Systematic Patterns in Land Precipitation Due to Convection in Neighboring Islands in the Maritime Continent During MJO Propagation

The land‐sea contrast in the Maritime Continent (MC) has been found to influence the Madden–Julian Oscillation (MJO). However, the specific contribution from individual islands to the precipitation over the surrounding islands during MJO propagation is not well known. We found that when an island is removed in the presence of lower‐tropospheric westerlies, precipitation increases over islands that are located to its east due to the strengthening of the westerlies. Frictional convergence of the stronger westerlies, aided by Coriolis, leads to an increase in vertical advection of moisture and precipitation over an island located to the east. On the other hand, the reduced heating over the removed island reduces the westerlies and precipitation to the west of the removed island and is consistent with the response of large‐scale circulation to tropical heating. During background easterlies prior to MJO arrival, a systematic decrease in precipitation was found in the surrounding islands to the west side of the removed island. But, on the eastern side of the removed island, no systematic change in precipitation was found. The results imply that changes in large‐scale circulation in response to convection (or a lack thereof) over a removed island may significantly influence precipitation in the neighboring islands. Therefore, biases in model precipitation over an island in the MC may arise from bias in precipitation over a neighboring island. Moreover, the presence of different island chains in the MC has led to a more conducive environment for more overall precipitation over the islands in the MC. Plain Language Summary The Maritime Continent (MC) with its islands and seas receives a large amount of precipitation and influences the global weather and climate. Therefore, understanding the spatial distribution of precipitation in the MC is important, in particular, during the times of enhanced convection. One such period of enhanced convection is associated with the Madden–Julian Oscillation (MJO) as it propagates over the MC from west to east with a period of 20–100 days. In this study, the specific role of individual islands in modulating rainfall on other islands during the MJO propagation is explored using regional model simulations. We found a systematic pattern in change in rainfall during the westerly phase of MJO propagation. Key Points Precipitation increases over islands that are located to the east of removed island during MJO propagation under backgrou