Geography 1111 Exam 2 Study Guide
Geography 1111 Exam 2 Study Guide GEOG 1111
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Geography 1111 Exam 2 Study Guide Lecture 11: Condensation Events; Formation and Types: o Clouds, Fog, and Dew all have 2 properties in common: 1. They must form from saturated or nearly saturated air RH = 100% Dew point temperature = air temperature 2. They must have a surface (solid or liquid) upon which the water vapor can condense o Dew: the condensation event (water vapor changing to liquid water) wherein liquid water droplets form on the ground, vegetation, a car, or similar surface near the ground o Cloud and fog: condensation events wherein the droplets form suspended in the air They form on solid particles known as condensation nuclei Condensation nuclei: a microscopic particle which is necessary as a surface on which water vapor condenses to form moisture droplets These can be particles of dust, sea salts, soot, ash, sulfate & nitrate crystals, etc. Clouds: form of condensation best described as a dense, visible aggregation of minute moisture droplets and/or tiny ice crystals. o How do they form? A parcel of warm, moist air rises, cools and reaches the dew point temperature wherein saturation of the air parcel is reached Once this occurs, condensation will begin because some of the water vapor will change to liquid water droplets If enough water droplets form, they may become dense enough to see o Ice crystals will form if air temperatures are below freezing, the process of deposition Alternately, the air parcel may have water vapor added to it (the d.p.Tº is thus rising) to reach saturation So, either by cooling the air temperature or the d.p.T° OR by adding more water vapor can saturation be reached Cooling the air Tº is the most common event o Cloud Classification: Two basic criteria are used for classifying clouds: altitude at which the cloud occurs and the shape of the cloud o Altitude: Four altitudinal classes: 1. Low Clouds: those which lie from near the surface up to 2,000m (6,500 ft) o These clouds typically consist primarily of liquid water droplets Can consist of ice crystals, especially in winter o Ex: stratus, stratocumulus, nimbostratus 2. Middle Clouds: those which lie between 2,000m and 6,000m (20,000 ft) o Ex: altostratus, altocumulus 3. High Clouds: those which lie between 6,000m and 13,000m (43,000ft) o Ex: cirrus, cirrostratus, cirrocumulus 4. Vertically developed thru the troposphere: those cloud masses which may stretch from near the surface to over 13,000m o These typically consist primarily of liquid water at lower levels and ice crystals at higher levels o Ex: cumulus, cumulonimbus o Shape: Three basic forms: 1. Flat Clouds: those which show primarily horizontal development and are often layers o These are stratiform clouds 2. Puffy Clouds: those which show more vertical development o These are cumuliform clouds 3. Wispy Clouds: those which form at high altitude and consist of ice crystals o These are cirroform clouds o Some common cloud types: Stratus clouds: layered, horizontally developed and usually low altitude Cumulus clouds: puffy like “cotton balls” and vertically developed Cirrus clouds: the wispy-shaped “curls of hair” o They form high in the atmosphere and are composed of ice crystals Nimbus clouds: refers to those which are producing precipitation (rain, snow, etc.) There are two types of nimbus clouds: 1. Cumulonimbus, or more commonly called Thunderstorms (T-storms) are cumulus clouds which are producing precipitation 2. Nimbostratus Fog: basically a cloud in contact with the ground, but the air parcel does not reach saturation by rising and cooling o It either cools to the d.p.T° or has water vapor added to reach saturation at the ground o As the water droplets get bigger they become visible, this decreases visibility (being able to look through the droplets) If visibility is reduced to 1 km, the haze or cloud is categorized as fog o Four main categories of fog: 1. Radiation fog: produced over land as the ground emits LW radiation, thus losing heat energy and cooling Cools the air in contact with the ground and if the air temperature drops to the d.p.Tº, then condensation may occur o This process is known as radiational cooling This type of fog is also called ground fog o This the most common type of fog which forms the Athens, GA area If it forms in mountainous area, then it may be called valley fog o This occurs as cold, heavy air drains downhill (cold air drainage) It forms best on calm, clear nights in late fall and winter and is usually deepest around sunrise 2. Advection fog: occurs when warm, moist air moves over a colder surface and the air cools to its d.p.T° This is most common as warm air from off a large water surface (ocean, gulf) moves over the colder, costal land Remember that advection means the horizontal movement of air o Ex: West Coast of U.S. (San Francisco area), Gulf of Mexico coastal area, especially in the winter 3. Upslope fog: forms as warm, moist air flows up along an elevated plain, or mountain range The air temperature reaches d.p.T° by adiabatic cooling as it rises o Ex: Western Great Plains of the U.S. along the eastern side of the Rocky Mountains 4. Evaporation fog: forms when the air reaches saturation (d.p.T° = air temperature) by having water vapor added to it and not by lowering of the air temperature In other words, liquid water evaporates into the air parcel from off a water body or wet surface