ATPL Meteorology - Class 14: Pressure Systems and Air Masses.

Summary

This script delves into the world of meteorology, focusing on pressure systems and air masses. It explains how isobar charts depict equal pressure lines, leading to weather patterns like cyclones and anticyclones. The video explores the effects of low and high-pressure systems on wind and cloud formation, and how air masses, classified by their origin and surface type, influence weather predictability. It also discusses the impact of air mass movement on temperature, humidity, and visibility, providing a foundation for understanding weather forecasting.

Takeaways

• 🌍 Isobar charts display lines of equal pressure on Earth's surface, which can be used to predict weather patterns.
• 🌀 Low pressure systems, or depressions, are characterized by air flowing inwards and rising, leading to unstable conditions and often resulting in cumulonimbus clouds and heavy weather.
• 🔄 The Coriolis effect causes winds to rotate counterclockwise around lows in the Northern Hemisphere, influencing the formation of weather systems.
• 🌪 Deeper lows with steeper isobars indicate stronger winds and more intense weather phenomena, such as hurricanes or cyclones.
• ☀️ Anticyclones represent high pressure areas with winds flowing outwards and descending, typically resulting in clear skies and stable conditions.
• 🌡️ The size of pressure systems can vary greatly, from small localized systems to large-scale patterns spanning thousands of miles.
• 🌈 Air masses bring predictable weather based on their temperature, humidity, and origin, influencing the type of clouds and precipitation they produce.
• 🌍 Different air masses are classified by their source region (e.g., equatorial, tropical, polar, Arctic) and the surface type they move over (e.g., maritime, continental).
• 🌡️ As air masses move towards the equator, they warm up, decrease in stability, and experience a drop in relative humidity due to increased water vapor capacity.
• 🌬️ When air masses move away from the equator, they cool down, increasing in stability and relative humidity as the saturation water vapor pressure decreases.
• 🌦️ Specific air masses, such as tropical maritime or Arctic continental, have distinct weather implications depending on their movement and interaction with the environment.

Q & A

What is an isobar chart and what does it represent?

An isobar chart is a type of meteorological map that shows lines of equal pressure at mean sea level, either measured directly or calculated using temperature lapse rates. These lines, called isobars, are spaced typically two or four hectals apart, and areas where they are closely packed indicate a steeper pressure gradient, which corresponds to faster changes in pressure.

What are the typical weather patterns associated with low pressure systems on an isobar chart?

Low pressure systems, also known as depressions or cyclones, are characterized by isobars that are closely packed around a center of low pressure. These systems typically bring unstable conditions, leading to cumuliform clouds, showers, and in extreme cases, tropical revolving storms such as hurricanes or cyclones.

How does the wind flow around a low pressure system?

In the Northern Hemisphere, wind flows into the center of a low pressure system and turns anti-clockwise due to the Coriolis force, creating a general motion of air towards the center of the low pressure area.

What is the opposite weather pattern to a low pressure system?

The opposite of a low pressure system is a high pressure system, also known as an anticyclone. These systems have isobars that are further apart, indicating lighter winds and generally clear skies with stable conditions.

How does the Coriolis effect influence the wind flow around an anticyclone?

In the Northern Hemisphere, the Coriolis effect causes the wind to flow clockwise around an anticyclone, with air diverging away from the center at the surface and converging at higher levels, leading to descending air and generally clear weather conditions.

What are the differences between a trough, a ridge, and a cut-off low on an isobar chart?

A trough is a valley of low pressure, extending out from a cyclone and associated with cumuliform clouds and showery conditions. A ridge is a valley of high pressure, extending from an anticyclone, associated with clear skies and stable conditions. A cut-off low is a high pressure area that is isolated from the main belt of high pressure, leading to very still conditions and often clear skies.

How do air masses form and what factors influence their properties?

Air masses form in regions of the Earth where the temperature and humidity are relatively uniform. They are influenced by their source region's temperature and the surface type over which they travel, such as maritime (over the sea) or continental (over land), which affects their humidity levels.

What are the general rules for how air masses behave as they move towards or away from the equator?

As air masses move towards the equator, they warm up, leading to increased instability and a decrease in relative humidity due to rising saturation water vapor pressure. Conversely, as they move away from the equator, they cool down, becoming more stable and increasing in relative humidity as the saturation water vapor pressure decreases.

How do the properties of an air mass affect the weather when it moves over a different region?

The temperature and humidity of an air mass, along with the surface type it moves over, determine the weather conditions it brings. For example, a warm maritime air mass moving over land may bring high humidity and drizzle, while a warm continental air mass may result in clear skies and high temperatures.

What is the significance of the Hadley cells in the formation of predictable high pressure areas?

Hadley cells are responsible for the formation of predictable high pressure areas, particularly in the tropics. Warm air rises at the equator, creating a low pressure zone, and as this air moves away from the equator, cools, and descends, it creates areas of high pressure known as the tropics, often associated with clear skies and stable conditions.

How do air masses from different source regions affect the weather in Europe?

In Europe, various air masses from different source regions can affect the weather. For example, a tropical maritime air mass moving north towards Europe would likely bring warm, wet conditions with high relative humidity, while a polar continental air mass could bring clear skies and very cold temperatures in the winter.