Convective systems can develop in a thermodynamically unstable atmosphere. Such systems may quickly reach high altitudes and can cause severe storms. Meteorologists are thus especially interested in identifying such storm potentials while the system is still in a preconvective state. A number of instability indices have been defined to describe such situations.

Traditionally, these indices are taken from temperature and humidity soundings by radiosondes. As radiosondes are only of very limited temporal and spatial resolution there is a demand for satellite-derived indices.

The GII product consists of a set of indices which describe the layer stability of the atmosphere. These indices are highly empirical in nature. The colours in the K-Index and Lifted Index displays are chosen such that stable conditions are shown in different shades of brown, while increasing instability is displayed in blue to yellow to red, using some commonly accepted thresholds.