Equatorial Waves Triggering Extreme Rainfall and Floods in Southwest Sulawesi, Indonesia

Abstract

On the basis of detailed analysis of a case study and long-term climatology, it is shown that equatorial waves and their interactions serve as precursors for extreme rain and flood events in the central Maritime Continent region of southwest Sulawesi, Indonesia. Meteorological conditions on January 22, 2019 leading to heavy rainfall and devastating flooding in this area are studied. It is shown that a convectively coupled Kelvin wave (CCKW) and a convectively coupled equatorial Rossby wave (CCERW) embedded within the larger-scale envelope of the Madden-Julian Oscillation (MJO) enhanced convective phase, contributed to the onset of a mesoscale convective system which developed over the Java Sea. Low-level convergence from the CCKW forced mesoscale convective organization and orographic ascent of moist air over the slopes of southwest Sulawesi. Climatological analysis shows that 92% of December-January-February floods and 76% of extreme rain events in this region were immediately preceded by positive low-level westerly wind anomalies. It is estimated that both CCKWs and CCERWs propagating over Sulawesi double the chance of floods and extreme rain event development, while the probability of such hazardous events occurring during their combined activity is eight times greater than on a random day. While the MJO is a key component shaping tropical atmospheric variability, it is shown that its usefulness as a single factor for extreme weather-driven hazard prediction is limited.

Record‐Breaking Precipitation in Indonesia's Capital of Jakarta in Early January 2020 Linked to the Northerly Surge, Equatorial Waves, and MJO

“…Baranowski et al (2020) also found evidence that Kelvin waves play a critical role in the majority of flooding events in Sumatra. Similarly, Latos et al (2021) reported that Kelvin waves and equatorial Rossby waves can double the probability of floods and extreme rain events in Sulawesi. Despite clear evidence from these regional studies, it remains elusive the role of equatorial waves in the major flooding incident in Jakarta in early January 2020.…”

“…Occurrences of extreme rainfall and corresponding flooding events are often associated with the MCS, which is more favorable in the presence of the CENS, equatorial waves, and MJO (Latos et al., 2021; Mapes et al., 2006; Schumacher & Johnson, 2008; Wu et al., 2007). This section explains the characteristics of the MCS during the period of the extreme rainfall event.…”

A Global High‐Resolution Mesoscale Convective System Database Using Satellite‐Derived Cloud Tops, Surface Precipitation, and Tracking

“…This example shows that most mesoscale PFs that produced heavy precipitation were associated with tracked MCSs. In fact, several long-lived heavy precipitating MCSs near the central Maritime Continent region of southwest Sulawesi, Indonesia (5°S, 120°E) caused devastating flooding on 22 January 2019 (Latos et al 2021). In addition, the detect-and-spread CCS identification technique in FLEXTRKR (Feng et al, 2018) is able to separate nearby MCSs that shared cold anvil cloud shields but have separate PFs (e.g., the two MCS clusters around 10°S, 125°E).…”

Compound Wind and Precipitation Extremes Across the Indo‐Pacific: Climatology, Variability, and Drivers

“…These, together with some unknown processes, contribute to the class of “others” weather types in the study. It is worth noting that these convective systems should not be interpreted as independent phenomena but point to processes that are intertwined with each other (Latos et al., 2021).…”