ABSTRACT

The Madden-Julian Oscillation (MJO) dominates the tropical climate variability in the troposphere on the 30-to-60-day timescale. During the winter, convective storms associated with the MJO excite planetary-scale wave disturbances that impact the U.S. weather and perturb the stratosphere. The Quasi-Biennial Oscillation (QBO) governs the variability in the tropical lower stratosphere and guides how planetary-scale wave disturbances penetrate into the stratosphere. Observations reveal that the QBO can modulate the occurrence and eastward migration of the MJO pattern. However, this QBO-MJO relationship is not evident in existing global climate models (GCMs). This research seeks to better understand this relationship and address why it remains elusive in models. New insight about the QBO-MJO connection may advance current knowledge of the coupling between the troposphere and stratosphere, extend the forecast range of weather prediction, and guide new GCM improvement. The work will support and train a full-time graduate student and leverage the National Center for Atmospheric Research Whole Atmosphere Community Climate Model (namely, WACCM6-110L), a GCM that simulates realistic MJO and QBO.

The research objective is to assess several positive feedback mechanisms that may contribute significantly to the observed QBO influence on the MJO. A key mechanism to assess involves the increased tropical upwelling and destabilization of the tropical upper troposphere/lower stratosphere (UTLS) region during the easterly phase of the QBO (i.e., QBOE) due to the absorption and dissipation of extratropical Rossby waves. These waves are influenced by both the MJO and the QBO. Five tasks are: (1) To quantify the observed differences between QBOE and the westerly phase of the QBO (i.e., QBOW) of the wintertime UTLS temperature and static stability as a function of latitude and longitude; (2) To determine the strength of the MJO-induced extratropical Rossby wave train and resulting upward wave activity flux as a function of MJO strength and QBO phase; (3) To diagnose the strength of the wave train and wave activity flux during the QBOE relative to QBOW; (4) To evaluate if WACCM6-110L can simulate the observed QBO-MJO connection and the observed QBO phase differences in UTLS temperature, subtropical jet structure, and wave activity flux; and (5) To perform new experiments on WACCM6-110L to identify needed model improvements.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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