Influence of the Quasi-Biennial Oscillation and the Madden–Julian Oscillation on Midlatitude Circulation and Surface Temperature and Precipitation Anomalies

The Madden-Julian Oscillation (MJO) is the primary driver of intraseasonal weather and climate variability in the tropics and has been linked to subseasonal-to-seasonal variability in midlatitudes. Recent studies have shown that the stratospheric quasi-biennial oscillation (QBO) modulates the amplitude of the MJO in Northern Hemisphere winter, where larger amplitudes occur during the easterly phase of the QBO (QBOE) compared to the westerly phase (QBOW). The larger MJO amplitudes are linked to reduced static stability in the upper troposphere and lower stratosphere during the QBOE phase. The opposite occurs during the QBOW phase. While there appears to be a significant relationship between QBO phase and MJO amplitude on average, it is unclear how the QBO-MJO interaction influences the typical midlatitude circulation anomalies associated with the varying phases of the MJO.

The aim of this presentation is to examine the influence of the QBO on midlatitude circulation, temperature, and precipitation anomalies associated with the MJO. Specifically, composites of daily-mean fields derived from gridded reanalyses are constructed for strong MJO events (defined as amplitudes > 1.5) during November-April 1979-2015 for days stratified by the QBOE and QBOW regimes. Results show that stronger MJOs are more common during QBOE compared to QBOW. While the midlatitude circulation anomalies associated with the MJO show similar composite patterns in QBOE and QBOW, there is a westward phase shift in the blocking pattern over the North Pacific in QBOW for MJO phases 2-5. This westward phase shift allows for a more robust trough in the lee of the Rockies and enhanced southerly low-level flow over the central U.S. resulting in increased warm air outbreaks over eastern North America. The westward phase shift also seems to have implications on the low-level flow along the west coast of North America, resulting in onshore flow with positive anomalous precipitation for MJO phases 2-5, and offshore flow with negative anomalous precipitation for MJO phases 6-8. These emerging results suggest that the influence of the QBO and MJO on midlatitude circulation anomalies is a potentially important factor in subseasonal-to-seasonal climate variability.