A167-04
Equatorial waves triggering extreme rainfall and floods in southwest Sulawesi, Indonesia
Equatorial waves triggering extreme rainfall and floods in southwest Sulawesi, Indonesia
Monday, 14 December 2020: 17:42
Virtual
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 enhanced convective phase the Madden-Julian Oscillation (MJO) contributed to the onset of a mesoscale convective system which developed over the Java Sea. Overall, the MJO was in its enhanced convective phase over the Maritime Continent ensuring a large-scale envelope of enhanced convection. MJO-associated lower tropospheric westerly anomalies across the whole western Maritime Continent led to enhanced moisture transport into the flood region. Then, within this large-scale MJO envelope, a CCERW propagated westwards through the region. Its circulation induced the northerly cold surge over the South China Sea with its southward moisture transport, and this then fed into the CCERW-associated eastward moisture transport over the Java Sea. Therefore, the CCERW gave a large boost to the moisture transport to southwest Sulawesi. Finally, a CCKW propagated eastward into the region, and triggered the intense convection over the flood zone in its convergence region.
Climatological analysis shows that 92% of December-January-February 1999/2000-2018/2019 floods and 76% of extreme rain events in this region were immediately preceded by positive low-level westerly wind anomalies. 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 Madden-Julian Oscillation 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.
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 enhanced convective phase the Madden-Julian Oscillation (MJO) contributed to the onset of a mesoscale convective system which developed over the Java Sea. Overall, the MJO was in its enhanced convective phase over the Maritime Continent ensuring a large-scale envelope of enhanced convection. MJO-associated lower tropospheric westerly anomalies across the whole western Maritime Continent led to enhanced moisture transport into the flood region. Then, within this large-scale MJO envelope, a CCERW propagated westwards through the region. Its circulation induced the northerly cold surge over the South China Sea with its southward moisture transport, and this then fed into the CCERW-associated eastward moisture transport over the Java Sea. Therefore, the CCERW gave a large boost to the moisture transport to southwest Sulawesi. Finally, a CCKW propagated eastward into the region, and triggered the intense convection over the flood zone in its convergence region.
Climatological analysis shows that 92% of December-January-February 1999/2000-2018/2019 floods and 76% of extreme rain events in this region were immediately preceded by positive low-level westerly wind anomalies. 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 Madden-Julian Oscillation 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.