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A persistent high-pressure system that traps hot air over a region for days or weeks, causing extreme and prolonged heat.
A heat dome is a large and persistent area of high atmospheric pressure that sits over a region for days or even weeks, trapping hot air beneath it. Air within a high-pressure system sinks, and sinking air is compressed by the increasing pressure at lower altitudes, which heats it — a process called adiabatic compression. The same subsidence suppresses cloud formation, so clear skies allow the sun to heat the surface without obstruction. The two effects reinforce each other day after day, producing temperatures far above normal that persist rather than breaking.
Type: PhenomenonA persistent high-pressure system, often described as a blocking high or ridge
Sinking air warms by adiabatic compression as it descends into higher pressure
Subsidence suppresses cloud formation, maximising solar heating at the surface
Often associated with an omega block, where the jet stream bends into a shape resembling the Greek letter omega
Persists for days to weeks because the blocking pattern stalls the normal eastward movement of weather systems
Covers a very large area, unlike a localised event such as a cloudburst
Frequency: Extreme weather phenomena and their mechanisms have become a recurring theme in UPSC Prelims and Mains as climate topics gain prominence
Atmospheric pressure increases as you go down. When a parcel of air descends, the surrounding air squeezes it into a smaller volume, and compressing a gas raises its temperature. This happens without any heat being added from outside, which is why it is called adiabatic warming. In a heat dome, high pressure drives continuous subsidence over a wide area, so the air arriving near the surface is warmer than the air that left aloft. Because the descending air is also becoming drier relative to its capacity, clouds cannot form, and the cloudless sky then lets the full force of the sun reach the ground. Heat accumulates day after day because nothing disperses it.
It works like a bicycle pump: press the plunger down and the barrel becomes hot, even though you added no heat. Squeezing the air is enough.
| Aspect | Heat Dome | Heatwave | Cloudburst |
|---|---|---|---|
| Nature | A persistent high-pressure system trapping hot air | A period of abnormally high temperature meeting defined thresholds | Extreme rainfall of 100 mm or more in an hour |
| Duration | Days to weeks | Typically a few days | About an hour |
| Spatial scale | Very large, regional to subcontinental | Regional | Highly localised, about 20-30 sq km |
| Relationship | A heat dome is a cause; the heatwave is the effect experienced on the ground | The measured outcome, as declared by a met agency | An unrelated convective rainfall event |
Heat domes turn heat from a discomfort into a mass-casualty hazard, because the danger comes from duration rather than from any single day's peak. Buildings and the human body both cope with a hot afternoon if the night brings relief; a heat dome removes that relief, keeping night-time temperatures elevated so that neither structures nor people cool down. Sustained heat also compounds other problems: electricity demand for cooling peaks precisely when transmission efficiency falls, water demand rises as reservoirs evaporate, crops fail during flowering, and dried vegetation raises wildfire risk. A warming climate does not create blocking patterns, but it raises the baseline temperature on which they act, so the same atmospheric configuration now produces hotter extremes than it once did.
Heat dome: a persistent high-pressure system trapping hot air for days or weeks
Mechanism: sinking air warms by adiabatic compression
Subsidence suppresses cloud, so clear skies maximise solar heating
Often linked to an omega block in the jet stream
The June 2021 Pacific Northwest heat dome, 24-28 June, is the standard example
Danger comes from duration and elevated night temperatures, not just daytime peaks
A large, persistent high-pressure system that traps hot air over a region for days or weeks, causing prolonged extreme heat.
The high pressure causes air to sink, and sinking air is compressed by the greater pressure below, which raises its temperature. This adiabatic warming happens without any heat being added from outside.
A jet stream pattern in which two low-pressure systems flank a blocking high, bending the stream into a shape resembling the Greek letter omega. It stalls the normal eastward movement of weather systems, which is why the heat persists.
The heat dome is the atmospheric cause — a blocking high-pressure system — while the heatwave is the effect experienced on the ground, declared when temperatures cross defined thresholds.