Let’s Get Started – Ground School: Weather
& Meteorology
Solar radiation
is short wave. It hits the earth and is
reflected back as long wave radiation.
Long wave is then absorbed by water vapor as latent heat.
Rising warm air at the equator creates a low. It then travels to the poles where it cools
and sinks, creating highs.
The atmosphere is thicker at the equator than at the
poles.
Air flows from areas of high pressure to low pressure
(wind). The strength of the wind depends
mostly on the pressure differential between the two areas, and partly on the
temperature differential.
The atmosphere consists of 78% nitrogen (N2),
21% oxygen (O2), and 1% trace gases.
Permanent trace
gases include Argon (AR), Neon (NE), Helium (HE),
Hydrogen (H2), Krypton (KR), and Xenon (XE).
Variable trace
gases include carbon dioxide (CO2), ozone (O3),
methane (CH4), sulphur dioxide (SO2), and water vapor (H2O).
Atmospheric layers:
1.
Troposphere:
Up to 20,000 feet, although this height often varies significantly. Temperature decreases with height, +20 oC
to -70 oC.
2.
Stratosphere:
20,000 to 160,000 feet. Temperature increases with height, -70 oC
to zero.
3.
Mesosphere:
160,000 to 280,000 feet.
Temperature decreases with height, zero to -100 oC.
4.
Thermosphere:
280,000 feet (50 miles) up to 350 miles or 500 km. Temperature increases with height, -100
oC to over 1000oC.
5.
Exosphere.
The transition
zones found between the strata are where there is a change in the lapse rate.
“Space” starts about 50 miles or 80 kilometers above the
Earth’s surface (at the beginning of the thermosphere). This is a slightly vague definition.
About 99% of the atmosphere is found within the first
forty kilometers above the surface. Half
of this is located within the first 5km, in other words, more than half of the
total volume of the atmosphere is found within the troposphere.
Lapse Rate –
The temperature change with height. The
defined Standard Lapse Rate is 1.98oC per 1000’ (in the
troposphere).
Most “weather” takes place in the troposphere. About 99% of the water vapor in the
atmosphere is found within the troposphere.
Troposphere:
-
Means “region of mixing,” has vigorous air
currents.
-
Temperature and water vapor decrease rapidly
with altitude.
-
Average temperature is -56oC.
-
Although we defined the upper boundary of the
troposphere to be around 20,000 feet, it can actually be quite a bit higher,
depending on the season and the location on earth. The height varies seasonally, and it is
higher in the summer than in the winter.
-
The tropopause is the boundary layer between the
troposphere and the stratosphere above it.
Stratosphere:
-
Temperatures increase as altitude increases, up
to zero.
-
Because the air temperature increases, it does
not permit convection, so weather that transits through the tropopause cannot
rise any further.
-
This lack of convection has a stabilizing effect
on thunderstorms.
-
The stratopause (formerly mesopeak) is the
boundary layer between the stratosphere and the mesosphere above it.
Mesosphere:
-
Temperature decreases as altitude increases.
-
Concentrations of ozone and water vapor are
negligible.
-
The chemical composition of gases at any given
altitude depends strongly on altitude.
Gases start to form into layers according to their molecular mass, so
lighter gases settle at higher layers than heavier gases.
-
The mesopause is the boundary layer between the
mesosphere and the thermosphere above it.
Thermosphere:
-
The temperature increases significantly with the
altitude, very rapidly.
-
Temperatures can get well over 1000oC. These temperatures are caused by intense
solar radiation.
-
This is the layer which hosts the northern
lights.
-
The thermopause is the boundary layer between
the thermosphere and the exosphere above it.
Exosphere:
-
Starts at about 500km.
-
The upper boundary is undefined. Perhaps between 1,000 and 10,000km, depending
on whom you ask.
-
Pressure is little more than a vacuum.
At altitude of approximately 150km, you start to enter
the altitude for satellites, and aerodynamic lift can no longer be used for
maintaining height.
Definition of Standard
Atmosphere:
-
At sea level.
-
+15oC.
-
Change of 1.98oC per 1000’ (the
standard lapse rate).
-
29.92” Hg or 1013.25 millibars/hectopascals.
-
1” drop in mercury per 1000’ increase.
-
Dry air, no humidity.
Pressure measurements:
-
Aviators use pressure of mercury (Hg) in inches.
-
Meteorologists use millibars.
29.92” Hg = 1.0 atm = 101.325 kPa = 1013.25 mb
Station Pressure
– The weight of air pushing down on a station, then the station “adds” an imaginary
column of air between the station and sea level, which translates the physical
reading to a theoretical reading that estimates sea level pressure at the
station.
With respect to temperature, the average surface
temperature of the station over the past twelve hours is what is used.
Isobars –
Lines on a weather chart that connect areas of equal pressure. Isobars are correct for sea level pressure. The standard is to have them 4 millibars
apart. Widely spaced isobars mean a
shallower pressure gradient and relatively light winds.
The standard airflow
tends to be
counterclockwise/upwards/inward around a low pressure system, and clockwise/down/outwards
around a high pressure system.
Pressure Gradient
– The change in pressure over a given distance.
Although warm air usually creates a low, and cool air
usually creates a high, remember that you always have to think in relative
rather than absolute terms, in comparison to nearby air. Also, other factors can come into play.
Pressure Systems
include highs, lows, troughs, ridges,
and cols.
High Pressure
Center:
-
Air is sinking.
-
In the northern hemisphere, air rotates
clockwise and gently flows outward and downward.
-
Also known as an anti-cyclone.
-
Large blue “H” on a weather map.
-
In general, is a region of subsiding air.
-
Suppresses the upward motion that is needed to
support the development of clouds and precipitation.
-
Commonly associated with fair weather and light
winds.
-
Can remain stationary for days at a time.
Low Pressure
Center:
-
Rising air rotating counterclockwise. This flow tends to increase as you move
toward the center of a low. Strong
inward and upward flow.
-
Also known as a cyclone.
-
On a weather map, it is a red “L”.
-
Air rises and becomes less dense as it rises.
-
Rising motions favor the development of clouds
and precipitation.
-
Lows usually tend to move quickly, perhaps 500
miles/day in summer and 700 miles/day in winter.
Trough:
-
Elongated area of low pressure.
-
Symbol is a long purple line.
-
Likely to bring about a wind shift at the
surface.
-
A trough can act like a weak front.
Ridge:
-
Sawtooth pattern on a weather map, although it
is quite rare.
-
Area of elongated high pressure.
Col:
-
A neutral region between two highs and two lows.
-
Weather at a col tends to be unsettled.
-
In the winter, expect fog.
-
In the summer, expect showers and thunderstorms.
Boyle’s Law –
At a given pressure, warm air will take up a greater volume than cold air. This greater volume will typically exert
itself by moving vertically upwards.
On cold winter days, when flying IFR, we need to factor
cold weather corrections into altitude calculations.
At a given altimeter setting, an airplane will be much
closer to a ground obstacle in the winter than it would be in the summer.
Turning the altimeter sub-scale down results in a lower
altitude.
If you set the altimeter (on the ground) in the Kollsman window and it shows a
difference of more than 75 feet from aerodrome elevation, you need to
re-calibrate it.
As you progress on a cross-country and keep adjusting
your altimeter, try to always use a setting from a station within 100 miles of
your position.
When flying towards a low, if maintaining what appears to
be a constant altitude on the altimeter, the aircraft will gradually descend
unless an altimeter correction is made.
From high to low, look out below!
The altimeter does not compensate for non-standard
temperatures! If terrain or obstacle
clearance is a factor, a conservative higher altitude should be flown to ensure
adequate clearance. “From hot to cold,
don’t be bold, or you won’t grow old.”
When the air temperature is above standard, density
altitude will be higher than pressure altitude.
Remember that higher density altitude means that the “air is less dense,” so the
aircraft will not perform as well at that higher temperature.
True altitude is our exact height above sea level. Cold temperatures cause the pressure level to
compress. Our indicated altitude must be
corrected for temperatures, especially for IFR or obstacle clearance! Use the left window in the E6B for
calculations of true altitude.
Rule of thumb for True
Altitude calculations:
Multiply
temperature variation from ISA (15oC) by 4 feet per 1000.’
The two main ways that the atmosphere is heated are
radiation (terrestrial, not solar) and convection.
The atmosphere is heated from the bottom up!
Variations in Heating:
-
Diurnal
variation: Day and night.
-
Seasonal
variation: Due to the axial tilt of the
Earth. A shallow lighting angle in
winter results in less heating, but there is a steeper lighting angle in
summer. Also, there are more hours of
daylight in summer.
-
Latitude: Closely related to seasonal variation,
although of course this is a constant factor rather than a cyclical one.
-
Topography: Land absorbs radiation faster than water, and
also releases heat more quickly at night.
Items such as vegetation, soil type, slope, and aspect can significantly
affect the amount of heating.
Methods of Heat
Transfer:
1.
Convection: Air near a warm surface is heated, and rises
due to its buoyancy. Different surfaces
(water, trees, and buildings) convect heat differently. Convection transports heat in the vertical
sense quite efficiently.
2.
Advection: Air is carried from one region to another by
wind. Air is then warmed by the surface
below. This moves heat laterally.
3.
Conduction: Heats layers of air that are in immediate contact
with the Earth’s surface.
4.
Latent
Heat: Heat energy that is stored in
water vapor. When water vapor rises and
condenses, the heat in the water vapor is released during condensation.
5.
Compression: When a large parcel of air sinks, it is
compressed. Pressure increases, and the
temperature increases.
6.
