Weather and Climate

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Welcome to class! 

In today’s class, we will be talking about weather and climate. Enjoy the class!

Weather and Climate

Weather is defined as the condition of the atmosphere of a place at a certain time or within a short period. The weather of a place is always very brief and changes regularly e.g. the weather of a day could be sunny, rainy or cloudy etc.

Climate is defined as the average atmospheric condition of an area over a long period of time. Unlike weather, the climate of a place lasts for a very long time before it can change.

Elements of weather and climate

The elements of weather and climate include:

1. Temperature
2. Rainfall
3. Wind
4. Pressure
5. Relative humidity
6. Cloud cover
7. Sunshine

The climate varies from one part of the world to another due to the effects of the following factors:

1. Latitude
2. Altitude
3. Continentally or distance from the sea
4. Ocean currents
5. Planetary winds and pressure belts
6. Slope and aspect
7. Cloud cover
8. Natural vegetation and soil

 Evaluation 

1. What is weather?
2. Differentiate between weather and climate.

Importance of weather and climate to man

1. Human settlement: Weather and climate affect the rate at which human being live in a place.
2. Health: Humid or damp environment encourages the growth of micro-organisms which cause diseases hence, the death rate is higher in the tropical region than in the temperate countries.
3. Environment hazards: Hazards like soil erosion, rainstorm, flood and drought are caused by differences in weather and climate.
4. Vegetation: Temperature and rainfall are the major determinants of the type of vegetation in an area which could be light or thick.
5. Clothing: The type and nature of clothing worn by different people in a different part of the world are due to the differences in climate. Cold climate requires black and thick dresses while hot climate requires light dresses.
6. Housing: The type and nature of houses built in different places is also influenced by differences in climate. E.g. hot region requires air-condition houses whereas, polar region do not.
7. Agriculture: Rainfall and temperature are important elements that determine the type of crops to be cultivated in an area.
8. Soil formation: Soil is formed from parent rocks which have been broken by elements of weather and climate. The rate of disintegration of rocks to form soil is principally a factor of climate.
9. Communication and transportation: The type of transportation used in an area is greatly influenced by weather and climate.
10. Occupation: The climate of a place does determine the occupation of the people in that particular region. E.g. People living in the equatorial type of climate are more likely to be involved in cash crop farming and lumbering of hardwood.
11. Cultural Activities: The climate of a place can also affect the cultural activities of some people e.g. winter or summer sports.
12. Health: The health status of a particular area can be determined by the type of climate. The subtropical climate is said to favour the breeding of mosquitoes, which causes malaria fever.

Evaluation

1. Mention any four elements of weather and climate.
2. State any three importance of weather and climate to man.

Keeping weather records and instruments

• Measurement of rainfall

An instrument called Rain-gauge is used in measuring rainfall.

Description

A rain gauge consists of a metal funnel that leads to a glass bottle enclosed within a copper cylinder. The gauge is usually erected high above the ground to avoid splashing and it is sited far away from buildings and tall trees that might shelter it. The rain gauge must be examined every day and daily records were taken. Record is taken by removing the funnel and the contents of the glass bottle are emptied into the measuring cylinder.

Formula

1. Mean monthly rainfall =Add total rainfall for the month / No of days in the month
2. Annual rainfall = Add the total rainfall (Jan-Dec)
3. The annual range of rainfall = Month with the highest rainfall  – month with the lowest rainfall
4. Mean annual rainfall =  Total rainfall (Jan – Dec) / 12
5. Highest rainfall = Month with the highest rainfall
6. Lowest rainfall = Month with the lowest rainfall

Example:

Calculate

1. the month with the lowest rainfall
2. the month with the highest rainfall
3. annual rainfall
4. the annual range of rainfall
5. mean annual rainfall using the table below:

Month	J	F	M	A	M	J	J	A	S	O	N	D
Rainfall	10	80	20	18	5	50	45	40	90	20	50	40

Solution

1. The month with the lowest rainfall = May (5cm)
2. The month with the highest rainfall = September (90 cm)
3. Annual rainfall = Total rainfall for 12 months =10 + 80 + 20 + 18 …+ 50 + 40 = 468 cm
4. Annual range of rainfall = 90 – 5 = 85 cm
5. Mean annual rainfall =Total rainfall for 12 months / 12= 468 /12   = 39 cm

• Measurement of temperature

An instrument called thermometer measures the temperature of a place.

Description

The thermometer is a narrow glass tube filled with mercury or alcohol. It works on the principle that mercury and alcohol expand when heated and contract when cooled. Temperature is commonly recorded in centigrade (^oC) or Fahrenheit (^oF) scale. The freezing (lowest) point for the centigrade scale is 0^oc while Fahrenheit is 32⁰F. The boiling (or highest) point for centigrade scale is 100^oC while that of the Fahrenheit is 212^oF. It is possible to convert from one scale to another.

