When Will the Rains Come?

Simon de Szoeke; assistant professor; College of Earth, Ocean, and Atmospheric Sciences
Simon de Szoeke; assistant professor; College of Earth, Ocean, and Atmospheric Sciences

Researchers at the College of Earth, Ocean, and Atmospheric Sciences are trying to improve our ability to forecast a phenomenon known as the Madden-Julian oscillation (MJO). This eastward-moving pulse of heavy rainfall and strong winds travels around the equator and has broad impacts on climate and weather. While statistical indices of the MJO from past records show that it has a cycle of about 30 to 60 days, predicting when it will start remains a challenge for forecasters.

An observational study in the Indian Ocean, the region where the MJO starts and grows to its full strength, hopes to answer some outstanding questions about its genesis. A paper by CEOAS professors Jim Moum, Simon de Szoeke and co-authors presents new in-situ observations and describes the interactions between the ocean and atmosphere. Improved forecasting will help scientists anticipate events under the influence of the MJO, from seasonal rain forecasts in the tropics to El Niño to tropical cyclones.

“We don’t know the physical laws, or the reason an MJO happens. If we knew that, we could make a deterministic model,” de Szoeke said.

De Szoeke is particularly interested in the relationship between evaporation and rainfall in the MJO. “Evaporation is important, because that’s how the ocean loses most of its heat. But evaporation alone is not closing the moisture budget and explaining the rainfall in the MJO.”

The question remains, then, if evaporation does not account for all of the MJO’s rainfall, what else might be contributing?

“We know moisture converges on a large scale over the warmest sea surface temperature in the Indian and Pacific Oceans, and on a small scale into the rain storms found in the MJO. We don’t know if the ocean is important for the MJO. That’s a fascinating basic question,” de Szoeke said.

He has a few theories that he will be exploring in future research, but determining such air-sea interactions and their effect on the MJO has both basic and broad implications.

“The more we learn about it, the less we understand about it,” de Szoeke said. “At the same time, seasonal forecasting is really important for people trying to grow crops and anticipate when the rains will come.”