Brazil vs American mid-West

The circle of interior Brazil is centered over the equator. The entire area within the circle is shown in the bright orange color. The legend shows this color is the warmer half of a range from 15.5 to 30.5 degrees C. We do not know where the break is between the light orange and the bright orange. It may be half way but we cannot be certain of this.

For this discussion let us use the value of 25 degrees C as the temperature of the bright orange. This is equivalent to 77 degrees F. Of course the temperature within the circle may be less than this or more than this. And, it probably varies from place to place within the circle. But, for this discussion let us assume it is 25 degrees C plus or minus a few degrees.

What you should see is that the colors within the circles over Brazil in January and July are the same. This brings us back to the point that there is little variation in temperature along the equator from month to month throughout the year.

When does it get cold along the equator? When the Sun goes down. It does cool down at night.

In equatorial areas the average difference in temperature between day and night is greater than the difference in temperature between the warmest and coolest months.

Remember elevation? There are a few places at high elevation along the equator where it is cold simply because it is so high. But, even in these high places there is little variation in temperature from month to month.

Now let us look at the circles for the American mid-west. This circle is positioned so that it extends from Missouri on the south to Minnesota on the north and from Illinois on the east to Iowa on the west. It overlaps into other states too. This circle is centered at about 40 degrees north latitude and is distinctly in the middle latitudes.

The circle on the July map looks very much like the circles in Brazil. This indicates that the temperature in the mid-west in July is basically the same as that of equatorial Brazil. At the north edge of the circle over the mid-west there is a small patch of the lighter orange. This shows that the northern part of the mid-west is slightly cooler than further south. Most people should not be surprised that on the average northern Minnesota is slightly cooler in summer than southern Missouri.

The middle latitudes may be as hot in summer as equatorial areas. Why not? Remember in our summer we get more hours of daylight than places along the equator and the Sun at noon is as high or higher than it is at the same time along the equator.

But where we differ from Brazil is in winter. Look at the mid-west circle on the January map. Here there is a gradation of color from the light yellow in the south to the light gray in the north.

The legend shows these colors indicate a range of temperature from warmer than 0 degrees C in the southern part of the circle to colder than -15 degree C in the northern part. This would be equivalent to warmer than 32 degrees F to colder than 5 degrees F.

We will take -8 degrees C (about 18 degrees F) as the average within the circle for the American mid-west in January.

What is the average range in temperature in the mid-west between January and July? 25 - (-8) = 33 degrees C

A range of 33 degrees C is equivalent to about a 59 degree F range between the average temperatures in January and July.

How good are these interpretations from the map? Let us look at some numbers from Appendix K from our text, on pages A-17 to A-20. The numbers are in degrees F.

Manaus, Brazil, is in the center of the circled area in Brazil. It is listed as having January and July temperatures of 82 degrees F. So, for equatorial Brazil, 28 degrees C might have been a better estimation.

St. Louis, Missouri, near the southern part of the circle in the mid-west has January and July values of 32 and 78 degrees F respectively.

Fargo, North Dakota, at the northern end of the circle in the mid-west has January and July values of 7 and 71 degrees F respectively.

Based on our interpretation of the map we computed an average range in temperature within the mid-west circle as 59 degrees F (33 degrees C)

Based on the statistics in the text, St. Louis has a 46 degree F average range and Fargo has a 64 degree average range.

Not bad. This should give us confidence to make more interpretations from these maps.

One more thing. Remember than great variation in temperature in the mid-west in January, from above 0 degrees C in the south to below -15 degrees C in the north. We call this a temperature gradient -- the change in temperature over distance. Such temperature gradients are common in the middle latitudes in winter. We will see that such gradients are responsible for creating the winds and storms of the middle latitudes.