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Captured QBO-MJO Connection in a Subseasonal Prediction System

Presentation Date
Monday, December 12, 2022 at 9:55am - Monday, December 12, 2022 at 10:06am
Location
McCormick Place - E350
Authors

Author

Abstract

The Quasi Biennial Oscillation (QBO) leaves dominant impacts on the Madden-Julian Oscillation (MJO) activity in observations with a stronger and more eastward-propagating MJO in QBO easterly (QBOE) winters than in QBO westerly (QBOW) winters. However, such QBO-MJO connection is poorly represented in the uninitialized simulations by current general circulation models (GCMs). For the first time, this paper applies a stratospheric zonal-mean nudging in a subseasonal prediction system to capture the QBO-MJO connection. Two strong MJO cases in a QBO neutral winter are selected for the experiment. The QBO temperature and zonal wind anomalies are nudged separately as well as together for the hindcasts of two selected MJO cases. Results show that only by nudging the QBO temperature anomalies while leaving the zonal wind free, the prediction system could capture the observed QBO-MJO connection. The tropopause instability is found to be positively correlated to the MJO amplitude in the hindcasts, but it is not the responsible mechanism for the captured QBO-MJO connection. Instead, the freely-evolving zonal wind anomalies as a result of the thermal wind balance to the nudged QBO temperature are likely to be the key for such capturing.

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