Weather 101 From Doppler Radar and Long Range Forecasts to the Polar - Climatologia (2024)

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You will continue to receive exclusive offers inyour inbox.http://www.simonandschuster.com/ebook-signup/front/9781507204641CONTENTSINTRODUCTIONWHY DO WE HAVE WEATHER?WEATHER AND CIVILIZATIONLEARNING TO PREDICT THE WEATHERWEATHER AND WARSWORLD WAR IIHAARPTHE DOPPLER RADARWEATHER AND CLIMATEWHAT’S THE ATMOSPHERE?THE WATER CYCLETHE THREE LEVELS OF CLOUDSHOW TO BUILD A CLOUDHAIL AND SNOWTHE POLAR VORTEXSLEET OR FREEZING RAIN?HIGH PRESSURE AND LOW PRESSURETHE JET STREAMWHAT’S A FRONT?CREATING AN AIR MASSOCEANS AND WEATHEREL NIÑOSOLAR WINDORBITS AND OCEANSDETERMINING THE SEASONSDEVELOPING THERMOMETERSTHE TOOLS OF METEOROLOGYTHE ART AND SCIENCE OF FORECASTINGFORECASTING MODELSLIGHTNINGSPRITES, ELVES, AND BLUE JETSTAMING LIGHTNINGWHY WE HAVE FLOODSTHE DANGER OF DROUGHTSHURRICANESTORNADOESTORNADO FORMATIONVOLCANOES AND OTHER DISASTERSTHE JOHNSTOWN FLOODTHE GREAT GALVESTON HURRICANETHE SUPER OUTBREAKHURRICANE ANDREWHURRICANE FLOYDKATRINA AND SANDYSTAYING SAFE IN THE WEATHERFLOODS AND TORNADOESTHE WEATHER AND YOUR HEALTHTEMPERATURE AND YOUR BODYOUR CHANGING ATMOSPHERETHE CLIMATE CHANGE CONTROVERSYTHE CAUSES OF GLOBAL WARMINGTODAY’S TECHNOLOGYINDEXINTRODUCTIONLightning. Supercells. Blizzards. All of it’s weather, and allof it affects your life. But what exactly is weather?It’s one of the most complicated and difficult-to-predictsystems in existence. Since the beginning of the humanrace, people have tried to understand it in order to benefitfrom good weather and protect themselves from bad.Today’s scientists have come a long way in predictingmajor weather events, but they still can’t make accuratelong-term forecasts.This is despite the fact that there’s a lot of informationtoday about the weather: it’s on television, on the radio, innewspapers, blogs, vlogs, and on YouTube. That’s whymany people want to know more about how weatherworks.In Weather 101 you’ll find out such things as:•The causes of storms such as hurricanes and tornadoes•What the different kinds of clouds mean• What terms like “high-pressure front,” “the jet stream,”and “El Niño” mean•How to stay safe in a stormWeather 101 will also tackle issues like pollution, acidrain, damage to the ozone layer, and climate change. Themore you learn about the weather, the stranger thingsyou’ll find: from supercells to exotic lightning forms (calledsprites, elves, and blue jets), from polar vortices tomicrobursts. Scientists have developed sophisticateddevices to study and measure all these things and more;including not only instruments here on Earth but alsoweather satellites that can look at atmospheric changesfrom space. All of this helps them understand thecomplexity and ever-changing nature of weather systems—and relay this information to you so you can planaccordingly: everything from your vacation to when tostart your drive to work in the morning.If you’re fascinated by the range of global weatherpatterns, if you want to learn about important weather-related disasters, or if you just want to know how to copewith the weather in your area, you’ll find the answers toyour questions in Weather 101.Knowing more about the weather isn’t just important—it’s essential in our rapidly changing world. It’s time to getstarted.WHY DO WE HAVE WEATHER?Something We All Have in Common“Don’t knock the weather; nine-tenths of the people couldn’t start a conversation if it didn’tchange once in a while.”—Kin Hubbard, US journalist, humoristSimply put, weather is what’s going on in the atmosphere in anyone location at a particular time. Understanding weather allowsus to plan our day, our vacations, and our crops. And it’s ahandy conversation starter.WHY IT’S A BIG DEALIn fact, weather is a complex and dynamic process driven bythe Sun; the earth’s oceans, rotation, and inclination; and somany other factors that many of its mysteries still remainunexplained. Being prepared for what the weather brings canbe as simple as turning on the TV to catch the latest forecastbefore heading for the beach, or as complicated as examininglong-range forecasts to decide which crops to plant. Weatherconstantly affects people in small ways, but weather can alsohave major consequences when hurricanes or tornadoesthreaten their well-being and livelihoods, or even their lives.The weather can even affect your health, especially duringextremes in temperature or precipitation. If you’re not dressedproperly in cold weather, you can fall victim to hypothermia,which occurs when the body’s core temperature drops belowthe point where things function normally. The flip side ofhypothermia is hyperthermia, where the body’s coretemperature rises too high. Hyperthermia can cause heatexhaustion or even heat stroke, which can be fatal.A Cold? Or Allergies?During the summer, a stuffy nose and postnasal drip may have you convinced you’resuffering from a cold. But the same symptoms may be due to allergies. Remember thatcolds last an average of three to seven days, while allergic reactions can go on for ten daysto several weeks. If you’re still miserable after a week, chances are you’ve got allergies.Weather can also affect your health in less obvious ways.Long spells of gray winter weather can lead to seasonalaffective disorder (SAD), a malady that causes depression and adebilitating lack of energy; it’s thought to be caused by lowerlight levels during the winter as the days become shorter andthe Sun rises lower in the sky. Many arthritis sufferers complainof worsening symptoms when atmospheric pressure falls, andthere is a statistical rise in the number of heart attacks afterabrupt weather changes such as passing storm fronts.THE BIG PICTUREOn a larger scale, weather plays a big role in the economichealth of every nation on Earth. A timely soaking rain canrescue a crop from ruin, while a sudden torrential cloudburstcan wash it away. And farmers aren’t the only ones at risk;those who depend on natural gas for heat often watch indismay as a particularly cold winter sends prices skyward.Hurricanes can drive tourists away from areas that depend on aregular influx of visitors for their livelihoods. Even a gentlephenomenon like fog can result in disaster, as the captains ofthe Andrea Doria and the Stockholm learned one fateful Julynight in 1956. And during the Dust Bowl of 1936, one of thehottest and driest summers ever recorded, more than 15,000people died of malnutrition and dust-related diseases.Ancient HurricanesScientists look for evidence of ancient hurricanes in a branch of science calledpaleotempestology. Evidence of past storms can be found in coral skeletons, sedimentsfrom the ocean bottom, and even in caves, where stalactites retain the chemical signaturesof abrupt cloudbursts caused by tropical cyclones.With a growing realization of the weather’s importance andso much weather news readily available on TV and the Internet,it’s no wonder that interest in the subject is soaring. It seemsthat almost every day a weather disaster is happeningsomewhere in the world. Yet it’s important to remember thatextreme weather events, from droughts to hurricanes, havebeen happening for millennia, long before there were camerasto record them or buildings and people to get in their way.One of the reasons weather is so compelling is because it isuniversal: snow falls just as heavily on poor neighborhoods as itdoes in well-to-do suburbs, and a flash flood can destroy bothmansions and shacks with equal force. Weather is theone thingeveryone has in common.WEATHER AND CIVILIZATIONA Historical ForceAncient people did their best to understand and predict theweather. Lacking modern scientific instruments, earlycivilizations observed nature and kept records of the seasons.They understood how important the Sun was for growing theircrops, which explains why many ancient cultures worshipedsun gods. In Mesopotamia the Babylonians counted on theweather gods Hadad and Marduk to bring them good harvests.The Hittites left the weather-producing chores to their primarydeity, Teshub; while in Greece, a violent thunderstorm meantthat the weather god Zeus was throwing a thunderbolt tantrum.As far back as 1800 B.C., Hindus in India counted on theirweather god, Indra, who carried a lightning bolt, to commandthe weather from his perch atop a large white elephant. InScandinavia, Norse god Thor protected farmers and serfs fromweather disasters.EARLY FORECASTSAround 580 B.C., the philosopher Thales of Miletus is said tohave issued the very first seasonal crop forecast based on pastolive harvests. According to legend, Thales was so confident ofhis forecast that he reserved the use of all the olive presses inhis area before the harvest and made a tidy profit leasing themback to farmers when the bumper crop arrived.The first real effort to gather all known weather informationinto one place was accomplished by the philosopher Aristotlearound 350 B.C. In his essay “Meteorologica” the philosophercorrectly guessed that the Sun put large masses of air intomotion, and that water vapor could condense into clouds. ButAristotle was hamstrung by his era’s notion that everything wasmade of four elements: fire, water, air, and earth. His attemptsto force those elements to agree with the realities of naturelimited his investigations. The other fallacy of his time was thebelief that the earth was the center of the universe, which madeit impossible to correctly explain the origin of the seasons.Naming a ScienceAristotle’s largest contribution to weather science was theterm “meteorology,” which we still use today. The word comesfrom the Greek meteoros, which means “high in the sky.” InAristotle’s day anything falling from or appearing in the sky(like