Geog 150 ch8_2024.pdf

GEOG 150 Chapter 8 Geosystems: An Introduction to Physical Geography Updated Fourth Canadian Edition Chapter 8 Weather Copyright © 2019 Pearson Canada Inc. 8-2 ...

GEOG 150 Chapter 8 Geosystems: An Introduction to Physical Geography Updated Fourth Canadian Edition Chapter 8 Weather Copyright © 2019 Pearson Canada Inc. 8-2  Water's Role Water influences air masses' stability Meteorology and interactions, creating powerful Meteorologists study the effects in the lower atmosphere. atmosphere's physical characteristics, Air masses conflict, moving and chemical, physical, and geologic shifting, dominating regions with processes, atmospheric systems, and varying strength and characteristics. weather forecasting. Computers handle data from ground instruments, aircraft, and satellites for accurate forecasting and studying long-term trends. Weather and Climate Weather is the short-term, day-to-day condition of the atmosphere, contrasting with climate, which is the long-term average of weather conditions and extremes. Weather-Related Damage Weather elements include Climate change and population temperature, air pressure, relative increase have increased weather- humidity, wind speed and direction, related destruction, with estimates of and seasonal factors. global annual damage losses exceeding $1 trillion by 2040. This chapter explores North American air masses, atmospheric lifting mechanisms, stable and unstable conditions, and cyclonic systems. It highlights the impact of water on weather, linking meteorology and weather forecasting to physical geography and human activities. Elements Contributing to Weather Temperature Air pressure Relative humidity Wind speed and direction Seasonal factors such as insolation and Sun angle Learning Objectives Describe air masses that affect North America and relate their qualities to source regions. Identify and describe four types of atmospheric lifting mechanisms and give an example of each. Explain the formation of orographic precipitation and review an example of orographic effects in North America. Air Masses Each Earth's surface imparts temperature and moisture characteristics to overlying air. The surface's effect creates a homogenous mix of temperature, humidity, and stability. This distinctive air mass, known as an air mass, reflects the characteristics of its source region. Examples include "cold Arctic air mass" and "moist tropical air mass." Interaction of various air masses produces weather patterns. Air Masses Affecting North America Air Mass Classification Moisture: m (wet) or c (continental) Temperature: (Directly related to latitude). A (arctic), P (polar), T (tropical), E (equatorial), AA (antarctic) These are combined to create categories Air Mass Classification and Characteristics Air mass Abbreviation Source Temperature Relative Humidity Subtropical ocean areas Maritime Tropical mT e.g. Azores. High Very High Subtropical deserts Continental Tropical cT e.g. Sahara Very high Very low Temperate continental area e.g. Northern Varies with Continental Polar cP Europe season Low Ocean areas latitude Maritime Polar mP >50O Low High Arctic A Arctic ice cap Very low Low AA AA Antarctic ice cap Very low Low Air Masses Affecting North America in Winter Air Masses Affecting North America in Summer  Continental Polar (cP) Originates in Northern Hemisphere, most developed in winter and cold weather. Major players in middle- and high- latitude weather. Cold, dense air displaces moist, warm air, lifting and cooling it. Winter areas experience cold, stable air, clear skies, high pressure, and anticyclonic wind flow. Southern Hemisphere lacks necessary continental landmasses for cP air mass creation. Warms as it travels south from -50o C at its source Passes over warmer Great Lakes to make lake effect snow Great Lakes Maritime polar (mP) Over northern oceans. Predominantly cool, moist, unstable conditions. Aleutian and Icelandic subpolar low-pressure cells. Well-developed winter pattern. Maritime Tropical (mT) Maritime Tropical Pacific (mT) stable to conditionally Gulf Atlantic unstable Unstable lower in moisture content Active from late and available energy spring to early fall Becomes more stable as it moves north Creates humidity in North America East and Midwest. Air Mass Modification Air masses' physical attributes become more definite over time as they migrate from source regions. E.g. mT temperature and moisture characteristics change with each day's passage northward. Below-freezing temperatures can reach southern Texas and Florida, but warm to above –50°C in northern Canada. Air Mass Modification cP air modification creates snowbelts east of the Great Lakes. Below-freezing cP air absorbs heat energy and moisture, enhancing the lake effect. This results in heavy snowfall downwind into Ontario, Québec, Michigan, northern Pennsylvania, and New York. The severity of the lake effect depends on a low- pressure system north of the lakes. Climate change is expected to increase lake-effect snowfall over the next few decades. Some models predict a decrease in lake-effect snowfall as temperatures rise, but increased rainfall over the regions leeward of the Great Lakes. Lake effect snowstorm approaching Buffalo, New York from Lake Eerie Source Four Atmospheric Lifting Mechanisms To form precipitation, air masses must lift and rise in altitude, cool adiabatically (by expansion), to reach the dew-point temperature, condense, and form clouds. 1. Convergent lifting: Air flows towards low-pressure areas. 2. Convectional lifting: Air stimulated by local surface heating. 3. Orographic lifting: Air forced over a barrier like a mountain range. 