More important than tropical cyclones: Scientists finally track the hidden weather systems behind most tropical rainfall

For the first time, researchers in Australia have identified and tracked the weather systems that are collectively more important to rainfall across the tropics than tropical cyclones.

The work, published in the journal Weather and Climate Dynamics, has advanced a new way to investigate how tropical rain may change as the Earth warms up.

Weather outside the tropics is commonly understood through recognisable systems such as cold fronts, high-pressure systems and low-pressure systems. However, in the tropics, scientists have lacked an equivalent framework for identifying many of the systems responsible for organising day-to-day clouds and rain. Previous work has tended to either focus on following individual thunderstorms, or looking at planetary-scale atmospheric waves that influence many weather systems at once.

In recent decades, emerging theories have predicted the existence of moisture modes, relatively slow-moving systems which can organise tropical thunderstorms and rainfall over several days. Other work has focused on large-scale atmospheric gravity waves, influencing broad regions of rising and sinking air, and moving clouds and rainfall over vast distances.

Unlike tropical cyclones, however, these moisture modes and gravity waves have received little attention beyond specialist areas of atmospheric science.

“Tropical cyclones are the divas of the tropics,” said Professor Christian Jakob of Monash University.

“It’s fair that they receive a lot of attention because they have such major impacts. But less dramatic systems occur much more frequently, and collectively they are very important for rainfall.”