Weather is the state of the atmosphere which occurs at the place at a specific period.
Weather is the atmospheric condition which recorded for short period of time or a specific period of time. Or it refers to the atmospheric condition of a place over a short period of time in relation to various elements.
Importance of weather.
- Thick cloud prevents the sun heat from striking the earth`s surface this lowering temperature of place during the day.
- Water vapour in the atmosphere determines the amount of precipitation received in an area.
- Water vapour absorbs reflect and scatters solar radiation. In doing so it regulates temperature.
- Ability to predict weather condition helps people to plan their activities property.
- Temperature affects the food, dress and type of houses human beings build.
- Rainfall gives life to plants and animal.
Elements of weather.
Temperature refers to the amount of heat or coldness in a given space
Generally, a high temperature is experienced on sunny days and low temperatures on cloudy days and in the night.
IMPORTANCE OF TEMPERATURE
TYPES OF THERMOMETER
- It determines the growth of a plant.
- High temperature causes sunburn and also the increases the risks of skin can temperature.
- Temperature determines the types of shelter, clothing and even the type of food people end.
- Temperature is one of the factors that determine soil formation.
- Temperature is measured by an instrument called thermometer.
- lines drawn on the map with the same amount of temperature is isotherms
[*]Maximum and minimum thermometer.
The maximum thermometer
is made up of a glass tube which contains mercury.
A mercury column extends along a grass capillary tube form a bulb at one end of the thermometer. The grass tube is marked in degree centigrade or Fahrenheit.
When the temperature rises, the mercury expands and pushes the index along the tube, as the temperature falls the mercury contracts and index which was in contact with the mercury. The index is then drawing back to the mercury by a magnet.
The minimum thermometer
is made by glass tube but contains alcohol instead of mercury. It is used to record the minimum temperature, Alcohol is used because it has a lower freezing point than mercury, and therefore even a small change in temperature causes an effect to the thermometer reading.
When the temperature falls, the alcohol contracts and its meniscus pulls the index along the tube.
When the temperature rises, the alcohol expands but the index remains in the position to which it was pulled. The minimum temperature is obtained by reading the scale at the end of the index which is nearer to the meniscus.
[*]The Six’s thermometer.
This is used for recording both maximum and minimum temperature
It consists of a U-shaped glass tube with mercury and alcohol on either iron of the glass. There is a metal index one in each limb.
This is used to measure body temperature.
FACTORS AFFECTING TEMPERATURE
Measuring and Recording temperature.
- Distance from water mass
- Prevailing winds
- Cloud cover
- Human activities
- Ocean currents.
- Daily temperature range=The difference between maximum-minimum temperature
- Daily mean temp=The average of the maximum and minimum temperature
=maximum temperature + minimum temperature
- Mean monthly temperature =It is the average temperature for the month
Mean monthly temperature= Total daily mean temperature
No of days in the month.
- Annual temperature range= Is the difference between highest mean temp – lower mean temp
=Highest mean temp – Lower mean temp
The Sunshine is the light received on the surface of the earth from the sun. This varies from time to time and from place to place because of the cloud cover and the position of a place.
IMPORTANCE OF SUNSHINE
- Provide heat energy necessary for drying clothes and grains.
- Human health as it is a good source of vitamin D.
- It can be converted to solar power for generating electricity.
- It is used by plant during the process of photosynthesis
An instrument used to measure the sunshine is called Campbell Stokes and Gunn-bellani radiometer.
Precipitation is the deposition of moisture from the clouds in the atmosphere. It can be a liquid form that is rainfall or solid in form of snow, hail and sleet.
Rainfall is the type of the precipitation which is in the form of shower
TYPES OF RAINFALL
- Convectional rainfall.
Convectional rainfall occurs when the air cools as it rises vertically. Is associated with thunderstorms and lighting.
It occurs in the afternoons when the ground has received maximum heating, it is usually heavy and lasts for a short period and in Tanzania, conventional rainfall is common along the coastal strip and Lake Victoria region.
- Cyclonic or Frontal rainfall.
This rainfall formed when large masses of air with different levels of moisture and temperature meet (converge) at a front. One air may be cold and dry while the other is warm and moist.
The warm moist air is forced to rise up over the cool dry air. At higher altitude, the warm air cools and water vapour content condenses to form clouds and rain.
-Cyclonic rainfall is common to the coastal town of Kenya and Tanzania.
- Relief or Orographic rainfall.
This type of rainfall is formed when moist air from the sea is forced to rise over hills or mountains that lie parallel to the coast.
The side of the mountain that receive rainfall is known as the wind ward side and the side of the mountain which is dry is known as Leeward or Rain shadow.
FACTORS AFFECTING RAINFALL.
IMPORTANCE OF RAINFALL.
