WEATHER, CLIMATEAND NATURAL REGIONS

Weather is the atmosphere condition of an area recorded within a short period of time which can be day after day or week after week or after a certain period of time.

The weathercondition of the area is determined by recording to the behaviorof weather elements such as temperature, humidity, sunshine cloud cover, rainfall, wind etc.

Climate is the description of the atmospheric condition which is recorded over a long period of time which can be above 30 years.

It is determined by measuring or recording the behaviors of weathers elements within a long period of time.

Climatology is the science which involves analysis of spatial distribution of atmospheric phenomena. It is a scientific study of different processes and conditions taking place in the atmosphere.

Micro- climate refers to the atmospheric condition of a small area which is different from the surrounding area.

Isolation is the solar radiation from the sun received in the atmosphere and on the surface of the earth or it is the total energy generated from the sun and received in the atmosphere and on the surface of the earth.

Weather stationis the place where all elements of weather are observed, measuredand recorded.

Weather forecasting is the practice of predicting future weather condition of the given area. It can be done into two ways

i.                                        Traditional ways

ELEMENTS OF WEATHER

1.            TEMPERATURE

Temperature is the degree of hotness or coldness of an area or a body. Temperature is measured or expressed in terms of centigrade’s

Temperature of the earth’s surface originates from the sun and it called solar energy. Solar energy when reached on the earth’s surface is transformed into heat by the land and the atmosphere before it reaches the surface of the earth.

The amount of incoming solar radiation or isolation receivedin the area depends on intensity and duration of radiation from the sun. There are determined by both angles at which sunrays strike

the earth and the number of day light hours. The two fundamental factors plus the following five factors determine the temperature of any given area on the surface of the earth.

Other factors which influencetemperature are;

i.                                        Earth’s inclination (angle of the sun towardsthe earth)

The axis of the earth that is the imaginary line connecting the North Pole through the South Pole always remains in the same position.

It is titled at about 23.5 away from the perpendicular. Every 24hours the earth rotates once at that axis, while rotating the earth slowly revolve around the sun in a nearly circular, annual orbit. If the earth was not titled from the perpendicular, the solar energy received at given latitude would not vary during the course of the year. The rays of the sun would strike the equator and all other parts of the earth equally. When the Northern hemisphere is directly titled towards the sun, the vertical rays of the sun are felt as far North as 23.5 North latitude. Tropical of

cancer and this occurs on June 21^st and it is called summer solstice, and also winter solstice in the southern hemisphere.

ii.                                     Cloud cover

Clouds which are denser concentrated normally tend to reflect a great deal of energy light, colored surface especially snow cover also serve to reflect large amount of solar energy, therefore the amount of cloud cover amount of sunrays that would reach the surface of the earth. More cloud cover reduces the amount of heat on the surface of the earth. Energy is lost through re-radiation as well as reflection. In re-radiation process the earth’s surface act as a communicator of energy, the energy that is absorbed into the land and water is returned to atmosphere in the form of terrestrial radiation.

iii.                                 Nature of earth’ssurface.

Some kinds of earth’s surface materials especially water stone solar energy more effectively than others. Because water is transparent solar rays can penetrate a great distance below its surface. If water currents are present, heat is distributed even more effectively.

The land surface are opaque, so all the energy received from the sun is concentrated at the surface therefore the temperature of the earth between water bodies and the land is different where by the land earth experience more high temperature than the water bodies. Because the earth’s heats and cools faster than water, hot and cold temperature are recorded on the earth or on the land and not in the sea or water bodies.

iv.                                The distance of elevation abovethe sea level

The temperature on the surface of the earth vary with the variation in altitudes but in every 100m rise above the sea level,the temperature decreases to the rate of

0.65 and this process is called temperature lapse rate.

v.                                    The distance from the sea

Note that, coastal areas have lower summer temperatures and higher winter temperatures than those places at the same distance from the equator excluding sea coasts. This difference in temperature during different season is influenced by water bodies.

vi.                                Ocean currents

Ocean currentsare divided into two types as;

a.           Warm ocean currents: warm ocean rises the temperature over the areas they flow

b.            Cold ocean currentslowers the temperature of the areasthey flow

TEMPERATURE LAPSE RATE AND TEMPERATURE INVERSION

Temperature lapse rate

A temperature lapse rate is the atmospheric condition where temperature decreases with an increase in altitudes. It is mostly found in troposphere and mesosphere. There are two types of temperature lapse rate.

i.                                        Normal lapse rate

It is also called environmental or static lapse rate. It refers to the decrease in temperature due to increase in altitude in the rate 0.65 forevery 100m above the sea level.

ii.                                     Adiabatic lapse rate

Is the rate of decrease in temperatures with the rising air mass. It is divided in two types.

a.              Dry adiabatic lapse rate (DALR)/ un saturated.

