PPL-MET Flashcards
what layer contains the ozone layer
stratosphere
in the troposphere, what percentage is water
0-5%
what easily produces ozone
high voltage electrical arc
what are the ISA standards
1013.25 Hpa
15 degrees c
1225 grams/m^3
at what height is the density approximately half that of sea level
20,000 ft
what are three ways heat is transferred
radiation
absorbtion
conduction
what is advection
horizontal wind
why do we get a sea breeze
low pressure system on land, high pressure system of sea air fills gap, thus creating wind.
why do we get a land breeze
land cools faster than sea, therefore higher pressure over land moves in to replace low pressure air over sea
which is stronger, sea breeze or land breeze
sea breeze
what is katabatic wind
air that is cooled down, and then flows down slopes as a result of the force of gravity
when is katabatic wind strongest
dawn
what is anabatic wind
air heats up and rises to replace air that has gone down (cuz it cooled down)
why is anabatic wind weaker than katabatic wind
because it has to oppose the force of gravity
what causes fohn wind
air rises up a mountain, loses its moisture through rain/precipitation, and then heats up as it goes down the other side of the mountain. it doesn’t rise because the density of air is GREATER than that of water vapour.
what causes low level jet streams
high pressure system coming into contact with mountains, thus creating a Venturi effect.
what speed can low level jet-streams reach
70 kts
at what altitude are low level jet streams expected, and at what altitude are they strongest
< 3000 ft, 2000 ft
in terms of low level jet streams, why does wind speed increase during the night
the air cools, and provides a layer with less friction for the winds to pass over, thus creating faster winds
which direction do low level jet streams usually come from in aus
the south
what is sublimation
phase change from solid to gas
what is the equation for relative humidity
(vapour present/vapour possible) X 100%
what does it mean when air is said to be saturated
when the amount of water vapour present is such that the parcel of air cant hold anymore
what are the two ways for air to reach the saturated state
at a constant temperature, water can be added
with a constant amount of water, reduce the temperature
what is the dew point temperature
the temperature at which saturation occurs
to reach saturstion, a parcel of air with high relative humidity requires….
just a little amount of cooling
when is a cloud formed
when a parcel of air is cooled to its dew point temperature
what is the adiabatic process
changes in pressure resulting in a change in temperature
what is the dry adiabatic lapse rate
unsaturated air will cool at 3/1000
what is the saturated adiabatic lapse rate
1.5/1000
what are the four core triggers of unstable air
convection
orographic uplift
widespread ascent
turbulence and mixing of air
what pressure systems is stable air often associated with
high pressure systems
what is frontal uplift
when a cold and hot front meet, the hot front rises above the cold front
what is orographic uplift
like the precursor to fohn wind, it flows up a mountain, and reaches the dewpoint temperature, thus causing clouds to occur.
what height are high level cloud bases
25000 ft and above
what height are medium level cloud bases
7500-20000 ft
what height are low level cloud bases
below 7500 ft
describe cirrus clouds
high level
no chance of icing
little turbulence
describe cirrostratus clouds
high level
too high for significant icing
little turbulence
describe cirrocumulus clouds
high level
turbulent
too high for significant icing
looks grainy
describe altostratus clouds
medium level
virga
some turbulence
some icing risk
describe thick altostratus clouds
Medium level
snow/ice
light turbulence in cloud
heavy/moderate turbulence at fronts
describe thin altostratus
Medium level
Virga
Little turbulence
Medium ice risk
describe altocumulus
Medium level
light turbulence
nil icing
describe lenticular altocumulus
Medium level
Light rime ice
forms on mountain ridges
strong turbulence
Describe altocumulus castellanus
medium level
moderate to severe turbulence
indicator of unstable moist air
possible thunderstorms forming
Describe cumulus
Low level cauliflower
light/moderate turbulence\little ice risk
Describe Towering cumulus clouds
sign of instability
moderate/severe turbulence in andbelow
definite ice risk
Describe Cumulonimbus
Cellular Large vertical component Anvil shaped Severe turbulence in and below snow hail definite icing risk
Describe stratocumulus
Baked buns
light / moderate turbulence
drizzle
describe stratus cloud
flat cloud
describe nimbostratus cloud
low/medium level
grey
continuous rain
definite icing risk
describe mammatus BASE
not a cloud, but a base
seen after a thunderstorm
What differentiates stratus cloud from fog
stratus cloud is basically fog that is above 50ft AGL
What is virga
rain that experiences a phase change into vapour before it touches the ground
how long do showers last for
15-30 minutes
How long does intermittent precipitation last for
up to 50 minutes
How long does continuous precipitation last for
> 50minutes
What (who) do we need for a thunderstorm to form
Trigger
Instability
Moisture
What are the types of thunderstorms
Frontal/squall line thunderstorms Nocturnal Equatorial thunderstorms Cold stream thunderstorms Orographic thunderstorms Thermal convective thunderstorms Convergence thunderstorms
What are the stages of development for a thunderstorm
Growing stage
Mature stage
Dissipation stage
What winds are associated with each stage of the thunderstorm
Growing: Updrafts
Mature: Updrafts and downdrafts
Dissipation: Downdrafts
The effects of a thunderstorm can be felt from how far away
10 miles
How can you generally describe a microburst
Localised areas of INTENSE downdrafts
What is mechanical turbulence
Eddies (turbulence) that forms as a result of air flowing over objects
To what height can mechanical turbulence be felt
20 times the height of the object it passed over
How long do dust-devils last for, and what is their height reach?
30-60 min, 7000ft AGL
What are mountain waves
Critical turbulence on the lee side of a mountain
what is a good indicator that mountain waves are present
Lenticular waves forming at the crest of a mountain
When do you have to report windshear
ALWAYS
Would an aircraft taking off or landing produce the most wake turbulence
Aircraft taking off (less flap results in more wake turbulence)
when is ice-fog formed
when the temperature is less than -20
When is advectionfog formed
when warm moist air flows over a cool surface and reaches its dew-point temperature
What is an occluded front
Cold and warm front collision
What are the three core types of global circulation
Polar cell
Tropical (convective cell)
Subtropical cell (causes as a result of the other two cells)
What pressure system can be expected at the equatorial trough
Low pressure system
What pressure system can be expected at the subtropical range
High pressure system
What pressure system can be expected at the poles
High pressure system
What direction does a convergent pressure system move in
inwards from the bottom
What direction does a divergent pressure system move in
Outwards from the bottom
what is a ridge
elongated finger for high pressure systems
what is a trough
elongated finger for a low pressure system
what is a col
are between high and low pressure systems
what us the coriolis force
air appears to accelerate as it moves away from the equator (because the equator has a higher velocity than southern or northern parts).
what pressure system is the Coriolis force associated with
high pressure system
when does the coriolis force cease to exist
+- 5 degrees of the equator
airflow that flows parallel to isobars is known as…
geostrophic wind
what direction does a high pressure flow in the southern hemisphere
anticlockwise
what direction does a low pressure flow in the southern hemisphere
clockwise
direction of backing
left
direction of veer
right
over land, what is the strength reduction and veer value
2/3 and 30 degrees
over sea, what is the strength reduction and veer value
1/3 and 10 degrees
what temp is rime ice most common in
-10 -20
what temp is good for cyclone breeding
28 degrees
what coordinates are cyclones commom
5 and 15 degrees south latitude
what is a key difference in the stages of a cyclone
pressure (lower pressure for more severe conditions)
weather changes associated with a cold front
rise in pressure
drop in temp
dew point after passing will be lower