Turbulent
Mixing: Turbulence that is caused by
friction between the air and ground will create eddies with vertical
components. This will allow warm air
near the surface to be lofted into the atmosphere.
Atmospheric cooling causes things like clouds, fog, and
precipitation. This can happen through
radiation, advection, and adiabatic cooling.
Radiation Cooling:
-
After the sun sets, the surface continues to
radiate heat.
-
This causes the ground to cool, then air in contact
with the ground is cooled through conduction (heat passing from the air to the
colder ground surface).
-
Radiation cooling rarely has an effect beyond
the first few thousand feet above the Earth’s surface.
Advection Cooling:
-
Air is carried from a warm area to a cooler
area.
Adiabatic Cooling:
-
Rising air starts to expand, and this leads to
cooling.
-
This can happen near mountains, near fronts, and
in areas with a lot of convection.
-
This cooling occurs at different rates depending
on whether the air is saturated (with humidity) or not.
-
Unsaturated air will cool at the dry adiabatic
rate of 3oC per 1000’.
-
Once saturated, it cools at 1.5oC per
1000’.
-
Air with some humidity, if not yet saturated, is
still subject to the “dry” adiabatic rate.
Environmental
Lapse Rate – This is the observed actual change in temperature with a change
in altitude. This changes over time and
is not a constant value. It changes from
day to day, and even throughout the day.
Inversion:
-
Occurs when temperature increases as altitude
increases.
-
Air is very stable.
-
Acts as a barrier to vertical movement of air.
-
A common cause of surface based inversion is
radiation cooling from the surface on cool nights.
-
During a low level inversion, if the relative
humidity is high, expect smooth air and poor visibility due to haze, fog, and
stratus cloud.
Isotherm – A
line on a chart connecting areas of equal temperature. Usually dashed. May be darker for an important isotherm such
as 0oC.
Isothermal Layers
– When the temperature remains the same at different altitudes. Like an inversion, it gives rise to very
stable air.
Transpiration
– Moisture (water vapor) that is released by plants.
Sublimation –
When a substance changes directly from a solid to a gas. This is how dry ice and snow forms.
Deposition –
When a substance changes directly from a gas to a solid. This is how hoar frost is formed.
Dew Point –
The temperature that air must be cooled to in order to reach 100%
saturation. Knowing the dew point also
gives us a measure of how much water the atmosphere is currently holding. When the temperature is close to the dew
point, humidity is high. Also, the
higher the dew point, the greater the amount of moisture present.
As air warms up, it can hold more water vapor.
Relative Humidity
– The percentage of saturation of a parcel of air at that given temperature.
Adding moisture to the air (by evaporation or
sublimation) increases the relative humidity
and the dew point.
An adiabatic
parcel will not add or remove heat from the surrounding atmosphere. When such a parcel rises, it expands and
cools. When it sinks, it will be
compressed and warm.
Adiabatic Lapse
Rate – Theoretical, can be calculated.
If a dry parcel of air does not mix with the surrounding
air, then it can be considered adiabatic.
Dry Adiabatic
Lapse Rate (DALR) – 3oC per 1000’.
The change in dew point temperature:
-
The dew point also falls as the column of
unsaturated air rises.
-
Decrease in dew point temperature is 0.5oC
per 1000’.
-
Therefore, in a parcel of unsaturated air, the
temperature and dew point converge at a rate of 2.5oC per 1000’.
-
Use this for calculations of cloud base.
Saturated Adiabatic
Lapse Rate (SALR):
-
Accounts for latent heat released as water
condenses.
-
Once air has cooled to the dew point and starts
condensing, the air parcel cools more slowly because condensation releases energy.
-
1.5oC per 1000’.
Freezing level in feet above cloud base:
Freezing Level = (1000 x Dew point) /
1.5
Note that the dew point changes with altitude. A new dew point must be calculated at the
freezing level by decreasing the surface dew point by 0.5oC per
1000’ AGL.
Steep lapse rates lead to instability.
Precipitation - Occurs when condensing water droplets
become large and heavy enough to overcome lifting agents such as fronts &
updrafts.
Icing is worse near the top of a cumulus cloud.
Three types of
rainfall:
1.
Frontal.
2.
Relief.
3.
Convectional.
Frontal Rainfall:
-
Also known as convergent or cyclonic rainfall.
-
Caused by the convergence of two air masses
(fronts).
-
Warm front rainfall tends to be steady.
-
Cold front rainfall tends to be showery.
Relief Rainfall:
-
Also known as orographic rainfall.
-
Warm moist air is forced to rise over an
obstacle such as a mountain range.
-
This cooling causes condensation, forming clouds
and rain.
-
Most of the rain is on the windward side of the
mountain.
-
Mountains will also cause air streams to converge
and funnel through valleys.
-
Rainfall totals will increase when mountains are
parallel to the coast.
Convectional
Rainfall:
-
The ground surface is locally heated, adjacent
air expands and rises, convection rainfall occurs.
-
This heating occurs daily in summer.
-
Large cumulonimbus clouds are likely to form.
-
Rain cools the air as it falls, because some of
it evaporates as it falls.
-
The unstable conditions, possibly helped by
frontal or orographic uplift, force the air to rise in a strong vertical
updraft or chimney.
-
The updraft is maintained by energy released
through latent heat as water vapor condenses then freezes.
-
The top of the cloud is characterized by ice
crystals in an anvil shape.
-
The top of the cloud is flattened by reaching
the temperature at the troposphere.
-
When the ice crystals and frozen water droplets
(hail) become large enough they fall in a downdraft.
-
This downdraft reduces the warm air supply to
the “chimney” and will limit the lifetime of the storm.
-
These storms are usually accompanied by thunder
and lightning.
-
Ice crystals have a positive charge.
Snow forms under the same conditions as rain except that
the dew point temperatures are below freezing so the vapor condenses straight
to a solid (deposition).
Snow:
-
Ice crystals will form if there are small
particles present for them to form onto.
These may aggregate to form snowflakes.
-
Since warm air holds more moisture than cold
air, snowfalls are heaviest when the air temperature is just below freezing.
Sleet:
-
Starts off as ice/snow when upper air is below
freezing.
-
A lower air temperature as it is falling allows
it to partially melt.
-
Then it goes through another cold layer and
refreezes before it hits the ground.
Freezing Rain:
-
Droplets stay in liquid form as they fall but
are very close to freezing.
-
They then hit frozen objects or ground, and
freeze on contact.
Hail:
-
Frozen raindrops that are more than 5mm in
diameter.
-
Hail keeps circulating up and down through a
frozen layer until it is heavy enough to punch downwards, form a downdraft, and
fall to the ground.
-
Can occur anytime, but is most likely to occur
during summer and in cold fronts.
Stable Air – A
small change will be resisted and the system returns to its previous state.
Unstable Air –
A small change initiates a bigger change, and so on. Lifting actions in the atmosphere decrease
stability.
A rising (isolated) adiabatic parcel of air can only cool
at one of two rates:
-
Dry (unsaturated) adiabatic rate: 3oC per 1000’
-
Saturated (wet) adiabatic rate: 1.5oC per 1000’.
Stable Air:
-
Smooth flying.
-
Poor visibility.
-
Steady precipitation.
-
Layer cloud (stratus).
-
Ultimately ends in fog.
Unstable Air:
-
Bumpy flying.
-
Good visibility.
-
Showery precipitation.
-
Cumulus cloud.
-
Ultimately ends in thunderstorm.
If the layers of air closest to the surface are cooled,
we increase the stability of the atmosphere.
This can happen by radiation at night, or by influx of cold air (cold
advection).
Stability can also
be increased by warming air at higher altitudes:
-
Radiation cooling.
-
Warm advection aloft.
-
Large scale sinking of air.
Subsidence
Inversion:
-
Air mass sinks and compresses.
-
Upper part of layer sinks/compresses more
(relatively) than the bottom.
-
Upper part therefore increases in temperature
more than the air at the bottom.
-
Common in winter.
Things that enhance
unstable conditions:
-
Daytime radiation.
-
Warm air moving into a region (surface warm
advection).
-
Surface cold advection also. If cold air is warmed by a warm surface, then
it emulates the same behavior as if it had been warm air advecting.
-
Effects are enhanced if there is moist air near
the ground, and dry air aloft.
Dark earth absorbs more heat (solar radiation) than
lightly colored earth.
Cooling of the upper atmosphere:
-
Also causes instability.
-
If cold air moves into higher altitudes and causes
temperatures to cool faster than at the surface.
Different lapse
rates:
-
Steep: Temperature decreases rapidly with altitude
(leads to instability).
-
Shallow: Temperature decreases slowly with altitude,
fairly stable.
-
Inversion: Temperature increases with altitude, stable.
-
Isothermal
layer: Temperature stays constant,
stable.
If the environmental lapse rate is less than the DALR or
the SALR, stability is favored. In this
case, a parcel of air that attempts to rise will end up cooler than the air around
it.
Ways to cause heating
of air near surface:
-
Radiation:
Long wave from ground.
-
Conduction:
Warm air contacting cold.
-
Advection:
Horizontal movement of air.
-
Convection:
Unequal surface heating.
Lifting processes
that can cause instability:
-
Convection:
This happens due to unequal surface heating.
-
Convergence:
Excess air rises as pressure systems meet.
-
Mechanical Turbulence: Surface friction.
-
Orographic Lift:
Air moving up hills/mountains (anabatic/katabatic).
-
Frontal Lift:
Advancing air being pushed up by cold air on the bottom.
Four types of
stability:
-
Absolute
Stability: DALR and SALR are steeper
than ELR.
-
Conditional
Stability: ELR is between DALR and SALR.
