Heat Budget.

The-NASA-Earth's-Energy-Budget- source :Wikipedia commons

The quantity of heat received in an environment depends on the intensity and duration of sunlight of the day. The heat generated varies from place to place and from one season to another. In most of the tropical environment, the quantity of heat received remain constant throughout the year while the quantity of heat received at the poles vary.
Heat budget involves the total sum of all heat energy received from the sun(incoming radiation) given off over a stated period. It shows the relationship existing between the quantity of heat received by radiation and the quantity of heat given out by both reflection and convection processes.
The total amount of solar energy emitted by the earth and the atmosphere through reflections exceeds the total solar energy absorbed and retained by the earth's surface.

Heat Budget Equation

The heat budget equation is the total heat energy provided by radiations and used for heating of the land, the air, the sea and for evaporation of water from the water bodies. It includes the heat energy used for the thawing of ice thereby changing the ice from solid form to liquid. The sum of these heat energy can be represented as:

Q = Tb+Tl+Tv+Ts+Tn+Tr+TBio ......(16)

Where;

Q = The total radiative balance

Tb = Heat transmitted into land mass (Tm= heat transmitted into the sea).

Tl = Heat used for warming of the air (sensible heat)

Tv = Heat transmitted to the air by evaporation (latent heat of water vapour) .

Ts = Heat used in melting ice and snow.

Tn= Heat used to warm precipitation (rain) as they fall.

Tr = Heat generated by wind friction with the ground.

TBio = Energy used for biological processes which involves the growth of the living matter, the heat of decomposition as well as plant respiration.

A large quantity of radiation or heat from the sun is absorbed by both the land mass and the sea (Tb) and a corresponding value of the heat energy is also reflected and released back to the atmosphere (Tl) is called the sensible heat and is used to warm the air. This is why the air is either hot (high temperatures) or cold (low temperatures). A given quantity of heat is also used during evaporation processes (Tv). This heat makes it possible for a given quantity of water on a surface to rise into the air where they cool, saturates, condense and fall back at the earths surface as rain. It is usually called latent heat of water vapour. Ice and snow on the earth's surface are changed to water by the absorption of a given quantity of heat. The heat for melting the ice (Ts) is used to change the solid material (ice) into liquid material (water). Similarly, a given quantity of heat reflected from the earth's surface is used to warm precipitation as it falls. This is common at the commencement of the rainfall event which decreases with time.

The wind movements and it's contact with the earth's surface generate a given quantity of heat through the process. The surface of the becomes hot when wind carrying some quantities of materials (soil, gravel, rock) move across the surface of the earth. TBio is the only energy component used for biological processes which comprises all metabolic activities, plant growth, respiration and photosynthesis processes as well as the energy required for plants decomposition and other related activities.

Energy Balance in Oceans and Continents

The oceans act as a gigantic heat reservoir by absorbing heat in spring and summer and transmitting the same heat in autumn and winter ( rainy and dry seasons) with a system of powerful currents that ensure an effective exchange and distribution of heat. This phenomenon produces a decrease in diurnal (daily) and annual range of temperatures and a lag in the times of maximum and minimum temperature in the surrounding areas. At the continents (hinterland), the sun's heat is absorbed and released more slowly by water than by land and the air temperature decreases from the coast to the inland. In the summer, land surfaces are warmer than the sea hence the air over the land mass is warmer than over the sea. It is necessary to say that :

• The air moves from hot region to a lower or cooler region through the wind distribution.

• At the day, the land get warmer than the sea hence the air pressure is lower over the land than the sea.

• The air then blows from the sea to the land and this is the sea breezes.

• At night the land cools more rapidly than the sea.

• The pressure is lower over the sea than the land hence the air flows from the land to the sea and this is called the land breeze.

Vertical Heat Exchange

The movement of heat vertically from the region of high potential to that of the lower potential is called the vertical heat exchange. The exchange of heat between the ground surface and the air above is affected by vertical air transfer which depends directly on the strength of the wind blowing across the ground surface . The transfer of the sensible heat (Tl) is the product of the exchange coefficient (A), the vertical gradient of the temperature and the specific heat of the air at constant pressure. Similarly, the vertical exchange coefficient (A) varies with time, the temperature gradient and the wind velocity. If the ground surface is colder than the air above the surface, the sensible heat moves downwards. If on the other hand, the air is colder than the ground surface, then the air is heated from the ground surface by turbulent or eddy heat transfer. These changes in the direction of heat are referred to as the "temperature inversions" and this phenomenon is noticed before and after a rainfall event. In a rainfall event, the cold water droplets hit the warm ground surfaces which generates the heat that moves vertically from the ground surfaces to the air hence the air temperature after the rainfall event increases.

Horinzontal Heat Exchange

This is the exchange of heat from one end to another along the horizontal surfaces. This horizontal heat exchange is due to the

gradient between the hot end and the cold end of the ground surface. The horizontal heat transport plays an important role in the heat budget of the ocean currents. At the surface of the sea, the distribution is due to the wind while at a greater depth, the energy is provided by the differences in water density determined by the temperature and salt content of the sea water. In a pure water condition about thirty-five percent (35%) of the incident solar radiations penetrate to a depth of between 0.1 and 10m below the surface water. This is strongly wavelength dependent.
In most of the water surface, the penetrais greatest at the shortest wave length and poorest at the longer wavelength. The transmission of the sunlight by natural coastal waters depends on the turbidity (the level of sands and silty content of the water) and the growths in such water. In general, the more turbid the water, the smaller the amount of radiation that can penetrate to a given depth and the higher the reflectivity constant - albedo (a).

Thanks for reading!

Reference

[1]Earth's Energy Budget
[2]Atmospheric Temperature
[3]The Heat Budget and Isolation
[4] Earth's Heat Budget and Global Warming
[5]What is Heat Budget?

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