Humidity and Rainfall

Humidity and Rainfall

• Water vapour is formed through evaporation when water is heated intensely.
• Moisture in the atmosphere plays a crucial role in the formation of clouds, rain, snow, hail, sleet, and more.

Humidity

• Humidity is the amount of water vapour or moisture in the air.
• The more water vapour in the air, the greater the humidity.
• Humidity varies greatly from place to place, with deserts having almost zero water vapour and coastal areas and rainforests having up to 4% of the total volume of air.
• High humidity makes sweat evaporate slowly, making us feel sticky and uneasy, while low humidity makes skin feel dry and lips get chapped.

Measuring Humidity

• Absolute Humidity: measures the amount of water vapour present in a unit volume of air, usually in kilograms per cubic metre.
• Relative Humidity: measures the ratio of water vapour in the air to the total amount of water vapour the air can carry at that temperature and pressure, expressed as a percentage.

Condensation

• Condensation is the change of water vapour to its liquid or solid forms when warm, moisture-laden air comes into contact with a cold surface.
• The temperature at which the amount of water vapour in the air is at its maximum limit is called the dew point of air.
• Condensation usually occurs around small particles of dust in the atmosphere.

Forms of Condensation

• Dew: forms when saturated air comes into contact with a cold surface above 0°C.
• Frost: forms when saturated air comes into contact with a cold surface below 0°C.
• Mist or fog: forms when a larger layer of air near the ground cools.
• Clouds: form when condensation occurs high up in the air.

Clouds

• Clouds are floating masses of supercooled water droplets and ice crystals.
• There are many types of clouds, including cirrus, stratus, and cumulus clouds.
• Cirrus clouds are thin, wispy clouds found high up in the atmosphere and made up of ice crystals.
• Stratus clouds are low-lying clouds that appear as large, grey sheets covering the entire sky.
• Cumulus clouds are massive, billowing clouds.

Precipitation

• Precipitation occurs when the amount of water vapour in the air becomes more than the capacity of the air to hold it.
• Precipitation comes in different forms, including snow, hail, and rain.
• Snow forms when temperatures are so low that water vapour turns directly into ice.
• Hailstones are ice pellets that are too large to fall as snow.
• Rain forms when the condensed cloud droplets come down to Earth.