-
Absolute
Instability: ELR is steeper than both
the DALR and SALR.
-
Potential
Instability: Instability would depend on
some sort of a trigger mechanism, such as lift.
An example would be when the air is initially stable and unsaturated,
but after becoming saturated, the lapse rate changes and “adds” heat. This situation somewhat resembles conditional
instability. Another scenario would be
an ELR that becomes steeper with altitude.
Layers of the sun:
-
Photosphere (main mass).
-
Chromosphere (similar to Earth’s atmosphere).
-
Corona (all the stuff well above the surface).
Solar Wind – Charged atomic particles coming from the
corona, moving quickly enough to escape the sun’s gravity. These solar particles interact with the
Earth’s magnetic field and with other particles in the upper atmosphere (aurora
borealis or aurora australis).
Sunspots:
-
Operate on an eleven year cycle (but varies from
nine to fourteen years).
-
Tied to the sun’s periodic/variable energy
output.
Solar Flare:
-
Occurs when the area above a sunspot brightens
and releases huge amounts of energy in the forms of ultraviolet, x-ray, and
radio electromagnetic radiation, and high speed solar particles.
-
Can yield spectacular aurora, interfere with
radio and television reception, and knock out satellites and power grids.
Earth’s axis is tilted at 23.5o with respect
to Earth’s orbital motion.
The equator is equidistant from each pole at every point
along the equator.
Summer Solstice – Has the most hours of daylight of any
day of the year, usually around June 21st.
Winter Solstice – Has the least hours of daylight,
usually around December 21st.
Equinox –
There are two of them, usually around March 21st and September 21st. On these two days, the sun is directly “over”
the equator. Spring is the vernal
equinox, and fall is the autumnal equinox.
At the two solstices, the sun is above 23.5o
latitude. One of the poles will
experience 24 hour daylight, and the opposite will experience 24 hour darkness
(this 24 hour darkness/light actually lasts for several days).
Atmospheric
Scattering – As sunlight and radiation passes through the atmosphere,
particles of gas and dust are able to scatter it. At the equator, there is not much scattering,
as light and radiation passes straight through the atmosphere’s normal
depth. However, light and radiation
reaching the poles does so obliquely, passing through the equivalent depth of
many atmospheres.
Cloud – A visible aggregate of tiny water droplets and/or
ice crystals. Air must be saturated for
clouds to form.
Air can be saturated in three ways:
1.
By lowering the air temperature to the dew point
temperature.
2.
By adding water vapor into the air.
3.
By mixing warm moist air to cold air.
Steam Fog –
When you have a parcel of air that has some water vapor, and you evaporate more
water into it, that becomes a cloud.
Okta – One
eighth of the celestial dome.
SKC:
Clear sky.
FEW:
1/8th or 2/8th.
SCT:
3/8th or 4/8th, scattered.
BKN:
5/8th to 7/8th, broken.
OVC:
Overcast, 8/8th, completely covered.
Ceiling:
-
Occurs with BKN or OVC, ie. more than half.
-
VFR pilots are not allowed to fly over BKN or
OVC, unless you have a VFR OTT rating.
-
Ceiling is VV, vertical visibility, on the TAF
or METAR.
-
Example:
VV003 = 300 feet.
-
Has a scalloped border on the GFA.
Clouds are
classified into four families based on altitude and vertical
development/appearance:
-
High:
Above 20,000 feet, with a top usually around FL400 in Canada but it can
be higher in other parts of the world.
Includes cirrus, cirrocumulus, cirrostratus.
-
Middle:
From 6,500’ to 20,000’, includes altostratus, altocumulus.
-
Low: Below
6,500’, includes stratus, cumulus, stratocumulus, nimbostratus, stratus
fractus, and cumulus fractus.
-
Vertical Development: Pass through two or all three of the above
categories, includes cumulus, altocumulus, towering cumulus, and cumulonimbus.
Cumulus clouds are always puffy or pillowy, and often
feature showery/inconstant precipitation.
Cumulus clouds frequently have roughly the same diameter, no matter what
their altitude.
Stratus clouds are flat clouds that feature constant
precipitation.
Nimbo clouds generate rain.
Cirrus (CI):
-
High and wispy.
-
Generally above 20,000’.
-
Sometimes called mares’ tails.
-
Made of ice crystals.
-
Generally appear in high pressure systems, warm
weather, and ahead of warm fronts.
-
Point in the direction of air movement at their
elevation.
Cirrostratus (CS):
-
Really good at producing halos.
-
Sheet-like, high level, composed of ice
crystals.
-
Tend to thicken as a warm front approaches,
signifying an increased production of ice crystals.
Cirrocumulus (CC):
-
Appear as a white sheet with a pebbly pattern.
-
Somewhat rare.
Altocumulus (AC):
-
Puffy, cotton ball.
-
On a warm, humid summer morning, they may be
followed by thunderstorms as the day progresses.
Altostratus (AS):
-
Layer cloud with no definite pattern.
-
Steely or bluish in colour.
-
Sometimes the sun or moon can be seen dimly
throughout.
-
Seem to make the sun look like it is behind
heavily frosted glass.
Stratus (ST):
-
Low layer cloud.
-
Resembles fog but does not rest on the ground.
-
No waves or patterns, gray.
Alto Cumulus
Castellanus (ACC):
-
Created from instability associated with air
flows having marked vertical shear and weak thermal stratification.
-
Can produce heavy precipitation.
Nimbostratus (NS):
-
Dark, low level clouds accompanied by light to
moderate precipitation.
-
Mostly water droplets, not ice crystals.
Stratocumulus
(SC):
-
Low, lumpy layer of clouds.
-
Sometimes accompanied by weak intensity
precipitation.
-
Stratocumulus on the windward side of a mountain
range may be super-cooled and may lead to icing.
Stratus Fractus
(SF):
-
Stratus cloud that has been torn by wind into
fragments.
-
May release drizzle.
Cumulus Fractus
(CF):
-
Stratocumulus torn by wind.
-
Can be differentiated from stratus fractus by
their more rounded tops.
Cumulus (CU):
-
Fair weather.
-
Appearance of floating cotton.
-
Have a lifetime of 5-40 minutes.
-
Given suitable conditions, can develop into
towering cumulus and then cumulonimbus.
Towering Cumulus
(TCU):
-
Growing cumulus cloud.
-
On the way to becoming a cumulonimbus.
-
Like a giant cauliflower in the sky.
Cumulonimbus (CB):
-
Much larger and more vertically developed than
fair weather cumulus.
-
Fuelled by vigorous convective updrafts that are
at times in excess of fifty knots.
-
Depending on the height of the troposphere and
the buoyancy of the updraft, the tops of cumulonimbus clouds can reach up to
60,000’.
Mammatus:
-
Powerful cumulonimbus clouds that may have
appendages protruding from the base.
-
Indicate that the atmosphere is extremely
unstable.
-
Severe weather possibly imminent.
Mountain Wave
Clouds:
-
Top:
Moist layer of air, lenticular clouds.
-
Middle:
Dry layer of air.
-
Bottom:
Cap cloud, rotor clouds.
Orographic Clouds
- Associated with mountains, develop when air is forced to rise by the Earth’s
topography. This can happen either prior
to encountering a ridge, or after.
Lenticular Clouds
– Form in the wave crest, very high and hundreds of miles long. Can look like a tortoise shell or like a
stack of pancakes.
Rotor Clouds
(roll clouds) – Form downward and below each wave crest. They are dissipating and forming at the same
time due to the rotation of air.
Cap Cloud –
Lie over the top of the mountain and extend partially down the leeward slopes,
indicating an extremely strong downdraft.
Contrails:
-
Cloud formed by the water vapour contained in
the exhaust of jet engines.
-
At high enough altitudes, the vapour turns
immediately to ice crystals.
-
Resemble a long thin line of cirrus.
Mountain Waves:
-
Oscillations on the lee (downward) side of a
mountain caused by disturbances in the horizontal air flow due to the impeding
terrain.
-
Can have speeds in excess of 5000 feet/second.
-
About 150 NM in length is common, and can be
much longer.
-
Most severe near the mountain or mountain
ridges, and at about the same height as the top of the summit.
-
Significant horizontal and vertical shear may
exist.
-
Average wave length is 8 NM.
-
A standing mountain wave is fairly stationary as
it propagates horizontally.
Conditions conducive to forming a mountain wave:
-
Wind direction must be within 30o
perpendicular to the mountains.
-
Wind velocity on leeward side must be 25 knots
or more.
-
Winds aloft increase with height.
-
Stable air mass layer aloft or an isothermal
layer or inversion near the mountain top.
Factors affecting wavelength:
-
Stability:
Higher stability makes shorter wavelengths.
-
Wind Speed:
Higher wind speed equals longer wavelengths.
-
Lateral Positioning of Ridges: Ridge spacing can also change the wavelength.
-
Ridges will need to be 5km apart.
Amplitude:
-
Half the vertical distance from the wave trough
to crest.
-
Varies with height above the ground.
-
Smaller amplitudes near the surface and near the
tropopause.
-
Larger amplitudes between 3000’ to 6000’ above
the ridge.
-
Generally, the greater the amplitude, the
shorter the wavelength.
Factors affecting amplitude:
-
Lower stability produces lower amplitudes.
-
Larger mountains produce greater amplitudes.
-
Ridges with widths similar to typically formed
wavelengths will produce greater amplitudes.
-
A sharp lee slope will produce greater
amplitudes.
-
Drops of greater than 3,000’ tend to produce the
largest amplitudes.
There must be sufficient moisture for clouds to form, so
lack of clouds does not always mean that it will not be turbulent.
