Climatology Atmospheric pressure Bar = a force of 10^6 dynes/cm^2 (dyne = force required to accelerate 1 gm. 1 cm./sec./sec.) Bar = 29.52 inches of Hg. a bar is divided into millibars, each of which = 0.03 inch Hg. Winds are designated by the direction from which it is blowing. Moisture One can measure water vapor in millibars. Dew Point = 100% relative humidity (saturation point) at a given temp. Absolute humidity = density of water vapor present (gms./meter^3). Specific humidity = amount of water vapor/unit mass of air (gms./kilo). Dew = condensation of water vapor on objects whose temperature is lower than the dew point. Frost = condensation of water vapor on objects whose temperature is below freezing. Snow = crystalline particles of water. Hail = water drops repeatedly carried aloft and additional layers are frozen to it to form concentric rings of ice. Sleet = rain falls through a freezing layer of air, freezing the rain drops as they fall. Slage = rain strikes objects that have temperatures below freezing, thus freezing the rain on contact. Air composition N2 = 78.09%. Numerous other inert gases + water vapor O2 = 20.95% make up the remainder. CO2 = 0.03% If air is saturated with water vapor in humid tropics, the air consists of ~4% water vapor. 3% water vapor produces a muffy day.