u7 Flashcards
what are mountain waves
oscillations on the leeward side of a mountain caused by disturbances in horizontal airflow from the mountains in the way
where is mountain waves most severe
downdrafts is most severe near the top of the mountain (5000 FPM)
can pilots always see mountain waves
when air is moist = clouds form = visual indicator that mountain waves are here
air is dry = no clouds = can’t see visual indicator
conditions to form a mountain wave: wind direction, speed, stable/unstable airmass aloft
- direction: must be 30º perpendicular to the mountains
- speed: at least 25KT perpendicular to mountain
- wind aloft must increase with height
- need stable airmass aloft
what is stable air mass over the mountains needed for mountain waves
it encourages oscillations
- wind tries to rise, stable air mass says no and pushes air down, repeat
average total distance from mountain to end of mountain waves
150 NM
an unstable atmosphere will result in a ____ mountain wave length
longer
the faster the wind, the _____ the wave length
longer
mountain waves near the surface have ______ amplitudes because of _____
small
friction
unstable atmosphere results in a mountain wave with _____ amplitude
small
a large mountain will generate mountain waves that have _____ amplitudes
large
can you fly over a lenticular cloud?
no because wind from the mountain wave extends to the tropopause so you can’t fly over because hella turbulence at top of lenticular
if you must pass through an area with roll clouds, where do you fly
over or around, but never beneath
what does a cap cloud indicate
strong downdraft
can mountain waves tell us the intensity of the turbulence
no just tell us position of wave crests and rotors, but nothing about how strong the waves are. just assume its always strong turbulence
flying towards mountain, your ground speed ______, experiencing mountain waves for ____ time, feel ____ bumpy turbulence
decreases
longer
less
flying away from mountain, your ground speed ______, experiencing mountain waves for ____ time, feel ____ bumpy turbulence
increases
shorter
more
GFA will indicate mountain wave activity when turbulence is ____ (level)
moderate or severe
when flying into a mountain wave, the altimeter will read ______
higher than you actually are becase wind speed increases = drop in pressure = alt thinks ur higher
anabatic wind vs katabatic wind
anabatic wind: sunny side of mountain heats up so updrafts
katabatic wind: shady side of maountain cools down so downdrafts
what is galcier wind
extreme katabatic wind from cooling
what are funnel winds
wind through valley: small zone = drop in pressure = increase wind speed
it’s recommended to fly _____ ft or ___% higher than mountain range at a ___º angle
3000 ft
50%
45º
what is convective/thermal turbulence
hot pockets of air rise (updraft), expand, cool, form clouds and cool air falls from the side of the cloud downwards (downdrafts)
how to avoid convective/thermal turbulence.
fly over the clouds
what is mechanical turbulence
smooth air strikes ground objects (home, terrain) = friction = turbulence
what is frontal turbulence
turbulence caused by friction between two fronts or when one front is moving really fast
what is orographic turbulence
turbulence from air currents along mountains (leeward side has strong downward currents)
T/F: mountain waves are stationary
true
what speed should be my limit when flying through MWT
Va
what is increased vs decreased-performance wind shear
increased-performance = headwind increases = more lift
decreased-performance = tail wind increases = less lift
when do you report low level wind shear within 1500 AGL
when pilot reports a loss or gain of IAS of 20 KT or more
causes of low-level wind shear
low level jet
nocturnal inversion
microbursts
virga
funnel cloud
what is virga
rain that falls brings cold air with it
rain falls into dry air below
rain evaporates into dry air
cold air still descends downwards = strong downdraft
what is clear air turbulence
high level turbulence from jet stream aloft
light, moderate, severe vs extreme turbulence
light - slight changes in altitude, less than 15 KT airspeed flux
moderate - stronger bumps but plane still in control
severe - large changes, momentarily out of control, over 25 KT airspeed flux
extreme - can’t control plane its getting tosses around, maybe even structural damage
explain the Coriolis force in terms of air circulation
- air doesn’t fly straight north/south from high to low pressure because earth rotates
- in northern hemisphere , air flow is deflected right due to earth rotation
how the coriolis effect affects wind flow ALOFT
causes resultant wind to flow parallel to isobars
what is the buys ballot law
if you stand with your back to the wind in the northern hemisphere, the low pressure is always on the left and the high pressure on the right
why is arazona always hot desert?
permanent high pressure zone - no clouds, always direct sun
climbing to high altitudes, winds ____ and ______
descending to surface, winds ____ and _____
veer and increase
back and decrease
why is wind parallel to isobars at high altitudes
because no friction
how much do wind tend to back and decrease in speed when flowing over ocean, small grass terrain, city rough terrain
ocean = back 10º and slows slightly
grass hill = back 20º and slows more
city = back 40º and slows most
i’m flying low from a city to the ocean. how will the winds change?
LESS friction
- winds veer 30º to an angle close to the isobars
- winds speed up
i’m flying low from ocean to flat land. what happens to the winds
MORE friction
- winds back 10º further from isobars
- winds slow down
at night, surface winds tend to ____ and _____
back and decrease
which direction does the wind flow at night on the coast?
land to sea
which way does the wind flow during the day on the coast?
from sea to land
what are rossby waves
as the jet stream flows from west to east, it can develop (rossby) waves which can result in small low/high pressure systems detaching from jet stream and moving around globe
the polar jet stream moves ____ during winter and ____ during summer
south (becomes stronger)
north (weaker)
why does the sub-tropical jet stream (STJS) move less than the polar front jet stream (PFJS)
smaller temperature difference between ferrell and hadley cell than ferrell and polar cells
the source region of an airmass always an area of ____ pressure
high
which air masses are most common in canada (from north to south) and what seasons do they form in?
cA - winter
mA - summer and winter
mP - summer and winter
mT - summer
why don’t we see cP and cT air masses in canada
cP made in canada and moves downwards to USA
cT only made in few locations like arazona and even if it tries to move upwards towards canada its blocked by rockey mountains
mA location in winter vs summer
winter - mA along coast
summer - mA in central canada because starts as cA but passes over lakes before hitting central canada so it turns into mA
what does it mean for a weather chart to have an airmass labeled as cAk
cA = continental arctic
cAk = moves to new region that’s warmer on the surface so the bottom of this airmass is colder than the surface below
at the tropopause, the temperature of warmer air masses (mT and mP) will be colder than the cold airmasses (cA and mA). why
because warm air masses reaches higher into troposphere so more adiabatic cooling
the weather that happens at a front is determined by:
___ and ____ of the warm air mass
____ of the cold air mass
stability and moisture
speed
cold front moves ____ so the bad weather lasts for a ___ period of time
fast
short
cold front causes the wind to _____
veer
bad weather _____ the cold front
behind
does a warm front or cold front have worse weather typically
cold front
because has a much steeper slope for air to rise = faster rise = more clouds/precipitaiton
cold front causes the wind to _____
veer
what is an occluded front / trowal?
a cold front catches up to a warm front , overtaking it and undercutting the warm front from behind. this forces the warm air to be pushed above the joined cold air mass
the clouds ahead of the trowal is similar to a ____ front, and the clouds behind the trowal is similar to a ____ front
warm
cold
what is the weather like at a stationary front
neither airmass is moving so there’s clouds and prolonged precipitation
frontogenesis vs frontolysis
genesis = form a front
lyrics = front dissipating because weakened
what is frontal fog
a warm front produces rain, it falls into cold air below. the cold air becomes saturated and results in fog
why can thunderstorms be formed during a fast moving cold front?
cold dense air moves fast = warm air ahead of it is forced to rise violently
if the warm air is moist and unstable, a squall line of thunderstorm can develop along here
stable vs unstable frontal waves
stable = there’s a wave but it doesn’t develop further
unstable = deepening waves causes the cold front to catch up to the warm front and forms a trowel
two conditions for icing to occur
visible moisture (clouds/rain)
OAT below 0ºC
three types of airframe icing
- rime ice = instantaneous freezing of small super cooled water droplets
- clear ice = large supercooled drops slowly freeze and wrap around the wing
- mixed ice = rime + clear
ice forms the most when water drops are ____, airfoil shape is ____ and plane speed is _____
large
thin
fast
differences between ice intensity: trace, light, moderate, severe
trace = can see but not hazard (unless encountered for +1h)
light = might be a hazard if encountered for over 1h
moderate = accumulates quick enough to be a hazard so must use de or anti-icing. may need to divert.
