Significant QBO Impacts on Tropical Cyclone Activity

The quasi-biennial oscillation (QBO) is a tropical climate mode characterized by alternating stratospheric easterly and westerly zonal winds. Recent reports suggest the impact of the peak westerly phase of the QBO on tropical cyclone (TC) activity has deteriorated in the last couple decades. This study extends the previous ones to examine the entire QBO lifecycle and its relationship to TC activity in all tropical ocean basins, and uses high spatial resolution to explore the changes within each basin. The results indicate that the QBO significantly affects TC activity in all ocean basins at certain stage of the QBO lifecycle. During the westerly phase of the QBO, TC genesis increases over the North and South Indian Oceans but decreases over the North Atlantic. As the QBO progresses through its lifecycle, regions of enhanced TC genesis migrate eastward in the western Pacific and westward in the central Pacific, and these signals remain symmetric about the equator, which is consistent with the fact that the QBO itself is a symmetric mode about the equator. Several ocean basins exhibit significant QBO-TC correlations for TC passage, TC intensity and TC accumulated energy. The robustness of these signals is demonstrated both by their level of statistical significance and their persistent recurrence during consecutive QBO cycles. Further, the effects of the QBO on TC genesis have generally strengthened in recent decades, signaling a potential for improved statistical forecasts. Exploratory environment analysis shows significant correlations between the QBO and certain oceanic and tropospheric variables known to influence TC activity. Although the physical mechanisms linking the stratospheric QBO to tropospheric TC activity remain elusive and continue to pose important questions to tropical meteorology, the QBO-TC relationship is demonstrably significant and could therefore facilitate improvements in TC operational forecasting.