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ISU GEO 211 - Exam 3 Study Guide
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GEO 211 1st EditionExam # 3 Study Guide Lectures: 15 - 19Lecture 15 (October 3)What is adiabatic process?A process that takes place without a transfer of heat between the system (such as an air parcel) and its surroundings. In an adiabatic process, compression always results in warming, and expansion results in cooling. - Rising in air parcel expands and cools- Expansion is due to decrease of pressure with altitude- Sinking air parcel is compressed and warms- As long as the air in the parcel is unsaturated (relative humidity is less than 100%), the rate of adiabatic cooling or warming remains constantHow does Dry Adiabatic Rate differ from Moist Adiabatic Rate?DAR- the rate of change of temperature in a rising or descending unsaturated air parcel. The rate of adiabatic cooling or warming is about 5.5°F per 1000 feet.MAR-the rate of change of temperature in a rising or descending saturated air parcel. The rate of cooling or warming varies but a common value of 3.3°F per 1000 feet is used.You should be able to calculate adiabatic cooling and warming of a parcel of air.Lecture 16 (October 8)How is stability of the atmosphere determined?Stability is determined by comparing temperature of rising parcel to that of its surroundings (environment). The temperature of both the rising air and of its environment must be measuredat various level about the earth.What do we mean by: stable atmosphere, unstable atmosphere, conditionally unstable atmosphere?Absolutely stable- exists when environmental lapse rate is less than moist adiabatic rate- Rising air parcel is always colder than air surrounding itAbsolutely unstable- occurs when ELR is greater than DAR-Rising air is always warmer than surrounding itConditionally unstable- occurs when ELR is between the MAR and the DAR- Atmosphere is stable if rising air is unsaturated, but unstable if rising air is saturatedHow does stable air differ from unstable air?Stable air- resists upward movement, when the rising air is colder than the environment, it will be more dense (heavier) and tend to sink back to its original levelUnstable air- when the rising air is warmer and thus less dense than the surrounding air, it will continue to rise until it reaches the same temperature as its environmentWhat conditions bring about unstable atmosphere?1. Cold air moving over warm surface2. Daytime solar heating of the surface3. Radiational cooling of clouds- Loss of heat energy to space from cloudsWhat conditions bring about stable atmosphere?1. Warm air moving over cold surface2. Nighttime radiational cooling3. Advection of cold surface airLecture 17 (October 10) How do cloud droplets grow larger?Droplets with a greater relative humidity than the equilibrium value allow the droplet to grow by condensation.Cloud condensation nuclei allow condensation to begin on particles wen the relative humidity iswell below 100 percent because they are hygroscopic (have an affinity in water vapor)What is the ice crystal process?Droplet growth in cold clouds with temperatures below 32°F- Cloud droplets don’t freeze at 0°C, freeze at -40°C- Is extremely important in middle/higher latitudes where clouds extend upward into regions where the air temperature is well below freezingWhat is collision and coalescence process?Droplet growth in warm clouds, larger droplets accelerated downwards by gravity collide and merge with smaller droplets- Terminal velocity- constant speed obtained when upward air resistance balances with downward force of gravity- Can play a significant role in producing precipitation- The greater the speed, the more air molecules the drop encounters each second- Larger drops fall faster than smaller drops- Coalescence- large drops overtake and collide with smaller drops in their path, this merging of cloud droplets in collision is called coalescenceHow does a cold cloud differ from a warm cloud?Warm clouds- clouds that have above-freezing temperatures at all levels, precipitation forms by the collision and coalescence processCold clouds- where clouds extend upward into regions where the air temperature is well below freezing Lecture 18 (October 13)Know all precipitation types and how each come aboutRain- falling drops must have diameter of 0.5mm (0.02 inch) or greater to be considered rain- Less than 0.5mm is drizzleVirga- rain that evaporates before reaching the surface, observed as streaks of falling precipitation (figure 7.14)Snow- snowflakes that will reach the surface, temperature profile underneath a cloud should bebelow freezing- Rain begins as snowflakes in cold clouds- Freeing level is above 12,000 feet in summer when snowflakes melt before reaching the ground (freezing level is much lower in winter)Sleet- translucent balls of tiny ice pellets- Form when melting snowflake falls through the deep subfreezing surface layer of air- Bounces wen striking the ground (figure 7.21)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 glazeIce storms- when freezing rain creates shimmering landscapeSnow 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 hailstoneHail- forms in cumulonimbus clouds, updrafts can reach 100mph- Form in clouds with abundant supply of supercooled waterLecture 19 (October 15)How is precipitation measured?1. Standard rain gauge- commonly used - Cross section= 10 times that of tube- Measurable amounts= 0.01 inch or greater- Less than 0.01 is reported as a trace2. Tipping buck rain gauge- consists of 2 buckets- Each time a bucket fills up with 0.01 inch of rain, it tips, sending an electric signal to the remote recorder3. Weighing gauge- collects rainfall in a cylinder that sits on a sensitive weighing platform- When cylinder fills up, electrical impulse is transmitted to a pen that records the


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ISU GEO 211 - Exam 3 Study Guide

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