GENERAL IDEA ON TEMPERATURE

EARTH ALBEDO

The earth albedo involves scatting, reflection and absorption of solar energy. Definition; Earth albedo is the capacity of a surface to reflect the solar radiation/energy. Albedo is the ratio between incoming radiation and the amount reflected back into space expressed in percentage.

In other words, albedo can be expressed as the ratio between the total solar energy (radiation) filling upon a surface and the amount reflected expresses as a decimal or percentage. For example the earth’s average albedo (including also albedo of the clouds) is about 0.4% (0.4% i.e. 4/10 of solar radiation is reflected into space).

Therefore; temperature is markedly higher for a place with low albedo than of the place with high albedo. Land and water surface ferexample have quite different characteristics. Water has tendency to store heat that it receives while the land quickly returns (reflects) it to the atmosphere.

On the other hand this experience, land has greater albedo or reflective capacity than water surface. Earth albedo form different surface. Dark  soil 0.03%, Snow field 0.8%, Water 0.02%, Grass land 0.25%.

Albedo is highly affected by:

i.                     Types of clouds. For example;

(a)    It is 30% - 40% in the thinner clouds such as cirrus clouds.

(b)   It is 50% - 79% in the thicker-clouds such as stratus.

(c)    It is 90% in the thickest clouds such as cumulo-nimbus.

ii.                  Land surface. For example.

(a)    It is less than 10% over ocean and dark soil.

(b)   It is about 15% over coniferous forests and urban areas

(c)    It is 25% over grass lands and deciduous forests.

(d)   It is 40% over light-clouded deserts

(e)    It is 85% over fresh snow.

NOTE: Albedo increases as deforestation and overgrazing occurs. This reduces the possibility of clouds and rainfall formation, hence increases the possibilities of desertification to occur.

NB: the figure above may vary depending on clouds thickness, amount of water vapor, dusts etc.

HEAT BUDGET ON EARTH AND ATMOSPHERE.

Heat budget is the balance between the amount of solar radiation received by the earth’s surface and its atmosphere and the amount of heat lost from the earth by outgoing terrestrial long wave radiation from earth’s surface and lost heat from atmosphere. Is the distribution of heat from the sun to the earth’s surface. It is approximate about 6000⁰C .

LAPSERATE.

Lapse rate refers to the situation where by temperature decrease with the increase in altitude or increase with the decrease of altitude. Also is the rate of change of temperature with the change of altitude.

Types of lapse rate.

1.      Environmental lapse rate.

Refers to the situation where by temperature decrease by the increase of altitude, i.e. 0.6⁰c decrease with increase of 100m. Also environmental lapse rate is called normal or constant lapse rate.

2.      Adiabatic lapse rate.

When the temperature change without addition or substitution of energy is called adiabatic  lapse rate processes change.

Types of adiabatic cooling.

(a)    Adiabatic cooling (wet/saturation adiabatic)

(b)   Adiabatic warming (dry adiabatic).

(a)   Adiabatic cooling

Takes place when there is cooling of pocked (parcel) of air without addition or substitution of energy. This change is 0.3⁰C – 0.9⁰C to 400m.

(b)   Adiabatic warning.

Takes place when pocked (parcel) of air warming without any addition or substitution energy.

TEMPERATURE INVERSION.

Temperature in troposphere normally decrease with increasing height or over age of 0.6⁰C per 100m (warm lapse rate). But sometimes this normal trend of decreasing of temperature with increasing heighten is reversed special circumstances.

Therefore; temperature inversion simply can be defined as increasing of temperature with increasing height/altitude it is also called “Negative lapse rate”. This phenomena may occur near the earth’s surface or at great height in the atmosphere. The rate of change of temperature is called reversed or abnormal lapse rate.

Causes of Temperature Inversion.

The following are some of the causes:

i.                     Radiation is caused by the use of energy on the earth’s surface during night.

ii.                   Air substance caused by the friction between airs leading to the production of temperature. This occurs during downward of air.

iii.                  Formation of front, if it takes place where two air masses with characteristics of temperature meet on the meeting the warm air is alone on cold air.

iv.                 Advection, it takes place when warm air passes over also are moving horizontally. Refers to the fog.

v.                   Water vapour, this keeps temperature at long time.

