Hurricanes gather strength over warm ocean water—over warm salty water—but the rain that falls is always fresh. What has happened to the salt?

Ask Tom Why
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Dear Tom,

Hurricanes gather strength over warm ocean water—over warm salty water—but the rain that falls is always fresh. What has happened to the salt?

Jerry Witon

Dear Jerry,

Rain water is fresh because only pure water evaporates from the ocean. The salt (and other impurities) remain behind in the ocean. At the moment of evaporation, the salt in ocean water comes out of solution—it separates from the water and remains in the ocean—and only pure water evaporates.

What can and does happen is that salty ocean spray flies into the air and mixes with rain to produce salty rain. Some of the spray also evaporates and leaves its load of salt floating in the air. This salt essentially “seeds” the atmosphere with condensation nuclei that are important in the formation of rain droplets. The sea salt plays in important role in enhancing hurricane rainfall.

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