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Enduring Understanding. Energy transfer between the Earths surface and the atmosphere creates the weather. The atmosphere remains in balance until acted on by an outside force. Weather. Weather is the current state and short term variations in the state of the atmosphere - PowerPoint PPT Presentation


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Enduring UnderstandingEnergy transfer between the Earths surface and the atmosphere creates the weather.The atmosphere remains in balance until acted on by an outside force.

2WeatherWeather is the current state and short term variations in the state of the atmosphereTakes place over minutes, hours, days, weeks, months

3Causes of WeatherClimate is the long term variations for a particular areaAveraged over 30 years or more of weather data

4Redistribution of WealthWithout the atmosphere this energy imbalance would continue and the tropics would be very hot and the poles very cold year roundThe oceans store the majority of heat at Earths surface

5Redistribution of WealthTemperature differences in the air result in differences in density which the cause upward and downward movementThe convection currents of the atmosphere redistribute the heat energy as air over the warmer regions rises, cools, then descends over cooler regions.

6Redistribution of WealthThis movement causes weather

7Air MassesAn air mass is a large body of air that takes on the characteristics of the body over which it forms. They can form over either land or water and are classified according to their source regions

8Air MassesContinental Tropical (cT) air masses contain warm, dry air that forms over warm areas of landMaritime Tropical (mT) air masses contain warm, humid air that forms over warm areas of the oceanContinental Polar (cP) air masses contain cold, dry air that forms over cold areas of landMaritime Polar (mP) air masses contain cold, humid air that forms over cold areas of the oceanArctic (A) air masses are basically the same as cP, but much colder and are associated with extreme cold 9North American Source RegionsAll five main air mass types can be found in North America because of our close proximity to the source regions associated with each type of air mass

10North American Source RegionsContinental Tropical (cT) air forms over the desert of the southwest United States and Mexico

11North American Source RegionsMaritime Tropical (mT) air forms over the southern Atlantic, Gulf of Mexico, and southern Pacific oceans

12North American Source RegionsContinental Polar (cP) air forms over the interior of Canada and Alaska

13North American Source RegionsMaritime Polar (mP) air forms in the northern Pacific and Atlantic oceans

14North American Source RegionsArctic (A) air develops over the extreme northern regions of the continent

15Stability and Air Mass MovementAir masses do not stay in one place indefinitely. They move and transfer their heat from one area to another establishing a balance of heat throughout the planet

16Stability and Air Mass MovementAir mass modification occurs when the moving air mass changes to become more like the surface over which it travelsHeat and moisture are exchanged with the surface as the air mass travels over it

17Stability and Air Mass MovementEventually the air mass will become modified to the point it is indistinguishable from the new surface over which it is traveling and simply becomes part of the air over the new source region

18Coriolis effectThe Coriolis Effect on Earth causes moving particles (air molecules ) to deflect to the right in the northern hemisphere and to the left in the southern hemisphere

19Global Wind PatternsTrade Winds occur at where the warm, rising air from the equator begins to cool and sink. They occur below 30 degrees latitude and blow in an east to west direction

20Global Wind PatternsPrevailing Westerlies flow between 30 and 60 degrees latitude and blow from west to east. This pattern is responsible for much of the weather in North America

21Global Wind PatternsWinds are named for the direction they blow from

22Global Wind PatternsPolar Easterlies blow from east to west between 60 deg and the poles and are characterized by very cold air

23Global Wind Patterns

24Jet StreamsOften the weather report will state that the jet stream is affecting todays forecast in some way. Earth weather is strongly influenced by atmospheric conditions and events between the wind zones

25Jet StreamsJet Streams are narrow bands of fast, high-altitude, westerly winds and flow at speeds of 185 km/hrTheir position varies and drives large-scale weather systems

26FrontsSince air masses of different characteristics are constantly in motion some of them are bound to eventually collide

27FrontsFront is the narrow region separating two air masses of different densitiesDensity differences are caused by differences in temperature, pressure, and humidity


29FrontsThere are four main types of fronts and the interaction of colliding air masses often causes dramatic changes in weather

30FrontsCold Fronts occur where cold, dense air displaces warm air and we see clouds, showers, and thunderstorms

31Fronts-Cold FrontGenerally, with the passage of a cold front, the temperature and humidity decrease, the pressure rises.


