Download Cloud, Fog and Dew: Formation and Types - Lecture Notes | GEOG 1112 and more Study notes Geography in PDF only on Docsity! CLOUDS, FOG, & DEW: FORMATION & TYPES Pg. 172-185 & pg. 146-151 ** Clouds, Fog, and Dew all have 2 properties in common: pg. 146, Table 5-3 1) Must form from saturated air RH = 100%, dew point T° = air T° 2) Must have a surface on which the water vapor can condense * Dew ---- the ground, vegetation, a car, or similar surface * Clouds & fog ---- need condensation nuclei --- Microscopic particles of dust,, salt, smoke, etc. --- Hygroscopic nuclei -- are very water absorbent condensation nuclei usually of sulfate & nitrate crystals *** CLOUDS : a form of condensation best described as a dense, visible aggregation of minute droplets of water or tiny crystals of ice. Pg. 172-185; Fig 6-15, pg. 173; Table 6-1, pg. 173) How do they form? a parcel of moist air reaches the point of saturation where the water vapor is changed to liquid water droplets. Either by cooling the air T° to the d.p. T° OR by adding more water vapor. Cooling the air T° is the most common method. Pg. 179, 181, 183 ** Cloud Classification: -- 2 criteria for classifying clouds; 1) Height of cloud base above the surface. Don’t worry about knowing altitudes Lower level clouds are predominately liquid water Middle clouds = mixture High-level clouds are predominately ice crystals. * 3 categories: low, middle, high 1. Low < 2000 m = strato clouds 2. Middle 2000 m -- 6000 m = alto 3. High > 6000 m = cirro 2) Degree of vertical development. -- Is an indication of the degree of stability/instability * 2 main categories: 1. Stratus = “layer,” horizontal development pg. 176 2. Cumulus = “heap, or cotton balls” vertical development pg. 177 * Some other common names used – pg. 174 Cirrus = “curl of hair,” clouds found in the highest up in the atmosphere, composed of ice crystals pg. 175 Nimbus = “violent rain,” cumulonimbus & nimbostratus pg. 176 & 178 See Figs. 6-15 to 6-33! 5 CLOUDS you MUST KNOW by sight! Cumulus Stratus (no precipitation) Nimbostratus (precipitation) Cirrus Cumulonimbus (thunderstorms) *** FOG : basically at ground level pg. 147-150 Condensation can occur in some instances where the RH is as low as 75% - 80% ** As the water droplets get bigger they become visible, this decreases visibility (being able to look through the droplets). If visibility is reduced to 1 km, the haze or cloud is categorized as FOG. Pg. 149 *** 4 main categories of fog: Radiation, Advection, Upslope, Evaporation pg. 150 & 151 1) Radiation fog: produced over land when radiational cooling decreases the air temp to the dew point temp pg. 148
