Introduction: The Sky and Ocean are Connected!
Hello everyone! In this chapter, we will learn about the "Atmosphere" above our heads and the "Ocean," which covers about 70% of the Earth's surface. You've likely heard terms like "low pressure" or "cold fronts" in weather forecasts, or "global warming" in the news—these are all topics very relevant to our daily lives.
It might feel a bit overwhelming at first with all the new terminology, but don't worry! Every phenomenon has a clear "reason" behind it. Once you understand the mechanism, Earth science becomes as fun as solving a puzzle. Let's master it together!
1. Structure of the Atmosphere: Dividing the Sky into Layers
Because temperature changes differently depending on altitude, the Earth's atmosphere is divided into four layers. Let's look at them from the bottom up.
① Troposphere (Ground level to approx. 11km)
This is where we live. The temperature drops as you go higher (about 0.65°C per 100m).
Key Point: Because the air is constantly being mixed (convection), this is where meteorological phenomena like cloud formation and rain occur.
② Stratosphere (Approx. 11km to 50km)
The layer just above the troposphere. It contains the ozone layer, which absorbs harmful ultraviolet radiation from the sun. Because of this, the temperature actually increases as you go higher here.
Trivia: Airplanes fly in the lower part of this layer to enjoy a smooth, stable flight.
③ Mesosphere (Approx. 50km to 80km)
The temperature drops again as you go higher. The coldest spot in the atmosphere (around -90°C) is found at the top of this layer.
④ Thermosphere (Above 80km)
Because it receives direct sunlight, the temperature becomes extremely high as you go up. This is also the layer where auroras occur.
【Study Tip】
Remember the sequence: "Convection (clouds form) → Ozone (stratosphere) → Middle (mesosphere) → Heat (thermosphere)." Try to visualize a graph where the temperature change forms a reverse "く" (ku) shape!
2. Solar Radiation and Earth's Heat Balance
The reason the Earth isn't too hot or too cold is that there is a perfect balance between the heat received from the sun and the heat the Earth releases back into space.
Solar Radiation and Terrestrial Radiation
Energy coming from the sun is called solar radiation, and the heat released by the Earth is called terrestrial radiation.
Solar radiation consists mainly of "visible light," while terrestrial radiation consists of "infrared rays."
Greenhouse Effect
This is the mechanism where gases like carbon dioxide (\(CO_2\)) and water vapor (\(H_2O\)) in the atmosphere absorb the heat (infrared) the Earth tries to escape and radiate it back to the surface.
Analogy: It’s like the Earth is wearing a "blanket." Thanks to this blanket, the Earth's average temperature stays at about 15°C. If there were no greenhouse effect, the Earth would be an icy world at -18°C!
【Common Misconception】
It's easy to think "Greenhouse gases are the bad guys!" but if they didn't exist at all, we would freeze. The real problem is "the excessive increase, leading to global warming."
3. Atmospheric Circulation: Why does the wind blow?
Since the Earth is spherical, the equator receives a lot of solar heat, while the polar regions (North and South Poles) receive very little. The general circulation of the atmosphere occurs as air moves to even out this "temperature difference."
Three Cells (Circulation)
- Hadley Cell: Air warmed at the equator rises and descends around 30 degrees latitude. Near the equator, this creates the Intertropical Convergence Zone (where squalls are frequent).
- Ferrell Cell: Circulation in the mid-latitudes (near Japan).
- Polar Cell: Circulation caused by cold air in the polar regions.
Coriolis Force (Watch the direction!)
An apparent force acting on moving objects due to the Earth's rotation.
In the Northern Hemisphere, the force acts to the right of the direction of travel.
Analogy: It’s the same as trying to throw a ball straight while on a spinning merry-go-round—the ball will seem to curve sideways.
Winds flowing over Japan
Above Japan, the westerlies blow from west to east. When a weather forecast says "the weather will turn for the worse from the west," it's because clouds are riding these winds toward us.
4. Structure and Flow of the Ocean
Just like the atmosphere, the ocean has different temperatures and currents depending on the region.
Layered Structure of Seawater
Looking at the ocean by depth, it is mainly divided into three layers:
1. Mixed layer: A shallow layer stirred by waves and wind, where the temperature is uniform.
2. Thermocline: A layer where the water temperature drops rapidly with depth. This acts like a "barrier" that prevents the mixing of water between the layers above and below.
3. Deep layer: A layer where light doesn't reach, holding very cold water at about 1–3°C.
Ocean Currents (Rivers in the Ocean)
The surface circulation that flows near the sea surface is mainly generated by the "wind."
Ocean currents around Japan:
・Kuroshio (Japan Current): A warm current coming from low latitudes. It has a deep, dark blue color (hence "Kuro" or black).
・Oyashio (Oyashio Current): A cold current coming from high latitudes. It is rich in nutrients and is a great fishing ground.
【Key Point】
Warm currents come from warm regions, and cold currents come from cold regions. It sounds obvious, but on tests, people often get confused about which direction they flow from!
Summary: Important Points of this Chapter
・Atmospheric Layers: Troposphere, Stratosphere (Ozone layer), Mesosphere, Thermosphere.
・Heat Balance: The balance between solar radiation (visible light) and terrestrial radiation (infrared). The greenhouse effect is crucial.
・Atmospheric Circulation: The mechanism that transports heat from the equator. The westerlies blow above Japan.
・Coriolis Force: Objects curve to the right in the Northern Hemisphere.
・Ocean: A three-layer structure consisting of the surface mixed layer, the rapidly cooling thermocline, and the cold deep layer.
Great work! The atmosphere and ocean work together, exchanging heat and moisture to create the Earth's environment. If you keep this connection in mind, your understanding will deepen naturally without just memorizing everything.
Next, we'll dive into the specific "weather" changes caused by these movements!