Science-ish: Lets talk About Rain

How do you feel about rain?
Even in the depths of winter does it make you happy? When you’re warm, the sound of rain can be so lovely. It can be a guarentee that yes, you can stay inside and read all day. Or do you prefer sunshine?
According to science wikipedia 505,000 cubic kilometres of rain hits the earth each year, most of it in the ocean. What is your experience with rain? Dry winters? Monsoons? Rainy seasons? Warm days and big drops of rain are retty much the best, maybe. 
Rain also smells really good, right? Here comes the science. That smell is called petrichor. During dry seasons, some plants ooze out oils that are absorbed into the earth and rocks and things.
When it rains, that oil and another compound geosmin are realeased into the air to intoxicate your nostrils and mind. Geosmin is the earthy smell and flavour – the kind you taste in beetroot. Geosmin is released when certian microbes die, and is also responsible for the muddy smell in fish from the bottom of rivers.
The human nose, you may have noticed, is extremely sensitive to this small and can sense it as low as five parts per trillion. And that is why the earth smells so good when it rains. Still magical? You bet! Great for Singin’ in.
 Rain in the cities is different, as you know, to rain in big open spaces. Cities create urban heat islands that effect their local weather. Urban heat islands are like they sound, warmer areas around buildings that store and emminate heat. The heat (and subsequent water evaporation) and also polution above cities creates clouds above cities that are more likely to cause rain.
  As commuters and commercial traffic cause pollution to build up over the course of the week, the likelihood of rain increases: it peaks by Saturday.
The heat from cities can push the clouds up higher, so the likelyhood of lightning and thunder is higher when it hits the cooler air above. Humans are having an effect on rain cycles on a large scale for example the Mediterranean.
And that is why it often rains on your weekend! Science! Rain.

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