severe = too much that de or anti-icing is useless. will need to divert
how does ice make worse aerodynamics
- less lift and thrust because of turbulence and separated flow
- more drag = need more power to sustain flight
- propellers are thin so accumulates ice easy = less power
some effects of plane icing
- increase stall speed
- trim less effective because thinner than regular wing so collects more ice
- asymmetric vibration of prop
- damaged flaps
- fuel vents blocked
- pitot blocked
- worse radio reception
what temperatures does clear ice vs rime ice form
clear = 0-10ºC
rime = -10 to -20ºC
why does cold soaked fuel occur
wing itself is super cold because of the cold fuel
when plane descends into warm climate with lots of moisture, when the moisture touches the cold wing, frost forms
i have impact icing over my air filter outside so i turn on carb heat to bypass this. how must i change my mixture setting?
carb heat= hot air = less dense = mixture becomes rich with less dense air
so must lean mixture
why should i definitely avoid flying in a winter warm front?
because freezing rain can happen
what is aerodynamic heating
increasing temperature of planes skin from the compression and friction as the plane moves through air
is aerodynamic heating enough to de-ice a plane?
no, if the ice is already on the plane, aerodynamic heat cannot remove it
but if there’s no ice on plane and once you’re going really fast, you won’t form any
3 ingredients to form a thunderstorm
- high moisture and high dew point
- steep lapse rate
- lifting agent
3 stages of thunderstorm
- cumulus/developing stage
- mature stage
- dissipating stage
the ____ the lapse rate, the quicker the vertical development of thunderstorms. why?
steeper
parcel of air rises faster when steep ELR because greater temperature difference
the _____ the troposphere, the more room for vertical development of storm
higher
the ____ the dew point, the more vertical depth of clouds formation. why?
higher
lower cloud base = quicker releases of latent heat = that parcel of air warms up a bit more = can continue to rise further = larger thickness of cloud
a squall line is ___ of a fast moving cold front
ahead
for lightning to form, there must be an ________ between two objects.
the electrons flow to the ___ charge to form lightning
electrical potential difference
positive
the highest probability of lightning to hit a plane at an altitude where the temperatures are between ____ to ____ ºC
-5 to 5ºC
a supercell thunderstorm results in the downdraft _____ of the updraft
ahead of
avoid flight near thunderstorms within ___ NM
20 NM
T/F: you can tell how severe a thunderstorm is by looking at it
FALSE
what is radar attenuation for thunderstorms
sometimes radar only picks up one side of rain showers, and doesn’t catch the other side of the storm (even if it’s heavier)
what is virgo
rain that evaporates before reaching ground but the downdrafts still continue to reach ground
key ingredients for fog
high moisture/relative humidity
condensation nuclei
light surface winds
cooling process
if the temp-dew point spread is ______ and _______ = anticipate FOG
3º or less and dropping
what is radiation fog
at night, land cools -> close to dew point -> radiation fog
especially in valley, it’ll collect a pool of cold air
what is advection fog
horizontal movement of warm, moist air over cold land = cooled from below = fog
what is upslope fog
moist air moves up rising terrain = expands and cools = condense into fog (because it’s still resting on the ground)
what is frontal fog
precipitation from warm front falls into colder air below = rain evaporates into cold air as stratus clouds (above ground) or fog (on ground)
what is steam fog
cold dry air flows over a body of water = cold air moves with the warm moist air over water = moist air cools until the excess water vapour condenses and fog forms
what is ice fog
when temperature less than -30ºC and exhaust from jet engines when doing run up on ground
when is it considered mist vs fog
mist (BR) if visibility greater or equal to 5/8 SM
fog (FG) if visibility less than 5/8 SM
