2. Subsidence and convergence – link to rainfall
Sinking (downward) motion in the atmosphere, usually over a broad area. Subsiding air usually leads to drier conditions.
Convergence in a horizontal wind field indicates that more air is entering a given area than is leaving at that level. To compensate for the resulting “excess,” vertical motion may result: upward forcing if convergence is at low levels. Moist converging air that rises usually leads to rainfall.
You may want to view the page on Global Dimming and its influence on the droughts in Sub-Saharan Africa.