rain or clouds) was called a meteor.False TalesSome people still depend on folklore for weather safety, but many of the beliefs that havebeen passed down through the generations are misconceptions. For instance, some stillinsist the major danger from a hurricane is the wind, when most victims actually die instorm-spawned flooding.Aristotle’s pupil Theophrastus picked up his teacher’s work,writing a journal called On Weather Signs that noted hownature can often be used to forecast the weather. He alsoestablished a link between the weather and certain kinds ofillnesses, and was the first person in recorded history toidentify sunspots.For the next 2,000 years, the science of meteorology wentdormant. Without accurate instruments to predict developingweather conditions or even measure the basic elements,weather forecasters leaned on folklore or nature for advice onplanting crops and avoiding weather disasters.LEARNING TO PREDICT THEWEATHEREvolution of a ScienceThings started falling back into place in the sixteenth centurywhen Nicolaus Copernicus appeared on the scene. In 1543 hepresented the theory that the Sun, not Earth, was at the centerof the universe. Although still incorrect, his theory at leastmade room for an explanation of the seasons, and he correctlydeduced that Earth rotated on its axis once a day and made thelong trip around the Sun once each year. This was a scandalousand shocking idea at the time, because it contradicted religiousdogma and suggested that man was just a part of nature,instead of being superior to it.Leonardo da Vinci was fascinated by the weather. He noticedthat a ball of wool weighed more on a rainy day than on a dryone, and further experiments led to his invention of thehygrometer, a device to measure the amount of watersuspended in the air. Da Vinci wasn’t content to measure theair’s water content; he also invented the anemometer, whichmeasures wind speed.Even though the air’s moisture level and speed now could bemeasured, for most of the sixteenth century no one could tellyou how hot it was, because there were no thermometers yet.Enter Galileo Galilei, who remedied the thermometer shortagein 1593.Galileo called his invention a thermoscope. It consisted of along-necked glass bottle that was placed, upside down, into avessel containing water. When the bottle was heated slightly,usually by the warmth of the experimenter’s hands, the airinside expanded and the water was pushed downward. Whenthe bottle cooled, the air contracted and the water rose back upinto the neck of the bottle. Unfortunately, the thermoscope hadno degree markings and was useless for determiningtemperature, but it paved the way for the more accurateversions to come.THE PRESSURE INTENSIFIESNow one could tell how humid it was and how fast the windwas blowing, and could get a vague idea of the temperature. Butwhat about the air pressure?Evangelista Torricelli, a student of Galileo’s, created the firstmercury barometer to measure atmospheric pressure in 1644,completing the list of instruments needed to develop anaccurate weather forecast.Verifying a VacuumAristotle’s contention that “nature abhors a vacuum” could be debated but not tested untilTorricelli created one inside his mercury barometer. Catholic Jesuits, alarmed by this breachof faith, theorized that the mercury was being held up by invisible threads. But by then therewas no stopping the weather revolution.A French mathematician, Blaise Pascal, theorized that if airhad weight, it should exert less and less pressure the higher youwent. In 1648 he convinced his brother-in-law, armed with oneof Torricelli’s barometers, to climb almost 5,000 feet up amountain. Sure enough, the higher he went, the lower themercury sank.The first recorded weather observations in the New Worldwere made by a minister named John Campanius Holm in 1644and 1645. Some people consider Holm, who lived in the colonyof New Sweden near Wilmington, Delaware, to be America’sfirst weatherman. In fact the National Weather Service gives anaward in his name to outstanding volunteer weather observerseach year.OPPOSING SCALESHave you ever wondered why the United States uses a methodof measuring temperature that’s different from the one used bythe rest of the world? Blame Daniel Gabriel Fahrenheit, aGerman instrument maker who, in 1714, came up with thetemperature scale that bears his name. He based his system onthe difference between the freezing point of water and his ownbody temperature. Sound arbitrary and confusing? Indeed.Celsius PreferredThe Fahrenheit scale is considered antiquated by scientists, who use the Celsius scaleinstead and wish everyone else would too. Old habits die hard—it’ll probably be some timeyet before everyone’s on the same page temperature-wise.Not content to leave well enough alone, Swedish astronomerAnders Celsius proposed another method. He divided thefreezing and boiling points of water into equal degrees, whichhe called the centesimal system. Celsius decided the boilingpoint of water would be 0°, and the freezing point would be100°. That must not have made any more sense at that timethan it does now, because after his death, the scale was turnedupside down, creating the measuring system still used today.In 1793, Englishman John Dalton wrote a book calledMeteorological Observations and Essays in which he advancedthe theory that rain is caused by a drop in temperature, not airpressure. Taking the next step, he realized in 1802 thattemperature actually affects the amount of water vapor the aircan hold, a concept now called relative humidity.WEATHER AND WARSWhen the Military DroveForecastingLooking back through the history of warfare, it’s evident thatweather has played no small part in effecting both victories anddefeats. The winter of 1777–1778 was no exception, and GeneralGeorge Washington’s Continental Army learned that theweather can be more deadly than any mortal enemy.After being defeated by the British Army in two majorconflicts, Washington’s troops marched to Valley Forge,Pennsylvania, 25 miles northwest of Philadelphia, in December1777. The army of about 11,000 men had little to eat andinadequate clothing, and lived in tents while they set to workbuilding huts in which to weather the coming winter.By all accounts, that winter was unusually severe. Conditionsgot so bad that Washington wrote at one point, “For some dayspast there has been little less than a famine in the camp. . . .Naked and starving as they are, we cannot enough admire theincomparable patience and fidelity of the soldiery, that theyhave not been, ere this, excited by their suffering to a generalmutiny and desertion.”FORGING A VICTORYAlthough a few soldiers did desert, the ones who stayed werefiercely loyal to Washington. By the spring of 1778, nearly afourth of the soldiers had died of smallpox, typhoid fever,malnutrition, and exposure to the severe cold, but theremaining troops were hardened by the experience. In May1778 word came of the new alliance between France and theUnited States, and the worst was over. Valley Forge marked theturning point in the war, and soon Washington and his menwere chasing the British from Philadelphia.Across the Frozen PotomacThe winter of 1780 was one of the worst on record. On the coast of Delaware’s DelmarvaPeninsula, ice formations towered 20 feet high, and the Potomac River froze over so solidlythat it was possible to walk across it.The French helped save the day at Valley Forge, but ended upwith problems of their own years later during Napoleon’sinvasion of Russia and one of the largest weather-assisted routsin history.WEATHER: RUSSIA’S SECRET WEAPONIn 1812, Napoleon controlled nearly all of Europe and had sethis sights on Russia as his next conquest. In June of that year hecrossed the Russian border with 600,000 troops and more than50,000 horses, planning to march all the way to Moscow, livingoff the land along the way. The Russians had other ideas: asthey retreated before the advancing French horde, they burnedfields and destroyed houses, leaving little for the French to eat.Dry, hot conditions prevailed all the way to Moscow, and uponarriving there on September 14, the exhausted French troopsfound the city all but abandoned, its supplies depleted andmuch of its shelter destroyed. More than 20,000 troops had diedof disease and exhaustion on the way, but the worst still layahead: winter was coming.In the middle of October, with no offer of surrender from thetsar, Napoleon finally ordered a retreat. He had waited too long.As the weary troops turned toward home, an early andunusually cold air mass descended over them, and the weakestsoldiers began to die.Germans versus RussiansThe weather has been Russia’s ally in repelling foreign invaders throughout recordedhistory. In 1242 the pope sent German Teutonic Knights to take control of Russia andconvert its people to Roman Catholicism. But Russian troops were more accustomed to thesevere winter conditions and defeated the Germans on the frozen channel between thePeipus and Pskov Lakes in what became known as the “massacre on the ice.”Suddenly the weather turned warmer again, and roads thathad been frozen solid turned into muddy quagmires. Streamsand rivers that had been solid ice were now raging torrents,slowing the retreating troops even more. Then as quickly as thewarm weather had arrived, it was replaced by an even colderair mass, and thousands more died in the driving snow andsubzero temperatures.In early December, Napoleon’s troops finally crossed backover the border into Poland, but of the 600,000 fighting menwho had invaded Russia just six months earlier, fewer than100,000 remained. Half a million people had died in the Russianwinter’s icy embrace.WORLD WAR IIWeather’s Important RoleFrom the very first battle