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.