Types Of Temperature Inversion.

1.      Ground surface inversion.

It is formed when ground surface becomes cold during winter in night due to excessive loss of heat in the form of long wave terrestrial radiation; the above layer of air come into the contact with cold ground is relatively warm. Consequently temperature inversion develops.

Ground surface inversion also called radiation inversion and sometimes called advection inversion.

2.      Upper air inversion.

The ozone layer absorbs most of the ultraviolet radiation from the sun and thus the temperature of this layer becomes much higher than the air below it. This inversion is obtained.

3.      Frontal or cry colonic inversion.

When two constructing air masses coverage (warm and cold air). The warm air pushes up the cold and thus the warm air overlies cold. This type of inversion is common at the sub-polar low where warm westerlies and cold polar winds converge.

4.      Surface inversion (advection)

Caused by the horizontal movement of air occurs in several inversion. Such inversion is caused when warm air involves the area of cold air moves into the area of warm air because warm air being higher is pushed upward by relatively denser cold air. So inversion of temperature occurs.

AIR TEMPERATURE. (LAPSE RATE AND TEMPERATURE INVERSION)

Air temperature refers to the degree of hotness of coldness in the atmosphere. Air temperature is influenced by the amount of heat which is generated at a point in time. By heat we mean the energy in transferring that influence the temperature of a matter.

The atmospheric temperature (temperature of the air) influences atmosphere conditions in the sense that:

i.         It affects the amount of water vapour and there by determining the moisture carrying capacity of air i.e. Warmer air is easily saturated hence carries more moisture as compared to cold air.

ii.       It affects the rate of evapotransipiration and condensation, thus; governs the degree of atmospheric stability or instability.

iii.      It influences the nature and type of clouds formed and consequently precipitation.

AIR TEMPERATURE VS LATITUDE (COOLING OF AIR AND ADIABATIC CHANGE OF TEMPERATURE LAPSE RATE).

The temperature is normally heated by condition of heat reflected from the earth. This is the reason as to why air nearest to the earth’s surface is warmer than that at higher altitude. The temperature of atmosphere (in the atmosphere) decreases with the increase in altitude.

The process by which atmospheric temperature decrease with the increase in altitude is known as lapse rate. Experimental observation of air temperature at different altitudes has verified the assumption that air temperature decrease as height increases.

NOTE:

1.                  The atmospheric lapse rate is never constant, it varies from place to place and from time to time for practical purpose, it said to be at the average of 0.6⁰C/100m of ascent or 6⁰C/100m.

2.                  Lapse rate is more in summer than in winter.

3.                  Lapse rate is greater by the day than at night

4.                  It is also greater in elevated lands than at level of land (plain)

Types of lapse rate.

1.      Environmental lapse rate (ELR). Environmental lapse rate is sometimes known as normal lapse rate (NLR) or vertical temperature gradient. This is the situation in atmosphere where by air temperature decreases with the increase in altitude at the average of 0.6⁰C per 100m of ascent. The average decreases of temperature in still air with altitude. The rate of decreasing is about 0.6⁰C per meter.

2.       Adiabatic lapse rate (ALR). Adiabatic means, without addition or subtraction of heat energy. This adiabatic lapse rate described what happens when a panel of air rises and cools down without any subtraction of heat energy. When the changes in air temperature takes place without addition or subtraction of heat energy, the changes are referred to as adiabatic process. Adiabatic lapse rate depends much on the moisture content of a particular parcel of air which is rising. Due to this fact we can distinguish two types of adiabatic lapse rate:

(a)    Dry adiabatic lapse rate (DALR). This occurs when dry air is forced to rise, expand and cools down adiabatically at the rate of 1⁰C per 1000m of ascend. When unsaturated air mass ascends vertically, it also expands and therefore cools diabolically. The loss of temperature is known as dry adiabatic lapse rate a meteorological constant, which is temperature decrease 1⁰C per 1000m.