Steam fog: forms when cold air moves over a warmer water and the warmer water evaporates into the unsaturated cold air causing saturation, condensation and fog formation o Ex: over a heated pool (especially in fall or winter), over hot springs and thermal pools, and in polar regions Frontal fog: forms as warm raindrops evaporate in a cool air mass as they fall o This type of fog associated with frontal systems and dreary, drizzly days Dew: water that has condensed onto objects near the ground when their temperatures have fallen below the d.p.T° of the surface air o In winter, however, this may form solid forms of dew o Frozen Dew: refers to dew which has formed and then has frozen Condensation occurs at a temperature above the freezing point, then the temperature continues to drop below the freezing point and the dew freezes condensation then freezing o Frost or Hoarfrost: a covering of ice produced by deposition because the d.p.T° is below freezing Water vapor changes directly to the solid state Lecture 12: Precipitation Process: o Simplified process: Rain: water vapor condenses into liquid water droplets forming clouds These droplets coalesce (join together) and become heavy enough to be pulled down by gravity as precipitation and do not evaporate before the hit the ground as a raindrop H2O V--------------------> liquid water ----------------------------> rain (Clouds) Snow: water vapor condenses into liquid water droplets forming clouds o Also within the clouds water vapor changes to ice crystals by deposition o These ice crystals coalesce (join together) and become heavy enough to be pulled down by gravity as precipitation and do not melt before they hit the ground as a snowflake H 2 V--------------------> ice crystals ----------------------------> snow (Clouds) Cloud droplet average size is about 20 microns in diameter and fall very slowly, about 1000 m/48 hrs o They usually evaporate 1 raindrop = about one million cloud droplets, so cloud droplets must coalesce or join together into a raindrop to avoid evaporation Two basic mechanisms to explain precipitation formation: 1. Bergeron Process or Ice-Crystal Process: the primary process for forming precipitation in the middle and high latitudes and the only process to form snow Need freezing nuclei to initiate change of water vapor to solid water and thus need temperatures below -10ºC, where both liquid drops and ice crystals can exist o Also need supersaturated conditions (RH > 100%), so ice crystals can collect more water vapor than they lose and thus grow The basic process is water vapor changing to ice crystals by deposition, and these ice crystals joining with other ice crystals to make snow crystals and then snowflakes o If they melt while falling, then they become a raindrop 2. Collision-Coalescence Process: the primary process in tropical areas for raindrop formation and in mid-latitudes during the summer The basic process is water vapor changing to liquid water droplets (cloud droplets) by condensation, and these droplets coalescing with other droplets to form raindrops The maximum size a raindrop will achieve is about 5 mm o If it gets bigger, then it gets pulled apart by friction and drag forces as it falls A combination of Bergeron and Collision-Coalescence processes is often seen in thunderstorms to form precipitation o Even in summer, ice crystals will form in the top of the thunderstorms and then melt as they fall forming raindrops Fall or Terminal Velocities of Cloud droplets and Raindrops: (don’t worry about memorizing numbers) Type Diameter (mm) Velocity (kph)/(mph) Typical cloud droplet .02 .04/.03 Drizzle .5 7/4 Raindrop 2-5 23-33/14-20 Precipitation Types: o Remember that all precipitation comes from either nimbostratus or cumulonimbus clouds o Rain droplets average between .5 mm to 5 mm in size and are a liquid form of precipitation Following the Bergeron Process: So, water vapor to ice crystal to raindrop (gas) (solid) (liquid) Following the Collision-Coalescence Process: So, water vapor to raindrop (gas) (liquid) o Snow, or snowflakes, are a solid form of precipitation and average 1 - 2mm in size They only form via the Bergeron Process So, water vapor to snowflake (gas) (solid) Know the conversion of snow to rain for the purpose of precipitation total o An average of ***10 inches of snow is equivalent to 1 inch of rain*** is commonly used, but this will be dependent on the amount of moisture in the snow however o Wetter snow will be fewer than 10 inches and drier snow will be more than 10 inches Sleet and Freezing rain are two other solid forms of precipitation commonly occurring in winter o Sleet is essentially a frozen raindrop If it starts as a snowflake (Bergeron Process), then it melts to form a raindrop that then freezes (re- freezes) before it hits the ground As the snowflake falls it passes through air which is at a temperature above 32° F, melts, then passes through colder air again and freezes frozen ---------------> liquid ------------------------> frozen (cloud) (melts) (in atmo) (re-freezes before it hits ground) OR liquid --------------------------------------------------> frozen (cloud) (freezes in atmo before it hits ground) Freezing rain is similar to sleet except it freezes (re-freezes) after making contact with the ground o This usually involves supercooled raindrops which allows them to freeze on contact with solid objects/surfaces Commonly referred to as Ice storms frozen --------------------> liquid ----------------------> liquid/frozen (cloud) (melts in atmo as it falls) (liquid as it hits the ground then re-freezes) OR liquid -----------------------------------------------------> liquid/frozen (cloud) (liquid as it hits the ground then freezes) o Sleet and Freezing rain are typically not counted in precipitation totals Hail is another form of solid precipitation consisting of hard, rounded pellets or lumps of ice o They are only produced in large cumulonimbus clouds, thunderstorms o They form in the network of updrafts and down drafts contained within the thunderstorm which move the hail stone up and down within the cloud causing it to grow o Unlike sleet and freezing rain, hail is primarily a summertime phenomena It also is not typically counted in precipitation totals Global Pattern of Precipitation: o An idealized pattern of precipitation would be quite simple with more in tropical areas where the air is warmer and can hold more moisture versus polar areas where it’s cold and dry But other factors complicate the picture: Air Pressure systems greatly affect precipitation patterns with areas of Low Pressure typically being unstable (ITCZ) and areas of High Pressure consisting of subsidence and being stable (STH) Wind directions affect precipitation patterns by whether it is flowing onshore or offshore, diverging or converging, encounters mountain ranges, etc. Seasonality or shifting of pressure belts (ITCZ & STH) during the year which shifts wind directions Landmass and Ocean locations which can affect wind flow, differential heating, rain shadows, etc. So, throw all this together and we could model an Idealized Continent for precipitation BUT some exceptions to the Idealized pattern give a truer picture of precipitation patterns: o Sub-Tropical High pressure cells (STH’s), which sit over oceans, don’t have the same characteristics on both the east and west side East side of STH: shows the typical subsidence, temperature inversion, and stable and dry conditions They are also affected by upwelling of cold ocean currents Ex: Sahara of northwest Africa, deserts of Baja California and Mexico West side of STH: shows little subsidence, more uplifting, convergence, and warm ocean currents which leads to greater instability and wetter conditions o Ex: Southeastern U.S. Rain shadow deserts: formed by mountain barriers and orographic effects such that the leeward side is often much drier than the windward side o Ex: Great Basin (Nevada deserts) of western U.S., Patagonia in southern Argentina Monsoon: an annual cycle of dryness and wetness, with seasonally shifting winds produced by shifting atmospheric pressure patterns o Ex: Southern Asia (India) Lecture 13: Air Masses and Fronts: o Air mass: an immense body of air, some 1600+ km across and -3 km thick, with relatively homogeneous physical properties (density, temperature and moisture) at a given altitude o Classification Scheme of air masses is based on the basic temperature and moisture (water vapor content or humidity) conditions of the air A two-letter abbreviation system is used to indicate the various types of air masses First letter is a reference to the surface over which the air mass develops and thus the level of moisture (dry vs. humid) o c = Continental for those air masses which move over a landmass and thus typically have a lower water vapor content Dry air o m = Maritime for those air masses which form over an ocean and thus typically have a higher water vapor content Humid air Second letter is a reference to the latitude of origin and thus the temperature (cold vs. warm) o A = Arctic bitterly cold o P = Polar cold to very cold o T = Tropical warm o E = Equatorial very warm o The Source Region in which an air mass originates determines the initial characteristics of the air mass Cold (polar) vs. warm (tropical) Dry (land) vs. humid (water) Keep in mind that cold and warm are relative terms For example, a cold air mass in winter may be 20° F, but a cold air mass in summer may be 70° F Types of Air Masses: o Continental Arctic (cA): Arctic basin and Greenland; Stable; bitterly cold and dry o Continental Polar (cP): Interior Canada & Alaska; Stable; cold to very cold and dry o Continental Tropical (cT): Northern interior Mexico and SW U.S. (Summer only); Usually Unstable; hot and dry o Maritime Polar (mP): North Pacific and northern Atlantic; usually Unstable in winter and Stable in summer; cool and humid o Maritime Tropical (mT): Gulf of Mexico, Caribbean Sea and west-central Atlantic, Subtropical, eastern Pacific; mT air in in the Gulf and east coast area of the U.S. is usually Unstable; warm and humid Fronts: refer to a boundary separating air masses of different characteristics, primarily temperature, warm vs. cold o Polar Front refers to the zone separating air masses of polar origin from air masses of tropical origin o Wave cyclones: refers to a weather pattern which may develop in conjunction with or along the polar front Low-pressure cells and fronts are the primary structure of a Mid-Latitude Wave Cyclone Types of Fronts: ***know what the fronts look like*** The symbols, triangles, point in the direction the air mass is moving toward o Cold Front: the boundary at the forward edge of an advancing cold air mass that is displacing warmer air Cumulus and cumulonimbus clouds are typically associated with cold fronts and thus quite often more violent weather is associated with cold fronts Warmer air is ahead of the cold front symbol Colder air is behind the cold