marking America’s involvement inWorld War II, weather played a major role. On November 26,1941, a fleet of four aircraft carriers and several other shipsunder the command of Admiral Isoroku Yamamoto steamedaway from Japan toward Oahu, Hawaii, twelve days and 4,000miles away.Most of the trip was very difficult, with high seas and cold,stormy winter weather, but the rough conditions helped thehuge fleet avoid detection. When the ships finally anchored 220miles north of Oahu on December 7, 1941, and prepared tolaunch a surprise attack on the US naval base at Pearl Harbor,America’s entry into the war was certain.THE ALLIES STRIKE BACKFor the next four months, most of the news coming from thePacific theater was negative, with defeats at Bataan andCorregidor disheartening the American public and militaryalike. On April 18, 1942, commander Jimmy Doolittle and hissquadron of sixteen B-25 bombers (still 200 miles from theirintended launch point) took off from the deck of the brand newaircraft carrier USS Hornet and turned toward Tokyo, morethan 700 miles away.Forced to take off early after the fleet was sighted by aJapanese patrol boat, the B-25s lumbered off the deck of the USSHornet in a light rain. The B-25s had been stripped of anyunnecessary equipment in order to carry more fuel, but on theway to Japan, they encountered a 20-mile-per-hour headwindthat accelerated their fuel consumption. Arriving over Tokyo,the Raiders loosed volleys of 500-pound bombs on war-industrytargets and then turned north along the coast toward China,where they hoped to find refuge.It soon became obvious that the bombers wouldn’t haveenough fuel to make it to the Chinese airfields due to theheadwinds they had encountered earlier. The situation got evenworse when they encountered fog over the East China Sea,followed by a hard rain. With visibility near zero, navigatorswere forced to rely on dead reckoning to chart their course.Suddenly, the winds shifted and the bomber crews foundthemselves being propelled by a strong tailwind. Still unable tosee through the storm and low on fuel, most of the planes wereforced to ditch in the ocean. In the end all sixteen B-25s werelost, seven men were injured, and three were killed. Eight crewmembers were taken prisoner by the Japanese, and only four ofthem survived the war. But the raid not only gave Americanmorale a huge boost after several crushing defeats, it also dealta shattering blow to Japanese pride.THE PLOESTI RAIDIn the summer of 1943, Operation Tidal Wave was launchedfrom a Libyan airfield against Nazi-held oil refineries in Ploesti,Romania. Once again the weather would have a markedinfluence on the outcome. To reach the target and return, themission’s 179 B-24 bombers would have to fly more than 2,400miles in eighteen hours. The flight over the Mediterranean wasuneventful, with beautiful weather and unlimited visibility.Then, on reaching land, the bombers encountered a bank ofhuge cumulus clouds over the 9,000-foot peaks of the PindusMountains. Flying blindly through the clouds at 12,000 feet, theplanes became separated into two groups, neither one aware ofthe position of the other.Because one bomber group arrived over the target well inadvance of the second, the late arrivals suffered heavycasualties since the Germans had been alerted to theirpresence. Although most of the planes were able to drop theirbombs, many important targets were missed in the confusion.Of the 179 planes in the mission, only ninety-nine returned tobase, and fifty-eight of the surviving planes suffered severecombat damage.THE BEGINNING OF THE ENDThe end of the Third Reich began with the Allies’ OperationOverlord, a culmination of yearsof planning that aimed for theinvasion of Europe and the end of the Führer’s stranglehold onthe embattled continent. Under the command of GeneralDwight D. Eisenhower, five beaches along the coast of Francenear Normandy were chosen as landing sites, and thousands oftroops that had been in training for the mission for up to twoyears were moved into position.D-Day WeatherIf Operation Overlord hadn’t taken advantage of the temporary break in the weather onJune 6, the invasion might never have happened. Just a few days later, one of the worstJune storms in English Channel history pounded the beaches, lasting for a full five days.Artificial harbors that had been created by the invaders at critical landing zones werecompletely destroyed by gigantic waves.But before the giant operation could begin, severalconditions had to be met in order to boost its chances forsuccess. Low tide should coincide with the breaking dawn,giving the Allies the maximum amount of beach to work with.There should be a rising full Moon to support airborneoperations, and a minimum visibility of 3 miles so navalgunners could see their targets. Winds should not exceed 8 to 12miles per hour onshore, or 13 to 18 miles per hour offshore. Nomore than 60 percent of the sky should be covered by clouds,and they could not be lower than 3,000 feet.Given these stringent requirements, forecasters estimatedthat there might be only three days in the entire month of Junethat would be suitable. Finally, June 5 was chosen as D-day, butafter the troop ships and landing craft were loaded with menand supplies on the fourth, a storm system moved in overEngland. With high winds whipping across the English Channeland clouds hovering only 500 feet above its churning waves,Eisenhower was forced to delay the invasion.On the night of June 4, Eisenhower’s chief meteorologicaladviser, James Stagg, informed him that there might be atemporary break in the weather on the sixth, and the generaluttered the fateful words “Okay, we’ll go,” throwing theformidable Allied invasion machine into gear. Six thousandlanding craft and other ships left British ports on their waytoward France, along with the 822 gliders and other aircraftthat would transport Allied soldiers behind enemy lines. Thefirst wave would be followed by 13,000 bombers, sent in tosoften Axis positions in advance of the invading forces. Thistime the weather cooperated, and although Allied losses wereheavy, especially at well-defended Omaha Beach, the invaderssoon controlled the coast of Normandy and began the long pushtoward Berlin.THE FINAL COUNTDOWNJust as weather had influenced the first major attack of WorldWar II against US forces, Pearl Harbor, the atmosphereintervened again in the last one: the mission to drop the atomicbomb that ended the war with Japan. The job of ending the warwas brought about not by the Enola Gay, the B-29 Superfortressthat leveled Hiroshima, but by another B-29, the Bockscar,which bombed Nagasaki. Although the Enola Gay’s mission wasaided by clear skies over its target, the Bockscar faced tougherconditions.In fact the residents of Kokura, on the northeast corner of theJapanese island of Kyushu, had the weather to thank forsparing their lives on August 9, 1944, when the Bockscar took tothe air. President Truman had offered to spare Japan furtheragony after Hiroshima’s destruction three days earlier, butpromised that “if they do not now accept our terms, they mayexpect a rain of ruin from the air the like of which has neverbeen seen on this earth.”With no response from the emperor, Kokura was selected asthe next primary target because of its automatic weaponsfactories. Two weather observation planes were dispatched tothe city an hour before the scheduled bombing, since thebombardier would need a clear sightline to the target. Reportsindicated there would be only a 30 percent cloud cover overKokura, but when Bockscar arrived, the crew found the entirecity socked in under a thick layer of clouds. Had the weatherbeen more accommodating, the bomb would have no doubtkilled a young Kokura college student named Tetsuya Fujita,who would later become famous for developing a tornadodamage scale that still bears his name.Frustrated, the crew turned toward their secondary target,Nagasaki, a major shipbuilding center. When they arrived, theyfound that it, too, was mostly buried under clouds. Againstorders, the crew decided to bomb by radar rather than returnto its base in Okinawa and attempt to land with a fully armedatomic bomb on board. In the last twenty seconds of thebombing run, the bombardier sighted the target through abreak in the clouds and released the bomb. Fifty seconds later,at 11:02 a.m., the crew experienced a white-hot flash followedby a violent shock wave.Five days after the attack, the Japanese announced theiracceptance of the Allies’ terms of unconditional surrender.The weather has been at the center of many major turningpoints throughout recorded history, and has been the singleconstant in all of mankind’s conflicts. In the near future it’squite possible that advances in weather-control technology willallow people to use weather as a weapon.HAARPManipulating the WeatherIn 1990 the United States Navy and Air Force, together with theUniversity of Alaska and the Defense Advanced ResearchProjects Agency (DARPA), began a project to research theionosphere. It is called the High Frequency Active AuroralResearch Program (HAARP) and has become the target ofconspiracy theories as well as genuine concern.HAARP’s research is intended to improve communicationsand navigation, but it’s possible that their findings could haveother uses. Some scientists cite the concept of “nonlinearprocesses,” in which a relatively small input of energy can bemagnified into a much larger transmission of power. Asprofessor Gordon J.F. MacDonald put it when he was a memberof the President’s Council on Environmental Quality, “The key togeophysical warfare is the identification of environmentalinstabilities to which the addition of a small amount of energywould release vastly greater amounts of