Winds Quiz For CPL

Wind speed is usually given in knots, but some countries use meters per second or the Met. Wind direction is always reported as the direction from which the wind is blowing. It is typically given in degrees true, but wind direction provided to a pilot by ATC or in an ATIS is given in degrees magnetic.

The Föhn wind is a warm, dry wind that blows on the downwind side of a mountain range. It is a local wind in the Alps.

The gradient wind occurs when the isobars are curved. The geostrophic wind blows parallel to straight isobars.

The Bora is a strong, cold wind that blows down the north Adriatic coast. It’s caused by a difference in pressure between Central Europe and the Balkans (high pressure) and the Adriatic Sea (low pressure). The Bora can reach speeds of up to 70 knots or more, with even stronger gusts. It’s most common and powerful during the winter months.

Polar frontal depressions are large-scale low-pressure systems. A back is a change in wind direction in a counterclockwise direction that occurs in low-pressure systems in the Northern Hemisphere.

Although Föhn winds are found in the Alps, the term is used generically for similar winds elsewhere. One example is the Chinook, which blows on the eastern side of the Rocky Mountains in North America.

Buys Ballot’s Law states that:

If an aircraft is experiencing starboard drift in the Northern Hemisphere, it is heading toward a low-pressure system.
If an aircraft is experiencing starboard drift in the Southern Hemisphere, it is heading toward a high-pressure system and away from a low-pressure system.

Surface wind is measured by a wind vane, which aligns with the wind direction, and an anemometer, which measures speed. The anemometer’s rotating cups drive a generator, with the output displayed in knots.

Both instruments are positioned 33 feet (10 meters) above ground and clear of obstructions to ensure accuracy. An anemograph records wind speed and sometimes direction.

A wind blowing against a mountain is impeded. If the barrier is interrupted by a gap or valley, the wind will blow along the valley at an increased speed due to the restriction.

In a high-pressure system, if air is moving steadily around the center, the centrifugal force acts in conjunction with the pressure gradient force, increasing the velocity of the wind.

The gradient wind speed around an anticyclone is greater than the geostrophic wind speed for the same isobar interval. Therefore, if the Geostrophic Wind Scale (GWS) is used, it will underestimate the actual wind speed.

If air is moving steadily around a high-pressure system, then the centrifugal force acts along with the Pressure Gradient Force (PGF), increasing the velocity of the wind.

In the Southern Hemisphere, winds blow clockwise around a low-pressure system. If you’re flying away from a low, the wind must be coming from your left to maintain this clockwise pattern.

Near the ground, friction slows the wind down, so it doesn’t flow exactly parallel to the isobars.

Since you’re flying away from a low, the wind will naturally want to flow towards it. This means you’ll also experience a slight headwind, even though you’re flying away.

During the day, a sea breeze blows from the sea toward the land due to cooler ocean temperatures. At night, a land breeze blows from the land toward the sea as the land cools faster.

On the downwind leg, winds come from the left, while on the final approach, winds shift and come from the right.

Since surface friction has reduced the wind velocity, resulting in a reduction in the Coriolis force, the Pressure Gradient Force (PGF) becomes more dominant. This causes the wind to blow across the isobars toward the low-pressure area.

Air moves from high to low pressure, creating a pressure gradient force. This force drives the movement of air, which we feel as wind.

Due to friction, the surface wind is slower than the geostrophic (freestream) wind. In the Northern Hemisphere, the surface wind backs. In the Southern Hemisphere, the surface wind veers.

As you go higher in the atmosphere, the air gets thinner. This means that the temperature has a bigger effect on the wind direction than the pressure does. Because of this, the wind tends to blow more and more from the west as you go higher. The strongest winds are usually found near the top of the troposphere.

1 kilometer is equal to about 0.54 nautical miles.
So, if you have 90 kilometers, you can multiply it by 0.54 to get 48.6 nautical miles.

In a low-pressure system, the wind tends to blow slower than it would if there were no friction. This is because the centrifugal force (which pushes outward) works against the pressure gradient force (which pushes inward).

So, if you use a scale that assumes the wind blows at a certain speed based on the pressure difference, you’ll end up overestimating the actual wind speed in a low-pressure system.

After sunset, the land will cool rapidly while the sea retains its heat. This will cause an increase in surface pressure over the land and a decrease in pressure over the sea, resulting in a land breeze. The speed of the land breeze will be approximately 5 knots, extending about 5 nautical miles out to sea.

The surface wind over land is backed by 30 degrees from the geostrophic wind, and its speed is reduced by 50%.

The Coriolis force (CF) is the force caused by the rotation of the Earth. It acts 90° to the wind direction, causing air to turn to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. CF is maximum at the poles and minimum at the equator.

True altitude and indicated altitude remain the same; hence, there is no crosswind.

The pressure gradient is the change in pressure over a distance. It is steeper in low-pressure systems and shallower in high-pressure systems. A steeper pressure gradient creates a stronger force that pushes air towards low-pressure areas. This force is related to the wind speed.

The geostrophic wind speed will increase as latitude decreases.

Wind is caused by air moving from high to low pressure. However, the Earth’s rotation deflects this flow, making it curve. In the Northern Hemisphere, winds are deflected to the right, and in the Southern Hemisphere, they are deflected to the left. This causes wind to flow around high and low-pressure areas rather than directly between them.

Buys Ballot’s Law states that if an observer stands with their back to the wind, the lower pressure will be on their left in the Northern Hemisphere and on their right in the Southern Hemisphere.

A corollary of this law is that if an aircraft is experiencing starboard drift in the Northern Hemisphere, the aircraft is heading toward low pressure.

As a result of thermal mixing, there can be a regular change in the surface wind every 24 hours. It veers and increases during the day, reaching maximum strength around 1500 hours.

In the diagram below, high pressure is shown to the right.

Jet streams generally flow in a westerly direction, reaching maximum speeds near the tropopause. In Europe, wind speeds of up to 200 knots have been recorded.

Buys Ballot’s Law states that if an observer stands with their back to the wind, lower pressure will be to their left in the Northern Hemisphere and to their right in the Southern Hemisphere.

A corollary is that if an aircraft is experiencing starboard drift in the Northern Hemisphere, it is heading toward low pressure.

Wind is the horizontal movement of air from high to low pressure.

Easterly and westerly jets are found in the Northern Hemisphere, whereas the Southern Hemisphere has westerly jet streams only.

Geostrophic wind occurs above the friction layer, where surface friction no longer slows the wind. Within the friction layer, friction reduces wind speed, weakening the Coriolis force, causing an imbalance. The height of the friction layer varies based on surface type and time of day, but geostrophic wind typically starts between 2,000 and 3,000 feet.

The Föhn Wind is a warm, dry wind that blows on the downwind side of a mountain range, common in the Alps. When moist air is pushed up a mountain, it cools as it rises. Once it reaches the condensation level, clouds form, and the air cools at the Saturated Adiabatic Lapse Rate (SALR).