Impacts of Detoured Madden-Julian Oscillations on the South Pacific Convergence Zone

Abstract

Madden-Julian Oscillations (MJOs) are a major component of tropical intraseasonal variabilities. There are two paths for MJOs across the Maritime Continent; one is a detoured route into the Southern Hemisphere and the other one is around the equator across the Maritime Continent. Here, it is shown that the detoured and non-detoured MJOs have significantly different impacts on the South Pacific convergence zone (SPCZ). The detoured MJOs trigger strong cross-equatorial meridional winds from the Northern Hemisphere into the Southern Hemisphere. The associated meridional moisture and energy transports due to the background states carried by the intraseasonal meridional winds are favorable for reinforcing the SPCZ. In contrast, the influences of non-detoured MJOs on either hemisphere or the meridional transports across the equator are much weaker. The detoured MJOs can extend their impacts to the surrounding regions by shedding Rossby waves. Due to different background vorticity during detoured MJOs in boreal winter, more ray paths of Rossby waves traverse the Maritime Continent connecting the southern Pacific Ocean and the eastern Indian Ocean, but far fewer Rossby wave paths traverse Australia. Further studies on such processes are expected to contribute to a better understanding of extreme climate and natural disasters on the rim of the southern Pacific and Indian Oceans.

Increase in Intraseasonal Rainfall Driven by the Arabian Sea Warming in Recent Decades

“…All terms are vertically integrated from 1,000 to 100 hPa; $$\frac{1}{g}{\int }_{\mathrm{p}\mathrm{b}}^{\mathrm{p}\mathrm{t}}\mathrm{d}\mathrm{p}$$, where, pt = 100 hPa is the pressure at the top of the atmosphere, pb = 1,000 hPa is the pressure at the bottom of the atmosphere, and g is gravitational acceleration. The equation has been widely applied to capture the thermodynamical influences of moisture on ISOs (e.g., Neelin & Held, 1987; Qin et al., 2020; Yanai et al., 1973; Zhou et al., 2021).…”

“…, where, pt = 100 hPa is the pressure at the top of the atmosphere, pb = 1,000 hPa is the pressure at the bottom of the atmosphere, and g is gravitational acceleration. The equation has been widely applied to capture the thermodynamical influences of moisture on ISOs (e.g., Neelin & Held, 1987;Qin et al, 2020;Yanai et al, 1973;Zhou et al, 2021). All terms in Equation 1 are composited on Day 0s in both the latter (red dots in Figure 2) and former periods (blue dots in Figure 2).…”

MJO Seasonality in Its Scale Selection: Perspectives From Space‐Time Spectral Analysis of Moisture Budget

“…One might immediately note that the “Maritime Continent (MC) barrier” (Zhang & Ling, 2017) likely plays a role in shaping the wavenumber‐2 MJO in DJF. During this season, the MJO frequently detours via the southern MC (Kang et al., 2022; Kim et al., 2017; Zhou et al., 2021; Zhou & Murtugudde, 2020) and might encounter a stronger MC barrier effect than during JJA (Li et al., 2020; Wang et al., 2022). Zhang and Dong (2004) also discussed that the two maximum centers of MJO convective signals over the Indian Ocean and western Pacific straddling zonally the MC, an area showing the minimum MJO variance (Sobel et al., 2008), might explain the wavenumber‐2 structure of the MJO in winter.…”