7.2 Wind and Currents - Practice Questions

You're operating a fixed-wing UA over barren ground on a hot day at low-altitude. You can expect to encounter

• good visibility.

• bumpy, turbulent air.

• smooth, moist air.

Answer explanation

Different surfaces radiate heat in varying amounts. Plowed ground, rocks, sand, and barren land give off a large amount of heat; water, trees, and other areas of vegetation tend to absorb and retain heat. This uneven heating of the air creates small areas of local circulation called convective currents.

Convective currents cause that bumpy, turbulent air sometimes experienced when flying at lower altitudes during warmer weather. On a low-altitude flight over different types of surfaces, updrafts are likely to occur over areas like pavement or sand, and downdrafts often occur over water or expansive areas of vegetation like a group of trees.

The change in wind speed and direction over a short distance is known as

• temperature inversion.

• wind shear.

• wind vortex.

Answer explanation

Wind shear is a sudden, drastic change in wind speed and/or direction over a relatively small area. Wind shear can occur at all altitudes, in all directions, and commonly associated with passing frontal systems, thunderstorms, and temperature inversions with strong upper level winds.

Low-level (low-altitude) wind shear can be particularly hazardous for remote pilots, due to the proximity of your UA to the ground. Wind shear can cause violent updrafts and downdrafts, and due to increased wind speed, it can push your aircraft around horizontally with sudden, unforeseen force.

There are many considerations when looking at wind. Which of the following is generally not a concern:

• Wind shear

• Tide pools

• Local wind

Answer explanation

Wind shear is an extremely important consideration when thinking about wind. So are the local wind conditions, particularly around mountainous environments or large obstructions like buildings. Tide pools are not a consideration when looking at wind.

Where does wind shear occur?

• Only at higher altitudes

• Only at lower altitudes

• At all altitudes

Answer explanation

Wind shear is a sudden, drastic change in wind speed and/or direction over a relatively small area. Wind shear can occur at all altitudes, in all directions, and it’s typically characterized by directional wind changes of 180° and speed changes of 50 knots or more.

When may hazardous wind shear be expected?

• When moist, unstable air crosses a mountain barrier

• Following frontal passage when cumulus clouds form

• In areas of low-level temperature inversion, frontal zones, and clear air turbulence

Answer explanation

Wind shear is commonly associated with passing frontal systems, thunderstorms, and temperature inversions with strong upper level winds (greater than 25 knots).

While operating around buildings, the Remote PIC should be aware of the creation of wind gusts that:

• Enhance stability and imagery

• Change rapidly in direction and speed causing turbulence

• Increase performance of the aircraft

Answer explanation

Obstructions on the ground can affect the flow of wind, and this can be an unseen danger. Ground topography and large buildings can break up the flow of the wind and create wind gusts that change rapidly in direction and speed.

These obstructions range from man-made structures like hangars, to large natural obstructions, such as mountains, bluffs, or canyons. Of course, the intensity of the turbulence associated with ground obstructions depends on the size of the obstacle and the primary velocity of the wind, but just know that you need to be especially vigilant when flying around large buildings or large natural obstructions.

You have received an outlook briefing from flight service through 1800wxbrief.com. The briefing indicates you can expect a low-level temperature inversion with high relative humidity. What weather conditions would you expect?

• Smooth air, poor visibility, fog, haze, or low clouds.

• Light wind shear, poor visibility, haze, and light rain.

• Turbulent air, poor visibility, fog, low stratus type clouds, and showery precipitation.

Answer explanation

A temperature inversion exists where there is an increase in temperature as altitude is increased. The air is stable, so you can expect smooth air and poor visibility due to fog, haze, or low clouds. The most frequent type of ground based inversion is that produced by terrestrial radiation on a clear, relatively still night.