First, What Is the Jet Stream?
Imagine a fast-flowing river of wind, thousands of kilometres long and several kilometres wide, snaking its way around the globe high up in the atmosphere. That, in essence, is the jet stream. These powerful air currents, typically found 7 to 12 kilometres above
the Earth's surface, are driven by the temperature difference between the cold polar regions and the warm tropics. In the Northern Hemisphere, the jet stream generally flows from west to east, acting as a great divider, separating cold air to its north from warmer air to its south. Its path isn't straight; it meanders in large waves, much like a river on land. These winds are so strong that aeroplanes often use them to save time and fuel on long-haul flights.
And What Is a Heat Dome?
A heat dome is exactly what it sounds like: an atmospheric lid that traps hot air over a region. It forms when a strong area of high pressure parks itself in the upper atmosphere for days or even weeks. This high pressure pushes air downward. As the air sinks, it gets compressed and heats up, creating scorching temperatures on the ground. The 'dome' acts like a cap on a boiling pot, preventing the hot air from rising and escaping. It also blocks clouds from forming, leading to relentless sunshine that further bakes the surface below. The result is a stagnant, suffocating bubble of extreme heat that can lead to dangerous, multi-day heatwaves.
The Unstable Connection
The link between these two phenomena is where things get serious. The jet stream's normal, wavy flow helps move weather systems along. But when the jet stream weakens, its waves can become larger, more pronounced, and slower. Instead of a steady west-to-east flow, it can develop deep, meandering bends that get stuck in place. When a large, high-pressure ridge in the jet stream stalls, it can create the perfect conditions for a heat dome to form and persist. This 'blocking pattern' essentially locks a weather system in place, preventing cooler air from moving in and leading to the prolonged periods of extreme heat that define a heat dome event. These stalled waves are responsible for some of the most persistent and severe heatwaves seen around the world.
A Warming World's Fingerprint
Scientists are increasingly pointing to global climate change as a key driver of these jet stream changes. The Arctic is warming at least twice as fast as the rest of the planet, a phenomenon known as Arctic amplification. This reduces the temperature difference between the cold Arctic and the warmer tropics. Since this temperature gradient is the engine that powers the jet stream, a smaller difference means a weaker, slower, and wavier jet stream. A wavier jet stream is more prone to the kind of blocking patterns that allow heat domes to lock in, making extreme heat events more frequent and intense.
The View From India
For India, these global atmospheric changes have severe local consequences. The stability and path of the jet stream are crucial for determining India's weather, including the timing and intensity of western disturbances in winter and influencing the monsoon. Recent research has shown how shifts in the jet stream are already affecting weather patterns over the subcontinent, leading to unseasonal storms and changes in rainfall. When these wavier jet stream patterns create persistent heat domes, Indian cities become particularly vulnerable. Combined with the urban heat island effect—where concrete and asphalt absorb and radiate more heat than natural landscapes—these events can create life-threatening conditions, straining power grids, depleting water resources, and posing a severe risk to public health, especially for the elderly, children, and outdoor workers.