4. Frontal lifting: Air displaced upward along leading edges of contrasting air masses (cold and warm fronts).  Convergent Convectional Lifting mechanisms Orographic Frontal Convergent Lifting Air flows toward an area of low pressure. Low pressure centre: air converging and ascending, cooling and condensation occurring. Air from different directions converging into low-pressure area. Southeast and northeast trade winds form intertropical convergence zone (ITCZ). Areas of convergent uplift, cumulonimbus cloud development, and high annual precipitation. Convectional Lifting Air mass transfer from maritime to continental regions The warmer surfaces produce convectional lifting due to local heating. Warmer land surface heating causes air mass lifting and convection. Other sources include urban heat islands and dark soil in ploughed fields. Unstable conditions lead to initial lifting and cloud development. Rising air continues ascent due to warmer, less dense surroundings. Convectional Lifting Process Unstable atmospheric conditions with environmental lapse rate of 12 C°/1000m. Specific humidity of air parcel is 8 g/kg. Beginning temperature is 25°C. Air with specific humidity needs cooling to 11°C for dew-point temperature. Dew point reached after 14 C° of adiabatic cooling at 1400 m. Dry adiabatic rate (DAR) used when air parcel is less than saturated, moist adiabatic rate above lifting condensation level at 1400 m. Convectional Lifting Florida's Precipitation Mechanisms Utilizes both convergent and convectional lifting mechanisms. Heating of land leads to convergence of onshore winds from Atlantic and Gulf of Mexico. Example: Day when Florida's landmass was warmer than surrounding Gulf of Mexico and Atlantic Ocean. Convectional showers form in the afternoon and early evening due to gradual Sun's radiation. Highest frequency of days with thunderstorms in the U.S. Orographic Lifting Oro means “mountain.” Acts as a topographic barrier to air masses. Orographic lifting occurs when air is forcibly lifted upslope. Stable air may produce stratiform clouds, unstable air forms cumulus and cumulonimbus clouds. Enhances convectional activity and causes additional lifting during weather fronts and cyclonic systems. Extracts more moisture from passing air masses, resulting in orographic precipitation. Orographic Lifting Orographic Lifting in Unstable Conditions Operates on windward slopes, causing moisture condensing and precipitation. On leeward slopes, descending air heats and evaporates remaining water. Air begins ascent warm and moist, ends hot and dry on leeward slope. The term "rain shadow" is applied to this dry, leeward side of mountains. Orographic Barriers/Mountain Ranges Precipitation Rain Shadow The Coast and Rocky Mountains orographically lift invading mP air masses from the North Pacific Ocean. Precipitation is squeezed onto the windward sides of the mountains, allowing dry air to descend the leeward sides. The Egg Island Weather Station and Mount Fidelity Station show precipitation on the windward slope of the Coast Mountains and the Rockies. Lesser annual precipitation is represented by 100 Mile House in Caribou and Calgary International Airport. Rain Shadow Some regions of lee shadowing are highlighted with red circles. This effect is strongest when the winds are perpendicular to the mountains, as shown by the prevailing wind direction (arrows). Rain Shadow The Olympic Rain Shadow on Vancouver Island is quite famous among pilots as it often accounts for the clear skies over the Victoria area while other parts of the area are cloudy and rainy. Rain Shadow Compare the total annual precipitation (mm) for: Cape Mudge Powell River Comox Victoria Vs: Port Renfrew Frontal Lifting A front is the transition zone between two air masses of different densities. Since density differences are most often caused by temperature differences, fronts usually separate air masses with contrasting temperatures. Front is a place of atmospheric discontinuity, conflict line between two air masses. Fronts 1. cold front 2. warm front 3. stationary front 4. occluded front 5. surface trough 6. squall / shear line 7. dry line 8. tropical wave 9. trowal Cold Front Cold air mass's steep face indicates ground-hugging due to its greater density and uniform characteristics. Warm, moist air in advance of cold front lifts upward abruptly, cooling. High cirrus clouds appear a day or two before a cold front's arrival. Shifting winds, dropping temperature, and lowering barometric pressure mark the front's advance. At the line of intense lifting, air pressure drops to a local low. Clouds may build along the cold front into cumulonimbus form. Precipitation is heavy, containing large droplets, and can be accompanied by hail, lightning, and thunder. Precipitation behind the cold front Cold Front Cold fronts are depicted as triangular spikes pointing in the direction of frontal movement. North American landmass's shape and size present conditions where cP and mT air masses are best developed. This contrast can lead to dramatic weather, especially in late spring, with significant temperature differences. Fast-advancing cold fronts can cause violent lifting, creating a squall line. A squall line is characterized by turbulent wind patterns, intense precipitation, and the formation of new thunderstorms or tornadoes. Cold Front Cumulonimbus clouds Cold Front Warm Front The leading edge of an advancing warm air mass is a warm front. Warm air moves up and over cold air. 1000 km wide!!!! Precipitation ahead of the warm front *note the various types of clouds ahead of the warm