Organization of rainfall by an unstable jet with an application to African waves

It is hypothesized that a shear instability can organize rainfall if it converges sufficient amounts of moisture. This convergence is calculated by specifying the amplitude of a downgoing wave just beneath the jet and calculating the ascent induced below as a function of the zonal wind. Data obtained question whether a jet can organize rainfall from an arbitrary large distance above the moist layer. While in the absence of shear, a wave can reach the moist layer with undiminished amplitude, the induced ascent is small - less than the estimated ascent during phase I of the GARP Atlantic Tropical Experiment (GATE) when rainfall remained unorganized. It is suggested that organization can occur only if the unstable jet is within a few kilometers of the moist and separated by large shear. A wind profile resembling the observed 600-mb African jet is considered as an example. The waves are found to be closer to the moist layer during the later summer, causing larger ascent at this time.