Weather and Climate

Introduction

In Primary school, you learnt about the solar system and the position of the planet earth in relation to the sun. In this chapter, you are going to learn about the shape of the earth, the movements of the earth and how
these movements affect time, climate and people’s ways of life in the different parts of the world.

In your home area, people usually take weather and climate to mean the same thing. In this topic, you are going to learn the difference between weather and climate and how you can measure and record weather in an area. Also, you are going to learn how weather and climate affect your own life and the way people in other parts of the world live.

Weather and How it is Measured

Activity 6.1: Understanding weather
1. Look outside. How would you describe the weather around your school?
2. What was the weather like around your school yesterday?
3. Is today’s weather different from that of yesterday or the last three days? If yes, describe the differences.
4. In your own words, explain what you understand by weather.

When we talk of weather, we are actually talking about the conditions of the air or atmosphere at a certain time. The weather may be sunny or cloudy. It may be hot or cold, windy or calm. It may be rainy. Our country has many different kinds of weather at any one time. You have probably realised that even a small area like the one where you live or go to school has different weather conditions every day.

Activity 6.2: Identifying weather conditions
In pairs, study the photographs in Figure 6.1 below and do the following:
1. Identify the different weather conditions in each.
2. Write a paragraph of at least four lines describing the weather conditions in each photograph.
3. Present what you have written to the class.

What are Elements of Weather?
Activity 6.3: Understanding elements of weather
1. In pairs, discuss and list the things you talked about when describing weather in the two activities above.
2. Write them down and share your list with the rest of the class.
The conditions that prevailed in the atmosphere around your school yesterday could have been different from what they are now. What are those conditions called? The things you have listed in Activity 1.3 (a) are called elements of weather. Rainfall, sunshine, heat and coldness (temperature), air pressure, air humidity or moisture in the air and clouds are all things which determine the weather conditions of a place.

How is Weather Different from Climate?

Activity 6.4: Understanding the difference between weather and climate

In groups, do the following:
1. Discuss the pattern of weather in a year in the area where you live.
2. Write at least two paragraphs describing that pattern.
3. Through discussion, share what you have written with the rest of the class.
4. Suggest a name we can give that weather pattern.

In your description, you have probably written about the times of the year or seasons in which you can expect heavy rain or drought in the area where you live. Or you may have talked about the months when temperatures become hotter than usual. When you describe such a pattern of weather, you are talking about the climate of your area. The
kind of weather a place has over a long period of time is its climate. The two most important elements used to describe climate are precipitation and temperature.

What is precipitation?
Activity 6.5: Understanding precipitation
In groups, study the pictures in Figure 6.2 and do the tasks that follow.

1. Identify the type of precipitation you see in each picture and write it in your notebook.
2. Which of those types of precipitation do you usually experience in your home area or around your school?
3. Write two sentences explaining what you understand by precipitation.

The earth’s surface receives moisture from the atmosphere in different forms. All forms of moisture falling from the atmosphere are called precipitation. It may be in the form of rain, snow, hail, sleet or mist. In Uganda and the rest of East Africa, rainfall is the most common and important form of precipitation received.

What is temperature?
Have you ever woken up in the morning when there is mist in the air outside the house? What did you feel on your body? What do you always feel when you sit under the sun? You have probably thought of coldness in the case of a misty morning, and hotness in the case of sitting under the sun. The atmosphere usually has different amounts of heat at different times. The amount of heat in the air is called air temperature. When you say the morning is cold or the afternoon is hot, you are actually talking about the temperature of the air surrounding you.

Measuring and recording elements of weather
Activity 6.6: Measuring weather

Study Figure 6.3 above and do the following:
1. Using previous knowledge, identify the weather instrument shown in each picture.
2. Copy and fill in the table below.

3. For each instrument you have identified, write at least three sentences explaining how it is used to measure and record weather.
4. Present what you have written to the class.
5. What is the name of the place where all weather recoding instruments are kept and used?

