equilibrium vapor pressure
the number of vapor molecules surrounding a droplet remains fairly constant so the droplet does not grow or shrink
the smaller a droplet is, the greater the curvature it has, which makes it easier for water to evaporate because of weak bonds
because smaller droplets have greater curvature, it requires ___ to maintain equilibrium.
greater vapor pressure is req'd to maintain equilibrium, and the pressure is provided by a RH > 100.1%
To keep a droplet in equilibrium...
vapor molecules must be around it to replace molecules that have evaporated
When the air is ____ with respect to flat surfaces, it is ______ with respect to curved surfaces
water-attracting particles, like salt, that allow condensation to begin in unsaturated air
Salt particles partially dissolve in water droplets, decreasing the saturation vapor pressure
Condensation can form rain drops, but _____.
It is so slow that it takes days and if they fall by chance before they get big enough, they will evaporate before reaching the ground
Two ways to grow raindrops besides condensation are____.
Collision-Coalescence process and Bergeron process
when the gravity and the air drag on a falling object become equal and the object begins to fall at a constant rate
Why are the first drops of rain large and heavy?
Because the larger drops fall fastest and reach the ground first.
Why don't smaller drops make it to the ground?
Because they evaporate on the way down or are absorbed into larger drops.
4 important factors in the production of raindrops
liquid water content of clouds, cloud thickness, updrafts of cloud, electric charge of droplets and electric field
enough water molecules join together within the droplet in a rigid pattern to form a tiny ice pattern and it acts as an ice nucleus
The saturation pressure above a water surface is ___ than an ice surface. Why?
greater, because water molecules evaporate more easily.
Ice-crystal - Bergeron Process
water evaporate from water droplets and migrates to ice crystals, so ice crystals grow at expense of water droplets
falling ice crystals collide with supercooled water droplets which freeze on contact and thus the ice crystal grows forming graupel
Fracturing ice crystals cause...
a greater number of ice particles to fall and grow by aggregation and accretion, like a chain reaction
For ice crystals to grow large enough to produce precipitation, there must be a ratio of...
1 ice crystal to 100,000 - 1,000,000 water droplets
falls from a layered cloud that covers a large area and has smaller vertical air currents (nimbostratus)
raindrops are > 0.5 mu(m) caused by strong upward winds, or an updraft that suddenly weakens or changes direction- short and intensive precipitation
rain drops evaporate before they reach the ground, making white streaks below clouds (happens in dry, warm atmosphere)
small ice crystals sublimate before they reach the ground, causing white streaks below clouds
tiny ice pellets formed when ice crystals fall and melt in the warmer atmosphere below the cloud, but then refreeze in the surface layer which is subfreezing.
supercooled liquid droplets fall and freeze when they make contact with an object, causing a glaze of translucent ice
when small liquid cloud or fog droplets land on frozen objects and freeze on contact (milky ice)
pieces of translucent or opaque ice of spherical or irregular shape ranging from pea to golf ball sized or larger
Hail is formed when...
particles or graupel grow by accretion, and stay in the cloud for 5-10 minutes
tipping bucket rain gauge
automated gauge that collects water in 1/10 inch collectors, and each time a collector fills, it tips to empty and a remote recorder registers the 1/10 in. rain