front symbol o Warm Front: the boundary at the forward edge of an advancing warm air mass that is displacing cooler air Usually stratus and nimbostratus clouds associated with warm fronts and thus less severe weather is associated with warm fronts Cooler air is ahead of the warm front symbol Warmer air is behind the warm front symbol o Stationary Front represents a situation when air movement is almost parallel to the boundary and the surface position of the front doesn’t move very quickly Usually stratus clouds (if any) associated with stationary fronts Cooler air is on the red side of the symbol Warm air is on the blue side of the symbol o Occluded Front: refers to a situation when a cold front has over taken a warm front Usually stratus and nimbostratus clouds associated with occluded fronts and thus less severe weather Lecture 14: Mid-Latitude Wave Cyclone is a low-pressure cell that forms and moves along a frontal boundary o It exhibits counter-clockwise circulation (NH) around the low center and produces a wavelike deformation of the front Stages of the Wave Cyclone Life Cycle: ***the main ones to remember are 3, 4 and 5*** o Stage 1: Two air masses, a cold (cP or mP) and a warm (mT) are set-up along a front and move parallel to it o Stage 2: A wave forms as warm air starts to move pole ward while cold air moves equator ward o Stage 3: Cyclonic (counter-clockwise) circulation develops, with general convergence at the surface and uplifting The warm air overrides the cold air (frontal wedging) and a Cold Front and Warm Front are established o Stage 4: The Cold front moves faster than the warm front and begins to overtake it This is the beginning stage of occlusion and the basic formation of an Occluded Front o Stage 5: Full development of an Occluded Front has a occurred and the system is at its maximum intensity It exhibits a steep pressure gradient and strong winds and it is in this stage when the severest weather (tornadoes, hail, etc.) will likely occur, if it is going to occur o Stage 6: The pressure gradient weakens, energy supply is exhausted and system dissipates A Mid-Latitude Wave Cyclone can be thought of as having 3 sections based primarily on temperature, but exhibiting different weather as well o Warm Sector: the area between the Warm Front and the Cold Front o Cool Sector: the area ahead of the Warm Front o Cold Sector: the area behind the Cold Front Winds of a Wave Cyclone: o Warm sector: the winds are primarily southwesterly and southerly o Cool sector: the winds are primarily southeasterly to easterly and then northeasterly as you move counter- clockwise o Cold sector: the winds in this sector are primarily northerly to northwesterly, then westerly as you move counter- clockwise o Remember, we name winds for the direction they are coming from Moisture, Sky and Weather Conditions: o Warm sector: Has humid to very humid conditions, often with clear skies to scattered cumulus clouds It exhibits warm temperatures Here in the U.S. this is primarily mT air off the Gulf of Mexico Precipitation may be associated with the advancing cold front o Cool sector: Has humid to very humid conditions with a large area of stratus and nimbostratus clouds Light to moderate precipitation along and ahead of the warm front It exhibits cool temperatures o Cold sector: This sector exhibits dry, clear air back from the cold front, but often has intense precipitation (thunderstorms) along the cold front It has cold temperatures Mid-Latitude Wave Cyclones usually take between 3-7 days to form and cross the U.S. as they are pushed by the geostrophic wind pattern, primarily the Jet Stream, from west to east along Storm Tracks o These tracks shift with the seasons, being more northerly in the summer and southerly in the winter Lecture 15: Thunderstorms: A thunderstorm (T-storm) is a cumulus cloud which has developed sufficiently to produce precipitation and thus be classified as a cumulonimbus (Cn) cloud o It also is producing the characteristic events of lightning and thunder o Severe T-storms are accompanied by strong winds and wind gusts, heavy rain, and sometimes hail and tornadoes o They are an indication of great instability in the atmosphere and show a great deal of vertical development Requirements for Formation: o Warm, moist air: releases Latent Energy when lifted and condensation occurs This provides buoyancy and maintains lift to develop updrafts o High surface temperatures: enhances instability, air parcel warming and uplift o These two conditions help establish and/or strengthen atmospheric instability which will strengthen the T-storm Stages of Formation: o Cumulus stage: the initial build-up of cumulus clouds fueled by updrafts (up to 160 kph) of warm, moist air cooling adiabatically Droplet formation is by the Bergeron and Collision- Coalescence processes Updrafts dominate during this stage o Mature stage: raindrops start to fall initiating downdrafts The process of entrainment (the influx of cool, dry surrounding air) helps to fuel the downdrafts Heavy rains, lightning and thunder are most intense during this stage It is also during this stage that hail or a tornado may occur Mixture of updrafts and downdrafts during this stage o Dissipating stage: occurs as the rate and amount of rain lessens with the loss of warm, moist air and latent heat energy The storm breaks up and the cloud mass evaporates On average they are of relatively short duration, 1 - 3 hours, but may last for up to 12 hours or more