11.1 Weather

The following is a weather forecast telecast on a particular day in November.

The following table shows some details of weather that a grade 6 student recorded.

(Humidity is a measure of the amount of water vapour in the environment)

Study the above table and answer the given questions.

1. What is the unit used to measure the rain fall?

2. What is the unit used to measure the temperature?

3. Which city recorded the highest rainfall on 17.09.2013?

4. Which city recorded the highest temperature on 17.09.2013?

5. Which city recorded the highest difference in the rainfall from

17.09.2013 to 18.09.2013 ?

6. Which city recorded the highest difference in temperature from

17.09.2013 to 18.09.2013 ?

7. Which city recorded the lowest humidity on 17.09.2013?

8. What was the humidity in that city on 18.09.2013?

The factors that determine the weather are:-

Rainfall
Temperature
Humidity
The speed and the direction of the wind

These factors change very often. So, the word weather can be defined

as follows:-

11.2 Climate

The Meteorological Department collects the daily weather reports of certain cities in Sri Lanka. The following table shows some data prepared using the weather reports for 30 years.

Study the above table and answer the given questions.

1. Which city has the highest average temperature?

2. Which city has the lowest average temperature?

3. Which city has the highest rainfall?

4. Which city has the lowest rainfall?

After studying the weather conditions of a certain area for a long

period of time (at least for 30 years) the climate of that area can

be decided.

11.3 Studying Data Related to Weather

The Meteorological Department keeps daily records about weather. The following graph shows the rainfall in Colombo during the 12 months of a particular year.

Study the graph and answer the following questions.

1. What is the month with the highest rainfall?

2. What was the rainfall?

3. What is the month with the lowest rainfall?

The following graph shows the average temperature in Colombo city during the 12 months of a particular year.

Study the graph and answer the following questions.

1.What is the month with the highest temperature?

2.What is the month with the lowest temperature?

11.4 Designing Apparatus to Measure Weather

Measuring the temperature

The temperature of the atmosphere is a very important factor in determining the weather conditions.The figure 11.4 shows a thermometer used to measure the temperature in the atmosphere.

The temperature changes from time to time during the day. The following table shows some recordings taken by a grade 6 student using this instrument from 7.30 a.m. to 1.30 p.m. on a particular day.

These data can be shown in a graph.

Through the above graph, we can understand that the temperature changes from time to time even at a same place.

Measuring the rainfall

The rainfall is a very important factor in determining the weather. So, the rainfall during 24 hours, is measured using a rain gauge. The data collecting centers use standard rain gauges to measure rainfall. You too can make a simple rain gauge and measure the rainfall.

The Meteorological Department forecasts daily weather. This weather report includes the places of minimum and maximum temperature and the places of maximum rainfall during the last 24 hours. The following table shows some such records collected during several days.

Measuring the speed and direction of wind

The speed and the direction of wind are very important factors in determining the weather. An anemometer is used to measure the speed of wind and a wind vane is used to find out the direction of the wind.

Measuring the humidity of atmosphere

You too can design a simple hygrometer to measure the humidity in atmosphere.

11.5 Natural Disasters Occured Due to Climatic Changes

Cyclones

Wind is a very important factor in determining the weather. Although wind is very important to us, sometimes it causes disasters. Cyclone is one such disaster.

A cyclone occurs when the pressure in some area decreases compared to other areas of the atmosphere. A pressure depression is created in a place with a low pressure. Then the air around that place is blown at a very high speed towards the pressure depression. This causes a cyclone.

Most of the cyclones that affect our country originate in the Bay of Bengal. Rain with storms, huge sea waves, thunderbolts occur due to cyclones. The destruction of lives and property caused by cyclones is very high.

The Meteorological Department is alert about cyclones during 24 hours of the day. As it is equipped with high technological instruments, it has the ability to warn about a cyclone before 48 hours. You can get details about cyclones on 0112686686 or from their web site.

Flood

Rain is a major factor that determines the weather. As Sri Lanka is an agricultural country, rain is very important for us. But heavy rains may cause disasters. Due to heavy rains, streams, rivers, reservoirs etc. are filled with a huge amount of water in a very short time period and they overflow. As a result of this overflow a large area of land is temporarily covered with water.This is known as flood. Although flood is a natural disaster, it can cause greater damage. Flood can occur due to human activities such as reclamation of lands, improper construction activities and sand mining.

Drought

Certain area gets less than 75% of expected rainfall at a certain time period a dry weather condition may occur in that area. The dry period that occurs due to lack of rain can be simply called as drought.

Collecting water during the rainy season is an action that can be taken to minimize the effect of a drought. Ancient kings built tanks for this purpose.Today many people make water collecting tanks to collect water during rainy seasons.