PNNL

Abstract

This study aims to improve understanding the seasonality of how the Madden-Julian Oscillation (MJO) interacts with the Maritime Continent (MC). Besides responding to the monsoonal east-west movement, observations show that the MJO amplitude and precipitation over the MC islands exhibit semi-annual variability, with apparent strengthening of MJO signal during March and September, when solar insolation is strongest over the MC region. Furthermore, during the high insolation months, soil moisture shows wetter conditions during the early phases of the MJO. Motivated by these results a series of regional convection permitting simulations are performed for the November 2014 MJO event as a case study under the following conditions: (i) increased solar insolation to mimic the local summer, (ii) reduced initial soil moisture and (iii) the two conditions combined. Results show that increased insolation increases precipitation including that associated with MJO moisture convergence over the MC region. On the other hand, decreased initial soil moisture slightly increases precipitation over the MC islands and reduces it over the surrounding waters, but such effect is short lived as the increased precipitation gradually restores the soil moisture to wetter conditions. Using a moisture budget analysis that isolates the MJO and non-MJO signals and additional idealized simulations, the MJO response to high insolation and initial dry soil conditions is demonstrated to be related to the response of the basic state moisture distribution over the MC region rather than a direct response of the MJO to the insolation and soil moisture anomalies.