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PPL Met > wind > Flashcards

wind Flashcards

1
Q

\__ how many knots is this?

A

10 knots

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2
Q

\__ (small) how many knots is this?

A

5knots

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3
Q

/\____ how many knots is this?

A

50 knots

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4
Q

what is a gust?

A

a sudden but brief increase in windspeed- often assoicated with rapid fluctuations in wind direction.

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5
Q

what is a lull?

A

corresponding decrease in wind speed

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6
Q

where are gusts and lulls most frequent?

A

near the ground caused by friction between moving air and obstacles like cliffs and buildings and by variation of earth temperature.

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7
Q

what is a squall?

A

they are blasts of wind which sets in suddenly- lasts for several minutes and faces usually associated with a rapidly moving cold front or thunderstorm.

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8
Q

how is surface wind measured?

A

using an anemometer, mounted at a standard height of 10m above ground in an open situation. Consisting of 3 hemispherical cups mounted on a vertical spindle that rotates as the wind blows.

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9
Q

what are the two groups of wind?

A

mean and variable

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10
Q

what acronym is added if wind speed is too hard to read?

A

VRB

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11
Q

what strength do windsocks come in?

A

15 and 25kts.

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12
Q

what are the different ways to detect wind?

A

smoke, dust and windsocks, cloud shadow, wind ripples, waves

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13
Q

how fast does wind have to be to produce wave ripple caps?

A

7-10kts

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14
Q

what does wind produce on the surface of water and what happens when it goes over 15kts?

A

wind lanes

over 15kts it may spray or foam in parllel lines called spindrifts.

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15
Q

what is the force that is responsible for starting a parcel of air to move?

A

pressure gradient force

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16
Q

what will the pressure gradient force always act on?

A

right angles(perpendicular) to isobars

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17
Q

what happens when isobars are closer together?

A

pressure changes occur over a short distance and gradent is said to be stronger.

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18
Q

what happens if isobars are far apart?

A

pressure changes are more gradual and so the pressure gradient is weak.

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19
Q

what is the relationship between wind speed and pressure gradient?

A

the speed of the air will increase with the magnitude of the pressure gradient.

20
Q

what will the winds do in isobars?

A

it will blow across isobars and equalize the pressure distribution - pressure gradients will weaken.

21
Q

what is the correlation between wind and pressure gradient?

A

the wind is caused by the strength of the pressure gradient, the stronger the gradient stronger the wind.

22
Q

what is coriolis force?

A

The rotation of the Earth produces the same deviating force on objects in motion whether they
are bullets or wind.

23
Q

what does the Coriolis force act as?

A

a deviating force on objects moving over rotating surfaces.

24
Q

how is the Coriolis force strength increased?

A

its strength increases with rate of rotation and speed of an object.

25
Q

what way does the Coriolis force deflect to in the northern hemisphere

A

right

26
Q

what way does the Coriolis force deflect to in the southern hemisphere

A

left

27
Q

what happens to wind at the equator of the earth and how does the Coriolis force affect it?

A

wind at the equator isn’t deflected because they’re completely parallel to the axis of rotation between two poles.

28
Q

what is the strength of the Coriolis force immediately north or south at the equator and at the poles?

A

at the equator north or south it immediately begins, and gets stronger the closer it is to the poles.

29
Q

what is geostrophic wind?

A

geostrophic flow is the theoretical wind that would result from an exact balance between the Coriolis force and the pressure gradient

30
Q

what is coriolis force dependent on?

A

the latitude due to the spherical shape of the earth

31
Q

what is wind veering?

A

wind that changes direction in a clockwise direction

32
Q

what is wind backing?

A

wind that changes direction in a counterclockwise direction

33
Q

what is the limitation of windsocks?

A

Wind direction indicators are reactionary, i.e. you will only see the
results of what the wind has been doing a short time later. They are also useful as trend
indicators, but they are not reliable in rapidly changing conditions

34
Q

how are shadow clouds used to detect wind direction?

A

The movement of cloud shadow over the ground gives the wind direction and some indication
of speed, at the cloud’s altitude. This is used only as a guide, however, as the wind on the
ground will probably be different.

35
Q

how are wind ripples used to detect wind direction?

A

Wind ripples may be evident on water or crop fields.

Waves and ripples form at right angles to the wind and move downwind

36
Q

how are wind shadows used to detect wind direction?

A

Wind shadow may be seen on the upwind side of a lake or pond

or around a coastline which will indicate wind direction

37
Q

what can geostrophic force be defined as?

A

a wind blowing along straight parallel isobars, not changing with time, under the balance of pressure gradient and coriolis forces only. if either forces become stronger isobars curve

38
Q

what is the steady flow of wind around isobars called?

A

gradient wind.

39
Q

state buys ballots law.

A

If the wind is Geostrophic and you stand (or sit) with your back to the wind in the Southern
Hemisphere, the low-pressure region will be on your right. By applying Buys Ballot Law,
certain general rules can be stated.

40
Q

how can buys ballots law be used to determine pressure areas and how can it be used as a forecasting tool?

A

Let’s say you’re flying an aircraft in the Southern Hemisphere, and you are experiencing drift
towards your left (wing tip).
If this wind is Geostrophic, then your aircraft is therefore flying towards a Low-pressure area.
Wind, however, does not always conform to Geostrophic flow pattern

41
Q

what is surface friction?

A

Friction always reduces the speed of the air. So, surface friction can affect the course of the
parcel of air quite substantially.

42
Q

what are the factors affecting surface friction?

A

the type of terrain and air density. during a cold night, friction layer is very dense and when its warm its less dense.

43
Q

what is the friction layer? and at what height is it generally not effective?

A

The Friction Layer. The lowest layer of the earth’s atmosphere, usually up to 3,300 feet. Surface friction is effective in slowing down wind up to approximately 1,500 to 3,000 feet above the ground.

44
Q

what is the relationship between the surface frictions reduction in wind strength with the coriolis force and pressure gradient force?

A

The reduction in wind strength from surface friction causes the Coriolis force to reduce, making
the Gradient force more dominant, thereby causing the air to flow across the isobars. Therefore,
surface friction over the sea, particularly with a warm evening, will cause the surface wind to
deviate slightly towards the low-pressure area.

45
Q

what happens to surface friction after sunset?

A

After sunset, the surface
friction becomes higher
then during the day due
to the colder, denser air.

46
Q

what happens to the wind strength when surface friction affects it after sunset?

A

This causes the wind strength to decrease and
for the wind to “Veer’ as it blows across the
isobars from High to Low pressure

47
Q

what happens to the wind strength when surface friction affects it after sunrise?

A

After sunrise (during the day), the wind strength increases, and the wind “Backs” as the wind flows along the isobars.

PPL Met (20 decks)

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