The state of Kerala in India experienced devastating floods during the South-West Monsoon of 2018, with anomalous rainfall trends reaching up to 150 mm departures from the mean daily precipitation in the northern districts. While many studies have explored hydrogeological factors that contributed to the floods, this study seeks to understand the underlying physics that caused such anomalous precipitation. The research finds that westward propagating convectively-coupled Mixed Rossby-Gravity (MRG) waves were excited by synoptic disturbances in the tropical Pacific at a pressure level of 700 hPa during the Indian Monsoon of 2018. These waves travelled across the Indian Ocean in two significant modes: a slow-moving wave with a period of 20-40 days (known as Madden-Julian Oscillation) and a secondary faster wave with a period of 5-8 days. The MRG waves are characterised by vertical phase propagation to the upper troposphere, which is a precursor to deep convection and intense precipitation. As these waves propagate through a medium, they enhance its relative vorticity, forming symmetrical gyres or circulations about the equator and leading to meanders in wind fields and widening of the Intertropical Convergence Zone. The MRG waves induced divergence in wind fields, fueling convection in tropics and bringing very heavy rainfall to Kerala during 2018. To conduct this research, daily rainfall data over the Indian Ocean region was obtained from Tropical Rainfall Measuring Mission (TRMM), while globally gridded data on zonal and meridional winds was obtained from NCEP/NCAR Reanalysis 1 for accurate representation of Earth's atmosphere. This study sheds light on how MRG waves can cause extreme weather events like floods and highlights their importance for future climate predictions and disaster management strategies.
In 2018, there were very bad floods in Kerala, India because of too much rain. Scientists wanted to know why this happened. They found out that big waves in the ocean caused the heavy rain in Kerala. These waves made wind and clouds that brought lots of rain. The scientists used special tools to study the waves and weather patterns. This helps us understand how floods happen and how we can prepare for them better in the future.
Definitions
- Devastating: causing a lot of damage or destruction
- Anomalous: different from what is normal or expected
- Precipitation: rain, snow, sleet, or hail that falls from the sky
- Convection: the movement of heat through liquids or gases by currents
- Divergence: when something moves away from a central point
Understanding the Physics Behind Kerala's Devastating 2018 Floods
The South-West Monsoon of 2018 brought devastating floods to the Indian state of Kerala, with anomalous rainfall trends reaching up to 150 mm departures from the mean daily precipitation in the northern districts. While many studies have explored hydrogeological factors that contributed to the floods, this study seeks to understand the underlying physics that caused such anomalous precipitation.
MRG Waves: The Cause of Extreme Weather Events
The research finds that westward propagating convectively-coupled Mixed Rossby-Gravity (MRG) waves were excited by synoptic disturbances in the tropical Pacific at a pressure level of 700 hPa during the Indian Monsoon of 2018. These waves travelled across the Indian Ocean in two distinct modes: a slow-moving wave with a period of 20-40 days (known as Madden-Julian Oscillation) and a secondary faster wave with a period of 5-8 days. MRG waves are characterised by vertical phase propagation to upper troposphere, which is a precursor for deep convection and intense precipitation. As these waves propagate through a medium, they enhance its relative vorticity, forming symmetrical gyres or circulations about equator and leading to meanders in wind fields and widening Intertropical Convergence Zone (ITCZ). MRG waves induced divergence in wind fields, fuelling convection in tropics and bringing very heavy rainfall to Kerala during 2018.
Data Sources Used For Research
To conduct this research, daily rainfall data over Indian Ocean region was obtained from Tropical Rainfall Measuring Mission (TRMM), while globally gridded data on zonal and meridional winds was obtained from NCEP/NCAR Reanalysis 1 for accurate representation Earth's atmosphere.
Implications Of This Study
This study sheds light on how MRG waves can cause extreme weather events like floods and highlights their importance for future climate predictions and disaster management strategies. Understanding these processes will help us better prepare for similar disasters in future so we can minimize their impact on human lives and property damage.
Kerala, the south-west coastal state of India, was ravaged by a series of floods during the South-West Monsoon of 2018. The season was marked by severely anomalous rainfall trends, with upto 150 mm of departures from the mean daily precipitation in the northern districts of the State. Although, there were many studies about the hydrogeological factors which aggravated the floods in Kerala, no attempt was made to delve into the physics which actually resulted in anomalous precipitation during the year. This study intends to document the dynamical phenomenon which caused the Kerala Floods of 2018. The westward propagating convectively-coupled Mixed Rossby-Gravity (MRG) waves were excited by the synoptic disturbances of the tropical Pacific at the pressure level of 700 hPa, during the Indian Monsoon of 2018. They travelled across the Indian Ocean in two significant modes -- a predominant slow moving wave of 20-40 days period (as Madden-Julian Oscillation) and a secondary faster wave of 5-8 days period. They are characterised by vertical phase propagation to the upper troposphere, a precursor to deep convection and intense precipitation. Further, the propagation of these waves through a medium enhances its relative vorticity and the gyres or circulations thus formed are symmetrical about the equator. Consequently, the meanders in the wind field and widening of the Intertropical Convergence Zone were observed. The MRG waves, especially the slow mode induced divergence in the wind field, which fueled convection in tropics and brought very heavy rainfall to the State of Kerala in 2018.
