Topic 3 Weather – Geography STD 5

Topic 3 Weather – Geography STD 5

Weather refers to the atmospheric conditions of a specific area recorded over a short period, usually hours or a few days.

Weather is measured and recorded at specific centres called weather stations. The study of the atmosphere and weather is known as meteorology. A person who is knowledgeable about weather is called a meteorologist or weather expert

Element of weather

1. Temperature
2. Rain
3. Sunlight
4. Clouds
5. Wind
6. Humidity
7. Atmospheric pressure

Measuring and recorded weather elements

1. Temperature

Temperature is the measure of heat or cold in a body, object or place. Temperature is measured using an instrument called a thermometer. Temperature readings are given in degrees on the centigrade (⁰c) or Fahrenheit(^oF) scales. There are various types of thermometers, such as medical thermometers used to measure body temperature, laboratory thermometers that measure the temperature of liquids and gases in experiments.

In the geographical used to measure the daily temperature of a location. In the geographical context, you will learn about ambient thermometer that measure the maximum or minimum temperature of the day

An ambient thermometer can be digital or analogue. A digital thermometer shows temperature using numbers on a screen. An analogue thermometer measures the temperature using numbers by showing how high a liquid, like mercury or coloured alcohol, rises in a glass tube

Measuring air temperature using an analogue thermometer

Air temperature is measured at weather stations using two types of thermometers

These are

1. Maximum thermometer
2. Minimum thermometer Maximum thermometer

This thermometer indicates the highest temperature of the day and is often read in the evening. Inside the thermometer, there is mercury that provides an accurate reading. If the day becomes hotter, the mercury expands and rises up within the thermometer. Even if the temperature drops later, the mercury remains at the highest level, allowing us to see the maximum temperature of that day. Mercury also has a reflective quality, making it easy to read. This is why mercury is used in maximum thermometers

1. Minimum thermometer

This thermometer indicates the lowest temperature, often read at night or early morning. It contains coloured alcohol because alcohol performs well in measuring low temperatures. Alcohol does not freeze easily. allowing the thermometer to function vein in extreme cold. It rises and falls as the temperature changes, which helps indicate the level of cold present. The alcohol is coloured so that is visible

Within the thermometer. Additionally, it is safer to use than other substances like mercury. This is why coloured alcohol is used in minimum thermometers. Figure 1 shows the maximum thermometer and the minimum thermometer

2. Maximum and minimum thermometer

The maximum and minimum thermometer are kept in a special box called a Stevenson screen. The Stevenson screen is a wooden box painted white. The white colour helps reflect light. This reflection prevents solar radiation from affecting the temperature readings. Figure 2 shows the Stevenson screen

Steps for measuring temperature using a maximum thermometer

1. Place the maximum thermometer outside where it can sense the day’s temperature, for instance, under a shaded area, but not in direct sunlight

2. Wait for the temperature to rise, as the temperature increases, the mercury inside the thermometer expands and rises in the glass tube

3. By the evening, take the thermometer and read the highest temperature by checking where the mercury has reached. Note that the highest point where the index has stopped indicates the maximum temperature of that day

4. Record the number closest to the index line to show the maximum temperature of the day

Steps for measuring temperature using minimum thermometer

1. Place the minimum thermometer outside, in a cool area, close to the ground, to measure the minimum temperature (cold)

2. Wait for the temperature to drop. As it gets colder during the night or early morning, the alcohol inside the thermometer will fall down the glass tube

3. In the early morning, before the sun rises, check where the alcohol has moved to. The point where the index stops shows the lowest temperature of the day

4. Record the number closest to where the index has stopped to show the coldest or minimum temperature of the day

2. Wind

Wind occurs due to differences in atmospheric pressure in the atmosphere. Thus, wind is air moving from areas of high atmospheric pressure to low atmospheric pressure.

Measurement of wind

When the wind blows, there are two things can observe: the direction of the wind and the speed of the wind

An instrument used to measure wind speed is called anemometer, and an instrument used to measure wind direction is called wind vane

1. Anemometer

This is an instrument with three or four bowl- shaped cups held by metal arms that rotate when the wind blows. The speed of the rotation of the cups indicates the wind speed. The number of rotations is recorded on a gauge within the device

Wind speed is measured in kilometers pr hour. Figure 3 shows an anemometer

Measuring wind speed

Steps to measure wind speed using an anemometer

1. Hold/place the anemometer in an open area where the wind can blow freely

2. Observe the rotation of the cups, which is measured on a gauge and converted into wind speed

3. Read the wind speed on the gauge connected to the anemometer

4. Record the wind speed in units of meters per second, kilometers per hour, or miles per hour

2. Wind vane

This is an instrument with an arrow on top that indicates the direction of the wind. The arrow is fixed on a rod. At the bottom of the arrow, there are boards or pieces of metal that show the four cardinal directions: East, south and west. When the wind blows, the arrow points towards the direction from which the wind is coming as shown in figure 4

