🌊 Chapter 11: Water in the Atmosphere
💧 Humidity
The water vapor present in the atmosphere is called humidity.
It is measured in grams per cubic meter (g/m³).
🌀 Types of Humidity
- Absolute Humidity:Amount of water vapor per unit volume of air.Unit: grams per cubic meter.
- Specific Humidity:Weight of water vapor per unit weight of air.Unit: grams per kilogram.
- Relative Humidity:Ratio of the water vapor present in the air to the maximum it can hold at the same temperature.Unit: %Formula:Relative Humidity (%)=Absolute HumidityHumidity Tolerance×100\text{Relative Humidity (\%)} = \frac{\text{Absolute Humidity}}{\text{Humidity Tolerance}} \times 100Relative Humidity (%)=Humidity ToleranceAbsolute Humidity×100
🌬 Saturated Air
When air contains water vapor equal to its capacity, it is called saturated air.
💦 Evaporation
Evaporation is the process of changing water from liquid to gaseous state.
Factors affecting evaporation:
- Temperature 🌡
- Surface area 📏
- Wind speed 💨
Latent Heat of Vaporization:
Energy used to convert 1 gram of water into vapor = ~600 calories 🔥
🌫 Condensation
Condensation is the process of changing water vapor into liquid or solid state.
Examples: Dew, Frost, Fog, Cloud ☁️
Saturated Air: Air with 100% relative humidity 🌡
Dew Point: Temperature at which air becomes saturated.
🌱 Dew
- Occurs when the earth cools at night, air touching the surface cools, and water vapor condenses into small droplets.
- Appears on leaves and other surfaces.
Favorable conditions for dew formation:
- Long nights 🌙
- Cloudless sky ☀️
- Cool air ❄️
- High relative humidity 💧
- Dew point > Freezing point 🌡
❄ Frost (Tushar)
- Forms when condensation occurs below 0°C, i.e., dew point ≤ freezing point.
- Appears as ice crystals on cold surfaces.
🌁 Fog
- Formed when air with high water vapor condenses on dust particles near the ground.
- Fog is essentially a cloud at ground level.
🌫 Fog vs Mist
☁️ Clouds and Rain
🌥 Clouds
Clouds are formed by the condensation of water vapor around fine dust particles (nuclei) present in the air.
☁️ Forms of Clouds
Clouds are classified based on height, density, and opacity:
- Cirrus Clouds
- Altitude: 8,000–12,000 m
- Appearance: Thin, scattered, feather-like
- Color: White
- Cumulus Clouds (Cotton Clouds)
- Altitude: 4,000–7,000 m
- Appearance: Fluffy like cotton, flat base
- Often scattered across the sky
- Stratus Clouds
- Appearance: Layered, covering large areas
- Formation: Caused by heat loss or mixing of air at different temperatures
- Nimbus Clouds (Rain Clouds)
- Color: Black or dark gray
- Formation: Close to middle or lower levels of the atmosphere
- Characteristics: Thick, shapeless, opaque, full of water vapor
☁️ Cloud Levels
- High Clouds: 5–14 km
- Mid-altitude Clouds: 2–7 km (between Stratus & Cumulus)
- Low Clouds: < 2 km (Layered rain clouds & Cumulus rain clouds)
🌧 Rain
Rain occurs when water vapor-laden air rises, cools, and condenses into water droplets around dust particles.
- Clouds collide with obstacles and release moisture on the Earth’s surface → Rain
🌦 Types of Rain
- Convectional Rainfall
- Happens when surface gets very hot
- Air heats, expands, rises, and cools → condensation → heavy rain
- Clouds: Cotton (Cumulus) clouds
- Orographic Rainfall (Mountain Rain)
- Occurs when air rises along a mountain slope
- Air cools and becomes saturated → water vapor condenses → rain
- Cyclonic Rainfall
- Caused by cyclones
- Also called retrograde rain
