MILITARY GEOGRAPHY
    FOR PROFESSIONALS AND THE PUBLIC

5. EARTH'S ATMOSPHERE

Motto of the U.S. Postal Service,
adapted from Herodotus

EARTH'S ATMOSPHERE, LIKE LAND AND SEA, IS A DISTINCTIVE GEOGRAPHIC MEDIUM. ARMED FORCES THAT operate therein must perform a much wider range of missions in foul weather than civil servants who deliver letters and packages. General George S. Patton, Jr., resorted to prayer during the Battle of the Bulge in December 1944, when God seemed to be giving all the breaks to his opponents. "Sir," he beseeched, "this is Patton talking. The last fourteen days have been straight hell. Rain, snow, more rain, more snow-- and I'm beginning to wonder what's going on in your headquarters. Whose side are You on, anyway? . . . I am not going to ask for the impossible . . . all I request is four days of clear weather . . . so that my fighter-bombers can bomb and strafe, so that my reconnaissance may pick out targets for my magnificent artillery. Give me four days to dry out this blasted mud."¹ Whether God granted his request is debatable, but good weather broke the following day, Allied air power tipped the balance favorably, the German drive stalled, and Allied ground forces resumed the offensive.²

Commanders, however, cannot consistently count on prayers to manipulate atmospheric phenomena. Long-range planners find climatological surveys more reliable, while military operators, who take shorter views, lean heavily on meteorological observations that must be timely, accurate, and tailored to specific circumstances. Results, for good or ill, influence military strategies, tactics, force development, task organizations, readiness, morale, and performance.

ATMOSPHERIC PHENOMENA

Half of Earth's atmosphere lies between sea level and 15,000 feet (4,500 meters). The next 20,000 feet or so (6,000 meters) contains half of the remainder. Most militarily significant atmospheric phenomena develop within that envelope or along its periphery: barometric pressures, winds, air currents, temperatures, humidity, fog, clouds, precipitation, and storms.³

BAROMETRIC PRESSURE

International authorities define "normal" atmospheric pressure as 14.7 pounds per square inch at mean sea level 45 degrees north and south of the Equator (29.2 inches or 1013.2 millibars on standard barometers). Irregular heating of Earth's surface, however, causes significant deviations. Relatively high pressures permanently surround both poles, where the air always is cold and dense; relatively low pressures predominate in the tropics, where the air always is warm and light; and alternating pockets of high and low pressure that give forecasters fits travel from west to east in middle latitudes, where variable temperatures prevail. Exceptions to the rule are plentiful, but clear skies usually accompany high pressure domes, whereas depressions presage poor weather. Atmospheric pressures everywhere decrease with altitude, since the air becomes progressively thinner. Barometric pressures are one-thirtieth less at 900 feet (275 meters) than at sea level, one-thirtieth less at 1,800 feet than at 900 feet, and so on.

WINDS AND AIR CURRENTS

Surface winds blow from high toward low pressure like water flows down hill, fastest where gradients are steep because great pressure changes occur over short distances, slowest where slopes are gradual because slight changes transpire over long distances. Winds as a rule are steadier and stronger over open water than over level land, where surface friction not only limits velocities but produces distinctive effects (see table 4 on page 54 and table 5 on page 71 for comparative consequences at sea and ashore). Gusts that fluctuate 10 knots or more between minimum and maximum velocities create horizontal turbulence that changes direction erratically and becomes "bumpier" up to about 1,500 feet (450 meters), after which the influence of surface friction is noticeably less pronounced.

Surface winds are individualistic. Light air, for example, flows up slopes on warm days, whereas cool air drains downhill after dark. Sea breezes blow toward locally low pressure systems that develop during daylight hours, then face about when night falls because land heats and cools faster than water (figure 14). Monsoonal winds that visit southern Asia reverse their fields seasonally rather than daily for similar reasons. Local winds that bear such exotic names as Bora, Buran, Chinook, El Nino, Föhn, Khamsin, Mistral, Santa Ana, Shamal, and Sirocco blow hot and cold, wet and dry, in various locales and various combinations. Hurricanes, typhoons, and winds that funnel through mountain passes or roar off Greenland's ice cap commonly atttain terrifying speeds.

Winds aloft are notably different. Turbulence due to surface friction disappears, but see-saw effects from powerful up-down drafts perpendicular to the main airflow often make aircraft unmanageable. Intense shearing also can occur along boundaries between strong currents that sometimes race in opposite directions above and below one another. Two serpentine jet streams, one in the Northern Hemisphere and a twin in the south, alternately loop toward the Equator and the poles at altitudes that vary from 30,000 to 40,000 feet (9,000 to 12,000 meters). Military air crews headed from west to east in middle latitudes take advantage of tail winds therein that reach 160 knots during winter months (90-100 knots when weather is warm) and avoid bucking head winds on return trips.