energy.” This leadsmany analysts to believe that HAARP’s ultimate purpose will beas a long-range particle beam weapon of mass destruction.Weather Service in the MilitaryIn its study entitled “Spacecast 2020,” the Air Force predicts that the National WeatherService will be absorbed by the Department of Defense. According to the report, weatherservice personnel would become paramilitary operatives, “supporting the military mission asa civilian during peacetime, becoming active duty military personnel during war, contingency(and) national emergency.”HAARP is only one part of a long-term, large-scale militaryprogram that aims to control and manipulate the weather fortactical and strategic advantages. In a report entitled “Weatheras a Force Multiplier: owning the Weather in 2025,” the benefitsof weather modification are detailed by the government. Bymanipulating fog and precipitation over an enemy’s location,the report says, visibility could be degraded in the target areawhile enhanced over friendly forces. The growth of developingstorms over enemy strongholds could be accelerated, andtriggering more lightning strikes on enemy targets wouldprovide a natural kind of firepower.One of the first steps in any military campaign is to obtain airsuperiority over a battlefield, but the report goes one stepfurther, asserting that space superiority will be essential infuture wars. That includes the HAARP concept of manipulatingthe ionosphere to produce lensing effects, which would not onlyenhance communications between friendly forces but could beused to disrupt the enemy’s capabilities.But these artificial electromagnetic fields can have a moreinsidious effect. They might be used by terrorists or bydictatorial governments seeking to control the population. Aswell,they have uses in dealing with security. Electromagneticsystems can produce mild to severe disruption, includingrendering its subjects disoriented. Given this, it’sunderstandable that the military would be interested.In other words, the same kind of focused electromagneticenergy created by HAARP is capable of disrupting mentalprocesses. It may sound like the stuff of science fiction, but allindications are that HAARP is currently fully operational.Until recently, mankind’s attempts to manipulate the weatherhave shown very little success, but new technological tools maybe changing that. As with any experiment involving multipleunknown variables, the results will be unpredictable. Let’s hopethey’re not detrimental to the earth and its inhabitants as well.THE DOPPLER RADARA Revolution in Weather ForecastingIn the mid-1930s, with the situation in Europe deterioratingrapidly, the director of Britain’s Air Ministry asked RobertWatson-Watt, superintendent of a radio department atEngland’s National Physical Laboratory, if there was some wayto develop a “death ray” that could shoot down aircraft from adistance. The request resulted not in a death beam but inWatson-Watt’s report “Detection and Location of Aircraft byRadio Methods,” which detailed how certain radio waves mightbe reflected off aircraft and back to the origin point, revealingthe planes’ positions.Watson-Watt’s invention came to be called Radio Detectionand Ranging, or radar, and by the beginning of World War II,the coast of England bristled with radar installations. On thoseearly radar screens, radar echoes from large storms wouldoften obscure the images of approaching planes, and largeareas of rain would show up as a green fog. By the end of thewar, both the Axis and the Allies would depend on radar just asmilitary forces do today.There must have been an “aha!” moment whenmeteorologists first saw those radar echoes. After all theguesswork and ground observations used in the past to trackweather systems, here was a system that could actually see theweather systems in motion. Radar was a forecaster’s dreamcome true. After the war, surplus radar systems were pressedinto service by the US Weather Bureau to track weathersystems. Further research led to more powerful radars, whichthe bureau began to install along the coastline in 1954 as part ofa hurricane early warning system.The surplus radar units served their purpose, but as theyears went by and the systems aged, spare parts became scarceand breakdowns were more frequent. Additionally, the oldradar units were unable to detect developing tornadoes oraccurately measure rainfall amounts. It became obvious thatsomething new was needed.DAZZLING DOPPLERIn the 1960s, the US Weather Service began experimenting withDoppler radar, which was a big improvement over the oldertypes. During the late 1970s and early 1980s, Doppler radarbegan to appear at a few television stations, and around thattime NOAA and the Department of Commerce joined forces toproduce a next-generation radar system—NEXRAD—that wouldgreatly improve severe weather forecasting. NEXRAD used theDoppler effect to spot rotating weather systems that oftenindicate a tornado is forming.What Is the Doppler Effect?Named after the nineteenth-century Austrian mathematicianand physicist Christian Andreas Doppler, the Doppler effectdescribes the change in wavelengths (of sound or light)between two objects as a result of motion. For example, thechange in sound as a motorcycle approaches, then passes, astationary observer demonstrates the Doppler effect.Light waves were much too fast to experiment with in thenineteenth century, so in 1845 Christoph Hendrik Diederik BuysBallot, a recent graduate of the Netherlands’ Utrecht University,set out to debunk Doppler’s theory with a real-world test usingsound waves. Ballot put a group of trumpeters on a train thatwould pass by a group of listeners. As the train passed with thetrumpeters blasting away, the listeners heard the din rising infrequency as the train approached and then dropping as itmoved away. On the train, however, the trumpets’ pitch stayedthe same.Instead of refuting Doppler’s theory, Ballot’s experimentproved that the frequency of light or sound depends on thespeed of an object’s movement in relation to the viewer. Theword “frequency” refers to how fast the peaks and valleys of asound or light wave are moving past an observer. Let’s sayyou’re standing at a station watching an approaching train.When the engineer sounds the horn, the pitch will seem to risebecause the speed of the moving train as it comes toward you isadded to the speed of those sound waves, meaning the soundwaves are pressed closer and closer together as they arrive atyour ear. Once the train passes, the distance between the wavepeaks is farther apart because the speed of the train issubtracted from the speed of the sound waves, and so the hornseems to shift to a lower pitch.Using the Doppler Effect to Study StormsIn Doppler radar, pulses of microwave radiation are usedinstead of sound waves, but the effect is the same. When aDoppler beam is aimed at a storm, the echoes that return arecoded by color: areas of precipitation moving toward the radarare shown in one color, while areas moving away from theradar are displayed in another. The National Weather Service’sWeather Surveillance Radar 1988 Doppler (WSR-88D) usesgreen to indicate rain that’s approaching the radar, and paintsreceding showers in red. When the radar sees green and red inclose proximity, it’s a sign of rotation within the storm that canindicate a developing tornado.Doppler radar can identify gust fronts and microbursts aswell, something conventional weather radar can’t do. Peeringdeep within storms, the Doppler beam can identifymesocyclones (rotating air masses inside a thunderstorm)swirling inside. This allows forecasters to discover a region thatmay spawn a tornado and give them much more time to alertthose in its path. Because about 30 percent of mesocyclonesgenerate tornadoes and 95 percent produce severe weather,Doppler radar has become a welcome addition to a forecaster’sarsenal.WEATHER AND CLIMATEWhat’s the Difference?The study of long-range weather patterns is called climatology.Weather is what’s happening locally in the atmosphere rightnow. Climate is the average, or accumulated, weather for aregion over a period of time, including extreme conditions andtheir frequencies. The longer data is gathered for an area, themore accurately its climate can be measured and its futureclimate predicted.Generally, it takes thirty years or more to develop a trulydetailed climatological profile for a region. So, if you wanted tofind out whether it was going to rain during your trip to WaltDisney World the next day, a climatologist probably couldn’thelp you. However, he might be able to tell you if the currentlylandlocked Mouse House might become a beachfront resort inthe future.What Is the Greenhouse Effect?A greenhouse protects plants by trapping solar energy during cold weather. Because only asmall fraction of the Sun’s heat ever reaches Earth, the atmosphere acts in much the sameway to sustain life. If not for the atmosphere’s heat-absorbing effects, the planet’s averagetemperature would hover around –30°F.In examining these global patterns, meteorologists have beenable to categorize Earth’s climates and group them into zonesthat share similar features. For instance, the Sahara desert inAfrica is nowhere near California’s Mojave Desert, yet bothshare many characteristics. You may tend to think of climates asencompassing huge areas of the earth’s surface, but climatescan be as small as a few hundred square feet. Such tiny areas ofaveraged weather are called microclimates, while weatherconditions in areas from a few acres to several square miles fallinto the category of a mesoclimate. The nextstep up is theclimate of a whole state or country—a macroclimate; theaverage climate over the entire globe is called the globalclimate.Studies have shown