front* Nimbostratus Stratus Altostratus Cirrostratus Cirrus Warm Front Gentle lifting of mT air leads to stratiform cloud development and nimbostratus clouds. Presents a progression of cloud development: high cirrus and cirrostratus clouds, lower altostratus clouds, and lower, thicker stratus clouds. A line with semicircles pointing in the direction of frontal movement signifies a warm front on weather maps. Warm Front Jet stream can transport warm air masses into colder regions. Example: "Pineapple Express" from Hawai‘i to North America. Warm air mass doesn't displace denser passive air. Warm air pushes cooler air into wedge shape. This results in temperature inversion, poor air drainage, and stagnation. Warm Front The narrow bands of heavy precipitation coming to B.C. are also known as "atmospheric rivers,'' which occur frequently in the fall and winter in B.C. Warm Front Nimbostratus → Stratus → Altostratus → Cirrostratus → Cirrus Warm Front Source Weather Maps and Forecasting Synoptic Analysis in Weather Prediction Evaluates weather data collected at a specific time. Builds database of wind, pressure, temperature, and moisture conditions. Key to numerical weather prediction and weather-forecasting models. Challenges include nonlinear atmosphere and chaotic behavior. Variations in input data or model assumptions can affect forecasts. Accuracy improves with technological advancements and understanding of atmospheric interactions. Weather Maps and Forecasting Weather data necessary for the preparation of a synoptic map and forecast include the following: Barometric pressure (sea level and altimeter setting) Pressure tendency (steady, rising, falling) Surface air temperature Dew-point temperature Wind speed, direction, and character (gusts, squalls) Type and movement of clouds Current weather State of the sky (current sky conditions) Visibility; vision obstruction (fog, haze) Precipitation since last observation Weather Maps and Forecasting Environmental satellites are crucial for weather forecasting and climate analysis. Large computers handle data from surface, aircraft, and orbital platforms for accurate forecasting. Data is used to assess climatic change. In Canada, Meteorological Service of Canada provides forecasts. In the US, National Weather Service (NWS) provides weather forecasts and satellite images. The World Meteorological Organization coordinates weather information internationally. Doppler radar is essential for accurate severe storm warnings. 31 WSR-88D Doppler radar systems are operational in Canada and 159 in the US. Weather Maps and Forecasting Automated Weather Observing System (AWOS) is the primary surface weather-observing network in Canada. AWOS includes various sensors such as rain gauge, temperature/dew-point sensor, barometer, present weather identifier, wind speed indicator, direction sensor, cloud height indicator, freezing rain sensor, thunderstorm sensor, and visibility sensor. Automated stations use the AWOS developed in partnership with the Atmospheric Environment Service and a private corporation. Canada has 31 upper air stations, six emergency stations, and five Department of National Defence stations. Over 800 hourly weather observation sites across the country, including 243 NAV Canada aviation observation sites, 243 Department of National Defence sites, and various automated observation sites. There are 302 Reference Climate Stations (RCS sites) and 1425 climate stations operated by volunteers. Weather Maps Source Weather Maps cP 71oF or 62oF or 21.7oC 16.6oC cold front Source Weather Maps occluded front warm front cold front stationary front Source Weather Maps 62oF or 16.6oC 71oF or 21.7oC cT Source warm front  Which town is warmer? A or B? A B  Which town is warmer? A or B? A B  Which is likely experiencing rain? A or B? A B  Which is likely experiencing rain? A or B? A B Each letter A represents the C source area for which air mass? A B C D D B  What type of frontal system is represented by the line? What time of air mass is represented by the x? 5o C ᵡ 9o C  A The map below shows the boundary between two air masses. The arrows show the direction in which the boundary is moving. B C Which weather map uses the correct weather front symbol to illustrate this information? D Review Questions 1. How does a source region influence the type of air mass that forms over it? Give specific examples of each basic classification. 2. Of all the air mass types, which are of greatest significance to Canada and the United States? What happens to them as they migrate to locations different from their source regions? Give an example of air-mass modification. 3. Explain why it is necessary for an air mass to be lifted if there is to be saturation, condensation, and precipitation. Review Questions 4. What are the four principal lifting mechanisms that cause air masses to ascend, cool, condense, form clouds, and perhaps produce precipitation? Briefly describe each. 5. Differentiate between the structure of a cold front and a warm front. 6. Differentiate between frontal lifting at an advancing cold front and at an advancing warm front and describe what you would experience with each one.  