Table 5. Beaufort Scale Related to Surface Winds Ashore

TEMPERATURE

Air temperatures near Earth's surface usually are measured in degrees Fahrenheit (⁰F) or degrees Celsius (⁰C), but upper atmosphere reports always cite Celsius. Military commanders and staffs express special interest in mean daily maximum and minimum temperatures as well as temperature extremes, which indicate the hottest and coldest weather that armed forces might encounter in any given month (table 6). The number of days below freezing is important in some operational areas, especially when coupled with wind chill factors (table 7), which indicate the combined effects of low temperatures and circulating air on exposed human flesh, taking "true" wind speeds into account. Personnel riding in open vehicles at 20 miles (32 kilometers) per hour, for example, experience the equivalent of a 30 mph (48 kph) buffeting if they buck 10 mph head winds. Back blasts by propeller-driven aircraft can give ground crews a bad case of ague long before thermometer readings dip below freezing, so alert commanders take appropriate precautions. Local inversions make cold, heavy air drain down steep slopes, but air temperatures as a rule decrease 3.5 ⁰F with every 1,000-foot (300-meter) increase in elevation above sea level. Readings drop at that rate up to 35,000 feet (10,670 meters) or so, where Fahrenheit thermometers generally register between -60 ⁰F and -65 ⁰F, then remain more or less constant up to an average altitude of 120,000 feet (36,575 meters), beyond the limit of most military aircraft.

Figure 14. Land and Sea Breeze Regimes

Table 6. Militarily Important Temperature Statistics

(A typical table in degrees Fahrenheit)

Table 7. Wind Chill Factors

RELATIVE HUMIDITY

"It's not the heat, it's the humidity," is an age-old adage, but those two atmospheric elements in fact are inseparable. Absolute humidity, defined as the volume of water vapor in a cubic foot or cubic meter of air, varies from nearly nil in deserts to four or five percent in some soggy climes. Relative humidity is the percentage of vapor present compared with the maximum amount possible, which is greatest in warm air. Saturation (100 percent relative humidity) occurs when contents and capacities become equal. Condensation from gaseous to liquid or solid states follows further cooling. Water droplets (dew) or ice crystals (frost) then form in the air or on Earth's surface, often between dusk and dawn.

Most humans find conditions acceptable when thermometers register 90 ⁰F (32 ⁰C), as long as relative humidity stands, say, at 20 percent, but that same temperature produces a sweat box when water vapor in the air reaches 60 percent or more, because neither precipitation nor perspiration evaporates rapidly in such environments and bodies cool slowly unless wafted by breeze. Damp cold also is debilitating. Bone-chilling winds and wet weather made life miserable for U.S. and Japanese Armed Forces who contested control of the Aleutian Islands during World War II and more recently discomfited British and Argentine troops who battled to determine sovereignty over the Falklands/Malvinas.

CLOUDS AND FOG

Clouds and fog are distinctive forms of condensation that consist of minute water particles suspended in air. Clouds remain aloft whereas fog hugs the surface, but the two are indistinguishable whenever low-lying clouds touch land or water and both obscurants limit visibility in various degrees regardless of their origin.

Fog. Ground fog, which most often develops on cool, calm, clear nights, appears first and becomes densest in depressions, then "burns off" after sunrise as soon as winds pick up and temperatures rise above the dew point (100 percent relative humidity). Poor visibility often causes nighttime traffic control problems in harbors surrounded by hills, because the atmosphere there is so close to saturation that contact with cool air above causes condensation. Industrial smoke and other manmade airborne pollutants convert fog into smog near many cities. (Table 8 displays maximum distances at which military personnel with 20-20 vision can identify prominent objects.)

Thin maritime fog, called "arctic smoke," forms in the far north and south when vapors rising from relatively warm water meet cold air, but perhaps four-fifths of all dense fogs at sea are found in middle latitudes where warm air collides with cool water. Light winds of 5 to 10 knots, which are strong enough to distribute but not disperse suspended vapors, help build huge fog banks off Newfoundland's coast where the Gulf Stream and the Labrador Current intersect. "Pea soup" fog occasionally blankets the British Isles and parts of Northwestern Europe in wintertime, when warm, wet air overrides cold land.

Table 8. Fog Linked to Visibility

Clouds. Three elemental cloud types are recognizable: cirrus and stratus, which spread horizontally; cumulus clouds, which develop vertically (table 9 and figure 15 ). All others are modifications. Wispy cirrus clouds composed of ice crystals habitually occupy thin, dry air above 20,000 feet (6,000 meters), whereas stratus clouds spread sheets across all or most of the sky far below. Fluffy, flat-bottomed cumulus clouds in contrast sometimes tower 30,000 feet (9,150 meters) or more from base to top. The prefix "alto" accompanies all middle level clouds, while "nimbus"--Latin for rain--designates turbulent storm clouds, including anvil-shaped cumulonimbus thunderheads that aviators try to avoid.