that the global climate is indeedchanging, and some feel it’s the fault of industries andautomobiles that continue to pump huge quantities of particlesinto the atmosphere. It was once thought that the atmospherewas so vast that nothing could affect it, but it’s now understoodthat it is actually very fragile. Views from orbit show theatmosphere as an impossibly thin, hazy blue line against thebackground of space. In fact if you could shrink the earth downto the size of a beach ball, the atmosphere would be about asthin as a human hair.WHAT’S THE ATMOSPHERE?The Air Up ThereEarth’s atmosphere is composed mostly of oxygen and nitrogen,with some carbon dioxide and other trace gases like argon andhydrogen thrown in for variety. Meteorologists divide theatmosphere into several layers, each of which blendsseamlessly into the next. Nitrogen makes up around 78 percentof the air we breathe at the surface, with oxygen taking upabout 21 percent. Unless you’re an astronaut, you spend most ofyour time in the bottom layer of the atmosphere, called thetroposphere, which extends anywhere from 5 to 10 miles updepending on how much of the Sun’s energy is reaching theearth at the time.THE TROPOSPHEREIn the troposphere, the temperature falls an average of 4°F forevery 1,000 feet you climb, a phenomenon called the lapse rate.Eventually the temperature stops falling, meaning you’vereached the tropopause and the beginning of the next layer, thestratosphere. Really, you wouldn’t want the temperature to fallmuch lower anyway: at the tropopause, it can dip as low as –70°F. You’d think the temperature would just keep on falling asyou leave the troposphere and gain more altitude, but that’s notthe case.THE STRATOSPHEREInstead, as you climb up into the stratosphere, the temperaturebegins to rise again, up to a high of around 40°F. One reason forthat is because the stratosphere contains the ozone layer, whichacts as a protective blanket to prevent harmful amounts ofultraviolet (UV) solar radiation from reaching the earth’ssurface (and the people on it) and helps to warm thestratosphere. Even where the amount of ozone is greatest—around 16 miles up—you’ll find only about twelve ozonemolecules for every million molecules of air, but that’s stillenough to block out the worst of the UV rays. That’s a goodthing, because UV radiation is known to cause skin cancer, andcan even induce genetic mutations in DNA.Climbing even higher, you finally reach the edge of thestratosphere, or stratopause, at around 30 miles above theearth’s surface. Now you’re really getting into nosebleedterritory: at this height, the air is much too thin to breathe, andatmospheric pressure is only about one millibar (the metricequivalent to mercury). By contrast, air pressure at sea level isabout 1,013 millibars. You’re now above most of theatmosphere.THE MESOSPHEREThe mesosphere is the next layer, extending from 30–50 mileshigh. With very little ozone to provide warmth, the temperaturebegins to fall again, to a low of about –130°F. It continues todecrease until you reach the mesopause, then begins to riseagain as you enter the thermosphere, which extends from 50 tomore than 120 miles above the earth.THE HOT ZONEPerhaps “rise” isn’t the right word—temperatures in thethermosphere can reach a blistering 2,700°F. The thermospheregets that hot because it’s the first layer of air the Sun’s rays hitas they zoom toward Earth. A space shuttle must pass throughthe thermosphere on its way to and from orbit, so the obviousquestion is: why doesn’t it burn up? Fortunately, at that heightthere are so few air molecules that the net amount of heatenergy hitting the shuttle isn’t enough to destroy it.Why Don’t All Meteorites Burn Up in the Atmosphere?Some are just too big or dense for the thermosphere to handle. Thousands of rocks fromthe size of pebbles down to grains of sand burn up each day, but space rocks larger thanabout 33 feet in diameter can usually make it to the ground (most often in pieces).The lack of air molecules would actually make it feeldownright cold if you could somehow sit out in thethermosphere for a few moments. It sounds crazy, but there justwouldn’t be enough air molecules to heat up your skin. It’s agood thing for us that the number of molecules in thethermosphere is still great enough to intercept and destroymost incoming meteorites, however.The thermosphere also contains most of the ionosphere, so-called because energy from the Sun smacks into molecules atthat height and separates them into ions, which carry a positivecharge, and free electrons, which are negatively charged. Manyyears ago, it was discovered that this layer reflects radio waves,especially at night, allowing the transmission of signals beyondthe curvature of the earth for hundreds of miles or more. Thisprinciple allows ham radio operators to receive broadcastsfrom faraway countries, although the effect is not alwayspredictable.A Planet Gone WrongAs an example of uncontrolled warming, scientists point to Venus, a planet nearly the samesize as Earth but with a much more hostile atmosphere. On Venus the “air” is about 96percent carbon dioxide with a temperature hot enough to melt lead. Scientists say the sameconditions may occur on Earth if pollution isn’t controlled.What lies above the thermosphere? If you think the answer isair, think again. The layer above 120 miles of altitude—theexosphere—contains so few molecules that many of them areactually able to escape Earth’s gravity and fly off into space. Theexosphere is the domain of satellites and space shuttles, atransitional zone between Earth’s atmosphere andinterplanetary space. The exosphere has no real upperboundary; it just becomes more and more diffuse until it’s nolonger detectable.THE WATER CYCLEIt’s RainingMost of the moisture in the atmosphere—about 90 percent—comes from the oceans. Water is constantly recycled from theocean into the air and back through a process called the watercycle. At any one time, the oceans contain about 97 percent ofthe earth’s water; the atmosphere contains only about 0.001percent. Landmasses and ice hold the remainder. Still, if thatseemingly tiny amount of atmospheric water vapor suddenlyturned into rain, it would cover the entire Earth with an inch ofwater.About 121,000 cubic miles of water evaporate from theearth’s surface each year, with around 86 percent of thatcoming from the oceans. The evaporation occurs due to theSun’s heating of the sea surface. Warm air can hold a lot ofmoisture (think of steam), so some of the ocean surfaceconverts to water vapor and is drawn up into the air.Water As CoolantWater can absorb a lot of heat before it begins to heat up itself. That’s why water makessuch a good coolant for automobile radiators and why oceans prevent abrupt seasonalchanges. Instead, winter comes on gradually as oceans slowly release their stored heat intothe atmosphere, and summer takes a while to set in as the sea begins to reabsorb heat.Evaporation occurs anywhere there is water, from lakes andrivers to storm drains and birdbaths. Plants even give off waterthrough a process called transpiration, as they ooze smalldroplets of moisture from the undersides of their leaves. All ofthis warm water vapor begins to rise, joining billions of otherwater molecules in a dizzying ascent into the troposphere.WHAT GOES UP MUST COME DOWNEventually the vapor reaches cooler layers and condensesaround small particles of dust, pollen, or pollution. As thecondensation process continues, the droplets become too big forthe wind to support and they begin a plunge toward thesurface. Not all the precipitation reaches the ground, however;some of it evaporates directly back into the atmosphereon itsway down. What’s left finally reaches the ground in the form ofrain, snow, hail, or sleet, sometimes ruining picnics or closingschools in the process.If the precipitation falls in the ocean, the cycle is ready tobegin again right away, and that’s exactly what happens to themajority of raindrops and snowflakes. After all, oceans covermore than 70 percent of the earth’s surface, making them a bigtarget. When it rains or snows over land, however, the cycletakes a little more time to complete.Most water reaching the land surface runs off into ditchesand streams where it finds its way back into lakes or the ocean.But some water seeps into the ground, percolating down until itis either trapped or it encounters a horizontal flow deep underthe surface. The seeping water goes with the flow until itencounters a large underground reservoir known as an aquifer.Most aquifers eventually drain off into streams, which carry thewater to rivers and canals and back to the sea. Then, of course,the whole cycle begins anew.THE THREE LEVELS OFCLOUDSWater in the AirThe air in the upper troposphere, the bottom layer of theatmosphere, is very dry and cold, so water vapor at highaltitudes can’t remain in a liquid state for long. Clouds thatform there are made of ice crystals and are usually very wispy.High clouds appear white because they’re not thick enough toblock the Sun. Cirrus is the most common type of cloud found atthese rarified heights of 20,000 to 60,000 feet.You might think a cirrus cloud’s upturned “tail” points in thedirection of the prevailing wind, but the opposite is true. As theice crystals that form the tail begin to fall, they encounter alevel where wind speed or direction suddenly changes, and thecloud gets pulled like taffy (or cotton candy) into a long, thinstreamer.Mare’s TailsSometimes known as mare’s tails, cirrus clouds often resemble thin filaments of white hairbeing stretched out by high-level winds. Cirrus clouds generally move from west to east andoften predict an approaching low-pressure system, which is a good hint to go find anumbrella.Cirrus