What is the Smell called which arises when there is rain on a hot soil after long day's ?

The piquant, musky odour that hangs in the air emanates from an odorous chemical buried in the soil called `geosmin' (literally, earth smell).

The smell is given off by Streptomyces bacteria, a genus belonging to the Actinomycetales order of Gram-positive eubacteria, also called actinomycetes. The soil normally contains a multitude of environmental saprophytic fungi.

Actinomycetes, a type of filamentous bacteria grow in soil when conditions are damp and warm. When the soil dries out, the bacteria produces the geosmin spores in the soil. Rain hitting the ground kicks up an aerosol of water and soil and spores into the air, where they are easier to smell. (just like an aerosol air freshener).

We breathe in fine particles of soil containing the bacteria.

extract fromN-ews paper - The Hindu dated 16 sept 2004

IT IS FRAGRANCE OF NATURE

I do  not really know how to describe it or give this aroma a name but here is what I would say:

It is perhaps the most luscious smell in the world; for as rain falls in the distance on the parched earth the mix of that moisture, soil and vegetation emits what can only be described as a sweet smell that utterly pervades the senses. That smell is all the richer and more exciting because of the promise it brings of an end to the long summer.