The tropopause is the boundary between the lower atmosphere, the troposphere, and the upper atmosphere, including the stratosphere and its ozone layer. Air temperatures are generally lowest at the tropopause, increasing above and below. A typical tropopause temperature over Europe or North America is -55 C. Cirrus clouds are high, thin clouds. In the tropics they can be formed at the top of convective systems, including cyclones, or by internal waves in the atmosphere causing local cooling. Both the Falcon and the Geophysica are equipped with instruments to measure the particles in sub-visible cirrus.
Convection is the rapid vertical transport of buoyant air, which usually leads to cloud formation.
If convection is sufficiently energetic, the air and cloud can reach the tropopause, where it can either deposit or remove water, depending on details of the cloud structure. Man-made CFCs are mixed thoroughly throughout the troposphere before being transported upwards in the tropics. CFCs and N2O are measured on board the Geophysica. CFCs and related man-made compounds perturb this balance, and reduce the amount of ozone in the stratosphere. This allows more damaging ultraviolet radiation to reach the surface.