Chapter 16 Section 4Water in the Atmosphere

By: Trisha Kelley, Adam Cook, Chantelle Cross, Anthony Ciampa

Humidity

Humidity is the amount of water vapor in the air. The amount of water

vapor the air can hold depends on the temperature in the area. Hot air can hold more water vapor than cold air. At 10 degrees Celsius, one cubic meter of air can hold a maximum of 8 grams of water vapor.

Measuring Relative Humidity• To measure relative humidity you

would use an instrument called a Psychrometer. The Psychrometer measures relative humidity with 2 thermometers called a wet bulb thermometer and dry bulb thermometer. If the relative humidity is low then the water on the wet bulb will evaporate slowly, and the temperature for it won’t change much. But if the humidity is high then the water in the wet bulb system will evaporate very fast and the temperature on it will go down. The relative humidity is found by comparing the temperatures on the 2 thermometers on a relative humidity table.

The difference between humidity and relative humidity

The difference between humidity and relative humidity is, humidity measures how much water vapor is in the air, while relative humidity measures how much percentage of water vapor is in the air, compared to how much that specific area can hold.

How Clouds Form

• Clouds form whenever air is cooled to its dew point, particles are present, and when water vapor in the air becomes liquid water, or ice crystals, depending on if the dew point is below the freezing point, or above it.

The Tops of Mountains

• Why are some of the tops of some mountains always covered by clouds? The reason the tops of some mountains are always covered by clouds is because the wind is constantly hitting the mountain so the warm air rises then cools, thus creating the constant clouds over the mountain.

Measuring Relative Humidity

• The instrument that measures relative humidity is called a Psychrometer.

• A Psychrometer Uses 2 thermometers, one dry bulb thermometer and one wet bulb thermometer. The wet bulb thermometer has a wet cloth over it that is moistened with water so when air is blown over them the wet bulb thermometer reading drops below the dry bulb thermometer. So if relative humidity is high, then the water on the wet bulb thermometer wouldn’t change very much, but if relative humidity is low then the water in the wet bulb thermometer will evaporate rapidly. The relative humidity can be found by comparing the two readings to each other on a relative humidity chart.

Conditions needed for clouds to form

• The conditions needed for clouds to form are whenever air is cooled to it’s dew point and when particles are present.

The three main cloud types• The conditions needed for clouds to form are whenever air is cooled it it’s dew point and

particle are present.• 3. Describe each of the three main types of clouds. - The main cloud types are cumulus,

stratus and cirrus.• Cumulus- Cumulus clouds form less than 2 kilometers above the ground, But may grow in

size and height, as much as 18 kilometers. Cumulus clouds are a sign of fair weather.• Stratus- Status clouds cover all or most of the sky. As a stratus cloud thickens it may

produce rain, drizzle or snow and it is then called a nimbostratus cloud.• Cirrus- Cirrus clouds form only at high levels, above about 6 kilometers where temperatures

are very low. And as a result Cirrus clouds are made mostly out of ice crystals.

Classifying Clouds

Each type of cloud classified as their height level, such as high, medium, and low.

• Altocumulus-high level• Altostratus-medium level• Cirrostratus-high level• Cirrus-high level• Cumulus-low level• Fog-low level• Nimbostratus- medium level• Stratus-low level

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