Chapter 7: Circulation of the Atmosphere

Transcription

1 Weather & Climate Spring 2011 Study Guide for Exam 3 Page 1 of 9 Chapter 7: Circulation of the Atmosphere Scales of Atmospheric Motion Large and Small Scale Circulation, All winds are highly integrated Macroscale (2 kinds) Planetary Can last for weeks or longer 1,000-40,000 km Westerlies and Trade Winds Synoptic Days to weeks 100 5,000 km Mid-latitude cyclones, anticyclones and hurricanes Mesoscale Minutes to hours km Thunderstorms, tornadoes and land-sea breezes Microscale Seconds to minutes Less than 1 km Turbulence, dust devils and wind gusts Local Winds Land and Sea Breezes Day/night shift Temp changes Mountain and Valley Breezes Day/night shift Temp changes Chinook Winds (Foehn) Air moves up and over mountain Comes down warmer and dryer Adiabatic (wet and dry) Katabatic Winds (Fall) Cold heavy air sinks Country Breezes City is warmer than country lower pressure Global Circulation 3-Cell Circulation Model Vertical Structure of the Atmosphere This describes the interconnections between the rising and sinking air patterns Hadley Cells Global Pressure and Winds Idealized Zonal Pressure Belts Polar High (90 N, 90 S) Subpolar Low (Polar Front) (60 N, 60 S) Subtropical High (30 N, 30 S) Equatorial Low (0 ) Global Scale Winds These are winds aloft (above the surface)

2 Weather & Climate Spring 2011 Study Guide for Exam 3 Page 2 of 9 Driven by the Pressure Gradient Force (H to L) & Coriolis Effect (NH = Rt) (SH = Lft) Form consistent and persistent directional global scale winds Polar Easterlies Prevailing Westerlies North East Trades / South East Trades Also Areas of notoriously low winds Inter-tropical convergence zone & Doldrums (Equatorial Low) Horse Latitudes (Subtropical High) Monsoons Monsoon refers to a SEASONAL change in wind patterns for a large geographic region Note: Monsoon does NOT mean heavy rain! Asian Monsoon Concerns the Indian Ocean and Southern Asia The yearly two-phase change is similar to the daily change of a land-sea breeze The Westerlies Jet Streams Polar Jet Stream Sub-Tropical Jet Stream Waves in the Westerlies Rossby Waves Season Shifts Global Winds and Ocean Currents Ocean Currents Follow Wind Upwelling (Eastern Shores) Chapter 8: Air Masses What is an Air Mass? An extensive body of air that has relatively uniform temperature and humidity derived from a source region Source Region The place where an air mass gets its temperature and humidity characteristics Air needs to sit over this area to get humidity & temp (air stagnates over this area and acquires characteristics) Moisture: Large uniform areas: m = Maritime (Humid) c = Continental (Dry) Temperature: Latitude A = Arctic (Very Cold) P = Polar (Cold) T = Tropical (Warm) E = Equatorial (Hot) Air Masses Affecting North America Continental Arctic (ca) Arctic Basin & Greenland Example: mt Maritime Tropical (Humid & Warm)

3 Weather & Climate Spring 2011 Study Guide for Exam 3 Page 3 of 9 Bitterly cold, very dry (winter) Continental Polar (cp) Interior Canada & Alaska Very cold, dry (winter) Maritime Polar (mp) North Pacific Cool, humid (all year) Northwestern Atlantic Cold, humid (winter) Cool, humid (summer) Continental Tropical (ct) North Mexico & Southwester US Hot, dry Maritime Tropical (mt) Gulf of Mexico, Caribbean, Western Atlantic Warm, humid (all year) Lake Effect Snow Heavy snow that falls on the leeward side of lakes Process Cold, dry air masses move over warmer lakes Air is warmed can hold more water vapor Evaporation from lakes fills air with water vapor Clouds move off of lakes over colder land Air is cooled can hold less water vapor Air becomes saturated precipitation begins (snow) Usually occurs within 50 miles of the lakes Chapter 9: Weather Patterns Polar Front Theory (1800s) Mid-latitude Cyclone Low pressure system Cyclone Counter-clockwise rotation Air spinning into the Low Mid-latitudes Continental US to Southern Alaska 600+ miles in size Term Fronts first used Fronts Boundary surfaces that separate different air masses Different temperature and humidity Fronts said to be Overrunning one another One front is overtaking the other Synoptic indication (how we show on a weather map) Colors Symbol Point in direction of movement