Cloud cover, expressed as scattered (1/8^th to 4/8^ths), broken (5/8^ths to 7/8^ths), and overcast 8/8^th), determines vertical visibility. One tier may tell the whole tale, but scattered or broken clouds on two or more levels also cause overcast conditions. The lowest cloud bases determine ceilings, which range from zero to unlimited and differ significantly from place to place over hilly terrain (figure 16).

Table 9. Cloud Classifications

PRECIPITATION

Steady, intermittent, and showery precipitation from clouds strike Earth as rain, sleet, snow, hail, or glaze, sometimes in combinations, the mixture of which depends primarily on air and surface temperatures. Intensities range from drizzles to downpours, with total accumulations characterized as a trace, light, medium, and heavy. One inch of rain (2.5 centimeters) normally is equivalent to 10 inches of snow (25 centimeters). There are no comparable conversion factors for sleet or hail, which sometimes pile several inches deep, or for glaze that turns turnpikes and ship decks into impromptu ice skating rinks. Monthly and annual averages mean little unless precipitation is evenly distributed. Military commanders and staffs need to know whether three inches of rain in April spreads over most of that month or generally arrives as a "gully washer" (comedians chortle about the statistician who drowned while crossing a normally dry stream).

STORMS

Tropical cyclones (hurricanes, typhoons) and frontal systems that form along the boundary between warm and cold air masses in middle latitudes feature low pressures, high winds, overcast skies, low ceilings, poor visibility, and precipitation that varies from trickles to torrents. The most violent storms usually pass in a few hours (even minutes), while others linger for days. Tornadoes that hop, skip, and jump erratically are by far the most furious, but rarely affect military operations and exert little or no influence over plans and programs because they are short-lived, localized, and unpredictable. Tropical cyclones, typified by devastating winds that circle around a calm core (the eye), only occasionally imperil ships at sea and military installations on or near seacoasts, but thunderstorms that bring gusty, shearing, shifty winds along the front, hazardous up-down drafts, hailstones, heavy rain, and destructive electrical discharges regularly occur over land and water (figure 17). Towering cumulonimbus thunderheads, which sometimes measure more than 5 miles high, 20 miles wide, and 60 miles long (8 x 32 x 96 kilometers), pose serious impediments to military aircraft in pursuit of critical wartime missions.

Figure 15. Cloud Types Depicted

Figure 16. Cloud Ceilings Related to Terrain

NATURAL LIGHT LEVELS

Sunshine, moonlight, and starlight are the main sources of natural illumination, which is measured in footcandles (fc). The sun at its zenith, unfiltered by clouds or fog, lights flat surfaces on Earth at about 10,000 fc compared with 0.02 fc for full moons under similar conditions (sufficient light for steady reading averages about 10 footcandles).

Daylight and darkness are not atmospheric phenomena, but staff weather officers routinely furnish military commanders with a wide range of light data for particular times and places. Relevant information includes sunrise, sunset, periods of morning and evening twilight, moon rise, moon set, lunar phases, and times that night vision devices would prove most useful. Four types of twilight, each with important military implications, are recognized universally:

• Astronomical twilight, which persists as long as any detectable glow remains in the sky, starts in the morning when the sun is 18⁰ below the horizon, lasts until sunup, reappears after sundown, then remains until dark.

Figure 17. Anatomy of a Thunderstorm

• The beginning of morning nautical twilight (BMNT) occurs before sunup when the sun is between the horizon and 12⁰ below, at which times large silhouettes are distinguishable and stars that serve navigational purposes are visible in clear weather.
• The end of evening nautical twilight (EENT) occurs after sundown when the sun is between the horizon and 12⁰ below.
• Normal outdoor activities are feasible without artificial light during civil twilight, when the sun is between the horizon and 6⁰ below at dawn and again at dusk.⁴

Levels of natural illumination vary according to latitude and seasons of the year. Civil twilight during spring and autumn equinoxes, for example, lasts twice as long at 60⁰ north or south as it does at the Equator. Regions near the North Pole experience 7 weeks of astronomical twilight from mid-September to mid-November, and 7 more weeks from mid-January to mid-March. Perpetual darkness prevails in the dead of winter, perpetual daylight during summertime in the "Land of the Midnight Sun" (Antarctica encounters analogous regimes in reverse order). The U.S. Naval Observatory in Washington, DC, annually updates and publishes a wide selection of light data for each day, together with conversion factors that enable users to tailor additional calculations that meet individualistic requirements.⁵

CLIMATOLOGY FOR MILITARY STRATEGISTS

Climatologists compile atmospheric statistics that disclose global and regional patterns. Displays that highlight daily-monthly-annual means and extremes become progressively more dependable, provided qualified observers compile specified information for particular places over periods that span several decades. Interpolations must supplement or supplant facts when they do not.⁶

