Impacts of Rossby Wave Breaking on Atlantic Tropical Cyclone Activity

With warm SST anomalies in the tropical Atlantic and cold SST anomalies in the East Pacific, the unusually quite hurricane season in 2013 was a surprise to the hurricane community. Our analyses suggest that the substantially suppressed Atlantic tropical cyclone (TC) activity in August and early September can be attributed to frequent breaking of midlatitude Rossby waves, which led to the equatorward intrusion of cold and dry extratropical air. The resultant middle to upper tropospheric dryness and strong vertical wind shear hindered TC development.

A robust relation was found between the RWB frequency and Atlantic tropical cyclone activity during 1979-2012 using the ERA-Interim reanalysis and IBTrACS data. Frequent RWB over the North Atlantic leads to a significant reduction in the column water vapor and an increase in the vertical wind shear over the Atlantic MDR, and thus a decrease in the basin-wide hurricane count and accumulated cyclone energy. The correlation between the RWB frequency and Atlantic hurricane count is comparable to the correlation of Atlantic hurricane count with the MDR relative SST, and higher than that with the Niņo 3.4 index. It was also found that the impacts of RWB over the East Atlantic differ from those over the West Atlantic. The linkages of RWB with different climate factors and the implication for the predictability of RWB will also be briefly discussed.