Clouds that might indicate the formation of mountain
waves include lenticular, rotor, cap, and banner.
Lenticular clouds:
-
Typically from 20,000’ to 40,000’.
-
As the air in a mountain wave rises, it cools by
expansion and condenses out moisture to form the leading edge of the lenticular
cloud.
-
After air flows over the crest, it continues
downward. Due to compression, the
moisture evaporates and is absorbed.
-
The associated winds extend to the troposphere,
making it difficult to avoid by simply flying over it.
-
Lenticulars form in the crests of waves, and can
be hundreds of miles long.
-
In a PIREP or METAR, it will be reported as
either Alto Cumulus Standing Lenticular (ACSL) or Cirrocumulus Standing
Lenticular (CCSL).
Cirro means ice crystals.
Rotor Clouds:
-
Indicate the presence of mountain waves.
-
Possess the greatest amounts of turbulence.
-
Avoid flying through, between, or below rotors!
-
Will form downward from each wave crest, land
within the lower turbulent zone.
-
Can be dissipating and forming at the same time
due to the rotation of the air.
-
Diameter between 600’ and two miles.
-
Center of rotation typically near the ridgeline.
-
The first rotor will be the most intense.
If you must
pass through an area with rotors, the best choice is above them, and the second
best option is around them. Never fly
under them if there is any alternative at all.
When flying downward into mountain wave turbulence, your
aircraft will hit the turbulence faster and more violently. Configure the aircraft for turbulence
penetration.
Altimeter effects from a mountain wave:
-
The drop in pressure associated with an increase
in wind speeds will cause the altimeter to read incorrectly.
-
This, coupled with non-standard temperatures,
may result in an altimeter over-reading by as much as 3,000’ feet.
Four types of winds
in mountain terrain include anabatic,
katabatic, glacier winds, and funneling.
Anabatic:
-
Formed as the sunward side of a mountain slope
heats up.
-
Warm air starts to rise up the slope, creating
an upwards flow on the mountain.
-
Pockets of turbulence are possible as the
mountain slope heats up at different rates.
Katabatic:
-
Flows downslope.
-
Can happen in areas that are shaded, although
they are typically more powerful at night when radiation cooling starts to
happen.
-
Wind will then flow down mountain valleys.
Glacier Wind:
-
Extreme type of katabatic wind.
-
Cools over glacier, starts to rush downhill,
sometimes faster than 80 knots.
Funneling:
-
Flows perhaps between two ridges, or around a
single peak.
-
Speeds up, pressure drops abnormally.
-
Very dangerous.
To limit exposure
to mountain winds:
-
When crossing ridges from downward, do it at a
45o angle and with a minimum clearance of 3000’ when strong winds
are present.
-
If caught in a downdraft, speed up to get out of
it rather than pitching for VY to attempt to outperform it.
-
Check AIRMETs and PIREPs.
Types of
Turbulence:
-
Convective.
-
Mechanical.
-
Frontal.
-
Orographic.
-
Mountain wave.
-
Shear (wind shear).
Convective
Turbulence:
-
Caused by uneven heating of the earth’s surface.
-
Darker areas such as soil, rocks, or sand heat
up faster than lighter areas such as grass or water.
-
Warm air will rise and be replaced by cooler
sinking air.
-
Indications include fair weather cumulus, TCU’s,
ACC’s, and CB’s.
-
If possible, fly above clouds to avoid
convective turbulence.
Mechanical
Turbulence:
-
Caused by friction between air and ground.
-
Created when wind encounters terrain like trees,
or man-made objects/buildings.
-
The GFA shows heights that MECH will be based
at, along with maximum height.
-
From the surface, usually extends to between
2000’ and 5000’ AGL.
-
Only shown on forecast if expected to be
moderate or worse.
Frontal
Turbulence:
-
Caused by friction between two opposing air
masses.
-
More commonly associated with cold fronts than
with warm fronts, although it can be either.
Orographic
Turbulence:
-
Caused by friction in air currents through
mountainous regions.
-
Airplanes approaching hills or mountains from
the windward side are helped by rising currents.
-
Aircraft approaching from the leeward side
encounter descending currents.
Mountain Wave
Turbulence:
-
The fact that mountain waves are stationary
means that the effects of turbulence on an aircraft are different when flying
downwind than when flying upwind.
Shear Turbulence:
-
Also known as wind shear.
-
A change in wind speed and/or wind direction in
a short distance.
-
Can exist in a horizontal or vertical direction.
-
The greater the speed/direction change, the
greater the severity.
-
Some forms include microbursts and virga.
Low Level Wind
Shear:
-
There are six
different types: Microbursts, virga,
rotor winds, low level nocturnal inversions, low level jets, and funnel winds.
-
Can present a significant hazard to aircraft
during takeoff/landing/climbing/descent.
-
Defined as a significant, non-convective wind
shear that could adversely affect aircraft operation within 1500’ over an
aerodrome.
-
On the TAF/METAR, the height of the top is given
first, followed by wind speed and direction at that height.
-
To a large extent, wind shear is an element that
cannot be satisfactorily observed from the ground. Aircraft reports and radiosonde reports are
often the only ways that we can determine its possible presence.
-
The main effect is rapid gain/loss of airspeed.
-
On a chart, seeing WS indicates strong
non-convective low-level wind shear expected within 1500’ AGL.
Wind shear reporting guidelines:
-
Change in wind speed of greater than 25 knots
within 500’ AGL.
-
Change in wind speed of greater than 40 knots
within 1000’ AGL.
-
Change in wind speed of greater than 50 knots
within 1500’ AGL.
-
Pilot reporting gain or loss of indicated
airspeed of greater than 20 knots within 1500’ AGL.
Radiosonde – A battery-powered telemetry instrument
package/probe carried into the atmosphere (usually by a weather balloon), which
measures various atmospheric parameters and transmits them by radio to a ground
receiver.
Low Level Jets:
-
Often associated with a frontal system.
-
A powerful jet of air following a front can
produce significant turbulence.
-
Represented by a double-line black arrow on the
charts.
Nocturnal
Inversion:
-
As night falls, winds aloft become decoupled
with surface winds.
Microbursts:
-
Formed by cold dense air and rain shafts as they
rapidly descend.
Virga:
-
Similar to a microburst. Rain that falls, dragging cold dense air
along with it.
-
Should this rain fall into a layer of drier air
below, it will evaporate.
-
The cold air that was falling with it will
continue downwards, but without any rain that would be a visual indicator of a
strong downdraft.
Funnel Winds:
-
Gently blowing winds can be forced into valleys,
where they will speed up and create an area of shear.
Clear Air
turbulence (CAT):
-
Frequently associated with a jet stream
aloft. Can also be caused by a sharp
temperature gradient, mountain waves, or wind profiles that vary significantly.
Turbulence Reporting:
-
Light:
Slight changes in attitude/altitude.
-
Moderate:
Greater intensity, aircraft under control.
-
Severe:
Large abrupt changes, temporarily out of control.
-
Extreme:
Airplane is violently tossed, control is impossible.
-
Chop:
Intermittent turbulence.
The Coriolis force always
makes things appear (to an observer in the northern hemisphere) to curve to the
right.
In the upper troposphere, the
air is unaffected by friction and we can see that there is a balance between
the Pressure Gradient Force and the Coriolis force.
Resultant Wind – Thanks to the balance between the pressure
gradient wind and the Coriolis force, the geostrophic wind blows parallel to
the isobars. However, it is also
slightly modified by friction from the surface which reduces the Coriolis force
and causes the wind to blow at a slight angle to the isobars.
Buys Ballot’s Law:
-
If you stand with your back to the wind (in the
northern hemisphere), the low is always on the left and the high is always on
the right.
-
Determining the highs and lows tells you the
direction that the pressure gradient wind is blowing.
-
Coriolis force is always in the opposite
direction to the pressure gradient force.
Tri-Cellular Model:
-
Warm air rising at the equator, then moving to
the poles and sinking, is just one aspect to consider.
-
The earth’s rotation, uneven distribution of its
land masses, and the oceans all play a part in air circulation.
-
This all means that there is more than one cell
responsible for recirculating the air through the atmosphere.
Latitude Regions:
-
Polar: From 60o latitude to the poles,
known as the polar cell, easterly winds.
-
Mid
Latitude: From 30o to 60o
latitude, known as the Ferrel cell, warm southwesterlies.
-
Tropical: From the equator to 30o, known as
the Hadley cell, northeast trade winds.
There is generally HIGH
pressure at the Poles and at 30o latitudes.
There is generally LOW
pressure at the Equator and at 60o latitudes.
Doldrums – Low pressure, light
wind area near the equator.
The equator is also known as
the Inter Tropical Convergence Zone (ITCZ).
The areas at 30o
latitude (which are generally high pressure areas) usually have clear skies and
stable conditions.
The areas at 60o
latitude (called the polar front) usually have low pressure, unstable
conditions, and cyclonic rainfall.
Veering: Wind direction changing
clockwise.
Backing: Wind direction
changing counter-clockwise.
A calm ocean surface is smooth
and has little effect on the wind. A
city has a great effect on the wind speed and direction.
Winds usually veer and
increase during a climb out, and usually back and decrease during an
approach. This is just the way things
generally work when you’re changing altitude.
Non-standard winds frequently indicate warm fronts.
Gust – A brief rapid change of wind direction and/or speed.
Squall – A prolonged change of wind direction and/or speed. Be careful, as another separate definition of
a squall is a long line of thunderstorms.
Diurnal Effects:
-
During the day, vertical currents are formed
that link the upper and lower winds, making them similar.