32Cold Front-crossing NYS - October 2008 (metars and satellite)

33FrontsWarm Fronts are where advancing warm air displaces cold air and we see extensive cloudiness and precipitation

34Fronts-WarmGenerally, with the passage of a warm front, the temperature and humidity increase, the pressure decreases.


35FrontsStationary Fronts are where the two air masses meet but neither advances. Little cloudiness and precipitation is seen

36FrontsOccluded Fronts occur where a cold air mass overtakes a warm front and wedges it upward. It then collides with another cold front and causes precipitation on both sides

37Fronts-OccludedOccluded front is formed when a cold front overtakes a warm front.

38Pressure SystemsThe vertical movement of air combined with the coriolis effect results in the formation of rotating low and high pressure systems

39High Pressure SystemHigh Pressure Systems are formed by dense, sinking air and move in a clockwise direction (in the northern hemisphere) High pressure is associated with fair weather

40Low Pressure SystemsLow Pressure Systems form by low density rising air moving in a counterclockwise directionLow pressure is associated with stormy weather

41Analyzing/Forecasting WeatherIn order to accurately analyze and forecast weather meteorologists must be able to reliably gather the necessary data about the atmosphere. The quality and amount of data available for a certain location greatly affect the outcome of the forecast

42The Instruments of MeteorologyThermometer measures temperature. They usually contain liquids such as mercury or alcohol that expand when heated

43The Instruments of MeteorologyBarometer measures air pressure. The common types are mercury and aneroid

44The Instruments of MeteorologyPsychrometer measures relative humidity. A wet and dry bulb thermometer is the most common type

45The Instruments of MeteorologyAnemometer measures wind velocity. The simplest type has cupped arms that rotate as the wind blows

46Technology in MeteorologyThe accuracy of weather forecasting has greatly improved over the last 40 years. Many technological advances from other sciences have been found to have practical applications in Meteorology

SunnyRainyCloudyMild47Technology in MeteorologyWeather Radar allows us to track real-time movement of precipitation inside the coverage area. Today most of the United States is covered by one or more weather radar sites

48Technology in Meteorology

49Technology in MeteorologyWeather Satellites take photographs and other images of the Earths surface at regular intervals.

50ImageryThese images are plotted and combined with radar data to determine where both clouds and precipitation are occurring

51Technology in MeteorologyInfrared Imagery is allows us to see temperature differences in the surface and moving air masses and allows us to predict a systems potential to produce severe weather

52Weather AnalysisOnce the weather observations are gathered meteorologists plot the data on a map using universally recognized symbols for the various pieces of information to be represented

53Weather AnalysisStation model is a record of the weather data for a particular site at a particular time and allows a large amount of data to be plotted in a small space

54Large Scale Weather Plotting Once the information for individual sites is plotted meteorologists can construct large scale (nationwide or worldwide) weather maps that represent the current state of the whole troposphere

55Large Scale Weather Plotting Isopleths are lines that connect equal or constant values and are similar to the contour lines used in geographyIsobars connect areas of equal air pressure

56Large Scale Weather PlottingIsotherms connect areas of equal temperature

57Short Term ForecastingWeather forecasting has improved much over the past few decades and continues to do so as we advance in our ability to obtain and process weather data

58Short Term ForecastingDigital Forecasts are the main method used by modern meteorologists. They rely on numerical data and are highly dependent on the density of data available. The more (accurate) data the more reliable the forecast

59Short Term ForecastingAnalog Forecasts compare current weather patterns to those that took place in the pastThe Farmers Almanac is an analog forecast

60Long Term Forecasting Regardless


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