstaff, Arizona for the period January-December 1995. If you want to make this kind of comparison for non-U.S. stations, you need to choose the "Global Historical Climatological Network Data" option.)

You can also make contour plots illustrating spatial patterns of climatic variables across the U.S. for specified dates. You might want to try experimenting with this as the contour plots may help to understand the relationship between the temperature trends at the two stations you picked earlier (only works if they are both continental U.S. stations. This is not required.)

Write up some general comments on how the observed patterns do or don't conform to what you would expect based on the book's discussion of factors affecting both seasonal patterns and spatial patterns of global temperature.