-
At night, a nocturnal inversion develops and
there is no link between upper and lower surface winds; they back and decrease.
-
There can be a large difference between upper
and lower winds.
-
Winds at surface can be stronger and gustier
during the day.
Sea Breezes:
-
A high develops over water (in the day) and a
low over land.
-
Air flows from highs to lows, ie. a cool breeze
will be coming off the ocean towards the land (during the day).
-
The reverse (a land breeze) happens at night,
with winds blowing out to the ocean.
Types of Wind Shear:
1. Speed:
Wind is blowing at different speeds at different altitudes.
2. Directional: Wind is blowing in different directions at
different altitudes.
3. Increased Performance: An increasing headwind or decreasing
tailwind.
4. Decreased Performance: A decreasing headwind or increasing tailwind.
Rossby Waves – Very strong winds in the upper troposphere,
organized into wave patterns. They are
the result of temperature variations and the rotation of the earth. Depending on the season and circulation,
there can be anywhere from three to seven existing at any given time.
Jet Streams:
-
Blow in excess of 230 km/hr.
-
Rapid transfer of energy around the globe.
-
Can distribute debris from eruptions around the
world within a week.
-
Usually at least 60 knots.
Main Jet Streams:
-
Polar
Front (PFJS): From about 40o
to about 60o latitude.
-
Subtropical
(STJS): At around 25o to 30o
latitude.
-
Easterly
Equatorial (EEJS): At the equator.
Polar Front jet stream (PFTS):
-
When it moves south, it brings cold air, which
gives us dry and stable conditions with high pressures.
-
When warmed, it moves northward, giving strong
winds and heavy rainfall.
-
As winter approaches, it becomes stronger and
plunges far to the south.
-
The wind speed is greater in winter, due to
large temperature differences between the Polar and Ferrel cells.
-
During summer, it moves northward and wind
speeds usually decrease.
Sub-Tropical (STJS):
-
Found on the boundary between the Ferrel and
Hadley cells.
-
Weaker than the polar front jet stream due to
lower temperature variations between cells.
Easterly Equatorial jet stream (EEJS):
-
Tends to form aloft along the ITCZ (equator).
-
Fairly seasonal, associated with summer monsoons
in India.
-
Gentle jet stream.
Air Mass:
-
A large body of air (usually at least 1000 miles
across) that has similar properties of temperature and moisture throughout.
-
The most likely source region is a large flat
area where air can be stagnant long enough to take on the characteristics of
the surface below.
-
The source region is always an area of high
pressure. Slowly moving highs are the
best. Wind varies little with height.
-
Usually named based on temperature and humidity,
which of course is determined by the source region. The name will be two parts, with the first
part identifying the moisture region and the second part identifying the
temperature region.
-
Moisture Regions: Continental (dry) or maritime (moist).
-
Temperature Regions: Arctic (coldest), polar (mid-temp), or
tropical (warmest).
Canada doesn’t have many
continental-polar air masses because we’re actually a source for them. We don’t have many continental-tropical air
masses either. That leaves CA, MA, MP,
MT: Continental Arctic, Maritime Arctic,
Maritime Polar, and Maritime Tropical.
Air masses are generally modified
by either warming or cooling from below:
-
An air mass being warmed from below results in
instability and convection.
-
An air mass being cooled from below results in
an inversion and stability.
Fronts cause abrupt changes in
temperature, wind, and stability.
Frontal weather is determined
by:
-
Stability and moisture content of warm air.
-
Speed of cold air.
-
The slope.
A front is named after the
advancing air mass.
Symbols for fronts on maps: Warm fronts are red semi-circles, cold fronts
are blue triangles, and occluded fronts are a mix of each.
Types of fronts:
1. Cold.
2. Warm.
3. Occluded.
4. Stationary.
5. Trowal.
6. Upper
fronts.
Cold Front:
-
Transition zone where cold air is replacing
warm.
-
Tends to move more quickly than warm front.
-
Tends to undercut a warm air mass.
-
Tends to produce CU, CB, and TCU clouds.
-
Isobars make a V-shape in the vicinity of the
front.
-
Maybe 500 miles wide.
Before passage of a cold
front:
Winds:
South or southwest.
Temperature:
Warm.
Pressure:
Falling steadily.
Clouds:
Increasing; CU, TCU, CB.
Precipitation: Short period of showers.
Visibility:
Fair to poor, haze.
Dew Point:
High, remains steady.
As the cold front passes:
Winds:
Gusty and veering.
Temperature:
Sudden drop.
Pressure:
Slight rise.
Clouds:
CB.
Precipitation: Heavy rain, thunder and lightning, may hail.
Visibility:
Poor but improving.
Dew Point:
Sharp drop.
After the cold front has
passed:
Winds:
West to northwest.
Temperature:
Steadily dropping.
Pressure:
Rising steadily.
Clouds:
CU.
Precipitation: Showers, then clearing.
Visibility:
Good, except in showers.
Dew Point:
Lowering.
Warm Front:
-
Warm air mass replacing cold.
-
Slower than a cold front, overrides cold air.
-
Slope very shallow, typically one half of one
degree.
-
Maybe 200-250 miles wide.
Before passage of a warm
front:
Winds:
South to southwest.
Temperature:
Cool to cold, slowly warming.
Pressure:
Falling gradually.
Clouds:
In order, CI, CS, AS, NS, ST, and sometimes fog, CB in summer when fast
moving warm air.
Precipitation: Light to moderate, rain, snow, sleet, and
drizzle.
Visibility:
Poor.
Dew Point:
Steady rise.
As the warm front passes:
Winds:
Variable veering.
Temperature:
Steady rise.
Pressure:
Leveling off.
Clouds:
Stratus type, NS.
Precipitation: Drizzle or none.
Visibility:
Poor but improving.
Dew Point:
Steady.
After the warm front has
passed:
Winds:
South southeast.
Temperatures: Warmer then steady.
Pressure:
Slight rise, followed by a fall.
Clouds:
Clearing with scattered SC, occasional CB in summer.
Precipitation: Commonly none, sometimes light rain or
showers.
Visibility:
Fair in haze.
Dew Point:
Rises, then steady.
Occluded Front:
-
When a cold front associated with a low “catches
up” to the warm front, overtaking and undercutting it. Does a wrap-around, disconnecting the warm
air from the surface.
-
Usually shows on a weather chart as alternating
purple half circles and triangles.
Trowal:
-
Used in Canada as another name for an
occlusion. Stands for “trough of warm
air aloft.”
-
Usually a blue line with red quadrilaterals on a
weather chart.
-
Can vary significantly depending on moisture
content of warm air, ie. anything from dry to heavy precipitation.
-
Generally resembles a warm front ahead of the
trowal, and a cold front trailing.
-
In relation to the associated low, maximum
precipitation, icing, and convective activity will typically be in the
northeast sector.
At a trowal/occlusion,
remember that there are three air masses present: cold air, cool partially mixed air, and warm
air.
Stationary Front:
-
Not moving, neither air mass is replacing the
other.
-
Noticeable temperature change and/or change in
wind direction is common when crossing from one side to the other.
-
Winds will be blowing parallel to the front.
Frontogenesis – Occurs when the temperature gradient becomes
sharper.
Frontolysis – A dissipating front.
Upper Fronts:
-
Can happen when air is trapped on the surface
and the frontal weather is pushed aloft.
-
There will be few indications of the frontal
passage to a ground observer. No wind
shift and no temperature change.
However, precipitation is still likely to fall.
-
Upper fronts have empty symbols on a weather
chart.
Frontal Fog – Associated with weather fronts, particularly warm
fronts. Caused when frontal
precipitation falling into the colder air ahead of the warm front causes the
air to become saturated through evaporation.
With the passage of a cold
front, the surface wind usually veers and increases with speed.
Airframe Ice – Forms when super-cooled water droplets strike an
airframe that is at a temperature of less than zero degrees. The three main types are rime, clear, and
mixed.
Rime Ice:
-
Likes to form in layered cloud, like stratus.
-
Rough, milky, opaque.
-
Lots of air pockets, like what you see when you
open your freezer.
-
Freezes instantly.
Clear Ice:
-
Larger drops, may be cumuliform.
-
Smooth and transparent.
-
Hits the leading edges, does not freeze
instantly. Flows a bit, filling in
cracks and pockets, then freezes.
-
Larger accumulations are characterized by upper
and lower horns.
-
Extremely dangerous.
Always do everything possible
to stay out of freezing precipitation. It is one of the most dangerous things out
there for pilots.
Factors having an effect on
the rate of ice accumulation:
1. Shape: Thinnest surfaces collect the most ice.
2. Speed: Higher airspeeds result in greater rates of ice
accumulation.
3. Droplet
size: Large droplets are more likely to
strike the wing than a smaller droplet.
Icing Intensity comes in four levels: trace, light, moderate, and severe.
Trace icing:
-
Ice becomes perceptible.
-
The rate of accumulation is slightly greater
than the rate of sublimation.
-
Generally not hazardous unless you’re in it for
a while (well over an hour).
-
There is no symbol on the weather charts for
trace icing.
Light icing:
-
The rate of accumulation will create a problem
if the flight is prolonged (over an hour).
-
There is no symbol on the weather charts for
light icing.
Moderate icing:
-
Even short encounters are potentially hazardous.
-
Has a symbol on the weather charts.
-
De-icing or anti-icing equipment will be
required to clear it, and a diversion may be necessary.
Severe icing:
-
The rate of accumulation is fast enough to
render de-icing or anti-icing equipment useless.
-
An immediate diversion is necessary.
When icing is encountered:
1. Make
an immediate decision.
2. Climb,
descend, or go back.
3. Activate
de-icing or anti-icing equipment, if available.
4. Turn
on pitot heat and cabin heat.
Dangers of icing:
1. Poor
aerodynamics.
2. Increased
drag and weight.
3. Decreased
lift and thrust.
Effects:
-
Aircraft’s performance will decrease.
-
Increase in drag caused by rough surfaces.
-
Decrease in power due to intake blockages.
-
Engine failure due to carb icing or blocked air
intake.
-
Engine foreign object damage (FOD) is likely for
turbine engines.
-
Ice alters the wing shape, you become a test
pilot.
-
The angle of attack decreases, perhaps low
enough to happen before the stall alarm sounds.
-
Deteriorating trim effectiveness.
-
Asymmetric shuddering and vibrations if one prop
blade sheds ice.
-
Control surfaces may freeze in place.
-
Flaps can be damaged during
extension/retraction.
-
Landing gear may freeze in place or be damaged.
-
Fuel vents may become blocked, which can lead to
fuel starvation.
-
Pitot tube blockages will lead to airspeed
errors.
-
Obscured cockpit visibility.
-
Antenna problems, poor radio reception.
-
Bank angles greater than 5o can cause
a stall.
How to deal with potential
icing:
-
Consider climbing through ice more quickly, if
you’re stuck in it.
-
File a PIREP.
-
On landing approach, use more power and higher
airspeed.
-
Clear ice tends to form in cumuliform clouds,
try to avoid them whatever the season.
The worst icing in these clouds is between -10oC and 0oC.
-
Rime ice tends to form in stratiform
clouds. Accumulation is greatest between
-10oC and -20oC.
De-Icing and Anti-Icing
equipment:
-
Balloons.
-
Heaters.
-
Jets may use bleed air from engines.
-
Weeping Wing systems (also known as TKS) may
pump fluid through mesh screens on the leading edges of the wing and tail.
Frost forms on the aircraft
when the surface temperature of the aircraft is below the dew point and below 0oC.
Frost can reduce wing lift by
30% and increase drag by 40%.
Cold Soaking – Typical when an aircraft comes down from the flight
levels (where it is cold) and into warmer air below. Warm moist air will then condense and freeze
as it comes into contact with the cold portions of the wings.
If you start losing power,
impact ice may be causing a problem.
Select carb heat or alternate heat.
Lean the mixture if carb heat is used continuously.
How to Avoid:
1. Stay
out of clouds and visible moisture when the outside air temperature (OAT) is
below freezing.
2. Fronts
and low pressure systems are often associated with clouds.
3. If
you must fly through a front, do it directly instead of at an angle.
4. A
winter warm front is terribly dangerous.
Carry extra fuel, in case a
diversion is needed!
Tail Stall:
-
Tail can collect ice a lot faster than the wing.
-
Horizontal stabilizer produces a down force that
keeps the nose up.
-
If the tail stalls due to excessive icing, we
would have a sudden and violent pitching of the nose down.
-
This would be preceded by oscillations in the
control column, as opposed to the sensation of wing buffeting.
Recognition of a Tail Stall:
-
Can lead to abnormal pitch forces when flaps are
extended, so don’t extend.
-
A buffeting may be felt in the control column(s),
instead of in the airframe.
-
A pilot induced oscillation may be an early
indication.
Recovery:
-
Raise flaps to previous setting immediately.
-
Pull back on the yoke, and reduce power if
altitude permits.
-
Do not increase airspeed unless necessary to
avoid a wing stall.
If you suspect tail icing:
-
Approach at the proper speed for your configuration.
-
Keep the flaps retracted.
-
Keep small bank angles for turning.
-
Avoid abrupt pitch-down movements and thrust
changes.
Hoar Frost:
-
Caused by cooling on clear/calm nights.
-
Dew point of surrounding air is below zero.
-
Water vapor turns directly to ice (deposition).
-
Frost colour is white and opaque.
-
Melts quickly.
Thunderstorm Development Requirements:
-
High moisture content.
-
Steep lapse rate.
-
A lifting agent.
Development Stages:
1. Cumulus/developing
stage: Updraft dominated.
2. Mature
stage: Updrafts and downdrafts.
3. Dissipating
stage: Downdraft dominated.
Cumulus Stage:
-
Warm moist unstable air is forced to rise.
-
Moisture rapidly cools into liquid drops of
water due to the cooler temperatures at high altitude, which appears as cumulus
clouds.
-
As this water vapor condenses into liquid,
latent heat is released. This warms the
air, causing it to become less dense than the surrounding dry air.
-
Upward growth rate of 5 to 20 m/s, which is 10
to 45 mph.
-
The updraft holds all the water droplets and ice
crystals, so the rain is unable to fall.
-
Usually, there is no precipitation in this
stage.
Mature Stage: (Air Mass
Storm)
-
Warmed air continues to rise until it reaches
existing air which is warmer, then the air can rise no further.
-
This cap is often the tropopause.
-
Air is forced to spread out, giving it an anvil
shape.
-
Water droplets coalesce into larger and heavier
droplets and freeze into ice particles.
As they fall, they melt into rain.
-
The cloud may have already reached a height of
60,000’ and the updraft may be travelling at more than 6,000 feet/minute.
-
While updrafts are still present, falling rain
also creates downdrafts.
-
There will be strong downdrafts in areas of the
heaviest precipitation.
-
The heavy rain cools and drags down the air with
it, at speeds of up to 2000’ per minute.
-
Precipitation/turbulence/thunder/lightning are
at their most intense.
-
Turbulence is high due to the opposite rushing
air currents at the middle level.
-
Updrafts continue to dominate the inner
portions.
-
Most of the downdrafts form on the outside
edges.
-
Typically lasts fifteen minutes, but can last
for an hour.
Dissipative Stage:
-
As heavy precipitation falls through the cloud,
the cloud cools, and then downdrafts dominate the base of the cloud.
-
If atmospheric conditions do not support “super
cell” or “squall” development, this stage occurs rather quickly.
-
The downdraft will push down out of the
thunderstorm, hit the ground, and spread out, causing a microburst.
-
This cooling causes the cloud to lose energy and
the rainfall gradually ceases.
-
Cool air carried to the ground by the downdrafts
cuts off the inflow, so the updraft disappears and the thunderstorm will
dissipate.
Methods of Lift that create thunderstorms:
1. Orographic (Air Mass thunderstorm) –
Form in mountains, created as air moves up a steep slope.
2. Convection (Air Mass thunderstorm) –
Rising hot air creates the energy source.
Often seen on a summer afternoon.
Can even be triggered by wildfires.
3. Frontal – Created by frontal lift. Fast moving cold fronts can create energetic
storms (known as Steady State thunderstorms).
Squall Line:
-
A line of thunderstorms moving in unison.
-
Frequently found well ahead of a fast moving
cold front.
-
Exercise extreme caution when close.
-
Leading edge will be where updrafts and
downdrafts are most severe.
-
If you have to pass through, penetrate the
lightest areas.
Do not mistake a shelf cloud
for a tornado. This happens commonly.
Lightning:
-
Air has an electrical resistance.
-
When the electric potential or difference is
large enough to break down this resistance, the electrons flow to the positive
charge, forming lightning.
-
There can be lightning from clouds to the air,
to the ground, or to other clouds.
-
The greatest likelihood of lightning hitting an
aircraft is between -5oC and +5oC.
-
Lightning can strike an aircraft flying in clear
air in the vicinity of a thunderstorm.
-
Lightning may or may not cause problems if it
hits an aircraft.
There is no useful correlation
between the external visual appearance of a thunderstorm and the severity or
amount of turbulence or hail in it. The
visible thunderstorm is just a portion of a violent system of updrafts and
downdrafts that often extend far beyond. Severe turbulence may extend up to 20
NM from severe thunderstorms. No flight
path through an area of strong or very strong radar echoes that is separated by
less than 40 NM can be considered to be free of severe turbulence.
Engine Water Ingestion – The strength and velocity of updrafts in a
thunderstorm are strong, and heavy concentrations of water collect in
clouds. This moisture may exceed the
amount that a turbine engine can ingest, and the engine can flame out, so turn
on the igniters if you’re in a turbine.
The pressure ahead of a
thunderstorm falls rapidly, then rises abruptly after the rain starts.
Whenever possible, do not take
off or land when a thunderstorm is approaching.
They can have gusts exceeding 50 KTS, and wind direction can reverse in
seconds.
If flying over a thunderstorm,
clear the top by at least 1000’ for each 10 knots of wind speed at cloud top.
Hurricane – A huge destructive
cyclonic storm originating in tropical waters.
Often 100 miles across.
Tornado:
-
Rotating funnel shaped cloud linking the ground
to a large thunderstorm.
-
The funnel cloud does not become a tornado until
it touches down.
-
Diameter is often only around thirty feet, but
can be up to half a mile.
-
Usually happens in spring/summer.
-
Average forward speed is 50 km/hr.
-
Wind speeds within the tornado can range from 65
km/hr to 450 km/hr.
-
The path of destruction is usually three to four
kilometers long.
Waterspouts – Funnel clouds
that touch water, usually slightly less powerful than tornadoes.
Put your airplane into a
hanger before a storm, if you have one!
Fog is not associated with
convection.
Dashed brown line on the
weather chart is usually fog.
Fog formation requirements:
1. High
humidity.
2. Condensation
nuclei.
3. Very
light surface winds.
4. A
process to either cool or to add moisture, to get the condensation going.
A temperature to dew point
spread of 3oC or less and dropping will probably lead to fog.
Six fog types include radiation, advection, upslope, frontal,
steam, and ice.
