NIGHT: LAND TO SEA
NIGHT: KATABATIC (↓)
ADIABATIC WARMING
Seasonal & Local Winds
Land & Sea Breeze · Mountain (Katabatic) & Valley (Anabatic) Winds · Foehn/Chinook Warming · Hot & Cold Local Winds (28 Micro-Realms)
Diurnal Reversals and Topographically Modified Airflow (NCERT Chapter 10)
Differences in the heating and cooling of Earth's surfaces and the daily cycles developing in mountainous regions create local and seasonal winds. Land and Sea Breezes occur because land heats and cools faster than water, driving a daily reversal of pressure gradients. Mountain and Valley Winds are driven by daytime slope insolation causing updrafts (Anabatic valley breeze) and nighttime radiation cooling causing dense air to drain into valleys (Katabatic mountain breeze). As winds cross mountain ranges, the descending air on the leeward side warms adiabatically, creating dry, hot winds like the Foehn (Alps) and Chinook (Rockies), while other regions experience distinct thermal local winds like the hot Loo, Sirocco, and Harmattan or the freezing Mistral and Bora.
I. Coastal Diurnal Winds & Differential Heating (NCERT Core)
Differential Heating (NCERT)
FAST HEAT
SLOW HEAT
- Land absorbs & transfers heat rapidly
- Water heats up slowly (high specific heat)
- Creates diurnal (daily) pressure reversals
Sea Breeze (Daytime)
- During the day, land heats up faster than sea
- Air rises over land creating Low Pressure
- Wind blows from High (Sea) to Low (Land)
Land Breeze (Nighttime)
- At night, land cools down faster than sea
- Sea remains relatively warm (Low Pressure)
- Wind blows from High (Land) to Low (Sea)
Monsoon: Macro Land/Sea Breeze
- Edmond Halley (1686) proposed that monsoons
- Are just a giant seasonal land and sea breeze
- Summer (Sea $\to$ Land); Winter (Land $\to$ Sea)
Fisherman's Routine
- Traditional coastal sailing relies on this cycle
- Land breeze takes boats out to sea at night
- Sea breeze brings them back to shore by day
Sea Breeze Front & Cooling
- Onset of sea breeze acts like a cold front
- Drops coastal afternoon temperatures sharply
- Increases humidity and brings relief from heat
II. Mountain & Valley Winds (Topographic Airflow — NCERT Core)
Valley Breeze (Anabatic / Day)
- During day, slopes get heated & air moves UP
- Valley air expands and moves up the slopes
- Also known as Anabatic (upward) wind (NCERT)
Mountain Breeze (Katabatic/Night)
- At night, slopes cool down rapidly by radiation
- High density cold air moves DOWN into valley
- Also known as Katabatic (downward) wind (NCERT)
Air Drainage & Frost Pockets
- Heavy cold air draining into valley bottoms
- Traps warmer air above it (Temperature Inversion)
- Valley floor experiences severe frost (NCERT)
Fall Winds (Ice-Cap Katabatic)
- Extreme form of katabatic wind
- Dense, freezing air plunging off high ice caps
- Common in Antarctica & Greenland coasts
III. The Foehn Effect & Global Hot Local Winds
The Foehn Effect
- Wind forced over mountain loses moisture (rain)
- Descends leeward slope as dry air
- Warms rapidly via dry adiabatic lapse rate
Dry vs. Wet Adiabatic Imbalance
-6°C / KM
+10°C / KM
- Rising wet air cools slowly ($~6^\circ\text{C/km}$ latent heat)
- Descending dry air warms fast ($~10^\circ\text{C/km}$)
- Result: Air arrives hotter than it started!
Foehn / Föhn (The Alps)
- Strong, dusty, dry, warm wind in European Alps
- Melts snow rapidly in winter
- Beneficial for early ripening of grapes!
