Adverse Wind & Fog 15&16

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BBCC Aviation Meteorology

Chapter 15

Adverse Winds

https://www.youtube.com/watch?v=B4tT7xFUEuc

 

Types Of Adverse Winds

  • Types
  • Crosswinds
  • Gusts
  • Tailwinds
  • Variable wind
  • Sudden wind shift
  • The book says you’re most at risk during takeoff and landing
  • It also says little planes are affected most

Adverse Winds

Crosswind

  • This wind blows from one side or the other
  • Breaks off the landing gear
  • Gust
  • This is where the wind speeds up suddenly (10kts or more)
  • Breaks or bends the spar
  • Tailwind
  • This wind blows up your tail
  • Runs you off the end of the runway or into the trees on takeoff
  • A 10% increase in landing speed will result in at least a 21% greater landing distance
  • Variable wind/Wind shift
  • This is when the wind is variable and is shifty
  • Wind shear
  • This one is trickier than the rest, it pretends it’s your friend then whammy

Computing X-wind & Headwind

  • For x-wind use the sin of the angle between the wind and the runway
  • Wind 280@20 runway 36
  • 360-280=80
  • Sin(80)=.984807753 x 20=19.69kts
  • For the headwind use the cos of the angle between the wind and the runway
  • Wind 280@20 runway 36
  • 360-280=80
  • Cos(80)=.1736481777 x 20=3.47kts

žCHAPTER 16

Obstructions to Visibility

žWeather Related Accidents

—žCategorical Outlooks

  • žAIM 7-1-7 defines 4 categories:
  • —LIFR Ceilings less than 500 vis less than 1 mile
  • —IFR Ceiling 500 to less than1000 vis 1 to less than 3 miles
  • —MVFR Ceiling 1000 to less than 3000 vis 3 to 5 miles
  • —VFR Ceiling greater than 3000 vis greater than 5 miles

žVisibility

  • žThere are 3 types of visibility:
  • —In flight
  • —Slant range
  • —Surface
  • žSurface vis in Metars is given in SM
  • žFlight vis is reported in SM as well
  • žVFR pilots on average loose control after about 3 minutes

žRestrictions to Visibility

  • žFog
  • žHaze and smoke
  • žDust and blowing dust
  • žVolcanic ash
  • žBlowing sand
  • žBlowing snow
  • žPrecipitation

žFOG

  • žDefined as surfaced based clouds of water or ice crystals
  • žFog is the most common cause of vis less than 3 miles
  • žFog can form rapidly dropping vis to less than a mile in a few minutes
  • žFog is one of the most hardest weather phenomenon to predict

žFog

  • žSmall temp/dew point is needed
  • žThis usually occurs just after sunrise due to small temp/dew point spread
  • ž3º and closing usually get fog
  • žcondensation nuclei must be present
  • ž5/8 to 6 miles is mist BR
  • žLess than 5/8 of a mile is classified as fog

žžFOG FORMATION

  • ž1. Cool air to the dew point
  • ž2. Add moisture near the ground

žFog Formation Mechanisms

  • žWarm moist air in contact with cooler ground or water
  • žUpslope flow causing adiabatic cooling
  • žEvaporational cooling releasing latent heat
  • žSurface dew point increasing to temp due to evaporation
  • žAir flowing over a moist surface (swamp, lake, ocean, rain soaked ground ect.)
  • žWarm rain falling through colder air
  • žCombination of any of the above

žžTypes of Fog

  • ž1. Radiation fog
  • ž2. Advection fog
  • ž3. Upslope fog
  • ž4. Precipitation-induced fog/Frontal fog
  • ž5. Ice fog
  • ž6. Steam fog

žRADIATION FOG

  • žUsually relatively shallow
  • žAlso known as Ground Fog
  • žClear sky, little or no wind, small temp dew point spread
  • žWarm moist air over low flat areas
  • žHowever it may form in valleys as well
  • žAreas of cold air drainage lend to formation
  • žThis type of fog forms almost exclusively at night or daybreak
  • žLook for this fog in the am after an evening/night rain and clearing sky
  • žOr in winter when it gets warm enough to melt snow cover

