adjacent to the Earth's surface

varies in height from 55,000 feet over the equator to 28,000 ft over the poles

50% by weight, lies below 18,000 ft and 90% within 53,000ft

temp normally decreases with increasing altitude

transition zone between troposphere and stratosphere

temp is isothermal with increase in altitude

Troposphere - large amounts of moisture and condensation nuclei are found there because of its closeness to the Earth's surface and nearly all weather occurs there, winds are generally light and increase with altitude.

Tropopause - strongest winds, those of the jet stream, occur just below tropopause. mod to svr turbulence sometimes assoc with wind shear  caused by jet stream.  can identify by anvil tops of TS's spreading out at base of Tropopause. haze layer with a definite top exists at the tropopause

stratosphere - smooth, good vis, no weather

the pressure exerted on a surface by the atmosphere due to the weight of the column of air directly avove that surface.

the avg weight of air on a square inch of the Earth's surface at sea level conditions is 14.7 lbs.

inches of mercury (in Hg)

Millibars (mb)

station pressure - the atmospheric pressure measured directly at an airfield or other weather station

sea level pressure (or reported altimeter setting) - the pressure measured from the existing weather if the station were at MSL

Flying toward lower pressure, the altimeter indicates higher than actual and the actual MSL altitude is lower than indicated by the altimeter

Flying toward higher pressure, the altimeter indicates lower than actual and the actual MSL altitude is higher than indicated by the altimeter

the rate of pressure change in a direction perpendicular to the isobars(horizontal distance) is called the pressure gradient.

Isobar spacing represents the size of the pressure fradient force (PGF)

PGF is the initial mvmt of air from high to low pressure, thus initiating force for wind

PGF is steep or strong when isobars are close together - strong winds

PGF is shallow or weak when isobars are far apart

Explain and identify gradient winds with respect to the isobars around high and low pressure systems in the Northern Hemisphere.

• the result of PGF and Coriolis force is gradient winds, which flow perpendicular to the PGF. 
• This means gradient winds flow parallel to the isobars and results in circulation flowing clockwise around highs and counterclockwise around lows. 
• Gradient winds are found above 2,000 ft AGL

States that if the wind is at your back, the area of lower pressure will be to your left

it's a rule of thumb to help remember the direction of the wind in relation to a pressure system

Coriolis force still tries to turn the wind to the right, from its initial intended direction of the PGF, but it does not turn to the right quite as much as with gradient winds, due to surface friction.

thus, surface winds still move clockwise around highs and counterclockwise around lows, but since they blow across the isobars at 45 degrees angle, they also have a component of motion that moves air out of the high pressure and into the low.

a narrow band of strong winds of 50 knots or more that meanders vertically and horizontally around the hemisphere in wave like patterns

average winds are 100 to 150 kts, but may reach speeds in excess of 250kts

it is found in segments from 1000 to 3000 miles in length, 100 to 400 miles in width, and 3,000 to 7,000 feet in depth.

average height is about 30,000 feet MSL

during winter, the position of the jet stream is further south, the core rises to higher altitudes and its speed is faster than in the summer

Sea - during the day, the pressure over the warm land becomes lower than over the colder water

 the cool air over the water moves toward the lower pressure, replacing the warm and rising air over the land

this results in an onshore wind, blowing from the sea.

Land - During the night, the circulation is reversed so that the air movement is from land to sea, prducing an offshore wind called the land breeze.

Valley - occurduring daytime when sun heats the mtn slopes. as the air adjacent to the slopes is heated, it rises and is replaced by warmer air near the ground. Dince that wind is flowing from the valley it is called a valley wind.

Mountain - Occur at night, when air adjacent to the slopes is cooled by outgoing terrestrial radiation and becomes more dense than the surrounding air.  The denser air flows downhill from the top of the mountain and is called a mtn wind.

showers - characterized by a sudden beginning and ending, and abruptly changing intensity and/or sky conditions.  Showers are associated with cumuliform clouds.

