fss 309.2 - describe the effect of the boundary layer on wind velocity

The boundary layer is that layer which is generally considered to be from ______ to _____.

surface, 3,000 feet

In the boundary layer, wind is impacted by _____, which results when the wind interacts with ____.

“friction force”, the Earth’s surface

Due to the friction force, the ______ is diminished.

Coriolis effect

Over the water, the change is negligible, whereas over built up areas such cities, or areas with rough terrain, there is a significant impact.

Friction _____ wind speed and modifies wind direction.

diminishes

As aircraft climb away from the influence of the Friction Force, they encounter a change in wind direction as it _____ and _____ in speed.

veers, increases

Landing aircraft can expect the wind to ___ and ___.

back, decrease

Surface Wind = ____ + ____ + ____

PGF, Fc, Ff

With strong friction, the wind will move towards the _____, with less friction the wind direction will be more in-line with _____.

the Pressure Gradient Force, the Coriolis Force

A considerable amount of friction (due to ______) will cause the winds to strongly counteract the Coriolis Effect and cross the isobars at a considerable angle.

rougher terrain or greater wind speed

What are the two effects that diminish the effect of friction?

Altitude and daytime heating

Daytime heating diminishes the friction effect by increasing the _____ in the boundary layer, and flying above the boundary layer will also diminish the effect of friction.

air mixture

A katabatic wind, from “katabasis” meaning “descending”, is the technical name for _____. It is a wind that carries _____ from a higher elevation down a slope under the force of gravity

a drainage wind, high density air

Katabatic wind will occur during the day over _____ but will be less intense due to mixing associated with _____.

ice covered slopes, daytime heating

Katabatic winds are sometimes called _____, and can rush down at hurricane speeds, but most are in the order of _____.

10 knots or less

Not all downslope winds are katabatic. Winds such as the chinook, are rain shadow winds where air driven upslope on the _____ of a mountain range drops its moisture and descends _____ drier and warmer.

windward, leeward

An anabatic wind, from “anabatos” meaning “moving upward”, is a _____ which blows up a steep slope or mountain side, driven by heating of the slope through _____.

warm wind, insolation

Anabatic wind is also known as _____.

an upslope wind

Because of anabatic winds, the air over the hill top is warmer than that around it and will rise through _____. This creates a lower pressure region into which the air at the bottom of the slope flows, causing wind.

convection

It is common for the air rising from the tops of large mountains to reach a height where it cools adiabatically to below its dewpoint and forms cumulus clouds. These can produce _____.

rain or even thunderstorms

Barrier effect is when barriers such as mountain range can act like a dam force and change the direction of the wind, forcing the air to either go over or _____ as much as ______ to go around the obstruction.

veer, 90 degrees

A pass in a range of mountain causes the wind to gush through with considerable speed, known as ______.

“funnel effect”

The “valley effect” is when a weak surface wind tends to follow any well-defined valley rather than ____.

the isobaric pattern

True or False: The angle of the wind direction across the isobars will be greater when the wind blows over water than over rough ground.

False

During a descent from 1,000 metres to the Earth’s surface, will the wind back and decrease or veer and increase?

Back and decrease

What can be used to determine the wind at 1,000 meters?

Pressure Gradient Force