Equatorial waves triggering extreme rainfall and floods in southwest Sulawesi, Indonesia

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  • 1 Institute of Geophysics Polish Academy of Sciences, Warsaw, Poland
  • 2 École Nationale de la Météorologie, Météo-France, Toulouse, France
  • 3 Naval Research Laboratory, Monterey, CA, USA
  • 4 Scripps Institution of Oceanography, University of California San Diego, CA, USA
  • 5 Agency for Meteorology, Climatology and Geophysics of the Republic of Indonesia, Jakarta, Indonesia
  • 6 Institute of Geophysics Polish Academy of Sciences, Warsaw, Poland
  • 7 Agency for Meteorology, Climatology and Geophysics of the Republic of Indonesia, Jakarta, Indonesia
  • 8 Centre National de Recherches Météorologiques, Météo-France, Toulouse, France
  • 9 Pacific Northwest National Laboratory, WA, USA
  • 10 Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences and School of Mathematics, University of East Anglia, Norwich, UK
  • 11 Naval Research Laboratory, Monterey, CA, USA
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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.

Corresponding author address: Beata Latos, Institute of Geophysics Polish Academy of Sciences, Warsaw, Poland. E-mail: blatos@igf.edu.pl

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.

Corresponding author address: Beata Latos, Institute of Geophysics Polish Academy of Sciences, Warsaw, Poland. E-mail: blatos@igf.edu.pl
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