Radiation fog:
-
Formed by radiation cooling on clear nights
where relative humidity is high and light winds are present.
-
Most likely to be present shortly after sunrise.
Advection fog:
-
Formed by the horizontal movement of warm moist
air over a cool surface.
-
The thickest advection fog will usually form at
night with low winds.
-
Common during winter warm-ups and early spring
thaws.
-
Typically dense and can last for several days.
Upslope fog:
-
Moist air moves up rising terrain.
-
Easterly wind flowing across the plains can
cause upslope fog.
Frontal fog:
-
Precipitation from a warm front or cold front
falls into colder air below it and ends up saturating it.
-
More typical with a warm front.
-
Also known as precipitation fog.
Steam fog:
-
Also known as arctic sea smoke.
-
Typical over a lake/river/pond at sunset or
sunrise.
-
The process begins when cold dry air blows over
warm water.
-
Water evaporates into the lower layers of the
air saturating it.
-
As the excess water vapor condenses, fog/mist
forms.
Ice fog:
-
Sometimes forms when temperatures are
significantly below zero.
-
Often created by exhaust from engines or
factories on cold winter days.
Naming conventions: Called Mist (BR) if visibility meets or
exceeds 5/8ths mile. Called Fog (FG) if
visibility is less than 5/8ths of a mile.
Haze - Forms on days with high temperatures and high humidity.
Each region in Canada has a FIC,
eight in total: Whitehorse, Kamloops,
Edmonton, Winnipeg, North Bay, London, Quebec City, and Halifax. You usually contact a FIC by calling
1-866-WXBRIEF.
FSS’s are sub-locations that
coordinate with the FIC. We normally
contact them by radio while en route.
They are referred to as “Radio” and their service is Flight Information
Services Enroute (FISE).
Sometimes, a FSS will be
responsible for overseeing the control of a Class E control zone, and FISE will
be done by the nearest FIC via VHF repeater.
Usually 122.5 or 123.XXX MHz.
Direct User Access Terminal (DUAT) – Can legally be used as the sole
source of pre-flight planning info.
Automatic Terminal Information
Service (ATIS) – A short, pre-recorded
audio summary of the current weather at an airport, which plays on constant
repeat. Reduces radio congestion.
VOMET:
-
Weather info via high frequency (shortwave).
-
Used for North Atlantic crossings.
-
Frequencies are found in the CFS.
PBS – Pilot Briefing Service
TWB – Transcribed Weather
Broadcasts
CAVOK – Stands for Ceiling & Visibility OK. This means visibility is greater than or
equal to 6 SM, ceiling is greater than or equal to 5000’, and no cumulonimbus,
precipitation, thunderstorms, fog, or drifting snow are present.
Understand the difference
between current reports (METARs,
AWOS, PIREPs) and forecasts (TAF’s
and GFA’s). Current reports are
measurements, and forecasts are estimates.
METAR:
-
Winds are knots true.
-
Cloud heights are AGL.
-
Visibility is in SM.
-
Times are in UTC/Zulu.
You must know how to decode a METAR, and know all of the
abbreviations. Memorize them.
METAR includes: The type of report, airport identifier,
date/time, wind direction and velocity, visibility, runway visual range,
weather phenomena, sky coverage, temperature/dew point, altimeter setting,
remarks.
SPECI – Special METAR report
RVR – Runway Visual Range
The RVR is always followed
with either /D or /U or /N to represent downward, upward, or no change.
An Automated Weather
Observation Station (AWOS) is noted by AUTO in the METAR. Use these observations with caution! Heavy rain or blowing snow can cause
incorrect readings.
If filing a PIREP, go through these nine items in
order:
1. Location
and time.
2. Altitude.
3. Aircraft
type.
4. Cloud
(base, amount, top).
5. Temperature.
6. Wind
direction and speed.
7. Turbulence.
8. Icing.
9. Remarks.
Mandatory PIREP codes:
UA:
Normal PIREP.
UUA:
Urgent PIREP.
/OV: Location
of the PIREP, in relation to a NAVAID, an aerodrome, or geographical
coordinates.
/TM:
Time the PIREP was received from the pilot, in UTC.
/FL:
Flight level, essential for turbulence and icing reports.
/TP:
Aircraft type, essential for turbulence and icing reports.
Optional PIREP codes: (at
least one is required)
/SK:
Sky cover. Used to report the
cloud layer amounts and the height of the cloud base.
/TA:
Ambient temperature, important for icing reports.
/WV: Wind
velocity referenced in terms of True north (magnetic north in US).
/TB:
Turbulence intensity, whether it occurred in or near clouds, and
duration.
/IC:
Icing, reported by type and intensity or rate of accretion.
/RM:
Remarks, any other weather conditions that are not covered already.
/WX:
Flight visibility and weather.
Identifiers:
-
2 letter are NDB’s.
-
3 letter are VOR’s.
-
4 letter are airports.
-
5 letter are intersections.
You need to be able to
completely decode all weather products for your written exam and flight test.
Notice To Airmen (NOTAM) – Contains info concerning
“stuff that’s happening” which might affect pilots or normal flight
operations. Usually distributed at least
five but no more than 48 hours in advance.
NOTAM’s are tailored by
locations and by who is affected. There
are about 210 files (location indicators) for Canada.
NOTAM Categories:
-
Aerodrome:
Anything within 25 NM of an aerodrome.
-
Flight Info Region: Of general interest throughout the FIR.
-
National (CYHQ):
Affects the entire country.
Criteria for Issuing a NOTAM:
1. Changes
to navigation aids.
2. Changes
in frequencies, etc.
3. Changes
in airspace or air traffic procedures/services.
4. Changes
to runways or approach systems.
5. Hazards.
6. Military
ops or airspace reservations.
7. Changes
in CYR/CYA.
8. Communication
problems.
9. Safety
issues.
10. Equipment/facilities
deficiencies.
Types of NOTAMS’s:
N – New.
C – Cancelling.
R – Replacing.
J – Runway Surface Condition Report.
Q – Query or Response NOTAM.
The reason why the RSC report
is identified by a J is because it stands for the James Brake Index.
Always check the NOTAMS!
Graphical Area Forecast (GFA):
-
Clouds and weather.
-
Icing, freezing, and turbulence levels.
-
Two sets of maps.
-
Depicts the most probable meteorological
conditions expected to occur below the 400 Mb or 24,000’ level.
-
Designed to meet en route weather forecasting
and pre-flight planning requirements of general aviation and regional air
carriers.
-
Issued four times daily, about half an hour
before the beginning of the forecast period.
Valid for six-hour periods starting 0000, 0600, 1200, and 1800 UTC.
-
Seven different coverage regions.
What is included in the GFA:
-
Six charts total for each six hour issue.
-
Three for clouds and weather (CLDS/WX).
-
Three for turbulence and freezing level
conditions (ICG/TURBC/FRLVL).
-
For each of these sets of three, a near term
forecast, a 6hr forecast, and a 12hr forecast are depicted individually.
-
Note that the 12hr CLDS/WX chart also includes
an IFR outlook for an additional 12-hour period, so it’s good for 24 hours.
-
Speeds are in knots, and heights are ASL.
-
Horizontal visibility is in SM.
-
Times are UTC/Zulu.
-
You will be asked to interpret a GFA on your
exam.
-
The scale on the map is in NM.
-
Memorize all of the standard abbreviations that
are found in the AIM meteorology section.
Category Ceiling Visibility:
-
IFR: Less
than 1000’ AGL, and less than 3 SM visibility.
-
MVFR: 1000’
to 3000’ AGL, and 3 to 5 SM visibility.
-
VFR:
Greater than 3000’ AGL, and greater than 5 SM visibility.
Synoptic Features – Weather features that are generally at least a
thousand kilometers across, ie. very large.
Planetary features are larger, and mesoscale features are smaller.
Mesoscale Levels:
1. Mesoscale
Alpha: From 1000km across down to 200km.
2. Mesoscale
Beta: From 200km across down to 20km.
3. Mesoscale
Gamma: From 20km across down to 2km.
If a synoptic feature is
forecast to be moving at five knots or faster, there will be an arrow and a
speed value. For speeds of less than 5
KTS, use the letters QS for quasi-stationary.
Clouds on GFA’s:
-
Bases and tops between the surface and 24,000’
are indicated.
-
The tops of convective clouds (TCU, ACC, CB) are
indicated even if they extend above 24,000’ ASL.
-
Cirrus clouds are not depicted.
-
Cloud types will be indicated if considered
significant.
-
A scalloped border indicates a ceiling where the
sky is BKN or OVC.
-
If the visibility is greater than 6 SM, and the
sky is SKC/FEW/SCT, then a scalloped border is not used.
-
When multiple layers are forecast, the amount of
cloud at each layer is based on the amount at that level, not overall. Bases and tops of each layer are indicated.
-
CIG stands for Ceiling, and implies AGL.
-
Visibility of greater than 6 SM is listed as
P6SM.
-
A dashed green boundary with an interior of
solid slanted bars is used to enclose areas of intermittent or showery
precipitation.
-
A solid green line with a dotted interior is
used to enclose areas of continuous precipitation.
Convective storm clouds:
ISOLD – Isolated – less than 25%.
SCT – Scattered – 25% to 50%.
NMRS – Numerous – Greater than 50%.
Surface Based Layer:
-
Referred to as OBSDCD.
-
Fog or Mist.
-
VV into surface based layers is AGL.
Obstructions to Vision (enclosed within a dashed orange line):
LCL – Local – Less than 25%.
PTCHY – Patchy – 25% to 50%.
XTNSV – Extensive – Greater than 50%.
Wind barbs:
-
Used if the sustained speed is 20 KTS or more.
