WEATHER AND CLIMATE LECTURE
WEATHER AND ATMOSPHERE
WEATHER - IS THE CONDITION OF THE ATMOSPHERE IN TERMS OF AIR PRESSURE, WIND, TEMPERATURE, AND MOISTURE AT A GIVEN TIME AND PLACE.
METEOROLOGY - THE STUDY OF THE ATMOSPHERE, INCLUDING ITS WEATHER.
ATMOSPHERE - ENVELOPE OF GASES SURROUNDING EARTH, HELD BY GRAVITY. WEATHER TAKES PLACE IN THE TROPOSPHERE (LOWEST LAYER FROM GROUND TO 18,000 KM)
THE COMPOSITION OF THE ATMOSPHERE IS 78% NITROGEN, 21% OXYGEN, 1% ARGON, 0.03% CARBON DIOXIDE, AND 0.01 ALL OTHER GASES.
STRATOSPHERE IS THE SECOND LAYER THAT EXTENDS FROM 18,000 TO 50,000 KM.
THE OZONE LAYER (10,000 TO 50,000 KM) ABSORBS 99% OF THE HARMFUL SUN RAYS (ULTRAVIOLET, XRAY, ETC)
OZONE THINNING RESULTS FROM THE RELEASE OF GASES CALLED CHLOROFLUOROCARBONS (CFCs)
IN THE HIGHEST LAYER, THE IONOSPHERE, (BETWEEN 65 AND 100,000 KM ABOVE EARTH) IONS AND ELECTRONS REFLECT RADIO WAVES. (26.6)
AT THE POLES, THE IONIZED PARTICLES (FROM SOLAR WIND) INTERACT WITH AIR MOLECULES TO FORM AURORAS, COLORED DISPLAYS OF LIGHT.
HEAT ENERGY ENTERS AND MOVES THROUGH THE ATMOSPHERE IN THREE DIFFERENT WAYS.
RADIATION IS THE TRANSFER OF HEAT AS ELECTROMAGNETIC (EM) RADIATION. SUNLIGHT.
CONDUCTION IS THE TRANSFER OF HEAT DUE TO CONTACT. HEAT ALWAYS FLOWS FROM HOTTER OBJECTS TO COOLER OBJECTS.
CONVECTION IS THE TRANSFER OF HEAT DUE TO MOVEMENT OF A FLUID (AIR OR WATER) WARMER AIR EXPANDS, BECOMES LESS DENSE, AND THUS RISES FORMING A CONVECTION CURRENT. THE TRANSFER OF WARM OR COLD AIR BY HORIZONTAL WINDS IS CALLED ADVECTION.
THE INCOMING SOLAR RADIATION IS CALLED INSOLATION.
THE EARTH’S SURFACE RADIATES INFRARED (HEAT). WATER VAPOR AND CARBON DIOXIDE TRAPS AND RERADIATES THIS HEAT. SCIENTISTS CALL THIS “TRAPPING” OR RERADIATION OF HEAT THE GREENHOUSE EFFECT.
SCIENTISTS HAVE MEASURED THE RATE OF COOLING WITH ALTITUDE. IT AVERAGES ABOUT 1 C FOR EVERY 160 METERS OF ELEVATION. THIS CHANGE IS CALLED THE NORMAL LAPSE RATE.
NORMALLY THE AIR GETS COLDER WITH HEIGHT IN THE TROPOSPHERE. SOMETIMES, HOWEVER, THE AIR AT THE SURFACE IS COLDER THAN THE AIR ABOVE IT. THIS UPSIDE-DOWN TEMPERATURE CONDITION IS CALLED A TEMPERATURE INVERSION.
TEMPERATURE IS THE AMOUNT OF MOLECULAR KINETIC ENERGY IN A SUBSTANCE.
TEMPERATURE IS MEASURED IN THE FAHRENHEIT SCALE ON THE SURFACE AND MEASURED IN THE CELSIUS SCALE ABOVE THE SURFACE. THE TWO TEMPERATURE SCALES ARE BELOW. (26.17)
CF
WATER BOILING POINT100212
WATER FREEZING POINT 0 32
1 C = 1.8 F1 F = 5/9 C
ISOTHERMS ARE LINES DRAWN ON MAPS THAT CONNECT PLACES WITH THE SAME TEMPERATURE.
