Aviation weather Flashcards
what is ideal air
lacks moisture. N2 78%, O2 21% and other 1%
air in coastal regions
water vapor 5% other 1% nitrogen 74% and oxygen 20%
Characteristics of troposphere
temp lapse rate. avg height in mid latitude 36000’. wind speed increase with altitude highest in trop. thicker at equator and thinner at poles (solar radiation). wx occurs here. unstable layer.
characteristics of tropopause
non continuous layer. abrupt change in temp lapse rate. jet streams are located in the breaks. avg depth no more than 1000’. turbulence due to strong windshear from jet streams
stratosphere
isothermal layer. thicker. wind speed decreases with altitude.
isa
29.92” of hg or 1013.25 hpa/mb 15deg c or 59 f. aircraft instrument are calibrated. standard for wx parameters. aircraft performance.
air desity
high elevation - density decreases. high temperature - density decreases. humidity increases - density decreases.
adiabatic
temp change by expansion and contraction with no heat added to or removed from the system.
freezing level
level at which temp is 0 degree c
temperature variation
LSDTA (lsd taste awful) latitude - high temp at equator
Seasonal- tilt of the earth. Diurnal variation- temp change during day and night. Topography- dessert semi arid land compared to vegetation or water bodies. Altitude- temp lapse rate 2 degree c per 1000’.
inversion
inverted temp lapse rate. increase in temp with increase in altitude.
surface based and aloft inversion
if the base is at surface then its called surface based inversion if not at surface then called aloft.
when does ground based inversion occur.
clear cool calm nights associated with stable layer of air
hazards of inversion
PIT poor visibility, icing and turbulence
station pressure QFE
actual pressure at field elevation
Altimeter setting QNH
the sea level pressure value. indicates true altitude and field elevation.
pressure lapse rate
1” per 1000’ upto 10000’ MSL
how temperature effects pressure
cold air- pressure decreases faster in colder air since its more dense.
true altitude
actual height above mean sea level
absolute altitude
actual height above the ground
indicated altitude
altitude that the altimeter reads when set to the local altimeter setting. (MSL)
Altimeter errors
high to low look out below. high temp/pressure to low tem/ pressure TA is less than indicated altitude.
TA=field elevation.
pressure altitude
indicated altitude when set to 29.92” of hg, at or above 18000’MSL.
why use PA
to simplify high speed flight procedure. to calculate aircraft performance. a/c have pa limits for takeoff and landing also called flight levels.
what is density altitude
pa corrected for non standard temp
what affects density altitude
high temp = low air density = high da
high humidity = low air density = high da
high elevation = low air density = high da
effects of high da on aircraft performance
increased ground roll, climb reduces, decreased performance
isobar
line of equal pressure. wind flow nearly parallel ( surface friction). close together wind speed increases. found on surface analysis chart.
isotach
line of equal wind speed. on aloft chart
isotherm
line of equal temp. on aloft chart
contour
line of equal height. winds flow parallel. found on aloft chart. wind speed increases as spacing decreases.
convection
rising air
advection
horizontal flow of air
pressure gradient force
force that drives winds from high pressure to low pressure
coriolis force
caused due to earths rotation, more at poles zero at equator. causes clockwise rotation around high in northern hemisphere. winds deflected to right in NH. Winds in US are westerlies high altitude. surface friction reduces wind speed and cf effects. no effect above 2000’agl
low
area of low pressure surrounded by high on all sides.
wind flow- cyclonic or anti clockwise, upward and inward.may have pressure higher than 29.92” of hg. cold low- blizzards warm low-tropical storms.
wx in low
bad except when lacks moisture
leaning low
when upper level winds are fast and the low moves with wind. poor wx will move quickly from the area
general movement of low in us
west or south west to east or north east. if no upper level winds than no horizontal movement in low. poor wx will linger in that area.
trough
elongated low pressure area. associated with turbulence
high
area of relatively high pressure surrounded by low on all sides. can have pressure lower than 29.92”hg. clockwise, anti cyclonic, downward and outward.
wx with high
good wx
Movement of high
similar to low
ridge
elongated area of high pressure. turbulence due to wind shear.
wind shear
change in speed over a relatively short distance, time or altitude
vertical wind shear
change in speed per 1000’ change in altitude. climb and descent. primarily experienced in vicinity of trop. step up climb
moderate vws
6kts or greater per 1000’
severe wind shear
10 kts or greater per 1000’
horizontal wind shear
change in speed over a distance of 150Nm. primarily experienced during cruise
moderate hws
18kts or greater per 150nm
severe hws
40kts or greater per 150nm
land breeze
at night
sea breeze
at day
relative humidity
amount of water vapor present in the air to the amount it can hold at that temp. expressed as percent
what determines how much water vapor that air can hold
temp
dew point
temp to which air must be cooled to be 100 percent saturated
spread
temp - dewpoint always positive
change of state
melting freezing condensation evaporation sublimation and deposition
virga
rain that evaporates before reaching the ground. implies turbulence common in south west us because of dry air
supercooled water
water that does not freeze at 0 deg c, eg FZRA and FZDZ these drops increase the rate of icing.
