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SPACE DYNAMIC



WEATHER AND CLIMATE

(a) Difference between weather and climate
There is a slight difference between weather and climate. Weather refers to as the actual state of atmosphere and climate refers to the average state of atmosphere.

By definition:
Weather is the condition of the atmosphere with regard to its elements for a certain place and at specific moment. It is the daily atmospheric condition of a place at particular time. It is the condition of being hot, windy, cold, foggy, or cloudy. Weather changes from time to time and from place to place. The condition of the atmosphere is determined by the elements of weather which are:
  • Temperature
  • Humidity
  • Atmospheric pressure
  • Clouds
  • Precipitation and
  • Winds

Climate is the average atmospheric condition over a long period of time over 30 to 40 years within a specific geographical area.
Factors that influence weather and climate
Weather and climate are influenced by the factors like;

-Temperature
-Precipitation
-Humidity
-Pressure
-Winds
-Cloud cover
-Sunshine
-Altitude and
-Ocean currents.
Measuring and recording the elements of weather and climate is done at a weather station.
WEATHER STATION is a place that is set aside for the purpose of observing measuring and recording weather elements.


Element of weather

1. TEMPERATURE
Temperature is the degree of a heat of a body. It is a measure or degree of hotness of an object or place .Temperature is measured by an instrument called thermometer. The lines joining all places with equal temperature are called isothems
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RECORDING TEMPERATURE
1. The mean (or overage) daily temperature is obtained by adding the daily maximum and the daily minimum temperature and dividing the sum by two.
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2. The daily range of temperature is obtained by substracting the daily maximum temperature by the daily minimum temperature which is,
daily max temp – daily minimum temperature
3. The mean (or average) monthly temperature is obtained by dividing the sum of daily mean temperature of a month by the number of days in that particular month
4. The monthly range of temperature is obtained by subtracting the lowest daily temperature of a month from the highest mean daily temperature of that particular month.

5. The mean(or average) annual temperature is obtained by dividing the sum of the monthly mean temperatures of the particular year by 12.
6. The mean annual range of temperature is obtained by substracting the lowest mean monthly temperature of a year from the highest mean monthy temperature of that same year.
FACTORS AFFECTING INSOLATION OR TEMPERATURE OF A PLACE
Factors that influence the amount of insolation received any point and therefore its radiation balance and heat budget vary considerably over time and space.They include the following.
(a) Seasons and angle of incidence
The earth as a planet moves along its orbit throughout the year under this movement inclination of the earth varies and the angle of which the sun rays strikes the earth’s surface changes with seasons.

Also the distance of the earth from the sun varies from month to month.At spring and autumn equinoxes.(21th March and 23rd September) the angle of incidence at the equator is 90º making an area to have high temperature throughout the year.Temperature is distributed equally in both hemispheres.At the summer and winter solsctice (21th June and 22nd December) due to earth tilting the sun is overhead at the tropics where the hemisphere experience summer will receive maximum insolation.The angle of incidence is the most important factor which influences the amount of insolation of a place on the earth’s surface.

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(b)Distance
from the sea
There is often a considerable differences between temperature of land and water surface. The reason for this is that land surface heats and cool more slowly than the sea.
Due to this summer temperature in coastal areas are lower than in continental interior. Likewise winter temperature will be higher in coastal areas than in continental interior if the winds blow towards the shore
During the day and during night the situation is related to land and sea breeze. Areas whose temperatures are greatly affected by the sea are reffered to as maritime .The greater distance from the sea the colder the winter it will be and the warmer the summer develops.
EcoleBooks | GEOGRAPHY A LEVEL(FORM SIX) NOTES - SPACE DYNAMIC

EcoleBooks | GEOGRAPHY A LEVEL(FORM SIX) NOTES - SPACE DYNAMIC
(c)Altitude
The rate at which temperature decreases with increasing altitude is called lapse rate. Normally air temperature decreases with increasing height at a rate of 0.6ºc R.r 100 meters.This is because when earth surface is heated it passes its heat on air making atmosphere being heated from below and not directly from the sun.This affect temperature because the higher you go the cooler it becomes. Altitude explains why highlands in the tropics are ever cold e.g Mt. Kilimanjaro in Tanzania.
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(d) Aspect

This refers to the direction in which a slope falls.Some slopes are exposed to the sun than others.The atmosphere of the north facing slopes of highlands in the northern hemisphere also called ubac are cooler than the slopes facing south adret.The same thing appears in the southern hemisphere