Strategic planners and programmers, who focus their attention on next month, next year, or the indefinite future, are the principal beneficiaries of climatology, which is most important for armed forces that must prepare to implement missions in unfamiliar territory. Specialized studies not only help high-level contingency planners determine whether weapons, equipment, supplies, clothing, and other resources are well suited for operations within regions where military responsibilities might arise on short notice, but they indicate what research, development, test, evaluation, and acquisition programs would best bridge gaps between requirements and capabilities. Theater-level campaign planners, force developers, and resource allocators likewise rely on climatic assessments. General William C. Westmoreland, in his capacity as Commander, U.S. Military Assistance Command, Vietnam, for example, annually approved a series of so-called "monsoon plans" that took wet and dry seasons into account on each side of Vietnam's mountain backbone. When the Northeast Monsoon turns coastal plains to quagmires from mid-October until early March Laos and Cambodia are dry. When the Southwest Monsoon takes over from May to September that regime reverses. ⁷

CLIMATOLOGICAL CLASSIFICATIONS

Every climatological classification is flawed in some respects, whether it emphasizes precipitation (arid, semi-arid, moderate, humid, wet), temperature (cold, tepid, warm, hot), or other atmospheric phenomena. Characteristically warm climes that exclude identifiable winters, cold regions that exclude identifiable summers, and intermediate climates identified by four seasons are much too broad for practical military applications. The "Torrid Zone" isn't uniformly hot (highlands in Kenya and Ecuador, which straddle the Equator, are delightfully cool). "Frigid Zones" poleward of the Arctic and Antarctic Circles aren't uniformly cold (Verkhoyansk and Omyakyon in northeastern Siberia are frozen solid in winter but swelter in summer). "Temperate Zones" are neither climatically moderate nor uniform. Classifications that focus on seasonal or annual precipitation at the expense of temperatures are equally faulty, because they fail to account for evaporation, which heat encourages--Basra, in the Iraqi desert, is notably drier than Russia's Kola coast 1,000 miles (1,600 kilometers) north of Moscow, which receives essentially the same amount of moisture but retains more of it. Most climatic maps moreover limit coverage to land and show sharp boundaries, whereas distinctive patterns appear over oceans and intersections between climatic regions generally are gradual.⁸

MILITARILY USEFUL COMPROMISES

Three basic climatic groupings with several subdivisions apiece serve most military purposes reasonably well, whether forces are aloft, ashore, or afloat: low latitude climates controlled by equatorial and tropical air masses; middle latitude climates controlled by tropical and polar air masses; high latitude climates controlled by polar and arctic air masses. Highlands create temperature and precipitation anomalies in each case (map 11 and table 10 elaborate).⁹

METEOROLOGY FOR MILITARY OPERATORS

Military commanders who seek to make capricious weather work for rather than against them require timely, relevant information about current meteorological conditions and anticipated developments within respective areas of responsibility. Staff weather officers armed with the best available information peer into the immediate future, evaluate variables, identify apparent trends, apply past experience, then predict meteorological events at particular places for specified periods of time.¹⁰ Their prognoses seldom cover more than a week (typically 1 or 2 days), because the reliability of longer outlooks remains spotty despite the proliferation of reporting stations and assistance from technologically advanced sensors on land, at sea, in the air, and in space.¹¹

IMPACT ON CONVENTIONAL LAND WARFARE

General George Washington capitalized on surprise when he deliberately picked a stormy Christmas night in 1776 to cross the ice-caked Delaware River, despite roiling waters and high winds that drenched his 2,400 half-starved, threadbare troops with cold rain, wet snow, and hail. He landed early next morning near Trenton, New Jersey, caught the Hessian garrison off guard, then trounced them in little more than an hour at the expense of four American wounded.¹² Mother Nature, however, punishes imprudent commanders who arrogantly or ignorantly disregard weather. Generalissimo Joseph Stalin learned hard lessons when he ordered poorly acclimated and equipped Soviet Armed Forces to invade Finland on November 30, 1939, after one of the worst winters on record had already begun. Skillful Finnish troops, who anticipated trouble and were well prepared for frigid land warfare, inflicted 10-to-1 casualties on Soviet adversaries before they were overwhelmed by sheer weight of numbers in mid-March, 1940.¹³

Trafficability. Information about the possible impact of precipitation and temperature on trafficability deserves a high priority, because ground forces cannot maneuver effectively when the footing is unfriendly. They move fast across open terrain that is frozen solid (dashing French cavalry captured a complete Dutch fleet at the Texel roadstead, including its embarrassed admiral, when thick ice unexpectedly covered the Zuider Zee in 1795¹⁴), but mud stalls men and machines. British artillery barrages before the Third Battle of Ypres in 1917 destroyed the drainage system during incessant rains and pocked the battlefield with more than four million new water-filled craters that made rapid progress impossible.¹⁵ German tank and truck columns stranded in muck on Soviet steppes during the next World War were cemented in place like Greek friezes when thermometers dipped below freezing after dark. Mud made a mess in mountainous territory as well as on level land during that same time frame, witness U.S. forces in Italy, where men and pack mules skidded up and down slippery trails that four-wheel drive vehicles never could negotiate.¹⁶