4 Weather & Climate Spring 2011 Study Guide for Exam 3 Page 4 of 9 Types of Fronts - UNDERSTAND HOW EACH OF THESE 4 WORKS! Warm Front Warm air overrunning Cold Cold Front Cold air overrunning Warm Stationary Front Air masses moving parallel Occluded Front Three air masses combining Cold-type The first front is colder than the last Warm-type The first front is warmer than the last Life Cycle of a Mid-latitude Cyclone Formation Cyclongenesis Beginning stage of cyclone development Cyclonic flow development Due to clash of cold and warm air masses Warm air rises begins the interaction Low pressure forms, causing CCW movement Occlusion the end begins Eventually, warm air is lifted over cold This inversion stops vertical development Process eventually stops Idealized weather of a mid-latitude cyclone Formation Cyclongenesis Chapter 10: Thunderstorms & Tornadoes Thunderstorms A storm that generates lightning and thunder Frequently includes Gusty winds & Heavy rain Sometimes includes Hail, Tornadoes Frequency 2,000 thunderstorms occurring right now (worldwide) 100,000 per year in US More than 1,000,000 lightning strikes per year in US Location Hot and Moist environments = more KNOW US pattern of Thunderstorms Two types of Thunderstorms Based on strength and (potential) destructiveness Air-Mass Thunderstorm Thunderstorm which occur within one air mass (mt) Produce heavy rain for a short periods, then light rain Stages of Development Cumulus Stage Mature Stage Dissipating Stage Severe Thunderstorm Very powerful (and dangerous) thunderstorms, 58+ mph winds and/or ¾ + hail Supercell Thunderstorms

5 Weather & Climate Spring 2011 Study Guide for Exam 3 Page 5 of 9 Most destructive thunderstorms 2,000 3,000 per year in US most damage and deaths Air-Mass Thunderstorm KNOW THE THREE STAGES! Thunderstorm which occur within one air mass Often mt (maritime Tropical Humid and Hot) Earth s heating is the cause Spring & Summer ground heating Mid- to Late-Afternoon ground heating Localized, short-lived thunderstorms Storms are scattered, isolated clouds, or small cloud cells Cloud Cell = Grouping of several individual clouds Produce heavy rain for a short period, then changing to light rain Air-Mass Thunderstorm 3 stages of development Cumulus Stage Start with mt air mass (Humid and Hot) Add heating from the earth (summer/afternoon) Warm air rises Expands/cools Condenses Cumulus Clouds This rising air is called Updrafts (convection) As the updrafts continue, the cloud gets larger and higher Precipitation (Bergeron) begins to form above the freezing line Precipitation begins to fall Entrainment begins Falling rain pulls in cold, dry air from outside the cloud top The cold dry air follows the path of the falling rain It evaporates most (all?) of the rain but continues falling (colder = denser = heavier) evaporation also helps cool the air (endothermic) Cold Downdrafts (or Gusts) blow out ahead of the storm cloud Mature Stage Precipitation increases and cold downdrafts continue Updrafts continue, bringing moisture and energy (latent heat) Expect: Updrafts Cold downdrafts Heavy precipitation Lightning and thunder Possible hail and occasional tornadoes Dissipating Stage Updrafts begin to slow and stop No additional moist, hot air is entering cloud Moisture within the cloud begins to lessen Entrainment weakens: less precipitation forms and falls Precipitation becomes light Eventually the rain and downdrafts stop Severe Thunderstorms Severe Thunderstorms are very powerful thunderstorms which produce

6 Weather & Climate Spring 2011 Study Guide for Exam 3 Page 6 of 9 winds > 58 mph and/or hail > 3/4 They also tend to include: heavy downpours flash flooding Straight-line winds Non-rotating, fast, local-scale winds. Very destructive. Large hail Frequent lightning Potential Tornadoes The structure of these thunderstorms allow the warm updrafts to reach great heights Updrafts tilt due to wind sheer (rapid horizontal and/or vertical movement) Entrainment does NOT interfere with the updrafts Thus they reach higher altitudes and build up more power The updrafts can actually create more updrafts, adding to the storms intensity Supercell Thunderstorms Most destructive severe thunderstorms 2,000 3,000 per year in US but responsible for most damage and deaths Lightning and Thunder Thunderstorm A thunderstorm is only a thunderstorm IF thunder is heard! Thunder can only be heard if lightning happens first Lightning Lightning is the discharge of an electric charge from a cloud Most lightning strikes occur from cloud to cloud (sheet lightning) Only 20% of strikes are cloud to ground But these account for most lightning caused damage and death Thunder Lightning bolt discharges in a small tube of air (10cm +/-) Air is superheated to 50,000 F in less than 1 second! The air expands explosively and creates a sonic boom = thunder Lightning Formation Lightning How lightning forms Lightning Flash: Bright streak of lightning, made up of multiple strokes (3-4) Lightning Stroke: Individual discharge, lights up the pathway As a cloud forms it begins to develop an electrical charge Since opposite charges attract and like charges repel How lightning forms As a cloud forms it begins to develop an electrical charge Scientists believe the cold ice crystals (Bergeron process) create a positive charge (+) in the upper cloud The warmer, lower cloud forms a negative charge (-) Under the cloud, the ground begins neutral: neither (+) or (-) Since opposite charges attract and like charges repel The negative charge at the bottom of the cloud Pushes away the negative (-) ground charges and