Downdrafts dominate during this stage Locations of Occurrence: o Thunderstorms occur in many parts of the world o They are a daily occurrence along the ITCZ o In the U.S. they form primarily east of the Rocky Mts. with Florida being the state with the greatest number of days per year with thunderstorm occurrence o The Great Plains is the region with the greatest number per year Lightning: flashes of light generated by the flow of tens of millions of volts of electrons (electrical charge) between oppositely charged parts of a cloud or between the cloud and the ground o What causes lightning? Charges are separated within the cloud as the thunderstorm develops with positive charges primarily near the top and negative charges at the base Lightning is essentially the clouds way of trying to equalize this charge difference or imbalance After a charge difference builds to millions or hundreds of millions, a lightning strike occurs to discharge the negative base of the cloud by moving positive charges to the base and negative charges to the top This is accomplished either by: within cloud lightning, Cloud-to-cloud lightning, or Cloud-to-ground lightning o The Lightning Strike: basic Cloud-to-ground lightning The first step is the establishment of an invisible step leader of charges formed from the cloud base toward the ground o This may contain several linked pathways, each reaching toward the ground Once one of these pathways reaches the ground, the connection between the areas of unlike charges is completed o The pathway which reaches the ground first is the main trunk of the lightning strike and is the most brightly illuminated The movement of opposite charges back cloud ward is the return stroke and what causes the illumination of the pathways, the flash of lightning This also illuminates all connected pathways Thunder: the sound emitted by rapidly expanding gases along a channel of lightning discharge o The lightning flash causes the surrounding air temperature to be heated to between 15,000º C to 33,000º C in a matter of milliseconds o The air being so quickly heated, explosively expands and you hear the pressure or shock waves (sound) waves as thunder o Thunder travels at a speed of about 1082 feet/sec (the speed of sound), so it takes about 5 seconds for it to travel 1 mile (5280 ft.) Tornadoes: violently rotating column of air or vortex which can be seen when filled by a funnel-shaped or tubular mass of cloud and debris o It extends downward from a cumulonimbus cloud in response to extremely low air pressure o Characteristics: Air (barometric) pressure at the center of the vortex can be upwards of 90 - 100 mb (estimated) below the surrounding air, thus yielding a very strong pressure gradient This strong pressure gradient yields winds upwards of 300 mph (estimated) The winds are measured on a modified version of the original Fujita Scale developed by Dr. Ted Fujita The Enhanced Fujita Scale ranges from an EF0 (winds 65-85 mph) up to an EF5 (winds > 200 mph) A tornado can travel horizontally at speeds up to 30-35 mph or more, with average distances traveled of 16 mi, but it go much further o Average diameters are 490 - 1700 feet, or about ½ mile wide They form in association with thunderstorms and are most likely to occur in the area of the thunderstorm in association with the updrafts Requirements for Formation: o As with thunderstorms, tornadoes require warm, moist air with a high degree of instability o They are more likely to be associated with a cold front and where the two air masses have a strong temperature gradient across the frontal boundary o Strong geostrophic winds, known as upper level support, can be can be essential to promoting greater surface uplift Tornado Formation: o Tornadoes will form in basically two different ways: Weaker tornadoes (EF0, EF1 & some EF2s) form as winds draw into the thunderstorm converge and form a vortex that is already in a vertical orientation, and is pulled upward into the cloud base Stronger tornadoes (EF2 – EF5) start out in a horizontal position As wind is drawn into the thunderstorm from tens of miles away, the air closest to the ground moves slower than the air above it, causing the air to tumble like a barrel rolling on the ground This mesocyclone is then drawn upward by the updrafts and becomes a vertically oriented column of spinning air of tornado Locations of Occurrence: o Tornadoes have occurred in many parts of the world, but they are most numerous in North America and especially the U.S. o The U.S. averages about 750-800 per year with the highest concentration in an area stretching from central Texas to Nebraska (Tornado Alley) o Even though tornadoes have occurred in every month of the year, they are quite seasonal with the SE U.S. tornado season in March/April (Spring) Thunderstorm and Tornado Watch vs. Warning: o Watch: means conditions are favorable for the occurrence of a severe thunderstorm or tornado in your area, within the time period stated in the watch announcement, but is not occurring as yet o Warning: means that this type of weather has been spotted by a trained observer, OR has been indicated by Doppler radar in your area Lecture 16: Hurricanes, Typhoons, and Cyclones: o It is an intense tropical cyclonic storm consisting of a warm-core loq pressure cell at its center, inward- spiraling rain bands, and having sustained winds in excess of 119 kph (74 mph) o They are called by different names in different parts of the world: Hurricane: Atlantic