(b)   Wet (saturated) adiabatic lapse rate (WALR). If saturated air mass ascends vertically, it also expands and cools and it is saturated to start with some of its water vapour is immediately condensed. This means a certain amount latent heat is lost, which reduces the rate at which the ascending air masses cools. Therefore, this occurs when a saturated air mass is forced to rise, expands, cools down, and some of its water vapour condenses. This lapse rate is between 0.5⁰C – 0.9⁰C per 100m.

SOLAR RADIATION AND HEAT BALANCE.

The sun is only important source of energy to the earth and its atmosphere. Millions of other stars radiate energy, but they are too far away to affect earth. Energy is also released from inside earth, primarily as radioactive minerals decay, but, only insignificant qualities. Tidal energy is also minor importance. Thus; the sun supplies essentially all the energy that supports life on earth and energize most of the atmospheric processes.

The sun is the star of average size and average temperature, but it is a proximity to earth gives it a far greater influence on our planet than that exerted by all other celestial bodies combined. The sun is a prodigious generator of energy. In a single second it produces more energy than the amount used by human kind since civilization began. The sun functions as an enormous thermonuclear reactor, producing energy by fusion, a process that burns only a very small portion of the sun’s mass but proud an immense and continuous flow of radiant energy that is dispersed in all directions.

The radiant energy from the sun is in the form of electromagnetic waves. These are the waves that can transport energy without requiring a medium (the presence of matter) to pass through. They traverse the greater voids of space in unchanging from. The waves travel outward from the sun in straight lines at a speed of light – 300,000 Kilometers per Second. Electromagnetic waves are classified on the basis of wave length which can be thought of as a distance from the crest of one wave to the crest of the next.

Wavelength.

Wavelength varies enormously, but for our purpose, the most important distinction is between short wave and long wave radiation. The dividing line between the two is a wave length of about 4 micrometers. Only a tiny fraction of the sun’s radiant output is intercepted by earth. The waves travel through space without loss of energy, but since they are diverging from a spherical body, their intensity continuously diminishes with uncreated distance from the sun.

Intensity of waves.

As a result of this intensity drop the distance separating earth from the sun, less than one two-billionth of total solar output reaches the outer limit of earth’s atmosphere, having travelled 150,000,000 Kilometers in just over 8 minutes. Although it consists of only a minuscule portion of total solar output, in absolute terms the amount of solar energy earth receives is enormous; the amount received in 1 second is approximately equivalent to all the electric energy generated on earth in a week.

BASIC PROCESSES IN HEATING AND COOLING THE ATMOSPHERE.

Before looking at the events that occur as energy travels from the sun to the earth, let us look at the physical process involved in the movement of heat energy.

There are three ways in which heat energy can move from one place to another by radiation, by conduction and by convections:

1.      RADIATION.

Radiation is the process by which heat energy is emitted from a body. It involves the flow of radiant energy out of the body and through the air. All bodies radiate, but hotter bodies are more potent radiators than cooler ones. The hotter is the object, the more intense is its radiation and the shorter is the wavelength of that radiation. Tem perature, however, is not the only control of radiation effects.

Objects at the same temperature may vary considerably in their radiating capability because the nature of the surface of the objects is an important determining factor.

2.      ABSORPITION.

Heat energy striking an object can be absorbed by the object like water into a sponge, this process is called absorption. When insolation strikes an object and is absorbed, the temperature of the object increases. Different materials vary in their absorptive capabilities. The basic generalization is that a good radiator is also a good absorber and a poor radiator is a poor absorber.

Mineral materials (like rocks and soil) generally, are excellent absorbers. Snow and ice are poor absorbers. One important distinction concerns colour; dark-colored surfaces are much more efficient absorbers than light-colored surfaces.

3.      REFRECTION

Reflection is the ability of an object to reflect waves without altering either the object or the waves. Thus; in some cases insolation striking a surface in the atmosphere or on earth is bounced away, unchanged, in the general direction from which it come, much like a mirror reflection, where nothing is changed. In this context, reflection is the opposite of absorption. If the wave is reflected, it cannot be absorbed. Hence, an object that is a good absorber is a poor reflector, and vice versa. A simple example is the existence of unmelted snow on a warm, sunny day. If it is melt, the snow must absorb heat energy from the sun. Although the air temperature may be well above freezing, the snow does not melt rapid because its white surface reflects away a large share of the solar energy that strikes it.

