TOKYO -- Many of us can seemingly detect two distinct odors that occur along with precipitation: one when rain begins to patter and another as it continues to pour. These can be considered almost nostalgic scents. Why is it that the mere water in rainfall gives rise to these fumes?

Kentaro Araki, a senior researcher at the Japan Meteorological Agency's Meteorological Research Institute who supervised how the weather was portrayed in the animated film "Weathering With You," said that rain-related smells are largely divided into two types. One is referred to as "petrichor" and the other is called "geosmin."

"Petrichor might be commonly described as 'earthy.' and it is a scent that you can pick up when rain has fallen for the first time in a while," explained Araki. The word is from the Greek for "rock essence." It is said to be created as dried soil and plant oils attached to the face of rocks are lifted into the air by rain.

While the scent of petrichor can be detected when rain starts to pour, geosmin is the smell that arrives mid- or post-rainfall. Its name comes from the Greek for "smell of the earth." It is also the name for organic compounds produced by bacteria in the soil, which are released into the air and become an odor with the rainfall. "I think it's a rather fishy, moldy smell," Araki said.

Which of the two is the stronger smell? According to Araki, it can depend on the season as each brings its own characteristics. In Japan, during the rainy season centered around June, when stagnant fronts often result in long rains, and in fall, geosmin creates a more powerful odor. Petrichor is believed to often be stronger over summer, when localized heavy rains are more common.

So, there you have it: the smells of rain are created by plants and rocks as well as bacteria in the soil. Do the smells differ depending on the environment in each location even when it pours in a similar style? Araki believes so, and said, "I've heard people say they used to smell the rain, but since coming to the city, they don't feel it as much anymore. Both petrichor and geosmin require soil such as fields to generate. Perhaps it is easier to smell them in the suburbs than in the city center."

(Japanese original by Yukiko Ono, Lifestyle, Science & Environment News Department)