Ocean and eastern Pacific Ocean Typhoon: western Pacific Ocean Cyclone: Indian Ocean Due to the necessary requirements for formation, they begin life only in warm, tropical waters, but may move to higher latitudes Characteristics: o It is a cyclonic storm with a warm-core low pressure at its center o They range in diameter from 100-600 miles (160 - 960 km) and average about 360 miles in diameter o A strong pressure gradient, generating strong winds, develops around the center, with the strongest winds in the eye wall o They are a large system of heavy rain, strong winds and lightning which may also have tornadoes within it Requirements for Formation: o These systems require warm, moist air which yields great instability and lift This is the systems fuel source o They must form over warm ocean waters with temperatures > 27°C (81°F) o The systems uplift is initiated by an easterly wave or area of disturbance, often associated with the trade winds along or near the ITCZ o The need for sufficient Coriolis Force to initiate rotation means they must form away from the Equator Hurricane Structure: o Eye: center of low pressure, usually with calm winds and weak downdrafts They average ~19 miles in diameter o Eye Wall: the area surrounding the systems eye and which exhibits the strongest pressure gradient and thus the most intense winds These winds are used to classify the systems to its stage and category The eye wall shows the greatest vertical cloud development, concentration of heavy rain and embedded tornadoes It is typically this section that causes the most damage o Spiral rain bands: typically the largest part of the storm in terms of areal coverage and consisting primarily of stratus and nimbostratus clouds, with light to moderate rain Often find thunderstorms imbedded within these bands Life Cycle of a Hurricane: o Tropical Disturbance is the term given to the initial, disorganized mass of thunderstorms showing a weak pressure gradient and little, if any, cyclonic circulation They sometimes originate in conjunction the ITCZ, but more often in association with or as an easterly wave, a large undulation or ripple in the normal trade wind pattern o Tropical Depression: occurs when the system shows stronger cyclonic circulation around a center, greater development of the cloud mass and has sustained winds near the center of the system between 25-39mph (40- 63kph) At this stage it is assigned a number o Tropical Storm is a system with well-developed cyclonic circulation around a strengthening low-pressure center, the beginnings of an eye wall and spiral rain bands, but usually no visibly distinct eye A tropical storm has sustained winds within the eye wall of between 38-73mph (63-118kph) and at this stage the system is given a name Hurricane: is a fully developed tropical system with strong cyclonic circulation, a visibly distinct center or “eye”, a strong eye wall and well organized spiral rainbands o The system has sustained winds within the wyw wall of 74mph (119kph) or greater o Different strengths of hurricanes can also be delineated: Category 1: 74-95 mph Category 2: 96-110 mph Category 3: 111-130 mph Category 4: 131-155 mph Category 5: >155 mph o Tropical systems have an average life span of 7-10 days, but may last over two weeks This covers from the first development of a Tropical Disturbance through to when a Hurricane finally dissipates Causes of Destruction from a Hurricane: o Winds: the strong, fast winds of the eye wall can cause great damage, as will any tornadoes which may develop within the eye wall or spiral bands Even tropical storm strength winds can do damage o Storm surge: the abnormal rise of sea level and high waves along the coast as a result of the strong winds and low pressure associated with the hurricane The storm surge is most severe on the right side of the storm as it makes landfall, because the winds here are blowing onshore and thus pushing even more water against the coastline o Flooding: will occur due to the heavy rains and the storm surge The flooding rain amounts of a hurricane may be experienced hundreds of miles inland from the coast, while the storm surge is primarily only along the coast o Storm surge, flooding and wind damage are usually more severe on the right side, especially the upper-right quadrant, of the system Tropical Cyclone Seasons: o Tropical cyclone systems on average will occur during the times listed below for each area, but they have occurred outside these dates on occasion Atlantic Ocean: June 01 – November 30; ***peak month is September*** E. Pacific Ocean: June 01 – October 31 W. Pacific Ocean: June 01- December 31 (NH); January 01 – March 31 (SH) Indian Ocean: June 01 – November 30 (NH); January 01 – March 31 (SH) Hurricane Watch vs. Hurricane Warning: o A Hurricane Watch: indicates that hurricane force winds (>74mph) from an approaching storm will be felt within the watch area within 24-36 hours o A Hurricane Warning: indicates that hurricane force winds from an approaching storm will be felt within the watch area within 24 hours o Tropical Storm Watch and Warning have the same time periods, but are issued for those areas likely to be affected by the tropical storm force winds and not the hurricane force winds Lecture 17: Climate Controls: o Latitude o Land/Water Heating Differences o Geographic Position and Prevailing Winds o Mountains and Highlands o Ocean Currents o Global Pressure and Wind Patterns Climatic Variables: o The daily, monthly and annual