20.7 High-Low, Combination, and Log Plots

Please click here for Climograph and Biome Activity

Activity 20.7.1 – High-Low graphs (Stock):  Plotting means and ranges of data

Researchers often want to plot a range of data, rather than individual points.  For this, the hi-low graph is often appropriate.  Stock market analysts are familiar with this type of graph because companies report the high, low, and closing values for stocks each day, month, or year. Scientists often report data in a similar manner.  Figure 20.24 shows the average high, low, and daily temperature for New York City.   The top of each line represents the average monthly high, the bottom represents the average monthly low, and the dot represents the monthly average.   

(1) How does a continental climate differ from a maritime climate?  Denver  (39ºN, 105ºW) and San Francisco (37ºN, 122ºW) are situated at approximately the same latitude, but San Francisco is near the ocean, while Denver is land-locked.  San Francisco is in a maritime environment, sitting on a peninsula with the Pacific Ocean on one side, and San Francisco Bay on the other.  Denver is in a continental environment, close to the center of the continent and far from large bodies of water (figure 20.24C).  Climatologists say that San Francisco has an equable climate, meaning that there is little daily, seasonal, or yearly variation in temperature. By contrast, they characterize Denver’s climate as continental, with substantial changes in seasonal temperature.  Create high-low graphs of the temperature profiles for both of these cities.  Do your graphs support the climatologists' characterization?  Explain.  Note:  make certain both graphs use the same scale.

Activity 20.7.2 – Combination graphs: Graphing two types of data on one chart

It is often helpful to plot two different types of data on the same graph.  For example, a climograph (figure 20.24F) is a single graph that charts both the average temperature and precipitation for a given locale throughout the course of the year, using separate axes for each variable.  As shown in figure 20.24F, the line graph represents temperature, while the bar chart represents precipitation.  The horizontal axis represents the months of the year. The climograph not only shows average temperatures for each month, but also illustrates seasonal variations in temperature over the course of the year.  Likewise, the climograph reveals monthly precipitation and seasonal variations in precipitation. Combination graphs, like the climograph, must have the same independent variable (x-axis), but can have different dependent variables (y-axes).  Note that the axis on the left is precipitation, measured in millimeters of rainfall, while the axis on the right is temperature, measured in degrees Celsius. 

(1) Analyzing climates with climographs. Compare the climographs for Quito’s, Peru, and Barrow, Alaska.  The graphs look very different with respect to temperature and rainfall, indicating that these are very different climates.  The temperature graph for Iquitos is linear and flat, indicating little or no variation in temperature during the course of the year.   By contrast, the temperature graph for Barrow appears like a sine wave, with a maximum in June, July and August, and a minimum in December, January and February.  From this we can conclude that Barrow is in the northern hemisphere (a city in the southern hemisphere would have maximum temperatures during December, January and February).  Although the summer months are much warmer than the winter months in Barrow, they are still very cool, indicating that this city must be located very far north.  Indeed, Barrow is on the northern coast of Alaska (Figure 20.24C). The climate in Barrow is cold and dry.  It is so cold, however, that water rarely evaporates from the soil, leaving the soils wet and often frozen, a characteristic of arctic tundra.  By contrast, the climate in Iquitos is warm and wet, indicating it will support a large amount of vegetation, and indeed it is found in the tropical rainforests of Peru. Analyze the climographs in figure 20.25 to answer the following questions. 

(a)   Which city has the most equable (constant) climate?  Explain.

(b)  Which city has what most people would consider the most comfortable climate?

(c)   Chicago and New York have approximately the same climographs, except that Chicago’s winter is colder.  Why might this be?

(d)  Which of these cities is located in a hot desert?

(e)   Which city is in the Southern Hemisphere?

(f)   Which of these cities is located in tropical rainforest?

(g)  Which of two of these cities have a Mediterranean climate, characterized by mild winters and warm, dry summers?

(h)  Which city would experience monsoon type rains (heavy, summer rains)?

(i)    Which city has the coldest, driest summers?

(j)    Which of the following cities has the most annual rainfall, Chicago, New York, Dallas, or Miami?

(k)  Which of the following has more summer rainfall, Denver, Los Angeles, or Seattle?

(l)    Which city has a climate most similar to Chicago?

(m) Which of the following cities would be best suited for outdoor ice skating rinks: Chicago, New York, Dallas or Miami?

(n)  Which has more winter rainfall, Mangalore, India, or Seattle, Washington?

(o)  Which city has two “wet” seasons?

(2) Biome/Climograph posters - Perform an Internet image search to find photographs of the biome in which each city is located.  Make posters for the bulletin board that include photos of the natural vegetation of the biome, correlated with climographs and written descriptions (figure 20.26).

(3) Create a climograph for a city close to you.  Collect average rainfall and temperature data for a city near you using an online almanac, NOAA (National Oceanic and Atmospheric Administration) website, or similar resource [sciencesourcebook.com, worldclimate.com, www.noaa.gov or search world climate].  Plot monthly precipitation using columns and monthly temperature using a line graph.  Alternatively, you can use the data for Dallas, TX shown in figure 20.24E.  Describe the climate you have plotted.

(4) How does species diversity and biomass change with elevation?  Figure 20.27A contains hypothetical data one might find in the mountains of the western United States.  Species diversity is measured as the average number of animal and plant species found within a one-hectare (10,000 square-meter) plot of land.   Average biomass refers to the average mass of all of the organisms in the same plot.  Generate a combination graph that plots species diversity on the left axis, and biomass on the right axis.  Your graph should look like figure 20.27B

Activity 20.7.3 – Semi-logarithmic plots: Plotting wide range data

Some data is difficult to plot because of an extremely wide data range.  Figure 20.28[i] shows such data for the distribution of earthquakes by magnitude.  Note that in an average year, there are more than 100,000 earthquakes worldwide between magnitude 3 and 4, and only 2 greater than magnitude 8.  If the data is plotted on a simple linear scale (figure 20.28A), the number of larger earthquakes is virtually invisible because the number of small earthquakes dwarfs it.  Even though massive earthquakes are much more important, they do not appear due to the scale of the graph. If, however, the data is plotted on a semi-logarithmic graph (figure 20.28B) one can clearly read the number of earthquakes of any magnitude.  The graph is referred to as a semi-logarithmic (semi-log) plot because the y-axis is logarithmic, while the x-axis is linear.  A logarithmic scale is constructed so that the data is plotted in powers of ten to yield a maximum range while maintaining resolution at the low end of the scale. Semi-logarithmic plots are also useful when demonstrating exponential relationships.  Figure 20.29 shows the growth of a colony of bacteria as a function of time, where t represents the time interval, and Pt represents the size of the population at that any given time, t.  When the data is plotted on a standard linear scale, a curve is drawn as shown in figure 20.29A. This is a classic exponential growth curve.  If the data is plotted on a semi-logarithmic graph (figure 20.29B), it plots as a straight line.  Straight lines on semi-log plots indicate an exponential relationship.  In this case the relationship is: