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Unit 6: Atmosphere Part 2 Notes Chapter 16: Weather I. II. 16.1: Weather and the Atmospheric Water a. What is Weather and Climate? i. __________________________ is what is going on in the atmosphere at a particular place at a particular time. ii. Weather can change rapidly iii. A location’s weather depends on: 1. Air temperature, air pressure, fog, humidity, cloud cover, precipitation, wind speed and direction 2. These are directly related to the amount of energy that is in the system and where that energy is 3. The ultimate source of energy is the ________________ iv. _________________________ is the average of a region’s weather over time v. The climate for a particular place is steady and changes only very slowly vi. Climate is determined by many factors including: 1. The angle of the Sun, the likelihood of cloud cover, and the air pressure b. Humidity: i. The amount of ___________________________________ in the air in a particular spot. ii. Relative Humidity – the percentage of water vapor a certain volume of air is holding relative to the maximum amount it can contain. iii. If the humidity today is 80%, it means that the air contains 80% of the total amount of water it can hold at that air temperature. iv. Since ________________________ air can hold more water than cold air, raising or lowering temperature can change air’s relative humidity. v. _________________________________________ - the temperature when air becomes saturated with water c. Clouds: i. Clouds have a big influence on weather: 1. By preventing solar radiation from reaching the ground 2. By absorbing warmth that is re-emitted from the ground 3. As the source of precipitation ii. When there are no clouds, there is less insulation: 1. Cloudless days can be extremely hot 2. Cloudless nights can be very cold iii. Clouds form when air reaches its dew point iv. Water vapor is not visible unless it condenses to become a cloud d. Fog: i. A cloud located at or near the ground ii. When humid air near the ground cools below its dew point, fog is formed e. Precipitation: i. An extremely important part of weather ii. The most common precipitation comes from clouds: 1. Rain and snow 2. Sleet is less common 16.2: Changing Weather: a. Introduction: i. The weather in a location often depends on what type of air mass is over it ii. Another key factor is whether the spot is beneath a front, the meeting place of two air masses. b. Air Mass and Air Mass Formation: i. Air Mass – a batch of air that has nearly the same __________________________ and ________________________ ii. Forms over a large region (a source region), in high pressure zones, most commonly formed in polar and tropical regions iii. Moves across temperate zones so the middle latitudes are prone to having interesting weather iv. c. Air Mass Movement: i. Air masses are _____________________ pushed along by high-level winds 1. When it moves over a new region, it shares its temperature and humidity with that region ii. Storms arise if the air mass and the region it moves over have different characteristics iii. In general, cold air masses tend to flow toward the ___________________________ and warm air masses tend to flow toward the __________________ 1. This is one of the many processes that act towards balancing out the planet’s temperature d. Fronts: i. Where two air masses meet ii. The two air masses have different ___________________________ and do not easily mix 1. One air mass is lifted above the other, creating a low pressure zone 2. If the air lifted is moist, there will be condensation and precipitation 3. Winds are common at a front iii. Fronts are the main cause of stormy weather iv. With a cold front and warm fronts, the air mass at the leading edge at the front gives the front its name III. 1. Example: A cold front is right at the leading edge of moving cold air, and a warm front marks the leading edge of the warm air e. Stationary Front: i. The air masses do not move ii. Could become stationary if is blocked by mountains iii. May bring days of rain, drizzle, or fog iv. Winds usually blow parallel to the front, but in opposite directions v. After several days the front may break apart f. Cold Fronts: i. When a cold air mass takes the place of a warm air mass ii. The denser, cold air pushes up the arm air causing the air pressure to decrease iii. At the front a line of rain showers, snow showers, and thunderstorms with blustery winds iv. ________________ line – a line of severe thunderstorms forms along a cold front v. Behind the front is a __________________ air mass vi. The weather at a cold front varies with season g. Warm Fronts: i. A warm air mass slides over a cold air mass ii. Less dense air moves over the colder, denser air, the atmosphere is relatively ____________________ iii. The transition from cold air to warm air takes place over a long distance, so the first signs of changing weather appear long before the front is actually over you iv. Initially the air is cold, the cold air mass is above you and the warm air mass is above it v. High circus clouds make the transition from one air mass to the other h. Occluded Front: i. Usually forms around a low pressure system ii. Starts when a cold front catches up to a warm front iii. The air masses, in