Back when I started this thing, one of the major goals was to answer the types of questions that a person might come up with at a bar, while on a bike, or at least during a non-biking interval of a cross-country bike trip. Questions of the “the hell / anyway” variety, one of which came up recently on my dad’s blog: How the hell does dew form anyway?
Well first of all, what (the hell) is dew (anyway)? Simply put, dew is just water droplets that form on exposed objects that have cooled to temperatures below the aptly-named “dew point –“ the temperature at which the relative humidity of air would be 100%.
(The difference between dew and fog is that the water droplets in fog remain suspended in the air [while the difference between fog and mist has to do with density, where fog is the denser of the two {and the difference between mist and haze is dependent on relative humidity, with mist occurring at >95% humidity and haze under drier conditions}])
Calm weather and a lack of moisture in the upper atmosphere generally contribute to dew formation by enhancing radiative cooling at ground level. In some cases, however, where the moisture that forms dew comes from the atmosphere, a very small amount of atmospheric turbulence is needed to replenish moisture at the ground and sustain dew formation. Wet soil is also a major source of water vapor, especially since the ground can remain significantly warmer even at shallow depths than at the surface. As water vapor moves up from the warmer subsurface to the cooler surface, the dew that forms is said to be produced by distillation (yum!).
Technically speaking, it is dew that forms on cold glasses, be they of the “pint” or the “eye” varieties, when they are exposed to warm, moist air. Interestingly (but not really), pint glasses are then said to be “frosted” (a type of dew), while the more generic term “condensation” is generally used for eye glasses. Guttation – which is basically how plants pee – should probably not be confused with dew.
Well first of all, what (the hell) is dew (anyway)? Simply put, dew is just water droplets that form on exposed objects that have cooled to temperatures below the aptly-named “dew point –“ the temperature at which the relative humidity of air would be 100%.
(The difference between dew and fog is that the water droplets in fog remain suspended in the air [while the difference between fog and mist has to do with density, where fog is the denser of the two {and the difference
Calm weather and a lack of moisture in the upper atmosphere generally contribute to dew formation by enhancing radiative cooling at ground level. In some cases, however, where the moisture that forms dew comes from the atmosphere, a very small amount of atmospheric turbulence is needed to replenish moisture at the ground and sustain dew formation. Wet soil is also a major source of water vapor, especially since the ground can remain significantly warmer even at shallow depths than at the surface. As water vapor moves up from the warmer subsurface to the cooler surface, the dew that forms is said to be produced by distillation (yum!).
Technically speaking, it is dew that forms on cold glasses, be they of the “pint” or the “eye” varieties, when they are exposed to warm, moist air. Interestingly (but not really), pint glasses are then said to be “frosted” (a type of dew), while the more generic term “condensation” is generally used for eye glasses. Guttation – which is basically how plants pee – should probably not be confused with dew.
1 comment:
Well, I have just come from dinner at a wonderful new Indian restaurant on the Avenue with friends, and I must admit that these distinctions are just flying past my little brain. But it sounds like your Papa encountered straight out, ordinary rain.
How is your training comeing along?
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