žRadiation Fog

  • žTerrestrial radiation cools the air close  the ground
  • žWind of 5 kts or less mix the layers of cool air and deepen the fog
  • žCalm wind results in transfer through conduction alone resulting in thinner fog
  • žA wind of +5 kts mixes the moist layers close to the ground with dryer air above preventing formation
  • žUsually only forms over land because of the terrestrial radiation
  • žUsually dissipates quickly if the sun comes out or a wind +5 kts picks up
  • žIf high overcast persists it will take longer for the temp/dew point spread to increase

žžRadiation Fog

  • žAt night a more complicated process is at work
  • žThe top of the fog more readily emits IR radiation skyward
  • žFog droplets absorb some of this IR radiation and reradiate back to the surface
  • žThe ground cools more slowly as a result
  • žThis shifts the max cooling rate to the top of the fog bank
  • žThis results in the fog becoming thicker and lowering vis further

žžLanding Problems

  • žOn approach this is what you see
  • žIn the flare this is what you see

žADVECTION FOG

  • žMoist air moves over colder ground or water
  • žThis fog is associated with horizontal air mass movement or advection
  • žThe surface over which it moves causes the change in temp
  • žThis is referred to as advective cooling
  • žExamples of this occurrence is mild humid air moving over snow covered ground

žAdvection Fog

  • žIt also commonly occurs along the coastal areas where warm moist air moves off the ocean over colder land
  • žDeepens with winds up to 15 kts
  • žDepends on the wind to exist (5-15 kts)
  • žMore than 15 kts tends to lift it into low stratus
  • žMoves in rapidly with the wind day or night and more persistent than radiation fog

žž Advection Fog

  • žA characteristic of the coastal areas of southern California in summertime is advection fog
  • žIt forms as warm, dry air from over the land is moved over the much cooler ocean.
  • žThe cold water chills the air to dew point, resulting in low clouds and fog.

žUPSLOPE FOG

  • žMoist stable air cooled adiabatically as it moves up sloping terrain
  • žDepends on wind to exist (5-15 kts)
  • žMixing of the layers as air is forced up can deepen the fog
  • žVery dense and can exist at high altitudes along the upsloping terrain
  • žUnlike radiation fog it may form under overcast skies
  • žOnce the winds stops the fog dissipates

žUPSLOPE FOG

  • žTerrain temp will modify the cooling rate
  • žVery persistent
  • žCovers a wide area
  • žObscures hills and mountains
  • žIf a downslope wind develops fog will dissipate
  • žThis fog is found along the west slope of the Cascades, east slope of the Rockies and east slope of the Appalachian mountains

žžPRECIPITATION INDUCED FOG FRONTAL FOG

  • žWarm rain or drizzle falling through cool air
  • žEvaporation from the precip saturates the cool air and “poof” fog
  • žAssociated with warm fronts mostly
  • žMay also form along cold fronts and stationary fronts
  • žLittle or no wind
  • žExtra hazards to look for are icing, turbulence and thunderstorms

žPRECIPITATION INDUCED FOG FRONTAL FOG

  • žVery persistant
  • žCovers a wide area
  • žMostly occurs with warm or stationary fronts
  • žFog forms on the cool air side of the front
  • žAdvective winds may spread the fog into other areas
  • žFormation ends when the precip stops
  • žThe fog may persist for several hours after precip stops however

žFRONTAL FOG

  • žThis is an example of frontal fog, forming in southern Indiana as a warm front was encroaching.
  • žWarm and humid air was moving north, and running into cooler air.
  • žFrontal fog is a result of contact cooling between two dissimilar air masses
  • žWhile referred to as Frontal Fog it is really a form of Advection Fog

žICE FOG

  • žOccurs when temp is below freezing and the vapor sublimates directly into ice crystals
  • žConditions are similar as they are for formation of radiation fog
  • ž-25º F or colder so usually found in arctic region or colder winter spots

žSTEAM FOG

  • žAlso known as Arctic Sea Smoke
  • žExtremely cold and dry air flows over warmer water
  • žEvaporation and heating from the water causes a rise in humidity
  • žHeating from below creates instability
  • žAdditionally vapor pressure is high next to the water surface but low in the dry air above
  • žThis sets up a vapor pressure gradient
  • žThis causes streamers to rise up giving the appearance of steam
  • žAlso occurs after a rain on a wet highway
  • žLow stratus clouds
  • žhard to predict bases
  • žscud running not advisable

