Contact: Kenneth Billings
STARKVILLE, Miss.--It's August, and the mercury continues to peak. Not surprisingly, many are mystified by the terms weather professionals use to describe the dog days of summer.
What do terms like "heat index," "relative humidity" and "dew point" mean and why does it seem so much warmer outside than the "official" temperature?
Michael Brown, associate professor of geosciences at Mississippi State University, says a host of terms are used to understand the impact of certain factors on temperatures. Methods of measuring "official" temperatures may yield results that are up to 15 degrees different than those recorded at most people's homes.
"The official air temperature is measured by instruments that are located in an instrument shelter 5 to 6 feet off of the ground and normally over a grass surface," Brown said. "The instrument shelter ensures the thermometer is shaded and therefore does not absorb radiation from the sun, which would give a higher and unrealistic air temperature reading."
The problem, Brown added, is that people tend to spend a great deal of time in the sun, experiencing a greatly different sense of temperature than that recorded as "official."
He lists a few common terms that may crop up in local weather reports:
Dew point temperature. The temperature in the atmosphere at which dew would begin to form if the air temperature were cooled. The higher the dew point temperature, the greater the amount of moisture.
Relative humidity. A measure of the percent of saturation relative to temperature. For example, if the air temperature is 72 degrees Fahrenheit and the dew point temperature is 70 degrees Fahrenheit, the relative humidity is 94 percent, a number indicating the air is 94 percent saturated.
Heat index. A number indicating what the body "feels" when heat and moisture are combined. The heat index equation quantifies the impact of air temperature and moisture on the body's ability to cool itself. The greater the air temperature and the greater the moisture, the higher the perceived body temperature.
For more information about Mississippi State University, see http://www.msstate.edu/.