In an effort to communicate important weather information, EIUWC has provided important information about the dangers of hot summer days and automobiles.

The Basics of Heat: Albedo

Heat is generated after solar radiation is absorbed by an object with a low albedo. Albedo refers to the reflective value of an object. If an object is white, more energy is reflected rather than absorbed. When an object has a dark color, more energy is absorbed than reflected. Heat is referred to as longwave energy such as infrared radiation. Consider for an example concrete and asphalt. The ambient temperature of concrete will be somewhat less than asphalt due to the difference in albedos.

Daytime Maximum Temperature

Contrary to common belief, the warmest part of the day is between 2pm and 4pm. This occurs because there is a temperature lag behind the solar maximum (the maximum energy received when the sun is directly overhead). As the sun rises in the east, solar radiation is absorbed by the earth's surface. The energy continues to accumulate at the surface. When the sun reaches its zenith (the point where the sun is directly overhead), the solar radiation without cloud cover is at its highest, but the temperature will not reach its maximum until a few hours later. It takes time for the energy to accumulate and begin to radiate as infrared radiation.

Other Factors that Contribute to Heat

Wind flow is another factor that can contribute to the daytime maximum temperature. If the winds are calm, more heat can occur. On the other hand, faster winds will help reduce the overall heat. Another aspect of wind flow is the direction from which the wind is flowing. If the winds are blowing in from the south, the maximum temperature will be higher than winds blowing in from the north.

Humidity is another important contributor to the "apparent" temperature. If the surface is dry or less humid, it is rather confortable. However, if the air is very humid, it "feels" very warm and unconfortable.

The Dangers of Automobiles: Combining the Above Concepts

The heat generated by an open environment is less intense than a closed environment. An automobile is a closed environment. When you take each of the concepts discussed above (albedo, maximum temperature, solar maximum, wind flow and humidity) and box them up, the effects are more intense. For example, as solar radiation enters through the glass of the car, longwave radiation is emitted by the low albedo of the car's interior. However, because longwave energy is less powerful than solar energy, it cannot pass through the car's windows but continues to increase with great intensity and speed. The result is an amplified interior temperature. There is a common myth that by cracking the windows you can increase wind flow through the car. However, this is not true because the heat is blocking wind flow into the car. The heated air within the car is expanding and flowing through the cracked windows. There is no relief because the radiation cycle continues (solar radiation, absorption, longwave radiation...repeated). The interior humidity is also a factor in this intense closed environment. Because the car's interior is a closed environment, the humidity will increase making it a harsh environment to breath even if the windows are cracked or open. Heat will accumulate quickly in a closed enviroment any time of the day...unlike an open environment.

The Moral of these Combined Concepts

DO NOT LEAVE ANIMALS OR HUMANS OF ANY AGE IN AN AUTOMOBILE FOR ANY TIME PERIOD! It only takes about 10 minutes for the interior of the automobile to heat to a temperature of 120F.

For the Latest Hazardous Information in your area, go to www.weather.gov.

Do you have more questions about Summer Heat and Automobiles? Send us an email, cdcraig@eiu.edu.