Cloud Formation

Formation of Clouds Clouds are formed when water vapour is cooled below the dew point during its upward movement. Dew point – the temperature at which water vapour is turned into water. The resulting moisture condenses into droplets on microscopic dust particles in the atmosphere.

Classification of Clouds There are three basic cloud types: Cirrus (Ice Crystals) Cumulus (Fluffy) Stratus (Wispy) Today’s classification has four main divisions: High clouds (6 100 – 12 200 m) Intermediate clouds (1 980 – 6 100 m) Low clouds (near ground level – 1 980 m) Clouds with vertical development (490 – 6 100 m)

High Clouds have the prefix of cirro Cirrus Cirrocumulus Cirrostratus Intermediate Clouds have the prefix of alto Altocumulus Altostratus Low Clouds have the prefix of strato Stratus Nimbostratus – continuous rain or snow Stratocumulus Clouds having Vertical Development Cumulus Cumulonimbus – produce rain showers, and light snow, hail, or thunderstorms

How Clouds Influence Climate Cloudiness – the proportion of the sky covered by any form of cloud Clouds have become an important focus in the study of global warming or cooling, including how the increase or decrease in cloud cover can effect the amount of radiation reflected from the earth back into space. Cirrus clouds reflect only a small percentage of the incoming radiation from the sun warming the earth. Low stratiform clouds reflect most of the radiation coming from the sun, causing a net cooling.

Humidity Humidity – the amount of water vapour in the air. Humidity indicates the likelihood of precipitation, dew, or fog. High humidity makes people feel hotter outside in the summer by preventing sweat from evaporating from the body. This effect is calculated in a heat index table.

Calculating Relative Humidity The amount of water vapor in the air at any given time is usually less than that required to saturate the air. Relative Humidity = (actual vapour density) x 100% (saturation vapour density) The most common units for vapor density are g/m3. For example, if the actual vapor density is 10 g/m3 at 23°C compared to the saturation vapor density at that temperature of 17.3 g/m3 , then the relative humidity is Calculation

Sample Problem 1 If the actual vapour density is 10 g/m3 at 22°C compared to the saturation vapour density at that temperature of 17.3 g/m3 , then the relative humidity is ...

Answer 57.8% When you use this percentage value and the given temperature along with your heat index you can estimate how hot it would actually feel outside.