It is the rate of cooling of a rising dry at the rate of 1 per100m or 10 per 1km.

b.            Wet adiabatic lapse rate (WALR)/saturated

It is the rate of cooling of a risingsaturated air at the rate of 6 for every 100m Temperature inversion

Under normal situation from environmental situation atmospheric temperature decreases with increase in altitude but in some occasions, Atmospheric temperature tends to increase with increase in altitude.

Temperature inversion is the atmospheric condition where temperature increases in height or altitude. It is mostly observed in stratosphere and thermosphere.

In stratosphere, temperature increases due to concentration of ozone layer or ozone gas which absorbs incoming solar radiation from the sun and converting it into heat energy making the upper part of the atmosphere to be more heated than the lower parts.

In thermosphere temperature increases with increase in height due to concentration of atomic oxygen and presence of electrically charged particles which absorbs incoming solar radiation.

Causes of temperature inversion

i.                                        Presence of ozone gas

In the atmosphere the gas absorbs solar radiation and changing it into heat which eventually increases the temperature on the upper part of the stratosphere and other layers of the atmosphere.

ii.                                     Presence of atomicoxygen gas and electrically chargedparticles

In the thermosphere these gas and particles increases heat on the atmosphere as the altitude increases.

iii.                                 Terrestrials radiation

During night, there is no sunshine thus the earth’s surface especially the land looses heat more rapidlyand this makes warm air to be uplifted or rise up from the land. The process warm up the upper part of the atmosphere increasing the temperature as the altitude increases.

Along wave radiation is responsible for this process.

iv.                                Convergence of air masses(formation of air fronts)

Convergence of air masses of different temperature condition makes warm air to be forced up by cold air which descends from the atmosphere to the surface of the earth.

v.                                    Presence of water vapour(atmospheric components)

Clouds, dust and other materials on the atmosphere which reflects and absorbs incoming radiation from the sun changing them into heat energy which lattes warm up the atmosphere.

SOLAR RADIATION

Weather results from the interaction of solar radiation on the earth’s atmosphere and the earth’s surface. The two movements (rotation and revolution) explain the changing elevation of the sun as well as latitudinal and seasonal variations in length of the day, receipt and escape of radiation and weather.

The sun is the source of all energy on the earth’s surface. Only a portion of sun radiation reaches the earth’s surface as direct radiation. The remainder being reflected, absorbed or scattered by the atmosphere or atmospheric components, therefore the sun emits almost 100% of the heat but all of it reaches the surface of the earth’ as shown below;

The total amount of solar radiation received on a horizontal surface is about 43%. Out of this 27% penetrates directly to the earth’s surface and 16% arrives as the diffuse sky radiation. So 43% reaches the ground together. The atmosphere including clouds absorbs 15%, the remaining 42% is reflected back into space, which represents the albedo of the earth. The ground which accounts for 33% and the defuse reflection which makes up remaining 9%

It is noticed that defuse radiation towards the grounds (16%) considerable greater than the returned to space (9%). This difference due to the fact that the larger dust particles scatter more radiation the direction away from the sun than the direction towards the sun.

In the figure the radiation received by the earth and atmosphere is counted positive (+ve) and the radiation emitted or reflected and scattered to space is denoted by negative (-ve).

42% of incoming solar radiation is returned direct back to the space and the remaining 58% is absorbed by the ground and the atmosphere.

This 58% must be radiated back to space since the yearly mean temperature of the earth as a whole remains the same. The radiation from the ground is called effective radiation.

The 24% represents the different between the actual radiation from the ground and radiation from the atmosphere to the ground. Out of these 24%, 16% is absorbed in the atmosphere while 8% returns directly to the space. The other 50% is radiated back to space by the atmosphere.