Continuous - also known as steady (not showery).  Intensity changes gradually, if at all.  Continuous or steady precip is associated with stratiform clouds.

Intermittent - Stops and restarts at least once during the hour.  Intermittent precip may be showery or steady and therefore may be associated with cumuliform or stratiform clouds.

• Rain - precipitation in the form of water deoplets that are larger than drizzle and fall to the ground.
• Drizzle - very small droplets of water that appear to float in the atmosphere
• Freezing rain - rain that freezes on impact with objects
• Freezing drizzle - drizzle that freezes on impact with objects
• hail/graupel - composed of irregular lumps of ice that develop in svr thunderstorms, consisting of alternate opaque and clear layers of ice in most cases.  It does not form structural ice.
• snow - white or translucent ice crystals, usually of branched hexagonal or star like form that connect to one another forming snowflakes.  When condensation takes place at temperatures below freezing, water vapor changes directly into minute ice crystals.
• ice pellets/sleet - small translucent and irregularly shaped particles of ice.  they form when rain falls through air with temp below freeaing.  ice pellots do not produce structual icing unless mixed with super cooled water.
• snow grains

Low - just above sfc to 6500 ft AGL

Middle - 6500 - 20000 ft AGL, prefix: alto-

High - 20000 ft AGL and up, prefix: Cirro-

Special - extensive vertical development (TCU's & CB's)

Low clouds - mainly composed of water droplets, may hide TS's; if below freezing icing may result and accumulates faster in low clds since they are denser than mid/high clds; turbulence varies from none to moderate; precip is generally light rain or drizzle.

Middle clouds - prefix "alto"; rain, rain and snow mixed or snow can be encountered in thick middle clouds; vis depends on cloud density from 1/2 mile to few feet; frequently these clouds are dark and turbulent enough to make formation flying difficult

High clouds - prefix "cirro/cirrus"; little or no precip and no icing hazard; svr or extreme turbulence often found in the anvil cirrus of TS's

Special clouds with extensive vertical development - TCU's and CB's.  TCU's are coouds nearing the TS stage and produce hvy rain showers and mod turbulence; CB clouds are TS clouds and produce svr to extreme turbulence, hail, icing, lightning and other hazards.

Atmospheric stability - lifted air that is colder than the surrounding air settles when the lifting action is removed, since it is dense.  This indicates a stable condition.

Atmospheric Instability - Lifted air that is warmer than the surrounding air continues to rise when the lifting action is removed because it is less dense.  This indicates an unstable condition.

Atmospheric Neutral Stability - Lifted air having the same temperature as the surrounding air after it is lifted will simply remain at the point where the lifting action was removed.

• Convergence - Convergence of 2 air masses, or parts of a single air mass, force the air upward because it has nowhere else to go. 
• Orographic - term indicating the force of the wind against a mtn side pushing the air upward.
• Frontal - the shape of cold fronts, as they move through an area, will lift air ahead of the cold air mass.
• Thermal - aka convective lifting, is caused when cool air is over a warm sfc and it is heightened by intense solar heating on a clear day.

• if the air mass is warmer than the surface, it is cooled by contact with the cold ground, becomes more stable, and is called a warm air mass
• if the air mass is colder than the surface over which it is moving, it is heated from below, resulting in convective currents and instability and is called a cold air mass.

• fronts are named according to the temp change they bring
• frontal characteristics diminish with inc altitude(15000-20000 ft); most significant frontal weather occurs in the lower layers of the atmosphere.

Temperature

moisture (dew point)

winds

pressure

• slope - vertical rise to horizontal distance; warm=shallow, extesive cloudiness with large areas of steady precip; cold=steep, move rapidly, hoarrow bands of cloudiness and showery precip;
• stability - degree of stability of lifted air;determines whether stratiform/cumuliform;stratiform=steady precip/little or no turb;cumuliform=showery precip/turb
• speed -fast moving=narrow band of svr weather;slow moving=less svr weather, but more extensive frontal zone
• moisture - amt of moisture availiable; determines the amt of weather associated with a front.
• contrast - contrast in the amts of temp/moisture btwn the 2 air masses; the greater the contrast in temp/moisture, the greater the possibility of weather (particularly svr weather) assoc with front.

