| VIOLENT WEATHER OR SEVERE WEATHER THUNDESTORMS 1. THUNDERSTORMS occur when Masses of WARM, MOIST AIR along the surface are FORCED RAPIDLY UPWARD into COLDER, DRYER LAYERS. Thunderstorms are likely to form in late afternoon or early evening on a hot summer day - although they can also form at other times. 2. As the Warm air is Forced aloft, it COOLS and CONDENSES, forming CUMULONIMBUS ("THUNDERHEADS") CLOUDS. These Clouds may reach heights of 20 000 m. After a turbulent period of Upward Movement of Air, RAIN Begins to fall. The Rain lasts about 30 minutes. Such Storms usually are accompanied by THUNDER AND LIGHTENING. It can also bring HAIL, STRONG WINDS, AND EVEN TORNADOS. 3. During Violent period of UPLIFT, ELECTRIC CHARGES BUILD IN CLOUDS. Bolts of Lightening LEAP FROM CLOUD TO CLOUD AND FROM CLOUD TO EARTH. Lightening Strikes when current flows BETWEEN Regions of OPPOSITE ELECTRICAL CHARGE. A SINGLE LIGHTENING BOLT CAN DISCHARGE MILLIONS OF VOLTS. A Lightening Bolt HEATS the nearby Air to a Temperature to 54 000 degrees F (30 000 Degrees C) - Five Times hotter than the surface of the sun! The Extreme Heat Causes Molecules in the surrounding Air to EXPLODE OUTWARD, creating a Shock Wave, or Sonic Boom. This Boom is THUNDER - the Sound of the Heated Air Exploding. 4. WHEN LIGHTENING OCURRS, KEEP AWAY FROM OPEN DOORS AND WINDOWS AND ELECTRICAL APPLIANCES THAT ARE CONNECTED. STAY OUT OF WATER AND OFF SMALL BOATS. A LOW POINT IN THE LANDSCAPE OR A DENSE GROVE OF TREES IS THE SAFEST SHELTER IF YOU ARE OUTSIDE. AVOID SOLITARY (LONE) TREES BECAUSE LIGHTENING IS ATTRACTED TO THE TALLEST OBJECT IN AN AREA. 5. THUNDER IS NOT DANGEROUS, IT IS THE SOUND CAUSED BY THE PRESSURE WAVE THAT ACCOMPANIES LIGHTENING. TORNADOS (TWISTERS OR CYCLONES) 1. TORNADOS, the MOST VIOLENT FORM OF WEATHER, ARE RELATED TO VERY SEVERE THUNDERSTORMS. They a produced when the GREATEST Contrast EXISTS in TEMPERATURE AND MOISTURE BETWEEN TWO AIR MASSES. 2. A Tornado is a Violent, WHIRLING WIND that moves in a narrow path over Land. Wind speeds in a Tornado can reach 250 miles per hour. Tornadoes may occur at many different times and places. They are most Common during the SPRING (BETWEEN MARCH AND JULY) in the US. Most of the world's tornadoes occur on the Central US. In the Area called TORNADO ALLEY, WHICH STRETCHES FROM CENTRAL TEXAS THROUGH NEBRASKA, OVER 200 TORNADOS OCCUR EACH YEAR. They are Associated with THUNDERSTORMS ALONG COLD FRONTS AND SOMETIMES HURRICANES. 3. In a VERY SEVERE Thunderstorm, WARM Air may be Forced UPWARD with Greet Speed and cause the WINDS to ROTATE VIOLENTLY near the Surface. Air Pressure DROPS RAPIDLY. A FUNNEL Cloud appears at the BASE of the CUMULONIMBUS CLOUD. As the Funnel touches the ground, buildings and trees are ripped apart by DESTRUCTIVE WINDS. Tornadoes may last for Hours, but the average life span of such a storm is 15 minutes. Buildings may "EXPLODE" from the expansion of air within, especially if the Doors and Windows are closed. 4. If a Tornado is likely to form in your area, radio and television stations will report the NATIONAL WEATHER SERVICE has issued a "TORNADO WATCH". This means that Tornadoes ARE POSSIBLE. If a "TORNADO WARNING" is issued, it means A TORNADO HAS BEEN SPOTTED, EITHER BY OBSERVERS OR ON RADAR SCREEN, AND YOU SHOULD TAKE COVER. 5. THE SAFTEST PLACE TO BE DURING A TORNADO IS IN A BASEMENT OR AN UNDERGROUND SHELTER. IF NOT AVAILABLE GO TO A ROOM IN THE CNETER OF YOUR HOME. HURRICANES 1. HURRICANES ARE TROPICAL CYCLONES THAT FORM OVER WATER. 