Scientists in Australia have developed a new way to identify and track weather systems responsible for much of the rainfall across the tropics. The research reveals how slow-moving atmospheric disturbances, often overlooked in traditional weather analysis, contribute to heavy rain in regions where millions of people depend on seasonal rainfall.
The study was published November 6, 2026, in the peer-reviewed journal Weather and Climate Dynamics. Researchers at Monash University in Melbourne analyzed more than three decades of satellite observations to identify weather systems that influence tropical rainfall without necessarily developing into recognizable storms.
Their findings show that systems known as moisture modes are associated with 45% to 75% of extreme three-hour rainfall events in certain tropical regions. The results suggest these less familiar atmospheric disturbances deserve greater attention alongside tropical cyclones.
The research could eventually help scientists improve climate projections and understand how tropical rainfall may change as global temperatures rise. However, the study does not demonstrate that current weather forecasts have already become more accurate.
Why Tropical Weather Systems Are Difficult to Track
Weather forecasting in temperate regions often relies on recognizable atmospheric features such as cold fronts, high-pressure systems and low-pressure systems. Meteorologists can follow these features as they move across continents and oceans, helping them anticipate changes in temperature, wind and rainfall.
The tropics present a different challenge. Warm, moisture-rich air frequently produces thunderstorms, but the larger systems organizing those storms can be difficult to identify using conventional methods.
Tropical cyclones are familiar examples of organized weather systems because their rotating cloud patterns are readily visible in satellite images. Yet many other atmospheric disturbances produce substantial rainfall without forming hurricanes or typhoons.
Christian Jakob, a professor at Monash University and one of the study's authors, explained that tropical cyclones attract considerable attention because of their destructive potential. He said less dramatic systems occur more frequently and collectively make an important contribution to tropical rainfall.
Researchers have long understood that large atmospheric waves influence tropical weather. However, connecting those theories to individual systems that can be tracked across the atmosphere has remained difficult.
The new research provides a framework for identifying these systems using their movement, cloud patterns and physical characteristics.
Scientists Identify Three Types of Tropical Weather Systems
The research was led by Muhamad Reyhan Respati, a doctoral student at Monash University who is also affiliated with IPB University in Indonesia. He worked with atmospheric scientists Martin Singh and Christian Jakob.
The team developed a method for dividing large tropical weather disturbances into three categories according to how quickly they move across the atmosphere.
The first category consists of moisture modes, which generally move slowly and are strongly influenced by variations in atmospheric moisture. These disturbances can organize thunderstorms over several days and produce substantial rainfall.
The second category includes inertio-gravity waves, which travel more rapidly through the atmosphere. These waves involve changes in pressure, temperature and air movement that can influence where clouds and rainfall develop.
The third category consists of mixed systems, which display characteristics between the two other types. Their behavior reflects interactions between moisture and the atmospheric processes associated with faster-moving waves.
The distinction matters because systems that appear similar in satellite images may behave differently depending on the forces controlling their movement.
Respati explained that the research transforms moisture modes from a largely theoretical concept into weather features that scientists can identify and track individually.
Instead of examining only broad atmospheric patterns, researchers can now follow these disturbances through time, much as meteorologists track tropical cyclones.
More Than 30 Years of Satellite Observations Analyzed
The research team examined satellite observations spanning 1984 through 2016. These records allowed scientists to investigate how tropical weather systems developed, moved and interacted with the atmosphere over several decades.
A central part of the analysis involved measuring radiation emitted from Earth toward space. Satellites detect this outgoing longwave radiation, which provides information about cloud temperatures and atmospheric conditions.
High clouds associated with strong thunderstorms are generally colder than Earth's surface. Because they emit less infrared radiation, scientists can identify large areas of organized tropical cloud activity in satellite measurements.
The researchers used these measurements to locate cloud systems associated with rising warm, humid air. This process, known as convection, is responsible for much of the thunderstorm activity across the tropics.
They then applied mathematical filtering techniques to separate atmospheric disturbances according to their movement. A computer-based tracking method followed individual cloud systems as they traveled across different regions.
The analysis also incorporated atmospheric information from the ERA5 global reanalysis dataset. That dataset combines observations with weather-model calculations to reconstruct past atmospheric conditions.
For the rainfall analysis, researchers used satellite-based precipitation estimates covering June 2000 through December 2016. This shorter period provided the detailed rainfall measurements needed to connect the identified systems with heavy precipitation.
By combining these records, the team could compare atmospheric disturbances with observed rainfall patterns across tropical regions.
Moisture Modes Linked to Extreme Rainfall
One of the most important findings involved areas near the northern and southern edges of the humid tropics. These regions experience significant seasonal variations in rainfall and are particularly sensitive to changes in atmospheric moisture.
The researchers found that moisture modes were associated with approximately 45% to 75% of extreme three-hour rainfall events in some areas around 15 to 20 degrees north and south of the equator.
This does not mean moisture modes produce 75% of all tropical rainfall. The percentage refers specifically to the association between these systems and extreme short-duration rainfall events in certain geographic regions.
Closer to the equator, the researchers found that mixed systems played a larger role. They were especially important near the Intertropical Convergence Zone, where warm, moist air rises and produces extensive cloud formation.
The results suggest that different kinds of atmospheric disturbances dominate rainfall patterns in different parts of the tropics.
Tropical Australia was one region of particular interest because it lies near the boundary between tropical and temperate weather patterns. Understanding these disturbances could provide useful information about rainfall during the Australian monsoon.
The findings also demonstrate that tropical rainfall cannot be explained by cyclones and individual thunderstorms alone. Larger atmospheric systems help organize the conditions under which heavy rain develops.
What the Discovery Means for Climate Change
The research raises important questions about how tropical rainfall could respond to a warming climate.
Warmer air can generally hold more water vapor, potentially changing the behavior of weather systems that depend heavily on atmospheric moisture. Scientists are still investigating whether those changes will make moisture modes stronger, more frequent or different in their movement.
Singh said the newly identified systems could provide a useful way to study future changes in monsoon rainfall and extreme precipitation. A clearer understanding of their underlying physics may increase confidence in long-term climate projections.
Such improvements could be valuable for regions where rainfall strongly influences agriculture, water supplies and flood risks.
However, the findings are not a prediction that tropical rainfall will increase everywhere. Climate change can alter atmospheric circulation and rainfall distribution in complicated ways, producing different outcomes across regions.
The researchers also acknowledged limitations in their classification method. Systems moving near the boundaries between categories can be difficult to separate, and movements toward the north or south may not be fully represented by a method focused on eastward and westward speed.
Their analysis identifies important relationships between atmospheric disturbances and precipitation, but those relationships do not establish that every recorded rainfall event was caused entirely by one system.
Researchers Plan to Examine Future Rainfall Changes
The study creates a foundation for investigating tropical weather systems that previously lacked a consistent classification framework.
Scientists can use the approach to compare atmospheric observations with climate simulations and examine whether models reproduce the same types of disturbances found in satellite records.
The work may also help researchers investigate changes in monsoon patterns, seasonal rainfall and short-duration extreme precipitation.
The study was supported by the Australian Research Council Centre of Excellence for the Weather of the 21st Century. Its findings provide a new way to connect theoretical atmospheric physics with the weather patterns observed across tropical regions.
The next major question is how moisture modes and related systems will behave as the planet warms. By identifying and tracking these disturbances, researchers now have a more detailed framework for investigating their role in future tropical rainfall.