17:15 〜 18:45
[AAS10-P11] Role of Kelvin wave-like response in the Madden Julian Oscillation:
Connection to the stratospheric QBO in December
キーワード：MJO, stratosphere, Maritime continent, Kelvin wave
The influence of the stratospheric Quasi-Biennial Oscillation (QBO) on the Madden Julian Oscillation (MJO) during December-February period becomes evident in recent studies. However, the process which produces such effect is still unknown. Adding to this, models are incapable to simulate such modulation effect by the QBO. In the previous study, we showed that the seasonal march of the tropical convection from the Indian Ocean (IO) to the Western Pacific (WP) sector during December is modulated by the QBO. It is suggested that the modulation of the MJO is produced through changes in Kelvin wave-like response by the QBO zonal winds in the lower stratosphere. It is also suggested that the same effect may produce the modulation of eastward propagation of the MJO across the Maritime Continent (MC). In the present study we focus on the QBO modulation of the MJO over the MC in December.
In this study, we selected 9 MJO events in December during 1979-2022 period, according to the criteria that the amplitude of the Real-time Multivariate MJO (RMM) index at the phase 4.5 (i.e. the active center of the MJO is located over the MC) is larger than one. To investigate detail structure, each individual event is examined rather than making a composite analysis. The result shows that during the QBO easterly phase (QBOE), larger low-temperature anomalies associated with the Kelvin wave-like response is produced by convection at the active center of the MJO. This low temperature anomalies around the tropopause in the east of the active center excite deep penetrative convective activity in the east, which facilitates the MJO to propagate from the Indian Ocean (IO) to the WP across the MC. In the case of the QBO westerly phase (QBOW), Kelvin wave-like response being small, little connection is made between the convection and low temperature anomalies around the tropopause, which results in a reduced amplitude of the MJO over the MC or a failure of the MJO to cross the MC.
In this study, we selected 9 MJO events in December during 1979-2022 period, according to the criteria that the amplitude of the Real-time Multivariate MJO (RMM) index at the phase 4.5 (i.e. the active center of the MJO is located over the MC) is larger than one. To investigate detail structure, each individual event is examined rather than making a composite analysis. The result shows that during the QBO easterly phase (QBOE), larger low-temperature anomalies associated with the Kelvin wave-like response is produced by convection at the active center of the MJO. This low temperature anomalies around the tropopause in the east of the active center excite deep penetrative convective activity in the east, which facilitates the MJO to propagate from the Indian Ocean (IO) to the WP across the MC. In the case of the QBO westerly phase (QBOW), Kelvin wave-like response being small, little connection is made between the convection and low temperature anomalies around the tropopause, which results in a reduced amplitude of the MJO over the MC or a failure of the MJO to cross the MC.