tropopause

The tropopause is the boundary between the troposphere and the stratosphere, marking a change in the vertical temperature gradient. It effectively separates weather phenomena, which are mostly tropospheric, from the more stable stratosphere.

Height varies by latitude and season. At mid-latitudes it lies roughly 8–12 km above sea level, in the tropics up to about 16–18 km, and in polar regions as low as 7–9 km. The exact height fluctuates with atmospheric conditions and weather patterns.

Definition and concepts. The conventional lapse-rate tropopause is defined by the altitude where the environmental lapse rate falls to 2 C per kilometer or less, averaged over a specified layer. A complementary concept, the dynamic tropopause, is defined using potential vorticity and geopotential height and is used in weather analysis to locate the boundary in a dynamically meaningful way.

Tropical specifics. In the tropics the tropopause can reach very low temperatures, creating a cold-point tropopause that limits dehydration of air entering the stratosphere. This cold trap helps determine the composition of the lower stratosphere, including water vapor.

Significance and processes. The tropopause acts as a barrier to vertical mixing, influencing the distribution of ozone and water vapor and shaping the location of jet streams near its upper boundary. Weather systems such as deep convection and cyclones can distort the boundary, producing tropopause folds and enhanced exchange between layers.

Observations and measurement. The tropopause is monitored through radiosondes, aircraft soundings, and satellite-based sensors. Its height and structure vary with season, latitude, and atmospheric dynamics, and accurate representation is important for weather forecasting and climate models.