averages (means) are calculated using a 30 year period of data The current averages use the period 1980 – 2010 o Average daily maximum and minimum temperature Mean monthly temperature = average temperature for a month Mean annual temperature = average temperature for a year Mean monthly precipitation = total precipitation for the month Mean annual precipitation = average total precipitation/year Köppen Classification Scheme: o Developed by Wladimir Köppen (Koeppen) and is the most widely used system over the past 120 years o It was originally based on patterns of vegetation and how those plant associations were associated with patterns of temperature and precipitation o Köppen system is a series of letters for temperature, precipitation values, and seasonal changes o It comprises 5 principal groups with 4 based on temperature, and 1 based on precipitation o First letter: upper-case letter and temperature based: A: warmest climates B: precipitation based C, D, and E: coldest climates o Second letter: may be an upper-case or lower-case letter For A, C, D climates a lower-case letter is used and this refers to the seasonality of precipitation ***know the lower case letters*** f: no distinct dry season m: monsoon s: distinct dry season in summer (wet winter) w: distinct dry season in winter (wet summer) For B climates the second letter is upper-case and refers to the severity of drought (upper case S or W) For E climates the second letter is upper-case and refers to the severity of cold (upper case F or T) o Third letter: For A and E climates there is none For B, C, D climates it refers to warmest or coldest temperatures Climographs: o Also known as climate diagrams or climate graphs are a graphical representation of a locations average monthly temperature and precipitation o It can reveal temperature range, seasonality of temperature and precipitation o May include the locations latitude and longitude, sometimes the climate type and elevation Lecture 18: “A” Climates: o Tropical Humid Climates: Those locations which have an average temperature > 18ºC for each month, are classified as ‘A’ climates Types: o Af: Tropical Rainforest Location: centered on the equator; Amazon basin; parts of W. Africa; parts of Indonesia, Malaysia, New Guinea, and ***Hawaii*** Characteristics: mean monthly temperatures are 25ºC+ each month with a low annual range (<= 3ºC) Total annual precipitation > 200cm (80in), with > 6 cm (~3 in) each month Mechanisms: the ITCZ (low pressure belt) is present all year with extensive heating all year o Aw: Tropical Savanna (Tropical Wet and Dry with dry winters) Location: primarily found in two “belts” or areas which fringe the Af climate areas These are found at approx. 5º or 10º to 15º or 20º N or S latitude Some Caribbean islands also and some NE coastal Mexico areas In the U.S., only the southern tip of Florida has Aw climate Characteristics: these areas have a distinct wet/dry season, with a winter dry season and a summer wet season 150 to 200 cm (60 - 80 in) of precipitation per year with the vast majority coming in only 5-6 months Mechanisms: the shifting of the ITCZ (low pressure belt) north and south with the seasons Summer: ITCZ is in the region and brings rain (wet season) Winter: ITCZ moves out (dry season) o Am: Tropical Monsoon o Location: Southwest coast of India; Bangladesh; Thailand; parts of West Africa; NE South America and some Caribbean Islands o Characteristics: Seasonal reversal in location of major pressure cells which causes a corresponding shift in the major direction of winds The winds shift 180° between the dry and wet seasons Develops a large Sea/Land breeze with very wet summers and dry winters o Mechanisms: there is a seasonal shift in the location of the ITCZ and STH between summer and winter The ITCZ is the primary mover in this event 'C' Climates: o Humid Mid-Latitude with mild winters Locations with an average temperature of the coldest month <18°C (64°F) and > -3°C (26°F) Types: o Cw: Subtropical Monsoon (Subtropical Winter Dry) Location: NE India; parts of southern Brazil; south- central Africa Characteristics: essentially the same as Am climate, but cooler temperatures than Am Very wet summers, with dry winters Mechanisms: seasonal reversal in direction of winds set-up by changing pressure patters; general pattern of wind changes 180° Shifting ITCZ in summer; STH influence in winter o Cfa: Humid Subtropical Location: east coast of continents, ~ 20° to 40° N or S U.S. Gulf Coast thru SE U.S. up to Washington, D.C.; southern Brazil and northern Argentina; South Korea; eastern China, southern Japan Characteristics: mild winters, hot humid summers Annual precipitation total > 100cm (40 in) Winter precipitation primarily from mid- latitude wave cyclones Summer precipitation from wave cyclones and more so from convective thunderstorms/showers Tornadoes and hurricanes most numerous in this climate region Mechanisms: dominated by mT and cP air masses Unstable air associated with western side of STH in summer o Cfb, Cfc: Marine West Coast Location: west side of northern continents, ~ 40° to 65° N or S Northern California to Alaskan Panhandle; NW Europe; southeast coast of South Africa and Australia; New Zealan Characteristics: rain all year round, winter max; no distinct dry season Mild winters with cool summers Mechanisms: high precipitation from orographic effects in some areas, especially Pacific northwest coast of North America Affected by nearness to oceans and mP