Chinook ("Snow-Eater")
- Warm, dry wind descending eastern Rockies slope
- Can raise temperature by $15^\circ\text{C}$ in minutes
- Melts winter snow, keeping pastures clear for cattle
Loo (North India Summer)
- Hot, dry, oppressive wind blowing from West
- Over northern Indian plains in May & June (NCERT)
- Often causes heatstroke fatalities
Harmattan ("The Doctor")
- Dry, dusty trade wind blowing from Sahara
- Towards West African Guinea coast in winter
- Called "The Doctor" because it relieves sticky humidity
Sirocco ("Blood Rain")
- Hot, dry Sahara wind blowing North to Mediterranean
- Picks up moisture over sea, drops dusty rain in Italy
- Red Saharan dust makes it look like "Blood Rain"
Sirocco Regional Variants
- Different names for the same hot Saharan wind
- Khamsin (Egypt — lasts ~50 days), Gibli (Libya)
- Chili (Tunisia) and Leveche (Spain)
Santa Ana (California)
- Extremely dry down-slope wind in Southern California
- Originates in inland Great Basin deserts
- Fan devastating autumn wildfires in LA region
IV. Cold Local Winds & Topographic Funneling
Mistral (France)
- Cold, dry, strong wind blowing from Alps
- Funneled down the Rhone Valley to Med. Sea
- Can reach 100+ kmph; drops temps below freezing
Bora (Adriatic Sea)
- Cold, dry fall-wind (katabatic) blowing from
- Dinaric Alps down to the Adriatic Sea (Croatia/Italy)
- Very violent and gusty during winter
Blizzard, Purga & Buran
- Blizzard: Violent, blinding snowstorms (USA/Canada)
- Buran: Extremely cold winter wind in Siberia/Central Asia
- Purga: Tundra variant of the Buran
Pampero (Argentina)
- Cold, severe wind or squall line associated with
- Active cold fronts moving across the Pampas
- Brings sudden drop in temperature & thunderstorms
Australian Local Winds
HOT DESERT
COLD SQUALL
- Brickfielder: Hot, dry, dusty wind from Outback
- Southerly Buster: Sudden, severe cold front
- Sweeping up the New South Wales coast
Indian Pre-Monsoon Squalls
- Kal Baisakhi: Violent April thunderstorms in Bengal
- Elephanta: Autumn equinox squalls on Malabar coast
- Not continuous winds, but local convective storms
Topographic Funneling
- Winds forced through narrow mountain gaps
- Accelerate significantly (Venturi effect)
- Reason Mistral is so fast through Rhone valley
Haboob (Sudan Dust Storm)
- Intense dust storm carried on an atmospheric gravity current
- Caused by thunderstorm downdrafts collapsing
- Common in Sahara, Sudan & Arabian Peninsula
Master Local Winds Matrix
- Completes Local Winds (NCERT Ch 10)
- Thermal diurnal vs Topographic vs Continental
- Transitions to Realm 72 (Air Masses & Fronts)
Core Distinctions
• Anabatic (Valley Breeze): During the day, slopes heat up. The air expands and moves up the slopes to fill the low pressure. This upward wind is called Anabatic.
• Katabatic (Mountain Breeze): At night, slopes cool rapidly via radiation. The dense, heavy cold air moves down the slopes into the valley. This downward drainage wind is called Katabatic.
When wind is forced over a mountain, it cools at the slower Wet Adiabatic Rate ($\sim6^\circ\text{C/km}$) as it rains/snows on the windward side. Once over the crest, it has lost its moisture. It descends the leeward side and warms at the faster Dry Adiabatic Rate ($\sim10^\circ\text{C/km}$). Result: The wind arrives on the leeward side significantly hotter and drier than when it started.
3. UPSC Prelims Matching Trap (Hot vs. Cold Winds)• Hot/Dry Winds: Foehn (Alps), Chinook (Rockies), Loo (India), Sirocco/Khamsin (N. Africa/Med), Harmattan (West Africa), Santa Ana (California), Brickfielder (Australia).
• Cold Winds: Mistral (France), Bora (Adriatic/Italy), Pampero (Argentina), Blizzard/Buran (Polar/Russia), Southerly Buster (Australia).
Local Winds Matrix
NCERT Chapter 10 Reference Guide