About one third of the total amount radiation from the sun is reflected back into space. This bounced radiation is called albedo. Albedo is a technical term of the reflectivity of the object. The higher is the albedo value, the more is radiation the object reflects. For example, dark soil reflects about 10% of radiation and absorbs the remaining 90% and a snow reflects around 90% of radiation and absorbs only 10% of radiation.

4.      SCATTERING.

Particulate matter and gas molecule in the air sometimes reflect light waves and redirect them in a process known as scattering. This reflecting involves a change in the direction of the light wave but no change in wave length. Some of the waves are coming back into space and thus are lost to the earth, but most of them continue through the atmosphere in altered directions.

5.      TRANSIMISSION.

Transmission is the process where by a wave passes completely through a medium as when light waves are transmitted. There is obviously considerable variability among mediums in their capacity to transmit rays. Earth materials for example, are very poor transmitters of insolation; sunlight is absorbed at the surface of rock or soil and does not penetrate at all. Water on the other hand, transmits sunlight well; even in very murky/dirty water, light penetrates some distance below the surface, and in clear water; sunlight may illuminate to considerable depths.

In some cases, transmission depends on the wavelength of the rays. For example, glass has high transitivity for shortwave radiation, but not for long waves. Thus; heat builds up in a closed automobile left parked in the sun because shortwave insolation is transmitted through the window glass but  the long wave that are reradiated from the interior of the car cannot escape in similar fashion.

In simplest terms, solar energy readily penetrates to earth’s surface, but reradiated terrestrial energy is mostly “trapped” in the lower troposphere and much of it is reflected back toward the ground. This entrapment keeps earth’s surface and lower troposphere at a higher temperature than would be in the case if there were no atmosphere. The circumstances just described are referred to as the green house effect. Green house maintain heat in the same manner the glass roof transmitting shortwave solar energy in, but inhibiting the passage of long wave radiation out.

6.      CONDUCTION.

Another way in which heat energy can move from one place to another is conduction. The movement of heat energy from one molecule to another without changes in their relative position is called conduction. This process enables heat to be transferred from one part of a stationary body to another or from on object to second object when the two are in contact.

Conduction comes about through molecular collision. The heat is passing from one place to another. The principle is that, when two molecules of unequal temperature are in contact with one another, heat passes from the warmer to the cooler until they attain the same temperature. The ability of different substances to conduct heat is quite variable. For example, most metals are excellent conductors, as can be demonstrated by pouring hot coffee into a metal cup and then touching your lips to the edge of the cup. The heat of the coffee is quickly conducted throughout the metal and burns the lips of drinker. On the other hand, hot coffee poured into a ceramic cup only very slowly heats the cup because such earthy materials are a poor conductor.

Earth’s land surface warm up rapidly the day because it is a good heat absorber and some of that warmth is transferred away from the surface by conduction. A small part is conducted deeper underground, but not much because earth materials are not good conductors. Most of this absorbed heat is transferred to the lowest portion of the atmosphere by conduction for the ground surface. Air, however, is poor conductor and so only the thin air layer touching the ground is heated very much. Moist air is a slightly more efficient conductor than dry air.

7.      CONVECTION.

In convection, heat is transferred from one point to another by moving liquid or gas. This method of heat transfer involves movement of the heated molecules from one place to another. Do not confuse this movement from one place to another with the conduction. In convection the molecules physically more away from the heat source. In conduction they don’t.

Although the principal action in convection is vertical, there is some horizontal motion. When the convecting liquid or gas moves horizontally, we can call the process advection. The heated air immediately above the fire is going upward because the heating has caused it to expand and therefore become less dense. The heated air rises-so the pressure is lower. Then the surrounding air moves to fill the empty space cooler air from above descends to replace that which  has moved in, and a cellular circulation is established – up, out, down, an in.

