Vertical Circulation in the Tropical Atmosphere During Extreme El Niño–Southern Oscillation Events

E. K. Semenov, E. V. Sokolikhina, and N. N. Sokolikhina

Scenarios for the development of large-scale vertical circulation anomalies during warm and cold phases of El Niño–Southern Oscillation are generalized based on the NCEP/NCAR reanalysis data for 1958–1998. Composite models of the cells of vertical circulation in the monsoon and trade-wind regions of the tropical Pacific are obtained for the first time for El Niño and La Niña separately. An unprecedented shift of the ascending branch of the zonal Walker circulation from the “maritime continent” of Indonesia to the east, to the central and eastern Pacific, was observed during the warm phase over the tropical Pacific; this shift was accompanied by an abrupt increase in the tropical cyclogenesis activity in the southern Pacific zone of convergence. On the contrary, during the cold phase, the ascending motions in the region of the summer Australian monsoon are subject to abrupt intensification. The reconstruction of the vertical meridional circulation during the warm phase manifested itself in the almost complete disappearance of the Hadley classic circulation over the central Pacific, characteristic of the trade-wind intertropical convergence zone (ITCZ), and in its replacement by the latitudinal monsoon circulation typical of the ITCZ over the Indian Ocean. During a cold phase, the Hadley circulation is both restored and intensified.

Joomla templates by a4joomla