The Science of Temperature and Humidity and Clouds

Imagine you have a big pot of water and you put it on the stove to heat up. As the water heats up, it starts to boil. When water boils, it turns into steam. Steam is a gas, and it rises into the air. The air in the sky is cooler than the air near the ground. So, when the steam rises into the sky, it cools down. As it cools down, it turns back into tiny water droplets. These water droplets are so small and light that they can float in the air. When these water droplets float together in the sky, they form a cloud.

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Background

Temperature is a measure of how hot or cold something is. It is typically measured in degrees Celsius (°C) or Fahrenheit (°F). Temperature is caused by the movement of atoms and molecules. The faster the atoms and molecules move, the higher the temperature.

Humidity is a measure of the amount of water vapor in the air. It is typically expressed as a percentage of the maximum amount of water vapor that the air can hold at a given temperature. Warmer air can hold more water vapor than colder air, so humidity is often higher in warmer regions. Relative humidity usually calculated using percentage (%). If the humidity is 100%, water vapor is likely to condense even at the same temperature. This is because at 100% humidity, the air is saturated with water vapor. This means that the air cannot hold any more water vapor at its current temperature.

Temperature, humidity, and dew point

Temperature and humidity are interrelated. When the temperature increases, the air can hold more water vapor, so the humidity decreases. Conversely, when the temperature decreases, the air can hold less water vapor, so the humidity increases.

Dew point is the temperature at which water vapor in the air condenses. The dew point is always lower than or equal to the air temperature. It is a measure of how humid the air is. The higher the dew point, the more humid the air is.

You can try to calculate the dew point using my dew point calculator.

For example, if you have a glass of cold water, you will notice that condensation forms on the outside of the glass. This is because the water vapor in the air is condensing on the cold surface of the glass. As the water vapor condenses, it releases heat, which warms the glass and the surrounding air. This makes the air around the glass more humid.

Using that dew point formula, we can predict that water vapor will likely condense on any cold surface below 27°C in Jakarta during the afternoon with the temperature and humidity of 36°C and 62%. Dew point at 27°C is considered to be “uncomfortable” because sweat is not likely to evaporate, making the natural cooling effect of our skin ineffective.

Humidity over 100%?

If humidity is over 100%, the air is supersaturated with water vapor. This means that there is more water vapor in the air than it can hold at its current temperature and pressure. This condition is unstable, and water vapor will quickly condense into liquid water droplets or ice crystals.

The most common way for water vapor to condense is on condensation nuclei, which are tiny particles suspended in the air. These particles can be dust, salt particles, or even pollen. In the absence of condensation nuclei, water vapor can remain in a supersaturated state for a short period of time.

When humidity is over 100%, the air will feel very muggy and uncomfortable. This is because sweat cannot evaporate from the skin as easily. This can lead to heat exhaustion and other health problems.

Supersaturated air can also be dangerous for aircraft. When air passes over the wings of an aircraft, it expands and cools. This can cause supersaturated air to form, which can then condense into ice crystals. This ice can build up on the wings and reduce lift, which can lead to a stall or crash.

Cloud and humidity

The air humidity around dense clouds is usually very high, close to 100%. This is because clouds are formed when water vapor in the air condenses into liquid water droplets or ice crystals. This process of condensation releases heat, which warms the air and allows it to hold more water vapor. As a result, the air around clouds is typically very saturated with water vapor.

In fact, the humidity around dense clouds can sometimes be even higher than 100%. This is because clouds can act as condensation nuclei themselves. When water vapor condenses on a cloud droplet, it releases even more heat, which further warms the air and allows it to hold even more water vapor. This can create a positive feedback loop, resulting in supersaturated air with a humidity of over 100%.

The positive feedback loop in cloud formation works as follows:

1. Water vapor in the air condenses on a cloud droplet, releasing heat.
2. The heat warms the air, allowing it to hold more water vapor.
3. More water vapor condenses on the cloud droplet, releasing more heat.
4. This process repeats itself, creating a positive feedback loop.

The positive feedback loop in cloud formation is broken as the cloud reaches its biggest formation and rain starts to fall. There are a few reasons for this:

• The cloud becomes too heavy to support itself. As the cloud grows larger and denser, it becomes heavier and heavier. Eventually, the weight of the cloud becomes too much for the rising air currents to support. At this point, the cloud begins to collapse and rain starts to fall.
• The cloud droplets become too large to remain suspended in the air. As more and more water vapor condenses on the cloud droplets, they become larger and larger. Eventually, the cloud droplets become so large that they can no longer remain suspended in the air. They then fall to the ground as rain.
• The cloud droplets collide and coalesce. As the cloud droplets fall to the ground, they collide with each other and coalesce into larger and larger droplets. This process continues until the droplets are large enough to fall to the ground as rain.

However, humidity is not the only factor that determines whether or not a cloud will form. Other factors, such as temperature and air pressure, also play a role. Additionally, dense clouds are not always associated with high humidity. For example, contrails, which are the clouds that form behind airplanes, are made up of ice crystals that have sublimated from water vapor in the exhaust of the airplane engines. The air around contrails is typically very dry, with a humidity of much less than 100%.

Overall, the air humidity around dense clouds is usually very high, close to 100%. However, there are other factors that can also affect cloud formation, and dense clouds are not always associated with high humidity.

Contrails and winglet trails

The humidity in the contrail and the area near the plane winglet is typically significantly different from the air surrounding the plane.

Contrails are formed when water vapor in the exhaust of airplane engines condenses into liquid water droplets or ice crystals. This process of condensation releases heat, which warms the air around the contrail and allows it to hold more water vapor. As a result, the air in the contrail and the area near the plane winglet is typically very saturated with water vapor, with a humidity close to 100%.

The air surrounding the plane, on the other hand, is not affected by the heat released from the airplane engines. As a result, the air surrounding the plane is typically much less humid than the air in the contrail and the area near the plane winglet.

The difference in humidity between the contrail and the surrounding air can be quite significant. For example, a study by the National Aeronautics and Space Administration (NASA) found that the humidity in the contrail can be up to 100% higher than the humidity in the surrounding air.

Summary

Here is a summary of what we have discussed:

• Humidity is the measure of the water vapor in the air. It is typically expressed as a percentage of the maximum amount of water vapor that the air can hold at a given temperature.
• Clouds are formed when water vapor in the air condenses into liquid water droplets or ice crystals. This process of condensation releases heat, which warms the air and allows it to hold more water vapor.
• The air around clouds is typically very humid, close to 100%. This is because the clouds are acting as condensation nuclei and the positive feedback loop in cloud formation.
• The humidity in the contrail and the area near the plane winglet is typically significantly different from the air surrounding the plane. This is because the water vapor in the exhaust of airplane engines condenses into liquid water droplets or ice crystals, releasing heat and warming the air in the contrail and the area near the plane winglet.
• Temperature and humidity are interrelated. When the temperature increases, the air can hold more water vapor, so the humidity decreases. Conversely, when the temperature decreases, the air can hold less water vapor, so the humidity increases.

References

• Dew Point Formula
• Recommended Relative Humidity