- Distance from a water body.
- Ocean currents.
- Source of water for rivers, stream and springs in the hydrological cycles
- Used for irrigation, domestic and industrial use.
- Rainfall can be harnessed for electric power generation
- Floods water makes the lower section of a river fertile
-An instrument used to measure rainfall is known as a rain gauge.
-Lines are drawn on the map to show the amount of rainfall is known as Isohyets.
This is the movement of air from an area of high pressure to an area of low pressure in a horizontal plane. There is Land Breeze's and See breezes.
During the day, land heats up faster than water in seas and Oceans. The air on the land surface expands and rises, creating allow pressure belt on the land surface and high pressure in the sea, Therefore winds blow from sea to land.
-Sea breezes are fairly strong and blow in the afternoon.
During the night the land becomes cooler than the sea. Land experiences high pressure and the sea has low-pressure wind blow from land to the sea.
-An instrument used to measure wind
- vane and wind sock
Humidity is the amount of water vapour in the atmosphere. Humidity varies in both place and time Example Dar es salaam is more humid than Mbeya, Iringa, Kilimanjaro, or Arusha. There is more water vapour in hot air than in cold air.
IMPORTANCE OF HUMIDITY
- The amount of water vapour in the atmosphere determines the amount of precipitation.
- Water vapour absorbs radiation therefore it regulates the heat loss from the earth.
Humidity is measured by instrument called Hygrometer or (psyctrometer).
Atmospheric pressure is the weight exerted by the atmosphere on the surface of the earth. It is greater on the sea level than the ground surface, it decreases with increase in altitude at the rate of 1 millibar for every 10 metres. The pressure is exerted equally in all direction. This can be demonstrated by doing the following experiment.
Importance of Atmospheric pressure
- Take a glass full of water.
- Cover the top of the glass with a piece of thin paper.
- Hold the grass upside down; the water will not spill because the air is pressing on the piece of thin paper.
- It is cause the movement of wind (Air)
- External and internal pressure, when balanced helps us in normal breathing.
- Pressure is used to fill types, Vehicles, aircraft, bicycles and other equipment
- Deep sea divers and astronauts use special equipment filled with which help us to equalise their body pressure and atmospheric pressure during their mission
-An instrument used to measure Atmospheric pressure is called Barometer
-Lines drawn on the map with the same pressure are Isobars.
Clouds are condensed tiny droplets of water or ice suspended in the air. Clouds are as a result of water vapour that has condensed around nuclei that is suspended in the atmosphere.
Dense cloud cover is experienced in equatorial regions. Desert regions are cloudless for most of the time of the year.
Importance of cloud cover.
- All the forms of precipitation originate from clouds.
- Clouds determine the visibility in the atmosphere.
- Clouds influence the weather of a place by determining the amount of sunshine that reaches the surface of the earth.
An instrument used to measure cloud cover is called Octas.
A weather station is a place where the elements of weather are measured and recorded accurately.
Factors that facilitate weather station.
- It must be sited in an open space, away from buildings, vegetation or other structure that may prevent air from circulating freely.
- It must be established on a flat or gently sloping ground.
- The area should be free from floods.
- Fencing the area with a lockable gate to keep the instrument safe.
A Stevenson screen is a wooden box found in a weather station. It is carefully designed house weather instruments especially thermometer.
The side of box are 50cm × 60cm ×60cm and it is raised about 121cm above the ground. The roof is made of double boarding to prevent the sun’s heat from reaching the inside of the screen.
Insulation is further improved by painting the box white to reflect it sunlight.
Weather forecasting is the prediction of weather conditions of a certain place for a short period of time. There are two ways of predicting weather namely traditional and modern ways.
- Traditional way is the method of predicting weather by observing the behaviours of the stars, position of the moon and the croaking of frogs, wind patterns, migration of butter flies and other traditional observations.
-These methods were based on astrological, traditional and religious theories.
IMPORTANCE OF WEATHER FORECASTING
- Modern ways is the method of predicting weather involves the use of advanced equipment such as electronic computer, satellites, balloons, radars and aircraft.
- It helps to plan the calendar of activities for various groups of people including farmers.
- It helps people to be in a position to select suitable clothes for the day.
- It helps the travellers to determine appropriate time to travel either by ship or air craft.
- It helps to arrange places and time for sporting activities.
- It helps to guide tourist activities.
- It helps the contractors to plan suitable houses for a given area.
Climate is the average weather condition of an area observed over a long period of time (over 30 years). When we say it is cool and dry for a long period, or it is hot and rainy throughout the year we describe climate.
It deals with all weather elements such as sunshine, temperature, Atmospheric pressure, wind, humidity and precipitation. Climate condition in the world varies considerable from one region to another although similar climate conditions often occur in several different regions.