THE NATURAL ENVIRONMENT
Geography 101
ToC
SKY
Origin
Air
Layers
Sunlight
Scatter
Refract
Hawai'i
Air
A major branch of Geography is climatology. Climatologists study long-term, or average, phenomena of the atmosphere. This distinguishes the field from Meteorology, which focus on short-term events and their physical causes, although there is much overlap between the two disciplines.
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The object of interest to both of these fields is a thin, relatively homogenous, layer of mostly Nitrogen and Oxygen called the atmosphere. How thin is it? If the entire atmosphere condensed into a liquid suddenly, it would form a layer only about 12 meters (40 feet) deep. If you drive to the top of Mauna Kea at 4206 meters (13,796 feet), you are above 40% of the entire atmospheric mass.
The weight of the air above any elevation contributes to the atmospheric pressure at that point. Pressure is commonly recorded in millibars (mb) and can be measured with a variety of instruments, including the common aneroid barometer. Sea level pressure near the Hawaiian Islands on a typical trade wind day averages around 1015 mb. Equivalent values in other units include: 14.7 pounds per square inch, 760 mm of mercury, and 29.92 inches of mercury.
Above sea level, air pressure decreases with altitude as shown in the figure. The air pressure for the summit of Haleakala at 3055 meters (10,023 feet) is about 700 mb, the top of Mauna Loa at 4206 meters (13,678 feet) is 600 mb, and if you climbed Mt. Everest to 8850 meters (29,028 feet), you would be gasping for air at only 300 mb. Every breath would have only about 30% of sea level oxygen (300mb/1015mb x 100 = 30%). The half-way point for air pressure is at about 5.5 km (3.5 mi) where the air pressure is about 500 mb.
How high in the atmosphere can humans survive unaided by flying machines? That record was held by USAF Captain
Joseph
Kittinger
for 52 years. He jumped out of a balloon with an open gondola at 31,340 meters (102,800 feet) in a standard Air Force partial-pressure suit and free fell for over 5 minutes before opening his chute and landing safely. Below, he's shown falling
toward the clouds. Kittinger's record has recently been broken a couple of times by adventurers with high-tech modern equipment, each exceeding the speed of sound on descent. 