What Is Heat Balance?

Heat balance is the condition when the heat budget of an object or system is equal. The study of the thermal budget of the Earth's surface, atmosphere, and ground-air system is one of the important topics in physical climatology. Radiation balances and other heat expenditures or compensations that they transform have a huge impact on the thermal conditions of the Earth's surface, the atmosphere, and the ground-air system. ^[1]

Thermal balance refers to the balance between the thermal budget and thermal storage of an object or system. Expressed by the heat balance equation, it is a special form of the law of conservation of energy. The physical processes and control factors represented by each revenue and expenditure item are different, and they constitute the heat balance equations of the ground-air system, the surface, and the atmosphere, thereby defining and restricting the relationship between the control parameters and heat inflow The change in the direction and size of the earth and the equilibrium temperature of the air is a specific manifestation of the law of conservation of heat.

The heat balance of the ground-air system refers to the situation when the heat layer of the underlying air surface per unit area (that is, there is no obvious temperature above the depth of seasonal change) and up to the upper boundary of the atmosphere. Atmospheric heat balance refers to the situation when the heat budget of a vertical gas cylinder per unit area that extends from the ground to the upper boundary of the atmosphere is equal.

The surface heat balance equation indicates that the radiant heat netted or lost by the ground during radiation exchange is in equilibrium with the heat lost or gained by the ground during heat exchange. The equation shows: After the ground has obtained (lost) radiant heat energy, in what way does the ground exchange heat with the ground and the atmosphere, and promotes water vapor exchange. In microclimate research, R can be directly measured, and other components of the equation can be calculated according to gradient observations of temperature, humidity, wind, and ground temperature in the near-surface layer, and calculated according to various diffusion formulas or heat balance formulas (see Farmland heat balance, farmland soil heat exchange).

For the earth, the heat balance equation is:

Ground surface: Q _d = LE + P + A

To the atmosphere: Q _da = F _a -L _r -P + H _a

Ground-to-air system: Q _ds = F _s + L (Er) + H _s

Q _d , Q _da , Q _ds are the radiation differences of the ground, atmosphere, and ground-air systems; L _r is latent heat; E is evaporation; r is the condensation rate of water vapor; LE is the heat consumption during evaporation; P is between the ground and the atmosphere. Turbulent heat flux; A is the heat flux between the ground and soil or water; F _a and F _s are the horizontal heat fluxes of the atmosphere and the ground-air system; H _a and H _s are the atmosphere and the ground-air system Changes in enthalpy per unit time. Each component can be obtained directly from observations or calculated from meteorological data.

The annual total heat dissipation characteristics of evaporation are:

The zonal distribution of evaporative heat is obvious on the ocean. The maximum value (greater than 120 kcal / cm · year) is at the subtropical latitudes in the southern and northern hemispheres, and decreases toward the middle and high latitudes. High-value centers (more than 160 kcal / cm · year and 140 kcal / cm · year) appear in the sea areas where the warm ocean currents (Gulf Stream and Kuroshio) flow;

The heat consumption of evaporation on the continent is much smaller than that of the ocean, and the contours are interrupted on the sea and land coasts;

The maximum value of evaporation heat consumption on the continent occurs in humid tropical rain forest areas (greater than 60 kcal / cm · year), and the minimum value occurs in subtropical desert areas and the Arctic Ocean coast (less than 10 kcal / cm 2 · year) . The annual total turbulent heat exchange distribution is opposite, but its contour is not continuous on the sea and land coasts; the values are large in warm ocean currents and small in the Arctic Ocean coasts, which are consistent with the annual total heat consumption of evaporation of. ^[2]

Surface heat balance is an energy factor for climate formation. The analysis and study of the surface heat balance can provide an important basis for studying climate formation, climate simulation, and the evolution of atmospheric circulation. The heat and water conditions on the ground surface directly affect the survival of humans, animals and plants, and are also important climate resources for agricultural production. Various artificial climate improvement measures are mainly achieved by changing the surface heat balance.

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Each component of the heat balance is different at different latitudes and different underlying surfaces. For example, the largest land evaporation occurs near the equator.

Heat balance

At the latitude of the subtropical high pressure zone, evaporation is drastically reduced due to the dry climate. In contrast, the maximum evaporation in the ocean occurs at the latitude of the subtropical high pressure zone, while the evaporation decreases significantly near the equator.

Studies have shown that in the northern hemisphere, heat is transported from low latitudes to high latitudes, and the southern hemisphere is transported to the northern hemisphere. Individual components of the heat balance can be obtained directly from observations or calculated from meteorological data. The research on the heat balance of a region is helpful for the quantitative analysis of the formation and change of the climate in the region.