Quizlets https://quizlet.com/77688930/chapter-8-weather-and-climate-flash- cards/ https://quizlet.com/14767616/geography-chapter-8-weather-flash- cards/ https://quizlet.com/78927874/air-mass-flash-cards/ Mid-Latitude Cyclones and Violent Weather Describe the life cycle of a midlatitude cyclonic storm system and relate this to its portrayal on weather maps. List the measurable elements that contribute to modern weather forecasting, and describe the technology and methods employed. Identify various forms of violent weather by their characteristics and review several examples of each. Midlatitude Cyclonic Systems Migrating low-pressure weather systems in middle latitudes, outside the tropics. Low-pressure center with converging, ascending air spiraling inward counterclockwise in Northern Hemisphere and inward clockwise in Southern Hemisphere. Influenced by pressure gradient force, Coriolis force, and surface friction. Term "wave" appropriate due to undulating frontal boundaries and jet streams. Emerging model identifies air mass flows as "conveyor belts." Midlatitude Cyclonic Systems large traveling vortices (rotating air) about 2000 km in diameter with centers of low pressure may have a surface pressure of less than 970 mb precipitation at center of the low and along the fronts generally travel eastward movement is often controlled by jet stream winds in the upper troposphere Midlatitude Cyclonic Systems travels about 1200 km in one day exist for about 3 to 10 days moving in a generally west to east direction the dominant weather event of the Earth’s mid-latitudes forming along the polar front Midlatitude Cyclonic Systems Dominating weather patterns in middle and higher latitudes of Northern and Southern Hemispheres. Originating along the polar front, especially in Icelandic and Aleutian Polar front subpolar low-pressure cells. Associated with cyclone development and intensification in the eastern slope of Rocky Mountains, Gulf Coast, and eastern seaboard. Source Midlatitude Cyclonic Systems February 2013 nor'easter resulted from merging of two low-pressure areas off the northeast coast. Record snowfall in Greenwood, Nova Scotia, and maximum snowfall in Hamden, Connecticut. High-speed jet streams guide cyclonic systems across North America along shifting storm tracks. Typical storm tracks are farther northward in summer and southward in winter. Spring shifts in storm tracks lead to strongest frontal activity, featuring thunderstorms and tornadoes. Midlatitude Cyclonic Systems Life Cycle of a Midlatitude Cyclone 1. Cyclogenesis: convergence of cold and warm air masses 2. Open Stage: warm air moves north and cold air moves south 3. Occluded stage: cold front overtakes warm front 4. Dissolving stage: the cold air mass completely cuts off the warm air mass from its source of energy and moisture Life Cycle of a Midlatitude Cyclone Cyclogenesis is the initial stage of midlatitude cyclones, where low-pressure wave cyclones develop and strengthen. It usually begins along the polar front, where cold and warm air masses converge. A compensating area of divergence must match a surface point of air convergence for a wave cyclone to form. Even minor disturbances can initiate the converging, ascending flow of air and a surface low-pressure system. Other areas associated with wave cyclone development include the eastern slope of the Rockies, the Gulf Coast, and the east coasts of North America and Asia. Life Cycle of a Midlatitude Cyclone In the Open Stage, warm air moves northward along an advancing front. Cold air advances southward to the west of the developing low-pressure centre. As the cyclone matures, the counterclockwise flow draws cold air mass from the north and west, and warm air mass from the south. Cross section shows profiles of both a cold front and a warm front and each air mass segment. Life Cycle of a Midlatitude Cyclone Colder cP air mass is denser than warmer mT air mass, moving faster than warm fronts. Cold fronts can travel at an average of 40 km/hr, while warm fronts average 16–24 km/hr. Cold fronts often overtake cyclonic warm fronts and wedge beneath them, creating an occluded front. When airflow on either side is almost parallel to the front, a stationary front results. Gentle lifting may produce light to moderate precipitation. The stationary front moves as one air mass assumes dominance, evolving into a warm or cold front. Life Cycle of a Midlatitude Cyclone In the Dissolving Stage, lifting mechanism is completely cut off from the warm air mass, which was its source of energy and moisture. Remnants of cyclonic system dissipate in the atmosphere. Cyclone passage patterns over North America vary in shape and duration. Source Violent Weather Weather events like ice storms, thunderstorms, tornadoes, and hurricanes can trigger destructive events. Over 500% of weather-related destruction has increased over the past three decades due to population growth and climate change. Canadian government's Science and Technology branch of Environment Canada conducts research on severe weather forecasting, nowcasting, disaster mitigation, ozone, risk assessment, and prediction. Hazardous weather information can be found on Environment Canada's website. In the U.S., NOAA's National Severe Storms Laboratory and Storm Prediction Centre conduct research and monitoring. Winter Storms and Blizzards Winter storms are violent weather conditions confined to mid- to high-latitude regions. Defined by Environment Canada as major snowfall combined with freezing rain, strong winds, blowing snow, and extreme wind chill. Can occur in late autumn and early spring, and throughout the winter season. In the US, an ice storm is a winter storm with at least 6.4 mm of ice accumulation on exposed surfaces. In January 1998, 700,000 residents of Canada and the US were without power for weeks due to ice-coated power lines and tree limbs. Blizzards are snowstorms with frequent gusts or sustained winds greater than 40 km/hr for a period longer than 4 hours and blowing snow reducing visibility to 400 m or less. Thunderstorms Thunderstorms are