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(e) Latitude
It is the angular distance from the equator to the poles. It determines both the length of day throughout the year and the intensity and possible duration of sunlight received.
As one moves pole wards from the equator he experiences gradual progressive decrease in temperature. This is because the sun strikes the equator more intensity than it does in the poles two observations can explain this phenomenon.
(i)At the equator the beam of light strike the earth’s surface covering a smaller surface area than in the poles where the same beam of light covers a larger surface area.
(ii)At the equator the beam of light strike travels a short distance hence experiencing less atmospheric effects like absorption reflection and scattering.At the poles the beam of light travels a longer distance and it experiences more effects in the atmosphere.
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(f) Cloud cover
The atmosphere of areas covered with heavy clouds is cooler than that of areas with clear skies.This is because clouds prevent insolation to reach sand sea surface.
(g) Length of day and night
Insolation is only received during day light hours and reaches its peak at noon .The longer the period of solar insolation the greater the quantity of radiation received at a given place on the earth’s surface.There are no seasonal variations at the
equator where days and nights are of equal length throughout the year.In contrast polar regions receive no insolation during part of winter when there is continuous darkness but may received up to 24 hours of insolation during parts of the summer when the sun never sinks below the horizon .This occurs in the lands of the midnight sun
(f) Prevailing winds.
Temperature of the wind is affected by the temperature of it’s area of origin and of the surface over which it blows normal winds blowing from the sea during winter warms the atmosphere of the land near the sea while winds blowing from the sea during summer cools the atmosphere of the coast

(g)Ocean currents
Warm ocean currents carry warm water pole wards and rise the air temperature of the maritime environments where they follow while cold ocean currents carry cold water to the equator and so lower the temperature of the coast areas.

Factors affecting the flow of ocean Currents
Ocean currents – this is the horizontal movement of mass water in a defined direction .The movement is due to density variation at various depths governent by the temperature and salinity .The meeting of two currents converging upon one another causes sinking of water which counter balances with ascending masses.
  • Salinity differences
Density of ocean water is caused by amount of salts the more salt in an ocean the denser the water will be.Denser water sinks in water with low density which causes the formation of ocean currents.
  • Temperature
Temperature causes differences in water density which causes ocean water to move. The cold water is denser than warm water, this tends to make polar cold water sink to the bottom then flow downwards towards the equator while the warmer less denser water at the tropic moves on the surface towards the poles .After being cooled it sinks again and moves towards the equator hence the ocean current.
  • Prevailing winds
When wind blows over ocean surface it pushes water surface and forms the ocean current .Prevailing winds therefore cause the water to move to the direction they blowing to winds cause drift currents. An example of drift currents is the north Atlantic drift which is caused by the westerly winds in the Atlantic ocean.
  • Rotation of the earth
This causes the current flow to be affected as they are deflected or pushed according to Ferrell’s law. Ferrell’s law slates that”Anything moving freely in the northern hemisphere will be deflected to its right while in the southern hemisphere it will be indirectly though the winds where in the northern hemisphere ocean current are deflected to their right while in the southern hemisphere to their left “.
  • Shape of landmasses
The flow of ocean water can also be directed by the landmass.The ocean currents are turned from their straight course by the shape of adjacent landmass or coast line.
What is a temperature anomaly ?
The term temperature anomaly is used specifically to describe temperature differences from a mean .It shows the difference between the mean temperature of a place and the mean temperature of other places with the same latitude in the same month.
For example:An area which has a mean January temperature of 4ºc, which is 20ºc higher than the average for other location laying at 58 degree latitude north.such anomalies result primary from the ueven heating and cooling rates of land and sea and are intensified by the horizontal transfer of energy by ocean cu
rrents and prevailing winds.
2. ATMOSPHERIC PRESSURE
Air has weight and therefore it exerts the pressure called atmospheric pressure on the earth surface.Pressure varies with the temperature and altitude, and an instrument which measure pressure is called barometer.