A similar convective pattern frequently develops in the atmosphere. As far as our study of insolation is concerned the important points to remember about convection is that, it causes warm air to rise. Unequal heating may cause a parcel of surface air to become warmer than the surrounding air. The heated air expands and moves upward. The cooler surrounding air then moves in towards the heat source and air from above sinks down to replace that which has moved in, this establishing a convective system, the prominent elements of the system are an updraft of warm air and a down draft of cool air

8.      ADIABATIC COOLING AND WARMING.

Whenever air ascends or descends its temperature changes. This invariable result of vertical movement is due to the variation in pressure. When air rises, it expands and less pressure is exerted on the surface. When air descends, it is compressed and more pressure is exerted on surface. The expansion that occurs in rising air is a cooling process even though no heat is taken away. Spreading the molecule over a greater volume of space requires energy comes from the molecules. The loss of energy slows them down and decreases their frequency of collision. The result is a drop in temperature.  This is adiabatic cooling, cooling by expansion in rising air. And vice versa – when air descends, it must become warmer.

The descent causes compression as the air comes under increasing pressure. The molecules draw closer together and collide more frequently. The result is a rise in temperature even though no heat is added from external sources. This is adiabatic warming—warming by compression in descending air.

9.      SPATIAL AND SEASONAL VARIATIONS OF HEATING.

The word’s weather and climate differences are fundamentally caused by the unequal heating of earth and its atmosphere. This unequal heating is the result of latitudinal and seasonal variations in how much energy is received by earth.

There are only basic reasons for the unequal heating of different latitudinal zones. See some of them:

(i)                 Angle of incidence.

The angle at which rays from the sun strike earth’s surface is called the angle of incidence. This angle varies with latitude. The larger is the angle, the more is concentrated energy and therefore, the more effective is the heating. Ray strikes the earth’s surface directly, when the sun is directly over head, and has an angle of incidence of 90⁰(as above equator 20^th of March and 21^st of September).

Ray striking the surface at a slant has an angle of incidence smaller than 90 degrees, and for a ray striking earth at either pole, the angle of incidence is zero. Because earth’s surface is curved and because the positional relationship between earth and the sun is always changing. If the angle of incidence is big, the energy is concentrated in a small area, and if this angle is small, it is meaning that, when ray strike earth’s surface not directly but obliquely, the energy is spread out over a large portion of the earth’s surface.

The more nearly perpendicular the ray is (in the words, the closer to 90⁰ the incidence angle),  the smaller is the surface are heated by a given amount of insolation and the more effective is the heating.

(ii)              Day length.

The duration of sun light is another important factor in explaining latitudinal inequalities in heating. Longer days allow more insiolation to be received and thus; more heat to be absorbed. In tropical regions, this factor is relatively unimportant because the number of hour between sunrise and sunset does not vary significantly form one month to another. At the equator, of course, daylight and darkness are essentially equal in length (12 hours each) every day of the year. In middle and high latitudes, however, there are pounced seasonal variations in day length.

(iii)            Atmosphere obstruction.

The clouds, particulate matter, and gas molecules in the atmosphere either absorb, reflect or scatter insolation. The result is reduction in intensity of the energy received at the earth’s surface. This weakening effect varies from time to time and from place to place, depending on two factors: The amount of atmosphere the radiation has to pass through and the transparency of the atmosphere.

The distance a ray of sunlight travels through atmosphere (commonly referred as ‘path length’) is determined by the angle of incidence. A large – angle ray (in other words, a nearly perpendicular ray) traverses a shorter course through the atmosphere than a small – angle one. A tangent ray (one having an incidence angle of zero) must pass through nearly 20 times as much atmosphere as a direct ray (one striking earth at 90 degree angle). Solar radiation is more depleted of energy in the high latitudes than in the low latitudes, thus; there are small losses of energy in the tropical atmosphere than in the polar atmosphere.

(iv)              Latitudinal radiation balance.

