Question

You and a friend are watching TV on a rainy day, when the weather reporter says, "The barometric pressure is 28.8 inches and rising." Hearing this, you say, "It looks like fair weather is on its way." Your friend responds with the following questions: "I thought air pressure had something to do with the weight of air. How does inches relate to weight? And why do you think the weather is going to improve?" How would you respond to your friend's queries?

Short answer

Inches measure atmospheric pressure in a mercury column. Rising pressure often signals good weather ahead.

Step-by-step solution

Understanding Barometric Pressure

Barometric pressure, also known as atmospheric pressure, is the force exerted by the weight of air in the atmosphere on a given surface area. The unit 'inches' refers to inches of mercury (inHg), a common way to measure atmospheric pressure using a mercury barometer.

Explaining Inches of Mercury

Inches of mercury (inHg) is a unit used to measure atmospheric pressure. A barometer uses mercury in a glass tube; as the air pressure increases, it pushes the mercury higher in the tube, and the height of the mercury column, measured in inches, indicates the atmospheric pressure. Therefore, '28.8 inches' means the mercury column is 28.8 inches high due to the air pressure.

Relationship Between Pressure and Weather

High air pressure, indicated by a rising pressure on the barometer, usually signifies good weather. This is because high pressure tends to bring dry and clear weather, whereas low pressure can lead to clouds and precipitation.

Connecting Pressure Changes to Weather Prediction

When the weather report mentions that the barometric pressure is '28.8 inches and rising,' it suggests that the high pressure is increasing. This rise typically indicates the approach of clearer and more stable weather conditions, hence the statement "it looks like fair weather is on its way."

Key concepts

Atmospheric Pressure

Atmospheric pressure is a vital concept in understanding the weather and how it changes. It refers to the weight of the air above a certain point on Earth. Since air has mass, it exerts a downward force due to gravity, and this force is called atmospheric pressure. At sea level, the "standard" atmospheric pressure is about 1013 millibars or 29.92 inches of mercury (inHg).

Weather varies with changes in atmospheric pressure. High pressure often means calm weather, while low pressure can lead to storms. Therefore, knowing the atmospheric pressure helps meteorologists (weather experts) predict weather patterns.

Inches of Mercury

The term "inches of mercury" (inHg) might sound confusing, but it's simply a unit to measure atmospheric pressure. This measurement comes from mercury barometers, which are instruments used to measure the weight of the air.

A mercury barometer works using a column of mercury. When air pressure rises, it pushes the mercury to a higher point in a glass tube. Therefore, stating the pressure as "28.8 inches of mercury" means that the column of mercury has risen to 28.8 inches due to the weight of the surrounding air.

Measuring pressure in this way helps keep track of whether air pressure is rising or falling, which can signal different weather conditions.

Weather Prediction

Weather prediction involves analyzing atmospheric conditions to forecast upcoming weather. One key tool for this is understanding changes in barometric pressure.

When weather reports say the pressure is rising, it often means the weather is improving, moving towards clearer skies and stable conditions. This happens because a rising pressure is usually associated with an incoming high-pressure area. Conversely, falling pressure can indicate deteriorating weather with possible rain or storms.

Thus, monitoring the changes in atmospheric pressure provides crucial information for predicting likely weather scenarios.

High and Low Pressure Systems

In the world of weather, high and low pressure systems play significant roles. High pressure systems are associated with sinking air. As the air descends, it warms up and tends to block cloud formation, leading to calm and clear weather. Low pressure systems, in contrast, involve rising air which cools and condenses, forming clouds and often bringing rain and thunderstorms.

Understanding the movement and effects of these pressure systems is essential for weather forecasting. High pressure systems are usually linked to good weather, while low pressure systems can bring clouds and precipitation.

• High pressure: Clear skies, calm weather.
• Low pressure: Cloudy, possibly rainy or stormy weather.

Tracking these patterns helps meteorologists provide accurate weather predictions to the public.