Interannual Variability of the Atlantic Hadley Circulation and Predictability of Tropical Cyclone Activity

The interannual variability of the Atlantic Hadley circulation is found closely associated with Atlantic tropical cyclone activity. When the ITCZ is stronger (weaker) than normal, more (less) TCs form over the East and Central Atlantic with a larger (smaller) percentage of storms intensifying into major hurricanes (category 3 and above). Analyses showed that the large-scale dynamic and thermodynamic conditions as well as the structure of tropical easterly waves associated with a stronger ITCZ are more favorable for TC activity. The variability of the Atlantic Hadley circulation is further examined in the retrospective seasonal predictions produced by the GFDL HiRAM (Chen and Lin 2013). The 21-year simulations are initialized with fixed SST anomalies in early summer and captures about 80% of the observed variance of Atlantic tropical cyclone counts. It was found the HiRAM simulates reasonably well the interannual variability of the Atlantic Hadley circulation, its linkage with different environmental parameters, and its impacts on tropical cyclone activity. The predictability of Atlantic tropical cyclone activity can be explained by the significant correlation between the spring-early summer SST and the Atlantic Hadley circulation in the hurricane season. This suggests that the Hadley circulation provides a useful unified framework to understand the variability and predictability of Atlantic hurricane activity.