EVAPORATION, CONDENSATION, AND PRECIPITATION
HYDROSPHERE - EARTH'S WATER ENVIRONMENT, INCLUDES OCEANS, LAKES, RIVERS, AND OTHER BODIES OF WATER, GROUNDWATER, ICE FROZEN IN GLACIERS, SNOW, AND WATER VAPOR IN THE ATMOSPHERE.
WATER CYCLE - THE CIRCULATION OF WATER AMONG THE DIFFERENT PARTS OF THE HYDROSPHERE. THE WATER CYCLE IS POWERED BY SOLAR ENERGY.
EVAPORATION - PROCESS IN WHICH WATER IN THE LIQUID STATE OR SOLID STATE PASSES INTO THE VAPOR STATE.
WATER VAPOR - THE GASEOUS FORM OF WATER.
SPECIFIC HUMIDITY - THE AMOUNT OF MOISTURE (WATER VAPOR) IN THE AIR.
WARM AIR BECAUSE IT IS LESS DENSE (MOLECULES ARE FURTHER APART) CAN HOLD MORE MOISTURE THAN AN EQUAL VOLUME OF COLD AIR.
SATURATED - AIR HOLDING ALL THE WATER VAPOR IT POSSIBLY CAN AT THAT TEMPERATURE. 100% RELATIVE HUMIDITY.
RELATIVE HUMIDITY - IS A MEASURE OF THE AMOUNT OF WATER VAPOR IN A GIVEN VOLUME OF AIR, COMPARED TO THE TOTAL AMOUNT OF MOISTURE THAT THAT VOLUME OF AIR COULD HOLD AT A GIVEN TEMPERATURE. (27.4
INSTRUMENTS USED TO MEASURE RELATIVE HUMIDITY ARE CALLED HYGROMETERS. ANOTHER FORM OF HYGROMETER IS THE PSYCHROMETER (CONTAINS WET & DRY BULBS) )
CONDENSATION - THE WATER VAPOR IN SATURATED AIR TURNS INTO LIQUID.
IF THE WATER VAPOR CONDENSES ON SURFACES SUCH AS GRASS, IN THE FORM OF A LIQUID, IT IS CALLED DEW.
THE WATER VAPOR COULD ALSO CONDENSE INTO DROPLETS, FORMING A CLOUD OR FOG.
DEW POINT - THE TEMPERATURE AT WHICH CONDENSATION OCCURS FORMING DEW.
THE TINY PARTICLES ON WHICH WATER VAPOR CONDENSES ARE CALLED CONDENSATION NUCLEI. FINE DUST, SALT CRYSTALS (SEEDING WITH AgI), SMOKE, SMOG.
IF THE AIR TEMPERATURE IS BELOW FREEZING BEFORE THE DEW POINT IS REACHED FROST WILL FORM. FROST IS NOT A TYPE OF PRECIPITATION. (27.8)
RADIATION FOGS, OR GROUND FOGS, FORM UNDER CONDITIONS SIMILAR TO THOSE THAT FORM DEW. THE NIGHTTIME SKY IS CLEAR AND THE GROUND LOSES HEAT RAPIDLY BY RADIATION. (27.9)
ADVECTION FOGS RESULT WHEN WARM, MOIST AIR BLOWS OVER COOL SURFACES.
CLOUD - IS A DENSE MASS OF SUSPENDED WATER OR ICE PARTICLES.
CLOUDS ARE CLASSIFIED ACCORDING TO THEIR SHAPES AND ALTITUDES.
FOUR BASIC CL0UD TYPES:
1. HIGH CLOUDS: 6 - 13 km, FORMED OF ICE PARTICLES
2. MIDDLE CLOUDS: 2 - 6 km
3. LOW CLOUDS: GROUND LEVEL TO 2000 m (2 km)
4. CLOUDS WITH VERTICAL DEVELOPMENT - EXTEND THROUGH GREAT ALTITUDE RANGE. USUALLY HAVE BASES IN THE LOW HEIGHT RANGE AND EXTEND UPWARD INTO THE MIDDLE OR HIGH ALTITUDES.