• fast moving - narrow band, svr, clears rapidly
• slow moving -  less svr, persist for hours
• cold fronts move SE at 20kts, wind shifts from SW to NW with greater speeds behind front
• ceiling and vis are VMC but can be IMC in hvy precip/TS's
• Turbulence
• precip and icing

• a line of violent TS's
• develop 50-300 miles ahead of the cold front & parallel to it
• most intense during late afternoon/early evening/after max daytime heating
• 90 degree wind shirft: SW to NW

• stratiform cloud is most common
• turbulence not likely; winds shift from SE to SW
• slower than cold front, gradual slope, not as well defined as a cold front
• low ceilings and fog
• altocu and CB clouds can be embedded in cloud masses
• Move at 15kts to NE

• sfc winds tend to blow parallel on both sides of the front therefore, a stationary front has a 180 degree wind shift
• weather conditions are similar to those found with warm front, but less intense
• may persist in one area for several days

• form when a faster moving cold front overtakes a slower moving warm front
• weather will be a combination of both types of frontal weather
• wind shift will be 180 degrees, SE to NW
• Cold occlusion = 20kts
• warm occlusion = 15kts
• front will move NE

Moisture, unstable air, lifting action

• Once moist air is lifted in an unstable environment, the rapidly rising unstable air quickly forms towering cumulus and eventual CB clouds

• cumulus - updrafts (from above sfc to several thousands of feet above visible cloud top);no precip; turbulence exists; strongest updrafts late in the stage (may b 3000ft per min)
• mature - precip begins;rain/hail = downdrafts have began
• dissipating - downdrafts ger stronger and updrafts weaken;once updrafts  end, TS's dissipate;anvil forms due to strong winds aloft
• Pressure variations - rapid fall in pressure as storm approaches; abrupt rise in pressure with the onset of the 1st gust/arrival of rain showers;gradual return to normal pressure as storm passes and rain ceases.

• extreme Turbulence (worst)
• hail (2nd worst)
• microburst
•  icing
• lightning
• tornadoes

downward flow diverges outward, producing a vortex ring of wind that can produce differential velocites from 20 to 200kts in an area of 1/4 to 2 1/2 miles in diameter

• have a short life of about 5-10min
• wind shear dangerous during takeoff, approach, and go around....

• locate/track CB cells & determine their intensities
• see large rain/hail which yield strongest returns;smaller driplets are dimmer and snow is faintest
• airborne radar can b used to identify and avoid the most intense echo patterns

• AVOID if possible
• stay 20 miles away of storms with overhanging anvils(hail)
• do not fly under TS in moutainous regions; extreme turbulence may exist btwn mtn. peaks
• avoid flying under TS's since updrafts/downdrafts can exceed acft performance
• do not takeoff or land if a TS is approaching
• do not fly into a cloud mass containing scattered embedded TS without airborne radar
• to avoid lightning do not penetrate a TS or fly through the cirrus anvil uf well developed/dissipating TS

Types: thermal, mechanical,mtn wave, frontal and large scale wind shear turnbulence

Intensities: light, moderate, severe and Extreme

occasional = less than 1/3 of the time

intermittent = 1/3 to 2/3 of the time

continuous = more than 2/3 of the time

• avoid if possible, otherwise fly 50% higher than height of mtn range
• avoid rotor, lenticular and cap clouds (they contain intense turbulence and strong updrafts/downdrats
• approach mtn range at 4 degree angle
• avoid leeward side (strong downdrafts)
• donot trust pressure altimeter readings near mtn peaks.
• slow to rubulence penetration airspeed

• caused by lifting of warm air, a frontal sfc leading to instability or the abrupt wind shift btwn warm and cold air masses
• most svr cases of frontal turbulence are associated with fast moving cold fronts

Jet Streams - because the wind speed and direction can change drastically over a short distance in both the horizontal and verticla plane.