Note: in meteorology, winds are named based on the direction they come from, for example, a wind that blows from south to north is called a south wind, and vice versa

Measuring wind direction

Steps to measure wind direction using a wind vane

1. Examine the top part of the wind vane which has an arrow mounted on a rod at the top

2. Check if the cardinal directions (North, East, South and West) are indicated below the arrow

3. When the wind blows, observe how the arrow moves

4. Note the direction of the arrow; this will help you determine where the wind is coming from and where it is heading

Note: i. if an arrow points south, it implies that the wind direction is from south to North

ii.If an arrow points North, It implies that the wind direction is from North to south

3. Humidity

Humidity is the amount of water vapour in the air. Sunlight causes water to evaporate from plants, the sea surface, lakes, rivers and other water bodies

This creates water vapour to the atmosphere

2. Humidity is measured in percentage (%) and instrument used to measure humidity is called a hygrometer

There are three types of hygrometers

1. Hygrometer with an arrow

Which measures humidity by directly recording and displaying the percentage of vapour in the air using an arrow

2. Dry and wet bulb hygrometer

Consists of two thermometers in a single tube. A dry thermometer that measures air temperature and a wet thermometer with a muslin cloth dipped in water that measures humidity

3. Digital hygrometer

Which provides humidity readings electronically. Figure 5 shows the three types of hygrometers

Types of hygrometer

Measuring humidity

Measuring humidity using a dry and wet bulb hygrometer

The following are the steps to measure humidity using a dry and wet hygrometer

1. Take one thermometer and wrap the lower part with a muslin cloth

2. Take the wrapped thermometer and dip the muslin into a container of water to allow the muslin to soak, to get a wet thermometer

3. Take another thermometer, leave it unwrapped, and position it in a dry area (the dry thermometer) next to the first thermometer

4. Take the thermometers (the dry and wet hygrometer) and place them outside in a clear area

5. Leave them for approximately 5 – 10 minutes

6. Read the record the temperature on the dry thermometer and wet thermometer

7. Calculate the temperature difference between the readings from the dry thermometer and the wet thermometer to determine the humidity level

8. In measuring atmospheric humidity, the difference in readings obtained from both thermometers is considered. If there is no difference in the readings, it implies that the air has a very high humidity level and cannot absorb any more moisture. A small difference which is below 40% indicates high humidity.

9. When a large difference exists, above 70% it indicates that the humidity level is low

10. When the difference is between 40% and 70%, it implies ana average humidity in the atmosphere. Hygrometers are stored in a Stevenson screen

4. Atmospheric pressure

Atmospheric pressure is the force created by the weight of air down towards the Earth’s surface. It is caused by the concentration of various gases in area of the atmosphere. These gases include oxygen, nitrogen and carbon dioxide.

The pressure created by these gases varies from one place to another. Additionally, even within the same area atmospheric pressure fluctuates depending on the increase or decreases in the concentration of air. Differences I atmospheric pressure lead to the formation of wind.

When the temperature in an area increase, atmospheric pressure decreases. The differences in temperature between two areas causes air to move from the area with higher atmospheric pressure to the area with lower atmospheric pressure

Measuring atmospheric pressure

Atmospheric pressure is measured in millibars using an instrument called barometer. There are three main types of barometers:

1. mercury barometers,
2. aneroid barometers and
3. digital barometers.

All three types serve the same function of recording atmospheric pressure. A mercury barometer is along glass tube with a measuring scale. The tube is filled with mercury and placed in a container with more mercury. When the atmospheric pressure changes, the level of mercury in the tube goes up or down. If the mercury is higher, it means the atmospheric pressure is high. If it’s lower, the atmospheric pressure is low many weather stations use mercury barometers because they are bigger and easier to read than aneroid barometers

A digital barometer has an atomic clock that electronic sensors to measure atmospheric pressure. It gives information about atmospheric pressure more accurately and quickly than mercury and aneroid barometers. Figure 6 shows the three types of barometers: a mercury barometer, an aneroid barometer and a digital barometer

Types of barometers

5. Rain

Rain consists of droplets of water that fall to the Earth’s surface from the atmosphere after condensation of frozen clouds.

Measuring rainfall

Rain is measured by collecting droplets that fall from the sky using a rain gauge

This helps determine the amount of rainfall in a specific area over a certain period

Rainfall is measured in millimetres. A rain gauge consists of four components a funnel, a cylinder, a container and measuring cylinder

How to measure rainfall

The cylinder is placed inside a container that is dug the ground and a funnel is placed on top of the cylinder to collect rain droplets and direct them into the cylinder. The container with the cylinder inside is left 30 centimetres above the ground.

If the cylinder fills up before the rain stops, it is taken out and emptied into a measuring cylinder to check the amount of rain, then returned to the container until the rain stops.