There are two types of mercury
(i)barometer
(ii)aneroid barometer

The lines which join all places with equal pressure are called bars.Thus pressure varies from one place to another it is not the same in one or all the regions.
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FACTOR INFLUENCING VARIATION IN ATMOSPHERIC PRESSURE
  • Temperature
As temperature decrease pressure rises at the same height due to low temperature cold air tend to sink, thus inducing high pressure to develop But as temperature increases hot air tends to rise making it possible for low pressure to develop over the area.
  • Altitude
Usually pressure of the atmosphere decrease with increasing height. Pressure is therefore lower at the mountain top than at the sea level.This is because at the sea level air has to support a greater height than it does on the top of mountain.Thus there is less force or weight of air at the mountain top than at the sea level.
  • Revoluation of the Earth
The earth revolution causes seasons where some seasons are warm while others are cold .Revolution of the earth affects the position of the low pressure belt i.e doldrum. Normally doldrum moves northwards and southwards of the equator depending on the seasons.
Earth rotation as a ball causes formation of subtropical high-pressure belt around 35º north and south of the equator where air sinks down and gets compressed .Due to this compression the sinking of air is heated up and rises again. The same situation takes place around circumpolar or temperature belt around 60º north and south of the equator.These are the areas where the warm subtropical air rises over the cold polar air expands and gets cooler.This situation result into Depression cyclonic or frontal.
PLANETARY PRESSURE BELTS
THE WORLD PRESSURE BELTS
These can be analyzed according to temperatures:
(i)Equatorial low pressure belt / equatorinally trough
This is called doldrum it is located around 5º north and south of the equator.The air here rises due to high temperature it is a wind a convergence zone. This means winds meet there and it is called intertropical convergence zone (ITCZ)
(ii)Subtropic high pressure belt (Horse latitudes)
This is located at 30º north and south of the equator with descending air current due to heat of temperature. High pressure is attributed by accumulation of cold air which moves from the equator towards poles.This belt is also referred to as the “horse belt”.

(iii)Temperature low pressure belt (sub polar low temperature belts)
This is found at 60º north and south of the equator. It is also known as cyclonic activities zone or zone of convergence. Existance of low pressure is mainly dynamic rather than a result of temperature change.
(iv) Polar high-pressure belt
This is confined at 90º north and south of the equator. Pressure is permanently high due to low temperature attributed by a dense descending air from the temperature low pressure belt.
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3. SUNSHINE
This is another element of weather. The duration of sunshine is party of a function of latitude. For the hours of light (that is possible sunshine) vary with these season in different latitudes.It is also a function of daytime cloudiness .

MEASUREMENT AND RECORDING OF SUNSHINE
The duration of bright sunshine is measured by means of campbell stokes recorder, a solid sphere of glass 10cm in diameter. This form the rays of sunshine onto a sensitized card graduated in hours and so burn a line during the time the sun is shinning .Faint sun,light sun, near dawn or dusk or when the sun is partially abscured is not recorded .Tables of sunshine data are prepared from these record, in the form of either absolute solution in hours per day or as percentage of possible sunshine per day or month. When means figures has been obtained over the requisite number of years, the value for each state can be plotted, and lines of equal mean duration of sunshine isohels can be interpolated.
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4. HUM
IDITY
This is refered to as the atmospheric moister .The moister is obtained from various sources such as oceans, lakes,seas, dams,ponds and rivers. It is of high importance as far as weather as climate is concerned. Air absorbs water through the process of evaparation which result in water changing from its liquid state to gaseous state,the gaseous state is called water vapour. The amount of water vapour in the air is called humidity and it is measured by an instrument called hydrometer placed in the Stevenson screen.
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FACTOR INFLUENCING HUMIDITY
-Air pressure
When air is compressed, it warms up and its density becomes lower .Thus at low altitude where pressure is high air will absorb more moister. At high altitude where pressure is lower air expands and cools and its capacity to absorb moister is reduced.
-Latitude

Humidity higher in lower latitudes than in higher latitude because there is greater rate of evaporation at lower latitudes due to high
temperature.Likewise the mount of moister in the air is higher in summer .

-Temperature
Arise in te
mperature lowers relative humidity if the amount of moister remains constant because when air is heated it expands .The volume increase and therefore distribution of water vapour per unit.Volume became less.The air will have a greater capacity of holding more water vapour if air is cooled it contracts and decrease in volume making the space which moister can occupy become less .That is why if air continues to cool it will reach saturation and it gets rid of excess water vapour through condensation .

-Moisture supply
If the supply of moisture increases the air will have more of it ,they making absolute humidity to be higher .If the temperature if the air increases it will absorb even more moisture .This situation makes all places which are near large water bodies to be humid especially if the temperature is high causing a lot of evaporation. Areas that are far away from large water bodies such as deserts center has little water vapour the air has high capacity of holding moisture.