-
Show speed and direction.
-
The “feathers” on the barb correlate to the
numerical wind speed.
-
G stands for gusting.
-
Uses true wind direction.
Icing on Charts:
-
Icing is depicted in blue whenever moderate or
severe icing is forecast.
-
Areas of light icing are described in the
comments box.
Turbulence on Charts:
-
Depicted in red.
-
Depicted whenever moderate or severe turbulence
is forecast.
-
The base and top of each layer are shown.
-
If turbulence is due to any of the following
five conditions, the cause will be identified with the appropriate
abbreviation: MECH (mechanical), LLWS
(low level wind shear), LEE WV (mountain wave), LLJ (low level jet), and CAT
(clear air turbulence).
Freezing level:
-
Contours are abbreviated by dashed lines.
-
Height is measured ASL.
-
Contour lines are at 2500’ ASL levels, starting
at the surface.
GFA Amendments:
-
Automatically amended by AIRMET’s.
-
Happens if there are significant deviations from
the forecast.
-
The GFA is automatically amended by SIGMET
bulletins, even though that is not explicitly stated in the SIGMET itself.
-
A chart will be reissued with comments if
necessary.
AIRMET – Airman’s Meteorological Event.
SIGMET – Significant Meteorological Event.
Look at the GFA first, then
the TAF, then the METAR. This lets you
look at the big picture first, then a five-mile region, then a point analysis.
Terminal Area Forecast (TAF):
-
Weather expected within 5 NM of the airport.
-
Cloud heights are AGL.
-
Wind degrees are true.
-
Typically issued 4 times daily, for either 12,
24, or 30 hour periods.
-
To add a forecast for low-level non-convective
wind shear, an example is: WS018/34045KT, which means that the surface to 1800’
AGL has shear, and at 1800’ the wind is 340o True at 45 knots.
-
Wind shear below 1500’ AGL, if expected to be
significant, is always included in the TAF.
Sky Cover in a TAF:
-
Cloud layers forecast as per METAR.
-
Only CB will be specifically identified in the
forecast.
For a TEMPO notation, in order
to be legal, the forecast “temporary” conditions cannot be expected to last
more than 50% of the total duration of the TEMPO, and none of the intermittent
occurrences can last for more than one hour.
FM – From, permanent change.
BECM – Becoming, permanent but
gradual change.
PROB XX – Probability of
XX%. Must be less than 50%.
Remarks on TAF:
-
RMK then details.
-
Unique to Canadian TAF’s.
Upper Winds and Temperatures:
-
Referred to as the FD charts.
-
Forecasts of wind direction and velocity, as
well as expected air temperatures at specific heights.
-
Forecasts are prepared every twelve hours.
-
It is rare that these forecasts are completely
accurate.
-
In flight, be prepared to use your ten degree
drift lines.
-
Wind direction is True, the speeds are in KTS.
-
Code of 9900 stands for light and variable
winds, no wind corrections are required for the Nav Log.
-
Unlike many other areas, a code of a minus sign does mean below zero degrees. If all temps are below 0o at
higher levels, then the minus sign will be omitted, so you have to look at
other parts of the chart to verify.
-
Field elevations above 1500’ will not report a
3000’ FD.
-
Temps are not reported on a 3000’ FD.
-
Different format: ie. 1921+14 means wind direction 190o,
speed 21 knots, temperature +14oC.
-
If the wind direction is between 51 and 86,
subtract 50 to get the wind track, and also add 100 knots to the wind
speed. For example, 731960 means 230oT
because (73-50)=23, x10=230, and wind speed is 119 knots, and the temperature
is minus sixty.
Airman’s Meteorological
Advisory (AIRMET) - Short term
weather advisory, designed to highlight weather that is not described in the
current GFA. Can be issued for:
-
Instrument Meteorological Conditions (IMC).
-
Freezing precipitation (unless it is in a
SIGMET).
-
Moderate icing.
-
Moderate turbulence.
-
Isolated thunderstorms.
-
Wind varies by greater than 60o
direction from forecast.
SIGMETS are more severe, and might be issued for severe
thunderstorms, squall line, hail, volcanic ash, hurricanes, tornadoes, severe
icing, marked mountain waves, widespread sand or dust storms, and low level
wind shear.
In-flight SIGMETS will be
broadcast on 126.7 MHz, and you can get more info on the FISE frequency.
Weather Charts: Surface
charts and upper level charts (constant pressure charts).
Most charts have pressures
reduced to sea level. The upper level
charts do not. They are very different!
Surface Analysis Charts: Actual observed information.
Surface Prognostic
Charts: Forecast info.
Surface Analysis Charts:
-
Actual weather as observed from the surface to
3000’ AGL.
-
Information can be a few hours old since it can
take up to three hours to create a map.
-
Info is based on observations taken at 00Z, 06Z,
12Z, and 18Z.
-
Allows you to see how the weather has been
developing over time.
-
Most symbols are the same as the ones used in
the GFA.
-
Black location dot is overcast.
-
Barbs on a wind flag are 10 knots for each long
barb, and less for shorter barbs.
Wind always veers at a front.
Surface Prognostic Chart:
-
Looks similar to the SAC. Don’t confuse them! Check the title.
-
Issued 48 and 36 hours before the standard
validity times of 00Z and 12Z.
Upper Level Charts:
-
Issued by the weather office at 00Z and 12Z.
-
Can give us a 3D view of the weather.
-
Analysis, not prognostic!
-
Levels used (standard) are 850 mB, 700 mB, 500
mB, and 250 mB.
-
If you’re doing commercial or ATPL, you might
use a fifth chart, the 400 mB.
-
There are also two prognostic charts: the Significant Weather Prognostic chart and
the Significant Weather Prognostic High Level chart (there are actually more,
but these are the two commonly used in Canada).
When we are looking at a
constant pressure chart, we are actually looking at the height of the air for a
given pressure at a given location.
Average altitudes for these
pressure levels:
850 mB –
5,000’ ASL – 150 dM (decameters)
700 mB – 10,000’ ASL – 300 dM
500 mB – 18,000’ ASL – 570 dM
250 mB – 34,000’ ASL – 1050 dM
An airplane that is flying
through different temperature columns of air up in the Flight Levels will have
its True altitude constantly changing.
This does not matter! All the
other airplanes will have their altimeters set to 29.92, and they will also
rise and fall with the changes.
Contour Lines – Lines connecting similar heights (of air pressure
levels). Therefore, lines on a CPC are
not isobars! The whole horizontal plane
of the map is an isobar, except in two dimensions as a layer, not as a single
line. It is still important to note that
tightly packed contour lines are still indicators of high wind speeds.
Satellite imagery is a good
complement to (not a replacement for) other information.
Geostationary Satellites:
-
Placed in orbit above the equator at an altitude
of about 36,000 kms.
-
The satellite’s motion through space matches the
pace of the earth’s rotation.
-
An observer on the ground sees the satellite as
motionless in relation to the stars and earth behind.
-
The satellite still completes one rotation of
the earth per day.
The National Oceanic &
Atmospheric Administration (NOAA) uses three geostationary satellites for
imagery: GOES West, East, and
South. These normally each see one half
of the earth, a disc which depends on their orbital parking spot. They produce a full image every thirty
minutes, although they can be tasked to “rapid scan” smaller areas more
quickly. However, because they are in
orbit over the equator, they don’t provide accurate information at latitudes
over 60oN.
Polar Orbiting Satellites:
-
Orbit at an altitude of about 850km.
-
They complete an orbit every 105 minutes, or 14
times/day.
-
Because the earth rotates beneath them, they
“appear” to move west by about two time zones per orbit.
-
Over any given time zone, there are about two
passes per day, which averages to about one pass per day during visual daylight
hours.
-
Currently, there are two NOAA satellites
working, one on each side of the planet.
Together, they provide images once every six hours.
-
They can provide images at very high resolution
since they’re so low.
Image types can be visible or
IR. Depending on the wavelengths used,
IR can tell us surface temps, cloud top temps, or moisture content of the
atmosphere.
For white temperature labels,
the coldest temperatures are bright whites.
On color temperature labels, green/purple are warm and down to
orange/yellow/red are very cold. These
are the Environment Canada standard colours.
For visible satellite images,
they use a white albedo style. IR images
use a temperature scale.
Infrared Images:
-
Fog, which can be quite shallow, can be hard to
pick out if it is the same temperature as the ground below it.
-
In an inversion, where temperatures aloft can be
even higher than the ground, clouds can even appear as dark objects.
-
The typical resolution on IR images is about 4km
at the equator and deteriorates further north, especially past 60o
latitude.
Visible Images:
-
Need to be taken during daylight hours.
-
Appearance changes throughout the day as the
angle of incident light changes.
-
Clouds are generally defined better than on IR.
-
Banks of fog and large cumuliform clouds are
easy to see.
-
Resolutions are around 2km at the equator and
deteriorate further north, especially past 60o latitude.
Water Vapor Imagery:
-
Starting to become more common.
-
Does not tell us where clouds are, but does tell
us where there is a lot of moisture in the air.
-
Areas of high moisture content will be bright
white, while areas that are relatively dry will be a dark shade, or black.
Conclusion
The topics included in a study of weather & meteorology have a far greater scope than I’ve covered here. It would also be wise to spend quite a bit of
time studying the various publications that I’ve linked to on this page:
http://www.djbolivia.ca/aviation.html
I have links there to several additional aviation-related
publications.
Thanks for reading, I hope this was helpful to pilots in
training. If you find any errors in the
above information, feel free to contact me at
jonathan.scooter.clark@gmail.com
-
Jonathan Clark
