Tuesday, April 26, 2011 Chapters 9, 10 & 15 Weather & Climate Chapter 9: Weather Patterns Polar Front Theory (1800s) Mid-latitude Cyclone Low pressure system Mid-latitudes 600+ miles in size Fronts Boundary surfaces that separate different air masses Usually having different temperature and humidity Fronts said to be Overrunning one another Warm Front, Cold Front, Stationary Front, & Occluded Front Life cycle of a mid-latitude cyclone Formation - Cyclongenesis Cyclonic flow development Occlusion THE FOLLOWING ARE NOT INCLUDED: Idealized weather of a mid-latitude cyclone Formation Cyclongenesis The Conveyor Belt Model (the modern viewpoint) Warm, Cold and Dry Conveyors 1
Polar Front Theory 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 after WWI (the air masses acted like army fronts ) Fronts 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 Types of Fronts 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 2
Fronts Warm Fronts Warm Front Warm air overrunning Cold Warm Cold Wedge shaped gentle slope Usually lighter, long-lasting rain Red line with semi-circles Has two types that tend to differ by season Summer: Air tends to be unstable (warmer than surrounding air) Precipitation tends to form in Cumulonimbus clouds (heavy, shorter rain) Other times of the year: Air tends to be stable (cooler than surrounding air) Precipitation tends to form in stratus clouds (lighter, longer rain) 3
Warm Fronts Warm Fronts SUMMER: (unstable air) 4
Cold Fronts Cold Front Cold air overrunning Warm Cold Warm Plow shaped (snowplow) steep slope Clouds tend to be Cumulonimbus Usually heavy, short-lived rain Often form into thunderstorms Can produce tornadoes Blue line with triangles Cold Fronts 5
Stationary Fronts Stationary Front Air masses moving parallel W W C W W W C W C C Fronts NOT overrunning each other Move either in same direction or opposite Can also be in a rotational relationship Alternating blue & red lines (with appropriate symbols) Occluded Fronts Occluded Front Three air masses combining A cold front overrunning a warm front which is overrunning a cold front More gentle slopes Tend to bring medium to light rain Purple line with BOTH symbols Cold-type The first front is colder than the last Cold Warm Cool Warm-type The first front is warmer than the last Cool Warm Cold 6
Occluded Fronts Life Cycle of a Mid-latitude Cyclone Formation Cyclongenesis Begining 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 7
Life Cycle of a Mid-latitude Cyclone Idealized Weather of the Mid-latitude Cyclone 8
Chapter 10: Thunderstorms Thunderstorms A storm that generates lightning and thunder Frequency & Location Two types of Thunderstorms Air-Mass Thunderstorm Thunderstorm which occur within one air mass (mt) Localized, short-lived thunderstorms Stages of Development Cumulus Stage Mature Stage Dissipating Stage Severe Thunderstorm Supercell Thunderstorms Lightning and Thunder A thunderstorm is only a thunderstorm IF thunder is heard! Thunder can only be heard if lightning happens first Interesting facts Thunderstorms 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 US pattern of Thunderstorms 9
Thunderstorms Thunderstorms 10
Thunderstorms 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 Most destructive thunderstorms 2 3,000 per year in US most damage and deaths 11
Air-Mass Thunderstorm Air-Mass Thunderstorm 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 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 12
Stages of Development: Mature & Dissipating 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 Stages of Development Entrainment Downdrafts Updrafts 13
Severe Thunderstorms Severe Thunderstorms are very powerful thunderstorms which produce 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 Severe Thunderstorms 14
Severe Thunderstorms Severe Thunderstorms 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 Severe Thunderstorms 15
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 Cloud to Cloud Lightning (80%) 16
Cloud to Ground Lightning (20%) 17
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 Positive and Negative Charges Like charges repel (+) (+) (-) (-) Opposite charges attract (-) (+) (+) (-) 18
Lightning Formation 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 Attracts the positive (+) ground charges The ground under the cloud becomes positively (+) charged Lightning Formation + + + + + + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + Positive Negative < air > Positive 19
Lightning Formation 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. Lightning Formation 20
Lightning Formation Chapter 10: Thunderstorms 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 21
Lightning and Thunder 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 Climate Types are based on Temperature Monthly and Yearly average Precipitation Monthly and Yearly totals 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) 22
Climate Classification: 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 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 Classification: A - Tropical Moist Climates All months avg. above 18 C B - Dry Climates Little precipitation during most 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 climates due to altitude change 23
A Moist Tropical Climate types A Climates Tropical climates with abundant precipitation during a portion of the year. Mean monthly climates must exceed 18ºC; precipitation exceeds evaporation. Further divisions f: mean precipitation of each month is at least 6cm m: short dry season is compensated for by surplus precipitation in wetter months w: well defined dry season producing a period of water shortage Moist Tropical Climates are known for their high temperatures year round and for their large amount of year round rain. A Moist Tropical Tropical Moist Climates (Af) RAINFOREST Rainfall is heavy in all months (total is often more than 100 in.) There are seasonal differences in monthly rainfall, but temperatures of 80 F are found year round. Humidity is between 77% and 88%. High surface heat and humidity cause cumulus clouds to form early in the afternoons almost every day. The climate on eastern sides of continents are influenced by maritime tropical air masses. These air masses flow out from the moist western sides of oceanic highpressure cells, and bring lots of summer rainfall. The summers are warm and very humid. It also rains a lot in the winter Average temperature: 18 C ( F) Annual Precipitation: 262 cm. (103 in.) Latitude Range: 10 S to 25 N Global Position: Amazon Basin; Congo Basin of equatorial Africa; East Indies, from Sumatra to New Guinea. 24