IMPORTANCE OF WATER VAPOUR IN THE ATMOSPHERE
– Evaporation forms precipitation ,which provides fresh water plants and animals.
– It absorbs both incoming and radiated energy from the sun.
– It conveys Latent heat into the atmosphere

The amount of water vapour the atmosphere can hold depends upon the temperature of the air the higher the temperature of the air the higher the capacity of it to hold water .

COMMON WAYS OF STATING WATER VAPOUR (HUMIDITY )

(I) Absolute humidity
This is the actual amount of water vapour in a specific volume of atmosphere i.e the mass of water vapour per cubic unit of air and it is normally expressed in g/m3

(II) Relative humidity
This is the proportion of water vapour present in the air compared to the maximum amount of water vapour, possible at the same temperature and it is usually expressed in percentage.Normally saturated air has relative humidity 100%.
5. PRECIPITATION
This refers to water that falls on the earth in liquid or solid forms.Some common forms of precipitation are rain, snow, sleet and hail.

Rain
This is most common form of precipitation spread every where and it is liquid form.It forms when tiny water droplets merge together around the nuclei to form rain drops.After becoming heavy enough they fall down to the earth surface as rain.Rainfall is measured by an instrument called rain gauge and the lines which join all places with equal rainfall are called isohyets.
S
now
This is refered to as solid precipitation, which forms when air cools to below the dew point or freezing point and fall down as ice while falling the ice crystals may join together to form snow flake.
Sleet
This is a frozen or partly frozen rain droplet; it so often referred to as frozen rain. It is hazardous as it may destroy crops, bring down power lines and tree branches
Hail
This is caused by super cooling of water particles in a convectional up shaft .This super cooling forms the hail stones .These stone vary in size depending on the intensity of cooling by that convectional cewent. It is more hazardous than sleet. Hail can cause coderable damage to property and plants some hail stones weight up to 2.5 Kilogram which may hit the ground at speed of up to 160 km/hr.
All forms of precipitation result from rising and cooling of air to below the dew point where condensation begins.The visible effect here is clouds in order for precipitation to occur the small droplets of water in clouds must join together in drops too large to remain or be sustained in the atmosphere thus they prefer to fall down on the earth surface as precipitation.

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CAUSES OF RISING OF AIR
When air rises there is less pressure on it at the new altitude.As a result the temperature of the rising air is lowered and cools causing that air to descend and become warm. The rate of cooling or heating that results from this vertical movement of air (ascending deslending) is called adiabatic rate.
For saturated air the rate of temperature change is 0.6ºc per 100 meters, which forms unsaturated air rate is 1ºc per 100 meters and it is called dry adiabatic rate.
CAUSES OF AIR RISING FOR PRECIPITATION
The causes of air rising are also known as the types of rainfall or the factors that influence rainfall. The factors include relief convection and the water bodies.

(i) Orographic or relief cause
Orographic cause of air rising forms orographic or relief rainfall.It forms when air is forced to ascend as a result of relief features such as mountains or plateaus. Where moist air reaches the mountain precipitation forms and it is called windward side while the other pass away from windward form the leeward side or rain shadow.
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When moist air is forced to rise over a mountain range,clouds and rain often occur.
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(ii) convectional cause
Here air is forced to rise as a result of intense heating the surface air is heated and vertical upshaft to air occur this process is called convection and it forms convectional rains it is common in summer or hot seasons.
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(iii) Frontal or cyclonic cause
Where two bodies of air masses coming from different directions and with different characteristics in terms of temperature and moisture content meet, the warmer air will be forced to rise and condense to form precipitation. The point where these two winds or air meet is called front hence frontal of cyclonic rainfall.
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Warm air is forced to rise when it is under cut by colder air,clouds and sometimes Rain.
Importance of precipitation
i. It may lower temperature
ii. It supplies water to streams and rivers
iii. It is a source of water watering crops
iv. It absorbs solar radiations
IMPACTS OF PRECIPITATION.
Impacts of precipitation can be categorized into positive and negative.
(i) Development of water bodies: precipitation encourages the development of water bodies such as rivers and lakes. These are important for irrigation, hydroelectric power generation ,transport, supply of H2O for domestic and industrial use and fishing.
EcoleBooks | GEOGRAPHY A LEVEL(FORM SIX) NOTES - SPACE DYNAMIC
EcoleBooks | GEOGRAPHY A LEVEL(FORM SIX) NOTES - SPACE DYNAMIC
EcoleBooks | GEOGRAPHY A LEVEL(FORM SIX) NOTES - SPACE DYNAMIC
EcoleBooks | GEOGRAPHY A LEVEL(FORM SIX) NOTES - SPACE DYNAMIC