As the direct rays of the sun shift northward and southward across the equator during the course of the year, the belt of maximum solar energy swings through the tropical. Thus; in the low latitudes, to about 30 degrees, there is an energy surplus, with more incoming than outgoing radiation. In the latitudes, north and south of this parallel, there is an energy deficit, with more radiant loss than gain.

The surplus of energy in low latitude is directly related to the large angle of incidence, and the energy deficit in high latitudes is associated with small angles. There is balance between incoming and outgoing radiation for the earth or atmosphere complex as a whole; in other words, the net radiation balance for earth is zero. The mechanism for exchanging heat between the surplus and deficit regions involves the general circulation patterns of the atmosphere and oceans, which we will discuss letter.

(v)                Land and water contrasts.

The atmosphere is heated mainly by heat reradiated from earth rather than by heat from the sun thus; the heating of earth’s surface is a primary control of the heating of the air above it. There is considerable variation in the absorbing and reflecting capabilities of the various kinds of surface found on the earth, for example soil, water, grass, cement, sand, roof tops. Their varying receptivity to insolation in turn causes differences in the temperature of the overlying air.

The most significant contrasts are those between land and water surfaces. The generalization is that land heats and cools faster and to a greater degree than water. So a land surface heats up more rapidly and reaches a higher temperature than comparable water surface subjects to the same insolation. These are several signifant reasons for this difference:

a.       Water has a higher specific heat than land. Specific heat is the amount of energy required to raise the temperature of 1gram of a substance by 1⁰C. The specific heat of water is about five times as great as that of land, which means that water can absorb much more solar energy without its temperature increasing.

b.      Sun rays penetrate water more deeply than they do land; that is, water is a better transmitter than a land. Thus; in water the heat is diffused over a much greater volume of matter, and maximum temperatures remain considerably lower than they do on land, where the heat is concentrated and maximum temperatures can be much higher. 

c.       Water is highly mobile, and ocean currents disperse the both broadly and deeply. Land of course is mobile and so heat is dispersing only by conduction (and land is a very poor conductor).

d.      When land and water have the same temperature, a land surface cools more rapidly and to a lower temperature than a water surface. During winter, the shallow heated layer of land radiates its heat away quickly. Water loses its heat more gradually because the heat has been stored deeply and is brought only slowly to the surface for radiation. As the surface water cools, it sinks and is replaced by warmer upwelling from below. The entire water body must be cooled before the surface temperatures decreases significantly.

The significance of these contrasts between land and water heating and cooling rates is that, both the hottest and coldest areas of earth are found in the interiors of continents, distant from the influence of oceans. In the study of the atmosphere probably no single geographic relationship is more important than the distinction between continental and maritime climates. A continental climate experiences greater seasonal extremes of temperature; hotter in summer, colder in water than maritime climate.

MECHANISM OF HEAT TRANSFER.

By definition, temperature is an expression of the degree of hotness or coldness of a substance. If there were not mechanisms for moving heat pole ward in both hemispheres, the tropics would become progressively warmer until the amount of heat energy absorbed equally the amount radiated from earth’s surface and the high latitudes would become progressively colder. Such temperatures trends do not occur because there is a persisted shifting of warmth toward the high latitudes and consequent of the low latitudes. This shifting is accomplished by circulation patterns in the atmosphere and in the oceans of these two mechanisms of global heat transfer, by far the more important is the general circulation of the atmosphere. Air moves in an almost infinite number of ways but there is abroad planetary circulation pattern that serves as a general framework for moving warm air pole ward and cool air equator ward.

The movement of the air (general circulation of the atmosphere) is caused mostly by uneven absorption of the heat at various latitudes, but also by the deflective force of earth’s ration, which called the Coriolis effects. There is close relationship between the general circulation patterns of the atmosphere and oceans. Various kinds of oceans water movements are categorized as currents and it is air blowing over the surface of the water that is the principal force driving the major oceans currents. In the other direction, the heat energy stored in the oceans has   important effects on atmospheric circulation. There is a close relationship between the general circulation patterns of the atmosphere and oceans. All the oceans of the world are interconnected, because of the location of land masses and the pattern of atmospheric circulation; however, it is convenient to visualize five relatively separate ocean basins – North Pacific, South Pacific, North Atlantic, South Atlantic and South Indian. Within each of these basins, there is a similar pattern of surface current flow, based on a general similarity of prevailing wind patterns.