Map 11. Regional Climates Depicted

Table 10. Regional Climates Described

Weapon Performance. Atmospheric phenomena significantly affect the performance of weapon systems and munitions. Pressure changes and relative humidity alter barometric fusing and arming calculations, dense air reduces maximum effective ranges, gusty crosswinds near Earth's surface make free rockets and guided missiles wobble erratically, while winds aloft influence ballistic trajectories. Rain-soaked soils deaden artillery rounds, but frozen ground increases fragmentation from contact-fused shells. Dense fog, which degrades visual surveillance and target acquisition capabilities, also makes life difficult for forward observers, whose mission is to adjust artillery fire. Line-of-sight weapons, such as tube-launched, optically tracked, wire-guided (TOW) antitank missiles, are worthless where visibility is very limited. Exhaust plumes that follow TOWs moreover form ice fog in cold, damp air, which conceals targets from gunners even on clear days, and reveals firing positions to enemy sharpshooters. Scorching heat makes armored vehicles too hot to touch without gloves, reduces sustained rates of fire for automatic weapons, artillery, and tank guns, and renders white phosphorus ammunition unstable.¹⁷ Brutal cold has quite different effects, as U.S. Marines discovered in subzero combat around North Korea's Changjin Reservoir (December 1950), where mortar base plates broke on the rock hard ground and hand grenades became unpopular, because users who removed mittens to pull the pin suffered frostbitten fingers if they held the cold metal for more than a moment.¹⁸

IMPACT ON CONVENTIONAL SURFACE NAVAL WARFARE

Winds, towering seas, and frigid temperatures influence naval operations more than any other atmospheric factors. Results sometimes are favorable--a kamikase ("Divine Wind") saved Japan from invasion by a Mongol fleet in the 13th century, and Britain benefited when storms dispersed the Spanish Armada in 1588--but foul weather at sea is seldom welcome.

Aircraft Carriers. Large aircraft carriers are less affected than their escorts by heavy seas, but even so may roll nine degrees or more when their flight decks are exposed to strong winds. Small wonder, therefore, that U.S. carrier battle groups plying back and forth between Bosnia and Norfolk Naval Base, Virginia, in August 1995 took special pains to bypass three hurricanes that then were active in the Atlantic Ocean. Less than gale force winds demand additional tie downs for fixed-wing aircraft and helicopters, repositioning becomes a complex proposition when decks are slick, and fighters may not be able to spread folding wings until they reach catapults. Underway replenishment, always a delicate business, becomes additionally hazardous in rough weather, when waves may wash away loads suspended on transfer lines and cargo handling on deck becomes infinitely more difficult. Foul weather procedures consequently emphasize smaller than normal loads, longer than normal transfer times, and greater than normal distances between support ships and recipients to prevent collisions.¹⁹

Other Surface Ships. Persistent heavy weather endangers surface ship stability, buoyancy, power, and structural integrity. Experienced helmsmen have a hard time maintaining course when beset by sharp pitching, swaying, surging, yawing, and heaving, but repeated wide-angle rolls from starboard to port and back again are exceptionally dangerous, because most surface combatants and support ships may capsize if efforts to restore stability fail. Conditions are worst when ships steer a course that parallels the storm path and their roll period (9 to 10 seconds for a typical destroyer) coincides with the period between wave peaks and troughs. Paths perpendicular to the onrushing sea minimize roll but maximize pitch, which alternately causes bows to slam and propellers to beat thin air at high speeds while the whole ship shudders. Nonnuclear ships maintain the lowest possible center of gravity primarily by replacing consumed fuel with salt water ballast, which maintains low-level weight and prevents partially filled tanks from sloshing. All savvy captains position heavy loads below deck to the greatest practicable extent, and engineers take special pains to maintain propulsive power, because wallowing ships are helpless.²⁰

Thick layers of ice can quickly form on decks, sides, superstructures, hatches, masts, rigging, exposed machinery, antennas, and weapon systems when salt spray hits ship surfaces at subfreezing temperatures. Two feet or more totaling several hundred tons may accumulate within 24 hours in very cold climes, depending on wind velocities and wave heights. Seaworthiness and combat effectiveness then suffer from top heaviness and increased wind resistance.²¹

Small Craft and Boats. Amphibious landing craft and naval special operations boats are especially sensitive to wind, waves, and surf. Cyclone class patrol boats, the most seaworthy vessels currently available to U.S. SEALs, are fully functional through Sea State 5 (winds 22 to 27 knots, waves 10 to 12 feet, or 3 to 4 meters, high), but struggle to survive stronger storms.²² Personnel transfers from seagoing "buses" to small boats are tricky under perfect conditions and fearful when they are not. One SEAL team aboard a slam-dunking tugboat on a training exercise in the frigid North Sea first fought to keep its six Boston whalers from washing overboard, then watched 50-knot winds flip three of them like flapjacks when they were lowered into foaming water. Forty-two heavily laden shooters had to time the swells, leap toward the boats, and pray they wouldn't be crushed or chewed by propellors.²³

