Impacts of Insolation and Soil Moisture on the Seasonality of Interactions Between the Madden‐Julian Oscillation and Maritime Continent

Abstract

This study investigates the seasonality of the interaction of the Madden‐Julian Oscillation (MJO) with the Maritime Continent (MC). Beside their seasonal east‐west migration with the monsoons, observations show that the MJO amplitude and precipitation over the MC islands exhibit semiannual 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 to isolate their local effects from their impacts on the large‐scale circulation. 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 is demonstrated to be related to an increase in the basic state moisture over the MC region rather than a direct response of the MJO to the insolation.

Influences of Oceanic Processes Between the Indian and Pacific Basins on the Eastward Propagation of MJO Events Crossing the Maritime Continent

“…However, considering several MJO events that passed eastward from the northern part of the MC region into the Pacific Ocean, follow-up studies are still needed. The impacts of interannual variabilities of the ENSO, the Australian monsoon, and solar insolation in the MC region on the eastward propagation of MJO events have been revealed in previous studies (Hagos et al, 2019(Hagos et al, , 2020Hu, Chen, et al, 2022;Kang et al, 2022;Kim et al, 2017), but the results above suggest that the occurrences of the MJO_SC and MJO_N events are not entirely determined by these interannual variability factors in the background. In addition, previous studies have demonstrated the possible effects of oceanic eddies (Hu et al, 2021;Wen et al, 2020), oceanic fronts (Bai et al, 2019;Chen et al, 2019Chen et al, , 2020; Guan…”

“…In the third and fourth sections, we will further investigate the differences in the accompanying climate effects and possible influencing mechanisms of oceanic processes. Furthermore, previous studies noted the impacts of interannual variability such as ENSO (Hagos et al, 2019;Hu, Wang, et al, 2022), Australian monsoon (Hagos et al, 2019;Kang et al, 2022;Kim et al, 2017), winter surface solar radiation in the MC region (Hagos et al, 2020) on the eastward propagation of MJO events during boreal winter. To remove the influence of interannual variability mentioned above, the anomalies are calculated by subtracting their annual winter average in the following sections.…”

“…After regional convection permitting simulations, Hagos et al. (2020) found that increased solar insolation on islands caused an increase in background humidity, which in turn led to an increase in precipitation associated with MJO events. Lim et al.…”

“…Kim et al (2017) pointed out that the horizontal moisture advection is a key process to the MJO detouring, which causes the difference between the southern and central regions of the MC. After regional convection permitting simulations, Hagos et al (2020) found that increased solar insolation on islands caused an increase in background humidity, which in turn led to an increase in precipitation associated with MJO events. Lim et al (2021) suggested the important contribution of vertical advection in moist static energy (MSE) growth when the MJO convection approaches the MC region.…”

An Observationally Trained Markov Model for MJO Propagation

“…In a complementary approach using physics‐based models of various degrees of complexity, environmental conditions such as SSTs, upper‐level wind, or insolation etc. (e.g., Back et al., 2020; Hagos et al., 2020) are modified to determine the impact of the phenomenon of interest on a case study basis. Such an approach assumes the model adequately represents MJO propagation and its relationship to the background state.…”