ATPL Meteorology - Class 3: Pressure.

Summary

In this meteorology class, we explore atmospheric pressure, its role in weather, and how it varies with altitude. The formula for pressure, p = f/a, is introduced, explaining how air pressure decreases with altitude due to fewer air particles and reduced weight. We learn about different pressure settings like QFE, QNH, and QFF, crucial for aviation, and their impact on altimeter readings. The video also delves into isobar charts, illustrating lines of equal pressure, and how they help predict weather patterns, such as wind strength indicated by the proximity of isobars.

Takeaways

• 🌍 Pressure is the force exerted per unit area and is a key factor in weather patterns.
• 📉 As altitude increases, air pressure decreases due to fewer air particles and reduced weight.
• 🔍 The standard rate of pressure decrease is approximately 1 hectopascal per 27 feet or 30 feet for quick calculations.
• 📏 Pressure is measured in hectopascals (hPa), which is equivalent to millibars (mb).
• 🌡 The international standard atmosphere at sea level has a pressure of 1013.25 hPa or 29.92 inches of mercury.
• ✈️ Altimeters use the difference in pressure to calculate altitude, applying a standard lapse rate.
• 🌡️ Temperature variations affect the lapse rate, which is why temperature corrections are crucial for accurate altitude readings.
• ✈️ QFE, QNH, and QFF are different pressure settings used in aviation, each with specific applications.
• 📊 Isobars on weather maps represent lines of equal pressure, and their spacing can indicate wind strength.
• 🌬️ Close isobars signify stronger winds, while widely spaced isobars indicate calmer conditions.

Q & A

What causes the sensation of ears popping during an aircraft's climb?

The sensation of ears popping is due to the sudden drop in pressure experienced as the aircraft ascends. This change in pressure is a result of the decrease in air density at higher altitudes.

How does pressure affect weather patterns?

Pressure changes on the Earth's surface are a significant driving factor in weather patterns. High and low-pressure systems influence the movement of air masses, which in turn affects temperature, humidity, and precipitation.

What is the formula for calculating pressure?

The formula for calculating pressure is p = F/A, where 'p' stands for pressure, 'F' is the force applied, and 'A' is the area over which the force is distributed.

Why does pressure decrease with an increase in altitude?

Pressure decreases with altitude because there are fewer air particles above exerting force per unit area. As altitude increases, the weight of the air column above decreases, leading to a reduction in pressure.

What is the standard rate of pressure decrease with altitude?

The standard rate of pressure decrease is approximately one hectopascal for every 27 or 30 feet of altitude increase.

How is pressure measured, and what units are commonly used?

Pressure is commonly measured in hectopascals (hPa), which is the same as millibars (mb). In some regions, inches of mercury (inHg) is also used. One hectopascal is equivalent to one millibar.

What is the sea level pressure in the international standard atmosphere?

In the international standard atmosphere, the sea level pressure is 1013.25 hectopascals (hPa) or 1013.25 millibars (mb), which is equivalent to 29.92 inches of mercury (inHg).

How do altimeters work, and what are the different pressure settings they use?

Altimeters work by sensing the difference in pressure between a datum point and the current pressure. They use different pressure settings such as QFE (field elevation), QNH (mean sea level pressure), and QFF (flight level pressure) to calculate altitude.

What is the difference between QNH and QFF in aviation?

QNH uses a standard lapse rate of 27 feet per hectopascal to calculate sea level pressure, while QFF factors in temperature corrections to provide a more accurate sea level pressure for the day's conditions.

How can temperature affect the pressure altitude reading in an aircraft?

In cold air, pressure levels become compressed, causing the true altitude to be lower than the indicated altitude. This is accounted for by applying temperature corrections to the pressure altitude reading.

What is an isobar, and how are they used in weather prediction?

An isobar is a line on a weather map connecting points of equal pressure. Isobars help predict weather patterns as they indicate areas of high and low pressure, which influence wind strength and direction.