Temperature inversions - can cause turb at the boundary bwn the inversion layer and the surrounding atmosphere.  the resulting turb can often cause a loss of lift and AS near the ground, such a swhen a headwind becomes a tailwind creating a decreasing performance wind shear.

• establish/maintain turbulent air penetration AS/attifude
• Do not chase airspeed
• trim acft for level flight at turbulent air penetration spd (do not change trim after)
• use attitude gyro to control pitch/bank
• do not make abrupt control inputs(to avoid overstresssing the acft)
• allow altitude to vary;do not chase altimeter

• Clear - 0 to -10 C, cumulus clouds, areas of freezing rain/drizzle, water covers large portion of sfc and freezes gradually;most svr because it builds up fast and can freeze controls and disrupt airflow over wing
• Rime -   -10 to -20, milky white/rough/opaque; stable conditions, stratiform clouds, upper portions of cumulus clouds;protrudes into the air stream at leading edges or airfoils
• mixed - clear/rime mixture; -8 to -15 C; lumpy but hard and dense;most frequent type of icing encountered
• Frost - thinlayer of crystalline ice that forms on exposed sfcs; clear and calm wind nights when air temp/dp are below freezing; forms in flight when a cold acft descends from freezing temps to high RH zone

super cooled visible water droplets

air temp/acft sfc temp below freezing

• cold fronts/squall lines:  narrow band of wx/icing - icing zone 10000 ft thick;100 mi wide; predominantly clear icing accumulating rapidly
• Warm/stationary fronts:  wider band of wx/icing;predominatly rime, but may contain mixed
• occluded fronts: icing covers widespread area, stratiform and cumuliform clouds; clear,mixed and rime, very rapid and heavy rate of accumulation

• most hazardous aspect is aerodynamic effects
• decreases lift, thrust and range, and increases drag, weight, fuel consumption and stall speed

Induction:  (air intake duct icing)reduced pressure that exists at the intake lowers the temp to the point that condensation and/or deposition take place.

Compressor:  Ice forming on comprfessor inlet screens and compressor inlet guide vanes will restrict the flow of inlet air, eventually causing engine flameout

hazardous because de icing fluids are highly corrosive to internal acft and engine parts

taxing on mud,water,slush...can create a covering of ice that can hamper mvmt of flaps, control sfcs and landing gear

ice/snow on rw affect braking action

Flight path: climb to colder, descent to warmer, (climb to warmer in an inversion)

anti icing/deicing equipment:  Deicing equipment eliminates/removes ice already accululated(mechanical boots/heat)

anti icing equipment prevents accumulation of ice (fluids/heat)

Types: rime,clear,mixed

Intensities: trace, light, moderate, severe

SKC/CLR - Sky clear - 0/8

FEW - Few - 1/8 to 2/8

SCT - scattered - 3/8 to 4/8

BKN - broken - 5/8 to 7/8

OVC - overcast - 8/8

VV - obscured - 8/8 (sfc based)

* CLR is used at automated stations when no clds below 12,000 ft, SKC - manual stations

• Condensation nuclei present
• high water content (low dp spread)
• light sfc winds

• radiation - due to nocturnal cooling; usually clear nights when earth releases large amts of radiation;if air temp cools to dp temp fog/low clouds form.
• advection - warm moist air moves over a cold sfc and temp cools to dp; common in coastal areas;becomes thicker/dense as wind increases to 15kts;only dissipates with a change in wind moving air from colder to warmer sfc;incoming solar radiation will not cause dissipation of advection fog...

• loss of thrust/engine flameouts
• leading edges/windshields sandblasted
• AS indications fluncuate due to volcanic ash blocking pitot system
• rise in oil temp indicates dust plugged oil cooler
• power surges, loss of thrust, high EGT, compressor stalls