Atmospheric Moisture Humidity Earth Science Mr Cloud Absolute

Atmospheric Moisture: Humidity Earth Science Mr. Cloud

Absolute v. Relative Humidity • Absolute Humidity: the actual amount of water vapor in the air • i. e. 25 g/ml • **Relative Humidity: Is the ratio of the amount of water vapor in the air to the maximum amount it can hold. • Expressed as a percent

How do we measure Relative Humidity? • The ‘tool’ or ‘instrument’ that measures relative humidity is called a psychrometer Sling Psychrometer

Anatomy of a Sling Psychrometer • Dry-bulb: the dry-bulb is an ordinary • • • thermometer that reads the actual temperature of the air Wet-bulb: the wet-bulb contains a wick around its bulb Wet-Bulb Depression: the difference between the wet and dry bulb temperatures Let’s figure out the relative humidity of the classroom!

Finding Relative Humidity • The wick is wet and the instrument is then whirled in the air • The temperature of the wet-bulb drops due to the cooling effect of evaporation • To find the relative humidity we must find the difference between the wet and drybulb temperatures, then go to the chart!!!

Dew Point • The temperature at which the air is filled with water vapor • If the air temperature drops below the Dew Point, water vapor in the air will condense to liquid water or sublimate to a solid • The amount of water vapor in the air directly affects the dew point.

Cloud Formation • In order for a cloud to form, air must rise. • As air rises, it cools. • When temperature decreases, the air’s capacity to hold water vapor decreases • The air reaches the dew point, causing water vapor to condense, forming a cloud.

Types of Clouds

Cumulus Clouds

Altocumulus Clouds

Cumulonimbus Clouds

Stratus Clouds

Cirrus Clouds

Determining Cloud Base Altitude • Goals: • 1. Determine the dry bulb and wet bulb temperatures of the air outside. • 2. As a group, determine dew point temperature and cloud base altitude. • 3. Formulate the step-by-step process of determining cloud base altitude.