TWO CLOUD FORMS:
1. STRATIFORM OR STRATUS - LAYERED CLOUDS
2. CUMULIFORM OR CUMULUS - GLOBULAR CLOUDS
HIGH CLOUDS:
CIRRUS Ci - HIGH, WHITE, FEATHERY CLOUD COMPOSED OF ICE CRYSTALS USUALLY ASSOCIATED WITH FAIR WEATHER, BUT MAY INDICATE BAD WEATHER IN THE NEAR FUTURE. "MARES TAILS"
CIRROCUMULUS Cc - THIN, WHITE CLOUDS, MAY LOOK LIKE RIPPLES, WAVES, OR GLOBULAR MASSES. USUALLY ASSOCIATED WITH FAIR WEATHER, MAY INDICATE APPROACHING STORMS."MACKEREL SKY"
CIRROSTRATUS Cs - VEILLIKE LAYERED CLOUDS THAT MAY CAUSE HALOS TO APPEAR AROUND THE MOON OR SUN. ASSOCIATED WITH FAIR WEATHER, BUT MAY INDICATE APPROACHING STORMS.
MIDDLE CLOUDS:
ALTOCUMULUS Ac - LIGHT GRAY GLOBULAR CLOUDS IN PATCHES OR ROLLS. USUALLY ASSOCIATED WITH FAIR WEATHER, MAY TURN INTO THUNDERSTORMS.
ALTOSTRATUS As - GRAY OR BLUISH BLANKET LAYER. MAY PRODUCE LIGHT CONTINUOUS RAIN (DRIZZLE).
LOW CLOUDS:
STATOCUMULUS Sc - SOFT GRAY CLOUDS IN PATCHES OR TOLLS THAT MAY FORM A CONTINUOUS LAYER.
STRATUS St - DENSE LOW LAYER OF GRAY CLOUDS THAT MAY COVER ENTIRE SKY. ASSOCIATED WITH LIGHT DRIZZLE. A STRATUS CLOUD ON THE GROUND IS CALLED "FOG".
NIMBOSTRATUS Ns - THICK LAYER OF DARK CLOUDS THAT BLOCK OUT THE SUN. ASSOCIATED WITH STEADY, LONG PRECIPITATION "SOCKED IN"
VERTICAL CLOUDS:
CUMULUS Cu - WHITE WOOLPACK MASSES FORMED BY RISING AIR, ASSOCIATED WITH FAIR WEATHER, MAY TURN INTO THUNDERSTORMS. (SUMMER CLOUDS)
CUMULONIMBUS Cb - LARGE, HIGH, DENSE ANVIL SHAPED CLOUDS. ASSOCIATED WITH RAIN, HAIL, THUNDER AND LIGHTNING.
NIMBUS - ANY CLOUD THAT PRODUCES PRECIPITATION.
PRECIPITATION - PARTICLES OF WATER, LIQUID (RAIN) OR SOLID (SNOW, HAIL,OR SLEET), THAT FALL FROM THE ATMOSPHERE AND REACH THE GROUND. (27.16)
RAIN - CONDENSED WATER DROPLETS. (USNWS SYMBOLS)
SNOW - FROZEN WATER DROPLETS. (27.17)
HAIL - CONTINUOUS FREEZING OF WATER ON TO ICE.
SLEET - RAIN THAT FALLS THROUGH SUPERCOOLED OR FREEZING AIR AND FREEZES.
FOG - WATER VAPOR CONDENSED ON PARTICLES IN THE AIR AT GROUND LEVEL.
