Differences in Vertical Structure of the Madden‐Julian Oscillation Associated With the Quasi‐Biennial Oscillation

• Published in: Geophysical research letters 2018-05, Vol.45 (9), p.4419-4428
• Main Authors: Hendon, Harry H., Abhik, S.
• Format: Article
• Language: English
• Subjects: Anomalies; Atmospheric models; Biennial; Convection; Destabilization; Equator; Lower stratosphere; Madden-Julian oscillation; MJO; Modelling; Phases; QBO; Quasi-biennial oscillation; Stability; Stratosphere; Temperature anomalies; Temperature effects; Tropical climate; Tropopause; Troposphere; Upper troposphere; Vertical profiles; Winter
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL077207

The Madden‐Julian Oscillation (MJO) during boreal winter is more active and propagates eastward farther into the western Pacific during the easterly phase of quasi‐biennial oscillation (QBO). Using atmospheric reanalyses for 1980–2012, we show that the MJO‐induced upper tropospheric positive temperature anomaly and overriding cold cap anomaly are stronger and more in‐phase with the equatorial MJO‐convective anomaly during the easterly phase of the QBO. These temperature anomalies combine to destabilize the upper troposphere more in‐phase with MJO convection, thus acting to promote stronger MJO convection during the easterly phase of the QBO especially eastward of the Maritime Continent. This enhanced destabilization is promoted by the negative temperature anomaly at the tropopause resulting from the QBO during its easterly phase. These findings can account for the enhanced strength and farther eastward propagation of the MJO during the easterly phase of the QBO, but await confirmation by theoretical and modeling studies that can isolate these effects. Plain Language Summary The tropical Madden‐Julian Oscillation (MJO) is observed to be more active and predictable during boreal winter when the stratospheric quasi‐biennial oscillation (QBO) is in its easterly phase in the lower stratosphere. However, the mechanism by which the QBO affects the MJO has yet to be elucidated. We show using reanalyses for the period 1980–2012 that the vertical structure of the MJO near the equator is different during QBO easterly and westerly phases and that these differences are consistent with stronger MJO convection during easterly phases of the QBO. The proposed mechanism is via a combination of MJO‐induced and QBO‐induced reduction in stability at the tropopause during easterly phases of the QBO, which act to destabilize and strengthen MJO convection. These findings provide further insight into the mechanism of the MJO and can be used to guide improved representation and prediction of the MJO with forecast models. Key Points The vertical structure of the MJO in boreal winter is different during QBO easterly and westerly phases Tropopause static stability is more reduced in‐phase with MJO convection during easterly phase of QBO, consistent with stronger MJO amplitude Anomalously cold tropopause during the QBO easterly phase promotes the destabilization