IMPACT ON CONVENTIONAL AIR WARFARE

Military aviators almost everywhere in peacetime must comply with visual and instrument flight regulations (VFR, IFR). VFR limitations for land-based, fixed-wing U.S. military aircraft generally prescribe a ceiling of at least 1,200 feet (365 meters), visibility of 3 statute miles (4.8 kilometers) at destinations as well as departure airfields, and minimum distances above, below, and around clouds en route. Lower ceilings or poorer visibility obligate pilots to file IFR flight plans.²⁴ VFR for land-based helicopters are more lenient.²⁵ U.S. aircraft carrier captains, who generally determine whether weather is agreeable for takeoffs and landings, consider prospects for successful recovery at suitable bases ashore as well as aboard the mother ship.²⁶ All armed forces shelve peacetime restrictions when combat or other high priority operations commence, because assigned missions then take precedence over safety.

Clouds and Fog. U.S. bomber crews during World War II fought weather along with Japanese adversaries on Umnak Island in the Aleutians, where fog was so dense that crew members poked their heads out of open windows to help pilots stay on taxi strips and steer straight courses down runways.²⁷ Bad weather all the way from air bases in England to drop and landing zones in Holland during Operation Market Garden on September 19, 1944, turned the third wave into a disaster--fewer than half of the troop transports and gliders laden with desperately needed reinforcements and supplies found their way through the "soup" to intended destinations.²⁸

Technological improvements make life much easier for modern airmen, but "socked in" airports and low ceilings still ground them occasionally regardless of pressing requirements, and low ceilings sometimes obscure approaches to target areas. U.S. and allied troops at highland outposts in Vietnam, for example, lacked close air support (CAS), assistance from gunships, and aerial resupply for all or most of many days during rainy seasons. High-performance, fixed-wing CAS aircraft at such times were limited to low-level, low-angle avenues that maximized their exposure to enemy air defense weapons and small arms (see chapter 19 for weather details in Vietnam and Laos). NATO more recently canceled or diverted nearly 360 military airlift missions in mid-December 1995, thereby delaying its initial buildup in Bosnia for more than a week.²⁹

Barometric Pressures. All aviators set altimeters to reflect barometric pressure at departure airfields before they take off and update readings before they land so they always know how high they are above land or water. Accurate indications are most important for military airmen whose missions demand low-level or nap-of-the-earth flights through mountainous terrain under blacked out or murky weather conditions. Barometric pressures, together with temperatures and humidity, determine air density, which limits the ability of any given type aircraft to get off the ground with any given load and thereafter perform effectively. Heavy air that is common on cold days at sea level provides the best possible lift, but density decreases when thermometers climb. Altitude thins Earth's atmosphere so rapidly that regulations require U.S. military air crews to use supplemental oxygen when cabin altitude exceeds 10,000 feet (3,050 meters),³⁰ although SS Hauptsturmführer (Captain) Otto Skorzeny proved that fantastic feats are possible in thin air when he landed 12 gliders atop Italy's boulder-strewn Gran Sasso Mountain in 1943, snatched Benito Mussolini from his Italian custodians, and whisked him away in a light airplane.³¹ Lieutenant Colonel Maden of the Nepalese Army conducted the world's highest helicopter rescue on May 13, 1996, when he plucked two half frozen survivors off Mount Everest at 19,200 feet (5,850 meters), then flew them to a hospital in Katmandu.³²

Winds. Wind velocities and vectors strongly affect military air operations in many ways that civilian fliers seldom experience. Expeditionary airfield users cannot switch runways every time strong crosswinds develop because they possess only one runway, so prevailing winds dictate the orientation of these fields. No ocean liner or cruise ship ever deliberately heads toward a storm, as carrier commanding officers often do in search of sufficient "wind over deck" (20 sustained knots or more) to launch and recover fixed-wing aircraft. Psychological operations (PSYOP) leaflets are worthless when winds blow in the wrong direction. Paratroopers of the 82nd Airborne Division had to accomplish their missions in July 1943 despite 35-mile-an-hour winds that scattered them across Sicily and slammed them against stone walls in the dead of night.³³ Efforts to rescue U.S. hostages that Iranian radicals held in Teheran (1980) failed when three of the eight mission-essential helicopters aborted, one because wind-blown dust storms turned it back.³⁴

IMPACT ON NUCLEAR, BIOLOGICAL, AND CHEMICAL WARFARE

Nuclear weapons respond to weather in several ways, of which winds on the surface and aloft perhaps are most important. Chemical and biological warfare (CW, BW) agents are sensitive to several atmospheric phenomena under somewhat different conditions.

