Weather Flashcards
What is the composition of the Atmophere?
78% Nitrogen, 21% oxygen, 1% other gasses
Height of the troposphere?
55K over equator, 28k over poles, 36k over USA
Where is standard lapse rate?
Troposphere
Where is isothermal lapse rate?
Tropopause
Where is inversion lapse rate?
Stratosphere
Where is the jet stream?
Just below tropopause
Average height of tropopause in USA?
36k
Characteristics of stratosphere
Above tropopause
has temp inversion
flying is smooth with excellent vis
standard temp lapse rate
2*c per 1000’
Average PSI at sea level standard day
14.7
How does pressure change as alt increases?
always decreases
2 units of atmospheric pressure
in of hg or millibars 15c or 59f
Station pressure definition
atmospheric pressure measured directly at an airfield or other weather station
sea level pressure
pressure measured if the station would be at mean sea level
what are ridges
high pressure good wx
what are troughs
low px bad wx
what is the adjustable part of an altimeter called
kollsman window
Temperature affect altimeter error how?
cold air then normal plane is lower
warm air than normal plane is higher
Temp dev on altimeter error
11*C causes 4% Error
Pressure change on altimeter error
high to low lookout below
low to high plenty of sky
Indicated altitude definition
alt as read on altimeter
absolute altitude
agl alt
true alt
alt referenced to mean sea level
pressure alt
alt above a standard datum plane
density alt
pressure alt corrected for non standard temperature deviations
What is density alt measure
aircraft performance
pennant
single barb
half barb speeds
50
10
5
parts of station model
wind direction and speed
temp and dew point
sea level pressure
pressure change
sky cover
isobar definition
lines of equal pressure
how far are isobars spaced on chart
4 millibars
close isobars means what for winds and illustrate what
the pressure gradient force, the closer the isobars are together the higher they will be and higher wind
Gradient winds definition
winds flow parallel to isobars due to coriolis force and turns air to the right
found above 2000’
surface winds definition
found below 2000 agl friction, pressure gradient, coriolis all balance and winds flow at 45 across isobars
Average height of jet stream
30,000 ft
average wind speeds for jet stream
100-150 but can be as high as 250
size of jet stream
1000-3000 miles long
100-400 miles wide
3000-7000 ft deep
Local winds definition
systems tens of miles across to long thin geographic areas
like mountain ranges
what is sea breeze
land heats fast, air rises and cold ocean air moves in to fill it 15-20
land breeze
land cools faster than water and air flows from land to ocean at night
valley wind
day mountain slopes warmed and warms air which begins to rise. cool air settles down to the valley floor and pushes warm air up the mountain
mountain wind
at night the cool mountain cools surrounding air which flows downhill
dew point definition
temp where saturation occurs
Relative humidity def
percent of saturation of air compared to max amount the air can hold at that temp
3 characteristics of precipitation
showers, continuous, intermittant
showers definitions
starts, stops, changes intensity or sky conditions rapidly, associated with cumuliform clouds
continuous definition
stady and changes intensity gradually, associated with stratiform clouds
intermittent def
stops and starts at least once during the hour
types of precipitation
drizzle, rain, frozen
low clouds def
surface to 6500 agl
can produce faster icing
middle clouds
form between 6500 to 20K
prefix alto
vis can be poor icing common
high clouds
20000 to 40K
cirro or contain word cirrus
no precip or icing hazard
CB clouds
thunderstorms with heavy rain and mod turbulence
Nimbostratus
heavy steady rain
What is stable atmosphere
cold air lifted and then sinks back down to the ground
What is unstable atmosphere
warm air lifted and continues to rise when lifting action removed
Neutral stability
air that has the same temp as surrounding air remains at the point where lifting was removed
4 methods of lifting
convergent
frontal
orographic
thermal
flight conditions for stable atmosphere
cloud type - stratus
turbulence - smooth
visibility - poor
winds - steady
precip - steady
icing - rime
Flight conditions for unstable atmosphere
cloud type - Cumulus
turbulence - rough
visibility - good
winds - gusty
precip - showery
icing - clear
Air mass definition
large body of air that has essentially uniform temp and moisture in horizontal plane
air masses are named by
moisture content, location, and temp with location most important
front definition
discontinuity that forms between two adjacent air masses
weather on either side of front is called
frontal zone
3 characteristics of fronts
always in trough of low px
