The U.S. is covered by a “heat dome”

A hot summer in the United States has prompted discussion about the heat dome, a phenomenon that leads to extremely high temperatures and unpleasant consequences for people and nature. What is a heat dome and how does it occur? Why is the southern United States suffering from this phenomenon right now?

A heat dome is a permanent area of high pressure that traps and retains heat in a certain area. It usually stretches over several states and can persist for days to weeks. This results in stagnant hot air below, which feels like an oven and harms people, crops, and animals.

Heat domes are usually associated with the behavior of jet stream, a band of fast winds high in the atmosphere that usually moves from west to east. The jet stream is wave-shaped and can meander northward, then southward, and then northward again. When these meanders get bigger, they move slower and can become stationary, which is what causes heat domes to form.

One of the contributing factors to thermal domes is downward warming. When a jet stream travels far north, the air accumulates and sinks, warming as it descends. If the air passes over the mountains and descends, it can get even warmer. This downward warming played a major role in the extremely high temperatures recorded in the United States and Canada in 2021.

Heat domes can have serious consequences for people and nature. The stagnant weather characteristic of heat domes leads to weak winds and increased humidity. Both of these factors increase the feeling of heat and make it more dangerous for humans. The heat index, which combines heat and humidity, is used to indicate this danger. High humidity also reduces the degree of cooling at night, which can lead to heat illnesses and deaths.

One of the worst examples of heat dome exposure occurred in the summer of 1995 in Chicago, when some 739 people died in five days. This confirms the danger that heat domes pose to society.

Heat domes can be caused by a variety of factors, including natural and man-made. Global warming caused by human activity can increase the frequency and intensity of heat domes. Scientists warn that without urgent action to reduce greenhouse gas emissions, heat domes could become increasingly common and dangerous.

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