Weather changes are very important in our daily lives. This is the reason we have to record weather conditions every day in order to make weather forecasts. Weather forecasts enable people to plan their activities and to take precautions against bad weather. A place where weather is measured and recoded is called a weather station.

Project: Measuring and recording elements of weather in the local area You are going to carry out a project to measure and record elements of weather around your school. You will need a book where you will record
information about the weather conditions on a daily basis. This is called a weather log.

Activity 6.7(a): Making a weather log
1. Write your name on a clean notebook.
2. Write out the days and dates of the month for which you will be recording temperature and rainfall.

Activity 6.7(b): Measuring temperature
Work as a group to carry out this activity at school on a daily basis for a period of three months. You will have to keep a record of the weather elements at your school in your weather log for those three months.
1. Get a thermometer from the science laboratory.
2. Measure and record the lowest and highest temperatures of the day.
The lowest temperature should be measured between 6.00 a.m. and 7.00 a.m. The highest temperature should be between 2.00 p.m. and 3.00 p.m.

Activity 6.7 (c): Rainfall and how it is measured
You are going to make a rain gauge which you will use to measure rainfall. This is a short-term gauge so it is checked after each downpour. Collect the materials listed below and follow the steps outlined to make the gauge.

Materials
• Sharp scissors
• Fine mesh screen/a transparent polythene sheet
• Nail file
• 2 two-litre bottles (or funnel)
• Permanent marker
• Ruler
• Masking tape
• Saucepan or basin

Read the following instructions before beginning the activity:
1. Carefully cut a two-litre bottle with straight sides and a flat bottom into half to make a funnel. File any sharp edges.
2. Place the cut bottle on the uncut bottle so that the spouts/edges are touching and in line.
3. Tightly fix the funnel onto the top of the bottle using the masking tape. Place a transparent polythene sheet over the funnel opening and press it slightly inwards. Tape it in place. Make a hole inside the polythene sheet to direct water into the bottle.
4. Mark the bottle from the bottom ½ cm apart upwards with the permanent marker. For more accurate readings, tape a ruler to the side of the bottle. Each ½ cm represents 500 millimetres.
5. Place the rain gauge outside in an open place.
6. Read off and record in your log book the amount of rainfall received once every 24 hours.

The amount of rainfall recorded during the month is the monthly total rainfall. The amount of rainfall recoded for a whole year is the annual total rainfall. Some months are wet while others are dry. To get the average picture of rainfall received in an area, we divide total annual rainfall by the 12 months in a year. The result is the mean monthly
rainfall. Rainfall figures for all the months in a year can be represented on a bar graph. This enables us to describe the rainfall pattern of an area.

To show how rainfall is distributed over a country like Uganda or a larger region like East Africa, places receiving equal rainfall amounts are plotted on maps and joined using lines called isohyets. The map produced is called a rainfall map or precipitation map (see Figure 6.4).

Atmospheric or Air Pressure
Have you ever slept on a hard surface for long hours? How did you feel when you got up? Why do you think you felt that way? You probably felt some pain in your body. This is because the weight of air that surrounds us or the atmosphere was pressing your body against the ground. This weight is called atmospheric pressure.

Measuring atmospheric pressure
Atmospheric pressure is measured using a barometer. There are two types of barometer, as shown in Figures 6.5 and 6.6 below.

The mercury barometer consists of a bowl in which mercury is put. A glass tube filled with mercury is then inverted into the bowl. As the air in the atmosphere uses its weight to push down the mercury in the bowl, the mercury level in the glass tube falls while the mercury level in the bowl rises. When the atmospheric pressure falls, the mercury in the glass tube also falls.

When the mercury levels stabilise, the column of the mercury in the glass tube is equivalent to the atmospheric pressure. Atmospheric pressure is measured in units called millibars.

Activity 6.8: How the aneroid barometer works
1. Carry out internet or library research on how the aneroid barometer is used to measure atmospheric temperature.
2. Write down your findings and present them to the rest of the class through discussion.