cold fronts move faster than warm
frontal passage accompanied by 90* shift in wind
shallow fronts
produce cloudiness and steady precip
steep fronts
produce showers and narrow bands of cloudiness
cold fronts
produce thunderstorms
wind shifts from SW to NW
Squall lines
line of violent thunderstorms dotted and dashed purple lines
50-300 miles ahead of cold front parallel
Warm fronts
Warm air overrides cold air causes cloudiness and steady precip up to 500-700 miles ahead of surface front
winds shift from SE to SW
Stationary front
wind has 180 shift
Occluded front
cold front overtakes warm front
type depends on which temp stays on ground
180* wind shift
most severe weather 100 miles south to 300 north of frontal intersection
Turbulence intensity classifications
light
mod
severe
extreme
Duration of turbulence
occasional less than 1/3
intermittent- 1/3 to 2/3
continuous- more than 2/3
4 Causes of turbulence
thermal
mechanical
frontal
wind sheer
Clear air turbulence
usually in jet stream although any wind shear is CAT
Thermal turb
also called convective
mechanical turb
caused by passage of wind over obstructions
mountain wave turb
winds blowing perp to mountain form standing waves
best determined by clouds
rotor cloud
downwind and parallel to range
cap cloud
covers mountain and dows not move
lenticular cloud
form on leeward side of mountain from standing waves
mountain wave turbulence intensities
50 knots at peak - extreme
up to 150 miles downwind - severe
up to 300 miles downwind - moderate
how to avoid mountain wave turbulence
circumnavigate
fly 50% higher than peak
avoid all clouds
approach range at 45*
2 main groups of icing
structural and engine
icing types structural
clear, rime, mixed, frost
engine icing
compressor icing and induction icing
icing requirements
visible moisture
supercooled water
air and skin temp below freezing
clear icing characteristics
0 to -10*c
large drops freeze slowly and assume shape of airfoil
cumulus clouds and unstable conditions
rime icing characteristics
-10 to -20*C
small drops freeze instantly
statiform clouds
mixed icing
combination of clear and rime
-8 to -15*c
Frontal icing warm front
rime icing
low rate of accumulation and stratoform clouds
frontal icing cold fronts
cumuliform clouds
clear icing
high rate of accumulation
frontal icing occluded front
mixed clouds
mixed icing rime clear and mixed
rapid and heavy accumulation
aerodynamic effects of icing
changes stall AOA
Performance effects of icing
decreases lift thrust range
increases drag weight fuel consumption and stall speed
Other effects of icing
pitot static system
inhibits control surface movement and antenna transmission
Icing conditions
visible moisture
0 to -20*C
How to get out of icing
climb or descend, anti ice or deice
Types of antiice or deice equip
fluid
mechanical
heat
fluid deice
lowers freezing point of water
mechanical deice
rubber bladders on leading edge of airfoils
Icing intensities reported by PIREP
trace
light
mod
severe
prevailing visibility def
equaled or exceeded throughout over half of the horizontal circle, in statute miles and need not be continous
slant range vis
distance on final which runway was in sight
must be reported on PIREP
Runway visual range RVR
distance seen looking down runway from approach end
reported in feet or meters
Obscurring phenomena
reported when visibility less than 6 miles
fog
haze
smoke
rain
sky coverage
reported in eights
ceiling
lowest broken or overcast layer in AGL
Fog Definition
visible layer of moisture with vis less than 5/8 mile
3 requirements for thunderstorm formation
moisture
unstable air
lifting action
Thunderstorm hazards
turbulence
gust front
roll and wall clouds (wind shear)
hail
lightning
tornado
microburst size
only 1/4 to 2.5 miles wide
5-10 minutes
from cumuliform cloud
how to detect microburst
virga
rain shaft
severe thunderstorms
radar
low level wind shear alert system
pirep
surface analysis charts
depict pressure centers, fronts, precip lines, not a forcast
forecast prognosis charts
predicts positions of fronts, pressure centers, forecast wx
nexrad radar
detects showers, tornados, hail size and location, areas of wind shear, gust fronts, microbursts
satellite imagery types
infrared and visible
sigmets
advise of potentially hazardous significant meteorological information other than convective activity
convective sigmets
used only for thunderstorms, tornados, hail
airmets
conditions of lower intensity than sigmets
3 types of airmets
sierra (seen)
Tango (turbulence)
zulu (icing)
When is atc required to solicit pirep
ceiling at or below 5000’
vis less than 5 miles
thunderstorms
light icing or greater
wind shear
mod turbulence
when are pilots required to submit pirep
unusual forecast wx
wx on ifr
missed approach due to wx
wind shear
volcanic activity
laser activity
birds