air masses o Csa, Csb: Mediterranean Location: west side of continents, ~ 30° to 45° N or S Central to southern California; Mediterranean Sea area Characteristics: dry summers and wet winters Annual precipitation between 40 & 80 cm (16-32 in) High incidence of fog in many Csa areas Mechanisms: dominated by Polar front and frontal activity in winter Dominated by stable eastern side of STH cells in summer Location adjacent to oceans usually with cold currents Lecture 19: 'D' Climates: o Humid continental and Subarctic climates o Average temperature of coldest month is <= -3ºC (26ºF) and average temperature of warmest month is > 10ºC (50ºF) o NO 'D' climates in the Southern Hemisphere; no large land masses in the correct latitudinal zone Types: o Dfa, Dfb: Humid Continental Location: ~ 40° to 55° N; Midwest U.S. to east coast; S. Canada; E. Europe and Scandinavia to central Russia Characteristics: COLD winters, warm summers; Large annual temperature variations cP air dominates Mechanisms: Far northern latitudes = relatively low amounts of solar radiation and thus little energy (heat) Continentality Dominated by the polar front o Dfc, Dfd, Dwc, Dwd: Subarctic Location: Poleward of Dfa, Dfb, Dwa, Dwb climates; south of tundra; western Alaska across Canada to Newfoundland; Norway across Russia to the Pacific Ocean Characteristics: Exhibit the greatest annual temperature ranges (Siberia up to 145°F) Precipitation < 50 cm (20 in)/year, again, cold air does not hold as much water vapor Mechanisms: high latitudes = little solar radiation = low temperatures 'E' Climates: o Polar climates: Locations with an average temperature of the warmest month < 10°C (50°F) o Sometimes considered humid, but only when compared to the low evaporation rates of polar regions o Little solar radiation so very low temperatures, BUT large temperature variation Types: o ET: Tundra Location: Primarily coastal areas in the polar regions north coast of Alaska and Canada; coastal Greenland southern tip of South America; northern Scandinavia and Russian coast Characteristics: Average temperature warmest month > 0°C and < 10°C Severe winters and cool summers with low precipitation Mechanisms: dominance by stable air and Polar High Pressure cell Cold air cannot hold much moisture = low precipitation o EF: Ice Cap Location: Confined to ice caps of Greenland and Antarctica Characteristics: Lowest temperatures ever recorded, -88.3°C(- 126.9°F) at Vostok, Antarctica Permanent ice and snow cover Mechanisms: high latitudes = low solar radiation input Permanent ice = low temperatures = permanent ice = low temperatures = … o An example of a negative feedback mechanism Highland Climates: o Areas of high elevation with generally cooler and wetter conditions than surrounding lowlands o Location: mountainous areas; Rockies, Sierra Nevada, Cascades, the Andes, Himalayas and Tibetan Plateau o Characteristics: Cooler and wetter on the windward side and relatively small areas o Mechanisms: High elevation means diverse, rugged topography Lecture 20: ‘B’ Climates: o Areas where the Potential Evaporation (PE) > Precipitation o Potential Evapotranspiration (PE): the amount of moisture that, if it were available, would evaporate from a given area Ex: If a location receives 12" of rain a year, but the PE for that location is 22", then that location has a deficit o 'B' climates are the only climates based on precipitation o General characteristics: ‘B’ type climates cover 25 - 35% of Earth’s land area Precipitation is quite variable, both spatially and temporally Types: o Arid locations (desert) receive <10inches of precipitation per year o Semi-Arid locations (steppe) receive 10-20inches of precipitation per year o Simple rule to determine an Arid area versus a Semi-Arid area is: Lower-case h = hot to warm average yearly temperatures Lower-case k = warm to cool average yearly temperatures o BWh and BSh: Tropical Desert and Tropical Steppe Location: centered on ~20° - 30 ° N and S BWh: o North America: northern Mexico, southwestern U.S. o South America: Atacama Desert o Africa: north Africa (the Sahara), southwest and south-central Africa (Namib & Kalahari Deserts) o Asia: southwest Asia (Saudi Arabia to Iran), Thar/Great Indian Desert o Australia: central to western deserts (Simpson, Great Sandy, Gibson, etc.) BSh: o North America: on the fringes of the deserts named above, central Mexico o South America: northeast Brazil, northern coast of Venezuela o Africa: the Sahel region, fringes of the Namib and Kalahari Deserts o Asia: on the fringes of the deserts named above, southern Afghanistan o Australia: on the fringes of the deserts named above Characteristics: Very low precipitation and often very high temperatures, often some of the hottest on Earth (136ºF in Libya Mechanisms: dominated by STH cells most or all of the year o BWk & BSk: Mid-latitude Desert and Steppe Location: Poleward of BSh and BWh areas BWk: o North America: Great Basin (Nevada) o South America: Patagonia o Asia: central Asia around the Caspian and Aral Seas; the Gobi and Taklamakan Deserts BSk: o North America: Great Plains in central U.S. o South America: Pampas area o Asia: Eurasian Steppe (from Ukraine to Mongolia) Characteristics: hot summers but cool to cold winters Mechanisms: o Rainshadow Effect: Great Basin and Great Plains, Patagonia, Eurasian Steppe, Great Plains o Remoteness from water sources (continentality) Gobi desert, Eurasian Steppe
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