Nuclear Weapons. Low air bursts beneath clouds amplify thermal radiation by reflection, whereas the heat from bursts above cloud blankets bounces back into space. Heavy precipitation raises the temperature at which thermal radiation will ignite given materials and reduces the spread of secondary fires. Detonations after dark increase the range at which flashes from nuclear explosions blind unprotected viewers. Blasts on, beneath, or at low altitudes above Earth's surface suck enormous amounts of debris up the stems of mushroom clouds that drift downwind. The heaviest, most contaminated chaff falls back near ground zero within a few minutes, but winds aloft waft a deadly mist hundreds or thousands of miles. The size, shape, and potency of resultant radioactive fallout patterns differ with wind speeds and directions, because terrain shadows, crosswinds, and local precipitation sometimes create hot spots and skip zones within each fan. Fallout from one test conducted atop a tower in Nevada, for example, drifted northeast and retained strong radioactive concentrations around ground zero, while a second test from the same tower on a different date featured a "furnace" that was seven times hotter than its immediate surroundings 60 miles (95 kilometers) northwest of the test (figure 18). Such erratic results are hard to predict even under ideal conditions.³⁵

Figure 18. Nuclear Fallout Related to Wind

Biological Warfare Agents. Biological warfare agents conceivably could create international chaos on a grand scale by infecting enemy armed forces, civilian populations, livestock, and crops en masse. Small laboratories can generate BW products so quickly in militarily significant quantities that refrigerated storage facilities no longer are necessary, but microbiol pathogens and toxins as a rule last only a few hours when exposed to high temperatures and low humidity inside bombs, missile warheads, spray tanks, and artillery shells. Some biological munitions, inherently unstable, can neither tolerate sharp strains associated with projectile flights nor stand direct sunlight.³⁶

Chemical Warfare Agents. Chemical warfare agents, in sharp contrast, thrive under weather conditions that biological weapons cannot tolerate. Heat and humidity help rather than hinder. Mustard and lewisite are particularly effective in hot weather, because perspiration promotes blisters. Protective clothing, masks, and gas-proof shelters are the best insurance against CW weapons of any kind, but fatigue followed by heat prostration afflicts personnel who "button up" very long in warm climes, while air conditioned facilities that lack fool-proof filters become death traps. Persistent agents laid down as liquids last longer than aerosols and are less sensitive to vagrant winds, so chemical warfare specialists advise commanders to initiate vapor attacks when breezes blow in the right direction between three and seven knots, to avoid rainy days, and to wait for temperature inversions that trap agents in the lowest layer of air.³⁷

IMPACT ON ELECTRO-OPTICAL OPERATIONS

Active and passive electro-optical (E-O) systems include image intensifiers, typified by night vision goggles; infrared devices, such as night sights; laser designators, some of which assist "smart" munitions; and low-light-level television sets able to "see" in the dark. Research and development laboratories are rapidly expanding and improving existing inventories.

Adverse Atmospheric Influences. Windblown dust, fog, haze, high humidity, clouds, and precipitation degrade or defeat all E-O systems that gather visible light. Long wave lengths are less affected than short waves, although resolution is fuzzier. Atmospheric refraction, often less obvious than a mirage, can make targets seem to move (even disappear) in shimmering surface air and otherwise reduce electro-optical effectiveness. Heat is the most common cause of that phenomenon, but similar distortions sometimes appear above snow-covered ground when temperatures are well below freezing. Infrared and millimeter wave sensors, which depend on thermal contrasts to differentiate targets from backgrounds (warm engines, for example, concealed in cool woods), cannot discriminate as well as users would like when winds, rain, snow, or insulating clouds make temperature differences indistinguishable, so experimental programs continue apace.³⁸

Inadequate Light. Military operations in the past typically were timed to begin just before dawn, then continue in daylight, because few armed forces were well prepared for armed combat after dark. Light enhancement tools may some day enable soldiers, sailors, airmen, and marines to "own the night," but research and development technicians first must solve several weather-related problems. Too much light sometimes defeats night vision devices on relatively clear nights when the moon is full or nearly so, because amplifications so saturate viewing areas that light and dark almost merge. Too little light may be available on overcast nights that conceal starlight when the moon is dark or down. Most night vision implements now on the market are miniaturized compared with predecessors even a few years ago, yet remain too bulky for facile employment by foot troops. Research and development goals accordingly concentrate on sharper resolution, better depth perception, longer range, stereoscopic capabilities, smaller size, reduced weight, and greater overall versatility.³⁹

IMPACT ON DIRECTED ENERGY WEAPONS

Directed energy weapons, which attack at the speed of light, occupy two basic categories. Electromagnetic beams embrace high-energy lasers (HEL) and high-powered microwaves (HPM). Particle beams include charged particle beams (CPB) and neutal partical beams (NPB).

