QBO/Solar Modulation of the Madden Julian Oscillation: A Composite Analysis

The Madden-Julian Oscillation (MJO) is the primary driver of intraseasonal weather and climate variability in the tropics, and has been linked to weather variability in the midlatitudes through the forcing of increased meridional flow. 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 on average during the easterly phase of the QBO (QBOE) compared to the westerly phase (QBOW). The larger amplitude MJOs are likely linked to reduced static stability in the lower stratosphere associated with ascent driven by the QBO-induced meridional circulation. Evidence has also been presented that indicates ascent changes in the lower stratosphere are also linked to the 11-year solar cycle, where increased (decreased) ascent and reduced (increased) static stability occurs during solar minima (maxima). The largest MJO amplitudes and occurrence rates, and weakest static stabilities in the lower stratosphere occur during the QBOE phase at solar minimum (SMIN) conditions. The smallest MJO amplitudes and occurrence rates, and strongest static stabilities in the lower stratosphere occur during the QBOW at solar maximum (SMAX) conditions.

The aim of this presentation is to examine precipitation, temperature, and wind information derived from the European Centre for Medium-Range Weather Forecasts Interim Reanalysis (ERA-I) to compare MJO events during QBOE/SMIN and QBOW/SMAX conditions from a climatology and composite perspective. The ERA-I dataset is available at 1x1 degree latitude-longitude grid spacing at 6-hour intervals for the period 1979-present. The MJO events for QBOE/SMIN and QBOW/SMAX conditions are stratified by MJO phase as determined from the outgoing longwave radiation-based MJO index (OMI). Preliminary results show that MJO events that occur during QBOE/SMIN conditions are characterized by increased precipitation rates compared to events during QBOW/SMAX conditions. Additionally, MJO events in phase 5 of the OMI show increased precipitation rates in the coastal northwest United States and British Columbia in association with atmospheric rivers in QBOE/SMIN conditions compared to QBOW/SMAX conditions. This result suggests that the MJO influence on midlatitude flow and atmospheric river events may be modulated by the QBO and solar cycle. Composite analysis of the lower stratospheric static stability and wind field stratified by QBO regime and solar cycle will also be presented. It is suggested that these results are potentially useful to for weather and climate applications regarding the effects of solar variability on tropical deep convection and seasonal-to-subseasonal variability.