WHEN AIR RISES HIGH ENOUGH AND IN LARGE ENOUGH QUANTITIES, PRECIPITATION OFTEN OCCURS. THE
THE WINDWARD SIDE OF MOUNTAIN RANGES. THE PREVAILING WINDS ARE FORCED TO CLIMB THE WINDWARD SIDE OF A MOUNTAIN RANGE TO GREAT HEIGHTS. BECAUSE THE AIR COOLS AS IT RISES, SOME OF ITS MOISTURE CONDENSES AND FALLS AS RAIN OR SNOW. (27.19)
THE LEEWARD SIDE OF THE MOUNTAINS HAS SPARSE VEGETATION FOR THE WINDS DESCEND WARM AND DRY. (27.20)
DESERTS OFTEN FORM ON THE LEEWARD SIDE OF MOUNTAINS. DESERTS RECEIVE LESS THAN 25 cm (10 in) OF RAINFALL ANNUALLY.
THE GOBI DESERT OF CHINA, THE SAHARA OF AFRICA, AND THE DEATH VALLEY ARE EXAMPLES.
CLOUD SEEDING IS USED TO TRY TO CONTROL PRECIPITATION. SILVER IODIDE PARTICLES OR DRY ICE ARE SPREAD IN CLOUDS TO ACT AS CONDENSATION NUCLEI. (27.21)
SULFUR OXIDES FROM BURNING COAL AND NITRIC OXIDES FROM INTERNAL COMBUSTION ENGINES REACT WITH WATER TO FORM SULFURIC AND NITRIC ACIDS, THE TWO MAIN COMPONENTS IN ACID RAIN. (27.22)
ATMOSPHERIC PRESSURE AND WINDS
PRESSURE IS DEFINED AS FORCE PER UNIT AREA.
AIR PRESSURE IS THE WEIGHT OF THE ATMOSPHERE PER UNIT AREA.
THE INSTRUMENT USED TO MEASURE AIR PRESSURE IS THE BAROMETER.
AT SEA LEVEL, THE COLUMN IS ABOUT 76 CM OR 29.9 INCHES OR MERCURY OR 1013.2 MILLIBARS.
THE MAIN REASON AIR PRESSURE CHANGES IS BECAUSE OF TEMPERATURE
WARM AIR IS LIGHTER AND LESS DENSE THAN COOL AIR.
THE MORE WATER VAPOR THE AIR CONTAINS, THE LIGHTER IT IS.
IN COOL AIR, THE MOLECULES MOVE CLOSER TOGETHER (AND LESS WATER), CAUSING THE AIR TO BECOME DENSER AND TO SINK CAUSING A HIGH-PRESSURE AREA.
IN WARM AIR, THE MOLECULES MOVE FARTHER APART (AND MORE WATER), CAUSING THE AIR TO BECOME LESS DENSE CAUSING A LOW-PRESSURE.
PRESSURE GRADIENT IS THE DIFFERENCE BETWEEN ADJACENT PRESSURE CELLS. A STEEP OR STRONG PRESSURE GRADIENT EXIST IF ISOBARS (AREAS OF EQUAL PRESSURE) ARE CLOSE TOGETHER.
AIR MOVES FROM AN AREA OF HIGH PRESSURE TO AN AREA OF LOW PRESSURE.
THIS MOVEMENT OF AIR DUE TO DENSITY DIFFERENCES IS WIND.
LOCAL WINDS EXTEND OVER 100 KM OR LESS.
WINDS ARE ALWAYS NAMED FOR THE DIRECTION FROM WHICH THEY COME.
SEA BREEZE OCCURS WHEN AIR OVER THE LAND IS WARMED DURING THE DAY AND RISES AND COOL AIR FROM OVER THE SEA FLOWS IN OVER THE LAND.
LAND BREEZE OCCUR AT NIGHT WHEN THE LAND COOLS FASTER RESULTING IN SINKING AIR (HIGH PRESSURE) AIR OVER THE OCEAN RETAINS HEAT AND RISES THUS WARM AIR BLOWS TOWARD THE SEA
CORIOLIS EFFECT - AIR MOVING FROM THE POLE TO LOWER LATITUDES WOULD APPEAR TURNING RIGHT (IN NORTHERN HEMISPHERE) DUE TO DIFFERENTIAL ROTATION OF THE EARTH (THE EQUATOR TURNING 1700 km/hr WHILE THE POLES DO NOT)
THE CORIOLIS EFFECT IS NOT A FORCE AND IS IMPORTANT FOR OCEAN CURRENTS TOO.