turbulent weather accompanied by lightning and thunder. Characterized by giant cumulonimbus clouds and heavy rain. Can develop within air mass, along a cold front, or where mountain slopes cause orographic lifting. Thousands of thunderstorms occur on Earth, with many in equatorial regions and the ITCZ. Kampala, Uganda, in East Africa experiences 242 days a year with thunderstorms. Most thunderstorms occur in areas dominated by mT air masses in North America. Thunderstorms Fueled by rapid upward movement of warm, moist air. Air rises, cools, and condenses to form clouds and precipitation. Condensation of large water vapor liberates energy. Local heat causes violent updrafts and downdrafts. Rising air pulls surrounding air into column and raindrops pull air toward ground. Thunderstorms We seem to have LOTS of water vapour in the form of clouds here in Prince Rupert. Why don’t we have lots of thunderstorms? Isn’t the cP unstable? Rising? Our air is moist, yes! BUT most thunderstorms occur in areas dominated by mT air masses! They are fueled by the rapid upward movement of warm, moist air and we are dominated by cold, moist air. Thunderstorms Thunderstorms Thunderstorms Thunderstorms Turbulence and Wind Shear Thunderstorms are characterized by turbulence, created by air mixing of different densities or layers moving at different speeds and directions. Activity depends on wind shear, which changes wind speed and direction with altitude. Thunderstorms can produce severe turbulence in the form of downbursts, strong downdrafts causing strong winds near the ground. Downbursts are classified by size: macrobursts are at least 4.0 km wide and over 210 km/hr, microbursts are smaller in size and speed. These turbulence events are short-lived and hard to detect. NOAA's 2012 forecasting model improves predictions for severe weather events and aviation hazards. Supercells Supercell thunderstorms are the strongest and most severe weather events globally. They often contain a mesocyclone, a spinning, cyclonic, rising column of air. A well-developed mesocyclone can produce heavy rain, large hail, blustery winds, and lightning. Climate change enhances conditions conducive to thunderstorms and intense supercells. Wind shear, a crucial factor in thunderstorm and supercell formation, may lessen in midlatitudes due to Arctic warming. Research is ongoing to determine the importance of these effects in determining severe thunderstorm frequency. Lightning Types of lightning: Within cloud Cloud to ground Cloud to cloud Cloud to air Lightning Lightning is a flash of light caused by large electrical discharges that briefly superheat air to temperatures of 15 000°–30 000°C. It is caused by a buildup of electrical-energy polarity within a cumulonimbus cloud or between the cloud and the ground. Lightning poses a hazard to aircraft, people, animals, trees, and structures, causing nearly 200 deaths and thousands of injuries annually in North America. Environment Canada and the NWS issue severe storm warnings when lightning is imminent. About 90% of all strikes occur over land due to increased convection over warmer continental surfaces. Causes nearly 200 deaths and thousands of injuries each year in North America Do NOT seek shelter beneath a tree – they are good conductors of electricity and often are hit by lightning! Lightning Lightning East of the Rocky Mountain continental divide, a pronounced area of higher lightning activity occurs over the Rocky Mountain Foothills and the Swan Hills of Alberta. Southern Saskatchewan and southern Manitoba have an area of relatively high lightning activity, which appears to be an extension of the active Great The average lightning flash density (flashes per Plains area of the United States. square kilometre, per year) in Western Canada (1999 to 2018)  This region is located in a lake- breeze convergence zone, where a Lightning lake air mass meets a land air mass, between Lakes Huron and Erie. Greatest single-year lightning flash density (flashes per square kilometre, per year) in southern Ontario (1999 to 2018) Hail Ice pellets larger than 0.5 cm form within a cumulonimbus cloud. Raindrops circulate above and below freezing level, adding layers of ice until the cloud's circulation can't support their weight. Hail can grow from moisture addition on a snow pellet. Common hail size is pea-sized (0.5 cm), but can This hailstone measuring 20.3 cm in range from quarters (2.5 cm) to softballs (11 cm). diameter fell in South Dakota during a Largest authenticated hailstone in the world fell supercell thunderstorm with winds from a thunderstorm supercell in Aurora, Nebraska, exceeding 129 km/hr. Its circumference in 2003. measured 47.3 cm, just under the world Largest hailstone by diameter and weight fell in record circumference. Vivian, South Dakota, in July 2010. Hail Hail is common in Canada and the US, occurring every 1 or 2 years in high-frequency areas. In Canada, hailstorms are typically heavy, localized showers associated with mature thunderstorms. Most hailstorms develop in the continental interior, central Alberta’s “hailstorm alley,” the lee of the Rockies, and southernmost part of Saskatchewan. The most frequent hail occurrence is May to July, with nearly three-quarters of all hailstorms occurring between noon and 6:00 p.m. Hailstorms cause the greatest economic losses in Canada, leading to millions of dollars in crop insurance. Hail, Graupel, Sleet They are all different! Graupel: Less than 5mm Crumbly Hail: Opaque or white Greater than a 5mm “ball” Sleet: Less than 5 mm Bounces when it falls Damaging Winds Straight-line winds from fast-moving