order from front to back, are cold, warm, and then cold again iv. Coriolis Effect curves the boundary where the two fronts meet towards the poles v. _________________________ and shifting winds are typical 16.3: Storms: a. Introduction: i. Weather happens every day but only some days have storms ii. The effect of storms also varies depending on weather may strike a populated area of a natural landscape iii. Hurricane Katrina is a good example; since the flooding after the storm severely damaged New Orleans, while a similar storm in an unpopulated area would have done little damage b. Thunderstorms: i. Extremely common – most drop a lot of rain on a small area quickly, but some are severe and highly damaging ii. From when ground temperature are high, ordinarily in the __________________ afternoon or early evening in spring and summer. iii. Birth of a thunderstorm: 1. As water vapor ________________________ to form a cloud, the latent heat makes the air in the cloud warmer than the air outside the cloud 2. This starts a downdraft, and soon there is a convection cell within the cloud 3. The thunderstorm is mature and it produces gusty winds, lightning, heavy precipitation, and hail iv. Death of a thunderstorm: 1. Convection shuts down – without ________________________ water vapor does not condense, no latent heat is present, and the thunderhead runs out of energy v. With severe thunderstorms: 1. The warm air gives the convection cell more energy 2. Can cause lots of damage because of high winds, flooding, intense hail, and tornadoes vi. Thunderstorms can form individually or in a _________________ line along a cold front vii. So much energy collects in cumulonimbus clouds that a huge release of electricity occurs (aka ______________________________) viii. Lightning heats the air so that it expands explosively, creating thunder 1. Sound waves travel much more slowly so a thunder clap may come many seconds after the lightning is spotted. c. Tornadoes (aka Twisters): i. Fierce products of severe thunderstorms 1. As air in a thunderstorm rises, the surrounding air races to fill the gap, forming a funnel ii. Can last a few seconds to several hours iii. Forms at the ___________________ of severe thunderstorms 1. Lines of theses thunderstorms form in the spring where a ______________ maritime tropical (mT) and continental polar (cP) air masses meet. iv. April 2011: 1. The deadliest set of tornado strikes in 25 years 2. Had many factors to encourage tornado formation: a. Meeting of the mT and cP air masses b. Jet stream was blowing strongly from the west 3. Results more than 150 tornadoes reported thought the day v. Meteorologist can only predict tornado danger over a very wide region vi. No one can tell exactly where and when a tornado will touch down vii. The exact path is unknown because tornado movement is not very predictable viii. The intensity of tornadoes is measured on the Fujita Scale – which assigns a value based on ______________ speed and damage F Scale (km/hr) (mph) Damage 64-116 40-72 Light-tree branches fall and chimneys may collapse 117-180 73-112 Moderate – mobile homes, autos pushed aside 181-253 113-157 Considerable – roofs torn off houses, large trees uprooted 254-332 158-206 Severe – houses torn apart, trees uprooted, cars lifted 333-419 207-260 Devastating – houses leveled, cars thrown 420-512 261-318 >512 >318 Incredible – structures fly, cars become missiles Maximum tornado wind speed d. Cyclones: i. Can be the most intense storms on Earth ii. A system of winds rotating counterclockwise in the Northern Hemisphere around a _____________ pressure system iii. Two types of cyclones: 1. Middle Latitude (mid-latitude) cyclones – the main course of winter storms in the middle latitudes 2. Tropical Cyclones – aka hurricanes iv. An anticyclone is the opposite of a cyclone – winds rotate clockwise in the N. Hemisphere around a center of _______________ pressure. e. Mid – Latitude Cyclones: i. Sometimes called extratropical cyclones, form at the ______________ front when the temperature difference between two air masses is large ii. Mid-latitude cyclones are especially fierce in the mid-Atlantic and New England states where they are called __________________________ - because they come from the northeast. f. Hurricanes: i. Tropical cyclones have many names: 1. ______________________________ - North Atlantic, Eastern Pacific Ocean 2. Typhoons – Western Pacific Ocean 3. Tropical Cyclone – Indian Ocean 4. Willi-Willi’s – Australia ii. Hurricanes arise in the tropical latitudes in summer and autumn when the surface temperature are 820F or higher iii. The warm air rises and forms a low pressure cell known as a topical ________________________ iv. Thunderstorms materialize around tropical depressions v. Hurricane are huge with high winds 1. Exception is the calm eye of the storm – where air is rising upward vi. Rainfall can be as high as 1” per hour vii. The release of latent heat generates enormous amounts of ___________________ 1. Nearly the total annual electrical power consumption of the US from ONE storm viii. Hurricanes can also generate tornadoes ix. Move with the prevailing winds – they originate in the trade winds and move to the west 1. Reach the latitude of the westerlies, they switch direction and travel toward the north or