FIG. 3. Contrast of the IH tracks for the 10 seasons between 1950 and
1990 when the two-month extrapolated (July to September) QBO 50mb zonal-wind
speed at 10°N latitude was weakest from the east (upper panel) versus
those 10 seasons when the 50-mb wind was strongest from the east (bottom
panel). The ratio of difference is 3.51 to 1.