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Modulation of MJO-Diurnal Cycle Interaction over the Maritime Continent

The Maritime Continent (MC) is a major “prediction barrier” to the Madden-Julian Oscillation (MJO) because observed behaviors of MJO events are erratic over that region. Some MJO events slowly propagate eastward relatively unaffected, some weaken, and others stall and terminate over the MC. As a consequence, MJO forecast skills of the current generation of models are quite low there. Recent studies suggest this prediction barrier might not be intrinsic but rather a manifestation of model limitations related to lack of understanding and accurate representation of the processes that allow or block the propagation of MJO. For example, the disruption of MJO propagation by the MC is often exaggerated in many numerical models. Therefore understanding the processes that allow or impede MJO propagation across the MC is an important first step toward addressing the associated modeling and prediction difficulties. Our recent study shows that, via non-linear interactions between cloud processes and surface fluxes, diurnal cycle over the MC islands can weaken and stall propagating MJO convection signals.
In this proposed study, we aim at investigating the processes that modulate this non-linear interaction and thereby explain why some events of the MJO cross the MC and others do not. We plan to use observations and cloud-permitting (3 km grid spacing) regional model simulations to tackle this issue. New high-resolution (15 minute, 0.05Ëš) precipitation data from passive microwave (PMW) sensors and surface and sounding data from Years of Maritime Continent campaign will be used to extensively document the diurnal cycle of precipitation as well as surface and atmospheric environmental conditions over and around the major islands of the MC before the arrival of MJO events that propagate through as well as those that are disrupted by the MC. These observations will be analyzed to assess the comparative roles of various environmental factors in the modulation of MJO-diurnal cycle interactions. Regional cloud permitting model simulations of the two groups of MJO events will be used to test hypotheses derived from the observations. We will individually swap initial land surface and lateral atmospheric conditions between the MJO events that successfully cross the MC and those that were disrupted. This would give us opportunities to isolate factors to which MJO propagation through the MJO is the most sensitive. The cloud-permitting model simulations will also be diagnosed to assess the extent to which information to be obtained from YMC/PISTON field observations at specific locations is applicable to other part of the MC.
This proposal is a response to the FY 2017 Climate Variability and Predictability Program (CVP) and it targets the competition on the Observing and Understanding Processes Affecting the Propagation of Intra-seasonal Oscillations in the Maritime Continent Region. The proposed work is aligned with NOAA’s mission to enhance community resilience in the face of weather and climate extremes by extending lead times at which extreme events such as heat waves, drought, and flooding are skillfully predicted.

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