northeast x. Hurricanes are assigned to categories based on their wind speed. The categories are listed on the Saffir-Simpson hurricane scale Category Kph Mph Estimated Damage 119-153 74-95 Above normal, no real damage to structures 154-177 96-110 Some roofing, door, and window damage, considerable damage to vegetation, mobile homes, and piers 178-209 111-130 Some building damaged, mobile homes destroyed 210-251 131-156 Complete roof failure on small residences, major erosion of beach areas, major damage to lower floors of structures near shore >251 >156 Complete roof failure on many residences and industrial buildings, some complete building failures xi. Damage from hurricanes comes from the high winds, rainfall and storm surge xii. Storm surge occurs as the storm’s low pressure center comes onto land, causing the sea level to rise unusually high 1. Often made worse by the hurricane’s high __________________ blowing seawater across the ocean onto the shoreline xiii. Flooding can be devastating, especially along low-lying coastlines, such as the Atlantic and Gulf Coast xiv. Hurricanes typically last for 5 to 10 days xv. Over _____________________ water or land the hurricane’s latent heat source shuts down and the storm weakens 1. When a hurricane disintegrates it is usually replaced with intense rain and tornadoes. xvi. As people develop coastal regions, property damage from storms continue to rise xvii. However, scientists are becoming better at predicting the paths of these storms and fatalities are decreasing xviii. The 2005 Atlantic hurricane season was the longest, costliest, and deadliest hurricane season so far 1. Total damage from all the storms together was estimated at more than $128 billion, with more than 2,280 deaths 2. Hurricane Katrina was both the most destructive hurricane and the most costly g. Blizzards: i. Blizzards have certain conditions: 1. Low temperatures, high winds, heavy snow with low ____________________ ii. Happen across the middle latitudes and towards the poles, usually as part of a midlatitude cyclone IV. iii. Are most common in winter, when the __________________________ has traveled south and a cold, northern air mass comes into contact with a warmer, semitropical air mass iv. Can also produce sleet of freezing rain h. Lake-Effect Snow: i. In winter, a continental polar (cP) air mass travels down from Canada ii. As the frigid air travels across one of the Great Lakes, it warms and absorbs moisture iii. When the air mass reaches the leeward side of the lake, it is very unstable and it drops tremendous amounts of snow i. Heat Wave: i. Is different at different locations 1. It is a long period of hot weather for at least three days in cooler locations 2. Much more longer and hotter in hotter locations ii. Heat waves have increased in frequency and duration in recent years 1. Can result when a high pressure zone keeps the ___________________________ further north/south than normal 16.4: Weather Forecasting: a. Introduction: i. Forecasters now use advanced technologies to gather weather data, along with the world’s most powerful computers 1. Together the data and computers produce __________________ models that more accurately represent the condition of the atmosphere ii. Weather is extremely difficult to predict because it is complex and chaotic systems b. Collecting Weather Data: i. Temperature, air pressure, and other characteristics of the atmosphere must be measured and the data collected ii. ____________________________ - measures temperature iii. ____________________________ - measures air pressure 1. A change in barometric pressure indicates that a change in weather is coming a. If the air pressures rises, a high pressure cell is on the way and clear skies ca be expected b. If the air pressure falls, a low pressure cell is coming and will likely bring storm clouds iv. Weather Stations – contain some types of thermometer and barometer v. Radiosondes – measure atmospheric characteristics, such as temperature, pressure, and humidity as they move through the air c. Radar (Radio Detection and Ranging): i. A transmitter sends out radio waves that bounces off the nearest object and then return to a receiver. ii. Doppler radar can also track how fast the precipitation falls iii. Radar can outline the structure of a storm and can be used to estimate its possible effects d. Satellites: i. Weather satellites are they best way to monitor large scale systems, such as storms ii. Are able to record long-term changes, such as the amount of ice cover over the Arctic Ocean e. Numerical Weather Patterns: i. The most accurate weather ______________________ are made by advanced computers, with analysis and interpretation added by experienced meteorologists ii. Meteorologists can use these results to give much more accurate weather forecasts and climate predictions f. Weather Maps: i. Simply and graphically depict meteorological conditions in the atmosphere ii. Meteorologist use many different symbols as a quick and easy way to display information on the map iii. _______________________ - lines of equal temperature, show temperature gradients and can indicate the location of a front iv. Isobars – lines of equal average air pressure at sea level 1. Closed isobars represent the locations of high and low pressure cells