TERRESTRIAL RADIATION

Terrestrial radiationis the radiation from the earth (from the land masses and water bodies)

The radiation emitted from water and land is a long wave radiation and the radiation from the sun to the surface of the earth and to the atmosphere is a short wave radiation.

2.            ATMOSPHERIC PRESSURE AND WIND SYSTEM

Atmospheric pressure

Atmospheric pressureis the downward force exited by weight of our per unit area of the earth’s

surface.

The distribution of it is not the same in all regions hence it differs from home time and from one place to another place.

Factors affecting atmospheric pressure

i.                                        The vertical heightabove the earth’ssurface (altitude)

The atmospheric pressure varying with the variation in altitude whereby on the surface of the earth. It decreases due to increase in the altitude.

Therefore near the sea level, pressureis higher than mountainous areas.

ii.                            Temperature radiation from one places to another causes variation the atmospheric pressure. When air is heated it becomes less denser and it rises up causing a low pressure zone and when it cools. It contracts hence start to exert high pressure

iii.                                 Overhead sun (apparent movement of overheadsun)

When the sun is overhead in the tropic, it creates a considerably seasons change of atmospheric pressure over the earth’ssurface in the respective area. And during that time, the rate of insulation is high resulting to low pressureas the air is heated and expand. Other areas which are not experiencing overhead sun, the insulation is low resulting to the cooling of air which creates a high pressure zone.

iv.                                Latitude

Atmospheric pressure varies from one place to another depending on the latitudinal position of an area, example in equatorial regions there is low pressure due to high solar radiation caused by high temperature at the equator.

In polar area, there is high atmospheric pressure because of low temperature caused by little insolation from the sun.

v.                                    The earth’s rotation

Rotation of the earth causes day and right which results to the variation in atmospheric pressure as the earth is inclined at different angle towards the

Wind system

Wind is an air in motion from the region of high pressure to the region of low pressure.

Wind can be classified into two types :

i.                                        Local winds

ii.                                     Interplanetary winds

i.                                        Local winds

These are wind system operating only in a small area within a short period of time.

These winds include the following

a.              Land breeze

This is the movementof air from the land to the sea or ocean.

Land breeze occurs during night when the land is colder than the sea hence the land develop high pressure and the sea develop low pressure.

b.            Sea breeze

This is the wind that moves from the sea to the land. It occurs during the day time when the ocean is cooler than the earth or the land. During that time, the water bodies especially the oceans and seas develophigh pressure and the land develops low pressure.

c.              Anabatic wind

The word anabatic is derived from the Greek word anabatos meaningthat moving upward. Anabatic is a warm wind which blows up steep slope maintain side, driven by heating of the slope through insolation. It is also known as upslope wind as it blows from the valley towards the mountain slope or valley slope.

This wind occursduring day time when hill side is heated by calm sunny weather. It is common in mountainous area.

d.            Katabatic winds

Katabatic, the word is derived from the geek word “katobasis” meaning that descending. It is the technical name for drainage wind, a wind that carries high density air from higher elevation down the slope under the force of gravity.

These winds are sometimes called fall winds. They occur during the right in mountainous area when the highland areas are losing more heat due to high rate of terrestrial radiation.

Monsoon winds

The word monsoon is derived from the Arabic word “mausin” meaning season. Monsoon winds are winds whose directions are reversed from one season to another due to the change of pressure belts caused by apparent movement of overhead sun. They develop due to difference in season when the sun is overhead in tropes. During summer when the sun is overhead in tropic of cancer, wind blows from high pressure belt in the southern hemisphere to the Middle East especially in Asia. During winter when the sun is overhead in tropic of Capricorn, the central Asia develop high pressure hence wind blows from Asia to Australia. Monsoon wind is common in India, Japan, Australia, Indonesia and other parts of Middle East.

ii.                                     Interplanetary winds are as follows:

a.              Trade winds

These are prevailing patterns of earthly surface winds found in tropes within the lower portion of the earth’s is atmosphere, in a lower section of the troposphere near the earth’s equator. They blow predominantly from the north East in the

Northern hemisphere and from the south East in the southern hemisphere strengthening during winter and when the arctic oscillation is in its warm phase. The wind blows from the sub-tropical high pressure belts, or towards the intertropical convergence zone. They are divided into two types:

i.                                        North East tradewind

These winds are blowingfrom North-Eastern directionin the Northern hemisphere because of rotation which reflects wind direction.

ii.                                     South East trade wind

They blow from South-Eastern direction in the Southern hemisphere.

b.            Mid latitude weasterlies

The westerly, it comprises the air flowing from the sub-tropical highs to the sub polar lows from about 30 to 60 N and S of the equator.

