FEATHERY ICE WISPS
COTTON WOOL PUFFS
RAIN-BEARING MASS
Clouds
Cirrus, Cumulus, Stratus & Nimbus · Altitude Combinations · Vertical Development Thunderheads (28 Micro-Realms)
The Four Principal Cloud Forms and Altitude Classes (NCERT Chapter 11)
A cloud is a mass of minute water droplets or tiny ice crystals formed by the condensation of water vapour in free air at considerable elevations. According to NCERT, clouds are grouped under four basic forms: 1) Cirrus (high, detached, feathery ice crystals at 8–12 km), 2) Cumulus (cotton wool patches with a flat base at 4–7 km), 3) Stratus (layered sheets covering large portions of the sky, formed by mixing/heat loss), and 4) Nimbus (black or dark gray, extremely dense/opaque, shapeless rain-bearing masses at middle or low levels). These combine into High (Cirro-), Middle (Alto-), Low (Strato-), and Extensive Vertical Development (Cumulonimbus) clouds.
I. Cloud Genesis & The Four Principal Forms (NCERT Core)
Cloud Definition (NCERT)
- Formed by condensation of water vapour
- In free air at considerable elevations
- Can assume various shapes and sizes
Adiabatic Cooling Genesis
- Air is lifted, expands, and cools adiabatically
- Temperature drops below the Dew Point
- Moisture condenses onto hygroscopic nuclei aloft
Four Basic Forms (NCERT)
- Based on height, expanse, density & transparency
- NCERT strictly classifies them into 4 primary forms
- All other clouds are combinations of these!
1. Cirrus Clouds (NCERT)
- Detached, feathery appearance
- Always white in colour & transparent
- Composed entirely of ice crystals!
Cirrus Altitude (8–12 km)
- Form at the highest altitudes (8–12 km)
- Where temperatures are far below freezing
- Hence they are ice, not water droplets
2. Cumulus Clouds (NCERT)
- Look like cotton wool, exist in patches
- Can be seen scattered here and there
- Have a flat base! (marks Condensation Level)
Cumulus Altitude (4–7 km)
- Formed at altitudes between 4–7 km
- Generated by localized surface heating
- Indicator of fair weather if they don't grow vertical
3. Stratus Clouds (NCERT)
- Layered clouds covering large portions of the sky
- Horizontal, blanket-like appearance
- Lack the distinct, lumpy shape of cumulus
Stratus Genesis
- Formed either due to loss of heat (cooling layers)
- Or the mixing of air masses with different temperatures
- Typical of warm fronts (Nimbostratus/Altostratus)
4. Nimbus Clouds (NCERT)
- Black or dark gray colored clouds
- Form at middle levels or very near the surface
- Latin for "Rain storm" — they bring precipitation!
Nimbus Opacity
- Extremely dense and OPAQUE to sun rays
- Shapeless masses of thick vapor (NCERT)
- So low they sometimes seem to touch the ground
II. High, Middle & Low Cloud Combinations (NCERT Core)
High Clouds (5–14 km)
- Highest family of clouds (Ice crystals)
- Cirrus (wispy)
- Cirrostratus (thin veil) & Cirrocumulus (ripples)
Cirrostratus (The Halo Cloud)
- Thin, whitish veil of ice crystals
- Refracts light to form a HALO around Sun or Moon
- Often the first sign of an approaching warm front!
Cirrocumulus (Mackerel Sky)
- Patches of small, white, flaky ripples
- Looks like the scales of a mackerel fish
- High altitude ice crystals arranged in waves
Middle Clouds (2–7 km)
- Mid-level clouds of water droplets & ice
- Altostratus (gray/blue uniform sheet)
- Altocumulus (larger puffy white/gray masses)
Altostratus (Watery Sun)
- Thicker than Cirrostratus; no halo
- Sun/Moon appears dimly as through frosted glass
- Usually precedes continuous rain (Nimbostratus)
Altocumulus (Sheep Clouds)
- White or gray patches, rolls, or bands
- Larger and darker puffs than cirrocumulus
- Often resembles a flock of sheep in the sky
Low Clouds (0–2 km)
- Lowest cloud family (Water droplets)
- Stratocumulus (lumpy layer), Stratus (flat fog-like)
- Nimbostratus (dark, wet, rain-producing)
Stratocumulus
- Low, lumpy, rolling masses of gray/white clouds
- Often covers the whole sky in winter
- Rarely produces significant precipitation
Nimbostratus (Warm Front)
- Dark, thick, shapeless gray blanket
- Blocks out the sun completely
- Produces steady, continuous rain or snow
III. Clouds of Extensive Vertical Development (Thunderheads)
Vertical Development Class
- Clouds that do not fit in a single height tier
- Driven by intense vertical convection (instability)
- Cumulus & Cumulonimbus (NCERT Ch 11)
Cumulus Congestus (Towering)
- Fair-weather cumulus that grows vertically
- Resembles a large cauliflower head
- Indicates strong updrafts & unstable air
Cumulonimbus (Cb / Storm)
- The ultimate thunderstorm cloud (Cold Front / Cyclone)
- Violent updrafts & downdrafts inside
- Produces torrential rain, lightning, and hail
The Anvil Top (Inversion Block)
- Updraft hits the Tropopause (stratospheric inversion)
- Cannot rise further; spreads horizontally
- Forms flat, icy "Anvil" top of a mature Cb cloud
IV. Cloud Physics, Albedo, Rain Shadows & Master Matrix
Cloud Albedo (Cooling)
- Thick clouds have very high albedo (70-80%)
- Reflect massive amounts of incoming SW insolation
- Daytime cloud cover drastically cools the surface
Cloud Greenhouse (Warming)
- At night, clouds act like a blanket
- Absorb outgoing LW terrestrial radiation
- Bounce it back, making cloudy nights much warmer!
Orographic Rain Shadow
- Windward side: Ascent $\to$ Clouds $\to$ Heavy Rain
- Leeward side: Descent $\to$ Adiabatic Warming $\to$ Clear
- Clouds dissipate, creating a dry rain shadow (e.g. Pune)
Master Cloud Matrix
- Completes the 4 basic cloud forms (NCERT Ch 11)
- Mastery of Altitude & Weather association
- Transitions to Realm 76 (Precipitation Types)
Core Distinctions
• Cirrus: Formed at high altitudes (8,000–12,000 m). Thin, detached, feathery, always white, made of ice crystals.
• Cumulus: Look like cotton wool, formed at 4,000–7,000 m. Exist in patches scattered here and there, and crucially, they have a flat base.
• Stratus: Layered clouds covering large portions of the sky. Formed by loss of heat or mixing of different air masses.
• Nimbus: Black or dark gray, forming at middle levels or very near the surface. Extremely dense and opaque to the rays of the sun (shapeless masses of thick vapor).
Both are widespread veil-like clouds. Cirrostratus is higher, made of ice, and refracts light to form a distinct Halo around the sun or moon. Altostratus is lower (mid-level water/ice mix) and thick enough to blur the sun into a dim, "watery" or frosted-glass appearance without a halo.
3. Cumulonimbus (Cb) and the Anvil TopA cloud of extensive vertical development. Fueled by extreme instability and latent heat release, its updraft can reach the Tropopause. Because the Stratosphere above is inverted (warmer), the rising air hits a thermal ceiling and spreads horizontally, forming the classic flat, icy Anvil Top of a severe thunderstorm.
Cloud Classification Matrix
NCERT Chapter 11 Reference Guide