thunderstorms can cause significant damage to urban areas and agricultural crops. Term names include straight-line winds, downbursts, microbursts, plough winds, or derechos. Microbursts damage less than 4 km2. Downbursts from convective storms can cover large areas. These winds pose hazards to summer outdoor activities, overturning boats, hurling flying objects, and causing broken trees and limbs. Their highest frequency is about 70% from May to August. Damaging Winds Derecho is a damaging straight-line wind event caused by severe thunderstorms. Named by physicist G. Hinrichs in 1888, derives from Spanish word meaning "direct" or "straight ahead." Strong, linear winds over 26 m/s blast in straight paths along curved wind fronts. Can cause widespread and long-lived wind damage of hundreds of kilometers. Reported derecho wind events have increased since 2000 and may continue to rise with climate change. Tornadoes Violently rotating air column in contact with ground. Visible as spinning vortex of clouds and debris. Ranges from a few meters to over a kilometer in diameter. Lasts from a few moments to tens of minutes. Tornadoes Initial stages: Thunderstorm squall lines and supercells. Less than half of supercells produce tornadoes. Tornadoes West Point, Nebraska on June 14, 2013. Mike Hollingshead Tornado Measurement Tornado pressures are 10% less than surrounding air, causing high wind speeds. Theodore Fujita, a meteorologist, designed the Fujita Scale to classify tornadoes based on wind speed and property damage. The Enhanced Fujita Scale (EF Scale) was adopted in 2013 in Canada and 2007 in the US to better assess damage and correlate wind speed to damage caused. EF Scale includes Damage Indicators and Degree of Damage ratings for wind estimates. Source Tornadoes Why North America? conflicting and contrasting air masses to have access to each other. the number of EF-4 and EF-5 tornadoes is on the increase “Tornado Alley” Texas Oklahoma Kansas May is the Nebraska peak month Tornadoes Tornadoes “Tornado Alley” is shifting toward the Mississippi Valley and the Southeast, where populations are higher! Tropical Cyclones Originates within tropical air masses, a powerful manifestation of Earth- atmosphere energy budget. Classified according to wind speed: hurricanes, typhoons, or cyclones. Names based on location: hurricanes in North America, typhoons in the western Pacific, cyclones in Indonesia, Bangladesh, and India. Full-fledged hurricane, typhoon, or cyclone has wind speeds greater than 119 km/hr (64 knots). About 80 tropical cyclones occur annually worldwide. About 45 tropical cyclones are powerful enough to be classified as hurricanes (North America), typhoons (台风) (China, Japan, Philippines), and cyclones (Australia, India, Indonesia) per year. The warmer the ocean and the atmosphere, the more powerful the storm. Tropical Cyclone Classification TABLE 8.2 Tropical Cyclone Classification Designation(s) Winds Features Tropical disturbance Variable, low Definite area of surface low pressure; patches of clouds Tropical depression Up to 63 km/h; up to 34 Gale force, organizing knots circulation; light to moderate rain Tropical storm 63 –118 km/h; 34 – 63 Closed isobars; definite knots circular organization; heavy rain; assigned a name Hurricane (Atlantic and East Greater than 119 km/h; 64 Circular, closed isobars; Pacific) Typhoon (West knots heavy rain, storm surges; Pacific) Cyclone (Indian tornadoes in right-front Ocean, Australia) quadrant Tropical Cyclones Super Typhoons Defined as a strong tropical cyclone with wind speeds reaching 241 km/h (130 knots). In November 2013, Haiyan hit Philippines with the strongest sustained winds ever recorded. Storm Development Tropical cyclones differ from midlatitude cyclones due to homogeneous air and warm seas. Warm air and seas provide abundant water vapour, enabling the conversion of ocean heat energy into wind energy. Cyclonic motion begins with slow-moving easterly waves of low pressure in the trade-wind belt. If sea-surface temperatures exceed 26°C, a tropical cyclone may form along the eastern side of migrating troughs of low pressure. Surface airflow converges into the low-pressure area, ascending and flowing outward aloft, acting as a chimney. To maintain vertical convective circulation, minimal wind shear is required. Tropical Cyclones Range in diameter from 160 km–1000 km to 1300– 1600 km. Dominates the full height of the troposphere vertically. Move along water at about 16–40 km/h. Strongest winds usually recorded in right-front quadrant. At landfall, dozens of fully developed tornadoes may be located. Example: Hurricane Camille in 1969 had up to 100 tornadoes embedded in its right-front quadrant. Source Physical Structure Tropical cyclones have steep pressure gradients, generating inward-spiralling winds towards the centre of low pressure. Storms with lowest central pressure are not always the strongest or cause the most damage. The lowest central pressure for a storm in the Atlantic is 882 mb, recorded for Hurricane Wilma in 2005. Winds rush toward the center, forming a wall of dense rain bands called the eyewall. The central area is the eye of the storm, where wind and precipitation subside. The structure of the rain bands, eyewall, and central eye are visible in Hurricane Gilbert. Physical Structure Tropical Cyclones Damage Potential Uses sustained wind speed to rank hurricanes and typhoons in five categories. Ratings are for winds at landfall, may decrease after the storm moves inland. Does not address storm surge, flooding, and tornadoes. Damage depends on property development, preparedness of citizens, and local