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Meteorology What is Meteorology? • Meteorology is the study of atmospheric phenomena • Anything that’s high in the sky: raindrops, rainbows, dust, snowflakes, fog and lightning • All of these are examples of meteors? What is Meteorology? • Atmospheric phenomena are classified as types of meteors • Cloud droplets (rain, sleet, snow) are types of hydrometeors. • Smoke, haze, dust – any particles suspended in the atmosphere are lithometeors. What is Meteorology? • Short term variations in atmosphere phenomena that affect the environment and life on Earth is weather. – These variations can be minutes, hours, days, weeks up to years long. • Climate is the long term average in weather for a particular area Heating Earth’s Surface • Sunlight is always heating some part of Earth • Over time the amount of thermal energy Earth gets is the same amount that Earth radiates back to space. • How is this solar radiation distributed around Earth? Imbalanced Heating • In January, which is warmer? Miami or New York City? • One reason is that Earth is tilted. Miami gets more solar radiation in January. • Another is that Earth is a sphere and different places are at different angles to the sun. Thermal Energy Redistribution • Places on Earth maintain about the same average temperatures over time due to the movement of air and water between land, water and atmosphere. Air Masses • An air mass is a large volume of air with the same humidity and temperature as its source region. • A source region is the area where an air mass forms. • Most form over tropical waters or polar regions. Types of Air Masses • Tropical air masses form in tropical bodies of water and are responsible for our hot, humid summers • Polar air masses form over the cold waters of the North Atlantic and North Pacific. These bring our really cold air in winter. • The flip side? Learning Targets • Compare and contrast weather vs climate • Analyze how imbalances in the heating of Earth’s surface create weather • Identify five types of air masses and explain how air masses form Global Wind Systems • If the Earth didn’t rotate, two large convection currents would cover the Earth. • Colder air would sink to the tropics where it would force warm air to rise. • This air would cool as it got higher and on and on Global Wind Systems • Earth rotating from west to east prevents this from happening. • The directions of our winds are influenced by the Earth’s rotation. • Its called the Coriolis effect. Coriolis Effect • Causes fluids and objects to move in a curved path. • Moving air curves to the right in the northern hemisphere • Moving air curves to the left in the southern hemisphere • http://www.youtube.com/watch?v=mcPs_ OdQOYU Global Wind Systems • The Coriolis effect and the heat imbalance on Earth create distinct global wind systems. • There are three main zones or wind systems: polar easterlies, prevailing westerlies and trade winds. Global Wind Systems • Polar easterlies – Between 60o N latitude and the north pole and 60o S latitude and the south pole – Begin as dense polar air that sinks – As the Earth spins, this cold air is deflected in an easterly direction: usually weak and sporadic Global Wind Systems • Prevailing westerlies – Found between 30oN and 60oN and 30oS and 60oS – Surface winds move toward the poles in a westerly direction (again due to the Earth’s rotation) – These move much of the weather across the US Global Wind Systems • Between the polar easterlies and the prevailing westerlies lie an area called the polar front. • This can bring stormy weather to us. Global Wind Systems • Trade winds are between 30oN and 30oS • These circulation belts move toward the equator in an eastern path Jet Streams • Atmospheric conditions and events that happen at the boundaries between wind zones strongly influence our weather. • On either side of the boundaries, surface air and upper level air differ in temperature and pressure. Jet Streams • The difference in air pressure at the boundaries causes wind. • Wind is the movement of air from an area of high pressure to an area of low pressure. Jet Streams • A large temperature gradient in upper level air combined with the Coriolis effect gives us strong westerly winds called jet streams. • Jet streams are narrow bands of fast moving winds. • Its speed varies with the temperature differences.. Jet Streams • The position of the jet stream varies with the season. • Its usually found in the region of strongest temperature differences on a line from the equator to a pole. • It is the strongest core of winds. • http://www.youtube.com/watch?v=CgMW wx7Cll4 Types of Jet Streams • Polar jet streams separate the polar easterlies from prevailing westerlies; the major jet stream • Weaker jet streams are subtropical jet streams; found where trade winds meet prevailing westerlies • Most storms form along jet streams and bring large scale weather systems Fronts • A collision of two air masses is a front; a narrow region between two air