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Asymmetric Modulation of MJO by Two Types of ENSO
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DOI：10.1175/JCLI-D-25-0248.1.png)
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Abstract
En 中文
The modulation of Madden-Julian oscillation (MJO) by El Ni & ntilde;o-Southern Oscillation (ENSO) has been widely investigated, yet the mechanisms particularly the combined influences of ENSO phase (El Ni & ntilde;o/La Ni & ntilde;a) and type (eastern Pacific/central Pacific) remain elusive. Here, we unravel that differences in MJO characteristics (convective intensity, propagation, and structure) between El Ni & ntilde;o and La Ni & ntilde;a are asymmetric across two types of ENSO. These asymmetries are interpreted through established MJO frameworks, involving vertical wind shear, moisture-convection feedback, and structure-propagation nexus. Due to greater interphase differences in low-frequency background winds and humidity, eastern Pacific (EP) ENSO exerts stronger modulation on MJO intensity and northward propagation than central Pacific (CP) ENSO. Weaker MJO modulation of CP ENSO also stems from its distinct regulations of low-and high-frequency MJO components. Moreover, MJO eastward propagation is consistently faster during EP ENSO than during CP ENSO, primarily attributable to stronger premoistening and larger front Walker cell zonal scale leading MJO deep convection, independent of ENSO phases. The MJO propagation over the Maritime Continent also exhibits asymmetry: While MJO events propagate coherently into the central Pacific during both EP ENSO phases, they are frequently blocked during CP La Ni & ntilde;a but not during CP El Ni & ntilde;o. To explain further these propagation asymmetries, we propose five diagnostics based on winds, convection, stratiform heating, and humidity across intraseasonal and low-frequency time scales. Variations in the strength and behavior of these diagnostics under different ENSO backgrounds effectively explain the diversity of MJO propagation. This study advances toward a more comprehensive understanding of how diverse ENSOs modulate the MJO.
Keywords:
MADDEN-JULIAN OSCILLATION
WESTERN NORTH PACIFIC
INTRASEASONAL OSCILLATION
EASTWARD PROPAGATION
EL-NINO
VARIABILITY
MOISTURE
TEMPERATURE
ATMOSPHERE
INTENSITY
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