ATPL Meteorology - Class 10: Visibility.

Summary

This video script delves into the critical aspect of visibility for aviation, explaining how fog and mist can impede safe landings at airports. It outlines various types of fog, including radiation, advection, evaporation, frontal, and orographic fog, all resulting from the cooling of humid air below the dew point. The script also distinguishes between fog and mist based on visibility metrics and addresses man-made visibility issues like smog and haze. It further clarifies the measurement of visibility, the concept of runway visual range (RVR), and the impact of visual segment on pilots' perception of fog density during landing approaches.

Takeaways

• 🌫️ Visibility is crucial for safe aircraft landings at airports, and understanding what causes low visibility can help determine the safety of landing.
• 🌞 Reduced visibility can be caused by natural environmental factors like sunlight glare or cloud cover, which reflects light and impairs viewing through a windscreen.
• ✈️ At higher altitudes, pilots rely on instruments and instrument flight rules, but near the ground, they depend on visual cues for takeoff and landing.
• 🌁 Fog or mist, which are types of clouds at ground level, are significant factors affecting visibility, with fog defined as having visibility less than a thousand meters and mist as less than 5000 meters.
• 🌡️ Radiation fog forms when cool ground temperatures radiate and cool the air above it to below the dew point, causing moisture to condense into fog, typically occurring in the early morning.
• 🌤️ Advection fog occurs when warm, humid air moves over a cold surface, cooling the air to below the dew point and forming fog, often seen in coastal areas.
• 💧 Evaporation fog happens when water vapor evaporates and then cools the air above it to below the dew point, forming fog, common in the Arctic regions.
• 🌦️ Frontal fog is created when a warm air front moves over a cold air mass, causing the warm air to rise and cool, leading to condensation and fog formation at the surface.
• 🏞️ Orographic fog results from air being forced to rise due to terrain, like mountains, cooling as it ascends and forming fog if it cools below the dew point.
• 🏭 Man-made visibility issues can arise from pollution, where dust and smoke particles accumulate at low levels and create haze or smog, especially in industrial or densely populated areas.
• 📏 Visibility is measured in increments and can be assessed using physical objects at known distances or more accurately with a transmissometer, which measures light transmission through the air.

Q & A

Why is visibility important for aircraft landing at airports?

Visibility is crucial for pilots to safely land aircraft at airports, especially during takeoff and landing maneuvers, which are not conducted using instruments but by visually assessing the environment outside the aircraft.

What is the primary difference between fog and mist?

Fog is characterized by visibility less than a thousand meters, while mist has visibility less than 5000 meters. This distinction is based on the level of visibility they create.

How does radiation fog form?

Radiation fog forms when the cold surface of the earth at night cools the air just above it through radiation, causing the air to cool down to below the dew point, leading to the condensation of moisture and the formation of clouds.

What type of fog is commonly seen in coastal areas?

Advection fog is commonly seen in coastal areas, which occurs when warm humid air blows over a cold surface, cooling the air to below the dew point and causing water vapor to condense into fog.

How does evaporation fog differ from other types of fog?

Evaporation fog forms when warm water vapor evaporates into colder air above it, causing the air to cool down to below the dew point and water vapor to condense into fog. This type of fog is often seen in the Arctic.

What causes frontal fog?

Frontal fog is created when a warm air front moves in and rises over a colder air mass. Precipitation from the warm front falls into the cooler air below, causing the warm air to cool down to below the dew point and form fog at the surface.

What is orographic fog and how does it form?

Orographic fog forms when humid air is forced to rise due to terrain, such as a mountain. As the air rises and cools adiabatically, if it cools to below the dew point, moisture condenses out to form fog close to the land.

Why do visibility levels differ between ground level and when in flight?

Visibility levels differ because when you are above a layer of fog, you are looking at it from an angle, allowing you to see further. However, as you descend and approach the ground, you look through more of the fog, reducing visibility.

How is visibility measured at airports?

Visibility at airports is measured in increments of 50 meters up to 800 meters, then 100 meters up to 5000 meters, and in thousand-meter steps up to 10 kilometers. Beyond 10 kilometers, visibility might be reported as '10k plus' or with 'four nines'.

What is Runway Visual Range (RVR) and why is it important?

Runway Visual Range (RVR) is a runway-specific visibility measurement that provides an accurate assessment of the visibility conditions on a particular runway. It is important for pilots to determine if it is safe to conduct an approach, especially when using automatic landing systems.

How does the presence of haze or smog affect visibility for aircraft operations?

Haze or smog, which are man-made visibility issues, occur when stable atmospheric conditions trap dust and smoke particles at low levels, causing reduced visibility during takeoff and landing. This is particularly prominent in areas with high industry and population.