masses of different densities • Fronts can cover thousands of square miles Cold Fronts • Cold front: cold, dense air displaces warm air • Less dense warm air rises, cools and condenses: intense precipitation occurs • A blue line with evenly spaced blue triangles is a cold front on a weather map Warm Front • Advancing warm air displaces cold air • Can cause widespread light precipitation • A red line with evenly spaced red semicircles Stationary Front • Two air masses meet but neither advances; the boundary between them stalls • A line of evenly spaced, alternating cold and warm symbols pointing in opposite directions Pressure Systems • Low Pressure – Air from outside replaces rising air, this air spirals inward to the center and then up in a counter clockwise direction – Rising air cools and condenses into clouds and precipitation Pressure Systems • High pressure systems – Sinking air moves away from the system’s center – Coriolis effect causes sinking air to move to the right, making air circulate in a clockwise direction in our hemisphere – Fair weather Learning Targets • Compare and contrast the three major wind systems • Identify four types of fronts and differentiate between each Gathering Weather Data • Meteorologists measure atmospheric conditions such as – Temperature – Air pressure – Wind speed – Relative humidity • Two important factors in weather forecasting are the accuracy of the data and the amount of data available Tools for measuring atmospheric conditions • A thermometer measures temperature in F or C. • A barometer measures air pressure. • An anemometer measures wind speed. • A hygrometer measures humidity. Thermometers • Usually some type of glass tube containing a liquid. • When heated the liquid expands when causing the column of liquid to rise. • When the liquid cools, the column drops. Barometer • Some have a column of mercury in a glass tube. • Changes in air pressure change the height of the mercury. Anemometer • The simplest has four cupped arms positioned at right angles from each other. • The arms rotate when the wind blows. • The wind’s speed is calculated by the number of revolutions of the cups over a specific period of time Hygrometer • Some have a wet bulb and a dry bulb thermometer and requires a conversion table to calculate. • The National Weather Service uses an automated surface observing system to gather data 24 hours a day Data From the Upper Atmosphere • Weather is largely the result of conditions in the upper atmosphere. • An instrument that measures those conditions is a radiosonde. – Contains a package of sensors suspended in a balloon that enters the upper atmosphere that collect data Weather Radar • Radar stands for radio detection and ranging • It generates radio waves and transmits them through an antenna at the speed of light. • The waves reflect when they hit particles (rain) Doppler Radar • Doppler effect is the change in pitch or frequency that occurs due to the relative motion of a waves. • Doppler radars measure the speed of precipitation as it moves toward and away from the radar. Weather Satellites • Some satellites move high above the earth using infrared imagery to make observations at night. • The imagery can detect differences in frequencies to map cloud cover or surface temperatures. Weather Satellites • Other satellites use visible light to photograph Earth. • These photos are sent back to weather stations to analyze cloud cover. Learning Targets • Discuss the importance of accurate weather data • Summarize the instruments used to collect weather data from Earth’s surface • Analyze the strengths and weaknesses of weather radar and weather satellites Surface Weather Analysis • Weather reports are generated from the data received from radars and satellites. • Station models – A record of weather data for a specific spot at a particular time – Symbols are used to represent the weather data – The symbols allow for the reporting to be uniform Surface Weather Analysis • Plotting station model data – To plot data nationally meteorologists use lines to connect points of equal or constant values – Lines of equal pressure are called isobars – Lines of equal temperature are called isotherms Interpreting Station Model Data • Using isobars, isotherms, and station model data, meteorologists can analyze current weather conditions. Types of Forecasts • Digital forecasts • Created by applying physical properties and math to atmospheric variables and then making a prediction • Analog forecasts – Based on comparing current weather patterns with weather patterns of the past Short Term Forecasts • The most accurate of all forecasts because weather conditions are fluid and change over time Long Term Forecasts • Forecasts for months or seasons are based on weather cycles or patterns. • Forecasts of 5 to 7 days are made using upper level atmospheric measurements and patterns. Learning Targets • Analyze a basic surface weather chart • Distinguish between digital and analog forecasting • Describe problems with long term forecasts