7 Weather & Climate Spring 2011 Study Guide for Exam 3 Page 7 of 9 Attracts the positive (+) ground charges The ground under the cloud becomes positively (+) charged Step leaders (downward ionized air pathways) form from the cloud bottom These step down to the surface As it nears the ground, the ground charge rises to meet the leader Now, negative (-) charged particles in the leader flow to the ground The Return Stroke, is the upward movement of the initial discharge making its way to the cloud base. When it reaches the cloud base, the negative charges flow from the cloud to the ground in several strokes. Each following stroke begins with a Dart Leader (a smaller ionized pathway) that allows the process to continue. The cloud base is now fully discharged of its negative charge and begins to build up again. Thunder The sound emitted from a lightning bolt heating the air it is passing through A lightning bolt discharges in a relatively small tube of air (10cm +/-) The air within that pathway is superheated It can rise 50,000 F in less than 1 second! The air expands explosively and creates a sonic boom = thunder Heat lightning When lightning occurs more than 12 miles away, we often do not hear the thunder We only see the lightning and this is referred to as heat lightning Interesting facts Lightning bolts can be up to five miles long It is not uncommon for lightning to strike out of the blue sky A single lightning bolt can pack a wallop! 100,000,000 Volts! Lightning can kill! 4,000+ killed in US since 1960 Odds of being hit by lightning? 1 : 700,000 per year 1: 3,000 in your lifetime! You can judge how far away the lightning is by counting the seconds between the flash, and when you hear the thunder 5 seconds = 1 mile Chapter 15: World Climates Köppen Climate Classification System The Köppen Climate Classification System is the most widely used for classifying the world's climates. Most classification systems used today are based on the one introduced in 1900 by the Russian-German climatologist Wladimir Köppen Köppen divided the Earth's surface into climatic regions that generally coincided with world patterns of vegetation and soils

8 Weather & Climate Spring 2011 Study Guide for Exam 3 Page 8 of 9 The Köppen system recognizes five major climate types based on the annual and monthly averages of temperature and precipitation. One additional type is a hybrid of the others based on altitude changes. Each type is designated by a capital letter. Climate Types o Temperature Monthly and Yearly average o Precipitation Monthly and Yearly totals o 6 Climate Types A - Tropical Moist Climates All months avg. above 18 C B - Dry Climates Little precipitation much of the year C - Moist Mid-latitude Climates with Mild Winters D - Moist Mid-Latitude Climates with Cold Winters E - Polar Climates Extremely cold winters and summers H Highland Climates Hybrid of multiple climate types due to change in altitude (colder temperatures at higher elevation) A Climates Tropical climates with abundant precipitation during a portion of the year. Mean monthly climates must exceed 18ºC; precipitation exceeds evaporation. Moist Tropical Climates are known for their high temperatures year round and for their large amount of year round rain. Tropical Moist Climates (Af) RAINFOREST know about this one! B Climates Arid and semiarid climates of the low and middle latitudes Evaporation exceeds precipitation. Dry Climates are characterized by little rain and a huge daily temperature range. Dry Tropical Climate (Bw) DESERT BIOME know about this one! C Climates Mild and humid climates primarily in the lower middle latitudes. Mean monthly temperature of the coldest month must be between 18 and 3ºC; at least one month must have a mean temperature of 10 ºC or higher. In Humid Middle Latitude Climates, maritime/continental differences play a large part. These climates have warm, dry summers and cool, wet winters. Mediterranean Climate (Cs) CHAPARRAL BIOME know about this one! D Climates Found in the upper middle latitudes and subpolar regions of the northern hemisphere. Humid continental climates with cold winters; mean monthly temperature of coldest month below -3ºC; mean monthly temperature of the warmest month must be 10ºC or higher. Continental Climates can be found in the interior regions of large land masses. Total precipitation is not very high and seasonal temperatures vary widely. Boreal forest Climate ( Dfc) TAIGA BIOME know about this one!

9 Weather & Climate Spring 2011 Study Guide for Exam 3 Page 9 of 9 E Climates Cold climates of the northern latitudes. All months must average below 10ºC. Cold Climates describe this climate type perfectly. These climates are part of areas where permanent ice and tundra are always present. Only about four months of the year have above freezing temperatures. Tundra Climate (Et) TUNDRA BIOME know about this one! H Climates Hybrid climates that have significant change in altitude which brings colder temperatures with elevation increases Highland climates experience a rapid change in temperature over a short distance due to elevation. They maintain similar climate patterns to the major Climate area in which they belong. Alpine Climate (H) Understand how this biome works ALTITUDE IS THE KEY! LABS INCLUDED ON EXAM 3 Lab 9: Air Masses and Fronts Air masses o Large body of air with similar characteristics Temperature Humidity o Form over source regions Large uniform areas of the surface Need to remain near stationary over these to obtain characteristics o Defined/Named Humidity m = Maritime = Ocean = Moist c = Continental = Land = Dry Temperature A = Arctic = Very Cold P = Polar = Cold T = Tropical = Hot E = Equatorial = Very Hot o Know the Air Masses that effect North America cp, mp, cp, mt, ct Fronts o Where two air masses meet o Types Warm Front Warm air overrunning Cold Cold Front Cold air overrunning Warm Stationary Front Air masses moving parallel Occluded Front Cold front overrunning warm front lifts warm air o Know the symbols for each