GEO 211 1st Edition Lecture 18 Outline of Last Lecture I Chapter 7 precipitation A Typical raindrop B Precipitation processes 1 Collision o Terminal velocity 2 Ice crystal Bergeron process Accretion Aggregation C Formation of raindrops in warm clouds depends on D Thin nimbostratus clouds have E Thick cumulonimbus have Outline of Current Lecture II Types of precipitation A Falling drops must have diameter of 0 5mm 0 02 inch or greater to be considered Rain B Virga C Snow D Sleet E Freezing rain F Ice storms G Snow pellets H Hail Current Lecture II Types of precipitation A Falling drops must have diameter of 0 5mm 0 02 inch or greater to be considered Rain Less than 0 5mm is drizzle B Virga rain that evaporates before reaching the surface observed as streaks of falling These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Precipitation C Snow snowflakes that will reach the surface temperature profile underneath a cloud should be below freezing Rain begins as snowflakes in cold clouds Freezing level is above 12 000 feet in summer when snowflakes melt before reaching the ground Freezing level is much lower in winter D Sleet translucent balls of tiny ice pellets Form when melting snowflake falls through the deep subfreezing surface layer of air Bounces when striking the ground Figure 7 21 E Freezing rain supercooled rain that freezes on contact with the ground Surface beneath a cloud is too shallow to freeze supercooled liquid drops Also called glaze F Ice storms when freezing rain creates shimmering landscape G Snow pellets small grains of ice formed by accretion in a cloud Doesn t bounce as sleet Also called graupel Can easily be crushed unlike a hailstone H Hail forms in cumulonimbus clouds updrafts can reach 100mph Form in clouds with abundant supply of supercooled water
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