Electromagnetic Beams. Atmosphere interferes with electromagnetic beams in at least four important ways:⁴⁰

• Scatter occurs when beams strike clouds, fog, invisible vapors, dust, smoke, and other matter buoyed by air.
• Absorption occurs simultaneously for similar reasons.
• Blooming occurs when heated air makes beams expand and splay.
• Turbulence occurs when up-down drafts, cross currents, heat waves, and other atmospheric phenomena disrupt beams, the efficiency of which may fall by a factor of 100 to 300 within a few miles

Particle Beams. Particle beams differ from lasers in that they project a stream of highly energetic electrons, protons, neutrons, hydrogen atoms, or ions rather than radiant photons. Charged particle beams propagate well in Earth's atmosphere regardless of weather, but ranges at this writing are strictly limited. Weather is irrelevant with regard to neutral particle beams, which propagate only in the vacuum of space.⁴¹

IMPACT ON MILITARY PERSONNEL

Military men and women exposed daily to the elements cannot decide whether extreme heat or extreme cold is worse, but informal polls put one or both of those abominations at the bottom of almost everybody's list, regardless of individual tolerances, physical conditioning, and degrees of acclimatization. Cold coupled with bitter winds and heat coupled with high humidity are the worst weather combinations by consensus.

Cruel Cold. Dry cold below freezing encourages frostbite among poorly clothed and trained personnel. German Armed Forces in Russia suffered 100,000 casualties from that cause during the winter of 1941-1942, of which 15,000 required amputations. Human breath turned to icicles in that brutal cold, eyelids froze together, flesh that touched metal cold-welded, gasoline accidentally sprayed on bare skin raised blisters the size of golf balls, butchers' axes rebounded like boomerangs from horse meat as solid as stone, and cooks sliced butter with saws. Dehydration, contrary to popular misconceptions, can be prevalent in frigid weather when personnel exhale bodily moisture with every breath. Low temperatures, which inhibit clotting, cause wounds to bleed more freely, and severe shock due to slow circulation sets in early unless treated expeditiously. U.S. medics armed with morphine for that purpose once kept syringes in their armpits so they would be warm enough to work when needed. High-Altitude High-Opening (HAHO) parachutists who exit aircraft in subzero temperatures experience extreme chill, first when they free-fall at up to 120 miles per hour (193 kilometers per hour), then while they drift for as much as 30 minutes or more. Survival often becomes the only practicable objective of forces on the ground when wind chill factors plummet far below freezing.⁴²

Wet cold is even more debilitating in some respects. Crippling trench foot, a classic casualty producer, is caused by prolonged immersion of lower legs and feet at temperatures a bit above freezing. Prominent symptoms begin with numbness, followed by swelling, terrible pain and, in untreated cases, gangrene. During World War II, in the European Theater of Operations, trench foot assumed epidemic proportions among U.S. combat infantrymen who for days on end waded rather than marched through chilly muck, lived in water-filled foxholes, and lacked access to shelter or dry shoes and socks. More than 45,000

of them filled field hospitals to overflowing between November 1944 and February 1945, a loss equivalent to the front-line rifle strength of 10 divisions.⁴³

Oppressive Heat. Armed forces in enervating heat face a different set of difficulties. Water consumption soars to prevent dehydration, since exertions over an 8-hour period in 100 ⁰F (38 ⁰C) heat demand about 15 quarts a day (14 liters). Logisticians in the desert are hard pressed to supply huge loads, which amount to 30 pounds per person, or 270 tons for an 18,000-man U.S. armored division. Heat coupled with high humidity saps strength more quickly, especially when military personnel wear flak jackets or don protective clothing in anticipation of enemy chemical warfare attacks.⁴⁴ Myriad other matters attract concerted attention. Food handlers, for example, fight a ceaseless war against bacteria that contaminate unrefrigerated perishables in mobile kitchens lacking modern amenities. The rate of gum accumulations in stored gasoline quadruples with each 20 ⁰F increase in temperature, which clogs filters and lowers octane ratings when forces deplete stockpiles slowly.

Hypothermia occurs when human body temperature drops below normal (98.6 ⁰F), whether surroundings be cold, cool, or warm--individuals can become hypothermic in 80 ⁰F (26.7 ⁰C) water if immersed too long. The first visible signs may be uncontrollable shivering and impaired abilities to accomplish simple tasks. Sluggishness and amnesia appear next if body temperature continues to drop, then shivering ceases, stupor sets in, and respiration slows. Heart failure, internal bleeding, and death occur below about 78 ⁰F (25.6 ⁰C) unless warmth, dry clothing, and perhaps stimulants reverse that process in time.⁴⁵ Combat swimmers in seas between 60 and 40 ⁰F wear wet suits that trap a thin layer of warm water next to their skin (synthetics that "breathe" better than rubber are preferred materials). Watertight dry suits over thermal underwear are essential in colder water.⁴⁶

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