These belts more north and south with the seasonal changeof pressure belts

These winds originate from high pressured area in the horse latitude (30N and S of the equator towards the 60N and S of the equator (sub polar low pressure belts). The winds are predominantly from the south west in the northern hemisphere and from the north – west in the southern hemisphere.

Westerlies are strongest in the western hemisphere and at times, when the pressure is lower over poles while they are weakest in the southern hemisphere and wind pressure is higher over the polar.

c.              Polar winds

They blow from the polar ice towards the equator wards. The movement is pronounced in the southern hemisphere and northern hemisphere. Polar winds are dry and cold wind that blows from high pressure area of the polar at the north and south towards low pressure area (sub-polar low pressure 60N and S)

AIR MASSES

Air masses are formed resulting from when air remains stationary over a place for several days. During this time the air is likely to assume the temperature and humidity properties of that area.

Air masses are a body of air covering a relatively wide area, exhibiting approximately uniform properties through any horizontal section.

Air masses are a large volume of air in the atmosphere that is mostly uniform in temperature and moisture.

For a place to develop air mass it should have the following conditions.

i.                              There should be a large uniform surface for Example Ocean or a desert or any other surface which is uniform.

ii.                            There should be stagnation in atmospheric circulation or no change of weather condition.

iii.                                 There should be relative constanttemperature

Air masses can be divided into groups according to their source regions and characteristics, both of temperature and humidity.

On basis of temperature, they are known as polar or tropical and on the basis of humidity they are known as marine (having crossed the oceans and so moist) or continental (originating over the continent and so dry). Their combination allows four main categories of air masses to be distinguished.

i.                                        Polar continental air masses (pc)

This air originates over the continental interiors, the northern Tundra land of northern America, Asia and Greenland forming mass of cold dry air, their air mass yield little / no rainfall

ii.                                     Polar marine time air masses

These are air masses which originates and travel over high latitude oceans 60N andS such as northern Atlantic Ocean. They are cooler in winter but warm in summer. They have low temperature and low moisture content.

iii.                                 Tropical continental air masses (TC)

These are air masses which originates and develop from tropical deserts such as Sahara and Australian desert. They are warm and generally tropical continental air masses originate from tropical desert.

iv.                                Tropical marine tire air masses

These originate in tropical latitudes but having crossed the water bodies towards the north and South Pole or originate from tropical oceans such as pacific and Atlantic. They are warm and most, yielding heavy rainfall with lighting and thunders.

FRONTAL ZONES

A frontal zone is the point where two air masses of different characteristics in terms of temperature and humidity meet each other after they have moved outward from the various major                                       high                                       pressure                                                areas. The situation result in the condition of large scale atmospheric instability in the frontal zones.

Conditions for the occurrence of frontal zones

i.                                        There must be two contrasting air masses movingtowards one another

ii.                                     There must a convergence of two air masses

TYPES OF FRONTALZONES

i.                    Warm frontalzones

This is formed when a strong warm air is moving or advancing and is forced to over ride a weak cold air mass. It is formed when a strong warm air mass meet with a weak cold air mass and slide up over it. The whole surrounding to be covered by warm air.

Weather conditions associated with warm frontalzones

i.                                        Formation of clouds

ii.                                     There will be a formation of warm weathercondition

iii.                                 Formation of cyclonicrainfall characterized by lightning and thunderstorms

ii.                                     Cold frontal zones

If occurs when a strong advancing cold air mass overcome a body of weak warm air mass. During air meeting, weak warm air is forced to rise above causing the surrounding to be covered by cold air mass.

Weather conditions associated with cold frontalzones

i.                                        formation of little/ sparsed clouds

ii.                             formation of cold weathercondition because the surface will be characterized with low or cool temperature

 STABILITY

Air is said to be stable since dew point may not be reached and therefore making atmosphere produced few clouds with little or no rainfall at all.