2. They usually form in Latitudes between 5 and 20 degrees, and Move TOWARD HIGHER LATITUDES. 3. Air over Tropical Oceans is Vary WARM and HUMID. Sometimes a center of VERY LOW PRESSURE develop with a Rapid INFLOW of Air, forming a near CIRCULAR STORM (TROPICAL DISTURBANCE). Air near the CENTER is Forced Aloft and Flows OUTWARD at Upward Levels. WIND SPEEDS Increases as the storm develops (TROPICAL DEPRESSION) AND FINALLY A TROPICAL STORM. 4. When Wind Speed reach 74 MILES PER HOUR (120 km/h), the storm is CALLED a HURRICANE. An Eye forms at the CENTER as Air SINKS and is WARMED by COMPRESSION. Much of the energy of a Hurricane is released through CONDENSATION, as it pumps large amounts of Moist Warm Air into the Upper TROPOSPHERE. Hurricanes may be hundreds of miles across. They have a Circular Shape, with intense Winds and long bands of Clouds Spiraling in Toward the Center. In the middle of the Hurricane is the EYE, a Calm Area with Clear Skies. 5. Hurricanes that strike land may cause violent WINDS, HEAVY RAINS, AND FLOODS. The Gulf and South Atlantic Coastal States have experienced many disastrous hurricanes. The biggest problem occur while the hurricane is still well out to sea. The Storm creates HIGH WAVES that can Flood Coastal Areas. When the hurricane hits the Coast, High winds and Blinding Rains can wipe out entire towns. To make matters worse, many hurricanes cause Tornadoes after they reach land. Fortunately, Hurricanes WEAKEN and eventually Fizzle out after they hit the coast. 6. Hurricanes occur in other parts of the world, but they have different names, like "WILLY-WILLY" in Australia, "TYPHOON" in India, and "BAGUIO" in the Philippines. 7. The National Weather Service issues a "Hurricane Watch" when a hurricane threatens to pass over a particular area. When it appears that the storm will strike the area within 24 hours, a "Hurricane Warning" is issued. OTHER WATCHES AND WARNINGS 1. The National Weather Service issues advisories when severe weather has been observed, or when conditions are such that severe weather could occur. 2. When a "WATCH" is issued, you should prepare for severe weather. Watches are issued for SEVERE THUNDERSTROMS, TORNADOES, FLOODS, BLIZZARDS, AND HURRICANES. 3. When a WARNING is issued, SEVERE WEATHER CONDITIONS EXIST: SEVERE THUNDERSTORMS HAVE ALREADY BEEN REPORTED IN THE AREA; A TORNADO HAS BEEN SPOTTED; STREAMS AND RIVERS IN THE AREA HAVE REACHED FLOOD STAGE. 4. A HURRICANE OR BLIZZARD WARNING IS ISSUED WHEN THE STORM IS ACTUALLY APPROACHING THE AREA. FORECASTING WEATHER 1. A PERSON WHO STUDIES THE WEATHER IS A METEOROLOGIST. 2. Predicting he weather requires accurate measurements of TEMPERATURE, PRESSURE, WINDS, AND HUMIDITY. 3. Meteorologist make weather observations by collecting DATA from INSTRUMENTS and SATELLITES. 4. INSTRUMENTS USED AT MANY WEATHER STATIONS INCLUDE THERMOMETERS AND BAROMETERS. AN ANEMOMETER MEASURES WIND SPEED. RAIN GAUGES ARE USED TO MEASURE THE AMOUNT OF RAIN OR SNOW. COMPUTERS ARE USED TO GATHER DATA AT MANY WEATHER STATIONS TODAY. 5. CONDITIONS OF THE UPPER ATMOSPHERE, INCLUDING TEMPERATURE, RELATIVE HUMIDITY, AND ATMOSPHERIC PRESSURE ARE MEASURED WITH INSTRUMENTS SENT ALOFT BY BALLOONS. 6. WEATHER STATION COMMUNICATES WITH ONE ANOTHER ABOUT LOCAL CONDITIONS. 