A heat wave is a natural weather event caused when an area of high pressure remains stationary over a particular location. Due to the natural effects of a high pressure system on weather, the area experiences high temperatures which do not dissipate as normal. The high pressure air limits cloud cover and slows air currents so that wind is minimal. These two factors combine to create a heat wave which lasts as long as the high pressure remains stationary. The longest recorded heat wave lasted for one hundred and sixty days in Marble Bar in Australia.
A heat wave, described simply, is when an area experiences prolonged temperatures that are higher than those normally recorded. There is no direct definition of a heat wave because it is only comparable to the normal temperatures experienced by the location. Heat waves are a common occurrence across the globe and are caused by systems of high pressure remaining in one place. In an area of high pressure, cloud cover is limited so the sun shines constantly throughout the day, causing higher than normal day time temperatures. Normally weather systems such as rain and wind would dissipate this heat, however the high pressure means there is a severe lack of both in the local environment.
There are also dangers in heat waves, as the air remains stationary, all of the chemicals pumped into it through industry and the burning of fossil fuels also remain. This then reacts together in the bright sunlight and mixes with the water in the air to create smog. Smog is a deadly mix of smoke and fog. As heat waves limit vertical convection currents, the smog remains around ground level and can become lethal in cities.
There are also other causes of heat waves, but the common factor between all types is that weather conditions are unable to enter and cool down the environment. Heat waves can be caused by desert winds. These can blow warm air into areas which, for geographic or meteorological reasons, are unable to then reduce that temperature. If the area cannot reduce the temperature naturally, then it will experience a heat wave.
Heat waves can also affect cities in a phenomenon known as Urban Heat Islands. This is when cities do not cool down as much as their rural surroundings and due to weather conditions are unable to naturally dissipate the heat. This is caused because the amount of the surface that is covered by materials that retain heat. This mainly affects night time temperatures, making them much warmer than normal; however not all cities are affected by Urban Heat Islands.
Put simply, heat waves are caused by an area being unable to naturally cool down. Whether this is because of high pressure systems or geographic location, the common factor is that the Earth’s natural methods of cooling are unable to work. Rain and wind are the main methods of cooling, and in high pressure systems these are rare. This is how a heat wave is formed.