The situationoccurs when dry adiabatic lapse rate is greater than normal lapse rate.

The atmosphere stability is associated with low degree of dampness in the atmosphere with no cloud, high day temperature.

AIR ISTABILITY

Air instability occurs when the rising saturated air cools less rapidly than the surrounding air. The rising air remains warmer and lighter than the surrounding air.

If the air gets sufficient moisture and the dew point is reached this condition may reduce heavy clouds, thunderstorm, heavy rainfall and high degree of atmospheric dumpness and very small daily range temperature

It occurswhen environment lapse rate is greater than dry adiabatic lapse rate

HUMIDITY AND PRECIPITATION

HUMIDITY

Humidity is the amount of water vapour in the atmosphere. It can be absolute or relative humidity.

Absolute humidity

Is the actual amountof water vapourpresent in a certain volume of air at a given temperature. Relative humidity

Is amountof water vapourpresent in a mass of air expressesas the percentage Factors affecting humidity

i.                                        attitude

The amount of humidity increases as the altitude from the surface increases. This is because of normal lapse rate.

ii.                                     temperature

High temperature increases humidity in the atmosphere due to increasein rate of

evaporation from the earth’ssurface.

iii.                                 Rainfall

High rainfall increases the amount of water on the surface of the earth which when evaporates results to the formation of humidity or water vapour on the atmosphere. Also rainfall increases the amount of water in the atmosphere due to increased moisture on the surface.

iv.                                Availability and size of water bodies on the earth’ssurface

Many water bodies like oceans and seas increase the amount of water vapour or humidity in the atmosphere through evaporation.

v.                                    Vegetation cover

Areas covered by denser vegetation like equatorial region, atmospheric water vapour is high due to high rate of evapotranspiration from the vegetation.

vi.                         Human activities such as a forestation, construction of water reservoirs, also influence humidity on the atmosphere.

CONDESATION

A condensation is the formation of water droplets when a rising air has been cooled beyond its dew point.

A dew point is a temperature where air becomessaturated as a result of cooling process in the atmosphere.

It is the point where atmosphere do not containany further water vapour and condensation begin to take place.

The cooling of air in the atmosphere occursthrough the following ways:

i.                                        When there is horizontal movementof warm air on the cold surface

ii.                                     Through movement of air from warmer to cooler latitudes

iii.                                 Through ascending of warm air.

iv.                                By direct radiation from the earth’ssurface to the atmosphere.

HAZE.

Haze is impaired visibility of 1 to 2 km as a result of dust and other small particles on the atmosphere.

MIST.

Mist is impaired visibility caused by condensation of water vapour into small droplets that form clouds at the ground level. It reduces visibility – less than 2km.

FOG

Is the collection of liquid water droplets or ice crystals suspended in the air at or near the earth’s surface. Fog can be considered as a type of low – flying cloud and heavily influenced by nearby bodies of water, topography wind conditions and even human activities.

Fog forms when the differences betweenair temperature and dew point are generallyless than

2.5. They begin to form when water vapour condensesinto a tiny liquid waterdroplets suspended in the air.

TYPES OF FOG

1.            SMOG

It is the combination of smoke and fog, it reduces visibility to about zoom hence it is very dangerous and can cause accidents.

2.            RADIATION FOG

Is formed by a cooling of land after sun set by thermo radiation in calm condition with clear sky. Cooling ground produces condensation. Radiation fog occurs at night and usually do not last long after sun rise, but they can persist all day in water months.

3.            GROUND FOG

It is the fog that abs cure less than 60% of the sky and does not extend to the base of any overhead clouds

4.            ADVECTION FOG

It occurs when moist air passes over a cool surface by advection (wind) and is cooled. It is common as a warm from passing over an area with significant snow-pack. It is common at the sea when moist air encounters cooler waters including areas of cooler waters upwelling.

5.            EVAPORATION FOG (STEAMFOG).

These fog are formed over bodiesof water over lying by much coolerair.

6.            FREEZING FOG

A freezing fog is a composed of droplets of a super cooled water which freezes to surface on contact. They are very common in temperature regions and they occur during winter seasons.

7.            PRECIPITATION FOG

This fog are formed as precipitation falls into dryer air below the cloud the liquid droplets evaporates into water vapour. The water vapour cools and at the dew point it condenses and forms fog.

