2.5: Seasons and Latitude

Latitude

One of the most significant factors affecting a location’s climate is the location’s latitude – the distance from the equator (the equator represents a latitude of 0° and the poles are 90°N for the North Pole, and 90°S for the South Pole). Figure \(\PageIndex{1}\) displays lines of latitude on Earth for the Northern Hemisphere.

Figure \(\PageIndex{1}\): Lines of Latitude. (Public Domain; Wikimedia Commons). Alternative description of the image.

We’ll cover latitude more in depth when we investigate the Earth’s coordinate system in a future investigation. For now, just know that the further away you get from the equator, the larger your latitude is. The key impact that latitude has on climate is its effect on the angle of incoming sunlight, or the Angle of Insolation. To demonstrate the importance of the angle of insolation, do the following experiment: 

Using a flashlight and in a dark room, hold the flashlight so that the light is directly over the ground, as shown in Figure \(\PageIndex{2}\). Then, tilt the flashlight so it is low on the horizon, as shown in Figure (\(\PageIndex{3}\)). 

Figure \(\PageIndex{2}\): Flashlight directly over the surface. (CC BY 4.0; Alicia Mullens)

 

Figure \(\PageIndex{3}\): Flashlight lower on the horizon. (CC BY 4.0; Alicia Mullens)

14. When the flashlight is shining directly above the surface (Figure 2.5.2), the area illuminated on the surface is:
    1. a small, bright circle
    2. a large, dim area
15. When you lower the flashlight on the horizon (Figure 2.5.3). The area illuminated on the surface becomes:
    1. smaller and brighter
    2. larger and dimmer
    3. it doesn’t change

We can apply these conclusions to sunlight and how its intensity changes throughout the day. Specifically, when the sun is high in the sky, the incoming sunlight is more intense, whereas when the sun is low on the horizon, it is less intense. Now, let’s take a look at how this would relate to latitude. There are a few things to note here. If the Earth were NOT tilted, the sun would be directly overhead year-round, and the overall set-up of incoming sunlight would appear as shown in Figure \(\PageIndex{3}\).

Figure \(\PageIndex{4}\): Sunlight over the Equator (low latitude) vs. Sunlight near the poles (high latitude). The Sun is directly over the Equator. (CC BY 4.0; Alicia Mullens). Alternative description of image. 

16. Based on Figure 2.5.4, a beam of sunlight covers a _______ area over higher latitudes than near the Equator. 
    1. smaller
    2. larger
17. As a result, sunlight at higher latitudes would be ______ than near the Equator (hint: if the beam covers a smaller area, it is more concentrated; if it covers a larger area, it is more diluted). 
    1. more intense
    2. less intense

This can be further reinforced by checking how average air temperatures vary with latitude worldwide. A map of global average air temperatures is shown in Figure \(\PageIndex{5}\). Warmer temperatures are shown in red, while cooler temperatures are shown in blue.

Figure \(\PageIndex{5}\): Global annual average air temperatures. (CC-BY-SA 3.0; Wikimedia Commons). Alternative description of image.

18. While there is some variation caused by other factors (such as elevation, and ocean currents), the warmest temperatures are generally near the ______ while the coldest temperatures are usually near the ________.
    1. poles; equator
    2. equator; poles

Earth’s orbit.

However, our Earth IS tilted. In fact, it is tilted at an Angle of 23.5°. The result of this is that as the Earth orbits around the sun (Figure \(\PageIndex{6}\)), the latitude at which the sun is directly overhead changes. Figure \(\PageIndex{7}\) represents the conditions in June, when the sun is directly over 23.5°N, while Figure \(\PageIndex{8}\) represents the conditions in December, when the sun is directly over 23.5°S.

Figure \(\PageIndex{6}\): Earth's orbit around the sun and corresponding northern hemisphere seasons. (Public Domain; Wikimedia Commons). Alternative description of the image.

Figure \(\PageIndex{7}\): Conditions in June. (CC BY 4.0; Alicia Mullens). Alternative description of the image. 

Figure \(\PageIndex{8}\): Conditions in December. (CC BY 4.0; Alicia Mullens). Alternative description of the image.

19. Investigate the North Pole in Figure \(\PageIndex{7}\). Notice that it is completely covered with sunlight. Now imagine the Earth completing one 24-hour rotation around its axis. In June, the North Pole would never:
    1. experience any sunlight
    2. experience any darkness
20. Now let’s investigate Figure \(\PageIndex{8}\), which represents conditions in December. In December, the sun is directly over:
    1. The Equator
    2. 23.5°N
    3. 23.5°S