ENSO influence on QBO modulations of the tropical tropopause



We examine the El Niño–Southern Oscillation (ENSO) influence on the quasi-biennial oscillation (QBO) modulation of the cold-point tropopause (CPT) temperatures. An analysis of approximately five decades (in most cases 1950s to near-present) of radiosonde data from 10 near-equatorial stations, distributed along the Equator, shows that the ENSO influence on the QBO is quite zonally symmetric. At all stations analyzed, the QBO has larger amplitude and longer period during La Niña conditions than during El Niño over this total period. We also show that as a consequence of the ENSO influences on QBO periods and amplitudes, the differences between the warmer CPT temperatures during QBO westerly shear conditions and colder temperatures during QBO easterly shear conditions are larger during La Niña than during El Niño for all stations for the entire period considered here. This strengthens earlier findings that the greatest dehydration of air entering the stratosphere from the troposphere occurs during the winter under La Niña and easterly QBO conditions. In addition, stratosphere/troposphere wind and temperature profiles are derived to establish the degree of QBO downward penetration necessary to influence zonal winds and temperatures in the upper troposphere.