What is barometric pressure?
According to Dr. Stephen Baig, an oceanographer at NOAA’s Hurricane Center in Miami, barometric pressure is defined as the weight or mass of an entire air column on a unit of surface area at sea level. It is instrumental in weather observations, since its fluctuation indicates the movement of weather fronts and systems. Liquid mercury (Hg) is commonly used in a barometer to measure air-pressure changes in inches (in.). “Imagine a U-shaped tube,” says Dr. Baig. “At one end is liquid mercury, whereas the other end is open to the atmosphere. When the air pressure rises, it pushes the mercury higher. When the air pressure drops, so does the mercury level.” Atmospheric pressure can also be measured in millibars (mb), with a “bar” being roughly equivalent to one atmosphere of pressure (one atmosphere equals 1.01325 bars). One bar is equivalent to 29.6 in. Hg.