WIND VANE - RECORDS WIND DIRECTION. POINTS IN DIRECTION WIND IS COMING FROM.
ANEMOMETER - MEASURES WIND SPEED.
A KNOT IS APPROXIMATELY 1.85 KM / HR OR 1.15 MILES PER HOUR
CONVECTION CELL - AIR IS WARMED AT THE TROPICS; THE WARM AIR RISES AND FLOWS TOWARD THE POLES. (HADLEY CELL)
IT'S REPLACED BY THE COOLER, DENSER AIR WHICH HAS MADE ITS WAY DOWN FROM HIGHER LATITUDES.
FROM THE EQUATOR NORTH ARE THE FOLLOWING PRESSURE BELTS AND WINDS.
WINDS ARE ALWAYS NAMED FOR THE DIRECTION FROM WHICH THEY COME.
DOLDRUMS - RISING WARM AIR NEAR THE EQUATOR. (LOW PRESSURE)
INTERTROPICAL CONVERGENCE ZONE (ITCZ) (EQUATOR)
TRADE WINDS - NORTHEASTERLY WINDS RETURNING TO THE DOLDRUMS FROM THE HORSE LATITUDES TURNED WESTWARD (TO THE RIGHT) DUE TO THE CORIOLIS EFFECT.
HORSE LATITUDES - THE DESCENDING AIR AT 30 NORTH OR SOUTH OF THE EQUATOR. (HIGH PRESSURE) (30 NORTH OR SOUTH)
PREVAILING WESTERLIES - AIR MOVING NORTH FROM THE HORSE LATITUDES TURNED EASTWARD (TO THE RIGHT) DUE TO THE CORIOLIS EFFECT.
POLAR FRONT - LOW PRESSURE AT 60 NORTH OR SOUTH
POLAR NORTH EASTERLIES
POLAR HIGH - HIGH PRESSURE AT POLES (90 NORTH)
EFFECTS OF CONTINENTS
LAND HEATS MORE IN SUMMERS AND COOLS MORE IN WINTER.
TWO EFFECTS:
HIGHEST TEMPERATURES (LOWEST PRESSURES) ARE AS FAR AS 30 DEGREES NORTH.
CONTINENTS BREAK UP THE PRESSURE BELTS INTO HIGHS AND LOWS.
MONSOONS ARE SEASONAL WINDS. IN THE WINTER COOL DRY WINDS BLOW FROM THE INTERIOR OUTWARD.
IN THE SUMMER WARM MOIST WINDS BLOW FROM THE OCEANS INTO THE INTERIOR RESULTING IN HEAVY RAINS. MONSOONS OCCUR IN INDIA AND SOUTHWESTERN UNITED STATES.
JET STREAMS - HIGH ALTITUDE WINDS FOUND IN THE TEMPERATE ZONE (AROUND 40 DEGREES NORTH) DUE TO THE DIFFERENTIAL TURNING OF THE EARTH.
AIR MASSES AND FRONTS
AIR MASS - IS A BODY OF AIR, TROPOSPHERE, THAT HAS THE SAME PROPERTIES AS THE SOURCE REGION OVER WHICH IT DEVELOPS.
SYMBOLS:
m - MARITIME - MOIST AIR DEVELOPED OVER OCEANS.
c - CONTINENTAL - DRY AIR DEVELOPED OVER CONTINENTS.
P - POLAR - COOL AIR MASSES THAT DEVELOP OVER HIGH LATITUDES.
T - TROPICAL - WARM AIR MASSES THAT DEVELOP OVER LOW LATITUDES.
AIR MASSES ARE NAMED FOR THEIR SOURCE REGIONS, OR PLACES OF ORIGIN.
A MARITIME TROPICAL (mT) AIR MASS COMES FROM TROPICAL SEAS. IT IS WARM AND HUMID.
A CONTINENTAL TROPICAL (cT) AIR MASS COMES FROM TROPICAL LAND ARIAS. IN NORTH AMERICA, THESE HOT, DRY AIR MASSES ORIGINATE IN THE DESERT AREAS OF SOUTHWESTERN UNITED STATES.