clouds can spread out until they cover the entire sky,forming a thin layer called cirrostratus. You can see rightthrough cirrostratus clouds, and because they’re composed ofice crystals, you’ll often see a halo where the Sun or Moonpeeks through this wispy veil. Because they often form inadvance of an approaching cold front or storm, cirrostratus canmean rain in the next twelve to twenty-four hours.One of the most beautiful cloud types is cirrocumulus, whichforms a series of small rounded patches or puffs that oftenextend across the sky in long rows. Because of their regular,repetitive pattern, cirrocumulus clouds can resemble the scalesof a fish, which is why a sky full of cirrocumulus is also called amackerel sky.STUCK IN THE MIDDLEForming at an altitude of 6,500–26,000 feet, clouds in thetroposphere’s middle levels can be composed of either water orice, or a combination of the two. Midlevel cloud types are easyto remember because the most common ones always begin withthe prefix alto-. The two main middle cloud types arealtocumulus and altostratus.Altostratus clouds are either gray or blue-gray, are often thickenough to blot out the Sun, and can blanket hundreds of milesof sky. Sometimes altostratus does allow a glimpse of the Sun,but it’s a dim view, like looking through tracing paper.Altostratus clouds are often confused with cirrostratus, butthere’s an easy way to tell them apart: if you look at the groundand don’t see a shadow, it’s probably altostratus. Also,altostratus clouds don’t produce halos. This type of cloud oftenmeans you’re in for an extended, steady rain in the near future.Altocumulus clouds have a distinctive patchy or puffypattern like cirrocumulus. They’re composed mostly of waterrather than ice, though, so they often appear gray instead ofwhite. The individual puffs are also larger than cirrocumulusand sometimes form little cottony “castles” in the sky, meaningit won’t be long before it will probably—guess what—rain!THE REAL LOWDOWNLow-level clouds, stratus clouds, form below 6,500 feet, and atthat height are almost always made of water droplets unless it’swinter. Stratus clouds are arguably the most boring clouds inexistence; they usually cover the whole sky in a uniform graycloak, sometimes completely blotting out the Sun. You won’tgenerally see much rain falling from stratus clouds, althoughthey can produce some light drizzle or mist. They usually formduring stable atmospheric conditions when a large, moist airmass rises slowly to a level where it can condense.On the other hand, nimbostratus is a dark gray cloud thatforms when a front of warm, moist air meets a mass ofrelatively cool air. When you’re under a nimbostratus layer, youoften can’t even see the cloud itself because of the rain and thethick mist formed by evaporation. If the air becomes saturatedenough, another layer of ragged, swift clouds called scud canform below the nimbostratus. When you see this type of cloudcoming, you might as well settle in with a good book or find anold movie marathon on TV, because it’s probably going to rainor snow for quite a while.Stratocumulus clouds are similar to altocumulus, but they’refound at lower altitudes and their individual cells are bigger.They don’t produce much rain and often form when cumulusclouds spread out across the sky and begin to merge.Stratocumulus clouds generally appear in patches, and you canoften see blue sky between them.From Fair to Middling—to MonsterCumulus clouds are often thought of as fair-weather clouds,and they usually are—but they can grow into something farmore ominous. Cumulus clouds look like big balls of white orlight gray cotton drifting across the sky, usually have a flat base,and don’t generate much precipitation in their young, puffyphase. They most often form when the morning Sun heats upthe earth’s surface and fills the sky with hundreds ofpopcornlike clouds floating serenely over your head.As the day progresses and it gets hotter, cumulus clouds canbegin to blossom upward, now resembling a cauliflower morethan a cotton ball. Called cumulus congestus, these toweringpillars of water vapor are the raw material of the mostdangerous cloud of all—the cumulonimbus.As the 300-pound gorilla of the cloud kingdom,cumulonimbus gets a lot of respect. These are the giantthunderstorm clouds that can produce lightning, hailstorms,and tornadoes. On color weather radar, cumulonimbus cellsglow bright red, a warning that their tops have grown high intothe atmosphere and severe weather is on its way. Violentupdrafts within the storm, which can reach speeds of 100 milesper hour or more, keep it growing ever higher into thetroposphere. If the monster cloud has enough energy, it willcontinue upward until reaching the tropopause or even breakthrough to the stratosphere, where it will begin to flatten andform an anvil shape.Cumulonimbus can also become nurseries for other types ofclouds. When a thunderstorm grows all the way up to thetroposphere, it’s in cirrus territory. The tops or anvils ofcumulonimbus can shear off and become cirrus or cirrostratusclouds, and are often swept hundreds of miles downwind tobecome an early warning of approaching storms.How Low Can They Go?Nimbostratus is included in the low-level cloud categorybecause thunderstorms always begin near the earth’s surface.But the winner in the lowest-cloud-ever category has to be fog,which is a cloud that forms right at ground level. Actually, fog isnothing more than a stratus cloud you can walk through.Acid FogFog that forms near sources of pollution (like industrial cities) tends to be thicker thanordinary fog since it contains so many more small particles for the water vapor to bond with.Unfortunately, these particles often include noxious chemicals that create acidfog, aconcoction that can cause serious respiratory distress and other health problems.Fog usually forms at night when a low layer of moist air iscooled by the ground, creating a surface cloud called radiationfog (caused by cool air radiating from the surface). A lightbreeze can actually cause the fog to become thicker, as it bringsmore warm air in contact with the cooler ground. Since warmair rises and cool air falls, you’ll most often find the heaviest fogin the lowest-lying areas, especially near sources of moisturelike lakes and streams. Fog can hang around long after the Suncomes up, because evaporation of the dew that formed thenight before adds even more moisture to the air, replacing thefog that has burned off as the morning Sun warms the ground.Of course, fog doesn’t really burn—if it did, San Franciscowould have been a cinder a long time ago. Rather, the Sun’slight and heat eventually penetrate the upper, middle, andfinally the lower layers of a fog bank, causing more and moreevaporation until the fog is gone.HOW TO BUILD A CLOUDUse Dirt and WaterAlthough there’s usually plenty of water vapor in theatmosphere, it could never condense without the presence oftiny particles—called condensation nuclei—because of the highsurface tension of each vapor droplet. Condensation nuclei areso small that a volume of air the size of your index fingercontains anywhere from 1,000 to 150,000 of them, but theymake the perfect seed for a cloud droplet. Some of these specks,such as salt particles, bond easily with vapor and are calledhygroscopic, or water seeking. Ever notice how difficult it is toget salt out of a shaker when the air is humid? Those saltparticles love their moisture. On the other hand, otheratmospheric bits are hydrophobic, or water repelling, likeparticles from petroleum by-products, and resist binding withwater vapor even when the humidity is more than 100 percent.So now you know a cloud’s dirty little secret. Putcondensation nuclei and water vapor together, and voilà—instant cloud, right? Well, as usual, there’s a bit more to it thanthat. You also have to have air that’s (a) rising; (b) expanding;and (c) cooling.BOILING UP A CLOUDIf you’ve ever watched a pot of spaghetti cooking, you’veprobably noticed that it seems to circulate in the pot even if youdon’t stir it. Through a process called convection, the hot watercarries the spaghetti toward the surface. When it cools slightly,more hot water rises to take its place, circulating the noodlesover and over.With cloud formation, the Sun heats the earth’s surface,causing it to radiate warmth. Any area that heats more rapidlythan its surroundings, such as deserts or large areas of asphaltor concrete, can create a bubble of warm air that rises into thesky, mixing with the cooler, drier air around it. When thishappens, the warm air expands and cools, and if this processcontinues, the air bubble will begin to fall back toward thesurface again, just like spaghetti circulating in the pot. But ifmore warm air arrives from underneath, it will keep growinguntil it reaches the saturation point and condenses, making afluffy little cumulus cloud.When the cloud gets big enough to cast a sizable shadow, itstarts to cut off its own heat engine as the ground below it cools.This throws a monkey wrench into the whole convectionprocess, and the cloud begins to show ragged edges as the windmoves it along, causing it to eventually dissipate. But now theground is free to heat up again, and soon another bubble floatsskyward, ready to make yet another cumulus cloud. That’s whyyou’ll often see one cloud after another form around the samespot on a sunny afternoon.Equilibrium and InstabilityOf course, when the atmosphere is unstable, even moreinteresting things can happen. When meteorologists use theword stable, they’re talking about the atmosphere being inbalance. Air that’s in a state of balance, or equilibrium, holdstrue to Newton’s First Law of Motion: when it’s at rest, it tendsto remain at rest, and so it