building codes. Hurricane Andrew in 1992 caused significant damage and left 200,000 homeless. Newer building codes may reduce structural damage, but local political pressure to weaken standards is active. Damage Potential Tropical cyclones cause additional hazards from storm surge and heavy rainfall flooding. Storm surge, the pushed inland seawater during a hurricane, can combine with normal tide to create a storm tide of 4.5m or more. Hurricane Sandy in 2012 caused a record storm surge in New York City, reaching 4.2m at the southern tip of Manhattan. Rising sea levels due to melting ice and warm seawater expansion increase storm tides. Formation Areas and Storm Tracks Figure 8.19a and 8.19b: Hurricane Formation Areas Identifies seven primary formation areas for hurricanes, typhoons, and cyclones. Highlights months of most likely storm formation. Shows actual tracks and intensities for tropical cyclones between 1856 and 2006. Formation Areas and Storm Tracks Tropical depressions intensify into tropical storms as they cross the Atlantic towards North and Central America. Early maturation of tropical storms curves northward towards the north Atlantic. Storms mature after reaching the longitude of the Dominican Republic increase the probability of hitting the United States. 2005 season broke records with the most named tropical storms, most hurricanes, and highest number of intense hurricanes, category 3 or higher. The 2005 season also recorded the greatest damage total in one year, exceeding USD $130 billion. Formation Areas and Storm Tracks No hurricane was observed turning from the equator into the south Atlantic until Hurricane Catarina in Brazil in 2004. Satellite image of Catarina shows an organized hurricane with a central eye and rain bands. Tropical cyclones are rare in Europe, but in 2005, Tropical Storm Vince became the first Atlantic tropical cyclone to strike Spain. Super Cyclone Gonu in 2007 became the strongest tropical cyclone in the Arabian Sea, eventually hitting Oman and the Arabian Peninsula. In 2011, a strong category 5 tropical cyclone hit northeastern Australia. Coastal Flooding from Hurricane Katrina One of the five deadliest hurricanes in the history of the United States. At least 1800 people lost their lives in the hurricane and the subsequent floods. Hurricane Katrina's 2005 landfall led to significant flooding due to human engineering and construction errors. Half of New Orleans' city is below sea level due to years of wetlands draining, soil compacting, and land subsidence. The city's 20th-century canal system was reinforced with concrete floodwalls and levees to prevent overflow. High rainfall and storm surges from Hurricane Katrina inundated the city, with some neighborhoods submerged up to 6.1 m. Polluted water remained in the city for weeks. New Orleans Hurricane Repair and Recovery Strengthening levees, floodwalls, floodgates, pumping stations. Costing over USD $12 billion. Hurricane Juan Hurricane Juan, a category 2 storm, made landfall in Nova Scotia on September 29, 2003. Initially a Tropical Depression number 15, it developed into a tropical storm and reached hurricane status 18 hours later. The storm ripped northward through Nova Scotia, reaching Prince Edward Island as a marginal hurricane. Rainfall amounts ranged from 25 to 44 mm, with storm surges of 1.0 to 1.5 m. Hurricane Juan Halifax Harbour recorded a storm surge of 290 cm, causing widespread flooding. The storm outside Halifax Harbour had significant waves reaching 9 m and maximum waves reaching 19.9 m. The storm claimed eight lives and caused millions of dollars in property damage. Hundreds of thousands of Nova Scotians and Prince Edward Islanders were affected, and it took two weeks to restore power. The greatest damage was the loss of trees throughout both provinces, especially Halifax’s Point Pleasant Park and Public Gardens. Hurricanes Katrina and Sandy: Storm Development and Links to Climate Change Katrina, a Category 5 hurricane, devastated the Gulf Coast in 2005. Sandy, a Category 3 hurricane, hit the mid-Atlantic coast in 2012. Both hurricanes were devastating, but their impacts differed significantly. Public awareness of climate change's impact on global weather events increased over the 7-year interval between them. Katrina was a textbook tropical cyclone, developed from warm View of Katrina from the GOES satellite on August 28, Atlantic waters. 2005, 20:45 UTC. Hurricanes Katrina and Sandy: Storm Development and Links to Climate Change Sandy’s Development and Effects Started as tropical depression number 18 in the Caribbean Sea. Reached hurricane strength on October 23. Moved northward over Cuba and Bahamas. Went between a stationary cold front and high-pressure air mass. Blocked north or east movement, driving it towards coast. Centre hit New Jersey shoreline after 11 p.m. Sandy’s Development and Effects Transitioned into a post-tropical storm before landfall, gaining energy from sharp temperature contrasts. Developed characteristics more aligned with nor’easters, midlatitude cyclonic winter storms. Wind patterns were asymmetrical, with a broad wind and cloud field shaped like a comma. Affected an estimated 20% of the U.S. population, resulted in over 100 fatalities, and cost USD $75 billion. Storm surges broke records along the New York and New Jersey coastlines, causing power outages, home destruction, and coastal erosion. A full moon made tides higher than average, with a record-setting 10-m wave recorded at the height of the storm. Hurricanes and Climate Change Rising sea levels have worsened hurricane damage, with Sandy's destruction worsened