supercooled water in abundance
0 to -10 deg c in stratiform clouds
0 to -15 deg celcius in cumuliform clouds
what is dew
is liquid that forms when surface temp of an object decreases to dew point
what is frost
forms when dew point is 0 deg or colder and temp is close to dew point
what does freezing rain indicate
warmer air above
what does ice pellets indicate
freezing rain at higher altitudes
what is stable air
air that resists vertical displacement
what determines stability
ambient lapse rate
when is air unstable
ambient lapse rate greater than 2deg c per 1000feet
characteristics of unstable air
cumuliform clouds, showery ppt, turbulent flying condition and good visibility
characteristics of stable air
stratiform clouds, smooth flying condition, poor visibility and continuous ppt
unsaturated cools at or dalr
3 deg Celsius per 1000 feet
dew point cools at
0.5 deg c per 1000feet
salr
cools slower than dalr
four families of clouds
low, middle high and clouds with extensive vertical development
what are high clouds made of
entirely ice crystals therefore contribute least to icing.
little or no turbulence problem.
middle cloud composition
primarily water drops may also have supercooled water droplets ice crystals when temp are below frreezing
whats an air mass
uniform temp and moisture content
what is a front
a boundary between the two air masses
types of fronts
cold, warm stationary and occluded
what is a cold front
when colder air takes over warmer air. often lies in a trough. has a steep slope. warmer air gets lifted above. bad wx lies on the side of the cold air.
warm front
when warmer air overtakes a cold air mass. shallow slope thus wide areas of ppt and cloudiness. bad wx ahead of the warm front where there is cold air.
stationary front
when neither air mass takes over.
occluded front
indicates frontal wave
formation of frontal wave
strong indication of poor wx. usually forms on slow moving cold front or stationary front, beginning stage of low pressure system usually develops into an occluded front
dry line or dew point front
moisture differences in air mass ex. dallas dry air from west and moist air from gulf of mexico. leads to thunderstorm and tornado
mountain wave formation
winds greater than 30 or 40kts, blowing perpendicular to the mountain and stable air on the lee side
where does mountain wave occur
on the lee side of the mountain, turbulence. can extend upto 5000feet above trop and 100 miles downwind of a mountain range
clouds associated with mountain wave
ciro cumulus standing lenticular, strato cumulus standing lenticular, alto cumulus standing lenticular and rotor clouds.(lowest under wave crest)
conditions required for icing
visible moisture and temperature 0 deg or colder
what are the intensities of icing
trace, light, moderate and severe
what is severe icing
the rate of accumulation is such that your system fails to remove it or it gets accumulated in weird spots like underside of a wing or aft of the leading edge.
what are the types of icing
clear rime and mixed
how is clear icing formed
large water droplets(cumulus clouds), difficult to remove, transparent.
rime icing how is it formed
small water droplets(stratus clouds), milky or opaque in appearance due to air being trapped freezes quickly easily removed, most frequently reported
mixed icing
combination of both small and large water droplets, irregular shape and difficult to remove
effects of icing on the aircraft
thrust decreases drag increases lift decreases and weight increases stall speed increases
when does frost forms
clear stable air with light winds
how does frost affect aircraft
produces roughness on the surface decreases lift by 30% and increases drag by 40%. prohibited to take off with ice snow frost on control surface, wings or props.
three conditions necessary for the formation of ts
lifting mechanism, unstable air and moisture
example of lifting mechanism
orographic lifting, front, convection, low pressure and surface convergence
types of thunderstorm
air mass and steady state
why are steady state thunderstorm more destructive
longer duration, associated with pressure systems
what are air mass thunderstorm
formed from convection ex florida afternoon shower short duration therefore less destructive in nature
three stages of thunderstorm
cumulus-updrafts. mature-updrafts and downdrafts beginning of rain on earth. dissipating- downdrafts
thunderstorm hazards
lightning, tornado, hail, microburst, icing, wind shear, turbulence, embedded cbs
what is a squall line
often develops ahead of a cold front. narrow band of bad thunder storm
what is severe thunderstorm
surface winds atleast 50 kts or greater and or surface hail 3/4 inches in diameter
cloud coverage
clear none. few 0-2/8 th of the sky, sct 3-4/8, bkn 5-7/8 th of the sky, ovc more than 7/8th and vv 8/8
what is ceiling
ceiling is defined as the height above earths surface of the lowest base of a cloud or any obscuring phenomena aloft classified as broken or overcast or vertical visibility into a total surface based obscuration.
low ifr
ceiling less then 500 feet and or visibility less than 1sm
ifr wx
ceiling less than 1000feet and or visibility less than 3sm
mvfr wx
ceilings 1000-3000feet and or visibility 3-5sm
vfr
ceilings 3000feet or more and visibility 5sm or more
when does fog form
when temp decreases and dew point increases
types of fog
radiation, advection, ppt induced, upslope fog ice and frontal fog
radiation fog how does it form
terrestrial radiation, clear cool calm nights restricted to land. winds greater than 5kts it will be lifted or dissipate
advection fog
warm moist air moves over cold surface(land or water), wind speed upto 15kts deepens it more than 15kts will lift it into low clouds
frontal fog
warm moist air gets lifted over a front
upslope fog
ex san antonio warm moist air from gulf moving over gradually rising terrain thus cooled adiabatically (Stable air)
ice fog
same like radiation fog when temp are -32cel or colder