žSTEAM FOG

  • žMost types of fog form in stable atmospheric conditions.
  • žThe exception is steam fog, shown in this picture of Maligne Lake, Alberta, Canada, just after sunrise in late summer.
  • žThe land cools off overnight while the water retains heat from the summer day.
  • žAs the cooled air slips over the lake, heat and moisture are added from below, resulting in a fog that twists and writhes– hence the term “steam fog”.

žSTEAM FOG

  • žThis type of fog may be persistent
  • žThe larger the lake the more persistent and the more widespread
  • žLow level convection must be present for formation
  • žAdvective winds may spread the fog downwind

žMIST

  • žVisibility from 5/8 to less than 7 statute miles
  • žLower Relative Humidity than fog at about 95-99%
  • žGenerally not as restrictive to visibility

žHAZE AND SMOKE

  • žHaze – dry particles not classified as dust or something else
  • žOccurs in stable air
  • žUsually only a few 1000 feet thick but may extend as high as 15,000 feet
  • žOften associated with an inversion which gives it a definite top
  • žHaze may lead to the illusion that something is farther away than it really is
  • žSmoke forest fires, industrial areas
  • žBoth can be bad under a temp inversion
  • žCan cause visual illusions as well

žBLOWING PHENOMENA

  • žPrecip- drizzle, rain, snow
  • žSnow however may present additional problems
  • žMay cause white out conditions or
  • žFlat light

žFlat Light

  • žFlat light is an optical illusion, also known as “sector or partial white out.”
  • žIt is not as severe as “white out” but the condition causes pilots to lose their depth-of-field and contrast in vision.
  • žFlat light conditions are usually accompanied by overcast skies inhibiting any good visual clues.
  • žSuch conditions can occur anywhere in the world, primarily in snow covered areas but can occur in dust, sand, mud flats, or on glassy water.
  • žFlat light can completely obscure features of the terrain, creating an inability to distinguish distances and closure rates.
  • žAs a result of this reflected light, it can give pilots the illusion of ascending or descending when actually flying level.
  • žHowever, with good judgment and proper training and planning, it is possible to safely operate an aircraft in flat light conditions.

žWhite Out

  • žAs defined in meteorological terms, white out is when a person becomes engulfed in a uniformly white glow.
  • žThe glow is a result of being surrounded by blowing snow, dust, sand, mud or water.
  • žThere are no shadows, no horizon or clouds and all depth-of-field and orientation are lost.
  • žA white out situation is severe in that there aren’t any visual references.
  • žFlying is not recommended in any white out situation.
  • žFlat light conditions can lead to a white out environment quite rapidly, and both atmospheric conditions are insidious: they sneak up on you as your visual references slowly begin to disappear.
  • žWhite out has been the cause of several aviation accidents in snow-covered areas

žSelf Induced White Out

  • žThis effect typically occurs when a helicopter takes off or lands on a snow-covered area.
  • žThe rotor down wash picks up particles and re-circulates them through the rotor system.
  • žThe effect can vary in intensity depending upon the amount of light on the surface.
  • žThis phenomenon can happen on the sunniest, brightest day with good contrast everywhere.
  • žHowever, when it happens, there can be a complete loss of visual clues.
  • žIf the pilot has not prepared for this immediate loss of visibility, the results can be disastrous.

žBLOWING PHENOMENA

  • žThe Haboob was covered in the wind chapter
  • žBlowing dust, sand
  • žWinds need to be at least 15kts to pick up your common variety dust
  • žSettles out at the rate of 1,000ft/hour
  • žUsually 3,000 to 6,000 AGL but can extend upwards to 15,000

žVOLCANIC ASH

žVOLCANIC ASH

žVOLCANIC ASH

žVOLCANIC ASH

žOBSCURATION

  • žSurface based phenomena
  • žClassified in 8ths and vertical visibility
  • žRestricted slant range vis
  • žCeiling may be noted but once below it horizontal vis may be severely restricted

ž

 

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