Explore the Elements of Weather and Climatic Conditions

• Weather is the average atmospheric condition of a place at a specific time or for a short period of time.
• It can also be said to be the state of the atmosphere at a specific time and place is called weather.
• Weather conditions are made up of different elements, such as sunshine or rainfall.

Climate

Weather is the average atmospheric condition of a place over a long period of time usually the minimum being 30 years.

The word climate refers to the average weather over a long period of time, such as over 30 years.

Climate is therefore the variation in weather in elements, such as temperature or rainfall, for a given area over a much longer time period than in the case of weather.

The difference between weather and climate

The words weather and climate are sometimes used as if they mean the same thing, but there is a difference between them.

• Both refer to the conditions of the atmosphere; that is, to what is happening in the layer of air that surrounds the earth.

• The difference lies in the time period that each word refers to, as explained below

Elements of weather

• Temperature
• Rainfall
• Humidity
• Pressure
• Cloud cover and sunshine
• Wind direction and strength.

These elements are measured and recorded at a place called weather station or meteorological
station.
• A weather station is a place where the elements of weather are measured and recorded as
accurately as possible.
• Each station has a Stevenson screen which contains four thermometers all hung from a frame in the centre of the screen.
• These are the maximum thermometer, minimum thermometer, wet bulb thermometer, dry bulb thermometer.

The Screen has the following features

• It is built so as to measure the shade temperature of the air.
• It has louvered sides of allow free entry of air.
• The roof is made of two wooden layers to form a bad conductor of heat
• The screen is painted white so as to improve insulation.
• The screen is placed on a stand about 121 cm above ground level.
• One side of the screen is hinged and it acts as a door.

Atmospheric temperature

• Temperature is the degree of hotness or coldness of something. It is how hot or cold something or an object is.
• Temperature is measured using an instrument called thermometer.
• Temperature is observed by measurering the highest (maximum) and lowest (minimum) temperatures of a day
• Temperature is measured in degrees centigrade (oc) or degrees Fahrenheit (oF)
• The Celsius or centigrade scale is commonly used on this scale 0oC represents freezing point of water, and the 100o represents the boiling point of water.
• On the Fahrenheit scale, the freezing point of water is 320F and the boiling point is 212oF. Measurement of temperature
• Maximum and minimum temperatures are measured by the maximum and minimum thermometers
• These are in form of separate thermometers or joined in a U – Shaped tube called a six’s thermometer.

Maximum and Minimum Thermometer

To measure maximum temperature

• Mercury in the glass tube expands when the temperature rises. This pushes the index in the right hand limb up to maximum
• The end of the index nearest the mercury gives the reading of the maximum temperature this is 30°C in our example
• To reset the index for next day’s reading; draw it back by a magnet.

To measure minimum temperature

Minimum temperature probably occurs early in the morning when temperature falls.

• The alcohol in the left – hand limb contracts.
• The mercury flows in the reverse direction.
• The index is pushed up along the left hand limb.
• When temperature rises, the alcohol flows past the index leaving it where it was pushed
• The end of the index farthest from the bulb gives the reading of the minimum temperature.
• This is 10°C in our example
• To reset the index draw it back by a magnet.

Temperature Record

The following are used to keep a temperature record;

Mean daily temperature:

• This is the average of maximum and minimum e. g (30oC+10oC) ^ 2 = 20oC Daily or Diurnal Range:
• This is the difference between the maximum and minimum temperatures of a day. e.g. (Max 30oC- Min10oC) = 20oC

The annual temperature:

• This is the difference between the mean temperature of the hottest month and that of the coldest month.

The mean annual temperature:

• This is the sum of mean month temperature for one year divided by 12 months.

The mean monthly temperature

• This refers to the sum of mean daily temperatures for one month divided by the number of days in that month.
• On weather maps places having the same temperature are joined by a smooth line. Such a line is called an isotherm.

Rainfall

• Rainfall is caused by the effect of solar radiation over land and water bodies.
• Solar radiation refers to the energy from sun.
• This energy gives rise, to various types of weather and climate.
• Solar radiation over sources or bodies of water causes evaporation.

The process of evaporation

• Solar energy causes water to be transformed into vapour. This vapour enters the atmosphere by: Evaporation from sea and land surfaces and transpiration from plants
• The combined total of evaporation and transpiration is termed Evapotranspiration.

The rate of evaporation depends on the following factors:

• The temperature of evaporating surface. Evaporation is higher if the temperature of evaporating surface is higher than that of the air.
• Relative humidity of the air evaporation is also highest if air is relatively dry.
• Wind speed. It is also high if winds are strongest evaporation is greater in summer than in winter.
• It is also higher in tropical latitudes than in winter. It is also higher in tropical latitudes than in temperate and polar latitudes.

Condensation

• When warm air rises, it is cooled and its capacity to hold water vapour is reduced
• Condensation will occur if the rising air contains water vapour
• The water molecules will pass into a liquid state and subsequently return to land and sea as precipitation, condensation may take the form of minute droplets of clouds, rain, mist dew or fog.
• Water of oceans, atmosphere and land moves in a great cycle
• This involves evaporation from sea and land, condensation to form clouds and precipitation in form of rain or snow
• This exchange is called the water cycle or hydrologic cycle.