A Moist Tropical Tropical Moist Climates (Af) RAINFOREST B Dry Climates Climate types B Climates Arid and semiarid climates of the low and middle latitudes Evaporation exceeds precipitation. Further divisions w: arid s: semiarid h: mean annual temperature above 18ºC k: mean annual temperature below 18ºC Dry Climates are characterized by little rain and a huge daily temperature range. 25
B Dry Climates Dry Tropical Climate (Bw) DESERT BIOME These desert climates are found in low-latitude deserts approximately between 15 to 30 in both hemispheres These latitude belts are centered on the tropics of Cancer and Capricorn and coincide with the edge of the equatorial subtropical high pressure belt and trade winds Winds are light, which allows for the evaporation of moisture in the intense heat. Air flow is dominated by subsidence (downward) thus they get little rain. This makes for a very dry heat. The dry arid desert is a true desert climate, and covers 12% of the Earth's surface. Temperature Range: 16 C Annual Precipitation: 0.25 cm (0.1 in). All months less than 0.25 cm (0.1 in). Latitude Range: 15-25 N and S. Global Range: southwestern United States and northern Mexico; Argentina; north Africa; south Africa; central part of Australia. B Dry Climates Dry Tropical Climate (Bw) DESERT BIOME 26
C Moist, Mid-Latitude: Mild Winter Climate types 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. Further divisions s: summer dry season w: winter dry season f: no dry season a: hot summer season b: long mild summer c: short cool summer In Humid Middle Latitude Climates, maritime/continental differences play a large part. These climates have warm, dry summers and cool, wet winters. C Moist, Mid-Latitude: Mild Winter Mediterranean Climate (Cs) CHAPARRAL BIOME This is a wet-winter, dry-summer climate Extremely dry summers are caused by the sinking air (subtropical high) and may last for up to five months Plants have adapted to the extreme difference in rainfall and temperature between winter and summer seasons Sclerophyll plants range in formations from forests, to woodland, and scrub. Eucalyptus forests cover most of the chaparral biome in Australia. Fires occur frequently in Mediterranean climate zones Temperature Range: 7 C (12 F) Annual Precipitation: 42 cm (17 in) Latitude Range: 30-50 N and S Global Position: central and southern California; coastal zones bordering the Mediterranean Sea; coastal Western Australia and South Australia; Chilean coast; Cape Town region of South Africa 27
C Moist, Mid-Latitude: Mild Winter Mediterranean Climate (Cs) CHAPARRAL BIOME D Moist, Mid-Latitude: Cold Winter Climate types 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. Further divisions s: summer dry season w: winter dry season f: no dry season a: hot summer season b: long mild summer c: short cool summer d: extremely cold winter Continental Climates can be found in the interior regions of large land masses. Total precipitation is not very high and seasonal temperatures vary widely. 28
D Moist, Mid-Latitude: Cold Winter Boreal forest Climate ( Dfc) TAIGA BIOME This is a continental climate with long, very cold winters, and short, cool summers. This climate is found in the polar air mass region. Very cold air masses from the arctic often move in. The temperature range is larger than any other climate. Precipitation increases during summer months, although annual precipitation is still small. Much of the boreal forest climate is considered humid. However, large areas in western Canada and Siberia receive very little precipitation and fall into the subhumid or semiarid climate type. Temp Range: 41 C (74 F), lows; -25 C (-14 F), highs; 16 C (60 F). Average Annual Precipitation: 31 cm (12 in). Latitude Range: 50-70 N and S. Global Position: central and western Alaska; Canada, from the Yukon Territory to Labrador; Eurasia, from northern Europe across all of Siberia to the Pacific Ocean. D Moist, Mid-Lat: Cold Winter Boreal forest Climate ( Dfc) TAIGA BIOME 29
E Polar Climates Climate types E Climates Cold climates of the northern latitudes. All months must average below 10ºC. Further divisions t: tundra f: polar or ice cap climate 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. E Polar Climate Tundra Climate (Et) TUNDRA BIOME The tundra climate is found along arctic coastal areas. Polar and arctic air masses dominate the tundra climate. The winter season is long and severe. A short, mild season exists, but not a true summer season. Moderating ocean winds keep the temperatures from being as severe as interior regions. Temperature Range: -22 C to 6 C (-10 F to 41 F). Average Annual Precipitation: 20 cm (8 in). Latitude Range: 60-75 N. Global Position: arctic zone of North America; Hudson Bay region; Greenland coast; northern Siberia bordering the Arctic Ocean. 30
E Polar Climate Tundra Climate (Et) TUNDRA BIOME H Highland Climates Climate types H Climates Hybrid climates that have significant change in altitude which brings colder temperatures with elevation increases Further divisions None: Climate is dominated by the seasonal patterns of temperature and precipitation of the major climate they are located within. 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. 31
H Highland Climate Alpine Climate (H) Highland climates are cool to cold, found in mountains and high plateaus Climates change rapidly on mountains, becoming colder with increased altitude The climate of a highland area is closely related to the climate of the surrounding biome. The highlands have the same seasons and wet and dry periods as the biome they are in Mountain climates are very important to midlatitude biomes. They work as water storage areas. Snow is kept back until spring and summer when it is released slowly as water through melting. Temperature Range: -18 C to 10 C (-2 F to 50 F) Average Annual Precipitation: 23 cm (9 in.) Latitude Range: found all over the world Global Position: Rocky Mountain Range in North America, the Andean mountain range in South America, the Alps in Europe, Mt. Kilimanjaro in Africa, the Himalayans in Tibet, Mt. Fuji in Japan. H - Highland Climate Alpine Climate (H) 32