6.2: Ocean-Atmosphere Interaction

How Water Influences the Climate

From water vapor in the air, let's now discuss the role of liquid water on the Earth. As we know, nearly 71% of the Earth's surface is covered by water. Our oceans are considered to be a tremendous reservoir of heat. Ocean currents distribute heat across the planet from areas of abundant sunlight and high heat (the equator) to areas of little sunlight and low heat (the poles). Ocean currents also play a crucial role in moderating the temperature of neighboring landmasses. Both of these topics were briefly covered in Investigation 1, but let's investigate them further. Figure \(\PageIndex{1}\) is a map of global ocean currents, with arrows showing the direction of motion and warm, blue, and black arrows showing warm, cold, and neutral currents. Based on this information, let's answer the following questions.

Figure \(\PageIndex{1}\): A map of global ocean currents. (Public Domain; Dr. Michael Pidwirny via Wikimedia Commons) Alternative description of the image.

11. Cold ocean currents, such as the California and Canary currents, carry cold water from:
    1. Tropical latitudes
    2. Polar latitudes
    3. both latitudes

12. Meanwhile, warm ocean currents, such as the Gulf Stream and the Kuroshio currents, carry warm water from:
    1. Tropical latitudes
    2. Polar latitudes
    3. both latitudes

Let’s focus on the United States to examine how these ocean currents impact our climate. Figure \(\PageIndex{2}\) shows the average monthly high temperatures for San Francisco, California, and Richmond, Virginia. Both cities are at 37.5°N, so they receive the same amount of sunlight. However, San Francisco is on the U.S. West Coast, near the cold California Current, while Richmond is on the East Coast, near the warm Gulf Stream.

Figure \(\PageIndex{2}\): Average Monthly Temperatures for San Francisco, CA, in blue and Richmond, VA, in orange. (CC-BY-NC 4.0; Alicia Mullens) Alternative description of the image.

13. Richmond, VA, next to the warm Gulf Stream, has __________ temperatures for most of the year (from approximately March to October), compared to San Francisco.
    1. much colder
    2. much warmer
    3. about the same

14. This is ______ due to the heat provided by the Gulf Stream to Richmond, VA.:
    1. Tropical latitudes
    2. Polar latitudes
    3. both latitudes

Specific Heat

While this holds true for Spring/Summer/Fall months, you'll notice that in late Fall and Winter, the relationship between San Francisco and Richmond is different. Let's investigate why that is. Imagine a warm, sunny day on the beach. You decide to get up from your beach towel and walk towards the ocean water. As you do so, you have to walk through brutally hot sand, but when you get to the water, you notice it’s much cooler. If you stayed at the beach all day and into the evening, you’d notice the opposite… the sand is cold at night while the ocean water is fairly warm. The reason for this is specific heat, which is the amount of heat required to raise the temperature of 1 kilogram of an object by 1°C. Table 3 presents sensible heat values for various surface cover types on Earth.

Table \(\PageIndex{1}\): Specific heat capacity of various surfaces.

Object	Specific Heat (J/kg°C)
Water	4182
Soil (wet, avg)	1480
Soil (dry, avg)	800
Concrete	880

15. Table \(\PageIndex{1}\) suggests that, for 1 kg of water to warm by 1 °C, it would need to absorb 4182 Joules of heat. This amount of heat is ______ the amount needed to warm soil and concrete.
    1. about the same as
    2. larger than
    3. smaller than

Let’s further examine the effects of this heat. Suppose we have 1 kg of liquid water and 1 kg of dry soil, both at 20°C. Suppose we now add 10,000 Joules of heat to both the liquid water and the dry soil (each receives 10,000 joules of heat). We could calculate their new temperature using the following formula:

New Temperature = 20°C + (10000 ÷ Specific Heat).

For e.g., (for wet soil) New Temperature = 20°C + (10000/1480)

= 20°C + 6.76°C = 26.76°C

16. Let's do the same for water. Adding 10,000 Joules of heat to 1 kg of water at 20°C will result in a new water temperature of:
    1. 22.39°C
    2. 17.61°C
    3. 32.5°C
    4. 07.5°C

17. On the other hand, adding 10,000 Joules of heat to 1 kg of dry soil at 20°C will result in a new dry soil temperature of:
    1. 22.39°C
    2. 17.61°C
    3. 32.5°C
    4. 07.5°C

In summary, water warms more slowly than land does because of water’s specific heat. The opposite is true: water cools much more slowly than land. So during the warm months of the year, inland locations become significantly warmer than areas near the ocean. Let’s illustrate this by comparing Long Beach, California (near the ocean), to Dallas, Texas (far inland), as shown in Figure \(\PageIndex{3}\).

Figure \(\PageIndex{3}\): Average Monthly Temperature for Long Beach, CA, in blue and Dallas, TX, in orange. (CC-BY-NC 4.0; Alicia Mullens) Alternative description of the image.

18. Dallas, which is much further inland than Long Beach, has a _______ yearly temperature range (difference between winter cold and summer warm) than Long Beach.
    1. much smaller
    2. much larger
    3. about the same

19. This ________ that cities closer to the ocean experience lower seasonal temperature variations than inland locations.
    1. confirms
    2. cannot confirm

So how does this relate to San Francisco vs. Richmond in Figure \(\PageIndex{2}\)? During winter, the prevailing wind at latitude 37.5°N blows from West-to-East. The Pacific Ocean is to the west of San Francisco, meaning that the wind blows over the Pacific Ocean before reaching San Francisco. Thus, San Francisco doesn’t get very cold in the winter months because the Pacific Ocean moderates temperatures.

20. Meanwhile, Richmond is on the East Coast of the United States, meaning that prevailing winds coming from the west are coming from over ______.
    1. land
    2. ocean

21. Therefore, although next to a warm body of water, Richmond’s winter temperatures are mostly influenced by the ________ air coming from the west. (hint: How was Dallas’ winter temperature compared to Long Beach)?
    1. warm
    2. cold

During summer, the jet stream (which drives the prevailing west-to-east winds) moves northward. This weakens the influence of cool continental air over Richmond and allows for more south- and southwesterly winds. These bring in warm, humid air from the Atlantic Ocean and the Gulf Stream, resulting in warmer and more humid summers.