Lesson 1 of 6 · Atmospheric structure
A layered atmosphere under pressure
9 minute lesson · 3 checks along the way
Your goal for this lessonConnect pressure with the weight of an atmospheric column, and distinguish a temperature-defined layer from a sharp edge to space.
Words with a dotted underline open a short definition right here in the lesson.
Start with moving molecules
Air can seem weightless because we usually feel it from every direction at once. Its molecules nevertheless have mass and exchange momentum when they strike surfaces. measures force per unit area. Near the ground, an approximately balanced atmospheric column supports the weight of the air above it. Climbing a mountain leaves less air overhead, so the surrounding pressure generally decreases. A lower reading does not by itself mean that a storm is approaching.
Gravity compresses the lower atmosphere, which contains a large share of its mass. The pressure decrease is therefore not a uniform number of pascals per kilometer. Temperature, composition, and gravity affect the relationship between pressure and height. Meteorologists often compare pressure adjusted to a common reference elevation when mapping weather systems; comparing unadjusted readings from a coast and a mountain would mix elevation with the weather signal.
Name layers by the pattern being measured
Most familiar clouds and weather occur in the , the lowest major layer. Its temperature usually decreases with height, although can reverse the local pattern. The stratosphere above it generally warms upward as ozone absorbs ultraviolet radiation. Farther up, temperature declines through the mesosphere and rises again through the thermosphere. These are broad thermal regions, and their transition heights vary rather than forming permanent solid shelves.
The uses a different classification: it describes regions with substantial ionization, overlapping several temperature-defined layers. Nor does the atmosphere abruptly stop at a chosen boundary of space. Sparse gas remains at satellite altitudes and can produce orbital drag. The can have a high particle temperature while its very low density limits heat transfer by collisions. Temperature alone therefore does not determine how a spacecraft exchanges energy with its surroundings.
Check 1 of 3
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Work through a decision
Weigh an imaginary column
Suppose an invented atmosphere is in , gravity is fixed at 10 meters per second squared, and pressure above its top is negligible. A one-square-meter column has ground pressure 100,000 pascals. Pressure times area gives a supported weight of 100,000 newtons; dividing by gravity gives 10,000 kilograms of overlying air. At a higher level where the pressure is 60,000 pascals, the remaining is 6,000 kilograms per square meter.
The difference, 4,000 kilograms per square meter, lies between those two pressure levels in this model. It is 40% of the original column mass, not 40% of the atmosphere’s geometric height. We have not specified a temperature profile or at each altitude, so there is not enough information to calculate that height. These rounded values are a teaching model, not a balloon sounding or a prediction for a particular mountain.
Pressure weighs the overlying column
Original hypothetical column with negligible pressure at the top and constant g=10 m/s². Boxes distinguish mass above each level; their heights do not represent altitude or uniform density.
Open full-size diagram in a new tab: Pressure weighs the overlying columnCheck 2 of 3
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Combine views from below and above
A weather balloon samples pressure, temperature, and humidity along its drifting path. A satellite instead detects radiation from a broad view, often with sensitivity spread across a range of heights. Turning those measurements into atmospheric profiles requires and a retrieval model. Their strengths complement one another: a local vertical record can help evaluate a much larger remotely observed pattern, while the satellite supplies context beyond the balloon’s route.
When reading an atmospheric image, ask whether its colors show visible appearance, brightness, or a retrieved variable. A bright cloud boundary is not automatically the boundary of a named atmospheric layer. Likewise, a pressure contour needs its reference level and units before it can be interpreted. Linking the measurement to its physical definition helps connect everyday weather with the thin environment through which rockets climb and satellites move.
Check 3 of 3
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Put it together
Your lesson progress
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