7. SINCE 1960, WEATHER SATELLITES HAVE PLAYED AN IMPORTANT PART IN WEATHER FORCASTING. Satellites monitor weather conditions, data are sent to ground by Microwave Transmission. As a result of Satellite Photography, Scientist who study weather can locate ICE FLOES AND ICEBERGS IN SHIPPING LANES, ISSUE SEVERE STORM WARNINGS, MAP JET STREAMS, AND BETTER FORCAST THE WEATHER. 8. A WEATHER MAP IS A COMPILATION OF WEATHER DATA FROM MANY COLLECTING STATIONS. STATION MODELS DESCRIBE LOCAL WEATHER OF THE COLLECTION STATION. 9. EACH STATION MODEL SHOWS THE WIND DIRECTION AND SPEED, ATMOSPHERIC PRESSURE, TEMPERATURE, DEW POINT, AMOUNT AND TYPE OF CLOUDS, TYPE OF PRECIPITATION, AND OTHER DATA. 10. A Computer uses information from all station models to draw ISOBARS on the map. ISOBARS are lines drawn to connect points of EQUAL AIR PRESSURE. Isobars show the SIZE and POSITION of PRESSURE SYSTEMS. The SPACING between Isobars indicate the pressure change occurring over a given distance or the PRESSURE GRADIENT. 11. Isobars that are Close Together indicate a STEEP PRESSURE Gradient and STRONG WINDS. WIND USUALLY FLOWS PARALLEL TO ISOBARS. 12. ISOTHERMS ARE LINES DRAWN TO CONNECT POINTS OF EQUAL TEMPERATURE. CLIMATE THE EARTH'S CLIMATE ZONES 1. Weather refers to the condition of the atmosphere at any given place and time. The weather changes constantly. 2. CLIMATE ON THE OTHER HAND, IS THE TYPE OF WEATHER THAT A PLACE USUALLY EXPERIENCES. 3. THE CLIMATE OF A REGION IS DETERMINED BY THE AVERAGE MONTHLY AND YEARLY TEMPERATURES AND PRECIPITATION OVER AT LEAST THIRTY (30) YEARS. 4. Climates differ from region to region, mainly because of the EARTH'S SHAPE. Because the Earth is shaped like a SPHERE, THE SUN'S RAYS STRIKE DIFFERENT PARTS OF THE SURFACE AT DIFFERENT ANGLES. 5. At latitudes near the Equator, the sun appears at the HIGHEST ANGLE IN THE SKY. THUS THE REGIONS NEAR THE EQUATOR HAVE THE WARMEST CLIMATE. 6. At latitudes near the POLES, the sun never appears very high above the HORIZONE. AS A RESULT, THESE PLACES HAVE THE COLDEST CLIMATES. 7. In the Middle latitudes, where the US is located, the angle of the SUN VARIES, FROM RATHER LOW IN THE WINTER TO HIGH IN THE SUMMER. 8. THE ANGLE OF THE SUN'S RAYS PRODUCE THREE BASIC CLIMATE ZONES ON EARTH. THEY ARE CALLED THE TROPICAL, TEMPERATE, AND POLAR. BODIES OF WATER AFFECT CLIMATE 1. Each of the three climate zones contains a variety of more specific climate regions. 2. The Tropic Zone, has High Temperatures Year Round, but some parts of the tropics have much rainfall, while others have very little. 3. Therefore, other factors besides the angle of the sun must affect the climate a place has. 4. One of these factors is the Presence of a LARGE BODY OF WATER. LAND NEAR AN OCEAN OR LARGE LAKE USUALLY HAS A HUMID CLIMATE. Water from the Ocean or Lake Evaporate into the Air. As the Moist Air moves over land, it can produce Precipitation. 5. Water WARMS AND COOLS MORE SLOWLY THAN DOES LAND. As a result Temperatures near an Ocean or Lake are MILDER than temperatures further inland. 6. Large bodies of water also have WARM and COLD CURRENTS that can influence Climate. The GULF STREAM is a WARM Ocean Current that flows Northward through the ATLANTIC OCEAN. Air masses that form over the Gulf Stream frequently move toward Europe. Even though England is about 1200 km further north than the New England states, their climates are similar. CONTINENTAL FEATURES AFFECT CLIMATE 1. North America has a variety of climates. Some of the climate regions are influenced by Ocean. Mountain Ranges and at places Elevation can influence climate. 