So I have been spending time in Moscow Russia which essentially records very similar climatic humidity to my home city of London. However in Moscow my throat is permanently dry, I need to consume more water, many people have humidifiers in there bedrooms and the government spray the roads with water to prevent citizens choking on the dry dusty air.

Clearly the climate is 'drier' (or another more accurate technical adjective). What metric will show this difference between Moscow and London ?

And why is the humidity metric the same ?

  • $\begingroup$ What you say is very odd. When I lived in London I was taking lessons in Russian language, and my language teacher ( a Russian) said he felt the cold much more in London than in Moscow, although Moscow was colder according to the thermometer. He said the reason for this was that the London cold was a damp cold, whereas in Moscow the air was dry. From what you say, he was right, so I don't see how London and Moscow can have similar humidity, especially as England has a marine climate and Russia doesn't. $\endgroup$ – Michael Walsby Oct 31 '19 at 13:24
  • $\begingroup$ Is this a difference between relative and absolute humidity? Not sure how it feels factors in, but if Moscow is colder then the same relative humidity will be a lower absolute humidity. $\endgroup$ – winwaed Oct 31 '19 at 13:28

Weather services rarely state the absolute humidity because it is not easy to determine. Instead, they state the relative humidity.

Absolute humidity is the mass of water vapor divided by the mass of dry air in a volume of air at a given temperature. The hotter the air is, the more water it can contain. Absolute humidity is expressed as grams of moisture per cubic meter of air ($g/m^3$).

Relative humidity is the ratio of the current absolute humidity to the highest possible absolute humidity (which depends on the current air temperature). A reading of 100 percent relative humidity means that the air is totally saturated with water vapor and cannot hold any more, creating the possibility of rain.

A better measure of how atmospheric moisture will affect people and the environment is the dew point.

The dew point is, in short, the point at which dew droplets form on objects like grass – in other words, when a relative humidity of 100 percent is achieved.

If you want a real judge of just how "dry" or "humid" it will feel outside, look at the dew point instead of the RH. The higher the dew point, the muggier it will feel.

  • $\begingroup$ thanks, this is very interesting $\endgroup$ – Iain Watt Nov 4 '19 at 10:55

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