21% Oxygen, 78% Nitrogen, and trace gasses

Troposphere (surface to tropopause) - The altitude of the tropopause varies with latitude and with the season of the year; therefore, it takes on an elliptical shape as opposed to round. Location of the tropopause is important because it is commonly associated with the location of the jet stream and possible clear air turbulence.

Stratosphere - from tropopause to 160,000ft. Generally stable. Very little weather.

A common location of clear air turbulence (CAT) and strong wind shear exists with a curving jet stream. This curve is created by an upper or lower low-pressure trough. The wind speed, shown by isotachs (lines of constant wind speed), decreases outward from the jet core. The greatest rate of decrease of wind speed is on the polar side as compared to the equatorial side. Strong wind shear and CAT can be expected on the low-pressure side or polar side of a jet stream where the speed at the core is greater than 110 knots. Air travels in a “corkscrew” path around the jet core with upward motion on the equatorial side. When high-level moisture is present, cirriform (cirrus) clouds may be visible, identifying the jet stream along with its associated turbulence.