resists any upward or downwardmovement. In other words, it doesn’t like to be pushed around.So if an air mass encounters surrounding air that’s cooler orwarmer, and quickly adapts to that temperature, the air mass issaid to be stable.On the other hand, the atmosphere becomes unstable whenthere’s a big difference in temperature between the upper andlower layers, or between warm and cold air masses. Generallyspeaking, a rising air mass will become unstable. Because warmair rises, instability usually results from the warming of surfaceair. If air at ground level is warm and moist and upper levelsare cold and dry, a process called convective instability canoccur, causing a rapid, often violent, cloud growth that canproduce severe thunderstorms and tornadoes quicker than youcan say, “Run for the basem*nt!”Growing PainsLet’s take a closer look at a cumulus cloud as it grows up tobecome a towering cumulonimbus. We’ve discussed howcumulus clouds form and dissipate in a stable environment, butwhen the air above is cooler than the layers below, more andmore heat is released inside the cloud as it rises and its vaporcondenses. Rain droplets and ice particles begin to form and arechurned and swirled by the turbulence from the rising air.Strong updrafts form in the cloud’s core, causing it to grow evenfaster. The rain and ice particles surge upward, getting largerand larger as they merge with other specks of moisture,creating a swirling mass of rain and ice within the cloud. Andeven with all this activity, no rain is falling yet, because thecloud is putting all its energy into the growth stage.Constant StormsThere are nearly 1,800 thunderstorms occurring worldwide at any moment, although mostlast an average of only thirty minutes. Out of the 100,000 or so storms that occur each yearin the United States, only about 10 percent are classified as severe, but even small stormscan create heavy rain and dangerous lightning.In the next phase, called the mature stage, the raindrops andice crystals get too large to be supported by the updraft and sothey start to fall. This creates downdrafts within the cloud, anda pitched battle between falling and rising air begins. Withupdrafts still raging at speeds of up to 6,000 feet per minute, thesevere turbulence causes a tremendous amount of friction inthe cloud, and jagged lightning bolts begin to stab outward anddownward as the storm mushrooms up toward thestratosphere. As the rain-cooled downdrafts reach the ground,they spread out horizontally into a gust front. Rain and hailbegin to hammer cars, trees, buildings, and anything elseunlucky enough to be caught in the storm’s path. The monstercloud’s top reaches the jet stream, and strong winds begin topull it into a long anvil shape.As the gust front spreads out underneath the storm, it cuts offthe cloud’s supply of warm air. Eventually, the storm’sdownward-moving air currents gain the upper hand, and thecloud’s growth slows and finally stops. Soon the internalupdrafts cease completely, and downdrafts are all that’s left,carrying the rest of the cloud’s moisture to the ground as rain,often for several more hours.Super-Sized StormsIf thunderstorms are the 300-pound gorilla of weather,supercells are the King Kongs. Although fewer than one ineighty thunderstorms develop into supercells, the ones that doare extremely dangerous and can be unpredictable. Supercellsare the storms that most often produce tornadoes, making themthe targets of storm chasers during springtime on the GreatPlains.Supercells feed off wind shear, which is the effect caused bywinds blowing in different directions and speeds at differentatmospheric levels. Wind shear actually tilts the storm, causingthe cooler air descending inside to be pushed completely out ofthe cloud. Warm moist air is still free to surge in, however, andwithout the cooler air toact as a stabilizer, the storm’sconsumption of warm air becomes a feeding frenzy, creating astrong, rotating updraft within the storm called a mesocyclone—the first stage of a tornado.Because of the strong vertical wind shear inside a developingsupercell (where updrafts can reach speeds of 150 miles anhour!), the updrafts and downdrafts can actually wrap aroundeach other, creating an extremely volatile environment. Theseviolent currents can keep hail suspended for so long that it canreach the size of grapefruit or larger before finally escaping thestorm and plummeting to earth.The National Weather Service gives supercells specialattention, using radar to peer deep into their cores to catchearly signs of developing tornadoes, which cause acharacteristic “hook echo.” When a severe thunderstorm ortornado warning is given for your area, believe it and takecover as soon as possible.HAIL AND SNOWDamaging and DangerousMost people enjoy watching a good snowfall. After all, there’snothing like sitting around a fireplace with a cup of cocoa,watching through the window as the landscape is transformedinto a beautiful white blanket. And many people like theexcitement of a hailstorm—the thud of hailstones as they hit theground. Unfortunately, both forms of precipitation have thepotential to cause a good deal of damage and even death.HAILWhile heavy rain can limit visibility and soak you to the skin, ahailstorm is capable of breaking windshields, decimating crops,and even injuring livestock. If it wasn’t for updrafts, hail wouldnever grow very large, and golf ball–sized and larger specimenswould be unheard of. But as ice particles fall through acumulonimbus cloud, they inevitably encounter strong verticalwinds and get swirled skyward again, picking up extra layers ofsupercooled water droplets as they zoom above the freezinglevel.If the updrafts are strong enough, like those in a supercell,the developing hailstones ride a wild roller coaster of wind asthey spin up and around inside the storm, growing larger by theminute. Finally some become so big that they overcome theupdraft’s power and begin to drop toward the ground. Falling atspeeds of up to 120 miles an hour, they can dent cars anddestroy crops, raising insurance rates wherever they strike.Size May VaryMost hail is relatively small—around 2 inches in diameter or less—but on July 23, 2010, thegreat-granddaddy of all hailstones fell on Vivian, South Dakota. The hailstones measured 8inches in diameter and weighed almost 2 pounds. Never mind an umbrella—with hail thatsize, you’d need a bomb shelter.If you cut a hailstone in half, you can see the multiple layersof ice that mark its journey through the thunderstorm.Generally, the larger the hailstone, the more severe the updraftswere in the storm that it came from.SNOWSnow forms from tiny particles of ice suspended in clouds upabove the freezing level. As the particles form, they arrangethemselves into hexagonal shapes due to the molecularstructure of water, which is why simple snow crystals alwayshave six points. Snowflakes that fall through a layer of slightlywarmer air, however, can bind with other flakes to form verylarge, intricate structures that look like beautiful silver jewelryunder a microscope.Much of the rain that falls in the summer actually begins assnow and ice high in the tops of cumulonimbus clouds. In thewintertime the freezing level is much lower, and if you live in asnow-prone region, you’re aware that snowflakes can easilymake it all the way to the ground, where they gather withbillions of their friends for an impromptu party on your lawn.Snow flurries usually fall from cumulus clouds and provide alight dusting of crystals that don’t cause much trouble for thosebelow. Snow squalls, on the other hand, are brief but veryintense snowstorms that are the equivalent of a summerdownpour. They arrive with little warning, and their intensedriving winds often create near-whiteout conditions in a matterof minutes.WhiteoutsA whiteout occurs when the clouds from which snow is falling take on a bright, uniformlywhite appearance. This happens when the light reflected off the snow is about the same asthe light coming through the clouds, making objects in the storm very difficult to see.Not Your Average SnowstormWind-driven snow officially becomes a blizzard when below-freezing temperatures are accompanied by winds of more than35 miles per hour and visibility down to a quarter mile or less.In a severe blizzard, winds exceed 45 miles per hour andtemperatures plunge to 10°F or lower. Blizzards can pile snowinto gigantic drifts that can make travel impossible. During thegreat blizzard of 1888, known as the Great White Hurricane,some snowdrifts were measured as high as 50 feet.The 1888 blizzard actually led directly to the creation of theNew York subway system, as city leaders vowed to prevent theweather from ever bringing the city to such a standstill again.The entire East Coast, from Maine to the Chesapeake Bay,buried in up to 50 inches of snow, was cut off from the rest ofthe world as telegraph and telephone wires snapped like twigsunder the crushing weight of snow and ice. Washington, NewYork, Philadelphia, and Boston were paralyzed for days. At least100 sailors were lost at sea, 200 ships ran aground, and, withlifesaving water frozen in pipes and hydrants, raging firescaused more than $25 million in property losses. More than 400people perished in what became known as the worstsnowstorm in American history.What Is a Frontal Passage?A frontal passage is the movement of the boundary between two air masses over aparticular location. Frontal passages are usually accompanied by a change in wind speedand direction, humidity, cloud cover, precipitation, and temperature.If you follow winter weather on TV, you’ve probably noticedthat cities like Buffalo and Syracuse, New York, seem to getmore than their share of snow. This is due to the “lake