by sea-level rise from North Carolina to Massachusetts since 1950. Climate change causes higher sea-surface temperatures, correlated with longer tropical storm lifetimes and greater intensity. Warming oceans increase the energy available to fuel tropical cyclones, as seen in the Atlantic basin. Continued ocean warming and increasing coastal population may result in substantial hurricane- related property losses. More-intense storms and rising sea levels could lead to population shifts along U.S. coasts and abandonment of coastal resort communities. An Avoidable Cycle Tropical cyclones are highly destructive, causing thousands of deaths annually. Bangladesh's 1970 cyclone killed 300,000 people, while 1991's cyclone claimed over 200,000. Central and North America's deaths are lower, with 1900 Galveston hurricane killing 6000. Hurricane Mitch was the deadliest Atlantic hurricane in two centuries, causing over 12,000 deaths in Honduras and Nicaragua. 2005's Hurricane Katrina caused over 1830 deaths in Louisiana, Mississippi, and Alabama. Despite these statistics, risk of fatalities is decreasing due to improved warning systems and forecasting. An Avoidable Cycle Major hurricanes in North America have a recurring cycle of reconstruction, devastation, and reconstruction, particularly on the U.S. Gulf Coast. The same towns that were devastated by Hurricane Camille in 1969 were obliterated again by Hurricane Katrina in 2005. Despite the potential for irreversible damage, the mantra of "the Gulf Coast will rebuild bigger and better" remains. Property damage will continue to increase until better hazard zoning and development restrictions are implemented. The property insurance industry is promoting these improvements, requiring tougher building standards or refusing to insure property along vulnerable coastal lowlands. Public, politicians, and business interests must respond to mitigate this hazardous predicament. Weather has significant consequences for human society, especially as anthropogenic climate change worsens severe weather events. The Human Denominator Weather → Humans Frontal activity and midlatitude cyclones bring severe weather that affects transportation systems and daily life. Severe weather events such as ice storms, damaging winds, tornadoes, and tropical cyclones cause destruction and human casualties. The Human Denominator Humans → Weather Rising temperatures with climate change have caused shrinking spring snow cover in the Northern Hemisphere. Sea-level rise is increasing hurricane storm surge on the U.S. east coast. Issues for the 21st Century Global snowfall will decrease, with less snow falling during a shorter winter season; however, extreme snowfall events (blizzards) will increase in intensity. Lake-effect snowfall, transitioning to rainfall, will increase owing to increased lake temperatures. Increasing ocean temperatures with climate change will strengthen the intensity and frequency of tropical cyclones by the end of the century.  The diagram below represents a cross section of air masses and frontal surfaces along line AB. The dashed lines represent precipitation. Which weather map best represents this frontal system? A C B D Review Questions 1. How does a midlatitude cyclone act as a catalyst for conflict between air masses? How do flows of warm, cold, and dry “conveyors” of air interact in such a system? 2. What is meant by cyclogenesis? In what areas does it occur and why? What is the role of upper-tropospheric circulation in the formation of a surface low? 3. Diagram a midlatitude cyclonic storm during its open stage. Label each of the components in your illustration and add arrows to indicate wind patterns in the system. Review Questions 4. What constitutes a thunderstorm? What type of cloud is involved? What type of air masses would you expect in an area of thunderstorms in North America? 5. Lightning and thunder are powerful phenomena in nature. Briefly describe how they develop. 6. Describe the formation process of a mesocyclone. How is this development associated with that of a tornado? Review Questions 7. Evaluate the pattern of tornado activity in Canada and the United States. What generalizations can you make about the distribution and timing of tornadoes? Do you perceive a trend in tornado occurrences in North America? Explain. 8. Why have damage figures associated with hurricanes increased even though loss of life has decreased over the past 30 years? Review Questions 9. How did the effects of Hurricane Katrina in part relate to engineering and flood control structures in New Orleans? 10. Explain several differences between Hurricanes Katrina and Sandy. How is present climate change affecting hurricane intensity and damage costs? Quizlets https://quizlet.com/339430840/mid-latitude-cyclones-flash-cards/ Summary of Chapter 8 (1 of 2) Weather is the short-term condition of the atmosphere. Air masses are categorized by their moisture content—“m” for maritime (wetter) and “c” for continental (drier)—and their temperature, which is a function of latitude: “A” (arctic), “P” (polar), “T” (tropical), “E” (equatorial), and “AA” (Antarctic). There are four atmospheric lifting mechanisms: convergent lifting, convectional lifting, orographic lifting, and frontal lifting. Summary of Chapter 8 (2 of 2) A midlatitude cyclone or wave cyclone is a vast low pressure system that migrates across a continent, pulling air masses into conflict along fronts. A tornado is a violently rotating column of air in contact with the ground surface. A tropical cyclone becomes a hurricane, typhoon, or cyclone when winds exceed 65 knots (119 kmph, 74 mph).