We decompose the CI into its components of near surface moist static energy and 700 hPa saturated moist static energy and find the former is the dominant term and the latter is secondary and has a slightly destabilizing effect over East Africa. Therefore, the dominant component of the near surface moist static energy is further decomposed into components associated with near surface temperature, moisture and geopotential and it is found that the temperature and geopotential components are much smaller in magnitude than the moisture component, which is shown in Fig. \ref{fig:LvqMon}. It has very similar spatial patterns to those of CI in Fig. \ref{fig:ciMon}. Hence the change in CI is dominated by the change in low level specific humidity, which is also the case for the CI annual cycle in observations \citep{Yang_2015}.