Thermosphere - Energy Input - Energy Budget

Energy Budget

The thermospheric temperature can be determined from density observations as well as from direct satellite measurements. The temperature vs. altitude z in Fig. 1 can be simulated by the so-called Bates profile

(1) T = T - (T - To) exp{-s (z - zo)}

with T the exospheric temperature above about 400 km altitude, To = 355 K, and zo = 120 km reference temperature and height, and s an empirical parameter depending on T and decreasing with T. That formula is derived from a simple equation of heat conduction. One estimates a total heat input of qo≃ 0.8 to 1.6 mW/m2 above zo = 120 km altitude. In order to obtain equilibrium conditions, that heat input qo above zo is lost to the lower atmospheric regions by heat conduction.

The exospheric temperature T is a fair measurement of the solar XUV radiation. Since solar radio emission F at 10.7 cm wavelength is a good indicator of solar activity, on can apply the empirical formula for quiet magnetospheric conditions.

(2) T ≃ 500 + 3.4 Fo

with T in K, Fo in 10- 2 W m−2 Hz−1 (the Covington index) a value of F averaged over several solar cycles. The Covington index varies typically between 70 and 250 during a solar cycle, and never drops below about 50. Thus, T varies between about 740 and 1350 K. During very quiet magnetospheric conditions, the still continuously flowing magnetospheric energy input contributes by about 250 K to the residual temperature of 500 K in eq.(2). The rest of 250 K in eq.(2) can be attributed to atmospheric waves generated within the troposphere and dissipated within the lower thermosphere.

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Energy Budget

An energy budget is a balance sheet of energy income against expenditure. It is studied in the field of Energetics which deals with the study of energy transfer and transformation from one form to another. Calorie is the basic unit of measurement. An organism in a laboratory experiment is an open thermodynamic system, exchanging energy with its surroundings in three ways - heat, work and the potential energy of biochemical compounds.

Fishes, like all organisms, use ingested food resources (C=consumption) as building blocks in the synthesis of tissues (P=production) and as fuel in the metabolic process that power this synthesis and other physiological processes (R=respiratory loss). Some of the resources are lost as waste products (F=faecal loss, U=urinary loss). All these aspects of metabolism can be represented in energy units. The basic model of energy budget may be shown as:

P = C - R - U - F or

P = C - (R + U + F) or

C = P + R + U + F

All the aspects of metabolism can be represented in energy units (e.g. joules (J);1 food calorie = 4.2 kJ). Energy used for metabolism will be

R = C - (F + U + P)

Energy used in the maintenance will be

R + F + U = C - P

The compilation of energy budget for fish has a fairly short history, with the result that literature on the subject is limited.

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