A MARITIME POLAR (mP) AIR MASS COMES FROM COLD OCEAN WATERS. IT IS COLD AND HUMID. (ALASKA & PENINSULA WEATHER)
A CONTINENTAL POLAR (cP) AIR MASS COMES FROM LAND AREAS IN HIGH LATITUDES. IT IS COLD AND DRY. (ALASKA & PENINSULA WEATHER)
A CONTINENTAL ARCTIC (cA) AIR MASSES ARE FROM LAND AREAS NORTH OF cP (NORTH POLE) AND ARE VERY COLD AND DRY. (ALASKA WEATHER)
AIR MASSES ARE SO LARGE (SEVERAL THOUSAND KILOMETERS IN DIAMETER) THAT THEY MAY TAKE MANY DAYS TO PASS A GIVEN PLACE.
THE WEATHER CHANGES BROUGHT BY NEW AIR MASSES MAY BE EXTREME OR SLIGHT.
FRONT - THE BOUNDARY BETWEEN TWO AIR MASSES, BECAUSE AIR MASSES OF DIFFERENT TEMPERATURE AND HUMIDITY DO NOT READILY MIX.
WARM FRONT - THE BOUNDARY ALONG THE ADVANCING WARM AIR MASS. THE FIRST SIGN OF THIS FRONT IS THE PRESENCE OF HIGH CIRRUS CLOUDS. LATER, STRATUS CLOUDS FORM AS THE FRONT CONTINUES TO MOVE.
WARM AIR OVER COOL AIR PRODUCES INVERSIONS AND SMOG.
COLD FRONT - THE LEADING EDGE OF A COLD AIR MASS. CUMULUS AND CUMULONIMBUS CLOUDS TEND TO FORM ALONG THE FRONT, PRODUCING RAIN SHOWERS AND THUNDERSTORMS.
COOL AIR OVER WARM AIR PRODUCES UNSTABLE AIR AND CONVECTION CURRENTS.
COLD FRONTS MOVE MUCH MORE RAPIDLY THAN WARM FRONTS.
OCCLUDED FRONT - OCCLUDE MEANS TO CLOSE OFF. AN OCCLUDED FRONT RESULTS WHEN TWO COOL AIR MASSES MERGE, FORCING THE WARMER AIR BETWEEN THEM TO RISE. HIGH WINDS AND HEAVY PRECIPITATION USUALLY ARE ASSOCIATED WITH AN OCCLUDED FRONT.
STATIONARY FRONT - OCCURS IF NEITHER AIR MASS IS BEING DISPLACED AND THE FRONTS DO NOT MOVE. THE ATMOSPHERIC CONDITIONS OF THE AIR MASS MAY BE MAINTAINED FOR MANY DAYS (WARM AND HUMID OR HOT AND DRY)
NOTE SYMBOLS OF FOUR FRONTS ON PAGE 548
METEOROLOGISTS OBSERVE TEMPERATURE, HUMIDITY, AND WIND OF AIR MASSES WITH A RAWINSONDE (RADIO TRANSMITTERS)
THE POLAR FRONT (60 DEGREES NORTH LATITUDE) IS THE BOUNDARY BETWEEN COOL AIR MASSES IN THE POLAR EASTERLIES AND WARM AIR IN THE PREVAILING WESTERLIES.
WAVES OR KINKS CAUSED BY THE JET STREAM CREATE LOWS OR CYCLONES WITH FRONTS ROTATING COUNTERCLOCKWISE AROUND THEM.
CYCLONE - THE CENTER OF LOW BAROMETRIC PRESSURE. "LOW" AIR FLOWS TOWARD THE CENTER OF A CYCLONE IN A COUNTERCLOCKWISE MOTION. USUALLY ASSOCIATED WITH BAD WEATHER.
