What is Heat Wave? What Causes a Heat Waves? Compile From Different Sources

 

What is Heat Wave?

When the temperature rise higher than normal for a number of days in a line is known as Heat Wave. According to UNICEF “Heat waves happen when the temperature is higher than normal for several days in a row. Humidity can cause it to feel much hotter.”

Notes

Projected changes in the number of days per year with a maximum temperature above 90°F and a minimum temperature below 32°F in the contiguous United States. Changes are the difference between the average for mid-century (2036–2065) and the average for near-present (1976–2005) under the higher scenario (RCP8.5). This map depicts a weighted multi-modal mean of 32 climate model projections.

Source

CICS-NC and NOAA NCEI by Russel Vose, available in Climate Science Special Report.

What Causes a Heat Wave?

There are several causes of heat waves. In this regard, some are compiled from different sources. According to UNICEF the heat wave causes are following:

“Heat waves result from warm air being trapped in the atmosphere and are a natural weather phenomenon. Heat waves are increasing in intensity and frequency due to climate change, resulting from greenhouse gas emissions, that is trapping heat for longer”

According to NEXTIAS.COM, Heatwaves can be caused by a combination of natural and human-induced factors. The main causes are:

High Atmospheric Pressure Systems: Heatwaves often occur when high-pressure systems stall over a region. These systems can trap warm air near the Earth’s surface and prevent the normal movement of air masses, leading to prolonged periods of hot weather.

Global Warming: The long-term increase in Earth’s average temperature, primarily driven by human activities such as burning fossil fuels (coal, oil, and natural gas), deforestation, and industrial processes, contributes to the frequency and intensity of heat waves.

Urban Heat Island Effect: Urban areas with high population density, extensive concrete and asphalt surfaces, and limited vegetation tend to absorb and retain more heat, creating localized zones of higher temperatures.

Drought and Dry Conditions: Prolonged periods of drought and lack of precipitation can dry out the soil and reduce available moisture, causing the land to heat up more quickly during heat waves.

Climate Variability: Natural climate variations, such as El Nino and La Nina events, can influence weather patterns and increase the likelihood of heatwaves in certain regions. During El Nino events, for example, warmer ocean waters in the tropical Pacific can lead to changes in atmospheric circulation and weather patterns worldwide.

Geography and Topography: Certain geographic features and topographical conditions can contribute to the development of heat waves. For instance, landlocked valleys and regions surrounded by mountains can trap hot air and lead to temperature spikes.

Changes in Wind Patterns: Shifts in wind patterns can transport hot air from one region to another, intensifying heat waves in areas that are not typically prone to such extreme temperatures.

Human Activities: Local factors, such as land use changes, deforestation, and irrigation practices, can alter the surface characteristics of an area and contribute to heatwave development on a smaller scale.

According to NYTIMES, causes of heatwaves are following:

In most parts of the country, temperatures must be above the historical average in an area for two or more days before the label “heat wave” is applied to a hot spell, according to the National Weather Service. But the definition can vary by region; in the Northeast, it is defined as three straight days in the 90s or above.

Heat waves begin when high pressure in the atmosphere moves in and pushes warm air toward the ground. That air warms up further as it is compressed, and we begin to feel a lot hotter.

The high-pressure system pressing down on the ground expands vertically, forcing other weather systems to change course. It even minimizes wind and cloud cover, making the air more stifling. This is also why a heat wave parks itself over an area for several days or longer.

According to SCIJINKS.GOV heat waves are

Heat waves are generally the result of trapped air. During the 2012 heat wave, air was trapped above much of North America for a long period of time. As opposed to cycling around the globe, it simply stayed put and warmed like the air inside an oven.

The culprit? A high-pressure system from Mexico. Between June 20th and June 23rd, this system migrated north. It grew in size, and it parked itself over the Great Plains of the United States.

High-pressure systems force air downward. This force prevents air near the ground from rising. The sinking air acts like a cap. It traps warm ground air in place. Without rising air, there was no rain, and nothing to prevent the hot air from getting hotter.