How to Subtract Negative Numbers: A Real-Life Example (from Weather Forecast)

To subtract a negative number, you simply change its sign from minus to plus. But why do we do this? What's the purpose of subtracting negative numbers? Let's explore a practical example to understand why this skill is important.

Subtracting Negative Numbers for Predicting Thunderstorms

Introduction

Ever wondered what causes thunderstorms? They happen when the atmosphere becomes unstable.

But what makes the atmosphere unstable? An unstable atmosphere occurs on very hot days, where warm air rises rapidly—so rapidly that when it reaches high altitudes, its temperature remains higher than the surrounding atmosphere.

For instance, the temperature of the lifted air mass might be -5 degrees Celsius, while the surrounding atmosphere might be -11 degrees Celsius (as shown in the animation below).

Animation demonstrating the ascent of warm air. At high altitude, its temperature is -5°C, while the surrounding air temperature is -11°C.

Calculating Lifted Index: An Example

Meteorologists use the term Lifted Index to describe the difference between temperatures. It’s calculated by subtracting the temperature of the lifted air mass from the temperature of the surrounding atmosphere. In our example, we subtract two negative numbers: from -11, we subtract -5. The Lifted Index is, therefore:

\[-11 – (-5) = -6\].

A negative Lifted Index indicates an unstable atmosphere. The more negative it is, the more unstable the air, and the higher the probability of a thunderstorm. This method is one of the ways meteorologists predict thunderstorms.

Conclusion

This example vividly demonstrates the practical application of subtracting negative numbers in meteorology. Calculating the Lifted Index is a standard practice used on a daily basis. While there are advanced technological solutions like satellites and weather balloons for measuring temperatures, basic mid-school mathematics remains invaluable for the necessary calculations.

Try it in interactive simulation!

We’ve created a special interactive simulation where you can try making a thunderstorm forecast by calculating the Lifted Index through subtracting negative numbers. Click on the picture below to access this simulation.

Screenshot of the simulation for calculating Lifted Index through subtracting negative numbers.

Check the Facts!

You can easily verify the accuracy of this information and explore more on your own. Try a Google search with the keywords “Lifted Index” or check out the Wikipedia article here about the Lifted Index, or visit the National Weather Service here.

Video version

We also have a video version available! It provides more in-depth information, additional examples, and explains how knowledge in physics, chemistry, geography, and biology is essential for understanding weather and climate. Check out the preview below or subscribe to the full video.

Further Reading:

Curious to discover more about how negative numbers are applied in real life? This article will delve into how negative numbers play a role in Smart Agriculture:

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