8.            UP SLOPE FOG

This fog forms when the moist air is rising up the slope of a mountain on hill which condenses into fog on account of adiabatic cooling and to a lesser extent the drop in pressure with altitude.

9.            VALLEY FOG

This fog forms in the mountainvalleys often duringwinter season.

CLOUDS.

Clouds are formed when water vapourfrom the earth’ssurface reaching the atmosphere cools

and condenses at different height in the atmosphere. Clouds may be classified basingon two main criteria

i.                                        According to theheight

ii.                                     According to the general form/appearance.

According to the heightclouds are classified into the following types:

1.            HIGH LEVEL CLOUDS

These clouds are formed above 20000 feet or 6000m and since the temperature is so cold at such high elevations, these clouds are primarily, composed of ice crystals. High level clouds are typically thin and white in appearance but can appearin magnificent array of colorswhen the sun is low on horizon.

High level of cloudsincludes,

a.              CIRRUS

These are fibers or feather like clouds in a blue sky. They indicate a fair weather condition (stable).

b.            CIRROSTRATUS

These are thin sheetclouds found at high altitudebut still spreadout to the large area.

c.              CIRROCUMULUS

A small heaped cloudswith ripples or wave appearance.

2.            MEDIUM LEVEL

The bases of medium level clouds typically appear between 6500 feet to 2000 feet. Because of their lower altitude they are composed of primarily water droplets however they can also be composed of ice crystals when temperature is cool enough.

Medium level clouds includes;

a.              ALTOCUMULUS

These are white – grey head clouds appearing like waves and are separatedby patches of blue sky.

b.            ALTOSTRARTUS

These are greyish sheetclouds which are much denserthan cirrostratus clouds.

3.            LOW LEVEL CLOUDS

These are mostly composed of water droplets since their bases generally lies below 6500 feet. However when temperature is cold enough these clouds may also contain ice particles and snow.

Low level clouds includes

a.              NIMBOSTRATUS

These are very low sheet clouds found at a very low height . If rain falls from these clouds are known as nimbostratus rain.

b.            STRATOCUMULUS

These are dark and heavy cloudswith pronounced waves

DEPRESSIONS, CYCLONESAND ANTICYCLONES DEPRESSIONS DEPRESSIONS

Depressions are large areas of low pressure due to the meeting of warm equatorial and cold polar air. They are oval or circular shaped on maps with closed isobars. Air of depression circulates in anti- clockwise direction in the northern hemisphere and in a clockwise in the southern hemisphere where they blow towards the centre.

Depressions mainly develop over the oceans, mid or temperate latitudes where humid tropical air meet with the cold polar air especially around latitude 60 North and south of the equator. It is at this pointwhere westerly winds meet with the polar

winds. The zone where these two winds meet or converge is called polar front and it is in this zone where depressions forms.

Weather conditions associated with depressions.

i.                                        Clear sky with the formation of circus cloudswhich are littlebit high.

ii.                            Winds blow from the south east after a definite time , a cloud cover develops and heavily occurs.

iii.                         When rain stops, wind direction changesand its starts blowing from south west, temperature rises and there occurs more humidity air.

CYCLONES AND ANTICYCLONES

A cycloneis a storm or a system of winds that rotates around a centre of low atmospheric pressure.

An anticyclone is storm or a system of wind that rotates arounda centre of high pressure.

Distractive weatherpatterns tend to be associated with both cyclonesand anticyclones are as follows;

i.                                        Cyclones (commonly as lows)

Generally are indicators of rain clouds and other forms of bad weather,(lightning & thundering)

ii.                           Anticyclones (commonly known as highs) They are predictor of fair weather.

iii.                         Wind in cyclones blow clockwise in the northern hemisphere and anticlockwise in the southern hemisphere

iv.                         In cyclones air close to the ground is forced inwards towards the centre of the cyclones where pressure is lowest, it then begins to rises up , expanding and cooling in the process. The situation increases humidity of the rising air which results in the cloud and high humidity in the cyclone.

v.                           Anticyclones, the situation are reversed. Air atthe centre of anticylone is forced away from high pressure that occurs there.

