Scientists in Australia have identified and tracked previously overlooked weather systems that collectively play a greater role in tropical rainfall than tropical cyclones. The discovery could improve understanding of rainfall patterns and help researchers predict how tropical weather may change as global temperatures rise.
The research conducted by scientists at Monash University and published in the journal Weather and Climate Dynamics, uses more than three decades of satellite observations to identify and track these weather systems.
Unlike tropical cyclones, which receive considerable attention because of their destructive potential, these less dramatic systems occur more frequently and contribute significantly to rainfall across tropical regions.
Christian Jakob of Monash University described tropical cyclones as the “divas of the tropics”, explaining that although they have major impacts other weather systems collectively play a much larger role in everyday rainfall.
Weather outside the tropics is commonly understood through familiar systems such as cold fronts, high pressure areas and low pressure systems. However, scientists have lacked a similar framework for identifying many of the systems responsible for organising clouds and rainfall in tropical regions.
Previous research largely focused on individual thunderstorms or large scale atmospheric waves. More recent theories have highlighted two important phenomena: moisture modes and atmospheric gravity waves.
Moisture modes are relatively slow moving atmospheric systems that organise thunderstorms and rainfall over several days. Gravity waves, meanwhile, influence large areas of rising and sinking air, moving clouds and rainfall across considerable distances.
Researchers have now developed a method to identify these systems as individual, trackable weather objects, much like tropical cyclones.
More Than 30 Years of Satellite Data Analysed
The research team examined satellite observations collected between 1984 and 2016 to identify large areas of high, cold clouds associated with organised tropical convection.
Convection occurs when warm, moist air rises into the atmosphere, forming clouds and producing rainfall. Because high clouds are much colder than Earth’s surface, they emit less radiation into space, allowing scientists to identify organised cloud systems through satellite measurements.
Researchers treated these cloud formations as individual objects and tracked their movement, speed, duration and development over time.
Their speed helped distinguish between different atmospheric systems. Slowly moving formations were classified as moisture modes, while faster moving systems were identified as gravity waves. Systems displaying characteristics of both were classified as mixed systems.
Lead researcher Muhamad Reyhan Respati, a PhD student at Monash University, said defining moisture modes as individual objects was a major breakthrough because it allowed scientists to track and study them rather than treating them only as a theoretical concept.
Moisture Modes Linked to 45–75% of Extreme Rainfall
The study found that moisture modes are particularly important near the northern and southern boundaries of the humid tropics, including areas around tropical Australia.
In some regions, these systems were associated with between 45% and 75% of extreme three hourly rainfall.
The findings are especially significant for Australia, where the continent extends across both tropical and temperate climate zones.
According to co-author Martin Singh, the discovery provides a new framework for understanding tropical rainfall and examining how these systems influence regional weather patterns.
Researchers say that tropical Australia has traditionally received considerable attention for its tropical cyclones, but moisture modes also deserve greater scientific focus because of their substantial contribution to rainfall.
Scientists now want to investigate how moisture modes and other tropical weather systems will behave as the planet warms.
A warmer atmosphere can hold more moisture, potentially changing the intensity and frequency of rainfall producing systems.
Researchers are investigating whether existing moisture modes could become stronger or whether more weather systems may develop into moisture modes under warmer conditions.
Understanding these processes could improve future projections of Australia’s monsoon patterns and extreme rainfall events.
The research offers a new way to identify, compare and study tropical weather systems potentially helping scientists better understand rainfall behaviour and prepare for changing climate conditions.