[AOS17-08] Does the tidal mixing affect the MJO in the Maritime Continent?
Keywords:MJO, Maritime Continent, Air-Sea Interaction
The intraseasonal convective precipitation over the Maritime Continent (MC) is primarily controlled by the propagating Madden-Julian Oscillation (MJO) from the Indian Ocean. But recent evidence suggests that MJO energetically interacts with a range of ocean-atmosphere-land processes local to MC. In particular, the MC region is known to have a robust tidal mixing signature that is reflected in cooler SSTs. However, the detailed mechanism by which the tidal effect affects the MJO in the MC is not well documented, and this is the focus of this study.
Two sets of ensemble simulations have been conducted using a high-resolution regional coupled ocean-atmosphere model with explicit convection, in which the ocean component of the coupled model is forced with and without tides. Prescribing tidal forcing in a coupled model creates a cascade of coupled ocean-atmosphere responses, resulting in a significant SST cooling of comparable magnitude to the intraseasonal SST response to MJO, and the significantly reduced MJO-related rainfall. In particular, the size of tide-induced SST cooling is strongly dependent on MJO phases; that is, the cooling is far more enhanced during the active phase than the suppressed. Considering that the tidal effect is of oceanic origin unrelated to MJO, the demonstrated tidal effect on the MJO could be another reason for the ostensibly random nature of MJO variability in the MC. Since the most substantial tidal effect on SST is fortnightly, co-occurring with the dominant time-scale of the MJO, it is also conceivable that the tidal effect would contribute to sub-seasonal to seasonal predictability of the MJO.
Two sets of ensemble simulations have been conducted using a high-resolution regional coupled ocean-atmosphere model with explicit convection, in which the ocean component of the coupled model is forced with and without tides. Prescribing tidal forcing in a coupled model creates a cascade of coupled ocean-atmosphere responses, resulting in a significant SST cooling of comparable magnitude to the intraseasonal SST response to MJO, and the significantly reduced MJO-related rainfall. In particular, the size of tide-induced SST cooling is strongly dependent on MJO phases; that is, the cooling is far more enhanced during the active phase than the suppressed. Considering that the tidal effect is of oceanic origin unrelated to MJO, the demonstrated tidal effect on the MJO could be another reason for the ostensibly random nature of MJO variability in the MC. Since the most substantial tidal effect on SST is fortnightly, co-occurring with the dominant time-scale of the MJO, it is also conceivable that the tidal effect would contribute to sub-seasonal to seasonal predictability of the MJO.