2. Differences between Land and Water Surfaces cause SEASONAL WINDS CALLED MONSOONS, AND THEY INFLUENCE CLIMATE IN MANY PARTS OF THE WORLD. 3. During the SUMMER, the Monsoon Winds Blow Moist air from the Ocean toward Land. The moisture Condenses and falls as RAIN. 4. In the Winter, the Monsoon is a DRY Wind that Blows from the COOL Land toward the Warmer Ocean. PEOPLE'S EFFECTS ON CLIMATE 1. The climate where we live has changed many times in the past due to such events as Ice Ages and the Formation of Seas. 2. Climate may be changing right now due to Human activity. 3. The Burning of Fossil Fuels Releases CARBON DIOXIDE into the Air. The added carbon dioxide strengthens the Greenhouse Effect, causing Temperatures to rise. 4. The presence of cities has a noticeable effect on climate. City Temperatures are generally HIGHER than temperatures in rural areas because building materials and asphalt pavements ABSORB and STORE more HEAT than do Soil and Plants. 5. The Waste Heat from Vehicles and Buildings adds further to a cities temperature. WHY SEASONS CHANGE 1. The Earth's Axis is tilted 23 1/2 degrees with respect to the plane of its orbit. If the Earth's Axis was not tilted, the Sun would always appear directly overhead at the Equator. Each point on the Earth would experience twelve hours of daylight and darkness every day of the year. 2. The tilt of the Earth's Axis is Responsible for our Seasonal Changes. 3. As the Earth Revolves Around the Sun, its axis is always points in the same direction. As the Earth travels around the sun, different parts of the Earth's Surface tilt toward the sun at different times of the year. 4. On June 20 or 21, the Earth passes through a point in its orbit known as the SUMMER SOLSTICE. The Northern Hemisphere is tilted directly toward the sun. It is the First Day of SUMMER in the Northern Hemisphere, and the First Day of Winter in the Southern Hemisphere, where the Earth is Tilted away from the sun. 5. During Summer, the Northern Hemisphere receives MAXIMUM Energy from the sun. The sun appears HIGH in the sky and takes a long time to cross the sky from Sunrise to Sunset each day. At this time of the year, DAYTIME IS LONGER AND TEMPERATURES ARE WARM. 6. As the sun moves from the Summer Solstice, each day the sun appears lower in the sky and periods of daylight are shorter. 7. On December 20 or 21, the Earth reaches the WINTER SOLSTICE. At this time, the Northern Hemisphere is tilted AWAY from the sun. This is the first day of WINTER in he Northern Hemisphere. 8. During Winter, the sun appears LOW in the Sky and takes only a few hours to cross the sky. The Northern Hemisphere receives MINIMUM Energy from the sun. Daytime is shorter and temperatures are cold. 9. As the Earth continues moving in its orbit, each day the sun appears Higher in the sky, and periods of daylight get Longer. These changes continue until the Earth returns to the Summer Solstice. 10. The Earth also has TWO EQUALNOXES when the Sum appears Directly Overhead at the Equator. 11. On March 20 or 21, the Earth passes through the Vernal Equinox, which marks the First Day of SPRING in the Northern Hemisphere. 12. On September 22 or 23, the Earth passes through the AUTOMNAL EQUINOX, marking the First Day of AUTUMN in the Northern Hemisphere. 13. At these times, both hemispheres have 12 hours of both daylight and Night |