A translator who hears only the meaning, not the noise in the hall, can accurately convey a conversation. Climatologists need such a translator to understand how the ocean and atmosphere influence each other. Their interaction resembles a conversation where voices are drowned out by background sounds. In a new study, tools originally designed for analyzing brain signals have been applied to climate data for the first time.

The methods work like an attentive listener. They don't just see that two signals change together; they compute which one sounds first. To do this, they build a model where the current value depends on the past of both signals, and noise is accounted for separately. The methods were first tested on synthetic data where the direction of influence is known. There, they clearly identified the correct direction, while the old method made mistakes.

Next, they took real data: ocean temperature in the tropical Pacific and rainfall over India. All methods agreed: El Niño influences the monsoon more strongly than the monsoon influences El Niño, and the connection lags by one to two years. For the South Atlantic Convergence Zone, the new method revealed, for the first time, years when the ocean truly drives the atmosphere. Now climatologists can test such connections in other regions, for example, how the ocean affects droughts.