EcoleBooks | GEOGRAPHY A LEVEL(FORM SIX) NOTES - SPACE DYNAMIC
EcoleBooks | GEOGRAPHY A LEVEL(FORM SIX) NOTES - SPACE DYNAMIC
This is the second part of homosphere lying above tropopause between 48 kilometres above the sea level. Much of the zone layer is concentrate within this zone particularly15 to 50 kilometres above the earth’s surface. Sometimes the term ozonesphere is used to refer the layer where there is concentration of ozone gases. Temperature remains unchanged with increasing height at tropopause but later it start to increase with height the lower stratosphere cover about 15 to25 kilometre from the earth’s surface this is the layer in which temperature remain constant. This steady is case in temperature (temperature inversion) is caused by concentration zone (O3) this gas absorbs incoming ultra violet (UV) radiations from sun. The stratopause which marks the upper limit of this zone is other isothermal layer where temperature does not change with increasing height.
The sun’s energy is called insolation or solar radiation which turns into heat energy at the earth surface. Insolation travels through space from the sun inform of waves and interact with outer edge of atmosphere before reaching the earth’s surface. Total amount of solar radiation released from the sun is 100% since the earth is neither warming up nor cooling down, there be a balance between incoming insolation and outgoing terrestrial radiation. The atmospheric condition therefore reduces the amount of solar insolation through three processes;
1. By absorption: About 15% of total solar radiation is absorbed in the atmosphere by the atmosphere components. The greater absorbers are water vapour, dust particles and clouds.
2. By reflection: Certain amount of solar radiation is reflected back into the space by clouds, dust particles and ground. The amount of insolation reflected depends on the surface but the average reflection amounts to 40% of total insolation.
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The ozone layer is found within the stratosphere and it sometimes re-termed as a shield of life. The layer is highly concerned with human and all other earth life and it sets in at an altitude of about 15km and even upward to about 55 kilometers. This layer serves as a shield protecting the troposphere and the earth surface from most violent rays or radiation from the sun. If these rays were to reach the earth directly, all bacteria exposed would be destroyed and animal tissues would be damaged.Destruction of this layer by some scientific discoveries has made the intensity of ultra violet rays reaching the earth surface to increase causing global warming. If this situation is left to continue, it will cause suffering particularly cancer , crop reduction in yield and killing of organisms on land, water and air.
Coastal regions: Rise in sea level, increase in height of storms result into more flooding especially around estuaries. Flooding affects housing, industry, farming, transport and wildlife. Flooding increases the susceptibility of water borne diseases along lake shores, coastlines, and other places liable to flooding. For instance in Uganda the outbreaks of malaria, bilharzia, and other water borne diseases were reported to as often occurring during and immediately after floods, (Ugandan NAPA 2007), According to the Tanzania NAPA (2007), Malaria prevalence has been reported tom occur in areas where it was not commonly found in the previous decade for example in some parts of Kagera, Musoma, Mwanza in Tanzania; Kisumu and Kiisi in Kenya. In addition to the even the ice caps for instance on the Kilimanjaro Mountain has tremendously reduced as a result of accelerated ice melt.
Water: Water is most likely to become scarce due to the increased rates of evaporation as well as the variation in the rainfall pattern in some areas. The anticipated climate variability in form of long droughts will worsen the availability of and accessibility to clean water particularly the poor or those who depend on rivers, streams, boreholes. This is because such source may be dried out or lowering of water levels, in springs, rivers, underground aquifers. Communities will veer to any available water irrespective of its quality hence pausing a danger for water borne diseases, harden the production of hydroelectric power, limit water transport. For instance the declining water levels of lake Victoria in 2002 to 2004 left many boat landing sites and harbours high and dry thus affecting water transport negatively; the extension of the Owen falls dam (Kiira and Nalubaale) opened in 2000 appears to have been designed to operate with conditions of high average water levels seen between 1960 1990 basing on the inability of the power plant to operate at full capacity during the low water levels of 2002. In Tanzania, the power cut off was extreme also as the mega like Kidatu could not operate at full capacity. This was portrayed through a more than 12 hours cut off.


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