405.1a - hazards to aviation posed by standing waves

Thunderstorm clouds will develop when the air is ______ to high levels, the relative humidity is _____, and the process of ______ is very strong.

unstable, very high, lift

The 3 stages in the life cycle of a thunderstorm cloud are ____, ____, and ___.

the cumulus stage, the mature stage, and the dissipating stage

The beginning of precipitation indicates the cell has begun _____.

the mature stage

The dissipating stage is characterized by?

downdrafts

The first downdrafts can be relatively abrupt; this will cause an abrupt rise in surface _____ and a fall in surface ______.

pressure, temperature

The stage characterized mainly by updrafts is called _____.

the cumulus stage

The two main categories of thunderstorms are _____.

air mass and frontal thunderstorms

A long line of thunderstorms is generally due to _____

a cold front

Severe clear and mixed icing is possible in ______ of development of thunderstorm clouds.

all stages

Heavy precipitation under a cumulonimbus cloud can rapidly reduce _____.

visibility and ceilings

List 4 effects of icing on aircraft

Modifies aerodynamics, engine stalls, instrument errors, and loss of visibility

Standing waves are waves or ripples which form in the atmosphere caused by air encountering ___________ at the surface of the Earth.

an obstruction or barrier

When the obstruction causing a standing wave is a mountain or range of mountains, the resulting waves are called ______

“lee waves”

For a standing wave to form, the 4 conditions required are:

• An obstruction or barrier

• A sufficiently strong wind must be blowing at ______ (at enough of an angle) across the barrier

• A layer of ______ above the barrier

• A strong vertical wind shear should exist ______

the height of the peak, stable air, above the peak of the barrier

What is the minimum wind speed required to create a mountain wave?

25 knots

For a 25-knot wind to hit a barrier with its full force, it must be blowing ______ to the barrier

perpendicular

Why do standing waves require stable air above the barrier?

Unstable air will tend to break up the wave

The usual horizontal extent of a mountain wave system varies from ____ or more on the lee side (downwind side) of the barrier. The wavelengths can vary _____.

80 to 240 km, 3 to 30 km

When sufficient moisture is present, characteristic cloud formations and patterns develop making it possible to visually identify the presence of a mountain wave system. Three different types of clouds are associated with mountain waves. These are:

Cap cloud, rotor cloud, lenticular cloud

How would a lenticular cloud be indicated in the remarks section of a METAR?

SC LENT, AC LENT, or CC LENT

Cap cloud will be found on ____ and often down ____.

the tops of the range, the leeward slope

Rotor clouds are found in _____ of the mountain wave system immediately below the ____ of individual waves.

the lower levels, crests

Rotor clouds are named because each marks the presence of turbulence in the form of _____.

powerful circular eddies

Lenticular clouds (lens or almond shaped) form on the wave crest aloft and may extend vertically in layers to well above the ____ level.

Horizontally, they may extend for several hundred kilometres (miles) parallel to the range.

40 000-foot (12 km)

Turbulence is present both ____ (possibly right down to ground level) the rotor cloud.

in and below

Turbulence is most common to ____ of the barrier at approximately the level of the peak, as this is the level at which friction occurs between the fast-moving air flowing over the barrier and the ground behind the barrier.

Often, the turbulence will extend down to the ground when the surface air moves out. This would be a form of _____.

the lee, mechanical turbulence

Turbulence may occur at higher altitudes in a mountain wave system and is most likely when ____ is present.

a jet stream