Interannual variability of the Atlantic Hadley circulation in boreal summer and its impacts on tropical cyclone activity

Hadley Circulation;Hurricane;Interannual Variability;Streamfunction;Intertropical convergence zone;Atlantic Ocean

Zhang, Gan ; Wang ; Zhuo

关键词: Hadley Circulation;    Hurricane;    Interannual Variability;    Streamfunction;    Intertropical convergence zone;    Atlantic Ocean;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/42219/Gan_Zhang.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

An original method was developed to define the regional Hadley circulation (HC) in terms of the meridional streamfunction. The interannual variability of the Atlantic HC in boreal summer was examined using the EOF analysis. The leading mode (M1), explaining more than 45% of the variances, is associated with the intensity change of the ITCZ. M1 is significantly correlated to multiple climate factors and has strong impacts on the Atlantic tropical cyclone (TC) activity. In the positive (negative) phase of M1, the ITCZ is stronger (weaker) than normal, and more (less) TCs form over the Atlantic main development region (MDR) with a larger (smaller) fraction of storms intensifying into major hurricanes. Composite analyses showed that the large-scale conditions are more favorable for the MDR TC activity in the positive phase.The role of tropical easterly waves in modulating the Atlantic TC activity is highlighted. In the positive phase of M1, the wave activity is significantly enhanced over the East Atlantic and the Caribbean Sea, which can be attributed to stronger coastal convection and a more unstable mean flow. In the context of the recently proposed marsupial paradigm, the frequency and structure of wave pouches were examined. In the positive phase of M1, the pouch frequency increases, and the number of pouches with a vertically coherent structure also rises significantly. A deep and vertically aligned wave pouch has been shown highly favorable for the TC formation. The HC perspective thus provides a complete dynamic framework for understanding the impacts of the different aspects of the large-scale circulation on the TC activity.