effect,” acondition that occurs when cold air moves over a warmer bodyof water, in this case the Great Lakes. Unlike the Great Plains,where snowstorms usually move through, release their quota ofsnow and leave, states to the south and east of the Great Lakesare often dumped on for days after a frontal passage, as cold airflowing south and east over the lakes picks up moisture andwarmth from the water’s surface and carries it shoreward.Snow WonderAs damaging as snow can be, however, it has a gentler side.Since snow doesn’t conduct heat very well, dry snow canactually act as an insulator, protecting plants below its surfaceby preventing the ground from losing all of its warmth. Just asair spaces within a down jacket help insulate you from the cold,tiny gaps between dry snowflakes act as buffer zones againstthe cold air above. This same effect is what causes snow toabsorb sound, making a walk through the woods after asnowfall a quiet, mesmerizing experience.Warm Great LakesThe Great Lakes, due to their size and depth, are able to retain much of their summerwarmth well into fall and winter. When an air mass warmed by its passage over a lakereaches the shore, it is forced to rise rapidly—a process called orographic lifting—andheavy snow and snow squalls are often the result.Have you ever heard someone say that it’s “too cold tosnow”? Is it really possible for the temperature to drop so lowthat snow can no longer form? Well, no. It’s true that there maybe a lack of snow on cold, still evenings, when high pressuredrives away any snow-producing clouds. But while it’s true thatcold, dry air can’t hold as much moisture as warmer air, there isalways at least some water vapor present, and where there’svapor, there can be precipitation.On the flip side, you may have seen snow fall when thetemperature at ground level is above freezing. For this tohappen, the air aloft must be very dry. As snow begins to fallfrom cloudsabove the freezing level, it encounters warmerlayers of the atmosphere and starts to melt. But because the airis dry, the melting snow evaporates quickly, cooling the air andmaking it possible for more flakes to penetrate downward.Eventually some of these flakes can make it to the surface,although they won’t last very long in a frozen state.THE POLAR VORTEXPrecipitating Bigger SnowstormsIn the winter of 2015, the northeastern United States receivedan unprecedented amount of snow and freezing temperatures.Boston, in many ways at the epicenter of the event, received arecord-breaking 110 inches of snow (the previous record hadbeen 107). Strong storms pummeled various parts of thecountry: in Colorado, at Wolf Creek Pass, which crosses theContinental Divide, 23 inches of snow came down withintwenty-four hours. At the same time, temperatures plummeted:Whiteface Mountain, part of the Adirondack Mountains in NewYork State, measured a record –114°F. New England wasbattered in February by a series of Nor’easters that piledsnowdrift upon snowdrift.A Nor’easterNor’easters can do some real damage when a high-pressure system over New England orthe northern Atlantic blocks the northern progression of a low-pressure system. As the lowstops moving, its counterclockwise winds meet the clockwise gusts of the high-pressuresystem, battering the coastline with severe winds.A Nor’easter storm, which begins as a low-pressure systemover warm Gulf Stream waters, forms off the East Coast of theUnited States and moves northward into New England. Thesestorms usually form between October and April, and as theymove up the coast and encounter frigid arctic air flowing downfrom Canada, instability increases and the chance for heavysnow and gale-force winds is great. Most Nor’easters don’t turninto major storms, but the ones that do, such as those of 2015,live in memory and folklore for generations.As the severe winter continued across the country, nightlytelevision viewers were increasingly treated to comments abouta “polar vortex.”WHAT THE HECK IS A POLAR VORTEX?A polar vortex refers to an area of low pressure that forms nearone of the poles. At the North Pole it rotates counterclockwise;at the South Pole, clockwise. Polar vortices are normally moreactive in the south than in the north, but 2015 presented ameteorological anomaly. The vortex probably causedtemperatures across much of the northern part of the countryto drop anywhere between 15°F and 35°F.In practical terms, this meant that very little of the heavysnowfall that came down across the Northeast and UpperMidwest had a chance to melt. Instead, it piled up, defyingefforts to clear it.An additional feature of polar vortices is that they tend todeplete the ozone layer, since their chemical compositioncreates chlorine, a gas that causes the ozone layer to dissolve.This has created a hole in the ozone layer near the South Pole.The strength of vortices can be increased by volcaniceruptions or by El Niño (for details, see the section dedicated toEl Niño). The latter is probably responsible for the intensifiednorthern polar vortex in the winter of 2014–2015, whichbrought so much misery to those living in the northern parts ofthe United States.SLEET OR FREEZING RAIN?There Is a DifferenceIf descending, partially melted snowflakes or raindrops fallthrough a colder layer near the ground, they can refreeze intosleet, which is tiny clear or translucent ice pellets that soundlike falling rice when they hit your window.When the layer of colder surface air is shallow, raindropsfalling through it won’t have time to freeze and will hit thesurface as freezing rain, which spreads out into a thin film ofice as soon as it hits any cold surface. While sleet is relativelyharmless, ice storms caused by freezing rain can be killers, asroads become slick with ice, causing auto accidents andbringing even foot traffic to a standstill. Freezing rain cancreate winter wonderlands by coating trees with a twinkling,crystalline glaze, but it can also bring down telephone andpower lines, cutting off communications and creating severeelectrocution hazards.Aren’t Sleet and Hail the Same Thing?Sleet can form only when the weather is very cold, while hail is a warm-weatherphenomenon based on heat convection. Hail forms while bouncing around in athunderstorm, while sleet is created when a snowflake or raindrop refreezes during a winterstorm.Aircraft are especially vulnerable to ice, which in a freezingrain can build up very quickly and is very difficult to remove. Acoating of ice on a plane’s wings increases its weight, whichmakes it more difficult to gain altitude at takeoff. Moreover, theice disturbs the airflow over the wings and fuselage, whichmakes it more difficult for the plane to stay airborne. Airportsin ice-prone areas maintain de-icing crews, who spray aircraftwith an antifreeze mixture designed to melt ice before it canaccumulate to dangerous levels.The National Center for Atmospheric Research (NCAR) hasfound that the most dangerous icing forms when planes flythrough supercooled drizzle in clouds. Although the drops aresmall, they freeze quickly and form a rough ice layer calledrime that decreases lift and increases drag much more than alayer of smooth ice would. The National Weather Service’sAviation Weather Center in Kansas City, Missouri, is usingsupercomputers to develop forecast maps that will enable pilotsto steer clear of icy drizzle while aloft.Down at ground level, however, even a good forecast isn’talways enough to protect people and property from the dangersof an ice storm. In January of 1998 a severe ice storm hit thenortheastern United States and Canada, causing forty-fourdeaths. In some places more than 3 inches of freezing rain fell,coating trees, buildings, and cars with ice that was more thanan inch thick. In the aftermath 500,000 people were withoutpower in the United States, including more than 80 percent ofthe population of Maine. Things were even worse in Canada,where more than three million people lost electricity. Damageestimates for both countries totaled $4.5 billion.HIGH PRESSURE AND LOWPRESSUREIt’s Windy OutsideTo understand why air moves, it helps to understand airpressure, which is the amount of force that moving air exertson an object. There are several ways of measuring atmosphericpressure, the most common being inches of mercury, which weuse in the United States, and millibars, the metric equivalent.If you could somehow isolate a 1-inch-square column of theatmosphere, from the surface all the way to the top of thetroposphere, it would weigh just about 14.7 pounds. Someteorologists say that air pressure at sea level is 14.7 poundsper square inch, or psi. That translates to 29.92 inches ofmercury (abbreviated as Hg, the symbol for mercury on theperiodic table of elements) or 1013.25 millibars. In case you’rewondering, one millibar is equal to 0.02953 inches of mercury.With nearly 15 pounds of pressure pushing against everysquare inch of your body, you’d think it would be hard to eventake a breath. Fortunately, nature does its best to stay inbalance, and there is just as much pressure pushing outward ineach cell of your body as there is outside pushing inward. Thisshows you just how well we’ve adapted to living on the surfaceof this planet. But what if you’re not on the surface, but uphigher where air pressure is less, as you find when climbing amountain or flying in a plane? As you climb higher, thepressure in your body becomes greater than the pressureoutside, and you’ll probably start to notice an uncomfortablepressure in your inner ear as those 14.7 pounds of pressure tryto get out.WEIGHING THE AIRAtmospheric pressure is measured using a device called abarometer, which is either liquid filled (which is where theinches-of-mercury method comes from) or metal based.Although you’ll hear your