Atmospheric Humidity or Air Humidity
Most of the time, the air around us is not dry. It contains some amount of water in the form of an invisible gas. This gaseous water or moisture is called water vapour. The amount of water vapour held in air is called humidity. The water in air comes from different sources, such as from open water bodies and soil by evaporation and from vegetation and other plants by transpiration. Humidity influences the formation of clouds and precipitation.

Activity 6.9: Proving that air contains water
Get a cold mirror or a piece of glass or if your classroom has glass windows, close the window and do the following:
1. Breathe onto the mirror or glass. What do you notice? Have you seen anything coming out of your mouth? Do you see anything on the glass? What happens when you let the glass stay for some time?
2. Write down your observations and share what you have written with your friends.

How is humidity measured?
Humidity in the atmosphere is measured using a hygrometer. The simplest hygrometer is a sling psychrometer. It consists of two thermometers, a wet bulb and a dry bulb thermometer. The wet bulb is wrapped in a wet cloth and dipped into a bowl of water. This keeps the muslin wet. The wet bulb records a lower temperature.

When water evaporates from the wet cloth it takes away heat with it. This leads to cooling on the wet bulb thermometer, thus giving a lower reading. The dry bulb records the hotter temperature. It is kept in the normal environment. The difference in temperatures recorded by the two thermometers gives the humidity in the air. A large difference means humidity is low and a small one means humidity is high. If there is no difference, the air is said to be saturated. This means that the air cannot take in any more water vapour.

Humidity is recorded as a percentage of the amount of water vapour that the air is holding compared to the amount the same air can hold before it gets saturated. This is called relative humidity.

Sunshine and How it is Measured
In most parts of our country, the sun shines almost every day. Sunshine benefits us in many ways.

Activity 6.10: How important is sunshine?
In your notebook:
1. explain how sunshine benefits you and your local area.
2. write an article for a local newspaper explaining what would happen if it did not shine for three months in Uganda.

Sunshine is recorded using a Campbell Stokes sunshine recorder. This consists of a glass sphere held by a metal frame. Inside the frame is a sensitive card labelled in hours and minutes at the margins. As the sun apparently moves across the sky, its rays burn traces on the card if the sunshine is not constant. If the sunshine is constant, its rays burn a continuous line on the card. The lengths of the burnt sections are added to get the total hours of sunshine for the day. We record sunshine on maps by drawing lines showing places with equal amounts of sunshine. These
are called isohels.

Clouds

Activity 6.11: Finding out about clouds
In groups, go outside the classroom, observe the sky and:
1. describe the appearance of the clouds.
2. describe the cloud cover using the key provided in Figure 6.10 below.
3. list the types of clouds that you know.
4. explain the importance of clouds to human beings.
5. write and present a report about cloud cover in the area around your school.

Types of clouds

Activity 6.12
In pairs, carry out library research on the types of clouds and fill in the table below.

The amount of cloud cover is estimated in oktas. One okta represents approximately one eighth of the sky covered with clouds. Cloud cover can be represented on maps using lines. These lines join areas with equal average cloudiness over a certain period. They are called isonephs.

Effects of Weather on your Life and that of your Community
You have already learnt how the different elements of weather affect people’s ways of life. A number of your activities and those of other people in your community depend mainly on sunshine, temperature and rainfall. During the rainy season, vegetation flourishes and people are busy in their gardens. Weather changes can affect you and your community positively or negatively.

Activity 6.13
In your notebook, copy and fill in the table below:

Chapter Summary
In this chapter, you have learnt:
1. that weather is the condition of the air around us at a certain time and it is described using its elements.
2. that weather changes in a short time, while climate takes long to change.
3. how to measure and record different elements of weather.
4. that precipitation and temperature are the most important
elements of weather used to describe the climate of our country.
5. that weather affects our day-to-day activities and general way of life.