The movement of the currents, although impelled partially by the wind, is caused by the Coriolis Effect. This force dictates that the ocean currents are deflected to the right in the northern hemisphere and deflected to the right in the northern hemisphere and to the left is southern hemisphere. Each major current can be characterized as warm or cool relative to the surrounding water at the latitude: North pacific drift (warm), California current (cool), Equatorial current (warm), West wind drift (cool), Humboldt current (cool), Gulf stream (warm), Labrador current (cool), North Atlantic drift (warm), Canaries current (cool), Brazil current (warm), Benguela current (cool), West Austrian current (cool), East Australia current (warm), Kuroshio current (warm), Oyashio current (cool)

VERTICLE TEMPERATURE PATTERNS.

Temperature in the troposphere is relatively predictable through the troposphere under normal condition; there is a general decrease in temperature with increasing altitude.  However, there are many exceptions to this general statement. Indeed, the rate of vertical temperature decline can vary according to season, time of day, amount of cloud cover, and a host of other factors. In some cases, there is even an opposite trend, with the temperature increasing upward for a limited distance.

The rate at which temperature decreases with height is variable, particularly in the lowest few hundred feet of the troposphere, but the normal expectable rate is about 0.6⁰C per 100 meters. This is average lapse rate, normally vertical temperature gradient. The lapse rate tells us that it a thermometer measures a temperature 100 meter above a previous measurement, the reading will be, on average 0.6⁰C cooler. The second measurement is 100 meters below the first; the thermometer will register about 0.6⁰C warmer.

The most prominent exception to a normal lapse rate condition is a temperature inversion, a situation in which temperature in the troposphere increases with a height. The most readily recognizable inversions are those found at ground level. These are usually classified as radiation inversions because they result from rapid radiation cooling. They occur typically on a long, cold winter night when a land surface (can efficient radiator) rapidly emits long-wave radiation into a clear, calm sky. The ground becomes soon colder than the adjacent air layer and now cools air by conduction. In a short time, the lowest 50-100m becomes colder than the air above. This type of inversion is more prevalent in high latitudes than elsewhere.

An inverted surface temperature gradient can also be the result of an advection inversion in which there is a horizontal inflow of cold air into an area. This condition commonly is produced by cool maritime air blowing into a coastal locally. Another type of surface inversion results when cooler air slides down a slope into a valley, thereby displacing slightly warmer air. This fairly common occurrence during winter in some mid latitude regions is called a cold – air – drainage inversion.

GROBAL TEMPERATURE PATTERN.

Gross patterns of temperature are controlled largely by four factors:

      Latitude,

      Altitude,

      Land/water contrast and

      Ocean current.

Generally the temperature decreases with altitude with some exceptions (inversion) and latitude (also with some exceptions, for example warm or cold oceanic current). Temperature distribution on the earth’s surface may be represented by using isotherms, lines jointing points of equal temperature. General trends of the isotherms are west-east, roughly following the parallel of latitude. If earth had a uniform surface and did not rotate, the isotherms probably would coincide exactly with parallels showing a progressive decrease of temperature pole ward from the equator. However earth does rotate and it has ocean waters that circulate and land varies in elevating. Consequently there is no precise temperature correlation with latitude and of course there are seasonal variations of the temperature. The isotherms follow the changing balance of insolation during the course of the year, moving northward from January to July and returning south ward from July to January.

ATMOSPHERIC HEAT BUDGET.

This refers to the metrological concept used to describe the balance achieved between the incoming and outgoing heat as no part on the earth’s surface experience overheat or over cooling. Normally the tropical experience heat surplus while the high latitude or polar and highland area experience heat deficit. Therefore, to avoid overheating on area heating surplus and over cooling on area with heat deficient heat transfer takes place.

Types of heat transfer.

1.      Horizontal/ lateral heat transfer  

      2.Vertical heat transfer