Geographers are interested in shade temperatures which are the temperature of the air to exclude the intensity of the suns radiant heat. To get accurate records, thermometers are kept in a standard shelter called Stevenson Screen to protect it from the effects of the radiant heat of the sun and rain. The Stevenson Screen is a wooden box raised above the ground to a height of 4ft or 1.2m.To measure the maximum and minimum temperatures of the day, a combined maximum and minimum thermometers are used.

Formulae

1. Mean daily temperature =   ( Max. temp. + Mini temp. for a day) / 2
2. Diurnal range of temperature = Max. temp – Mini. Temp that day
3. Monthly range of temperature = Difference between the hottest and the coldest daily temperature for the month.
4. Annual temperature = temperature of the hottest month – the temperature of the coldest month.
5. Annual temperature     =   Total temperature (Jan – Dec)
6. Mean Annual Temperature  =   total temp (Jan – Dec) / 12

Example:

Calculate using the table below

1. The month with the highest temperature
2. The month with the lowest temperature
3. The annual range of temperature
4. Annual temperature
5. Mean annual temperature

Month	J	F	M	A	M	J	J	A	S	O	N	D
Temperature(0o)	40	30	21	25	10	40	48	30	25	30	20	15

Solution

1. The month with the highest temperature = July (48^oc)
2. The month with the lowest temperature = May (10^oc)
3. The annual range of temperature = temp of the hottest month – Temp of coldest = 48^oc – 10^oc = 38^oc
4. Annual temperature = Total temp. (Jan – Dec) = 40 + 30 + 21+…… + 30 + 20 + 15 = 334^oc
5. Mean annual temperature = Total temp (Jan – Dec) / 12 = 334 / 12 = 27.8^oc

• Measurement of wind

The wind has direction and speed. The direction of the wind is measured by an instrument called Wind Vane while the speed of the wind is measured by a different instrument called Anemometer.

Description

1. Wind vane: wind vane is made up of two parts – one part is the arrow or vane on the top, which is free to move with the prevailing wind. The other part is stationary and consists of a frame and four compass points. The vane or arrow points to the direction from which the wind is blowing so that wind is named from the direction it blows e.g. South West Wind blows from South-West direction. The wind vane is located in an exposed position so that tall buildings and trees do not deflect the wind direction.
2. Anemometer: This consists of three or four semi-circular cups attached to the ends of horizontal spokes mounted on a high vertical spindle. As the wind blows, the cups rotate. The higher the speed of the wind, the greater the speed of the cups and vice versa.

• Measurement of pressure

The instrument used in measuring atmospheric pressure is called Barometer. The pressure is measured in a unit of force called millibars. A normal atmospheric pressure shows a reading of 760mm (76cm) or 1013 millibars. Mercury barometer consists of a beaker in which a glass tube is dipped and both contain mercury. Another instrument used for measuring pressure is the aneroid barometer. But a modified aneroid barometer used in aeroplanes is called Altimeter.

• Measurement of relative humidity

The instrument used for measuring relative humidity is called Hygrometer.

Description

The hygrometer consists of wet and dry-bulb thermometers placed side by side in the Stevenson screen. The dry bulb is an ordinary thermometer that measures the shade temperature. The wet-bulb is kept by a wick that is dipped in a container of distilled water. When the air is not saturated, evaporation, which produces a cooling effect, takes place from the moist wick. The wet-bulb always shows a lower reading than the dry bulb. The difference in the two readings, if high, indicates low humidity and if low, indicates high humidity. If there is no difference in their readings, it means that the air is saturated and therefore, the relative humidity would be 100 %.

Evaluation

• How do we calculate?

1. The annual range of temperature?
2. Mean annual range of temperature?
3. Mean monthly rainfall?

General evaluation

1. What is weather and climate?
2. Explain the importance of weather and climate.
3. Mention the instrument used for measuring rainfall.
4. Mention the three types of rock.
5. Explain the mode of formation of igneous rock.

Reading assignment

Read on weather and climate in Essential Geography Pgs. 75-77

Weekend assignment

1. The height of a place above the sea level is known as (a) Latitude (b) Altitude (c) Lapse rate (d) Spot height
2. Which of these factors does not affect weather and climate (a) Cloud cover (b) Humidity (c) Latitude (d) Natural Vegetation

3. The instrument used for measuring wind direction is (a) Wind vane (b) Thermometer (c) Anemometer (d) Rain gauge

4. Wet and dry bulb thermometer could be used for measuring (a) Rainfall (b) Relative humidity (c) Temperature (d) Wind speed

5. Which of the following weather elements is paired with the wrong instrument? (a) Wind direction and wind vane (b) Humidity and anemometer (c) Rainfall and rain gauge (d) Atmospheric pressure and barometer

Theory

1. What is Climate?
2. Highlight four importance of weather and climate to man.

 

In our next class, we will be talking about the Components of Geographic Information System (GIS).  We hope you enjoyed the class.

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