GEOG 111 1st Edition Lecture 23 Outline of Last Lecture I Clouds a Cloud types II Precipitation a Two processes i Bergeron Outline of Current Lecture I Two processes for growing hydrometeors a Bergeron process b Collision Coalescence II Controls on precipitation rate Current Lecture I Two processes for growing hydrometeors review a Bergeron grows ice crystals through multiple processes involving all 3 states of water often produces ice crystals that act as seeds for growing hydrometeors below in the warmer portions of clouds i Requires a cold cloud temperature 10 C where ice crystals water vapor and super cooled water coexist 1 High level clouds cirrus and cirrostratus 2 In the coldest time of the year winter the Bergeron process may occur in lower altitude clouds as well and can even create snow ii Processes 1 Deposition of vapor ice crystal growth vapor to ice a Freezing also occurs but mainly deposition 2 Removal of water around ice crystal so relative humidity drops 3 Evaporation of cloud water vapor 4 So ice crystals grow at the expense of cloud water 5 Rising air motions keep growing snowflake aloft until it becomes too heavy iii The Bergeron process provides a distinct glazed and or streaked appearance in clouds b Collision coalescence hydrometer grows as it collides with smaller droplets through the sky i It is the only precipitation formation process that operates in warm clouds ii Can supplement the Bergeron process in cold clouds e g super cooled droplets colliding 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 iii Large cloud droplet falls through smaller cloud droplets accumulating them along the way iv Often contributes to the seeder feeder process process in which you have precipitation forming from the Bergeron seeds and Collision coalescence process warmer droplets that are feeding the seeds 1 Two scenarios a Rain droplets from melted snowflakes seeds are fed by the warm cloud water droplets b Cloud water droplets freeze on falling snowflakes in a process called riming i The snowflakes grow in size as it falls through the warmer part of the cloud II Controls on precipitation rate amount of precipitation time a Amount of water vapor condenses deposited out of atmosphere i Air temperature higher temp higher SVP and proximity to warm body of water how much water is available ii Rate of lifting 1 Convective lift can be 10 50 times faster than frontal lift b Distinguish between two precipitation types i Stratiform from nimbostratus cause sudden changes in temperature humidity and pressure of air 1 Where warm tropical air meets cool air and warm air is forced to rise 2 Less intense with over a longer period of time than convective precipitation ii Convective from cumulonimbus precipitation falls as showers with rapidly changing intensity over a certain area for a relatively short time 1 Mainly in a conditionally unstable or moist atmosphere
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