WARM-FRONT WEATHER - A WARM FRONT AFFECTS THE WEATHER LONG BEFORE THE ARRIVAL OF THE RAINS. HIGH CIRRUS CLOUDS APPEAR FIRST, FOLLOWED BY CIRROCUMULUS AND CIRROSTRATUS. THEN ALTO STRATUS AND STRATUS APPEAR. FINALLY NIMBOSTRATUS BRING LONG SUSTAINED RAIN OR SNOW. STRATUS CLOUDS BECAUSE THE AIR IS STABLE WITH WARM FRONTS.
COLD-FRONT WEATHER - COLD FRONTS ARE STEEPER AND MOVE FASTER THAN WARM FRONTS. THE AIR AHEAD OF COLD FRONTS IS USUALLY UNSTABLE THUS CUMULI FORM CLOUDS RISE AROUND A COLD FRONT. HEAVY PRECIPITATION FALLS FROM CUMULONIMBUS CLOUDS, ALTHOUGH STORMS END QUICKLY. OCCASIONALLY TORNADOES FORM.
ANTI CYCLONE - THE CENTER OF HIGH BAROMETRIC PRESSURE. "HIGH" WINDS CIRCULATE AWAY FROM THE CENTER IN A CLOCKWISE MOTION IN THE NORTHERN HEMISPHERE. AN ANTI CYCLONE CREATES AREAS OF FAIR (BRIGHT AND CLEAR) WEATHER.
STORMS AND WEATHER FORECASTS
SEVERE WEATHER
THUNDERSTORMS OCCUR WHEN MASSES OF WARM, MOIST AIR ALONG THE SURFACE ARE FORCED RAPIDLY UPWARD INTO COOLER, DRYER LAYERS. AS THE WARM AIR IS FORCED ALOFT, IT COOLS AND CONDENSES, FORMING CUMULONIMBUS CLOUDS.
DURING THE VIOLENT PERIOD OF UPLIFT, ELECTRIC CHARGES BUILD IN THE CLOUDS. BOLTS OF LIGHTNING LEAP FROM CLOUD TO CLOUD AND FROM CLOUDS TO EARTH.
LIGHTNING IS A GIANT ELECTRIC SPARK BETWEEN REGIONS OF OPPOSITELY CHARGED PARTICLES. WHENEVER LIGHTNING IS DISCHARGED, THE AIR IN ITS PATH IS INTENSELY HEATED, CAUSING A VIOLENT EXPANSION. THIS SENDS OUT SOUND WAVES WHICH YOU HEAR AS THUNDER.
TORNADO - IS A VIOLENT, WHIRLING WIND THAT MOVES IN A NARROW PATH OVER LAND. IT IS A SMALL, VERY INTENSE WIND VORTEX WITH EXTREMELY LOW PRESSURE, FORMED BENEATH DENSE CUMULONIMBUS CLOUD.
WINDS IN TORNADOES ARE UP TO 400 km/hr OR 250 mi/hr.
TORNADOES ARE MOST COMMON DURING THE SPRING IN THE UNITED STATES.
BLIZZARDS COMBINE HIGH WINDS, LOW TEMPERATURES (-6 C OR LOWER), AND BLOWING SNOW. VISIBILITY IS NEAR ZERO.
WIND CHILL - THE COOLING EFFECT ON EXPOSED HUMAN FLESH DUE TO A COMBINATION OF TEMPERATURE AND WIND SPEED.
HURRICANES - ARE TROPICAL CYCLONES THAT FORM OVER OCEANS. THEY USUALLY FORM IN LATITUDES BETWEEN 5 AND 20 , AND MOVE TOWARDS HIGHER LATITUDES.
WIND SPEED INCREASES AS THE STORM DEVELOPS. WHEN WIND SPEEDS REACH 120 km/h, THE STORM IS A HURRICANE.
FORECASTING
METEOROLOGIST - A PERSON WHO STUDIES THE WEATHER.
METEOROLOGISTS COLLECT DATA FROM INSTRUMENTS, SATELLITES, AND WEATHER OBSERVATIONS.
WEATHER SATELLITES PLAY AN IMPORTANT PART IN WEATHER FORECASTING.
POLAR-ORBITING SATELLITES - ORBIT EARTH DIRECTLY OVER THE POLES.