Identifying the observed influence of the QBO on tropical tropospheric climate

The stratospheric Quasi-Biennial Oscillation (QBO) is characterized by descending bands of wind and temperature anomalies in the tropical stratosphere with a mean period of ~28 months. Numerous studies have argued that the QBO has a significant impact on tropical tropospheric climate. However, the observational support for such an impact is complicated by the competing signatures of internal tropospheric climate phenomena. Here we apply an observationally-based, "physical-kernel" methodology that identifies the "direct" component of the tropospheric response that arises from the combination of 1) the influence of the QBO on tropopause static stability and 2) the physical linkages between tropopause static stability, vertical motion, and clouds. Consistent with previous analyses, the results suggest that the westerly phase of the QBO is linked to robust decreases in vertical motion and cloud fraction over the Indian/western tropical Pacific Oceans; in contrast to previous analyses, they indicate only weak direct linkages between the QBO and tropical climate elsewhere. It is argued that the methodology provides a refined estimate of how the QBO directly influences tropical climate variability, with implications for its impacts on the Madden-Julian Oscillation.