TROPICAL CYCLONES

Tropical cyclones are areas of low pressure system which originates in temperature latitudes between 20 to 60 north and south of the equator. They occur all over the oceans except in the northern Atlantic ocean.

Tropical cyclone develops where the air mass brought by northern and southern trade winds meet, that is along the inter – tropical front. They from over the oceans as the air masses which have travelled over oceans.

Weather conditions associated with tropicalcyclones:

i.                                        The air becomesstill, temperature and humidity rises.

ii.                                     Thick clouds appearor develop

iii.                         Winds blow violently and finally dense clouds and torrential rainfall reduces visibility to a few meter.

Effects of tropical cyclones

i.                                        There is rapid rising of air givingrise to torrential rainfall that causesfloods.

ii.                            Strong blowing wind which cause considerable damage to property such as electricity, buildings etc.

iii.                                 Formation of ocean wave storms,radial surges resultingfrom high winds

iv.                         Landslide which can result from heavy rainfall where buildings have been erected on steep and stable slopes as in the case of hongkong where landslides were responsible for 480 deaths between 1948 to 1998.

NATURAL REGIONS OF THE WORLD

Is a large area of earth’ssurface with similarcharacteristics of temperature, rainfall and

vegetation cover.They are classified according to climatictype and naturalvegetation. CLIMATE TYPES

The major climatic types are classified basing on temperature and rainfall pattern. CLASSIFICATION OF CLIMATE BASING ON TEMPERATURTE

i.                                        If a place has a temperature above 20 is said to be hot climate.

ii.                                     If a place has temperature between 10 and20 is said to be warm climate

iii.                                 If a place has temperature between0 and 10 is said to be cool climate.

iv.                                If a place has temperature less than 0 is said to be coldclimate.

CLASSIFICATION OF CLIMATE BASINGON RAINFALL

i.                                        If a place has rainfallmore than 1500mmis said to be very wet climate.

ii.                            If a place has rainfall between 1000mm-1500mm, the climate is said to be wet climate.

iii.                        If a placehas a rainfall between 500mm and 1000mmm, the climate is said to be moderate.

iv.                         If a place has a rainfall between 250mm and 500mm, the climate is said to be dry climate.

v.                           If a place has a rainfall below 250mm the climate is said to be very dry climate or desert climate.

1.            HOT CLIMATE

Areas which experience hot climate includethe following climateregions;

i.                                        Equatorial climate

ii.                                     Tropical climate

iii.                                 Monsoon climate

iv.                                Hot deserts

I.                                                EQUATORIAL CLIMATE

places like

-                    Amazon basin

-                    Congo basin

-                    Guinea

-                    Southern eastern Asia

-                    Parts of west Africa Characteristics of equatorial climate

i.                               They experience high temperature throughout the year , sometimes a monthly temperature may be above 27

ii.                                     Have very small annual temperature range which is less than 4

iii.                         They have double maximumof rainfall ie. They receiveheavy rainfall twice a year.

iv.                                They have thick forest and even greensuch as Amazonforest and Congoforest.

v.                            They have high and low vegetations ie. Vegetations in this area are grownin layers with no undergrowth.

vi.                                The areas experience high humidity and high cloud cover throughout the year.

Economic activities taking place in Equatorial climate

i.                                        Lumbering activities examplesin Gabon ,Amazonforest

ii.                                     Tourism activities

iii.                                 Agricultural activities especially cultivation of rice , banana,cocoa, coffee etc.

II.                                                TROPICAL CLIMATE

It covers the areas located within the tropicalbelt. They are divided into two:

a.              Tropical continental climate(savanna)

It is found in the interior of continent and located within 5 - 20 north and south of equator. It includes places like

-                    Central Africa

-                    Venezuela

-                    South Australia

-                    Parts of Sudan

This climatein Africa and Australia is known as savanna becauseit is dominated by grassland. In Brazil, it is known as compass and in Europe is known as Steppe.