After the rain has stopped within 24 hours, record the amount of rain on that day’s chart. Ensure that daily rainfall measurements are recorded accurately. This process helps track the amount of rain in a specific area over time. Figure 7 shows a rain gauge

Rain gauge

5. Sunlight

Sunlight is the natural light and energy that comes from the sun and reaching the Earth’s surface without obstruction in the atmosphere

Measuring sunlight

Sunlight is measured in hours, week, month, year or as a daily average. An instrument called a sunshine recorded is used to measure sunlight. This instrument measures the duration of which sunlight reaches the ground in a specific area

The sunshine recorder has a glass sphere held by metal and has card with hour and minute marks. This card can sense sunlight each day when the sun shines, it burns the card.

At the end of the process, the card is taken out and read to see how many hours and minutes of sunlight there were in a specific day. Figure 8 shows a sunshine recorder

Sunshine recorder Steps to follow when measuring sunlight

1. place the sunshine recorded outside in ana open area where sunlight can shine directly on it.Ensure that no trees or buildings block the sunlight from reaching the sunshine recorder
2. make sure the glass sphere is oriented correctly to allow sunlight to pass through
3. the sunlight will burn the recording card. This will indicate how long the sun was shining
4. check the card to see the marks. Each mark shows how long the sun has been shining
5. the longer the sun shines, the more marks accumulate and become longer on the card
6. you can count the marks to see how much sunlight was recorded for that day; see figure 9
7. after finishing the exercise, clean the glass sphere to ensure it works well next time

CLOUDS

clouds are collections of tiny water or ice droplets floating in the atmosphere

clouds are formed from vapour-laden air caused by evaporation from plants, oceans and various water sources. After the vapour rises into the atmosphere, it meets cold air, which cools it down, leading to the formation of small water droplets in the sky

Types of clouds

Various criteria can be used to identify different types of clouds. Some of these criteria include considering the distance from the ground and examining the shape and appearance of the clouds. Using the distance criterion, there are three main types of clouds which are

1. High- level clouds
2. Mid- level clouds
3. Low- level clouds

In contrast, using the shape and appearance criterion, there are several types of clouds such as

1. Cumulus clouds

Which are white, fluffy and resemble small cotton balls.

2. Stratus clouds

Appear like grey blankets covering the sky

3. Cirrus clouds

Which look like horse tails or thin, curled fibres

4. Nimbostratus clouds

Which are thick and dark, often associated with rain

These clouds vary in shape, altitude and their relationship with other weather elements such as rain, temperature and atmospheric pressure

Generally, clouds protect us from intense sunlight during the day. Weather authorities monitor cloud patterns to predict short- term weather

Measuring clouds

Measuring clouds observing the coverage, direction, type and height to help us understand the weather. The amount of cloud cover can be assessed visually using the oktas measurement following are the

steps to follow when measuring cloud coverage

1. Stand outside and look at the sky
2. Imagine that you are dividing the sky into 8 equal sections
3. Count how many of the 8 sections covered by clouds
4. Write down the number of sections covered by clouds
5. Use the number of oktas to conclude about the sky conditions for that day

Note: The sky conditions can vary based on the number of oktas. If there are 0 oktas, it means there are no clouds and the sky is clear. If there are 1 to 2 oktas, it means the sky has few clouds.

If there are 3 to 4 oktas, it means the sky has scattered clouds. If there are 5 to 7 oktas, it means a large part of the sky is covered with clouds, and if there are 8 oktas, it means the sky is filled with clouds. See Figure below

Experts use a special instrument called ceilometer to measure the cloud height.

They also utilize weather Radars and Satellites for cloud measurement.

Refer to Figure 11(a) and (b) for more details. Knowing the height of clouds is essential for accurate weather forecasting and for pilots navigating through cloudy skies

Also, the direction, speed and type of clouds can be measured using a Nephoscope, as shown in Figure 12. This instrument helps weather experts understand the clouds ‘dynamics. It is usually used with other equipment like weather telescopes or aerial cameras

Weather data logger

A weather data logger is a device that collects and stores weather information automatically for a certain period for further analysis. This device is used to monitor and record weather such as temperature, humidity, wind speed and direction, rainfall, atmospheric pressure and sunlight using sensors for each element

The weather data logger can operate 24 hours a day without supervision and provides accurate records for the scheduled time. The collected data is stored in a digital format on a USB or SD card, which can be downloaded or sent for further analysis. This device is often used by weather authorities, in agriculture, for climate change research, and environmental monitoring. Figure 13 shows a weather data logger

In Tanzania, some weather stations use outdate weather recording instruments

However, due to advances in science and technology, these stations are being upgraded from manual to automated weather stations that use modern equipment to record and store weather data

Measuring and recording weather is important because it helps us understand the weather for a specific day or period. This enables individuals to plan their activities effectively and take environmental precautions. Furthermore, long– term weather measurements help identify the climate of different regions

Exercise

1. Explain the relationship between the following weather elements
   1. Atmospheric pressure and wind
   2. Clouds and sunlight
   3. Sunlight and humidity
   4. Clouds and rain
2. What is importance of studying weather in our local areas?
3. Explain the reason that causes air to move from one place to another

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