A circulation of sinking air around a high-pressure centre, turning clockwise north of the equator. It suppresses cloud and rain, and drives South Asian winter and heatwave weather.
PhenomenaWhat is an Anticyclone?
An anticyclone is a large-scale circulation of air around a centre of high atmospheric pressure. It is the mirror image of a cyclone in every respect that matters: air sinks rather than rises, spreads outward at the surface rather than converging inward, and rotates clockwise in the Northern Hemisphere rather than anticlockwise.
The two words are often used interchangeably with high pressure, but they describe slightly different things. “High pressure” names the pressure field — a region where the barometer reads above its surroundings. “Anticyclone” names the circulation that the pressure field creates. In practice they come together, and forecasters use whichever is more convenient.
For South Asia, anticyclones matter because they are the region’s off switch. The monsoon, the cyclones of the Bay of Bengal, the thunderstorms of the pre-monsoon and the winter rain of the western disturbances are all built on rising air. An anticyclone is a mass of descending air, and wherever one establishes itself, those things stop happening. That is good news for a farmer drying grain and bad news for a city waiting for rain to clear its air.
How an anticyclone works
Start at the top. Air converging in the upper atmosphere has nowhere to go but down. As it descends it comes under increasing pressure and warms by compression — the same effect that heats a bicycle pump. Warming air can hold more moisture relative to its capacity, so its relative humidity falls and any cloud within it evaporates. This is subsidence, and it is why anticyclones are associated with clear skies: the descending air does not merely fail to make cloud, it actively destroys cloud that is already there.
The descending air piles up near the surface, raising the pressure there and spreading outward. As it spreads, the Coriolis effect deflects it to the right in the Northern Hemisphere, and the outward flow curls into a clockwise rotation. South of the equator the deflection is to the left and anticyclones turn anticlockwise.
Two consequences follow that are worth knowing.
First, anticyclonic winds are gentle. Pressure gradients in a high are typically weak and spread over a large area, unlike the tight gradients around a cyclone centre. Anticyclonic weather is calm weather.
Second, subsidence builds an inversion. The sinking air warms as it descends but stops short of the ground, leaving a layer of warm air sitting on top of cooler surface air. That subsidence inversion acts as a lid, and everything released beneath it — moisture, dust, vehicle exhaust, smoke from crop residue and brick kilns — stays trapped in a shallow layer. This is the mechanism behind the region’s worst air quality episodes.
Meteorologists also distinguish cold-core anticyclones, which are shallow and driven by intense surface cooling, from warm-core ones, which are deep and driven by the general circulation. The winter Siberian High is the first kind; the subtropical ridge is the second.
The anticyclones that shape South Asian weather
The Siberian High. Through winter, extreme radiative cooling over Siberia and Mongolia builds one of the strongest surface anticyclones on Earth. Its cold, dense air spills southward and eastward, but the Himalaya shield the subcontinent from its cold northerly winds, so cold air reaches the north Indian plains mainly from the northwest, behind western disturbances. Over the Bay of Bengal, the same outflow becomes the northeast monsoon, picking up moisture over the sea and delivering it to Tamil Nadu, southeastern Andhra Pradesh and Sri Lanka from October to December.
The Mascarene High. In the southern Indian Ocean during the northern summer, a semi-permanent anticyclone near Mascarene waters drives southeasterly flow that crosses the equator, is deflected to become the southwesterlies of the monsoon, and carries moisture to the Kerala coast. A strong Mascarene High is one of the indicators forecasters watch ahead of monsoon onset.
The Tibetan anticyclone. In summer, intense heating of the elevated Tibetan Plateau creates a vast warm-core anticyclone in the upper troposphere over Asia. It sits above the monsoon rather than opposing it, and its position and strength are tied to how vigorous the monsoon circulation becomes.
The subtropical ridge. Around 30 degrees north, the descending branch of the global Hadley circulation maintains a belt of semi-permanent high pressure. It is the reason the world’s deserts cluster at that latitude, and in South Asia it explains the aridity of the Thar, much of Rajasthan, southern Punjab in Pakistan and Balochistan — places that sit under chronic subsidence rather than simply missing out on rain.
Anticyclones, heat and haze
Heatwaves. When an anticyclone aloft parks over northwest India and Pakistan during the pre-monsoon, three things compound. Subsidence heats the air from above, the cloudless sky admits full sunshine, and the stagnant circulation blocks cooler or moister air from moving in. Day after day the heat accumulates instead of being flushed out, which is why the most severe heatwaves are persistent rather than brief. The same blocking can hold the monsoon back or interrupt it once it has arrived, extending the heat into what should be the rainy season.
Break monsoon phases. Within the monsoon itself, spells of anticyclonic conditions over central India suppress convection for days at a time, producing the dry interruptions that farmers experience as an anxious wait between sowing and the next rain.
Fog and smog. From November to January, weak anticyclonic conditions over the Indo-Gangetic plain deliver light winds, clear nights and a firm inversion. Surface air cools rapidly, moisture condenses into the dense fog that halts flights and trains from Punjab to Bihar and Bangladesh, and pollution concentrates in the same shallow layer. The anticyclone does not create the pollution, but it decides whether it disperses.
Drought. Persistent, repeated anticyclonic dominance across a season is one route to drought — not a single dramatic event but the steady absence of the rising motion that rain requires.
Frequently asked questions
What is the difference between an anticyclone and a cyclone? Direction of motion. In a cyclone air converges and rises, cooling and condensing into cloud and rain, and it rotates anticlockwise north of the equator. In an anticyclone air descends and diverges, warming and drying, and it rotates clockwise. Cyclones bring storms; anticyclones bring settled weather.
Does an anticyclone always mean good weather? It means dry, stable weather, which is not the same thing. In summer that can mean a dangerous heatwave; in winter it can mean dense fog and severe air pollution. Anticyclonic weather is reliable, not necessarily pleasant.
Why does high pressure stop rain? Rain needs air to rise, cool and condense its moisture. Descending air in an anticyclone does the reverse — it warms and dries, which evaporates existing cloud and prevents new cloud from forming.
Are anticyclones connected to the monsoon? Closely. The Mascarene High in the southern Indian Ocean supplies the cross-equatorial flow that becomes the southwest monsoon, the Tibetan anticyclone sits above the monsoon circulation in summer, and the Siberian High drives the northeast monsoon in winter.
Where can I see settled anticyclonic weather in my city? Every city page on Mausam Online shows surface pressure alongside cloud cover, wind and air quality, so you can watch a high build in. The pattern is clearest at Delhi, Lahore, Kanpur, Bikaner, Karachi and Patna.