Characteristics of savanna climate

i.                                        It experiences moderaterainfall and convectional in type

ii.                                     Temperature is high during hot season and low during cold season

iii.                                 They have high annual range of temperature between 8 and 11

iv.                                The zone is under the influence of inter tropicalconvergence zone (ITCZ)

v.                                    They experience moderateand sometimes wet rainfall

vi.                         Natural vegetation which dominated the region are grasses with very little scattered trees

Economics Activities

i.                               Tourism activities because of natural vegetations or grasses which are good for wildlife

ii.                                     Cultivations of cropssuch as maize

iii.                         Pastoralism which is done in pastoral societies. Example Fulani in Northern Nigeria, Maasai in East Africa.

b.            Tropical marine climate

They are found in the Easternside of major landmass or of the continent especially where there is a steep highland. Such as areas are like;

-                    Philippines

-                    Mozambique

-                    Hawaii

Characteristics of tropical marineclimate

i.                                        They experience conventional and or graphic/ relief rainfall

ii.                                     They face trade wind coast

iii.                                 They experience high temperature with a very small fluctuation

III.                                               MONSOON CLIMATE

It is influence by seasonal wind.It is found in:

-                    South East Asia

-                    China

-                    North Australia

-                    Burma

-                    Indonesia

-                    Somalia Characteristics of monsoon climate

i.                                        They experience seasonalwind

ii.                                     The summer season is hot with warm air.

iii.                         The annualrainfalls vary one area to another, due to the influence of water bodies, relief and natural vegetation.

IV.                                                HOT DESERT/TROPICAL DESERT CLIMATE

iv.                        Hot deserts occur on the western side of the continent between 20  north and south of the equator. Example of the deserts are;

-                    Atakama desert

-                    Namib desert

-                    Sahara desert

-                    Kalahari desert

-                    California desert

Characteristics of hot desert

i.                               They experience very high daily temperature above 35, which vary from the day time tonight. The daytime is more high and night temperature is lower to about 16.

ii.                            The area is very dry as they receive very little or no rainfall. The annual rainfall in deserts is below 250mm but it changes by increasing as you approach the transitional zone between desert and tropical climate.

iii.                                 They are characterized by little or scarce vegetation cover

iv.                        The velocity of wind in desert is high due to lack of vegetation cover and little or no water bodies.

VEGETATION

Vegetation is the general assemblage of plant speciesand the ground cover they provide. Is the total plant community growing in a certain area under the influence of the natural and man- made conditions.

Vegetation can be dividedinto the followingtypes

1.            NATURAL VEGETATION

These are primary or original plant cover that goes (grows) in the area even when there is no human influence. They exist in the given geographical area naturally.

2.            SEMI- NATURAL VEGETATION

These are wild vegetation which their existence directly or indirectly have influence from man . Such vegetations are like palm, rubber, which were wild but now grown by human being.

3.            CULTIVATED VEGETATION

Refers to the crops and cultivated trees planted to replace the destroyed vegetation

Important terminologies used to describevegetation

1.            ECOSYSTEM

An ecosystem is a communityof living organismin conjunction with the non- living components of their environment (things like air , water and mineral soil) interacting as a system. These biotic and abiotic components are regarded as linked together through nutrients cycles and energy flows.

2.            HABITATS

Is a surface of the earth adjacent to the atmosphere in which all organisms live, or in which all organic life exist. It is the natural home or environment for animals, plants and other organisms.

3.            PLANT SUCCESSION

Plant succession is the changing of plant communities over time. Plant communities go through all sorts of changes over time depending upon various changing conditions, disasters, human influence, animal influence etc.

Or

A plant succession is the orderly process of one plant community gradually or rapidly replacing another.

The community begins with relatively few pioneering plants and animals and develops through increasing complexity until it becomes stable or self perpetuating as a climax community.

TYPES OF PLANT SUCCESSION

a.              Primary succession

A primary succession is a dynamic which begins with colonization of an area that has not been previously occupied by an ecological community such as newly exposed rocks, lava flows, newerly exposed glacial tills.

Stages of primary succession include;

i.                                        Pioneer plants (lichensand mosses)

ii.                                     Grass stage ; grasses , smaller shrubsand trees.

Animals begin to returnwhen there is food for them to eat

b.            Secondary succession

Is a successional dynamies following sever disturbance or removal of a pre- existing community. Dynamics in secondary succession are influenced by pre-disturbance conditions when the former vegetation is cleared or bunt by wild harm fire caused by volcanic eruption and later the area become colonized by a new vegetation or plant community quite different from the former vegetation. Disturbance of the former vegetation can be by natural forces and human being through his different activities.